Management of concentrate from desalination plants 9780128180464, 0128180463

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Management of Concentrate From Desalination Plants

Elsevier Radarweg 29, PO Box 211, 1000 AE Amsterdam, Netherlands The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, United Kingdom 50 Hampshire Street, 5th Floor, Cambridge, MA 02139, United States Copyright © 2020 Elsevier Inc. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein). Notices Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress ISBN: 978-0-12-818045-7 For Information on all Elsevier publications visit our website at https://www.elsevier.com/books-and-journals

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Management of Concentrate From Desalination Plants

Nikolay Voutchkov Gisela Noelle Kaiser

Contents Preface ..................................................................................................................... ix Acknowledgments ................................................................................................. xiii

CHAPTER 1 Introduction to concentrate management.................... 1 1.1 1.2 1.3 1.4

Current status of desalination ........................................................1 Enabling conditions for desalination .............................................7 Overview of existing concentrate management practices .............8 Concentrate management regulations ............................................8 References.................................................................................... 12

CHAPTER 2 Desalination plant discharge characterization ......... 13 2.1 2.2 2.3 2.4

Desalination plant waste streams.................................................13 Concentrate...................................................................................14 Spent pretreatment filter backwash water ...................................17 Chemical cleaning residuals ........................................................20 References.................................................................................... 23

CHAPTER 3 Surface water discharge of concentrate ................... 25 3.1 3.2 3.3 3.4 3.5 3.6 3.7

New surface water discharge .......................................................25 Potential environmental impacts..................................................27 Concentrate treatment prior to surface water discharge..............54 Design guidelines for surface water discharges ..........................56 Costs for new surface water discharge ........................................60 Codisposal with wastewater effluent ...........................................64 Codisposal with power plant cooling water ................................67 References.................................................................................... 75

CHAPTER 4 Case studies for surface water discharge ................. 79 4.1 Introduction ..................................................................................79 4.2 Surface water discharge case studies...........................................79 References.................................................................................. 129

CHAPTER 5 Discharge to sanitary sewer..................................... 131 5.1 5.2 5.3 5.4 5.5

Description .................................................................................131 Potential environmental impacts................................................131 Effect on sanitary sewer operations...........................................131 Effect on wastewater treatment plant operations ......................132 Effect on water reuse .................................................................133

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5.6 Design and configuration guidelines .........................................134 5.7 Costs for sanitary sewer discharge ............................................135 References.................................................................................. 136

CHAPTER 6 Deep well injection................................................... 137 6.1 6.2 6.3 6.4 6.5 6.6

Description .................................................................................137 Potential environmental impacts................................................141 Criteria and methods for feasibility assessment ........................142 Design and configuration guidelines .........................................142 Injection well costs.....................................................................145 Deep well injection case study ..................................................147 References.................................................................................. 148

CHAPTER 7 Land application ....................................................... 151 7.1 7.2 7.3 7.4 7.5

Description .................................................................................151 Potential environmental impacts................................................155 Criteria and methods for feasibility assessment ........................156 Design and configuration guidelines .........................................160 Land application costs................................................................167 References.................................................................................. 171

CHAPTER 8 Evaporation ponds .................................................... 173 8.1 8.2 8.3 8.4 8.5

Description .................................................................................173 Potential environmental impacts................................................178 Criteria and methods for feasibility assessment ........................178 Design and configuration guidelines .........................................180 Evaporation pond costs ..............................................................183 References.................................................................................. 185

CHAPTER 9 Zero-liquid discharge concentrate disposal systems...................................................................... 187 9.1 Overview ....................................................................................187 9.2 Disposal system technologies ....................................................188 9.3 SWRO systems for increased recovery and brine concentration ..............................................................................198 9.4 Potential environmental impacts................................................202 9.5 Criteria and methods for feasibility assessment ........................203 9.6 Design and configuration guidelines .........................................204 9.7 Zero-liquid discharge costs ........................................................204 9.8 Case studies ................................................................................206 References.................................................................................. 207

Contents

CHAPTER 10 Beneficial use of concentrate .................................. 209 10.1 Technology overview.................................................................209 10.2 Extraction of minerals from concentrate ...................................213 10.3 Feasibility of beneficial reuse ....................................................220 References.................................................................................. 220

CHAPTER 11 Regional concentrate management.......................... 223 11.1 Types of regional concentrate management systems ................223 11.2 Use of brackish water concentrate in SWRO plants .................224 11.3 Joint desalination and reuse .......................................................226 References.................................................................................. 230

CHAPTER 12 Nonconcentrate residuals management .................. 231 12.1 Spent pretreatment backwash water ..........................................231 12.2 Chemical cleaning residuals ......................................................242 Reference ................................................................................... 243

CHAPTER 13 Selection of concentrate management approach.... 245 13.1 Concentrate management alternatives .......................................245 13.2 The future of concentrate management .....................................251 13.3 Concluding remarks ...................................................................253 References.................................................................................. 256

Appendix 1: Abbreviations ...................................................................................257 Appendix 2: Units..................................................................................................261 Glossary .................................................................................................................263 Index ......................................................................................................................271

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Preface This book provides an overview of the alternatives for management of concentrate generated by brackish water and seawater desalination plants, as well as sitespecific factors involved in the selection of the most viable alternative for a given project, and the environmental permitting requirements and studies associated with their implementation. The book focuses on widely used alternatives for disposal of concentrate, including discharge to surface water bodies, disposal to wastewater systems, deep well injection, land application, evaporation, beneficial reuse, and zero-liquid discharge. Direct discharge through new outfalls, discharge through existing wastewater treatment plant outfalls, and codisposal with the cooling water of existing coastal power plants are described, and design guidance for the use of these concentrate disposal alternatives is presented with engineers and practitioners in the field of desalination in mind. Key advantages, disadvantages, environmental impact issues, and possible solutions are presented for each discharge alternative. Easy-to-use graphs depicting construction costs as a function of concentrate flowrate are provided for all key concentrate management alternatives. At present, membrane reverse osmosis (RO) desalination is the fastest growing technology for production of fresh water from saline water sources: desalination plants use less energy to produce the same volume of fresh water than thermal desalination facilities. Therefore, this book focuses exclusively on the concentrate management of RO desalination projects. Planning and design for locating, construction, funding, and operation of desalination plants is more complex and demanding than that for conventional water treatment facilities in terms of professional skills, knowledge and understanding of the environment, treatment processes, technologies, and equipment employed in desalination processes. As the advances in desalination technology make desalination more competitive with other alternative sources of water supply, planning and design, including preparation of accurate cost estimates for construction and operation of desalination projects becomes of critical importance for identifying the size and role of desalination in the mix of alternatives that provide a sustainable and reliable water supply portfolio for municipal coastal centers around the world. This book provides detailed information on how to manage concentrate in the implementation of seawater RO desalination plants. The book contains 13 chapters, covering current developments in desalination and essential knowledge of prevailing methods of concentrate management. Easy-to-use formulas and cost curves are included to facilitate development of estimated volumes and costs associated with the various types of concentrate management. Chapter 1, Introduction to Concentrate Management, provides a brief review to the current status of desalination worldwide and an overview of the most commonly used concentrate management alternatives. With the elevated risk of water

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scarcity due to climate change and demand growth, desalination is becoming increasingly popular for the production of fresh potable water, especially in highly urbanized coastal regions. As the number of plants and volumes of desalinated water increase, assurance must be provided of the environmental sustainability of such discharges over extended time periods. Potential environmental impacts can be minimized through treatment of concentrate and optimal discharge configuration and design, either directly into the water body or disposed together with treated wastewater or cooling water from power plants. Chapter 2, Desalination Plant Discharge Characterization, presents the key components of desalination plant waste streams. Discharge from desalination plants is constituted mainly of RO concentrate, but may also contain significant volumes of filter backwash water and cleaning solutions used in water conditioning and membrane cleaning. The quantity and quality of each source can be calculated based on the plant characteristics. The volume of concentrate is a function of the plant recovery rate, and given the large volumes discharged, concentrate management must be integral to preliminary design decisions. Chapter 3, Surface Water Discharge of Concentrate, covers the most common desalination plant concentrate disposal practice. As the number of developments and volumes of desalinated water increases, assurance must be provided of the environmental sustainability of such discharges over extended time periods. Potential environmental impacts can be minimized through mixing of concentrate with discharges of wastewater treatment plants or power plant generation stations, or by the use of diffuser systems for accelerated dissipation of the concentrate in the marine environment. If properly managed, the footprint of increased salinity can be minimized resulting in the elimination of potential negative impacts of concentrate and other desalination plant discharges on the receiving aquatic environment. Chapter 4, Case Studies for Surface Water Discharge, includes case studies of concentrate management practices in Australia, Israel, Spain, and the United States. Most large plants have direct discharge to surface water bodies. In this chapter, permitting practices are compared between countries. As the technology has evolved rapidly over the past decades, standardization within countries is often still lacking– most countries however have similar permitting requirements for desalination plant discharges. Chapter 5, Discharge to Sanitary Sewer, addresses the disposal of concentrate to the wastewater collection system as a common practice from small desalination plants. Typically, small volumes of brine are combined with the influent to large treatment plants. The cost of discharge relates only to conveyance into the waste stream and is thus low. Concentrate is managed as industrial effluent with both quantity and quality regulated to have no negative impact on plant operations. Increased salinity can have potential impact on effluent reuse, especially for irrigation. Chapter 6, Deep Well Injection, details how concentrate from desalination plants could be disposed of in deep confined saline aquifers. The capacity of such

Preface

aquifers is limited by permeability and transmissivity, while the underground injection zone must be compatible with the water quality of the membrane concentrate. The injection zone receiving concentrate must also be over 10,000 mg/L TDS. Concentrate may require pretreatment to prevent negative impacts on the receiving aquifer. Monitoring of groundwater in the area, and pressure in the aquifer are critical to early identification of leaks and regulating this form of disposal. Chapter 7, Land Application, explains how concentrate can be disposed in a manner which involves either spray irrigation on salt-tolerant plants or infiltration through earthen rapid infiltration basins. Land application is typically used for small volumes of brackish water concentrate only and its full-scale application is limited by climate conditions, seasonal demand and by availability of suitable land and groundwater conditions. Agricultural applications to vegetation tolerant to salinity holds promise of improving beneficial use. Chapter 8, Evaporation Ponds, describes the circumstances under which concentrate can be disposed to ponds, where water is evaporated through solar power, while the remaining salts are collected periodically in crystalized form and transported to landfill. Land area needed for the ponds is mainly dependent on the volume of concentrate and the site-specific evaporation rate. Additional storage capacity is required to allow for accumulation of the minerals that have crystalized at the bottom of the ponds. Solar ponds are evaporation ponds with an enhanced depth which are configured to generate energy. Chapter 9, Zero-Liquid Discharge Concentrate Disposal Systems, explores current developments in reducing both environmental impact and cost of concentrate management by substantially reducing concentrate volumes. Zero-liquid discharge technologies convert concentrate to pure water and dry crystals or dense brine which can be either used for commercial purposes or disposed of to a landfill. Process intensification combines a number of existing processes to improve the recovery, but disruptive technologies are likely to be necessary to significantly reduce costs and energy requirements. Chapter 10, Beneficial Use of Concentrate, builds on zero-liquid discharge in identifying potential markets for the byproducts derived from the brine such as high-value minerals and rare metals. Beneficial use of concentrate provides the opportunity to transform desalination, rendering it far more sustainable by not only reducing the negative environmental impact of discharge, but by providing revenue through mineral recovery. Chapter 11, Regional Concentrate Management, introduces the integration of concentrate from various sources in relatively close proximity to exploit potential efficiencies. Given the comparatively high cost of concentrate management, benefits can be obtained by consolidating effluent from a number of sources to provide infrastructure that minimizes environmental impact while taking advantage of economies of scale. Using a variety of sources and types of effluent (i.e., brackish and seawater) has the advantage of dilution that can further positively impact the environment.

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Chapter 12, Nonconcentrate Residuals Management, describes the disposal of nonconcentrate residuals such as spent filter backwash water from seawater pretreatment, spent membrane cleaning solutions and other process side streams. Pretreatment backwash quantity and quality varies depending on whether membrane or granular system is employed. Where quality is not detrimental to the environment, spent backwash water is blended with concentrate and discharged to water bodies. Alternatively, on-site treatment is required prior to blending. Chemicals used to periodically clean membranes result in residual discharge that typically needs to be either treated and blended with concentrate before disposal, or conveyed to the nearby wastewater collection system. Chapter 13, Overview of Concentrate Selection Management Approach, compares the various methods of concentrate disposal and highlights their advantages and disadvantages. Feasible methods of disposal need to be identified and then costed for the life of the project. Feasibility is influenced by regulations, environmental sensitivity and physical constraints. Cost of concentrate management is impacted by the size of the desalination project, source seawater quality, the type and sensitivity of the marine environment in the vicinity of the discharge, and preventive or mitigation measures that need to be implemented in order to minimize environmental impacts. This book is intended for desalination project planners, engineers, and designers; water utility professionals involved in development of water resource management plans; equipment and membrane developers; operation and troubleshooting specialists; as well as for students and teachers in the desalination field. It contains need-to-know desalination concentrate management practices and information, which would benefit practitioners, decision-makers, and scholars alike.

Acknowledgments We would like to express our sincere gratitude to all fellow professionals, colleagues, and associates who have reviewed various portions of this book and have provided constructive comments and suggestions. Special note of recognition to the many operators, desalination plant managers, equipment and membrane manufacturers, and public utilities in the United States, Australia, Bahrain, United Arab Emirates, Spain, Malta, Cyprus, Kingdom of Saudi Arabia, and other parts of the world who have contributed their valuable experience and technology-related information used in this book. We gratefully appreciate the assistance of Ms. Emma Kaiser for her artistic contribution toward the preparation of the figures and graphs included in the book. Her professional photography skills have enhanced the book’s quality. We extend special recognition to Eng. Meshal Alawad for his support work on the collection and analysis of concentrate management cost information from desalination plants worldwide and on the development of the cost curves included in the book. Finally, our deep and sincere gratitude to Dr. Boris Liberman and Mr. Leon Awerbuch for their inspiration, encouragement, and impetus to write this book.

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CHAPTER

Introduction to concentrate management

1

Desalination is becoming increasingly popular for the production of fresh potable water since many inland and coastal municipalities and utilities in arid regions of the world are looking for new, reliable, and drought-proof local sources of water. Climate change increases the risks of water scarcity, which are amplified in vulnerable communities lacking essential infrastructure. Desalination is a tried-and-tested adaptation option to increase the reliability of water resources but has relatively higher production cost, energy demand, and carbon footprint as compared to conventional water supply alternatives. Similar to conventional water treatment plants and water reclamation facilities, desalination plants also generate discharge, which contains the plant’s source water treatment byproducts. For a desalination project to be viable, plant discharge has to be disposed of in an environmentally safe and sustainable manner that is compliant with all applicable governmental regulatory requirements. One of the key limiting factors for the construction of new desalination plants is the availability of suitable conditions and location for disposal of the highsalinity waste stream generated during the desalination process, commonly referred to as concentrate or brine. Monitoring programs at existing plants worldwide have shown that impacts on the marine environment are nonexistent or very limited and localized with proper plant outfall configuration, siting, and design. Publicizing information of such monitoring programs have the capability of improving trust in desalination technology, and ensuring enhanced sustainability of future plant developments. This book provides an overview of existing concentrate management options, their advantages, disadvantages, and implementation constraints.

1.1 Current status of desalination Accessible freshwater makes up only a fraction (,2.5%) of total water on the planet. Populations around the world historically relied on surface water (from rainfall) and groundwater, but both of these sources are vulnerable to changes in climate and variability in weather. As populations grew in locations where

Management of Concentrate from Desalination Plants. DOI: https://doi.org/10.1016/B978-0-12-818045-7.00001-4 © 2020 Elsevier Inc. All rights reserved.

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freshwater was scarce, new supply sources were pursued. The first thermal desalination plants were built in the beginning of the 20th century, while the first commercial brackish and seawater reverse osmosis (RO) plants came into operation in the 1960s and 1970s, respectively. With technology advancing, recycling and reuse of water is now also viable, expanding the options of potable water supply. As the cost of water increases through diversification of supply beyond reliance on rainfall, so the value of water becomes more apparent. Sustainable water management requires that all water in the system is accounted for, and demand management forms an important aspect of reconciling demand and supply. Demand management should be the first, and is generally the least costly intervention to stretch available supply, but there are limits to efficiencies, beyond which additional water resources will inevitably be required. While the value of water needs to be better appreciated, and the world aspires to a circular economy and closed-loop resource systems, growth in population and quality of life will require additional potable water in the foreseeable future. The ocean has two unique and distinctive features as a water supply source: It is drought-proof and is practically limitless. Over half of the world population lives in urban centers bordering the ocean. In many arid parts of the world such as the Middle East, Australia, Northern Africa, and Southern California, the population concentration along the coast exceeds 75%. Usually coastal zones have the highest population growth as well, resulting in seawater desalination being a logical solution for sustainable, longer-term water resource management to match growing water demand pressures in coastal areas. Desalination removes the salts, pathogens and impurities from saline water to render it potable. Desalinated water is produced either from brackish water (saline water with total dissolved solids [TDS] content of less than 10,000 mg/L) or from seawater (TDS between 30,000 and 50,000 mg/L). Although brackish aquifers and surface waters have been used for production of fresh drinking water for over 50 years, these brackish water sources are of limited availability and have a long replenishment cycle resulting in limited long-term sustainability. In contrast, the world’s oceans contain over 97% of the planet’s water resources, providing an essentially unlimited raw material for seawater desalination. In most urban centers, the freshwater produced by desalination of seawater is returned back to the ocean in the form of treated wastewater. Usually wastewater treatment plants are within a 25 50 km radius of the desalination plants along the coast and the time to return over 80% of the desalinated seawater to the ocean as wastewater discharge is typically less than 1 week. Most of the remaining 20% of the desalinated water is lost to evaporation and ground percolation as drinking water and wastewater generated from it are mainly used for irrigation. This makes seawater desalination one of the water supply options with the shortest water cycle, shorter than lake, river, or brackish water sources. With growing water scarcity and significantly reduced cost, interest in desalination has risen in recent decades. This is particularly true in the Middle East, where severe water scarcity and relatively low cost of energy have facilitated the

1.1 Current status of desalination

early adoption of desalination as a main source of potable water supply. Driven by rising demand and commercial innovation, the cost of desalination has decreased significantly over time, and is becoming an increasingly feasible and sustainable option for most other countries worldwide. At present, over 16,000 desalination plants worldwide provide drought-proof water supply for a large number of arid urban coastal municipalities of the Middle and Far East, Europe, Africa, Australia, and the Americas (Jones et al, 2018). Almost half of these plants (44%) are in the still fast-growing Middle East region. However, other regions of the world, notably Asia (in particular, China), the United States, and Latin America are also experiencing accelerated desalination plant capacity growth of 6% 8% per year, which far exceeds the growth rate of conventional water supply sources (2% 3% per year). Production of freshwater by desalination in 2019 totaled approximately 95 million m3/day (24,300 MGD). The corresponding cumulative volume of concentrate generated by the desalination plants in operation at present is estimated to be 142 million m3/day (37,500 MGD). Approximately 74% of the existing desalination plants use membrane RO technology for salt separation; 21% apply thermal evaporation; and 5% use other salt separation technologies, such as electrodialysis (ED) and ion exchange (IX) to produce freshwater (see Fig. 1.1). After 2015, most Middle Eastern countries have drastically reduced the construction of new thermal desalination plants and have refocused on the use of membrane desalination due to its lower energy demand and operational flexibility.

FIGURE 1.1 Current status of worldwide desalination technology use. Data from IDA Desalination Yearbook 2018 19.

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Desalination of brackish and seawater is becoming increasingly popular for production of fresh potable water in the United States. Based on a 2017 survey (Mickley, 2018) at present there are approximately 400 desalination plants in the United States and their number is growing steadily (see Fig. 1.2). Most desalination plants use nanofiltration (NF) and RO membranes for salt separation. The steady trend of reduction of desalinated water production energy and costs coupled with increasing costs of conventional water treatment and water reuse, driven by more stringent regulatory requirements, are expected to accelerate the current trend of reliance on the ocean as an attractive and competitive water source. This trend is likely to continue in the future and to further establish ocean water desalination as a reliable drought-proof alternative for a majority of coastal communities worldwide in the next 15 years. At present, desalination provides approximately 10% of the municipal water supply of the urban coastal centers in the United States, Europe, Israel, and Australia, and over 50% of the drinking water of the Gulf Cooperation Countries; by 2030 this percentage is expected to exceed 25% and 80%, respectively. Increased reliance on seawater desalination is often paralleled with ongoing programs for enhanced water reuse and conservation with a long-term target of achieving a balance of conventional water supply sources, seawater and brackish water desalination, water reuse and conservation to the total water supply portfolio of large coastal communities. Surface water sources are usually significantly cheaper with well-developed management systems and operations in place.

FIGURE 1.2 Cumulative number of municipal desalination plants in the United States.

1.1 Current status of desalination

Adding more costly desalinated water to the supply mix requires improved demand management and deriving full value of reuse potential to optimize the value of potable water. Near- and long-term desalination technology advances are projected to yield a significant decrease in costs of production of desalinated water by 2030. In desalination, innovative technologies have been addressing longstanding issues that have hampered the development of this alternative resource. New technologies such as nanoparticle enhanced membranes, biomimetic membranes and forward osmosis as well as beneficial extraction of rare metals from the brine generated by desalination plants are aimed at reducing energy consumption (by 20% 35%), reducing capital costs (by 20% 30%), improving process reliability and flexibility, and greatly reducing the volume of the concentrate discharge.

1.1.1 Desalination as a strategic water resource option Despite significant reduction in cost, desalination remains more expensive than other bulk water sources and needs to be used strategically to address a limited range of problems. However, today the instances of these problems are fast expanding. Desalination is proving appropriate for certain markets that require a high quality and complete reliability of service and in which customers or governments can afford to pay the higher cost. For example, desalination can produce high-quality potable water that suits the needs of large cities in which there are high concentrations of people who demand a quality 24/7 water service and who are prepared to pay for that service. Desalination can also provide a reliable supply of large volumes of water to high-value industry, commerce, and tourism. These uses typically value water appropriately and can afford to pay unsubsidized cost for production of desalinated water. Desalination is of specific interest in certain locations in which the other supply alternatives are equally or more costly and/or the risk of supply failure or inability to secure sustainable alternative water resources is high. Desalination is, however, demanding in terms of location. Water has a very high ratio of bulk to value and is very expensive to lift or transport. This drives the location of a desalination plant: to be near its source, the sea, and to be close to its market or point of use. Hence, the typical location of a desalination plant is along a coastal city or coastal industrial zone, supplying a relatively well-off industrial, commercial, or domestic demand. Where the physical and socioeconomic conditions are right, seawater desalination provides a strategic solution for the sustainable, long-term satisfaction of part of this growing water demand. As water scarcity grows and with advances in desalination technology and reductions in production cost, policymakers around the world are rightfully asking whether desalination should play a part in closing the gap between supply and demand in future years. Although most of the supply demand gap solutions will still come from the traditional supply and demand side management options, desalination is one of the viable options with strategic relevance.

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Desalination also provides a solid response to exogenous risks such as dependency. Singapore, for example, opted for large-scale desalination to reduce its dependence on increasingly expensive imported water from Malaysia. The stable, efficient supplies of urban and industrial water that desalination provides can help governments manage a range of economic, social, and political risks.

1.1.2 Current desalination project risks and costs Desalination projects are often megasized with risk assessment, management, and mitigation comprising key components of project planning. All business decisions require not only an assessment of costs and returns but also an evaluation of the risks attached to a project and measures for managing or eliminating risks together with contingency arrangements for mitigating possible impacts. Clearly, the risks associated with mega projects are considerable and risk assessment forms a key part of planning. Key risks associated with desalination projects include (1) permitting or licensing risks, (2) entitlement risks, (3) technology risks, (4) construction risks, (5) regulatory risks, (6) financial risks, (7) source water quality risks, (8) power supply risks, (9) O&M risks, and (10) desalinated water demand risks. Selecting the right procurement method is important for matching risk exposure to managerial capacity and ultimately achieving the best value for money. The sponsor of an infrastructure project has alternative options to deal with each of these risks: (1) decide to manage it (keep the risk), if the sponsor believes there is the technical, managerial, or financial capacity required to handle it; (2) insure or hedge the risk, if and where the market offers such solutions; or (3) transfer it or share it with a third party. The conditions under which these risks are transferred or shared with a private partner are determined by the procurement instrument adopted to develop the infrastructure. In turn, the selection of the procurement instrument should be made to allocate the different risks involved with the party that is best placed to manage them in a cost-effective way, which is not necessarily always the private sector. Commonly used desalination project delivery methods include: 1. the turnkey approach, also referred to as “engineering, procurement, and construction” (EPC), in which the private contractor is responsible for the design and the construction of the facility; 2. the “design build operate” method (DBO), in which the contractor is also responsible for the operation of the plant for a limited number of years, usually two to five; and 3. the “build own operate transfer” method (BOOT), by which the private partner finances the desalination facility and operates it for a long period of time, usually 20 25 years, in exchange for tariff-based payments linked to plant capacity and actual water demand.

1.2 Enabling conditions for desalination

The traditional infrastructure procurement approach, also known as “design bid build” (DBB), is rarely used for desalination projects.

1.2 Enabling conditions for desalination The advance of the RO desalination technology is similar in dynamics to that of computer technology. While conventional technologies, such as sedimentation and filtration have seen modest advancement since their initial use for potable water treatment several centuries ago, new more efficient seawater desalination membranes and membrane technologies, and equipment improvements are regularly released. Similar to computers, the RO membranes of today are many times smaller, more productive and cheaper than the first working prototypes. The future improvements of RO membrane technology which are projected to occur by 2030 are forecast to encompass:

• development of membranes of higher salt and pathogen rejection, productivity, reduced trans-membrane pressure, and fouling potential;

• improvement of membrane resistance to oxidants, elevated temperature, and compaction;

• extension of membrane useful life beyond 10 years; • integration of membrane pretreatment, advanced energy recovery, and SWRO systems;

• integration of brackish and seawater desalination systems; • development of new generation of high-efficiency pumps and energy recovery systems for SWRO applications;

• replacement of key stainless-steel desalination plant components with plastic • • •

components to increase plant longevity and decrease overall cost of water production; reduction of membrane element costs by complete automation of the entire production and testing process; development of methods for low-cost continuous membrane cleaning which allow reduction in downtime and chemical cleaning costs; and development of methods for low-cost membrane concentrate treatment, inplant and off-site reuse, and disposal.

Although no major technology breakthroughs are expected to dramatically reduce the cost of seawater desalination in the coming years, the steady reduction of desalinated water production costs coupled with increasing costs of water treatment driven by more stringent regulatory requirements, are expected to accelerate the current trend of increased reliance on the ocean as an attractive and competitive water source by 2030. This trend is forecast to continue in the future and to further establish seawater desalination as a reliable drought-proof alternative for many coastal communities

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Table 1.1 Forecast of desalination energy use and costs for medium and large plants. Parameter for best-in class desalination plants 3

Total electrical energy use (kWh/m ) Cost of water (US$/m3) Construction cost (US$/MLD) Membrane productivity (m3/membrane)

2020

2022

2030

3.5 0.8 1.2 28

2.8 0.6 1.0 55

2.1 0.3 0.5 95

4.0 1.2 2.2 48

3.2 1.0 1.8 75

2.4 0.5 0.9 120

worldwide. These technology advances are expected to entrench the position of SWRO treatment as viable and cost-competitive process for potable water production and to reduce the cost of freshwater production from seawater by 25% in 2022 and by up to 60% by 2030 (see Table 1.1). The rate of adoption of desalination in coastal urban centers worldwide is dependent on the magnitude of water stress to which they are exposed and availability of lower-cost conventional water resources. In future, desalination is likely to be adopted as main water supply in arid and semi-arid regions of the world such and the Middle East, North Africa, the Western United States, and Australia and in locations of concentrated industrial demand for high-quality water such as Singapore, China, and Northern Chile.

1.3 Overview of existing concentrate management practices According to the 2018 report on concentrate treatment prepared by the United States Bureau of Reclamation (Mickley, 2018) the five most commonly used concentrate management alternatives in the United States are: (1) surface water discharge, (2) sewer disposal, (3) deep-well injection, (4) land application, and (5) evaporation ponds (see Fig. 1.3). The desalination concentrate management practices shown in Fig. 1.3 have similar frequency of application worldwide.

1.4 Concentrate management regulations At present, there are no federal regulations in the United States or state regulations elsewhere in the world specifically developed to address waste discharges from desalination plants (Water Reuse Association, 2011). Desalination plant discharges are classified by the United States Environmental Protection Agency (USEPA) as industrial waste despite the fact that these discharges are distinctively different from most industrial discharges. Several regulatory programs in the United States that impact the disposal of desalination plant discharges, including the Clean Water

1.4 Concentrate management regulations

FIGURE 1.3 Current concentrate management practices.

Act (CWA), the Underground Injection Control (UIC) Program, ordinances that protect groundwater, and the Resource Recovery and Conservation Act (RCRA) for any solid waste residuals. Disposal options for desalination plant discharges and associated regulatory and permitting agencies include:

• Disposal to surface water discharge requires a National Pollutant Discharge Elimination System (NPDES) permit.

• Sewer discharge requires a permit issued by the local sewer agency to meet its •

•

•

sewer ordinance and the CWA Industrial Pretreatment Program (IPP) requirements, as stipulated in the agency’s NPDES permit. Concentrate disposal by land application (percolation ponds, rapid infiltration basins, landscape and crop irrigation, etc.) must comply with federal and state regulations to protect groundwater, public health, and crops/vegetation. Land application requires a permit from state agencies. Concentrate disposal by deep-well injection is regulated by the UIC program of the Safe Drinking Water Act. The related construction, monitoring, and other permits are issued and enforced by the USEPA region or state agency that has primacy. RCRA regulates the disposal of solids, such as precipitated salts and sludge; if such solids contain arsenic or other toxins and do not pass the toxic characteristic leaching procedure (TCLP) test, they are considered a hazardous waste and must be handled accordingly.

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The most important regulations pertaining to disposal of desalination plant discharges are those related to the CWA, including the NPDES program. Under the CWA, desalination plant discharges are regulated as industrial wastes as the USEPA has not established specific regulations concerning the disposal of water treatment plant residuals, including desalination plant discharges. For surface water discharge, NPDES permit is required pursuant to the CWA; its antidegradation policy prevents the relaxation of discharge limits for contaminants specified in a NPDES permit, particularly if the receiving water is designated as sensitive or impaired. If a water treatment plant currently has a TDS discharge limit, combining high TDS concentrate from the desalination plant RO system with the existing discharge may not be allowed. Permitting practices in the Middle East are very similar to these in the United States. The regulations pertaining to desalination plants in Australia, Spain, and Israel, which at present have the largest number of desalination plants outside of the Middle East, have a number of similarities to those in the United States. In all of these countries the permitting process for such discharges is the same as this applied for permitting of discharges from wastewater treatment plants. Australia has discharge regulations most similar in structure to these in the United States, where the federal government has established the baseline legal framework for regulation of waste discharges and the individual states have enhanced the federal regulations with state and location-specific regulatory requirements (Mickley and Voutchkov, 2016). Despite the similarities, the permitting of medium and large size projects in the United States usually takes longer than that in Australia, Spain and Israel. For example, the permitting of the Tampa Bay and Carlsbad SWRO desalination projects was completed within 2.4 and 5 years, respectively. For comparison, the average time needed for permitting of similar size projects in Australia is 1.5 2 years and in Spain and Israel is 9 12 months. The main reasons are as follows:

• Streamlined regulatory process: Usually only one or two agencies are involved •

in the environmental review of the desalination project as compared to four to six agencies in most US states and up to 24 agencies in California. Priority review of desalination projects: Spain, Israel, and Australia recognize the national/state strategic importance of seawater desalination for securing sustainable and drought-proof long-term water supply in these countries. As a result, they have long-term plans for development and implementation of desalination projects, which are under the close oversight of the central government in Spain and Israel and the state government in Australia. Since the timely implementation of such plants is considered of high importance and priority for the respective countries, the regulatory agencies are given support at federal level in the case of Spain and Israel, and at state level in the case of Australia in terms of expertise, direction, and funds to expedite and give priority of the environmental review of desalination projects as compared to other types of projects.

1.4 Concentrate management regulations

• Superior expertise of regulatory agencies in permitting of desalination plants: In

•

the United States, mainly because of funding constraints, many of the regulatory agencies involved in the permitting of desalination projects usually do not maintain staff with all types of expertise needed to complete an expedited review of desalination projects such as marine biologists, experts in outfall discharge modeling, and engineers with experience in the design and operation of desalination plants. For comparison, the key agencies involved in desalination project review in Spain, Australia, and Israel have such experts on staff or if such experts were not originally available, they were retained in expeditious manner at the beginning of the project review to minimize time needed for environmental project review. For comparison, most of the agencies involved in desalination review in California do not have such experts and as a result the environmental review process goes through 6 12 rounds of requests for additional information by the regulatory agency reviewers since they learn on the job and work piecemeal on their questions as they learn more about the project. Sharing of regulatory expertise between various agencies: in all of the listed states, the key regulatory agencies involved in permitting of desalination projects have internal meetings where they share experience with various permitting issues. Such regulators also actively participate in professional conferences and public forums presenting in clear manner their requirements and expectations associated with the type and detail of information that needs to be submitted by the project sponsors in order to minimize time needed for project permitting. Mainly due to lack of funds, US regulators involved in permitting of desalination projects usually do not have such professional experience exchange opportunities in and out of state and rarely attend professional conferences or present their expectations in professional forums.

In all countries referenced earlier, the desalination plant permits are issued after a thorough environmental review of the impact of the plant discharge on the surrounding aquatic environment, which is determined based on

• Projections of concentrate water quality developed based on source seawater • •

•

quality characterization and the specific design features of the desalination plant (plant recovery, product water quality, type of intake, and discharge). Biological survey of the discharge area aiming to document the type and quantity of marine species inhabiting this area and their salinity tolerance. In all of the referenced countries the salinity tolerance of marine organisms is determined based on chronic (or in the case of some Australian states), acute whole effluent toxicity (WET) testing of the most sensitive species inhabiting the discharge area. In Australia the marine organisms are tested in embryonic stage of development, which has resulted in the most stringent requirements for concentrate dilution as compared to these in Spain and Israel where the test species used for determining salinity tolerance are in adult phase. The mixing requirements for the desalination projects are determined based on the WET testing study and hydrodynamic modeling of the discharge area.

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CHAPTER 1 Introduction to concentrate management

In Spain and Israel usually only one environmental regulatory agency has the right to make decisions and establish discharge permit requirements and mitigation measures. If other agencies are involved in the project review, they provide comments to the lead agency but have no right or jurisdiction to change permitting requirements except by internal consensus. In Australia, key decisions are made at state level by one lead agency. For comparison, the independent multiagency review process typical for states such as California results in numerous conditions and permits which regulate the discharge and which may have different requirements in terms of mitigation of environmental impacts. Such practices not only delay the permitting process but also put a significant burden on the project sponsor associated with project implementation, operations monitoring and data reporting. Regulations applicable to surface water discharge across the world are expanded on in Chapter 3, Surface Water Discharge of Concentrate.

References Mickley, M.C., 2018. Updated and Extended Survey of U.S. Municipal Desalination Plants. Desalination and Water Purification Research and Development Program Report No. 207. Denver: US Bureau of Reclamation. Mickley, M.C., Voutchkov, N., 2016. Database of permitting practices for seawater concentrate disposal. Water Environ. Reuse Res. Found. Jones, E., Qadir, M., van Vliet, M.T.H., Smakhtin, V., Kang, S., 2018. The state of desalination and brine production: a global outlook. Sci. Total Environ. 657, 1343 1356. Water Reuse Association, 2011. Seawater Concentrate Management, White Paper. WRA, Alexandria, VA.

CHAPTER

Desalination plant discharge characterization

2

2.1 Desalination plant waste streams Most membrane desalination plants have the following components, which are shown in Fig. 2.1:

• a point of intake to collect saline source water (ground- or seawater); • a type of pretreatment system with the main purpose of removing suspended solids, organics, and scaling minerals from the saline source water;

• a system of reverse osmosis (RO) membranes and equipment which process •

the source water to produce fresh, low salinity water (called permeate) by separating dissolved solids from the pretreated saline water; and a posttreatment system to add back necessary minerals to the product water to make it suitable for distribution and final use.

Brackish water desalination plants include most of the same key treatment process components as seawater desalination facilities. However, in many brackish plants, a portion of the source water is bypassed and blended with plant permeate to achieve target water quality. Desalination plant residuals typically include:

• Concentrate generated by the RO system, which contains dissolved and

• •

particulate contaminants removed from the feed water. Concentrate may also contain chemicals from the source water conditioning and the pretreatment facilities. Spent filter backwash water generated by the desalination plant pretreatment system. Spent cleaning solutions from the periodic chemically enhanced cleaning of the RO and pretreatment membranes (if membrane pretreatment is used). These waste streams contain a high concentration of the cleaning chemicals, along with the feed water contaminants removed during membrane cleaning.

Desalination plants are usually designed to operate and produce permeate continuously. Concentrate is generated as a byproduct whenever the plant is

Management of Concentrate from Desalination Plants. DOI: https://doi.org/10.1016/B978-0-12-818045-7.00002-6 © 2020 Elsevier Inc. All rights reserved.

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CHAPTER 2 Desalination plant discharge characterization

FIGURE 2.1 Schematic of typical membrane desalination plant.

operational. The volume and frequency of backwash water generated is dependent on the type of pretreatment system; granular media filters have backwash cycles with duration of 24
48 hours, while membrane pretreatment systems have cycles far shorter, typically between 30 and 60 minutes. Spent cleaning solutions generate far smaller volumes of discharge, depending on the required frequency of RO membrane cleaning while side-streams from pretreatment membrane clean-inplace (CIP) cleaning are usually generated monthly or once every several months (Voutchkov, 2011a). The RO and pretreatment membranes are typically cleaned with acid (mineral or citric) to remove inorganic foulants and with alkaline solutions (i.e., sodium hydroxide, often in combination with detergents/surfactants and sometimes with chelating agents) to loosen, dislodge, and remove biofilms and organic foulants. Sodium hypochlorite is also applied for periodic (once per day to once per week) enhanced backwash of the pretreatment membranes to control excessive biogrowth on the membrane fibers.

2.2 Concentrate Separating minerals and contaminants from source water results in two liquid streams: one with a much reduced concentration of minerals (fresh water), the other with far higher concentration. The stream with higher salinity concentration that contains the minerals removed from the source water is known as “concentrate.” The concentrate also contains the antiscaling chemicals added during the source water conditioning process prior desalination.

2.2 Concentrate

2.2.1 Quantity The volume of concentrate depends on the size of the desalination plant and on the ratio between the produced fresh water and the saline source water collected for its production. This ratio is typically referred to as a recovery rate and expressed in percent of the collected source water. Desalination plants are classified in terms of the volume of fresh water they produce, where small plants are considered facilities that yield less than 20 MLD while large plants produce hundreds of millions of liters per day. The recovery rates differ depending on the type of plant and other operational conditions: most seawater RO plants typically have recovery rates between 40% and 55% while brackish water desalination plants operate at significantly higher recovery of 65%
85% (Voutchkov, 2011a). The recovery rate of a plant (R) is simply the ratio of the volume of fresh water produced (Qp) divided by the volume of saline source water (Qs) collected for production of this fresh water. The volume of concentrate produced (Qc) is the difference between Qs and Qp. As desalination plants are classified in terms of the volume of fresh water produced and the recovery rather than the volume of source water required, the volume of concentrate can be calculated as (Voutchkov, 2011a): Qc 5 Qp 3 ð1 2 RÞ=R

(2.1)

Example For a large seawater desalination plant of freshwater production capacity of 100 MLD operating at a rate of recovery of 45%, the daily concentrate volume is calculated as follows: Qc seawater plant 5 100; 000 m3 =day 3 ð1 2 0:45Þ=0:45 5 122; 222 m3 =day With the same fresh water production capacity of 100 MLD, a brackish water desalination plant designed at recovery rate of 80% will generate nearly five times less concentrate than the seawater plant: Qc brackish water plant 5 100; 000 m3 =day 3 ð1 2 0:80Þ=0:80 5 25; 000 m3 =day

2.2.2 Quality The quality of concentrate is mainly a function of the composition of the source water, and is influenced by the recovery rate. The higher the recovery rate, the higher the concentration of minerals will be in the concentrate. With a recovery rate between 65% and 85%, the salinity of brackish plant concentrate can be between 4 and 10 times higher than that of the saline source water. The far lower recovery of seawater plants result in concentrate of between

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CHAPTER 2 Desalination plant discharge characterization

1.5 and 2.0 times higher in mineral content than the source seawater. This is due to the same amount of minerals now being contained in approximately half of the volume of the source water collected for desalination. The total dissolved solid content of concentrate can be calculated as (Voutchkov, 2011a)  
TDSconcentrate 5 ðTDSsource Þ 3 1=ð1 2 RÞ 2 ðRÞ 3 TDSproduct =½100 3 ð1 2 RÞ

(2.2)

Example For the example of a seawater desalination plant producing 100,000 m3/day (100 MLD) of fresh water, operating at 45% recovery, and having a source water TDS of 42,000 mg/L and product water TDS of 200 mg/L, the salinity of the concentrate will be:      TDSconcentrate sw 5 42; 000mg=LÞ 3 1=ð1 2 0:45Þ 2 ð0:45Þ 3 200mg=L =½100 3 ð1 2 0:45Þ 5 76; 362mg=L For a brackish water desalination plant of the same production capacity (100,000 m3/day), the same product water quality in terms of TDS (200 mg/L) and 80% recovery and feed TDS salinity of 4000 mg/L, the concentrate will have the following salinity:      TDSconcentrate bw 5 4000mg=LÞ 3 1=ð1 2 0:80Þ 2 ð0:80Þ 3 200mg=L =½100 3 ð1 2 0:80Þ 5 19; 992mg=L

The ion concentration factor can be calculated based on 100% rejection: CF 5 Concentration Factor ðdimensionlessÞ 5 1=ð1 2 RÞ

(2.3)

Example For a recovery rate of 48%, the concentration factor is: CF 5 1=ð1 2 0:48Þ 5 1:92

The ion concentration factor can also be calculated using the membrane salt passage (SP). SP is equal to permeate TDS (TDSproduct) divided by the feed TDS (TDSsource), which is also equal to 1 less the salt rejection percentage. The concentration factor is then calculated as (Voutchkov, 2011a): CF 5 ½1 2 ðR 3 SPÞ=ð1 2 RÞ

(2.4)

2.3 Spent pretreatment filter backwash water

Example For an RO system with recovery of 48%, and overall 97% salt rejection (3% SP), the CF is: CF 5 ½1 2 ð0:48 3 0:03Þ=½1 2 ð0:48Þ 5 1:90

The method of disposal impacts directly on the design of a desalination plant: If volume of concentrate needs to be minimized, a high brine concentration factor is required. In contrast, where disposing of high volumes of concentrate is a possibility, achieving low TDS is likely to be necessary. Increasing osmotic pressure and mineral scaling limit the brine concentration factor for seawater desalination plants to between 65 and 80 parts per thousand (ppt). For seawater, membrane recovery currently limits single pass recovery to around 40%
45%, which yields a concentration factor between 1.5 and 1.8 (Voutchkov, 2011b). Concentrate quality can largely be deduced from source water characteristics. Where source water contains heavy metals, these will be concentrated in the brine at a similar ratio to rejection of salts. Organics in source water will be nearly completely rejected through RO treatment with less than 5% remaining in the permeate and the balance in the concentrate. Similarly, due to increased alkalinity, brine pH is likely to be higher than that of source water. Pretreatment systems are likely to impact on the concentrate quality, with a possible increase in inorganic ions including chloride, iron and sulfate due to use of coagulants. Where acid is used, concentrate may be higher in organics. Nanofiltration results in concentrate with slightly different characteristics to that of RO. Nanofiltration has lower salt rejection capacity resulting in less salty concentrate. Furthermore, multivalent ions such as calcium, magnesium, and sulfate are more readily rejected than monovalent ions like chloride and sodium with the result that the ratio of monovalent to multivalent ions in the source water is different to that found in the concentrate. Pretreatment may result in the concentrate having lower turbidity, suspended solids, and biological oxygen demand than the surface water, should the pretreatment waste stream be treated separately in settling tanks prior to its mixing with the concentrate and ultimate disposal. Where these are blended, the concentrate will have characteristics similar but more concentrated than the source water. Any additives to the source water for conditioning after pretreatment, such as antiscalant and biocide will end up in the concentrate having been rejected by the RO membranes.

2.3 Spent pretreatment filter backwash water Pretreatment filtration systems require periodic cleaning (backwashing) of the filtration media to remove accumulated solids and organics, generating waste streams which need adequate disposal.

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CHAPTER 2 Desalination plant discharge characterization

2.3.1 Quantity The volume of backwash water generated depends in part on the quality of the source water but more so on the type of pretreatment: Granular media filtration typically requires between 3% and 6% of the source water to backwash. Membrane filtration takes nearly twice this volume (between 5% and 10%). If the source water has high turbidity, backwash frequency and intensity need to be increased, which results in increased volume of backwash water to be disposed of (Voutchkov, 2011a).

Example For a 100 MLD (100,000 m3/day) desalination plant with recovery of 48%, and a total daily backwash water volume of 5% of the daily intake flow, the backwash volume generated per day is:
Qbw 5 100; 000m3 =day 3 5%=48% 5 10; 416m3 =day

2.3.2 Quality Spent filter backwash is constituted mainly from solids removed from the source water during pretreatment, as well as any coagulants that may have been added to the source water for conditioning prior to filtration. Backwash water will contain coagulated solid and colloidal particles and ferric hydroxide if ferric chloride and/ or ferric sulfate are used (Voutchkov, 2011a). The concentration of total suspended solids in the spent backwash water is a function of the TSS concentration of the source water as well as the dosage of the applied iron coagulant and can be calculated as follows (Voutchkov, 2011a): TSSbw 5 ðTSSs 1 0:8 3 DoseFe Þ 3 Qs =Qbw

(2.5)

where: TSSbw and TSSs are the total suspended solids concentrations of backwash water and source water, respectively in mg/L; DoseFe is the dose of ferric salt expressed as iron concentration, in mg/L; and Qbw and Qs are the daily flows of desalination plant backwash water and intake source water, respectively in m3/day.

Example Using Eq. (2.5), the TSS concentration of the backwash water generated by the pretreatment system of the 100,000 m3/day desalination plant described in the previous example, with a TSS concentration in the source water of 2.5 mg/L, treated with 5 mg/L of ferric chloride coagulant (as iron) will be: TSSbw 5 ð2:5mg=L 1 0:8 3 5:0mg=LÞ 3 100; 000m3 =day=11; 111m3 =day 5 58:5mg=L

2.3 Spent pretreatment filter backwash water

This calculation shows that backwash water can contain a significant amount of solids, which could exceed the 30 mg/L TSS discharge limit commonly applied by regulatory agencies worldwide for surface water discharges. However, if mixed with the desalination plant concentrate, the TSS concentration of the spent pretreatment filter backwash water could be reduced below the regulatory threshold. As indicated in a previous example, a 100,000 m3/day seawater desalination plant with 45% recovery will generate a daily volume of 122,222 m3/day of concentrate. Since concentrate practically does not contain suspended solids (TSS 5 0 mg/L), the concentration of the blend of 122,222 m3/day of concentrate of 0.0 mg/L of TSS and 11,111 m3/day of backwash water with TDS of 58.5 mg/L will be (Voutchkov, 2011a):

TSSblend 5 58:5mg=L 3 11; 111m3 =day 1 0mg=L 3 122; 222m3 =day =
11; 111m3 =day 1 122; 222m3 =day 5 4:9mg=L

This calculation indicates that blending of the concentrate and the backwash water of seawater desalination plants will be beneficial if they are mixed and equalized prior to discharge. Backwash water is discharged periodically in short intervals and as a result the solids content in the discharge spikes over short periods of time, which is why it is beneficial to store this discharge in equalization tanks from where it can be released and mixed with concentrate to achieve consistency and reduce the overall content of discharged solids (Voutchkov, 2011a). In most cases, direct discharge of backwash water containing ferric hydroxide (also commonly known as rust) is often not allowed by the applicable discharge regulations or not advisable. The red color of the discharge is likely to cause discoloration of the entire concentrate stream, and while not harmful to the marine environment, it is not a esthetically acceptable as it alters the color of the receiving water in the area of discharge. For this reason, such backwash water needs treatment and solids handling to remove the iron hydroxide. For small plants, volumes of backwash water will be much less, and disposal to sanitary sewer can be an option. The backwash waste stream is disposed to the reticulation network, blended with sewage and treated at the relevant wastewater treatment plant (WWTP). While coagulant tends to have a positive impact on the WWTP primary clarification process, high salinity may have a negative impact on the biological treatment process (e.g., activated sludge system). The composition of the blend must be determined as safe during consideration of options for discharge. Spent backwash filter water may also include other chemicals used to condition the saline source water. This could include flocculants, chlorine compounds, acids, and biocides in small quantities. Where equalized backwash water is blended with concentrate, these chemicals typically have an insignificant impact but the potential usually necessitates an interim retention or buffer tank, where all the plant’s waste streams are blended prior to discharge (Voutchkov, 2011a).

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2.4 Chemical cleaning residuals Another stream of waste is generated through the cleaning of foulants accumulated in the RO and pretreatment membranes (if membrane pretreatment is used) to improve performance. Such cleaning is referred to as CIP as the membranes remain in their vessels during such cleaning. The frequency of cleaning depends very much on the quality of the feed water as well as on the type and age of the membranes. CIP chemicals are specifically selected to address the fouling experienced, both in type and combination. Fouling can be particulate, colloidal, organic, or microbiological, which generally occur in combination. The appropriate chemical for each of the fouling types may thus be mixed, and so form part of the waste stream (Voutchkov, 2011a).

2.4.1 Quantity The quantity of spent CIP chemicals is related to:

• the size of the desalination plant; • the type of pretreatment system (if granular media filters are in use, not applicable);

• the number of membranes (RO and Pretreatment); • the fouling potential of the saline source water; and • the type/combination of foulants that accumulates on the membrane surface (Voutchkov, 2011a). Fig. 2.2 presents a schematic of a typical CIP system.

FIGURE 2.2 Schematic of CIP system.

2.4 Chemical cleaning residuals

Typically, the “cleaning solution volumes” required during a CIP of RO membranes equate to 1.0
1.8 L/m2 (0.025
0.045 gal/sq ft) of membrane surface, excluding flush water volumes. The typical cleaning solution volume can thus be estimated by adding the total volume of the RO system plus the volume of the interconnecting pipe between the CIP tank and the membrane rack undergoing cleaning. The formula is (Voutchkov, 2011a): VRO system 5 Nt 3 Nvpt 3 Nepv 3 Aro 3 Ucl

(2.6)

where: VRO system is the Volume of the RO System; Nt is the Number of RO Trains; Nvpt is Number of Vessels per Train; Nepv is Number of Elements per Vessel; Aro is the Total Membrane Surface Ares of One RO Element (m2); Ucl is the Unit Cleaning Volume (L/m2).

Example Assume a 100 MLD SWRO system with 10 RO trains, 96 RO vessels per train and seven 8-inch elements per vessel, and RO elements with surface area of 37.2 m2, as well as 350 m long of distribution system pipe 400-mm in diameter. The total volume of cleaning solution for all RO trains will be approximately 418,936 L (374,976 L for the RO system and 43,960 L in piping) per cleaning chemical and per cleaning event. This volume is calculated for cleaning volume of 1.5 L/ m2 of membrane area: VRO system 5 10RO Trains 3 96Vessels per Train 3 7RO Elements per Vessel 3 37:2m2 per RO element 3 1:5L=m2 of Cleaning Solution 5 374; 976L The volume of the cleaning solution for 350 m of 400 mm (0.4 m) diameter pipe is 5 ð3:14 3 0:4m 3 0:4m=4Þ 3 350m 5 43:96m3 5 43; 960L This volume is specific for each chemical solution. RO system cleaning is often completed in multiple steps, so the total volume is the sum of the volumes used in each step. Depending on the foulants, a low-pH solution is usually followed by one with a high pH. The RO trains are also cleaned in steps. A typical approach for large RO trains (100 vessels or more) is to first clean the modules in one-half of the vessels in the first stage, then the other half of the first stage, and finally all modules in the second stage (Voutchkov, 2011a).

CIP membrane cleaning is followed by draining of the spent cleaning chemicals and flushing of RO membranes. The waste streams generated during the entire RO train cleaning process are: 1. Concentrated waste cleaning solution which contains the actual spent membrane cleaning chemicals. (The quality and quantity of this stream described earlier.)

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2. Flush water residual cleaning solution (first flush) is the first batch of clean product water used to flush the membranes after the recirculation of cleaning solution is discontinued. This first flush contains diluted residual cleaning solution. 3. Flush water permeate is the spent cleaning water used for several consecutive membrane flushes after the first flush. This flush water is of low salinity and contains only trace amounts of cleaning solution. 4. Flush water concentrate is the flush water removed from the concentrate lines of the membrane system during the flushing process. This water contains hardly any cleaning chemicals and is of slightly higher salinity concentration than the flushing permeate (Voutchkov, 2011a). It should be noted that the volumes of the spent membrane cleaning chemicals and flush water are several orders of magnitude smaller than the spent backwash water generated by the pretreatment system and the RO concentrate. Typically, the spent cleaning solution volume and flush water are less than 0.1% of the other plant waste streams.

2.4.2 Quality The water quality of the CIP residuals (spent membrane cleaning solution/s) has the chemical characteristics of a combination of the spent cleaning solution as well as the material removed from the membranes. Reactions with foulants will tend to raise the pH of acid solutions and lower that of basic solutions. Table 2.1 lists typical cleaning formulations developed to remove various types of foulants (Cotruvo et al., 2010). Note that membranes foul in many different ways and fouling rate would vary from one membrane supplier to another. It Table 2.1 Typical membrane cleaning solutions (Voutchkov, 2011a). Foulant type

Cleaning solution(S)

Inorganic salts including CaCO3, CaSO4, BaSO4 Metal oxides Inorganic colloids (silt) Silica (and metal silicates) Biofilms and organics

0.2% HCl; 0.5% H3PO4; 2% citric acid

2% Citric Acid; 1% Na2S2O4 0.1% NaOH/0.05% Na dodecyl benzene sulfonate/pH 12 Ammonium bifluoride; 0.1% NaOH/0.05% Na dodecyl benzene sulfonate/pH 12 Hypochlorite, hydrogen peroxide, 0.1% NaOH/0.05% Na dodecyl benzene sulfonate/pH 12; 1% sodium tripolyphosphate/1% trisodium phosphate/1% sodium EDTA

BaSO4, Barium sulfate; CaCO3, Calcium carbonate; CaSO4, Calcium sulfate; HCL, hydrochloric acid; H3PO4, phosphoric acid; Na2S2O4, sodium hydrosulfite; NaOH, sodium hydroxide; EDTA, ethylenediaminetetraacetic acid.

References

is recommended that an effective cleaning solution and procedures are developed with the assistance of the membrane supplier to optimize efficiency and thus the fresh water production capacity of a desalination plant. Citric acid is commonly used as cleaning solution. This chemical usually has a biological oxygen demand (BOD) concentration between 2000 and 3000 mg/L, which could contribute to an increase in the overall BOD of the plant’s discharge. Other acids like phosphoric and nitric acid could add undesirable nutrients to the discharge. When blended with the large volume of plant concentrate, these chemical containing waste streams are unlikely to result in any detrimental impact on the receiving environment because their volume is usually less than 0.1% of the volume of the concentrate. If further treatment is definitively required, waste streams can either be further treated on site by equalization and/or neutralization, or disposed of to wastewater treatment plants (Voutchkov, 2011a).

References Cotruvo, J., Voutchkov, N., Fawell, J., Payment, P., Cunliffe, D., Lattemann, S., 2010. Desalination Technology—Health And Environmental Impacts. CRC Press. Voutchkov, N., 2011a. Desalination Plant Concentrate Management. Water Treatment Academy. Voutchkov, N., 2011b. Overview of seawater concentrate disposal alternatives. Desalination: Int. J. Sci. Technol. Desalting Water Purif. 273 (1), 205
219.

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CHAPTER

Surface water discharge of concentrate

3

Where a desalination plant disposes of concentrate into the ocean, a tidal lake, or brackish canal, it is referred to as “surface water discharge.” Currently, surface water discharge most frequently takes the form of:

• discharging directly into a water body through an outfall or discharge structure specifically constructed with the desalination plant;

• discharging into a water body through an existing wastewater treatment plant (WWTP); or

• codisposal with the cooling water of an existing power plant (collocated desalination plant) (Voutchkov, 2011a). Each of the three alternatives has its advantages, challenges, and potential environmental impacts on the aquatic environment (Hoepner and Windelberg, 1996; Hoepner, 1999; Rhodes, 2006). Overview of key issues and solutions associated with the surface water disposal of concentrate generated by desalination plants is presented later in the chapter.

3.1 New surface water discharge More than 90% of large desalination plants worldwide discharge concentrate and other desalination waste streams through new surface water discharge systems, purpose-built with the plant and specific to environmental conditions. Disposal through near-shore discharge structures is suitable in areas with mixing through turbulent wave action. Alternatively, offshore outfalls need to be constructed to ensure adequate dispersion. Examples of large seawater reverse osmosis (SWRO) desalination plants with ocean outfalls include the 360 MLD plant in Ashkelon, Israel (Fig. 3.1), and the majority of large SWRO plants in Spain, Australia, and the Middle East. Minimizing the environmental impact of the discharge on the water body is the key design criterion, especially if concentrate has salinity outside of the typical range tolerated by local aquatic organisms in the area of the discharge. The aim in disposal is thus to accelerate the dispersion of concentrate to match the

Management of Concentrate from Desalination Plants. DOI: https://doi.org/10.1016/B978-0-12-818045-7.00003-8 © 2020 Elsevier Inc. All rights reserved.

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CHAPTER 3 Surface water discharge of concentrate

FIGURE 3.1 Near-shore discharge of Ashkelon SWRO plant, Israel.

ambient salinity as quickly as possible. Naturally occurring turbulent surf zones provide excellent mixing, but limited capacity to transport and dissipate the salinity load of the discharge further into the ocean. Where outfalls are used, diffusers are employed to aid dispersion over a larger, less concentrated area. It is recommended that hydrodynamic modeling be used, especially for medium and large desalination projects, to determine the threshold of the tidal zone’s salinity load transport capacity. For environmental protection of aquatic life, accumulation of excess salinity must be avoided so the effect of the salinity load introduced with the desalination plant discharge must be modeled to extrapolate the conditions over time (Bleninger and Jirka, 2010). The Ashkelon SWRO plant (shown in Fig. 3.1) discharges into the tidal zone, as do the large plants in Carlsbad, California (with capacity of 200 MLD), and Fujairah in the United Arab Emirates (UAE) (with 170 MLD capacity) (Voutchkov, 2011a). For very small desalination plants with production capacity of 1 MLD or less, the outfall is usually constructed as an open-ended pipe which is sometimes perforated, and extends into the tidal zone of the ocean for up to a couple of hundred meters. A discharge of this type relies on the tidal zone’s natural mixing turbulence to dissipate the concentrate and to bring the discharge salinity to ambient conditions quickly (Voutchkov, 2011a). Large SWRO desalination plants typically discharge concentrate beyond the tidal zone, with length of outfall varying between 400 and 1500 m. Such outfalls usually have diffusers to facilitate mixing of the concentrate with ambient water so that the discharge plume does not sink and accumulate at the bottom of the ocean around the discharge point. Diffusers direct the discharge plume toward the

3.2 Potential environmental impacts

ocean surface, from where it naturally moves downwards, and, in doing so the saline plume gets diluted and dissipates by mixing with the entire water column instead of settling directly on the floor. In design of offshore outfalls and diffusers, the dispersion of the saline concentrate should also be modeled using hydrodynamic modeling to ensure that negative environmental impacts are avoided not just instantaneously but over time. Ocean conditions vary vastly from coast to coast, and design has to be customized to the site-specific hydrodynamic and environmental conditions (Purnama et al., 2003; Purnama and Al-Barwani, 2004; Bleninger and Jirka, 2010).

3.2 Potential environmental impacts 3.2.1 Overview Compared to discharges of WWTPs, in which the main contaminants originate from human and industrial waste, the concentrate from seawater desalination plants primarily contains salts of natural origin, which have been collected with the source seawater to produce freshwater. As a result, the desalination process does not increase the total mass of salts contained in the ocean water in the discharge area: The mass of salts discharged back to the ocean is almost equal to the mass of salts collected from the ocean. In fact, the total mass of salts in the plant discharge is always slightly smaller than the mass of salts in the source seawater used for desalination as some of these salts remain in the desalinated water, which typically has salinity of between 100 and 500 mg/L of TDS. This contributes to desalination being a truly sustainable water supply alternative that usually has no long-term impacts on the salinity levels and water balance in the desalination plant intake and discharge areas. Furthermore, the freshwater produced from collecting seawater, is reunited with the salts separated from this seawater within 1 2 weeks after their separation by the desalination plant. While small amounts (estimated between 5% and 15%) of the freshwater produced from seawater is lost to evaporation, irrigation or human consumption, such loss is usually significantly smaller than the loss from evaporation that naturally occurs in the ocean in the vicinity of the desalination plant intake and discharge areas. Exactly the same characteristics such as color, odor, oxygen content, and transparency are exhibited by the concentrate as by the source water with open surface water intakes. Higher or lower salinity does not change its physical characteristics or aesthetic impact on the environment—more than 80% of minerals to be found in SWRO concentrate are sodium and chloride. Neither chemical nor biological oxygen demand are affected by salinity levels. Concentrate therefore provides neither macro- nor micronutrients to organisms in the receiving environment (Voutchkov, 2011b). In most coastal urban centers, seawater desalination plant intakes, concentrate discharge, and WWTP discharges through which the used desalinated water is returned to the ocean, are well within a 5 30 km radius. Therefore, the long-term

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regional environmental impact of surface discharge of seawater concentrate on the ocean is minimal and typically equivalent to the effect of naturally occurring evaporation. Ocean salinity varies naturally, as evaporation increases during hot, dry seasons leading to a slight salinity increase, while cool wet seasons result in slight salinity decrease. Taken over the year, natural salinity variation balances out with no net change. Similarly, SWRO desalination plants remove small volumes of seawater, and return these back to the ocean in two parts: a portion of concentrated seawater nearly immediately after extraction, and the used freshwater via WWTP discharges. The separated freshwater and salts reunite back in the ocean far more quickly than seasonal change. It is sensible to assess the overall balance in the water body rather than focusing only on concentrate discharge, when designing a new desalination plant. Consideration of natural variations as well as other discharges are likely to add an integrated point of view resulting in better balanced environmental impacts. Apart from changes in salinity, concentrate discharge to surface water bodies can result in further impacts unless mitigated through good design. For example, the density of concentrate plumes could reduce vertical mixing, which could result in a decrease in dissolved oxygen (DO) on the ocean bottom at the discharge point. Therefore, mixing energy introduced via diffusers or near-shore tidal movement is used to dilute and dissipate the salinity of the concentrate down to ambient levels before the concentrate reaches the bottom. Conventional water treatment plants use similar chemicals for water conditioning and membrane cleaning to those used in desalination plants, and thus have similar disposal challenges when treating surface or groundwater sources. Arguably, disposal of residual brine is seen as less of a challenge at water treatment plants. This is mainly due to:

• desalination plants require significantly more source water to produce the same volume of freshwater as water treatment plants;

• desalination plants generate discharge of significantly higher salinity than ambient source water; and

• desalination plants use more energy to produce the same volume of freshwater (Voutchkov, 2011b). WWTP discharges may cause a cumulative increase of both mass and concentration of artificial pollutants that are not contained in the seawater to which they are discharged. Pollutants contained in wastewater, such as antibiotics, cosmetic products, contraceptive substances, growth hormones, etc., are commonly referred to as endocrine disruptors due to the potential damage that they can cause on the hormonal balance of organisms, including humans. Such cumulative increase is more pronounced for the aquatic life in the discharge area of water reclamation plants that treat wastewater for direct or indirect potable reuse, as the RO membrane systems of these plants concentrate the artificial pollutants by between 5 and 10 times. These are typically not treated by the water reclamation plants, and ultimately are collected in and disposed of with the reclamation plant discharge.

3.2 Potential environmental impacts

The significant difference in the potential of discharges from water reclamation and seawater desalination plants to damage the aquatic environment in the area of their discharge should be taken into consideration when comparing the environmental impacts and long-term sustainability of desalination and water reuse as alternative water resources. Water scarcity is unlikely to decrease in the coming decades, and in many areas, other supply sources are likely to be very limited or nonexistent. While desalination concentrate discharge may pose specific challenges, these should be balanced against the overall impact of water scarcity, as well as all other feasible sources of water supply, including groundwater, water reuse, and surface water, cognizant that none of these are immune to the impact of climate change. At present, many conventional water supply sources in densely urbanized coastal areas worldwide are overused and their further depletion would have long-lasting environmental and socio-economic impacts. For example, long-term overpumping of freshwater aquifers in a number of regions of the world has resulted in measurable environmental impacts on traditional water resources such as reduction of riparian habitat and saltwater intrusion. Recent examples of such water supply practices are the extraction and transfer of freshwater from the San Francisco Bay Delta in Northern California to Southern California; and from freshwater aquifers, rivers, and lakes in northern Israel and Spain and their conveyance to the southern regions of these countries. Such long-term water transfers are threatening the sustainability of the system by impacting the eco-balance of the freshwater resource habitats (Voutchkov, 2011b). A holistic approach to water supply, considering the impacts of all alternative water sources, is necessary to ensure the best option is chosen, specific to environmental constraints, climate risk, and economic affordability in each case. Desalination provides improved assurance of supply in an environment where climate change threatens conventional water security. To date, chemical and biological monitoring programs have proved that ocean discharge at a number of large SWRO plants worldwide does not have significant impacts on the marine environment (Shemer and Semiat, 2017). It is in the industry’s best interest to continue building trust in its technologies, ensuring that environmental review processes are transparent and environmental impacts managed sustainably.

3.2.2 Overview of environmental issues and considerations Site selection for discharge to surface water is important to minimize environmental impact. Any protected marine habitats and other sensitive coastal areas where endangered species exist and are already stressed by other preexisting environmental impacts, must be avoided. The impact of concentrate on the aquatic environment is reduced in areas with strong currents as the energy of the currents aids in dissipating the discharge salinity. Cost of constructing outfall infrastructure can be minimized by finding appropriate locations relatively close to shore and at shallow depth. Marine vessel

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routes are less preferable to discharge concentrate if ship traffic impacts natural mixing patterns. Once potential sites for open ocean discharge have been identified, the impact of concentrate on the area, compatibility with receiving waters, sensitivity of ocean floor habitat (especially during construction), and environmental impacts of existing organisms in close proximity of the discharge area must be studied. The composition of concentrate must be modeled as accurately as possible, and harmful levels of metals and radioactive ions established. All species in the study area must be identified and evaluated for tolerance to salinity, and potential sensitivity to nutrient discharge (Voutchkov, 2011a). While the material impact of concentrate discharge from a single plant into a bay may be minimal, the combined effect of multiple discharges into one enclosed water body or water body with limited exchange with open ocean waters may accumulate over time (Missimer and Malive, 2018). Therefore installation of desalination plant discharges in areas with good and frequent natural tidal flushing is recommended. The feasibility assessment of the identified discharge location must include modeling to establish a number of threshold conditions in the receiving water body. Requirements established by regulatory authorities will determine factors such as the maximum distance required to full dilution (typically between 50 and 300 m) and both qualitative and numeric discharge water quality standards. Potential of whole effluent toxicity (WET) or concentrate should be considered, as well as the recirculation via natural currents of the discharge back to the plant intake structure (Voutchkov, 2011a). Development of desalination plants is often triggered in response to drought, with a sense of urgency. As impacts have been shown to be highly site-specific, standardized environmental regulations may not be sufficiently developed or broad enough to cover all likely outcomes. To ensure sustainable desalination, seawater quality monitoring in the area of the discharge has to be completed both before and after the installation of the outfall, and monitoring results need to be made publicly available to build confidence in the process (Kampf and Clarke, 2012).

3.2.3 Evaluation of concentrate dispersion rate and area The zone of initial dilution (ZID) is defined as the area around the discharge of the desalination plant at which boundary the concentration of the TDS of the mix between concentrate and ambient water reaches 10% of the TDS level. TDS concentration must be calculated throughout the zone, but particularly at the bottom, midway of the water column and at the surface of the ZID. These points are indicative of the impact of the added salinity in the discharge plume on surrounding habitats—mainly benthic organisms on the ocean floor, predominantly invertebrates midway and mostly plankton at the surface. The ZID is commonly assumed to be located within 300 m radius from the point of discharge for

3.2 Potential environmental impacts

preliminary analysis. Naturally occurring mixing intensity in the discharge area will influence the size of the ZID. For many existing large desalination plants with site-specifically designed surface water discharge, experience has shown that the edge of the ZID is within 50 100 m from the point of discharge. Hydrodynamic modeling is the study of liquids in motion. The distribution of concentrate in the ZID is established through such modeling, given the characteristics of the concentrate and prevailing ocean conditions. The modeling results are used to inform the discharge design including best location; sizing of discharge outfall length and points; configuration of infrastructure, requirements for diffusers, such as number, inclination and exit velocity; desirability of codisposal with wastewater effluent etc. Once a model has been developed, the impact of the saline plume can be established for a range of possible conditions and design configurations to determine the best fit for least environmental impact and lowest construction cost. Such modeling typically requires customized fluid dynamics software to analyze the discharge of the specific project (AWWA, 2007; Bleninger and Jirka, 2010; Cotruvo et al., 2010; Voutchkov, 2011b). In order to assess the long-term impacts of desalination plant discharges on the marine environment, the Southwest Municipal Water District of Florida in collaboration with the University of South Florida, completed a study entitled “Effects of the Disposal of Seawater Desalination Discharges on Near Shore Benthic Communities” (Hammond et al., 1998). The study focused on the environmental impact in the discharge area of a small desalination plant located in Antigua, in the West Indies. The SWRO plant’s production capacity was 7 MLD, with a concentrate salinity of 57,000 mg/L discharged 100 m offshore through an outfall without diffusers. The ambient salinity was between 35 and 38 ppt, while the salinity at 1 m from the discharge point was between 45 and 50 ppt. The study involved six radial transects from the discharge point to monitor all marine organisms encountered over a 6 month period. Organisms encountered included macrofauna, benthic foraminifera, benthic microalgae, macroalgae, and seagrass. Macrofauna consisted of sea stars, worms, anemones, pelagic fish, gastropods, bivalves, oligochaetes, and polychaetas. The study determined no detectable impact of the desalination plant discharge on seagrass production, biomass or density, nor any statistically significant effect on the biomass and numerical abundance of the organisms inhabiting the discharge area (Voutchkov, 2011a).

3.2.4 Whole effluent toxicity Potentially detrimental impacts of concentrate on the aquatic environment have to be identified and mitigated during project construction and operation. WET testing is used to establish potential acute and chronic toxicity impacts of the discharge on species endogenous to the discharge area. Both average and worst case discharge conditions are usually required to be modeled and tested for having

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WET impacts. Discharge with effluent from WWTP requires that at least one species of echinoderms taxa (e.g., sea urchins, starfish, sand dollars, or serpent stars) to be tested in a worst case scenario as this will provide indication of potential toxicity impacts from discharge ion imbalance caused by blending seawater concentrate and wastewater effluent. The combination of concentrate and effluent likely to elicit a worst case has been shown to be average concentrate discharge combined with maximum wastewater effluent flow (Voutchkov, 2011a). Echinoderms are marine species that are sensitive not only to the salinity of the seawater but also to the changes of the ion makeup of the aquatic environment measured as a ratio between the TDS concentration of the seawater and the concentration of key ions in this water such as calcium, magnesium, sodium, chloride, and sulfate. Protocols for testing exist in some countries such as the United States and Australia, specifying WET bioassay testing on species sensitive to pollutants. USEPA has protocols for acute, chronic toxicity and bio-accumulation in sensitive biota. Cases have been recorded, especially in Florida, where WET failure was observed, in the presence of high calcium levels, complicated with simultaneous high fluoride levels in the blend of wastewater effluent and concentrate (Mickley, 2006). Toxicity from heavy metals and pesticides is decidedly difficult to address, while that of chemical imbalance due to high levels of ions is relatively easy to remedy. Regulations in Florida cater to ion toxicity in concentrate by providing exceptions where ion-imbalance triggered toxicity is the only type of toxicity exhibited by the discharge (Mickley, 2000).

3.2.5 Numeric effluent discharge water quality requirements Environmental regulations typically define a number of numeric water quality thresholds that have to be met at the edge of the ZID in order to provide adequate protection of the receiving aquatic habitat. Such desalination plant discharge water quality parameters typically include TDS, turbidity, some metals, such as copper, nickel, lead, mercury, etc., and radionuclides. Regulatory agencies worldwide determine maximum TDS allowed for each site for each specific project which is considered to be issued a discharge permit and national standards applicable to all projects are not available at present (Einav et al., 2002; Mauguin and Corsin, 2005; Sadhwani et al., 2005). Seawater is naturally low in content of metals, but where concentrate is mixed with wastewater effluent, numerical limits of toxic metals may be exceeded. Where desalination plants are collocated with power plants, this issue also deserves specific attention as equipment of older power plants may release small quantities of metals such as copper and nickel into the cooling water used as blending water for the desalination plant concentrate. Many desalination plants with open ocean intakes use coagulants, especially ferric sulfate or ferric chloride for conditioning of the saline source water prior to pretreatment and desalination. Ferric chloride is converted to ferric hydroxide after blending with the source

3.2 Potential environmental impacts

seawater and is attached to the solids separated from it during the pretreatment process. The solids containing ferric hydroxide will impact on the numeric concentration of iron and turbidity in the discharge, if these solids are released directly with the plant discharge before prior treatment (Voutchkov, 2011a). In both the Atlantic and Pacific Oceans, the limit of gross alpha radioactivity specified in regulatory standards is often naturally exceeded. Sufficient sampling of water quality and mapping of levels of radionuclides is key in ensuring that this does not become an obstacle in approval and monitoring of concentrate discharge. Desalination and the concomitant requirement for its water quality testing of concentrate are relatively new and standard methods for water quality analysis, which were developed for freshwater quality analysis may not always yield accurate test results due the impact of salinity on some of these methods, for example, tests for total suspended solids and some metals. One needs to be mindful of the impact that the elevated salinity may have on the results of such standard tests, including the likelihood of misleading results and false positives. When selecting laboratories to undertake testing of source water, WET, etc., having prior experience in saline, brackish, and seawater testing is of critical importance for the accuracy of the test results.

3.2.6 Salinity tolerance of marine organisms The salinity tolerance threshold is defined as the maximum level of TDS that an organism can survive in a saline environment for a period of time, and varies markedly between organisms (Mickley, 2006). The organisms naturally inhabiting the zone of concentrate discharge will vary from site to site, as will the specific composition of the concentrate. The variability of the ocean conditions and habitats from one location to another is such that it is all but impossible to establish a general specification of salinity tolerance. Sensitivity to salinity varies greatly among marine organisms. At the most sensitive side of the scale, some organisms (described as osmotic conformers) cannot control their own cellular osmotic pressure which can lead to dehydration and cell death as they respond to the changes in ambient salinity. In contrast, osmotic regulators are able to control their response to changes in salinity and regulate their osmotic pressure to adopt to the changes of the outside environment. Most marine fish fall into this category (as well as reptiles, birds and mammals). Most shellfish can withstand reasonable salinity variation but may not be able to control their response to very large increase in salinity; this includes clams, mussels, scallops, crabs and oysters, as well as reef-building corals (Voutchkov, 2011a). Seawater salinity naturally varies seasonally, with the result that many marine organisms are adapted to salinity variation. As long as the actual salinity increment caused by the desalination plant discharge is within this variation range, the salinity impact from the discharge is negligible. Causes of natural salinity variation include inflows from snowmelt and notable rain events and evaporation. The natural

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salinity fluctuations can be determined relatively easily by water quality testing over an extended period of time. It is preferable that more than one full cycle of seasons is covered, but given climate variation, at least worst case periods of extreme salinity changes must be sampled. In an open ocean environment the range of salinity variation has been established to be at least 6 10% of the average annual ambient seawater salinity concentration, and this figure has been used as a yardstick for a conservative approach to determine whether concentrate discharge may trigger environmental impacts. It has been shown that most marine organisms have an actual salinity tolerance way in excess of 10% of average conditions and can survive long-term exposure to salinities of over 40 ppt (Cotruvo et al., 2010).

3.2.7 Method for salinity tolerance evaluation A methodology for evaluation of salinity tolerance was developed to facilitate environmental compliance during the Carlsbad desalination plant development in Southern California. Four steps were defined (Voutchkov, 2011a):

• • • •

establishing of the test salinity range; identifying test species inhabiting the discharge area; undertaking biometric tests at discharge salinity; and testing for tolerance at various rates of dilution.

Determination of test salinity range. The salinity of the concentrate to be discharged can be established using the source-water salinity, the desalination process flow and any other streams which may be added to the concentrate prior to discharge. The concentrate dispersion in the discharge area is influenced by a host of natural factors such as ocean tides and currents, wind patterns, storm events, temperature differentials, etc. It is also determined by the energy the concentrate is discharged with into the ocean, which is impacted by the discharge pressure, and amplified by the use of diffusers. For plants of medium and large size, where more than 50 MLD of concentrate is disposed of daily, the complexity of variables requires computer generated hydrodynamic modeling to determine the distribution of salinity in the discharge area (Jenkins and Wasyl, 2001; Einav and Lokiec, 2003). As previously indicated, the ZID edge is defined as having salinity of 10% higher than ambient. The range of test salinity needs to be taken from the center of the discharge water column, the center of the ZID on the surface, and the edge of the ZID on the ocean bottom (Jenkins and Wasyl, 2001). Identifying test species. Selection of test species needs to be undertaken by an expert marine biologist, familiar with the area of discharge. It is recommended that the species of flora and fauna most sensitive to changes in salinity be selected for testing. As a minimum, each of three species abundantly prevalent in the discharge area needs to be distinguished, one representative of each: macroalgae, invertebrate, and fish populations (Chapman et al., 1995; California State Water Board, 1996; Graham, 2004).

3.2 Potential environmental impacts

The suggested criteria for selection are:

• • • •

abundance in the discharge area; possible commercial or recreational value; salinity sensitivity, and general environmental sensitivity, such as marine protected or endangered organisms.

These will be used in Biometrics and Salinity tolerance tests, described next (Voutchkov, 2011a). Biometrics test. This test is undertaken to determine the impact on the test species of long-term exposure to the anticipated elevated salinity in the center of the ZID once concentrate is being discharged. This anticipated salinity to be modeled is the level, which will not exceed 95% of the time in the center of the ZID. Two large marine aquariums need to be prepared. The first, referred to as the test tank, will have concentrate blended with seawater to the target level of salinity, with all other variables being held constant. The second, control tank, will be identical, but filled with seawater, and with all the other conditions the same as the test tank. Both tanks need to be maintained and monitored to compare the impact of the increase of salinity on the marine species in the tanks for the duration of the test, which should be a minimum of three, but preferably 5 months. Selection of the test species need to consider that both tanks are populated with specimens of similar characteristics, which include appearance, size, eagerness to feed, etc. All specimens need to be monitored frequently (at least every 2 days) and key biometrics recorded. Of particular importance is fluctuation in weight, fertilization, and mortality. A marine biologist will be required for the duration of the test to record the metrics, and at the end of the test period, to compile a report on the statistically significant quantitative and qualitative parameters (Voutchkov, 2011a). Salinity tolerance test. Unlike the biometrics test, the salinity tolerance test models mortality and reproductive capacity of selected species over a short-term period of maximum salinity. The duration modeled is the maximum period such discharge is likely to occur under a worst case scenario, which will be determined by hydrodynamic modeling. Experience has shown this period usually is 1 2 weeks. As with the biometrics test, a number of marine aquarium tanks have to be prepared, with a control tank containing seawater and a number of tanks with varying salinities, increasing in increments between 1000 and 2000 ppm up to the maximum. The range of salinities has to model the maximum salinity anticipated on the seabed at the edge of the ZID, to the average salinity in the ZID. Concentrate dissipation as predicted with hydrodynamic modeling should be used to ensure that a conservative approach is taken. As before, test species need to be selected and distributed among the aquariums, and their wellbeing monitored and recorded over the test period (Voutchkov, 2011a).

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Also see the Carlsbad case study (Chapter 4: Case Studies for Surface Water Discharge) on the application of STE procedure.

3.2.8 Potential environmental impact of elevated discharge temperature Older designs of thermal desalination plants may release concentrate of elevated temperature, which if it exceeds a particular threshold may cause a notable impact on the receiving environment. Over time many of these plants have been phased out, or their discharge process modified to ensure that the impact on the ZID was reduced within 50 m of discharge point, and the discharge temperature is not higher than 2 C 4 C of the ambient water temperature. Technological advances in membranes and RO processes have resulted in new large-scale desalination plants mainly using membrane processes, which do not change the temperature of seawater between intake and discharge.

3.2.9 Potential environmental impact of source-water conditioning additives Water treatment plants have been successfully treating highly contaminated surface water and safely disposing of chemicals used in such treatment for many decades. Environmental impacts can be minimized looking to past practices at conventional water treatment plants as chemicals used at desalination plants are very similar. Product water is conditioned using food-grade quality chemicals, which are biodegradable and not toxic to the marine environment. Desalination plants use the same chemicals as conventional water treatment plants and usually dispose of the spent chemicals in the same manner. Chemicals used in conventional granular media pretreatment tend not to be suitable for blending and discharge with concentrate to surface water bodies unless they are equalized or pretreated by sedimentation, as the blend may have elevated suspended solids and turbidity concentrations. Furthermore, where ironbased coagulants are used, the discharge will be discolored unless equalized or treated prior to discharge. Ideally then the pretreatment waste stream needs to be disposed of either to sanitary sewer (for small plants) or processed through a solids handling system which is custom built with the desalination plant. Where membrane pretreatment is employed, often coagulant is not used and discoloration will not be an issue in the discharge. Where scale inhibitors and acids are added to the source water to facilitate salt separation, the environmental impact of these chemicals need to be assessed before discharging it to surface water together with the desalination concentrate. These conditioning compounds are usually added in very low concentrations unlikely to alter the composition of the concentrate, and rejected by the RO membranes. Permitting conditions may preclude their discharge without pretreatment,

3.2 Potential environmental impacts

but this is unlikely given that food-grade quality of chemicals safe for human consumption is used. Usually, scale inhibitors commonly used in desalination plants are biodegradable and have very high toxicity thresholds—over 2000 mg/L—while they are used in low dosages—typically 0.5 2.0 mg/L. Most seawater desalination plants do not add acid to enhance source-water pretreatment. Acid addition is commonly practiced, however, in brackish desalination plants to prevent scaling.

3.2.10 Environmental permitting Although desalination practice has matured over the past decades, permitting approaches worldwide differ widely. As impacts are location specific, environmental impacts need to be considered locally. It would be useful if permitting guidelines converged internationally. This will result not only in development of timeframes and cost envelopes being more predictable, but more importantly, improved environmental protection through standardized management of environmental impacts worldwide. Countries at the forefront of development of large desalination plants which include Australia, Israel, Spain and the United States have developed permitting practices as outlined below (Mickley and Voutchkov, 2016).

3.2.10.1 Analysis and comparison of permitting practices in the United States Similarities in the General Permitting Process and Permits. The framework for issuing discharge permits is set by Federal regulations and begins with submission of a discharge application to the appropriate state regulatory agency. In some states this is not delegated and application needs to be made to the regional USEPA office. The California permitting process is a typical example of the general permitting process (SWRCB, 2014):

• The applicant/project developer needs to submit an application to the appropriate Regional Water Quality Control Board.

• The application is reviewed for completeness of information by the applicable water board.

• The content of the application is then reviewed and a decision made by the

• •

water board on whether the discharge is to be permitted or prohibited. Where a permit is needed, a notice is prepared for the 30-day public comment period to commence. The applicant is responsible for publishing of the notice via the largest newspaper circulated within the municipality (or legislative region) for at least 1 day, and provides evidence of circulation to the water board. Once the public participation period has passed, the water board has to hold a public hearing, where the application can be rejected, approved, or approved

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•

with amendments. If a draft permit is issued, the USEPA has a further 30 days in which to appeal. The permitting process can be concluded within 6 months, or longer where particular environmental sensitivities exist.

The general flow of events described above is also representative of permitting processes in Florida, Texas, and other states. The specific form of state permits can differ but at a minimum all NPDES permits contain the necessary requirements to ensure compliance (USEPA, 2015). This includes information both of the specific and general conditions applicable. The permit specifies the effluent limits to be met. Such limits are developed by the regulatory agencies specifically for the project scope. This is often the most time consuming aspect of permit development, deriving appropriate effluent limits through technology- and water quality-based standards that apply to the project area, based on the information of effluent provided by the applicant. Requirements for monitoring and reporting are included, which have to be met by the applicant to provide the permitting authority with information relevant to assess whether conditions are fully adhered to. Comprehensive project details are typically included in the cover page to clearly demarcate the scope covered by the permit. Differences in the State Permitting Effluent Limits. The latitude given to the states in how they conform to the general Federal NPDES guidelines results in some policy and procedural differences among different states. Examples of this include:

• Automatic inclusion of mixing zones in initial permit feasibility determination • • • •

(e.g., Texas) which differs from each mixing zone considered individually (e.g., Florida and California). Specifying mixing zone parameters. WET testing required for all concentrate generated through membranes in municipal areas (e.g., Florida) versus case-by case consideration (e.g., Texas). Different water quality standards (all must be at least as stringent as the federal guidelines). Different permit formats.

Differences in permit effluent limits occur from such policy and procedural differences as well as the site-specific nature of the concentrate discharge and the receiving water. Both of these factors are evident when comparing the permit limits given in permits for the Carlsbad, Huntington Beach, and Tampa Bay desalination plants, which are the largest seawater desalination plants permitted in the United States to date. Differences in the State Permitting Guidelines. There are also differences in the availability of regulatory guidelines for implementing SWRO desalination facilities. Both the Texas Water Development Board and the California Coastal Commission developed guidance documents in 2004. The Guidelines for

3.2 Potential environmental impacts

Implementing Seawater and Brackish Water Desalination Facilities developed by the Water Research Foundation in cooperation with the WateReuse Research Foundation and U.S. Bureau of Reclamation and the California Department of Water Resources (Stratus Consulting, 2010) provide a general overview of permitting and regulatory requirements and challenges in the United States. Texas and California have state-specific general guidelines for desalination project environmental planning, review and permitting (Beck, 2004; CDWR, 2008). These documents do not contain any specific technical details and engineering guidance (such as found in the Ten State Standards or the USEPA Water Reuse Guidelines) related to the scope and nature of environmental studies needed and specific design and planning recommendation to complete a successful desalination project. Thus at present, there are no legally binding desalination project specific regulations or publicly available regulatory guidelines specifically for desalination projects in the states of California, Florida, and Texas issued by the state agencies responsible for environmental review and permitting of such projects. State regulators issue desalination projects based on their prior experience with similar projects. Differences in Complexity of the Regulatory Process. In most US states, four to six agencies are involved in the regulatory process for permitting an SWRO desalination plant. In California there are 24 agencies involved in an independent multiagency review process that typically results in numerous conditions and permits, which regulate the discharge and other permits that may have different requirements in terms of mitigation of environmental impacts. Such practices not only delay the permitting process but also put a significant burden on the project sponsor associated with project implementation, operations monitoring, and data reporting. Differences in Salinity Limits. Generally, in the United States, salinity is regulated indirectly via WET tests. Although regulations do not explicitly spell this out, WET limits/requirements in conjunction with mixing zone requirements ultimately regulate the salinity of the discharge. This allows the maximum salinity limit for the regulatory mixing zone to also be established for the site-specific conditions of the project. The maximum limit is based on the level of dilution, which is required for marine species inhabiting the area, or for predetermined standard test species defined by the respective regulatory agency, not to exhibit chronic toxicity. The marine organisms selected for testing are identified based on a biological survey of the discharge area usually completed during the initial environmental review phase of the project. At present there are no numerical salinity limits incorporated in the Federal regulations that are developed independently of the site-specific WET tests. However, salinity limits for desalination concentrate discharge have become a focus of the January 28, 2017, amendment of the 2015 California Ocean Plan, which incorporates a generic maximum incremental salinity limit at the edge of the 100-m mixing zone of 2 ppt.

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A concern is that such a prescriptive “one-size-fits-all” limit is overly restrictive and not reflective of the site-specific aquatic environment in the area of the plant discharge. For instance, if the concentrate passes the WET test and the discharge salinity is higher than 2 ppt of the ambient ocean water salinity, then it is unlikely for such salinity to result in negative impacts on the environment. From this perspective, the addition of a maximum salinity limit to the desalination project permit requirements may introduce an overly constraining burden in terms of compliance costs and delay to the regulatory process because the WET toxicity compliance requirements are already reflective of the potential negative effect of elevated salinity on the ambient aquatic life. Further, such a limit is not reflective of the site-specific conditions, and salinity tolerance of the flora and fauna in the discharge area.

3.2.10.2 Analysis and comparison of permitting practices in Australia Regulatory Bodies Involved in Permitting. The Environmental Protection and Biodiversity Conservation Act (Australian Government, 1999) sets out a range of matters of national environmental significance (such as threatened species or ecological communities), where an activity impacts or has the potential to impact on one or more of these matters requiring approval. This Act is not specific to the activity of desalination but where listed matters are impacted, it would require assessment and approval under the Act. The Australian and New Zealand Environmental and Conservation Council (ANZECC) establish guidelines which are then applied by the individual State jurisdictions as they see appropriate within their own legislation. Each of the five Australian states which have SWRO desalination plants (Western Australia, South Australia, Queensland, New South Wales and Victoria) have their state and local governing bodies (environmental protection agencies or authorities) which issue and enforce the plant discharge permits. In addition to the issuing of licenses/permits for the discharge from the desalination plant, most states also have other approvals associated with the development of the desalination facility itself, which include consideration of environmental impacts including those associated with the discharge of saline concentrate. Highlights for the relevant states are summarized below: Queensland. The regulatory body involved in discharge consent approval in Queensland is the Department of Environment and Resource Management (DERM). Direct discharge of RO concentrate to surface water in Queensland is regulated under the Environmental Protection Act 1994 and other subordinate legislation (Vargas et al., 2011). Environmentally relevant activities (ERA) need to be licensed as a requirement of this Act, where the DERM can approve such activities in terms of the Integrated Planning Act 1997. The role of DERM is to protect and improve the water environment in Queensland and to achieve a continuing overall improvement of coastal waters within the water quality objectives and environmental values for a specific location stated under the Environmental Protection (Water) Policy 1997. The aim is

3.2 Potential environmental impacts

further to ensure that consequences are borne by those responsible—otherwise known as the polluter pays principle. DERM is responsible for ensuring that appropriate standards are set and adhered to in protecting the environment. In meeting the conditions of the approval, the discharge quality will meet or exceed the minimum requirements set under the Environmental Protection (Water) Policy of 1997. At present the only large SWRO desalination plant in Queensland is the 132 MLD Gold Coast desalination facility. Western Australia. The Western Australia Office of Environmental Protection Authority (OEPA) has primary responsibility for the development and enforcement of environmental legislation within Western Australia, and more specifically the Environmental Protection Act of 1986. The Western Australia Department of Environment and Conservation (DEC) has introduced environmental legislation which regulates the storage, transportation and treatment of hazardous chemicals and waste which ultimately can reach surface waters. DEC is also responsible for the implementation of National Water Quality Management Strategy—the Environmental Quality Management Framework (EQMF) which contains Environmental Values (EV) and Environmental Quality Objectives (EQO) for use in Western Australia’s coastal water management. The compliance with the EQO for a specific desalination project is judged from an assessment and monitoring data of the discharge area collected before and after the initiation of desalination plant operations. Western Australia has three large SWRO desalination plants— the 143 MLD Perth I (Kwinana) plant; the 280 MLD Perth II plant; and the 140 MLD Cape Preston Plant. South Australia. The South Australian Environment Protection Act of 1993 sets out that the activity of desalination is a prescribed activity of environmental significance that requires a license. The relevant water quality criteria are established through the Environment Protection (Water Quality) Policy of 2003. The actual permit is issued by the Environmental Protection Authority of South Australia. South Australia has only one large SWRO desalination facility—the 300 MLD Adelaide Desalination Plant. New South Wales. The Marine Water Quality Objectives for NSW Coastal Waters provide the guiding principles used for the development of the permit of the Sydney Water Desalination Plant. The state agency issuing the permit is the New South Wales Environment Protection Authority (NSW EPA). The license is issued under the Section 55 of the Protections of the Environment Operations Act 1997. New South Wales has one large desalination plant—the 250 MLD Sydney Desalination Plant. Victoria. At present, the state of Victoria has one large seawater desalination project—the 414 MLD Wonthaggi Desalination Plant, which is the also the largest desalination plant in Australia and one of the largest SWRO desalination plants in the world. The discharge permit for this plant was issued by the Department of Sustainability and the Environment under the Environmental Effects Act of 1978. Ultimately the state owns the project in public private

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partnership with Suez Environment. The Secretary to the Department of Sustainability and Environment (DSE) is the proponent for the Project on behalf of the Minister for Water. The Capital Projects Division of DSE is responsible for both development and permitting of the Project. This includes preparing the Environment Effects Statement (EES) and discharge permit application. The proponent of the Project takes overall responsibility for these actions. Tasmania. At present, Tasmania does not have any medium or large desalination plants in operation, planning or development. The regulatory agency which issues permits for wastewater discharge, including these from desalination plants, is the Environment Protection Authority of Tasmania. The primary mechanism for environmental protection and minimization of pollution is the Environmental Management and Pollution Control Act 1994 (EMPCA). The approach adopted by the legislation is that of prevention, reduction and remediation of environmental damage, through performance-based legislative mechanisms. Existing Australian Regulations Governing Concentrate Management. ANZECC published the revised Australian and New Zealand guidelines for fresh and marine waters in year 2000 (ANZECC, 2000). The National Water Quality Management Strategy (NWQMS) established by ANZECC forms the basis for water quality policy development for the states. The states have adopted the ANZECC guidelines in various ways. Within the states different water bodies have specific water quality targets similar to those in the United States. The ANZECC guidelines recognize a mixing zone at the discharge point and indicate that the water quality limits included in the guidelines are applicable to the boundary of the mixing zone. The extent and nature of the mixing zone depend on the design parameters of the discharge structure and conditions at the discharge area. The ANZECC guidelines aim to minimize the size of mixing zones over time, while a holistic approach to the broader environment is followed, that is environmental impact within the mixing zone is more readily accepted as long as the size of the zone is minimized. The mixing zone is accepted as a receptacle for discharge of soluble substances, not prone to bio-accumulation. The holistic approach is further evident in the toxicity testing of the combination of the effect of all chemicals, their bio-availability and their potential interaction and ecological impact, in favor of component specific testing. For various marine environments along Australia’s coasts the ANZECC guidelines contain default trigger values above which undesirable environmental impacts are very likely. Such trigger values for the states large seawater desalination plants are listed in Table 3.1. Table 3.2 was compiled based on the ANZECC limits for “marine” and “estuarine and marine” environments. Southeast Australia limits apply for the desalination plants in Sydney and the Victoria desalination plant. Tropical Australia limits apply to the Gold Coast SWRO desalination plant located in Queensland. Southwest Australia trigger values apply to the Perth I and II and Cape Preston SWRO desalination plants. The South-central Australia regulations apply to the Adelaide SWRO desalination plant.

3.2 Potential environmental impacts

Table 3.1 Australian regulations pertinent to desalination permit requirements.

key discharge Southcentral Australia

Southeast Australia

Tropical Australia

Southwest Australia

Chlorophyll a—inshore/offshore, µg/L

1

0.7 1.4/ 0.5 0.9

1

Total phosphorous—inshore/ offshore, µg/L Filterable reactive phosphate, µg/L Total nitrogen—inshore/offshore, µg/L Nitrates—inshore/offshore, µg/L Ammonia—inshore/offshore, µg/L

25

15/10

0.7/20 0.3/20 20

10 120

5 100

5 230

10 1000

5 15

5 5

50 50

90/110

2 8/1 4 1 10/ 1 6 90

90

90

8.0/8.4 10

8.0/8.4 20

8.0/8.4 2

6.5/9.0 10

Discharge parameter

Dissolved oxygen (% of saturation)—lower and upper limits, % pH—lower and upper limits Turbidity, NTU

100

Table 3.2 Australian regulations pertinent to desalination—metal concentrations. Permit discharge parameter Cadmium, µg/L Chromium III, µg/L Chromium IV, µg/L Cobalt, µg/L Copper, µg/L Lead, µg/L Mercury (inorganic), µg/L Nickel, µg/L Silver, µg/L Vanadium, µg/L Zinc, µg/L

HEPA (protection of 99% of species)

MEPA (protection of 90% of species)

LEPA (protection of 80% of species)

0.7 7.7

14 48.6

36 90.6

0.14

20

85

1 0.3 2.2 0.1

14 3 6.6 0.7

150 8 12 1.4

7 0.8 50 7

200 1.8 160 23

560 2.6 280 43

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CHAPTER 3 Surface water discharge of concentrate

The discharge from a given desalination plant will have to contain concentrations of contaminants which are lower than the applicable trigger values listed in Table 3.1. If the trigger value for a given parameter is exceeded at the boundary of the mixing zone, then the desalination plant has to treat (or in some cases it is allowed to dilute) their discharge in order to meet this regulatory limit. Usually, dilution is allowed only for parameters which are inert and nonreactive such as salinity. The local government agencies involved in project permitting have the right to use more stringent trigger values for specific projects and circumstances. It should be noted that the water quality targets indicated in Table 3.1 are not always the criteria that are actually used to determine the desalination plant discharge limits. Often, the states have their own requirements, which differ from the ANZECC guidelines. For example, while all states allow for a mixing zone they have different requirements for this zone. Therefore the water quality limits incorporated in the permits of the desalination plants case studies presented in Chapter 4 differ from the limits presented in Tables 3.1 and 3.2. Usually, all desalination plant discharges comply with the limits listed in Table 3.1 and their site-specific discharge permits without any additional treatment of the waste streams except for turbidity. As seen from this table, the discharge turbidity limit is very low and can only be achieved if the spent filter backwash water which is generated during seawater pretreatment is processed onsite—usually by lamella settling followed by mechanical dewatering of the sludge generated in the settlers. In addition to the parameters listed in Table 3.1, the desalination plant would need to comply with the metal levels (triggers) presented in Table 3.2. Which value applies depends on how the discharge area is classified by the regulatory agency—High Ecological Protection Area (HEPA); Medium Ecological Protection Area (MEPA); and Low Ecological Protection Area (LEPA). If a trigger is exceeded at the boundary of the mixing zone, then the plant will have to modify its operation to meet the respective regulatory requirement. These regulations also contain requirements for organic toxicants similar to these included in the USEPA Clean Water Act. Based on ANZECC recommendations, each state has developed its own desalination project discharge permit requirements for local site-specific data, type of receiving water body and actual environmental conditions. For all desalination plants built to date, these limits are within 25% of the values listed in Tables 3.1 and 3.2. The ANZECC guidelines also contain specific requirements related to the observable impact of the desalination plant discharge on the aquatic flora and fauna. Such impact is assessed based on aquatic surveys of the discharge area before and after the commissioning of the desalination plant. The specific parameters of the health and biodiversity of the aquatic life measured before and during plant operations are:

• whole effluent toxicity; • chemical and biochemical changes in marine organisms;

3.2 Potential environmental impacts

• whole-sediment laboratory toxicity assessment; • structure of macro invertebrates and/or fish populations/communities using rapid, broad-scale or quantitative methods;

• seagrass depth distribution; • imposex in marine gastropods (imposex is a disorder in sea snails caused by

• • • • • • • •

the toxic effects of certain marine pollutants. These pollutants cause female sea snails (marine gastropod mollusks) to develop male sex organs such as a penis and a vas deferens) frequency of algal blooms; density of capitellids; in-water light penetration; filter feeder densities; sediment nutrient status; coral reef trophic status; habitat distributions; and assemblage distributions.

It is interesting to point out that the Australian regulatory requirements do not require project proponent to quantify and to mitigate for impingement and entrainment of marine organisms by the desalination plant intakes. However, impingement and entrainment potential by the intakes is acknowledged in the project environmental review related documents and these effects are typically minimized by designing the intake such that the through screen velocity is between 0.10 and 0.15 m/s. Permitting Support Studies in Australia. Permitting support studies common for all large SWRO desalination projects in Australia consist of at least 1 year of source-water quality characterization and pilot testing of the proposed desalination system; numerical modeling of the desalination plant discharge to develop projections for mixing (dilution factor) of the discharge at the boundary of the mixing zone; and discharge area flora and fauna surveys for 1 year before and after the commissioning of the desalination plant. There are a number of small SWRO desalination projects that have lesser requirements such as not having to do pilot testing. Analysis and Comparison of Permitting Practices in Spain Urban water demand in remote areas of Spain has been met through desalination since 1969. Such areas include the City of Ceuta in Northern Africa and Lanzarote, Fuerteventura and Gran Canaria in the Canary Islands. Desalination capacity in Spain reached 2 million m3/day in 2006. In 2010 this capacity was 2960 MLD and the country had over 750 desalination plants. The population of Spain in 2010 was 47 million. The main centers of desalination are The Canary Islands (33%), Andalusia (23%), Murcia (13%), and the Region of Valencia (13%). Together these account for more than 80% of installed capacity. The largest Spanish desalination plants are located along the Mediterranean coast (see Fig. 3.2).

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CHAPTER 3 Surface water discharge of concentrate

FIGURE 3.2 Main desalination plants along Spain’s Mediterranean coast.

The Canary Islands has a paucity of freshwater resources and seawater desalination is the prime source of drinking water supply. The island of Lanzarote relies on desalination for over 80% of its drinking water needs, while the average for the Canary Islands is approximately 20%. The remaining 20% is provided by water reuse. The largest Spanish SWRO desalination plants are Torrejvieja (Alicante) 240,000 m3 /day and Barcelona 200,000 m3 /day. Spanish Regulatory Bodies Involved in Permitting. The Spanish Ministry of the Environment and Rural and Marine Affairs (MARM), within the framework of the AGUA Program (Actuaciones para la Gestio´n y la Utilizacio´n del Agua), develops and implements a long-term plan for construction of new desalination facilities which is updated from time to time. All matters relating to water are managed by a number of Basin Agencies (Confederaciones de Cuencas Hidrogra´ficas), the President of which is proposed by the MARM Minister and nominated by the Cabinet. Broad participation in water matters is encouraged, and structurally achieved through each Basin Agency reporting to a Board, with an active Council and user assembly participating in decision making in planning and operations.

3.2 Potential environmental impacts

Agencies are responsible for water resource master planning, implementing water infrastructure projects, operating water supply infrastructure, authorizing and monitoring water quality standards, and providing advisory services. Existing Regulations Governing Concentrate Management in Spain. The Water Law (Ley de Aguas) was promulgated in 1985, and updated in 2001 and 2005. This provides the legal framework for water and sanitation in Spain. No single ministry is responsible for policy or regulation of water and sanitation. In December 2010, Law 41/2010 was introduced to specifically address protection of the marine environment and set out regulations governing wastewater discharges, including concentrate from desalination plants. The regulations establish standards both at the point of discharge (“effluent standards”) as well as at the boundary of the mixing zone (“ambient standards”). Spanish desalination regulations address environmental issues and concerns associated with project implementation at all phases of project development: (1) planning; (2) construction; and (3) operation.

• Planning Phase

•

•

During the planning phase, the desalination project proponent is required to prepare an environmental impact assessment (EIA). Such an EIA has to contain all relevant information of the discharge area such as biology, water quality, bathymetry as well as of the discharge itself including composition of concentrate and modeling of dispersion from point of discharge. Along Spain’s Mediterranean coast, two seagrasses sensitive to salinity have been identified, meriting special consideration in permitting of any discharge along this coast. Cymodocea nodosa grows densely, like an underwater lawn (known as sebadales) on sandy and muddy seafloors up to 20 m deep. This seagrass provides a spawning area for many aquatic organisms and is home to many endangered species. Posidonia oceanica grows in large, wide beds from the coast up to 3 km offshore and is sensitive to salinity in excess of 40,000 mg/L. Construction Phase During the construction of the desalination plant, the project developer is required to monitor seawater quality for any detrimental impact of construction activities. The condition of seagrass, consistency of dredged materials and seawater silt content are indicators of where corrective action may be required. Operation Phase Once the plant is commissioned, the permit conditions need to be regularly monitored and reported on throughout the life of operations, including compliance with water quality requirements, impact on biodiversity and integrity of infrastructure. Regulatory agencies in Spain do not usually consider impingement and entrainment of marine organisms by the intakes of desalination plants a significant environmental impact and do not regulate or require mitigation for potential marine life losses caused by intake operations.

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Table 3.3 Spanish regulations pertinent to desalination—key discharge permit requirements (Mickley and Voutchkov, 2016).

• • • • • • • • • • •

Parameter

Maximum concentration

TSS, mg/L pH Total nitrogen, mg/L Total phosphorus, mg/L BOD5, mg/L

35 6 9 15 2 25

Key Permits and Permitting Agencies in Spain. All desalination plants operate under a waste discharge permit issued by the General Direction of Environmental Quality (Direccion General de Calidad Ambient). Prior to issuance the permit is reviewed by various offices of the Ministry of the Environment and Rural and Marine Affairs—the Office of Water Quality; the Office of Environmental Planning; the Office of Industrial Waste Regulation; the Office of Protection of the Environment; the Office of Sustainable Environmental Management as well as local and regional regulatory agencies with jurisdiction over marine coastal environment and industrial and recreational activities. Key permitting requirements incorporated in most SWRO desalination plant permits are shown in Table 3.3. Permitting Support Studies. Support studies for environmental review and permitting of desalination projects in Spain vary significantly from one project to another and as a minimum involve source-water quality characterization, bathymetric and biological surveys of the discharge areas before and after plant commissioning, and modeling of the salinity plume of the discharge. Desalination projects of all sizes are required to do source-water quality characterization for at least 6 months, especially during the summer period when algal blooms may occur. Data collected for source-water quality characterization as a minimum include the following compounds: total dissolved solids, conductivity, pH, temperature, dissolved oxygen, silt density index, oil and grease, total hydrocarbons, sodium, chloride, calcium,

3.2 Potential environmental impacts

• • • • • • • •

magnesium, iron, manganese, bromide, boron, nitrates, phosphates, and silica.

In addition, source-water quality is characterized for all metals and organics regulated in the plant discharge as well as compounds which are regulated by pertinent public health agencies. For small plants the collected source-water quality information is used to project the quality of the desalination plant concentrate based on the selected plant design. For plants larger than 100,000 m3/day, concentrate is generated using a pilot system specifically built for the project. Such concentrate is used to complete chronic and acute WET studies of methodology and test protocols similar to the standard USEPA WET tests. All desalination projects are required to complete a bathymetric survey of the discharge area in order to document the configuration of the bottom in this area as well as area depth, currents and waves. Bathymetric survey produces a map of the ocean bottom in the area of the discharge and identifies the depth of the sand cover of the bottom. The information collected during the bathymetric surveys is used to complete biological survey of the discharge area as well as hydrodynamic modeling of the concentrate dispersion. The environmental review of all projects entails the completion of biological survey of the marine habitat in the area of the discharge. Such survey includes identification of marine species inhabiting the ocean bottom and water column along the length of the plant intake and outfall. The biological survey identifies and maps the location and type of marine habitats in the mixing zone of the discharge, including seagrass beds, kelp forests, coral outcroppings, borrows of benthic organisms and fish, and other habitats that could be impacted by the desalination plant operations. The outcome of this biological survey is a map and marine life information documenting the condition of the discharge area in “timezero” before the plant operation begins. The scope of such survey includes:

• installation of underwater current velocity meters at a depth of 1 m from the bottom;

• documentation of conductivity temperature depth relationships; • characterization of the water column (pH, suspended solids, DO, nitrate, and total phosphorus);

• bottom sediment characterization; • seagrass beds mapping and characterization (coverage, density, speed growth); and

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• mapping and identification of other marine habitats in the discharge area (coral reefs, kelp forests, rocky habitats of crustaceans and other marine species). Hydrodynamic mathematical modeling of ocean water discharges is usually completed for projects of capacity of 20 MLD or larger. CORMIX is the most popular hydrodynamic model used for desalination projects in Spain. For plants larger than 150,000 m3/day, a to-scale physical model of the outfall is constructed in specialized hydraulic laboratory and the model is used to study and document the projected size, depth and concentration of the discharge salinity at different discharge volumes, mixing conditions and salinity concentrations (i.e., wave and wind speeds) using tracer dye. Such model is used to validate the results of the hydrodynamic mathematical modeling.

3.2.10.3 Analysis and comparison of permitting practices in Israel The Israeli government developed a long-term large-scale desalination program in 1999, in response to projections of insufficient supply to meet demand and persistent drought since the mid-1990s. The program consisted of a number of projects with a cumulative national target volume of water produced annually. The program has subsequently been amended when circumstances require to account for actual supply and demand variation, and when finalized in 2008, a target of 750 million m3 (MCM) per year was set for 2020. Regulatory Bodies Involved in Permitting in Israel. The Ministry of Environmental Protection (MEP) of Israel is the main regulatory entity involved with the development, implementation and enforcement of regulations related to the discharge of concentrate and other waste streams from desalination plants. The Israeli government actively encourages the construction of desalination plants and considers diversification of country’s water supply as a national goal of upmost importance. Permitting is the responsibility of a committee constituted of seven different ministries plus one public member, representing environmental organizations. The Ministry of Environmental Protection takes responsibility for advising, and administering the committee through its Marine and Coastal Division (Safrai and Zask, 2008). Existing Israeli Regulations Governing Concentrate Management. Over time, environmental policy and regulations pertaining to the marine environment have been informed by the National Master Plan for desalination of seawater (34B3), the Ministry of Environmental Protection requirements and practical experience in desalination. According to the Law for Protection of the Coastal Environment of 2004, desalination plant discharges should be constructed such that they protect the coastal zone of Israel. The coastal zone is defined as 300 m inland, 30 m depth and one nautical mile (1.852 km) offshore. In addition, the discharge of concentrate is regulated by the Land-based Sources (LBS) Law of 1998, its regulations of 1990 and amendments of 2005 (Safrai and Zask, 2008). The LSB Law is based on the Barcelona Convention for protecting the Mediterranean Sea from negative environmental impacts of point discharges.

3.2 Potential environmental impacts

The Israeli Policy for the Protection of the Mediterranean Marine and Coastal Environment from Desalination Facilities (MEP, 2002) defines the following general criteria for marine outfall construction and operation and addresses three key issues:

• discharge type and characteristics, • marine outfall, and • discharge monitoring program. Discharge Characteristics in Israel. Key discharge characteristics used to assess desalination plant discharge impact on the environment are:

• discharge composition—which is mainly driven by the source-water quality • •

•

• • • • •

and the type and quantities of chemicals used at the desalination plant; pretreatment waste streams—what waste streams generated by the pretreatment system will be discharged to the ocean and would they be treated before discharge; treatment chemicals—of specific interest are chemicals which can exhibit effluent toxicity such as antiscalants and membrane cleaning chemicals as well as such that can trigger algal bloom effects—that is phosphate antiscalants, phosphoric acid, citric acid, nitric acid and others; plant recovery rate—the percentage of source water which is converted into freshwater. Recovery rate dictates the salinity of the plant discharge and potential concentration of algal toxins, organics, solids or other compounds that may result in effluent toxicity; operational regime—intermittent or continuous discharge of concentrate and spent filter backwash and associated maximum loads of solids and salinity spikes; flowrate—which has impact on loads of solids discharged in a particular area; increase of turbidity caused by the discharge should not be more than 10% of the seasonal average; suspended particulate matter (total suspended solids) should not exceed the seasonal average by more than 10 mg/L; and color of ambient water should not be affected by the discharge outside of the mixing zone.

Marine Outfalls. The Law of 2004 for protection of coastal environment includes specific guidelines and requirements for desalination plant discharges. The following aspects should be considered when determining the most suitable location of the ocean outfall for a given project:

• • • • •

natural sand movement; ecosystems in the coastal environment; fishing activities; marine vessel traffic; safety of bathers and surfers in shallow waters; and

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• the impact of onshore coastal facilities servicing the plant outfall (i.e., pump stations, storage tanks, etc.). Discharge Monitoring Program. The environmental law in Israel prescribes the implementation of monitoring program of the area of the discharge before and after the desalination plant outfall is built. The monitoring program typically has to incorporate the following information:

• water quality characterization of the receiving ocean area including measurement of physical, chemical and biological parameters;

• sediment accumulation in the discharge area; and • biota—type and diversity. Israeli Permitting Support Studies. Permitting support studies required in Israel are at least 1 year of source-water quality characterization; numerical modeling of the desalination plant discharge and discharge areas flora and fauna surveys 6 months to 1 year before and after the commissioning of the desalination plant. Desalination projects are required to collect source-water quality data for at least the parameters listed below and to determine by projections the concentration of these parameters in the concentrate:

• • • • • • • • • • •

total dissolved solids, conductivity, pH, temperature, dissolved oxygen, total hydrocarbons, nitrates, phosphates, turbidity, total suspended solids, and BOD5.

Projects larger than 100 MLD are required to complete a biological survey in the mixing zone, which is defined as a circle with radius of 330 m from the point of discharge. The purpose of such survey is to identify marine species living in the area and to determine their salinity tolerance. Hydrodynamic mathematical modeling of ocean water discharges is usually completed for projects of capacity of 40 MLD or larger. The CAMERI 3D model has been used for numeric modeling of the discharges of most SWRO desalination plants in Israel such as Ashkelon, Hadera, and Sorek. Operating large-scale desalination plants for well over a decade in locations as diverse as Israel and Australia has proved that direct discharge to surface water does not have a significant impact on the marine environment when thoughtfully sited and designed, with due consideration to local conditions (Shemer and Semiat, 2017).

3.2 Potential environmental impacts

Most countries with large desalination plants have developed a framework of regulatory guidelines and requirements which provide adequate protection of the aquatic environment in the vicinity of the desalination plant discharge. For medium and large desalination plants, such regulations usually incorporate both end-of-pipe and offshore water quality monitoring requirements which provide adequate protection of the aquatic habitats receiving the concentrate discharges from desalination plants. Operators of desalination plants are typically required to report discharge water quality to the pertinent regulatory agencies on a monthly basis and to complete WET testing and offshore discharge water quality monitoring quarterly.

3.2.11 Monitoring of desalination plant discharges Seawater desalination technology has evolved over the past five decades, over the same period that general awareness of environmental sensitivity increased across the world. Limiting the negative consequences of concentrate discharge and safeguarding of the environment is in the industry’s best interest, to encourage expansion of desalination as sustainable bulk water source in a progressively water scarce world. Comprehensive systems have been developed to prevent, predict and monitor impacts in feasibility, planning, design, construction and operations of desalination plants. These systems have been implemented worldwide to comply with discharge water quality standards and environmental regulations with the aim of protecting the aquatic environment. An EIA is required during project inception and planning to progress to implementation, should regulatory approval be obtained. EIAs have evolved into comprehensive project documents covering exact methods of construction and operation to be employed to ensure compliance. All impacts and mitigation measures are enforced and monitored by subject matter specialists for the entire lifecycle of the project. Usually, a construction completion certificate will only be issued if full compliance has been achieved. At large desalination plants, professionals charged with all matters related to environmental compliance monitoring and wellbeing of the aquatic environment typically form part of the full-time operational staff. Marine biologists monitor environmental health and marine habitat diversity, while scientists monitor water quality at the plant and in the ocean. Discharge permits commonly include requirements for comprehensive water quality monitoring of the receiving marine environment and the concentrate composition at the point of discharge. In continuous monitoring, the on-site scientists can quickly identify problem areas and institute corrective action. Environmental permit requirements are monitored by local or regional authorities responsible for regulation, and provide oversight to safeguarding the environment from any negative impact of the discharge. Such authorities are usually equipped with independent laboratories and well-qualified professional staff to provide independent assurance of regulatory compliance.

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3.3 Concentrate treatment prior to surface water discharge 3.3.1 Potential brackish water reverse osmosis concentrate treatment requirements The possibility of effluent toxicity is an issue that must be addressed in planning for concentrate discharge in brackish water reverse osmosis (BWRO) projects, or where SWRO concentrate is mixed with wastewater effluent prior to discharge. The American Water Works Research Foundation undertook a comprehensive study which found that when brackish concentrate was disposed of through surface water discharge, toxicity may be exhibited (Mickley, 2000). The study found the cause of toxicity to be in the composition of ions in the brackish water source rather than being influenced by the membrane process. Predicting toxicity requires evaluation of the concentrate salinity from brackish groundwater compared to the receiving body’s seawater salinity, referred to as the percent difference from balance (PDFB) approach (Mickley, 2001). The PDFB approach compares the ion compositions of the concentrate, with that of seawater which has been brought to the same TDS level as the concentrate. The seawater is taken as balanced and thus has to be either diluted or concentrated to match the concentrate TDS—which is called reference seawater. Typical seawater will not exhibit toxicity triggered by ion-imbalance at 33 ppt, resulting in a PDFB of zero (Voutchkov, 2011a). The risk of toxicity is increased if the ion concentration of the main minerals in the concentrate is very different from that in the reference seawater. This includes sodium, chloride, sulfate, calcium, magnesium, and bicarbonate. The PDFB threshold level that exhibits toxicity is dependent on the specific characteristics of the discharge area and the organisms that inhabit the area. The most accurate method to determine the threshold is thus through pilot testing, which requires the generation of concentrate of quality similar to that of the full-scale plant. Chronic and acute WET testing can then be performed and the required level of concentrate dilution established where toxicity is absent. Once this has been confirmed, the dilution required to safeguard the ZID can be calculated, and the discharge infrastructure sized accordingly. In practice this means that where chronic WET testing indicates the requirement for threefold dilution of flow concentrate to prevent toxicity, the outfall has to be designed to ensure such dilution is completed within a 300 m radius from the discharge point (Voutchkov, 2011a). The chronic toxicity threshold needs to be met at all times, while acute toxicity allows maximum salinity for short duration likely to be encountered under certain circumstances. If average annual salinity in concentrate is 8 ppt, and the maximum daily salinity is 12 ppt, occurring for a maximum of 3 days, acute WET tests should be undertaken at the maximum salinity of 12 ppt over 3 days. The acute WET test will establish the dilution required to obviate toxicity occurring over the 3 day period, known as the acute toxicity dilution ratio. Where this ratio exceeds the chronic ratio, the design will need to be based on the acute

3.3 Concentrate treatment prior to surface water discharge

toxicity ratio. For example, should a ratio of fivefold dilution be required, then the outfall will need to be designed so that fivefold dilution is completed within the 300 m radius from the discharge point. Such design will accommodate both the acute and chronic toxicity dilution thresholds (Voutchkov, 2011a).

3.3.2 Potential seawater reverse osmosis concentrate treatment requirements Ion-imbalance toxicity is typically not a challenge for concentrate from SWRO desalination plants as the concentrate’s ion composition corresponds to that of seawater. Particularly where source water is collected through open intake, concentrate can usually be discharged back to the ocean without further treatment. This could be either through diffusers to aid mixing, or blended with source seawater and discharged directly back into the ocean. Though it is a simple process, the disadvantage of blending with ambient seawater to dilute the concentrate is that the possibility of impingement and entrainment of marine organisms is increased. The design of the intake structure to minimize impingement and entrainment is thus all the more important. Where source water is collected via subsurface intake, the composition of concentrate may be such that treatment is required prior to open ocean discharge. Examples are desalination plants which use alluvial shallow beach-well supply water for SWRO desalination plants. Such source water may contain contaminants that are not typically present in seawater collected by open intakes, such as high levels of iron and manganese, as well as the source seawater may have relatively low oxygen content and require either additional pretreatment prior to membrane separation, or treatment of concentrate. Iron and manganese are colorless when dissolved in water without exposure to oxygen. Once separated from freshwater in the RO process, concentrate may be exposed to air, at which point it may result in oxidation of ferric sulfide to ferric hydroxide which is red in color. Prior to discharge to the ocean, such concentrate will require sedimentation treatment to remove the ferric hydroxide or pretreatment of the source seawater by iron oxidation and removal of the oxidized iron by filtration followed by sedimentation in a solids handling facility. DO in source-water collected from beach-wells tends to be very low, not more than 2 mg/L. Discharge of appreciable volumes of concentrate with low DO could lead to oxygen depletion in the discharge area and stress aquatic life. USEPA requires daily average DO of 5 mg/L, and minimum DO of 4 mg/L for concentrate to be compliant. As the SWRO processes do not provide much additional oxygen to the feedwater, the concentrate would need to be aerated prior to discharge. Increase of the DO level of the discharge from 2 to 5 mg/L will require an appreciable amount of energy for aeration, which would add significantly to the cost of producing freshwater. The overall economic and environmental cost of the selected intake and discharge will be site-specific, and the benefit of shallow

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beach-wells or coastal intake wells may be neutralized by the requirement for aeration of the desalination plant discharge. Concentration of DO in the discharge from SWRO desalination plants with open ocean intakes mirrors DO concentration of seawater, which is in the range of 5 8 mg/L and can thus be discharged back to the ocean without the need for aeration. Whereas blending of this concentrate with wastewater effluent will improve the DO in the discharge, concentrate from plants with beach-well intake will further deplete the DO of such a blend, requiring significant aeration. A rule-of-thumb measure for avoiding contamination from port activities, industrial or wastewater discharge points is to locate an open ocean intake at least 1 km away from such sources of seawater contamination. This would generally safeguard concentrate from contamination with carcinogenic and endocrinedisrupting compounds. If found in the source-water, these compounds will be rejected by the RO membranes and thus will be contained in the concentrate. As artificial pollutants multiply in the environment, contamination of source water is likely to increase. The quality of source water from beach-wells may pose additional problems should the groundwater contain contaminants such as endocrine disruptors, heavy metals, fuel oil contaminants, arsenic, formaldehyde, etc. Potential sources of possible contamination of coastal aquifers are cemeteries, landfills, industrial parks, military installations, gas station storage reservoirs, and septic tank leachate. Additional treatment (and disposal) will be required to address such contamination, thereby minimizing the benefit of using beach-wells to collect source seawater for the desalination plant. Technologies which could be employed in treating hazardous compounds include UV irradiation, activated carbon filtration, ozonation, hydrogen peroxide oxidation etc. The additional treatment required will contribute to an increase in cost of water production.

3.4 Design guidelines for surface water discharges 3.4.1 Outfall pipeline For practical reasons, the discharge site should be located as close to the plant as possible to minimize the length of conveyance infrastructure. Concentrate is corrosive and the material for conveyance has to be selected with this in mind. Currently, plastic high-density polyethylene (HDPE), glass-reinforced plastic (GRP) and polypropylene (PP) pipe materials are favored for all sizes of desalination plants. The most economical discharge solution frequently practiced is a plastic pipe outfall secured to the ocean floor with concrete blocks (Fig. 3.3). Table 3.4 lists the most commonly used type and maximum size of plastic pipes for outfall construction. Until the 2000s, large diameter outfall pipes were usually fabricated from concrete, steel or cast iron. Since then PP, GRP and HDPE are the materials of

3.4 Design guidelines for surface water discharges

FIGURE 3.3 Outfall discharge pipeline supported on concrete blocks.

Table 3.4 Plastic piping materials used for outfalls. Plastic material

Typical maximum acceptable diameter

High-density polyethylene (HDPE) Glass-reinforced plastic (GRP) Polypropylene (PP)

2000 mm/78 in. 600 mm/24 in. 600 mm/24 in.

choice for ocean outfalls as they are chemically inert, resistant to corrosion and galvanic attack and lighter in construction. The benefits listed contribute to a far lower lifecycle cost than traditional materials. While GRP is typically less costly than HDPE, it has the disadvantage of being positively buoyant while not being resistant to negative pressure, as well as of cracking quite easily This means that GRP pipe would need to be installed underground with special bedding and fill material if the outfall is located in an exposed beach location, which will add to the overall cost. In some instances, reinforced concrete tunnels provide the optimal solution for concentrate outfalls. This is particularly true for very large desalination plants, where outfalls will be subjected to strong underwater currents. Such stability is also beneficial in areas where shipping traffic is heavy, and beach erosion extreme. As construction of concrete tunnels is likely to be far more costly than discharge through plastic pipes, they should be considered only where conditions merit the additional expenditure (Voutchkov, 2011a). To prevent accumulation of scale deposits inside the pipe, discharge pipelines should be designed for a minimum velocity of 0.7 m/s. So as not to incur

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pumping cost, the optimum pipe size should be calculated given the discharge pressure and maximum velocity. The design volume is usually selected to be equal to the intake volume: this provides for the variation encountered in commissioning and eases routine plant maintenance. During commissioning, the permeate is often discharged with the concentrate until consistent freshwater quality is achieved. The additional capacity is also useful in instances of short-term contamination for example in the event of an oil spill, where process equipment will be protected from exposure by bypassing the desalination plant treatment facilities and direct discharge of the contaminated water. Sometimes, outfalls are sized to accommodate only concentrate and other plant waste streams rather than the intake volume, in an effort to limit construction costs. This saving should be assessed against the decrease in operational flexibility, particularly where the plant is likely to be used intermittently—for example, in hot or long-term standby. Intermittent use by its nature will require more than once off commissioning and bypassing of some or the existing plant facilities.

3.4.2 Concentrate conveyance The pressure of concentrate at the exit point of the RO system varies between atmospheric pressure to a maximum of 2.5 bar, depending on the impact of the energy recovery system on the concentrate. This is generally sufficient to convey the concentrate to the discharge point without additional pumping to compensate for friction loss. Pumping of concentrate will add to the cost of product water as additional infrastructure will have to be constructed, while operational and energy costs will also increase. Where possible, efficient design should be applied to avoid the need for pumping of concentrate (Voutchkov, 2011a).

3.4.3 Outfall termination design Two types of termination are common in concentrate outfall pipes:

• Open-ended with perforations. Open-ended configuration was used in plants

•

constructed prior to 1980 and is still common for small outfalls. Typically, the pipe is perforated along the last 10% 30% of its length, to encourage mixing by increasing the area over which the discharge is expelled into the ocean. Where ambient conditions are sufficiently turbulent to meet discharge quality standards, this is the lowest cost option; Multiport diffuser. This requires the pipe end to be capped, with rows of small diffuser nozzles or ports located along the end section of the outfall and is now common on large diameter outfalls.

Diffusers are mostly angled upwards, directing the heavier concentrate toward the surface, away from the ocean bottom. The energy to dissipate the concentration plume must be sufficient to result in adequate dilution in the ZID, thus must

3.4 Design guidelines for surface water discharges

provide adequate amount of energy to eject the concentrate toward the ocean surface and maximize mixing time with seawater while engaging the entire water column in the concentrate dissipation process. Design of the diffuser system will define the diameter and length of outfall pipe required and will be a function of the discharge volume, pressure, and water column depth at which it will be released. The diffuser port parameters which need to be established in the design include the port diameter and angle from pipeline, the number of ports to be used and the distance between them. Further parameters to be determined are the materials to be used, the depth and exit velocity at the diffusers. Hydrodynamic models are typically used to optimize design of diffuser systems. Guideline parameters which are useful in preliminary design include (Voutchkov, 2011a):

• • • • • • •

diffuser system angled perpendicular to ocean current; minimum diffuser port size of 75 mm to avoid obstructions; diffuser port size to increase toward the end of the pipe; distance between ports to be established to avoid overlapping of plumes; diffuser angle between 45 and 60 degrees from horizontal delivery pipeline (see Fig. 3.4); cross-sectional area of diffuser ports not to exceed 70% of outfall pipe area; and exit velocity through the diffuser orifice of between 2 and 4 m/s.

Diluting concentrate with seawater prior to discharge results in a smaller differential in density between the concentrate and ambient seawater. This may either obviate the need for a diffuser system, or simplify the design thereof. An

FIGURE 3.4 Outfall diffusers with check valves.

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FIGURE 3.5 Sydney Water SWRO diffuser structure.

example of a diffuser system is that at Sydney’s SWRO desalination plant, where four outlet structures at depth between 20 and 30 m eject concentrate at an angle of approximately 60 degrees towards the surface (Figs. 3.5 and 3.6). Other diffuser structures simply have risers with ports directing concentrate discharge upwards such as the Perth and Gold Coast SWRO plants in Australia (Voutchkov, 2011a).

3.5 Costs for new surface water discharge Site-specific factors which have an impact on the cost of surface water discharge infrastructure include:

• construction material and configuration of outfall (e.g., above or below ground surface);

• discharge type: • near-shore being inside the tidal zone; • offshore being beyond the tidal zone; • discharge flowrate and volume; • diffuser system complexity; • conveyance cost to point of discharge; • treatment required prior to discharge; and • environmental monitoring costs. Directional drilling of the pipeline outfall under the ocean bottom is three- to fivefold more costly than dryland excavation for the same size pipe. The outfall construction cost is also significantly influenced by soil conditions as well as

3.5 Costs for new surface water discharge

FIGURE 3.6 Diagram of Sydney outlet structure.

climate. As mentioned previously, a common solution to minimize cost and time for outfall construction is to secure a plastic HDPE pipe to the ocean floor, anchored by concrete blocks spaced at between 5 and 10 m apart as shown in Fig. 3.3.

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Much of the cost of concentrate conveyance is specific to the project site, to emphasize the importance of consideration of concentrate disposal during site selection. The infrastructure to be constructed is a function of the concentrate flowrate, complexity of diffuser system required, length and material of outfall and hydrodynamic conditions in the receiving seawater (Voutchkov, 2011a). Fig. 3.7 provides a simple order-of-magnitude representation of cost of a nearshore discharge as a function of concentrate flowrate. For preliminary planning, the indicative unit construction costs as a function of concentrate flowrate is shown in Fig. 3.8, for both HDPE pipeline, and for concrete tunnel directionally drilled under the ocean bottom. Note that these estimates exclude many costs which may be required depending on the site selected, such as treatment of concentrate prior to discharge, lengthy conveyance between plant and outfall, as well as specific environmental management and monitoring costs, for example water quality monitoring equipment. Environmental monitoring cost is further influenced by the sensitivity of

FIGURE 3.7 Construction cost of near-shore discharge.

3.5 Costs for new surface water discharge

FIGURE 3.8 Unit outfall costs.

the particular open water body, for example where natural flushing is limited, additional monitoring will be required. Any predischarge aeration will also add to the total discharge cost (Voutchkov, 2011a).

Cost example To determine the approximate cost range for a hypothetical SWRO desalination plant with projected discharge of 25,000 m3/day, for both near-shore and offshore configuration.

Discharge construction cost Near-shore

Reading off Fig. 3.7 for construction of near-shore discharge, the estimated cost is US$6.0 million. (Continued)

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Cost example (Continued) Offshore Should near-shore disposal not be possible, options of discharge via concrete tunnel, or HDPE pipe are considered. If the length required for the outfall is 1000 m, then:

• •

From Fig. 3.8, the unit cost of HDPE outfall is US$9600/m resulting in the total outfall construction cost estimate of US$9.6 million. The construction of directionally drilled concrete tunnel would be more costly, and at unit tunnel cost from Fig. 3.8 of US$29,000/m, the construction of the 1 km long tunnel would cost approximately US$29 million.

Intuitively, near-shore discharge will cost less than deeper discharge outfall, and this is confirmed by the example. While HDPE offshore cost is around a third of that of concrete tunnel construction, it is more than 50% more costly than the near-shore discharge. Note that these construction expenditures provide an order-of-magnitude estimate and exclude all costs related to concentrate treatment, acquisition of land, long dryland conveyance costs etc.

3.6 Codisposal with wastewater effluent 3.6.1 Description The principle advantage of blending SWRO concentrate with wastewater effluent is enhanced mixing due to the density differentials. This is of benefit to both the concentrate and wastewater effluent discharge impacts. Concentrate is heavier than seawater while wastewater, being less saline, is lighter. Should the waste streams be thoroughly mixed prior to discharge, the size of the discharge plume may be significantly reduced, and cost of diffuser infrastructure decreased. Dissipation is further accelerated by the plume floating upwards thus expanding the volume of ocean water with which it mixes. An advantage specific to the wastewater effluent discharge is the dilution of effluent, which typically has a far higher content of metals, pathogens and organics than concentrate, thus reducing the overall waste discharge load (Voutchkov, 2011a). The very real benefit of using existing infrastructure in the wastewater effluent outfall has a twofold advantage: reduced environmental impact from construction of additional outfall infrastructure, and the cost of such infrastructure.

3.6.2 Potential environmental impacts As mentioned before, ion-imbalance toxicity may be triggered when wastewater effluent is blended with either SWRO or BWRO concentrate as the resulting ion composition differs markedly from that of the receiving seawater. Testing is required to confirm the absence of toxicity prior to implementing such joint discharge.

3.6 Codisposal with wastewater effluent

A practical example of this was undertaken in Santa Barbara, California, where wastewater effluent blended with desalination concentrate proved to be toxic to the eggs of sea urchins (Strongylocentrotus purpuratus) in bioassay tests. In a parallel test, when seawater was used to dilute the desalination concentrate to the required TDS level, toxicity was found to be absent. This result was amplified through long-term testing at the Carlsbad desalination plant, where exposure of sea urchins to a blend of concentrate and seawater (from the collocated power plant cooling system) showed no negative impact on the urchins despite longterm exposure to elevated salinity (Voutchkov, 2011a). Mineral ions found in seawater are almost uniformly rejected at the same level by reverse osmosis membranes with the result that the ratios between the concentration of ions such as calcium, sodium, chloride, magnesium and sulfate and the total TDS concentration of the discharge are virtually the same in desalination concentrate as in the source seawater. This results in an absence of ion-imbalance when the concentrate is discharged to ambient seawater. In contrast, the ratio between ions and TDS in wastewater effluent is likely to differ considerably from that of seawater, and such a difference is the likely cause of toxicity to sensitive aquatic organisms (Mickley, 2000). Blending concentrate with WWTP effluent also creates the potential for contaminants to aggregate into larger clusters than they would naturally which may have a detrimental impact on the environment. Metals and other solids could impact the wellbeing of phytoplankton and benthic organisms in the discharge area (Voutchkov, 2011a,b).

3.6.3 Feasibility considerations While the benefits of codisposal with wastewater effluent are outlined in the section above, site-specific conditions need to be thoroughly assessed during evaluation of the feasibility of surface water discharges. Considerations of feasibility are numerous, and require the owner/operator of the WWTP to be invested in finding the best discharge solution holistically. Not only does feasibility depend on the availability of capacity in the wastewater outfall and fees that may be due for such discharge but also on the WWTP operator accepting liability for any environmental impacts caused by the joint discharge. Disruptions during alterations of the discharge infrastructure and tie-in of concentrate pipeline requiring downtime are likely to disrupt operations. Discharge infrastructure, such as the number and configuration of the existing WWTP effluent diffusers, may require modification given that the buoyancy of the discharge will be altered by the addition of concentrate. A further complicating factor is the daily flow variation of the WWTP effluent flow as compared to the near constant flowrate of concentrate. All of these matters are magnified where the volume of concentrate is large (Voutchkov, 2011a). The impact of the variation in buoyancy introduced by the constant flow of concentrate may well require redesign of diffuser infrastructure. The impact of heavy concentrate will reduce the discharge buoyancy (especially at night), and

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decrease the initial mixing energy, which in turn may cause less efficient mixing of the WWTP effluent with the ambient seawater. Hydrodynamic modeling will be needed to confirm the adequacy of existing infrastructure, or the necessary modifications to be implemented, if required. These modifications may be as simple as adjusting or closing nozzles or as complex as construction of flow equalization tanks and pump station for delivery of the blended discharge through the existing WWTP outfall. Variation in flow of the two streams being blended is likely to impact on the dilution achieved in the ZID as well. This may result in reducing the amount of concentrate generated by decreasing the desalination plant production at night, so that the blend ratio can be maintained. An alternative solution would be construction of storage facilities—either to accommodate the excess concentrate generated at night, or to serve as holding tanks for the wastewater effluent to even out daily fluctuations. This will of course add to the cost of water production.

3.6.4 Cost factors and analysis Once codisposal of concentrate with wastewater effluent has been found to be feasible, the various project cost components need to be considered. Additional costs specific to such codisposal are:

• • • •

conveyance cost of concentrate between plants; tariffs or fees payable to the WWTP owner for use of outfall capacity; construction of connection from concentrate pipeline to outfall; and expenditures for modification of existing WWTP diffuser structure, and any storage tanks for concentrate or effluent, if needed. Impact on seasonal or year around water reuse, taking into consideration that a certain minimum WWTP effluent volume would be needed to dilute the concentrate discharge at all times and would not be available for reuse.

3.6.5 Examples of concentrate codisposal with wastewater effluent BWRO concentrate codisposal with WWTP effluent has been successfully implemented in California, in the United States. The Santa Ana river interceptor (SARI) in Southern California conveys effluent from several WWTPs, power plants as well as concentrate from six inland BWRO desalination plants. A combined volume of 65,000 MLD is discharged together with effluent from the Orange County Sanitation District’s WWTP in Huntington Beach. The SARI line is a gravity pipeline 150 km in length, with diameter of 400 2100 mm and has a nominal capacity of 114 MLD, transporting approximately 130,000 tons of salt annually. The ocean outfall at the Orange County Sanitation District’s WWTP has a 3100 mm diameter. At present just over a quarter of the capacity of 1817 MLD of the outfall is in use.

3.7 Codisposal with power plant cooling water

FIGURE 3.9 Barcelona desalination plant.

Codisposal of SWRO concentrate with WWTP effluent has found less practical application. The largest known operational plant is in Barcelona, Spain where the 200 MLD desalination plant’s concentrate is discharged with wastewater effluent (Vila et al., 2009); see Fig. 3.9. On a far smaller scale, the Santa Barbara desalination plant concentrate is blended with municipal wastewater effluent prior to disposal through the existing WWTP outfall. The volumes of discharge in this case are approximately equal.

3.7 Codisposal with power plant cooling water 3.7.1 Description In some cases it could be expedient to colocate a SWRO desalination plant with a seawater cooled power plant where such power plant is situated on the coast. There are a number of site-specific benefits to such a configuration, including shared infrastructure, optimization of discharge density and potential reduction in electricity cost for desalination due to proximity to generation. A typical colocation configuration as shown in Fig. 3.10 connects the desalination intake to the cooling water discharge prior to its entrance into the ocean.

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FIGURE 3.10 Typical configuration of collocated desalination plant.

After collecting some of the power plant warm cooling water for production of desalinated water, the concentrate generated is discharged back into the same power plant discharge canal, downstream from the intake point. The cooling water is thus used as source water for the desalination process, as well as serves to dilute the concentrate prior to discharge back to the ocean. Coastal power plants with once-through cooling systems are known to require large volumes of seawater for cooling purposes. The power plant cooling system collects seawater from the ocean, which is screened to remove solids and then pumped through the power plant condensers. Water is pumped through the condensers in tubes, typically not larger than 10 mm diameter. The benefit of using cooling water for desalination thus starts with the elimination of a separate desalination plant intake structure, with associated screening infrastructure. Depending on the site-specific condition, the cost of an intake system ranges between 5% and 30% of the total construction cost of a desalination plant. Collocation and sharing infrastructure with a power plant thus has the benefit of reducing the required capital outlay for construction of an intake system (Voutchkov, 2011a). Screenings removed at the bar racks and fine screens of the power plant intake are usually removed and disposed of to landfill. In instances where this is not the case, screened solids may be added back to the used cooling water to be disposed of in the discharge to the ocean. If the desalination plant intake is downstream of the point where screenings are added, then screening infrastructure will be required prior to pretreatment, and some of the benefit of cost reduction will be lost.

3.7 Codisposal with power plant cooling water

As water moves through the condensers, waste heat generated during the process of electricity generation is transferred to the water, resulting in heating of the water by between 5 C and 15 C (Voutchkov, 2004). Along coastlines with cold oceans this can be beneficial as the added heat reduces viscosity of the water thereby requiring lower osmotic pressure for salt separation and therefore, overall lower power demand. Additional to the cost saving of the construction of a new intake, environmental disturbance is also reduced by using existing infrastructure. Entrainment, impingement and entrapment of marine organisms at intake structures is an environmental concern, and some advances have been made in intake design to reduce these impacts. Where the cooling water is used as source water for desalination, the number of intakes is reduced from two to one also minimizing this impact as the biomass of marine organisms impacted is proportional to the intake volume. Proximity to the point of generation of power can have marked cost benefits. Electricity tariffs are usually structured to include a production and a transmission cost component. The transmission cost component varies greatly, and could be between 30% and 50% of the cost. Connecting directly to a power plant could significantly reduce or even eliminate the transmission cost component of the desalination plant power tariff, which leads to a reduction in the cost of water produced. The benefit to the power plant owner/operator is that it gains a customer, with high energy usage, power load factor and consistent demand. The stability in load required can lead to a reduction in operational cost at the power generation plant. Collocating desalination and power plants has the potential to completely remove the need to construct a separate outfall for the desalination plant. The discharge salinity is a key determinant of the outfall length and configuration. Where the salinity is low, dilution to required environmental levels is easily achieved closer to the shore, without the need for complex diffusers. When the desalination concentrate is discharged into the cooling water discharge canal, blending with the cooling water results in lowering of the concentrate salinity closer to that of seawater. Depending on the volumes of cooling water and concentrate, the discharge could approach the natural variation of salinity in the ambient seawater, thereby obviating the need for any special discharge infrastructure. Even where cooling water is not used in the desalination process, the benefit of joint discharge is distinct. Such collocation can be found at the 120 MLD Carboneras plant in Spain. The desalination plant has an independent intake to provide source water, but the concentrate is discharged into the cooling water discharge canal of a nearby power plant. This allows for the concentrate to be discharged at a salinity which is safe for the receiving environment. The environmental benefit is extended to the cooling water discharge. Given that some of the discharged cooling water is desalinated to freshwater, the thermal discharge load of the power plant is reduced, which decreases the effect of the thermal plume on the receiving environment. Both salinity and temperature influence the density of seawater: added salinity causes an increase in density while

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added temperature causes a decrease. As the cooling water is warmer than ambient seawater, it is lighter and therefore, it floats to the ocean surface even though it has the same composition but at lower temperature. The addition of concentrate adds to the density of the blend, so that the thermal discharge load is distributed more uniformly across the depth of the water column. This decreases the time of dissipation that both discharge streams would otherwise have required, which also reduces the footprint of impact. The ideal mix would be where the salinity induced increase balances the temperature induced decrease in density. The synergy was maximized at the Carlsbad desalination plant collocated while the power plant was operational. Ambient seawater at this location has temperature of 18 C, salinity of 33,500 mg/L and density of 1024.12 kg/m3. The concentrate from the desalination plant has the same temperature, but with a salinity of 67,000 mg/L, the density is significantly higher at 1050.03 kg/m3, which would cause the discharge to sink to the ocean floor with concomitant negative impact of increased salinity on the marine habitat. Blending with cooling water from the power plant results in a reduction of salinity down to 36,200 mg/L and a temperature of 26 C. Both the salinity and temperature are thus far closer to that of ambient seawater than the individual discharge streams, with sufficient buoyancy from the elevated temperature to carry the salinity plume to the surface and increase its dissipation rate (Voutchkov, 2011b). To achieve the same dilution without the benefit of blending with cooling water, significant energy is required to propel concentrate through diffusers at high velocity (in the region of 2 4 m/s) for adequate mixing (see Fig. 3.11).

3.7.2 Potential environmental impacts Where a desalination plant is collocated with an existing power plant, the discharge infrastructure of the power plant will need to be assessed, and if necessary redesigned with the required modifications implemented (similar to collocation with a WWTP). Should a power plant be decommissioned (such as the case at the Carlsbad plant), the designs of intake as well as discharge have to be revisited and amended as necessary, to compensate for the loss of the positive effects of collocation. For example, due to the absence of an increase in temperature, the concentrate would need to be further diluted to reduce density, thereby potentially increasing impingement and entrainment at the intake.

3.7.3 Source-water treatment requirements Part of the feasibility consideration for collocation with a power plant and dual use of intake structure is the quality of the cooling water. If during the cooling process, cooling water is contaminated with copper, iron or nickel to levels significantly higher than that found in seawater, the impact on the desalination process could be significant and diminish the benefit of collocation.

3.7 Codisposal with power plant cooling water

FIGURE 3.11 Comparison of concentrate diffusion of conventional and collocated desalination plants.

As mentioned previously, where seawater intake screenings are not disposed of off-site but added back to the discharge canal, the desalination plant may have to provide for separate screening infrastructure. Even where screenings are disposed of remotely, it is important to consider that this may change over time, as was the case at the Tampa Bay SWRO desalination plant. The power plant owner, Tampa Electric Power Company (TECO) decided to change disposal process while the desalination plant was under construction. The desalination plant had been designed to accept the screened cooling water as intake and thus did not provide for separate screening infrastructure. The change in regimen resulted in the screenings being disposed of upstream of the desalination intake point. The late change introduced significant challenges during startup and operations. The solids content of the source water detrimentally impacted on the pretreatment filter piping, airlifts and sand media. The resultant filter quality was poor and reduced the cartridge filter useful life.

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Table 3.5 Desalination plant collocation considerations. Advantages

Disadvantages and feasibility considerations

• Capital cost savings: construction of new

• Use of warmer seawater may accelerate

•

•

•

•

•

•

intake, discharge and outfall not needed Decrease of the RO system feed pressure and power cost savings as a result of using warmer water Reduction of marine organism impingement and entrainment if intake infrastructure is shared Reduction of impact on marine environment as a result of accelerated r discharge dissipation Reduction of power plant thermal discharge load to the ocean with a portion of discharge converted to potable water Use of already disturbed land at the power plant minimizes environmental impacts along the coast Reduction of power costs by elimination of power transmission component of the electricity tariff

membrane biofouling

• Accelerated fouling of RO membranes if

•

•

• •

•

•

cooling water has high iron, copper or nickel content Source seawater may have to be cooled: temperature must be below 40 C to protect membrane integrity Permeate water quality diminishes slightly with an increase of source-water temperature Warmer water also results in lower boron rejection Verify that source-water screening will remain in place over the useful life of the desalination plant Confirm that the power plant has adequate cooling flow to provide concentrate dispersal Desalination plant operations may need to be discontinued during periods of heat treatment of the power plant facilities

The challenge could be resolved either by providing a separate screening infrastructure at the desalination plant, or by moving the screening discharge point to downstream of the desalination intake. The desalination plant developer opted to provide screening infrastructure, which resolved the operational issues. The need for close cooperation and comprehensive legal agreements with the collocated power plant and desalination plant owners is highlighted by this example. Table 3.5 presents the main considerations to be evaluated in determining feasibility of collocation with a power plant.

3.7.4 Design and configuration guidelines To consider collocation as an option, the first variable to be confirmed is that the host power plant’s cooling water volume is several times higher than the planned desalination plant production capacity. Secondly, the layout of the cooling water intake and discharge needs to be such that the desalination intake will be safeguarded against recirculation under all possible conditions of power production, tides and storm events.

3.7 Codisposal with power plant cooling water

Ideally, blending of concentrate with cooling water should be complete at the point of discharge to optimize the benefit of collocation. The cooling water discharge canal must thus have sufficient distance between the concentrate discharge and ocean discharge points. The distance required is a function of various factors, including power plant and concentrate discharge flow rates, temperature and salinity of the two streams, angle of entry of concentrate stream and size of the entry pipe into the cooling water canal/outfall. Fluid dynamics computer modeling is advised to establish the best discharge point and angle of where the concentrate will enter the cooling water canal (Voutchkov, 2011a). The computational fluid dynamics modeling for the two alternative entry configurations of a 760 mm (30-in.) concentrate discharge pipe into the 2743 mm (108-in.) cooling water outfall at the Tampa Bay collocated plants are shown in Figs. 3.12 and 3.13. The first figure models a 45-degree angle, while the second figure models a 90-degree angle.

FIGURE 3.12 Tampa Bay SWRO discharge entrance configuration: Case 1.

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FIGURE 3.13 Tampa Bay SWRO discharge entrance configuration: Case 2.

The conditions shown as Case 1 in Fig. 3.12, with the concentrate pipe protruding 0.75 m into the canal proved to be optimal, and resulted in total mixing within a distance of 25 m. As the power plant infrastructure already existed, it was important to design for maximum initial mixing given the limited distance available. Entry at a 90 degrees illustrated in Case 2 is far less efficient although the option is easier to construct.

3.7.5 Cost factors and analysis A benefit that was highlighted on power plant collocation is the anticipated reduction in energy demand due to the increase in SWRO feedwater temperature from

References

cooling water. Typically, within limits of desirable desalination temperatures of 12 C 35 C the feed pressure required is between 2% and 3% less for every 10 C increase in source seawater. Collocation thus offers significant benefit in areas with cold sea temperatures. The energy component of the overall water production cost is in the range of 30% 40%, thus a decrease in energy requirement will have a significant impact on cost of water production. It has been noted that intake and discharge designs need to be revisited and modifications brought about should the power plant be decommissioned. Power plant cooling systems in the United States for example, are being switched from water cooled to air-cooled to comply with Section 316 (b) Federal Regulatory requirements for reduction of the environmental impacts associated with plant intake operations. Should this be implemented at a collocated desalination plant, the design and configuration will need to be revisited. While operational benefits will cease once water cooling stops, the major capital cost of construction of intake and discharge structures will still be of benefit in the lowering the overall production cost of water. The anticipated capital cost savings are typically in the range of 20% 30% of the total desalination plant construction costs.

References American Water Works Association, 2007. Reverse Osmosis and Nanofiltration. Manual of Water Supply Practices, M46. ANZECC (Australian and New Zealand Environment and Conservation Council); Agriculture and Resource Management Council of Australia and New Zealand. Australian and New Zealand Guidelines for Fresh and Marine Water Quality; National Water Quality Management Strategy Paper No. 4; Australian and New Zealand Environment and Conservation Council: Canberra, Australia, 2000. Australian Government. Environment Protection and Biodiversity Conservation Act; Act 91; Department of the Environment, Canberra, Australia, 2015, 1999. Beck, R.W., 2004. Guidance Manual for Permitting Requirements in Texas for Desalination Facilities Using Reverse Osmosis Processes. Texas Water Development Board, Austin, TX. Bleninger, T., Jirka, G.H., 2010. Environmental Planning, Prediction And Management of Brine Discharges from Desalination Plants. 2nd Periodic Report. Produced for the Middle East Desalination Research Center Muscat, Sultanate of Oman. Institute for Hydromechanics, University Karlsruhe, Karlsruhe. California State Water Board, 1996. Procedures Manual for Conducting Toxicity Tests Developed by the Marine Bioassay Project, 96-1WQ. CDWR (California Department of Water Resources), 2008. California Desalination Planning Handbook. California State University, Sacramento, CA. Chapman, G.A., Denton, D.L., Lazorchak, J.M., 1995. Short-term Methods for Estimating the Chronic Toxicity of Effluents and Receiving Waters to West Coast Marine and Estuarine Organisms, USEPA Report No EPA/600/R-95/136.

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Cotruvo, J., Voutchkov, N., Fawell, J., Payment, P., Cunliffe, D., Lattemann, S., 2010. Desalination Technology—Health and Environmental Impacts. CRC Press. Einav, R., Lokiec, F., 2003. Environmental aspects of a desalination plant in Ashkelon. Desalination 156, 79. Einav, R., Harussi, K., Perry, D., 2002. The footprint of the desalination processes on the environment. Desalination 152, 141. Graham, J., 2004. Marine Biological Considerations Related to the Reverse Osmosis Desalination Project at the Encina Power Plant, Carlsbad, CA, Environmental Impact Report for Carlsbad Seawater Desalination Plant, City of Carlsbad. Hammond, M., Blake, N., Hallock-Muller, P., Luther, M., Tomasko, D., Vargo, G., 1998. Effects of Disposal of Seawater Desalination Discharges on Near Shore Benthic Communities, Report of Southwest Florida Water Management District and University of South Florida. Hoepner, T., 1999. A procedure for environmental impact assessments (EIA) for seawater desalination plants. Desalination 124, 1. Hoepner, T., Windelberg, J., 1996. Elements of environmental impact studies on coastal desalination plants. Desalination 108, 11. Jenkins, S.A., Wasyl, J., 2001. Hydrodynamic Modeling of Dispersion and Dilution of Concentrated Seawater Produced by the Ocean Desalination Project at the Encina Power Plant, Carlsbad, California, Environmental Impact Report for Carlsbad Seawater Desalination Plant, City of Carlsbad. Kampf, S., Clarke, B., 2012. How robust is the environmental impact assessment process in South Australia? Behind the scenes of the Adelaide seawater desalination project. Marine Policy 38, 500. Mauguin, G., Corsin, P., 2005. Concentrate and other waste disposals from SWRO plants: characterization and reduction of their environmental impact. Desalination 182, 355. MEP (Ministry of Environmental Protection), 2002. Policy for the Protection of the Mediterranean Marine and Coastal Environment From Desalination Facilities; Tel Aviv, Israel. Mickley, M.C., 2000. Major Ion Toxicity in Membrane Concentrate. AWWA Research Foundation, Denver, CO. Mickley, M.C., 2001. Membrane concentrate disposal: practices and regulation. Final report. Agreement No 98-FC-81-0054. Desalination and water purification research and development program report no 69. U. S. Department of the Interior, Bureau of Reclamation. Technical Service Center. Water Treatment Engineering and Research Group. Mickley, M.C., 2006. Membrane Concentrate Disposal: Practices and Regulation, Desalination and Water Purification Research and Development Program Report N. 123, second ed. U.S. Department of Interior, Bureau of Reclamation. Mickley, M.C., Voutchkov, N., 2016. Database of Permitting Practices for Seawater Concentrate Disposal. IWA WERF Research Report Series. Missimer, T.M., Malive, R.G., 2018. Environmental issues in seawater reverse osmosis desalination: intakes and outfalls. Desalination 4343, 198. Purnama, A., Al-Barwani, H.H., 2004. Some criteria to minimize the impact of brine discharge into the sea. Desalination 171, 167. Purnama, A., Al-Barwani, H.H., Al-Lawatia, M., 2003. Modeling dispersion of brine waste discharges from a coastal desalination plant. Desalination 155, 41.

References

Rhodes, M., 2006. Marine management is high priority. Inter. Desal Water Reuse Quarter 16, 30. Sadhwani, J.J., Veza, J.M., Santana, C., 2005. Case studies on environmental impact of seawater desalination. Desalination 185, 1. Safrai, I., Zask, A., 2008. Reverse osmosis desalination plants—marine environmentalist regulator point of view. Desalination 2008, 220, 72-84. Shemer, H., Semiat, R., 2017. Sustainable RO desalination—energy demand and environmental impact. Desalination 424, 10. Stratus Consulting, 2010. Guidelines for implementing seawater and brackish water desalination facilities, WateReuse Research Foundation. SWRCB, 2014. National Pollutant Discharge Elimination System (NPDES)—Wastewater. California Environmental Protection Agency, SWRCB: 2014. ,http://www.waterboards.ca.gov/water_issues/programs/npdes/.. USEPA, 2015. Water Permitting 101. Office of Wastewater Management, U.S. EPA: Washington, DC. ,http://water.epa.gov/polwaste/npdes/basics/upload/101pape.pdf.. Vargas, C., Viskovich, P., Gordon, H., Walker, T., 2011. The Challenge of Managing Reverse Osmosis Brine Disposal: Experience at QLD; Ref. IDAWC/PER11 075; Proceedings of the IDA World Congress, Perth, Australia, International Desalination Association. Vila, J., Compte, J., Cazurra, T., Ontanon, N., Sola, M., Urrutia, F., 2009. Environmental Impact Reduction in Barcelona’s Desalination and Brine Disposal. In: Proceedings of World Congress in Desalination and Reuse, International Desalination Association, IDAWC/DB09 309, 7 12 November, Dubai. Voutchkov, N., 2004. Seawater desalination costs cut through power plant collocation. Filtr Sep Mag 41, 7. Voutchkov, N., 2011a. Desalination plant concentrate management, Water Treatment Academy. TechnoBiz Communications, Bangkok, Thailand 2011. Voutchkov, N., 2011b. Overview of seawater concentrate disposal alternatives. Desalination 273, 1.

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Case studies for surface water discharge

4

4.1 Introduction Over the past 15 years, the development of large-scale reverse osmosis (RO) plants has grown exponentially. Much has been learned regarding project design for reduced costs and environmental impacts, especially in arid regions where desalination is the dominating alternative technology for production of drinking water, such as the Middle East, Australia, and the United States. Nearly 28,000 million liters a day of seawater reverse osmosis (SWRO) and 23,000 million liters a day of brackish water reverse osmosis (BWRO) has been added to water supplies worldwide since 2013, bringing the global desalinated water production capacity to more than 110 million m3/day. This chapter includes a number of case studies of large desalination plants worldwide, with a specific focus on how concentrate is managed to minimize environmental impacts. All case studies in this chapter are for desalination plants with surface water discharge. Cases are ordered by country.

4.2 Surface water discharge case studies 4.2.1 Australia: Perth I desalination plant 4.2.1.1 Perth 1 facility description As reported at the November 2009 World Congress of the International Desalination Association (Christie & Bonnelye, 2009), the 143,000 m3/day Perth Seawater Desalination Plant has been in continuous operation since November 2006. This plant supplies over 17% of the drinking water for the City of Perth, Australia, which has over 2 million inhabitants. The treatment facilities of the Perth seawater desalination plant (Fig. 4.1) are very typical for state-of-the-art seawater desalination plants worldwide. Since its construction the Water Corporation of Western Australia (Water Corporation) has built a second desalination plant, Perth II, to provide drought proof and reliable water supply to the City of Perth.

Management of Concentrate from Desalination Plants. DOI: https://doi.org/10.1016/B978-0-12-818045-7.00004-X © 2020 Elsevier Inc. All rights reserved.

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FIGURE 4.1 Perth I seawater desalination plant.

This plant has a velocity-cap type open intake structure extending 200 m from the shore. Source seawater is treated using 24 single-stage dual granular media pressure filters, 14 5-micron cartridge filters, and 12 two-pass reverse osmosis membrane system trains with pressure exchangers (16 ERI PX 220 per RO train) for energy recovery. The RO permeate is posttreated by lime stabilization and sodium hypochlorite disinfection (Mickley & Voutchkov, 2016). Fig. 4.2 provides a general schematic of the Perth I SWRO desalination plant. The desalination plant concentrate is discharged to the ocean via an offshore outfall with diffusers. Plant source water salinity varies in a range of 30,000 39,000 mg/L (average 37,000 mg/L) and intake temperature is between 15 C and 25 C, and averages 20 C.

4.2.1.2 Perth 1 receiving water characterization Perth I SWRO plant discharge is located in Cockburn Sound, which is a shallow and enclosed water body with a very limited water circulation and an average salinity of 37,000 mg/L. Cockburn Sound frequently experiences naturally occurring low oxygen levels during periods of low currents/low wind intensity. This water body is connected to the Pacific Ocean. Cockburn Sound is characterized by relatively closed access to the Pacific Ocean and a variable offshore current. This Sound consists of a 10 m shelf near the shore location of the desalination

4.2 Surface water discharge case studies

FIGURE 4.2 General schematic of Perth I SWRO plant, Australia.

plant, which becomes 20 m basin at its deepest part, which is enclosed by the Garden Island further west. The main areas of environmental concern faced at the desalination plant and its discharge included:

• dilution of the concentrate discharge at the edge of the “mixing zone”: 50 m in all directions of the diffuser;

• toxicity of the concentrate and its effect on the surrounding ecosystem; • a perceived threat to dissolved oxygen levels in Cockburn Sound by the •

environmental regulator and the Cockburn Sound Management Council (who monitor the environmental “health” of Cockburn Sound), and discharge of other waste products such as sludge from the dual media backwash water.

4.2.1.3 Description of Perth 1 discharge streams The desalination plant discharge to the ocean consists of concentrate and spent pretreatment filter backwash water. Concentrate is discharged from the RO system under pressure and after conveyance to a small retention chamber is discharged to the plant ocean outfall. The spent filter backwash water is pretreated in lamella settlers and equalized prior to discharge with the concentrate. Sludge generated in the lamella settlers is dewatered in a belt filter press and disposed offsite to a sanitary landfill. Neutralized membrane cleaning solution generated from RO membrane clean-inplace is discharged to the sanitary sewer.

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FIGURE 4.3 Perth I SWRO plant discharge configuration.

4.2.1.4 Description of Perth 1 plant outfall Since the Perth I SWRO plant discharge area has very limited natural mixing, the desalination plant is equipped with a diffuser-based outfall which is located approximately 500 m offshore and has 40 ports along the final 200 m at about 0.5 m from the seabed surface at a 60-degree angle. The diffuser system was designed to provide a dilution ratio of 45:1 within the mixing zone. The diffuser ports are spaced at 5 m intervals with 220 mm nominal port diameter at a depth of 10 m; see Fig. 4.3. Diffuser length is 160 m. The outfall is a single glassreinforced plastic (GRP) pipeline with diameter of 1600 mm. This diffuser design was adopted with the expectation that the plume would rise to a height of 8.5 m before beginning to sink due to its elevated density. It was designed to achieve a plume thickness at the edge of the mixing zone of 2.5 m and, in the absence of ambient cross-flow, to extend to approximately 50 m laterally from the diffuser to the edge of the mixing zone (see Fig. 4.4). Plant operations data (Christie and Bonnelye, 2009) show that the actual dilution ratios achieved with this design were between 50 and 120 (measured at the edge of the mixing zone) depending on the actual direction of local currents, which is well above the plant permit dilution ratio requirement of 45:1. It should be noted that the plant has a provision (which is allowed by the permit) to recirculate intake seawater into the plant concentrate discharge during periods of reduced plant capacity to increase discharge velocity and improve dilution and oxygen content, if needed, for compliance with the minimum dilution ratio defined in the permit.

4.2 Surface water discharge case studies

FIGURE 4.4 Perth I desalination plant mixing zone.

The diffuser design was optimized using computer fluid dynamic models based on Roberts equation, which allowed to select the optimum size of the diffuser nozzles, the diffuser system configuration, and the diameter and angle of discharge. During the design phase, studies were performed at the University of New South Wales using a hydraulic calculation model as well as physical 1:15 scale model for the confirmation of the design of the outfall (plume thickness and height, impact, ultimate dilution, and compliance of the target objective of achieving TDS concentration of less than 1.2 ppt within 50 m from the diffusers).

4.2.1.5 Key Perth 1 discharge permit requirements Table 4.1 presents a summary of key requirements included in the plant discharge permit. The plant discharge permit (referred to as “operational environmental license”) is issued by the Department of Environment and Conservation (DEC) of Western Australia. This permit prescribes that the discharge should achieve a dilution factor of 45:1, at a distance of 50 m in all directions of the diffuser (the edge of the defined mixing zone). The dilution factor is calculated based on the salinity of the concentrate and the ambient seawater (measured in practical salinity units [psu]) as follows: Dilution Factor 5

SB SD

SS SS

(4.1)

where SB 5 salinity of the discharged seawater concentrate in psu; SD 5 salinity at 50 m from the diffuser (average of the concentrate plume—see explanation of the average later) in psu; and SS 5 salinity of intake seawater in psu.

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Table 4.1 Perth I SWRO desalination plant: key discharge permit requirements (permit no. L8108/2004/4). Permit discharge parameter Distance factor at the edge of mixing zone Distance from diffusers to edge of mixing zone Salinity increment above average at edge of mixing zone Turbidity concentration Oxygen concentration pH units Conductivity of undiluted concentrate

Average

Maximum

Minimum 1:45

50 m 0.8 ppt

1.2 ppt 8 NTU 8.3 92,999 µS/cm

5 mg/L 7.0

The seawater salinity at the edge of the mixing zone is measured as close as practicable to 0.5 m intervals in the bottom 5.0 m of the water column. The pycnocline due to the diffuser discharge is identified and only those depths below the pycnocline are averaged to determine the diffuser performance. Salinity is required to be measured for at least three minutes at each depth then time averaged prior to the determination of the pycnocline depth and any depth averaging. (A pycnocline is the layer where the density gradient is greatest within a body of water.) The discharge permit requires salinity monitoring to be completed 12 times per year during the first year in order to obtain data representative for seasonal salinity variations. The frequency of salinity measurement is reduced to two times per year after the first year. In addition, to the requirements of the discharge permit issued by the Department of Environmental Conservation, the Western Australian Environmental Protection Authority (EPA) has also added a permit condition to complete whole effluent toxicity (WET) testing at the time of plant commissioning and after 12 months of operation. These tests aim to confirm that the actual plant dilution is adequate to prevent chronic toxicity of the marine flora and fauna. One of the key concerns of the regulators was that the concentrate, which is denser than the ambient seawater, would sink to the deeper 20.1 m basin of Cockburn Sound and will cause the formation of hypoxic layer and dissolved oxygen suppression. Hypoxia would in turn result in potential fish kills. Therefore the plant permit requires the operator to monitor dissolved oxygen (DO) levels in the deeper basin of Cockburn Sound and the plant has to limit production to onesixth of its capacity when the oxygen concentration decreases under certain prescribed level.

4.2.1.6 Permit compliance observations Extensive real-time monitoring was undertaken in Cockburn Sound for 12 months before and after the plant began operation in November 2006 to ensure that the

4.2 Surface water discharge case studies

marine habitat and fauna are protected. This monitoring includes continuous measurement of dissolved oxygen levels via sensors located on the sandy bed of the Sound. Visual confirmation of the plume dispersion was achieved by the use of 52 liters of Rhodamine dye added to the plant discharge. The dye was reported to have billowed to within approximately 3 m of the water surface before falling to the seabed and spilling along a shallow sill of the Sound toward the ocean. The experiment showed that the dye had dispersed beyond what could be visually detected within a distance of approximately 1.5 km, which is well within the protected deeper region of Cockburn Sound located approximately 5 km from the diffusers. The environmentally benign dye experiment was first commissioned in December 2006 and repeated in April 2007 when discharge conditions were calm. The expulsion of the Rhodamine dye from one of the plant diffusers is shown on Fig. 4.5. In addition, to the dye study, the project team has completed a series of toxicity tests with a number of species in larval phase to verify that the actual mixing ratio of the plant outfall diffusers is higher than the minimum dilution ratio needed to be achieved at the edge of the zone of initial dilution:

• • • • •

72-hour macroalgal germination assay using the brown kelp Ecklonia radiate; 48-hour mussel larval development using Mytilis edulis; 72-hour algal growth test using the unicellular algae Isochrysis galbana; 28-day copepod reproduction test using the copepod Gladioferens imparipes; and 7-day larval fish growth test using the marine fish pink snapper Pagrus auratus.

FIGURE 4.5 Perth SWRO Plant discharge diffuser: rhodamine dye test.

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The results of the toxicity tests indicate that the plant concentrate dilution needed to be achieved at the edge of the mixing zone to protect the sensitive species listed above is 9.2:1 15.1:1, which is well within the actual design diffuser system mixing ratio of 45:1. In addition, to the toxicity testing, the Perth desalination project team has also completed two environmental surveys of the desalination plant discharge area in terms of macrofaunal community and sediment (benthic) habitat (Okel et al., 2007; Oceanica Consulting, 2009). The March 2006 baseline survey covered 77 sites to determine the spatial pattern of the benthic macrofaunal communities, while the repeat survey in 2008 covered 41 sites originally sampled in 2006 and five new reference sites. Some of the benthic community survey locations were in immediate vicinity of the discharge diffusers, while others were in various locations throughout the bay. The two surveys have shown no changes in benthic communities that can be attributed to the desalination plant discharge. Water quality sampling completed in the discharge area has shown no observable effect of ocean water quality, except that the salinity at the ocean bottom increased with up to 1 ppt, which salinity level is well within the naturally occurring salinity variation (Christie and Bonnelye, 2009). Fig. 4.6 depicts the conductivity of the Perth SWRO plant discharge over the period of January 2007 to September 2009. Taking into consideration that the ratio between salinity and conductivity is 0.78, the plant discharge salinity varied between 64,500 mg/L (88 µS/cm) and 56,200 mg/L (72 µS/cm), which is below the discharge permit limit of 90 µS/cm.

FIGURE 4.6 Perth desalination plant: discharge conductivity.

4.2 Surface water discharge case studies

Dissolved oxygen concentration of the discharge for the same period was between 7.6 and 11.0 mg/L, and was always higher than the minimum regulatory level of 5 mg/L. Similarly, concentrate pH was between 7.2 and 7.6, which was well within 10% of the ambient ocean water pH and the minimum pH limit of 7. Discharge turbidity for the same period (January 2007 September 2009) was always less than three Nephelometric Turbidity Unit (NTU) (see Fig. 4.7). It should be pointed out that the spent filter backwash water from the plant’s pretreatment system is treated on site in lamella settlers and the supernatant from this treatment process is discharged with the desalination plant concentrate. The solids generated as a result of the backwash treatment process are dewatered using belt filter press and disposed to a landfill. In summary, all studies and continuous environmental monitoring completed at the Perth seawater desalination plant to date, indicate that the desalination plant operations do not have significant environmental impact on the surrounding marine environment. Pictures taken of the discharge diffusers approximately 1 year after the plant operation (see Figs. 4.8 and 4.9) show that despite the high salinity of the concentrate (56,200 64,500 mg/L), the area around the discharge diffusers has abundant marine life rather than being a “dead zone” as speculated by the desalination project opponents. Fig. 4.9 is especially significant since it shows that seahorses (which are known to be sensitive to varying marine water quality conditions) inhabit the ZID of the Perth desalination plant.

FIGURE 4.7 Perth desalination plant: discharge turbidity.

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FIGURE 4.8 Perth desalination plant diffuser with swimming fish.

FIGURE 4.9 Seahorse inhabiting to Perth desalination plant diffuser.

In summary, all studies and continuous environmental monitoring completed at the Perth seawater desalination plant to date indicate that the desalination plant operations do not have any significant environmental impacts on the surrounding marine environment (Mickley & Voutchkov, 2016).

4.2.2 Australia: Gold Coast desalination plant 4.2.2.1 Gold Coast facility description This 132,000 m3/day desalination plant is located in South East Queensland, Australia in an area which is a renowned tourist destination (see Fig. 4.10). The desalination plant has been in operation since November of 2008, and employs open ocean intake; gravity dual granular media filtration system for seawater

4.2 Surface water discharge case studies

FIGURE 4.10 Gold Coast seawater desalination plant.

pretreatment; and two-pass/two-stage reverse osmosis desalination system. Desalinated water produced by the plant is posttreated by lime stabilization and sodium hypochlorite disinfection. The backwash generated by the pretreatment system is treated in lamella settlers, dewatered in belt filter presses and disposed as sludge to landfill. This plant is equipped with Double Work Exchanger Energy Recovery (DWEER) pressure exchanger system for energy recovery (Mickley & Voutchkov, 2016). A general process schematic of the Gold Coast desalination plant is shown on Fig. 4.11.

4.2.2.2 Gold Coast receiving water characterization According to a publication presented at the 2009 World Congress of the International Desalination Association (Cannesson, 2009), the aquatic habitat in the area of Gold Coast desalination plant discharge is sandy bottom inhabited primarily by widely scattered tube anemones, sipunculid worms, sea stars, and burrowing sponges.

4.2.2.3 Description of Gold Coast discharge streams The desalination plant discharges plant concentrate and treated spent filter backwash generated by the pretreatment system through its outfall. Spent cleaning solutions generated during RO train cleaning are equalized, neutralized and discharged to the sanitary sewer.

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CHAPTER 4 Case studies for surface water discharge

Reject to sea outfall

Open intake (w/passive screens) Shock chlorine Intake pumping station H2SO4 Fe2(SO4)3 Static mixer Flocculant Flocculation tank

Backwash water pumps

Backwash waste water treatment

Backwash waste water tank

Dual media filtration

Filtered water tank

Energy recovery booster pumps

RO booster pumps Antiscalant

2nd pass RO brine recirculation

NaHSO3 Energy recovery micronic filters

RO micronic filters

Recirculation pump

1st pass HP pumps

LP feed

HP feed 1st pass permeate storage for flushing

HP brine 1st pass RO

Energy recovery device

LP brine

1st pass rear product 1st pass front product

90

2nd pass HP pumps

CIP

Neutralisation tank

2nd pass RO 2nd pass RO permeate CO2

Remineralisation chamber Disinfection chamber

Lime clarifier

Neutralisation chemicals

Final chlorination & FSA injection

Clear water storage and pumping station

To treated water reservoir

FIGURE 4.11 Process schematic of the Gold Coast seawater desalination plant.

4.2.2.4 Description of Gold Coast plant outfall The Gold Coast plant is a standalone facility, which discharges concentrate of 67 ppt and volume of up to 360,000 m3 /day through a multiple diffuser system. The

4.2 Surface water discharge case studies

FIGURE 4.12 Discharge of Gold Coast seawater desalination plant.

regulatory mixing zone of this plant is 120 m 3 320 m. The Gold Coast plant discharge diffusers are located at the ocean bottom and discharge concentrate upwards into the water column to a height of approximately 10.5 m (see Fig. 4.12). A minimum concentrate dilution ratio of 40:1 was predicted at 60 m from a diffuser port, thus ensuring diffuser performance objectives would be met. This was taken to define the regulatory mixing zone for calm marine conditions (currents # 0.033 fps/0.01 m/s) as assumed by the model. Although, strong currents may enhance mixing and dilution, the size of the plume may increase, distorting in the direction of prevailing currents. Therefore the regulatory mixing zone was extended up to 200 m from any diffuser port under “high kinetic” marine conditions (currents $ 0.5 m/s).

4.2.2.5 Key Gold Coast discharge permit requirements Table 4.2 summarizes key discharge permit requirements of the Gold Coast desalination plant.

4.2.2.6 Gold Coast permit compliance observations The actual dilution ratio at the end of the mixing zone is typically 16:1 or more (as compared to regulatory target of 10:1 to meet WET requirements). For 18 months prior to the beginning of the desalination plant operations, the project team completed baseline monitoring to document the original existing environmental conditions, flora and fauna in the area of the discharge. Fig. 4.13 shows plant intake and outfall configurations as well as the location of the reference sites used for comparison. Once the plant began operations in November of 2008, the project team completed marine monitoring at four sites around the discharge diffuser area at the edge of the mixing zone, and at two reference locations 500 m away from the edge of the mixing zone in order to determine environmental impacts and verify salinity projections.

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Table 4.2 Gold Coast SWRO desalination plant: key discharge permit requirements (permit no. EPPR00881713). Permit discharge parameter Discharge volume Distance from diffusers to edge of mixing zone Salinity of plant discharge Turbidity of plant discharge Dissolved oxygen concentration of plant discharge pH of plant discharge, standard units Total chlorine

95th percentile

Max

Min

360,000 m3/day 60 m ,67 ppt if BG ,38; otherwise 67 3 BG/ 38 BG 1 5 NTU

# 75 ppt if BG ,38: otherwise 75 3 BG/ 38 BG 1 20 NTU 3.4 mg/L

8.5

9.5

0.12 mg/L

0.70 mg/L

BG, Background concentration in the ocean for sample collected at the plant intake.

FIGURE 4.13 Gold Coast plant location of discharge and monitoring sites.

5.5

4.2 Surface water discharge case studies

Based on this data the plant staff has completed Marine Contamination Risk Assessment (MCRA). The objective of the MCRA was to assess the ecological risk posed by each of the chemical additives used in the desalination treatment process that are likely to be retained in the effluent stream and discharged into the receiving environment. This MCRA identified the toxicological risks posed by all known compounds in the desalination effluent from the GCDP that could be considered as contaminants to the receiving marine environment in the vicinity of the discharge location. The MCRA was based on a review of existing information and a limited number of assumptions regarding operational performance of the desalination plant. The data obtained from the toxicity tests, in conjunction with data obtained from the Perth Seawater Desalination Plant, demonstrated a lowest observed effect concentration (LOEC) of concentrate, which was higher than the expected maximum concentration of brine at the edge of the mixing zone at sea (60 m from any of the 14 diffuser nozzles). As a part of MCRA, the water quality and benthic in-fauna abundance and diversity results after the start of the Gold Coast plant operations were compared with the baseline monitoring results as well as with the results of the monitoring sites. The results of pre- and postplant commissioning clearly indicate that the desalination plant operations did not have measurable impact on the marine habitat in the area of the discharge: The aquatic fauna has practically remained the same in terms of both abundance and diversity. The Gold Coast plant has been in operation for over 6 years and monitoring to date has confirmed that the plant’s discharge is environmentally safe (Mickley & Voutchkov, 2016). The results from the concentrate discharge monitoring completed at the Gold Coast SWRO desalination plant between March 2009 and February 2010 (Vargas et al., 2011) for the control and impact sites are summarized in Table 4.3. As shown on this table, the 12-month median values for temperature, dissolved oxygen, salinity, and turbidity were within the plant discharge permit requirements.

4.2.3 Israel: Ashkelon desalination plant 4.2.3.1 Ashkelon facility description The Ashkelon desalination plant is the first large SWRO desalination plant in Israel and it has a freshwater production capacity of 322,000 m3/day. The plant is in operation since 2005 and provides approximately 15% of the domestic water supply of Israel (Sauvet-Goichon, 2007). In 2011 the desalination plant produced 330,000 m3 /day of desalinated water (Drami et al., 2011). The desalination plant consists of an offshore intake with four intake towers located approximately 1000 m from the shore at a depth of 15 20 m. The source water from the intake towers is conveyed to the plant intake pump station shore via 63 in (1600 mm) high-density polyethylene (HDPE) pipes. The five (4 1 1) intake pumps deliver the source water to 20 single-stage dual media (anthracite

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Table 4.3 Gold Coast discharge water quality for permit regulated compounds for the period of March 2009 February 2010. Median value

Discharge limit

Depth

Parameter

Control

Impact

Min

Max

0 8m

Salinity, psu Temperature,  C Dissolved oxygen, mg/L Turbidity, NTU pH Salinity, psu Temperature,  C Dissolved oxygen, mg/L Turbidity, NTU pH

36.6 21.2 8.0 0.9 8.1 36.9 20.4 8.0 0.9 8.1

36.3 21.2 8.1 1.0 8.0 36.8 21.0 8.1 0.9 8.0

35.1 19.9 6.8 None 8.2 35.0 19.6 6.8 None 8.1

37.1 24.0 9.1 3.2 8.4 37.2 22.7 9.1 4.1 8.3

12 20 m

and sand) gravity filters. Coagulant (ferric sulfate or ferric chloride) is added to the source seawater and this water is pH adjusted with sulfuric acid prior to filtration (see Fig. 4.14). The pretreated water is processed through cartridge filters and then desalinated via membrane separation in 4-stage SWRO system. The complex 4-stage design of this plant is driven by the very stringent requirements for chloride and boron content in the product water: 20 and 0.4 mg/L, respectively. The energy contained in the RO system concentrate is recovered using DWEER devices. The desalinated water produced by the SWRO system is posttreated using limestone filters. Plant feed seawater temperature varies between 15 C and 30 C and its salinity is in a range of 39,000 41,000 mg/L (average 40,679 mg/L) (Mickley & Voutchkov, 2016). Fig. 4.15 shows the plant layout and the locations of the desalination plant intake and outfall.

4.2.3.2 Ashkelon receiving water characterization The receiving water area is a near-shore rocky environment with high level of natural mixing from currents, wind and tidal movement. Approximately 1 km south of the discharge there is a marine reserve (“Yam Shikma”). The near-shore waters where the discharge is delivered are characteristic with exceptionally low nutrient concentrations, algal content, bacterial, and other fauna. The near-shore area of the discharge was already modified by anthropogenic activity at the time of plant construction and the plant is located in an industrial area. The receiving near-shore waters of the Ashkelon plant are high-energy, well flushed environments with sandy bottoms devoid of aquatic life, unique biological resources, and endangered marine habitats.

FIGURE 4.14 Process schematic of the Ashkelon SWRO desalination plant, Israel.

FIGURE 4.15 Ashkelon desalination plant intake, outfall, and site locations.

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4.2.3.3 Description of Ashkelon discharge streams The main discharge stream from the plant is the concentrate which is approximately 95% of the total discharge volume. The remaining 5% are untreated backwash water from the pretreatment system and equalized and neutralized spent membrane cleaning solutions. When the plant began operation, the spent filter backwash water from the plant was discharged directly to the ocean as generated. Because of the high content of ferric hydroxide in the water, originating from the pretreatment coagulant, ferric chloride, the discharge was discolored in red every time a filter was backwashed for a period of 10 20 minutes. To address this concern, the plant has installed a backwash equalization tank which retains the individual filter cell backwashes and slowly and continuously discharges the filter backwash with the concentrate, thereby addressing the issue associated with the visible discoloration of the discharge area.

4.2.3.4 Description of Ashkelon plant outfall The Ashkelon desalination plant has on onshore outfall, which is located within 25 m from the outfall of the nearby Rothenberg power generation plant operated by the Israeli Electricity Company (IEC). The desalination plant discharge volume averages between 416,000 and 493,000 m3/day at average plant freshwater production of 274,000 320,000 m3/day. The power plant discharges 11,506,848 m3/day, which dilutes the concentrate in a ratio of 35:1 42:1. Under a worst-case scenario with only two of the four power plant outfalls discharging, the dilution ratio is 10:1.

4.2.3.5 Key discharge permit requirements at Ashkelon Table 4.4 summarizes key desalination plant permit requirements. All of these requirements are applied to the discharge from the desalination plant prior to its mixing with the ambient seawater.

4.2.3.6 Ashkelon permit compliance observations The Ashkelon desalination permit requires monitoring of the water quality near the surface and near the bottom of the discharge area for a number of parameters including temperature, salinity, total suspended solids, turbidity, pH, DO, BOD, total organic carbon (TOC), nutrients, chlorophyll a, and heavy metals. In addition, bottom sediments are analyzed for heavy metals and suspended particular matter, granulometry, TOC, infouna, and epifouna. Monitoring is carried out quarterly. The monitored zone around the discharge is an elliptically shaped area with major axe parallel to the coastline and extend up to 1.5 km to the north and south of the plant outfall. The minor axes are extended to a few hundred meters west and east of the outfalls. In Ashkelon the special distribution of the seawater salinity and temperature are also measured over wider areas—approximately 13 km from the outfall. The monitoring program includes a control station located 2.5 km away from the outfall.

4.2 Surface water discharge case studies

Table 4.4 Ashkelon SWRO desalination plant: key discharge permit requirements (permit no. 513102384). Permit discharge parameter

Daily average

Maximum

Suspended solids concentration, mg/L Turbidity (15-min average)

15

20

15 NTU

30 NTU not more than 4% of the time; 100 NTU not more than 1% of the time 9.0 190 tons/year 40 tons/year 5 C

pH Total iron Total phosphorus Temperature increment above Ambient water Total nitrogen Total organic carbon Ag, As, Cd, Cu, Cr, Hg, Ni, Pb, Zn Dissolved oxygen (DO) concentration

2 mg/L

Minimum

6.5

11 tons/year 24 tons/year Within 10% from ambient water $ 80% of ambient

The hydrodynamic model developed for this project indicates that the salinity of the discharge would reach 10% of the ambient seawater salinity within 400 m from the outfall. In situ monitoring, however, indicates that the salinity is well within 3% of the ambient within 500 m from the point of discharge. In 2005 the desalination plant completed a concentrate dispersion monitoring study (Safrai and Zask, 2008). The study was completed when the plant operated at only half of its capacity and the one of the power plant units was not in operation. The comparison of the marine environment before (2003) and after the commissioning of the desalination plant (2005) indicate that the desalination plant discharge resulted in some discharge exceedances (Safrai and Zask, 2008), including elevated content of total nitrogen, some occurrences of oxygen levels lower than 80% of the ambient intake water during the autumn of 2005 and elevated TOC concentrations on several occasions when comparing autumn and spring of 2003 and 2005. It should be pointed out that these effects are cumulative impacts from three discharges in the same vicinity, the Ashkelon desalination plant, the IEC power plant, which is a once-through power generation facility, and a smaller 2000 m3 /day BWRO desalination plant. While the BWRO plant has relatively small discharge volume, its content of nitrogen, phosphorous, and silica are an order of magnitude higher than these of the Ashkelon desalination plant.

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A study completed in 2008 2009 (Drami et al., 2011) has also evaluated the content of nutrients, chlorophyll a, pico-phytoplankton, and iron concentrations in the discharge area. At the time of the study the plant discharged 320,600 m3 /day of concentrate and concentrate salinity was 75,300 mg/L. The nearby power plant discharged an average of 7,392,000 m3 /day during the same period. The desalination plant discharge contained concentrate, untreated spent filter backwash, and spent cleaning solutions from periodic RO cleaning. The amount of iron discharged to the ocean in 2007 was 535 tons/year, while in the years 2008 and 2009 this amount has been reduced to 270 and 175 tons/year., respectively. The content of total iron in the concentrate varied between 0.2 and 1.1 mg/L, which is in compliance with the discharge limit for this plant of 2 mg/L. Since 2010, the backwash water is equalized and continuously mixed with the plant concentrate prior to discharge, which allows to keep the discharge level of iron in the source water always below 2 mg/L. The discharge also typically contains polyphosphonate antiscalant (34 tons/ year as TP); HCl (15 tons/year); NaOH (20 tons/year); and sodium bisulfite (NaHSO3; 70 tons/year). Fig. 4.16 indicates the sampling locations used for the 2008 2009 discharge study. On this figure, the Ashkelon SWRO plant is denoted as “A,” and the nearby power plant as “B.” The location of the desalination plant discharge outfall is indicated as “2,” while the three cooling water outfalls of the power plant are shown as “1.” Line “3” represents the coal unloading key of the

FIGURE 4.16 Sampling locations for the 2008 2009 Ashkelon discharge study.

4.2 Surface water discharge case studies

power plant; line “4” depicts the location of the discharge sampling area; while “W” is the location of the sampling station for background (ambient) seawater quality. The location of the seawater intake is depicted as “SWRO” while that for the power plant cooling water intake is shown as “CW.” Samples were collected before and during filter backwash discharges to capture peak and off-peak levels of iron in the discharge. Desalination plant and power plant discharges were sampled separately to discern the impact on the cooling water discharge on desalination plant plume dispersion. The 2008 2009 discharge study indicates that the power plant and desalination plant discharge blended within 50 m from the shore and blended concentrate/ power plant discharge was positively buoyant, which allowed to effectively disperse the concentrate to near background levels within 500 m. The maximum salinity measured in the sampling locations was 41.5 ppt as compared to a background of 38.42 ppt (8% increment). At this measurement the maximal temperature of the surface layer of the blended plume water (30.4 C) compared to background seawater temperature of 22.3 C; such temperatures were reached in the spring of 2008. The actual salinity measurements were lower than these projected using hydrodynamic modeling of the discharge. Nutrient concentrations (TN, TP, nitrates) were higher at the outfall but quickly diminished within 250 m of the discharge. The algal content (measured as chlorophyll a) was lower at the outfall and discharge sampling locations as compared to background levels, which indicates that the discharge of iron did not trigger accelerated algal growth and algal blooms as stipulated in some environmental groups concerned by the impact of desalination plant discharge on the environment. The decreased content of algae in the water was positively correlated with the salinity and temperature of the discharge: The higher the salinity and temperature the more significant suppression of algal growth was observed in the area of the discharge. Elevated turbidity and particular iron content in the discharge were found to also have suppression effect on the growth of algae in the area of the discharge. Similar effects of plant discharge were observed on bacterial production: Bacterial growth was reduced with increase in temperature, salinity, iron content, and turbidity (Mickley & Voutchkov, 2016).

4.2.4 Israel: Sorek desalination plant 4.2.4.1 Sorek facility description The Sorek desalination plant has freshwater production capacity of 410,000 m3/day, and is one of the largest membrane desalination plants in the world (see Fig. 4.17). A process schematic of the Sorek desalination plant is shown in Fig. 4.18. The plant has been in operation since the end of 2013 and has incorporated some of the latest technological developments in the field of desalination technology and equipment such as 16-inch SWRO elements, vertically installed pressure vessels, and an advanced energy recovery system.

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FIGURE 4.17 General layout of the Sorek SWRO plant, Israel.

FIGURE 4.18 Process schematic of the Sorek SWRO plant, Israel.

4.2 Surface water discharge case studies

The Sorek desalination plant is located 2.4 km away from the Mediterranean shore and approximately 15 km from Israel’s capital, Tel Aviv. The plant has an open intake with two intake towers, which are located approximately 1150 m offshore at a depth of approximately 6 m from the ocean surface and 4 m from the bottom. The source water is delivered to the desalination plant site via two feed water pipelines. The plant is configured to operate as two independent 205,000 m3/day facilities with separate pretreatment, RO and posttreatment systems. The plant pretreatment system consists of single-stage gravity filters with anthracite and sand media. The source seawater is conditioned with coagulant (ferric chloride) prior to filtration. After granular media filtration the pretreated water passes through cartridge filters and is fed to SWRO system designed with three-pressure center configuration, similar to Ashkelon, where all RO trains are fed by a common set of high pressure pumps and energy from the concentrate is recovered in an energy recovery system (ERS) common for all trains as compared to conventional designs where each RO train is serviced by a separate set of high pressure pump and ERS. The RO system employs 16-inch elements located in vertical pressure vessels. While such design makes the plant RO system fairly tall and complex it significantly reduces its footprint, which is an important feature for the desalination plant site because of the severe site constraints. The posttreatment of the desalinated water is identical for that in Ashkelon and employs limestone filters (Mickley & Voutchkov, 2016).

4.2.4.2 Sorek receiving water characterization The discharge area selected for the desalination plant outfall is an under water “desert” with sandy bottom and is void of flora and fauna with low salinity tolerance, endangered or sensitive marine species. The depth of the discharge area is approximately 20 m from the surface.

4.2.4.3 Description of Sorek discharge streams The average discharge volume of the plant concentrate is 490,000 m3/year and its salinity is 74,150 mg/L. The plant pretreatment backwash volume averages 60,600 m3/day. Compared to Ashkelon, the spent filter backwash from the pretreatment system is treated in lamella settlers prior to blending with the plant concentrate and discharge to the sea. The sludge generated in the lamella settlers is dewatered in centrifuges and disposed to a landfill.

4.2.4.4 Description of Sorek plant outfall The desalination plant outfall is a structure located 1850 m offshore at discharge depth of 20 m. The outfall structure has diffusers at the end of the discharge pipes. Based on discharge dispersion modeling, under worst-case natural mixing conditions in the sea, the discharge salinity is projected to be within 5% of ambient at a distance of 115 m from the diffusers and within 1% of ambient salinity in

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845 m away from the discharge (Kit et al., 2011). The discharge will be within 10% of the ambient salinity at a distance of 20 m from the diffusers (Sladkevich et al., 2011).

4.2.4.5 Key Sorek discharge permit requirements Table 4.5 presents the discharge requirements for the Sorek SWRO plant discharge.

4.2.4.6 Sorek permit compliance observations Since the plant began operation in late 2013, it has been in compliance with its discharge requirements. Follow up discharge area monitoring since then shows no measurable impacts of the desalination plant outfall on the aquatic habitat in the vicinity of the discharge. A recent study (Frank et al., 2019) completed at the Sorek, Ashkelon, and Palmahim desalination plants indicates that bacterial abundance and activity that includes bacterial growth efficiency were 1.3 2.6-fold higher at the outfall area than the reference stations outside of the zone of initial dilution of the discharge. Concomitant analysis pointed out that the bacterial community structure at the brine discharge area was also different than the reference stations, yet varied between each desalination facility. The study results demonstrate that the impact of brine effluent from desalination facilities on benthic bacteria is site-specific and localized (,1.4 km2) around the discharge point. Table 4.5 Sorek SWRO desalination plant: key discharge permit requirements (permit no. 8633520). Permit discharge parameter Suspended solids concentration, mg/L Turbidity (15-min average) pH Total iron Total phosphorus Total nitrogen Total organic carbon Ag, As, Cd, Cu, Cr, Hg, Ni, Pb, Zn Dissolved oxygen (DO) concentration

Daily average

Maximum

5

20

10 NTU

15 NTU not more than 7% of the time; 50 NTU not more than 3% of the time 9/0 56 tons/year 60 tons/year 16 tons/year 31 tons/year

0.5 mg/L

Minimum

6.5

Within 10% from ambient water $ 80% of ambient

4.2 Surface water discharge case studies

Namely, that the effects on benthic bacteria are prominent at the brine mixing zone and change according to the discharge method used to disperse the brine as well as local stressors (e.g., eutrophication and elevated water temperature).

4.2.5 Spain: Torrevieja (Alicante) 4.2.5.1 Torrevieja facility description The 240,000 m3/day Torrevieja desalination plant located in the City of Alicante (see Fig. 4.19) is the largest SWRO plant in Europe and one of the largest in the world. While this plant was built in 2006, it began operation in the fall of 2013 due to delays associated with the regional government of Valencia to grant the plant environmental discharge permit. As reported (WDR, 2011) the main reasons for delay are political in nature and relate to the change in Spain’s central government and its policies. This plant has an open intake located approximately 2.9 km from the site and is constructed as a box attached to the west dike of the Alicante harbor. This allowed avoiding intake location in areas which have Poseidonia and Cymodocea seagrass fields. The source seawater is conveyed to 32 dissolved air flotation (DAF) clarifiers from where it is processed through 56 pressure dual media filters, 23 cartridge filters, and SWRO system of 16 RO trains each equipped with a

FIGURE 4.19 Desalination plant Torrevieja, Alicante, Spain.

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separate ERS. The RO permeate is posttreated in lime/carbon dioxide conditioning system. Approximately 50% of the finished water produced by the desalination plant is dedicated to drinking water supply and the rest for agricultural irrigation (Mickley & Voutchkov, 2016).

4.2.5.2 Torrevieja receiving water characterization The plant discharge is completed through diffuser system which is located in an area of low biological significance (sandy bottom with no vegetation and scarce benthic marine life). The discharge is over 0.8 km away from seagrass fields, coral reefs, kelp forests and other habitats of marine life. Ambient salinity averages 37.5 ppt.

4.2.5.3 Description of Torrevieja discharge streams The desalination plant concentrate is blended with the treated filter backwash water, and neutralized spent RO membrane cleaning solution, and is discharged continuously through two ocean outfall pipes which are equipped with diffusers and located 1.6 km offshore. The filter backwash water is treated in lamella settlers and dewatered by centrifuges. The spent RO membrane cleaning solution is neutralized in a separate retention tank to pH of 7 9 and then blended with the rest of the plant discharge streams.

4.2.5.4 Description of Torrevieja plant outfall The desalination plant outfall consists of two pipes with diameters of 2400 and 2000 mm, respectively. Concentrate is discharged at a depth of 10 m. The section of the outfall pipes which has diffusers is 315 m long. Each outfall pipe has a total of 64 diffusers with diameter of 150 mm which are installed approximately 1.5 m above the ocean floor. The distance between diffusers is 5 m. The diffusers are oriented in 50 degrees upwards and are designed to operate at exit velocity of 4.47 m/s and exit flow of 0.079 m3/s. The diffusers are designed so they can be capped in order to maintain high concentrate stream ejection velocity (see Fig. 4.20) when the plant is operated at low production capacity.

4.2.5.5 Key Torrevieja discharge permit requirements Table 4.6 summarizes key desalination plant permit requirements. All of these requirements are applied to the discharge from the desalination plant prior to its mixing with the ambient seawater. The plant permit has maximum flow limits for the three key desalination plant discharge streams:

• Concentrate: daily (293,000 m3/day); instantaneous (3.39 m3/s); annual • •

(97,000 m3/year). Spent Filter Backwash: daily (29,000 m3/day); annual (9700 m3/year). Spent RO Membrane Cleaning Solution daily (736 m3/h); annual (4960 m3/ year).

4.2 Surface water discharge case studies

FIGURE 4.20 Torrevieja capped ocean outfall pipe diffusers.

Table 4.6 Torrevieja SWRO desalination plant: key discharge permit requirements (permit no. 0300008774). Permit discharge parameter

Maximum

Total dissolved solids, ppt Total suspended solids concentration, mg/L pH Total iron, mg/L Total phosphorus, mg/L Total nitrogen, mg/L Total organic carbon, mg/L Detergents (sodium lauryl sulfate) mg/L Dissolved oxygen (DO) concentration mg/L Temperature increment above ambient,  C

68.2 3.5 9.0 0.5 0.2 1.5 3.0 0.5 10 3.0

Minimum

7.0

.80% of ambient

4.2.5.6 Torrevieja permit compliance observations Since its commissioning in mid-September 2013, the plant has been in compliance with its discharge permit. At present the plant is operating at a portion 20% 50% of its capacity.

4.2.6 Spain: Alicante 1, Javea, and San Pedro del Pinatar plants 4.2.6.1 Description of plants An independent overview of the discharges of three desalination plants in Spain 22,000 m3/day, Javea SWRO Plant; 68,000 m3/day Alicante 1 SWRO Plant; and

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FIGURE 4.21 Location of Ja´vea, Alicante 1, and San Pedro del Pinatar desalination plants in Spain.

68,000 m3/day San Pedro del Pinatar completed by the University of Alicante, Spain (Torquemada, 2009) provides insights related to environmental impacts of combined desalination plant discharges. The three plants are located within 80 km from each other (see Fig. 4.21) and the salinity of their discharges is 68,000 70,000 mg/L. The Alicante 1 and San Pedro de Pinatar have well intakes while the Javea plant has open ocean intake. All plants have very similar treatment system—source water chemical conditioning with iron coagulant, pressure filtration with granular media (anthracite & sand), and two-pass/two-stage SWRO membrane desalination. Permeate of all three plants is treated by lime/carbon dioxide conditioning (Mickley & Voutchkov, 2016).

4.2.6.2 Receiving water characterization The Alicante 1 plant discharges its concentrate in turbulent and very well tidally mixed area via one onshore outfall. This feature of the desalination plant discharge allows the Alicante plant to operate without measurable environmental impacts even at relatively low mixing ratio of 1.5:1 5:1 between concentrate and ambient seawater at the edge of the mixing zone.

4.2 Surface water discharge case studies

4.2.6.3 Description of plants’ discharge streams All desalination plants discharge a combination of concentrate, untreated filter backwash water and spent membrane cleaning solution which is pH adjusted.

4.2.6.4 Description of plants’ outfalls The discharge of the Alicante SWRO plant, is located directly on the shoreline to take advantage of the turbulent tidal mixing that naturally occurs in the discharge area. The discharge of the San Pedro del Pinatar Plant is through a diffuser located 5 km away from the shore at 38 m depth. The discharge of the Javea SWRO plant is in an open canal which then carries the concentrate into the ocean. The concentrate from this plant is diluted in the channel from 69,000 mg/L down to 44,000 mg/L in a 4:1 mixing ratio. This salinity level was found not to have negative impact on the marine habitat in the discharge area.

4.2.6.5 Key discharge permit requirements The three desalination plants have discharge permit requirements similar to these of the Torrevieja SWRO Plant.

4.2.6.6 Permit compliance observations All three desalination plants have been in operation for many years. The water quality and environmental monitoring of the three discharges indicates that the size and time for dispersion of the salinity plume varied seasonally. These variations however, did not affect the benthic organisms inhabiting the seafloor. The desalination discharge of the Javea plant has high oxygen levels that diminish the naturally occurring apoxia in the area of the discharge. The independent overview emphasizes the fact that well designed desalination discharge can result in minimal environmental impacts, and in some cases can be beneficial to the environment due to its high oxygen content.

4.2.7 Spain: Maspalomas II desalination plant, Canary Islands 4.2.7.1 Maspalomas facility description This desalination plant located in Gran Canarias came into production in 1988 and has freshwater production capacity of 3000 m3/day. The plant is situated half a kilometer from the shoreline, between two popular tourist beaches (Fig. 4.22). The treatment plant has pressure driven pre-filtration system with anthracite/sand media, cartridge filters, and two-pass/two-stage SWRO system with ERI pressure exchangers.

4.2.7.2 Maspalomas receiving water characterization The Maspalomas discharge conditions are challenging: (1) very high salinity of the concentrate (90,000 mg/L); and (2) seagrass habitat for fish and other marine

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FIGURE 4.22 Location of Maspalomas desalination plant.

organisms. Due to the naturally occurring near-shore mixing, the salinity of the discharge is dissipated down to 38,000 mg/L (38 psu) within 20 m from the discharge point as shown on Fig. 4.23. The salinity on this figure is presented in psu (practical salinity units), which have the same value as ppt (parts per thousand) of salinity concentration (Mickley & Voutchkov, 2016).

4.2.7.3 Description of Maspalomas plant outfall The plant has two concentrate outfalls which extend 300 m away from the shore (Talavera and Ruiz, 2001). The outlet of the discharge outfalls does not have diffusers and the mixing between the concentrate and ambient seawater is mainly driven by the velocity of the discharge and the fact that the discharge is located in an area with naturally occurring underwater currents of high intensity. The depth of the discharge is 7.5 8.0 m.

4.2.7.4 Key discharge permit requirements at Maspalomas The three desalination plants have discharge permit requirements similar to these of the Torrevieja SWRO Plant.

4.2 Surface water discharge case studies

FIGURE 4.23 Salinity dissipation of discharge of Maspalomas desalination plant.

4.2.7.5 Permit compliance observations at Maspalomas The mixing zone of the Maspalomas II desalination plant is a sandy bed with practically no flora. However, this zone is surrounded by seagrass beds, which based on environmental study of the discharge area, are not significantly affected by the desalination plant discharge.

4.2.8 United States: Carlsbad desalination plant case study 4.2.8.1 Carlsbad facility description The Carlsbad Desalination Project (CDP) is located on a 2.5 hectare (6.8 acre) land parcel within the site of the Encina Power Station (EPS) on the south coast of California (see Fig. 4.24). The EPS was decommissioned in December 2018, but prior to this date, the CDP shared intake and discharge infrastructure with the power station. Under its original design, the CDP taps into this discharge tunnel for both desalination plant feed water and for discharging high-salinity concentrate downstream of the intake area (Fig. 4.25). This design allows for collecting 378,000 m3/day (100 MGD) of cooling water from the power plant discharge, producing 189,000 m3/day of freshwater and returning 189,500 m3/day of concentrate for blending with the remaining cooling water flow of the power plant shown as 1,893,000 m3/day (500 MGD) on Fig. 4.25. As a result, the cooling water dilutes the concentrate from 67 ppt down to 36.2 ppt thereby complying with the desalination plant discharge limit of 40 ppt. After the power plant was decommissioned in 2018, the desalination plant operates as a standalone facility (Fig. 4.26). Source water is collected from the Agua Hedionda lagoon and concentrate is discharged through the existing power plant onshore outfall.

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FIGURE 4.24 Areal view of the Carlsbad desalination plant.

FIGURE 4.25 Carlsbad desalination plant as originally designed to operate with the power plant. 1 MGD 5 3785 m3/day.

4.2 Surface water discharge case studies

FIGURE 4.26 Carlsbad desalination plant in standalone operation at present. Note: 1 MGD 5 3785 m3/ day.

An average daily flow of 189,000 m3/day of fresh potable water is produced by the CDP. Treatment processes at CDP consist of conventional granular media pretreatment, reverse osmosis desalination, and disinfection and product water stabilization (Fig. 4.27). The plant has 14 RO trains (racks) operating in parallel at the facility with a combined installed maximum capacity of 204,000 m3/day. Under normal operating conditions, one RO unit at a time is designed to be offline for membrane cleaning or maintenance. The fresh potable water produced by CDP is delivered to San Diego County Water Authority’s Twin Oaks WTP for distribution. The production of potable water results in the generation of an average of 205,000 m3/day (maximum flow estimated to be 228,000 m3/day) of combined filter backwash water and concentrated saline wastewater discharged back into the Pacific Ocean. The granular media filtration step uses ferric chloride or ferric sulfate to enhance removal of particulate matter. These added chemicals are backwashed, collected in a sedimentation basin (clarifier), removed as waste sludge, and disposed of at a landfill. The RO process generates membrane backwash cleaning solutions, collected in a separate tank, neutralized for pH value, and discharged to the sanitary sewer system. The backwash supernatant from the granular media

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FIGURE 4.27 Process schematic of the Carlsbad desalination plant.

filtration pretreatment is directed to the discharge channel (or can be partially recirculated to the plant inlet). While this is the first large SWRO desalination project permitted in California, the permitting process for this project has established a precedent for permitting of all SWRO desalination projects in California. The permitting process included a detailed source water quality and concentrate characterization, followed by salinity tolerance study for the marine species specific to the discharge area and hydrodynamic concentrate dispersal study to determine the level of mixing of concentrate and ambient seawater which has to be achieved in the zone of initial dilution of the concentrate. The results of the hydrodynamic concentrate dispersal study, the salinity tolerance study and the WET testing of the discharge-ambient water mix at the mixing ratio determined by hydrodynamic modeling were used by the regulatory agencies to determine project-specific mixing ratio and maximum TDS discharge requirements for the project which were incorporated in the plant NPDES discharge permit. The same permitting activities were implemented for the Huntington Beach SWRO Desalination Project, the West Basin Desalination Project in California, and the Tampa Bay SWRO project in Florida. Practically identical permitting processes were applied for all large desalination projects in Australia and Europe as well.

4.2.8.2 Carlsbad receiving water characterization The desalination plant concentrate is discharged into a small lagoon from where it is directed to an open channel extending approximately 215 m offshore (see Figs. 4.28 and 4.29).

4.2 Surface water discharge case studies

FIGURE 4.28 Carlsbad desalination plant: intake and discharge locations.

FIGURE 4.29 Carlsbad desalination plant: outfall canal.

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The discharge area of the Carlsbad SWRO desalination project is “underwater desert” with very limited presence of marine organisms. As indicated in the comprehensive marine tolerance study completed for the permitting of this project (Voutchkov, 2012), all marine species inhabiting the discharge area (i.e., sea urchins, sea stars, abalone, red rock crab, sand dollars, etc.) are tolerant to the salinity of the discharge.

4.2.8.3 Carlsbad description of discharge streams The discharge consists of concentrate and backwash (clarifier supernatant) from the granular media filtration step. Over 94% of the total plant discharge is concentrate and 4% 6% is spent pretreatment backwash water. Membrane backwash cleaning solutions are sent to the sanitary sewer. Waste sludge from the granular media filtration step and spent filter cartridges go to landfill. Plant concentrate has salinity of 60 68 ppt, diluted down to 40 ppt or less, using raw intake seawater. Plant spent filter backwash has salinity identical to that of the source seawater. The provision to use raw intake seawater for dilution during standalone operations of the desalination plant was found to be less costly and environmentally intrusive than the modification of the existing outfall structure or construction of new outfall. The use of intake source water for dilution was allowed under the existing desalination plant NPDES permit.

4.2.8.4 Carlsbad description of plant outfall The plant discharges an average of 204,000 m3/day of RO concentrate and filter backwash. Water collected from the lagoon is conveyed to the desalination plant to produce freshwater, and the concentrate from the desalination plant is returned into the discharge canal. The desalination plant concentrate, containing approximately twice the salinity of the source seawater (68 vs 33.5 ppt), is blended and conveyed to the ocean for disposal. The salinity range of the mixed discharge from CDP will be between 35 and 40 ppt. The average salinity in the middle of the salinity mixing zone was projected to be 36.2 ppt. Therefore the biometrics test was completed for this salinity, while the test range for the salinity tolerance test was 37 40 ppt in 1 ppt increments. Both tests were executed by marine biologist very familiar with the local flora and fauna in the area of the future desalination plant discharge (Le Page, 2004).

4.2.8.5 Carlsbad key discharge permits and permit requirements The key discharge permit for this facility is the plant NPDES discharge permit which pertains to the disposal of concentrate and other waste streams from the desalination plant. The permitting process for this project continued for over 5 years and involved the development and certification of project environmental impact report (EIR) as well as the submittal of NPDES permit application and permit review through seven sets of requests for additional information mainly by the California Coastal Commission (CCC).

4.2 Surface water discharge case studies

In order to support the EIR review and permitting process, the project proponent, Poseidon Resources completed the following activities: 1. Collected monthly samples of intake source seawater for a period of 2 years (2002 2004) in order to analyze the seawater in terms of all parameters regulated by the Clean Water Act and included in the NPDES permitting process as well as of the Safe Drinking Water Act. 2. Completed sanitary survey in 2004 2005 in order to identify and quantify all potential sources of pollution of the intake source water quality within a 3.2 km radius from the point of intake. This sanitary survey involved source water quality sampling and inventory of potential point and non-point sources of pollution of the source water located within the radius. 3. Installed and operated 27,000 gpd pilot SWRO plant for over 5 years to generate concentrate and test the proposed key desalination technologies including pretreatment, SWRO system and posttreatment facilities. The plant was operated during series of extremely high intensity (50-year repeatability) algal blooms, which showed that even in extreme algal bloom conditions the plant discharge was safe for the aquatic life in the vicinity of the discharge. 4. Completed detailed chemical characterization and analysis of the concentrate generated by the pilot plant as well as of all other waste streams including the spent filter backwash water and spent clean-in-place (CIP) chemicals generated from the cleaning of the SWRO membranes. This information was needed to prepare the NPDES permit application. 5. Completed acute and chronic WET testing of several blends of concentrate and discharge water from the power plant in order to determine the impact of the desalination plant discharge on standard test marine organisms defined and approved by the San Diego Regional Water Quality Control Board. 6. Completed hydrodynamic modeling of the desalination discharge dispersion for several operational conditions ranging with varying power plant discharge blending flows and ambient seawater factors influencing the mixing of concentrate and power plant discharge with ambient seawater including wave action, tides, wind, currents and seasonal salinity variations. 7. Based on the results from the hydrodynamic modeling and the WET testing, the project proponent completed a salinity tolerance study under the supervision of the SCRIPPS Institute of Oceanography and under scope and conditions approved by the San Diego Regional Water Quality Control Board. The salinity tolerance study was completed on species inhabiting the discharge area of the desalination plant and representing aquatic fauna sensitive to elevated salinity impacts. The results of the study were used by the RWQCB to establish the site-specific average and maximum salinity limits for this project—which was conservatively determined at levels of 40 and 42 ppt, respectively.

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8. Completed detailed 12-month impingement and entrainment study to assess the impact on desalination plant operation on the loss of marine life. The study was extended to capture conditions of collection of source water during the power plant operation and during times when the power plant was down in order to determine the impingement and entrainment impacts of the desalination plant. The studies listed earlier were used for the preparation of the project EIR and NPDES application. The NPDES application process was commenced after the EIR was certified. The NPDES permit was issued after 6-month review process. However, the overall project implementation process was delayed by the series of requests for additional information by the CCC, which mainly pertained to such issues as the mitigation of the loss of marine life due to impingement and entrainment, cost and energy use for production of the desalinated water, carbon footprint of desalination plant operations and feasibility studies for use of alternative intakes to minimize impingement and entrainment impacts. The CCC did not challenge the NPDES discharge permit conditions and was supportive of all the work completed to determine the salinity tolerance of the local flora and fauna (Mickley & Voutchkov, 2016). The NPDES permit for CDP was issued by the San Diego Regional Water Quality Control Board. The NPDES permit, CA0109223, dated 2006, had an initial expiration date of 2011. The permit was amended in May 2009 to accommodate standalone operations of the desalination plant which would occur when and if the EPS discontinues operation; and again amended in May 2010 to address the right of the project sponsor, Poseidon Resources, who is the owner of the project at present, to transfer ownership of the plant and permit obligations in the future to San Diego County Water Authority. At present, the permit is valid until year 2023 when it needs to be modified to completely reflect standalone plant operations and installation of a new open ocean intake in Agua Hedionda lagoon. The numerical limitations and monitoring requirements from the NPDES permit are summarized in Table 4.7. The numerical limits are for Discharge Point 001, which is the desalination plant discharge into the Encina Power Station discharge channel. In addition, to the numerical limits, there are narrative discharge prohibitions, discharge specifications, and receiving water limitations (thermal, bacterial characteristics, chemical characteristics, physical characteristics, and biological characteristics). Constituents that do not have reasonable potential or had inconclusive reasonable potential to cause environmental impacts are referred to as performance goal constituents and assigned the performance goals listed. Performance goal constituents are required to be monitored, but the results will be used for informational purposes only, not for compliance determination.

4.2.8.6 Permit support study—application of the STE test for the Carlsbad desalination project The salinity tolerance evaluation (STE) procedure was applied to assess the discharge impact of the 190,000 m3/day Carlsbad seawater desalination project.

4.2 Surface water discharge case studies

Table 4.7 Numerical effluent limitations and performance goals for CDP. Effluent limitations: desalination discharge Max

Ave

Ave

Daily

Monthly

Weekly

Parameter/constituent

Units

Maximum flow: median filtration TSS pH Oil and grease Settleable solids Turbidity Chronic toxicity

MLD

245

mg/L Standard units mg/L ml/L NTU TU

60 25 1 75

Instant Min

Max

6

9 75 3 225

40 1.5 100

16.5

Effluent limitation: combined discharge Parameter

Units

Ave daily

Ave hourly

Salinity

ppt

40

44

Parameter/constituent

Units

Max daily

10 metals Cyanide Total residual chlorine Ammonia, N Acute Toxicity Phenolic compounds (nonchlorinated) Phenolic compounds (chlorinated) Endosulfan Endrin HCH Radioactivityb 62 others (few metals, mostly organics)

µg/L µg/L µg/L µg/L TU µg/L

Instant max

Six-month median

Xa 66 132 39,600 0.765 1,980

Xa 165 990 99,000

Xa 16.5 33 9,900

4,950

495

µg/L

66

165

16.5

µg/L µg/L µg/L

0.297 0.066 0.132

0.446 0.099 0.198

0.148 0.033 0.066

µg/L

Monthly average

Xa

a

The X entries all have different numerical limits—in total, too numerous to list. Not to exceed limits specified in Title 17, Division 1, Chapter 5, Subchapter 4, Group 3, Article 3, Section 30253 of the California Code of Regulations. b

A list of the 20 marine species selected for the biometrics test for the Carlsbad Project is presented in Table 4.8. The salinity tolerance test was completed using three local species which are known to have highest susceptibility to stress caused by elevated salinity (Le Page, 2004): (1) the purple sea urchin (Stronglyocentroutus purpuratus), Fig. 4.30; (2) the sand dollar (Dendraster excentricus), Fig. 4.31; and (3) the Red Abalone (Haliotis rufescens), Fig. 4.32.

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CHAPTER 4 Case studies for surface water discharge Table 4.8 Marine species used for the Carlsbad biometrics test.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Scientific name

Common name

Number of individuals per species

Paralichthys californicus Paralabrax clathratus Paralabrax nebulifer Hypsoblennius gentilis Strongylocentrotus franciscanus Strongylocentrotus purpuratus Pisaster ochraceus Asterina miniata Parastichopus californicus Cancer productus Crassadoma gigantea Haliotis fulgens Megathura crenulata

California halibut Kelp bass Barred sand bass Bay blenny Red sea urchin

5 juveniles 3 juveniles 3 juveniles 5 4

Purple sea urchin

14

Ochre sea star Bat star Sea cucumber Red rock crab Giant rock scallop Green abalone Giant keyhole limpet Wavy turban snail Chestnut cowrie Sand castle worm

3 3 2 2 3 3 3

Aggregating anemone Brown gorgonian Red abalone Sand dollar

4

17

Lithopoma undosum Cypraea spadicea Phragmatopoma californica Anthropleura elegantissima

18 19 20

Muricea fruticosa Haliotis rufescens Dendraster excentricus

FIGURE 4.30 Purple sea urchin.

3 3 1 colony

1 colony 5 5

4.2 Surface water discharge case studies

FIGURE 4.31 Sand dollars.

FIGURE 4.32 Red abalone.

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The biometrics test continued for a period of 5.5 months. The results of this test are summarized in Table 4.9, and indicate that all organisms have remained healthy throughout the test period. No mortality was encountered, and all species showed normal activity and feeding behavior. The appearance of the individuals remained good with no changes in coloration or development of marks or lesions. The duration of the salinity tolerance test for the Carlsbad project was 19 days. The results of this test are given in Table 4.10 and show that two of the three tested marine organisms—sand dollars and red abalones—had 100% survival in all test tanks and in the control tank. One individual in the purple sea urchin group died in each of the test tanks and one died in the control tank. Therefore the adjusted survival rate for the purple sea urchins was also 100%. These test results confirm that the marine organisms in the discharge zone would have adequate salinity tolerance to the desalination plant discharge in the entire range of operations of the desalination plant (i.e., up to 40 ppt). All individuals of the three tested species behaved normally during the test, exhibiting active feeding and moving habits. The biometrics and salinity tolerance tests were completed in 420-liter marine aquariums (Fig. 4.33). In summary, the STE method applied to the Carlsbad seawater desalination project confirms that the elevated salinity in the vicinity of the plant discharge would not have a measurable impact on the marine organisms in this location and these organisms can tolerate the maximum salinity of 40 ppt that could occur in the discharge area under extreme conditions. Additional acute and chronic toxicity studies completed subsequently for this project using the United States Environmental Protection Agency’s standard WET test (Weber et al., 1998) have confirmed the validity of the STE method. WET testing using abalone (Haliotis ruefescens) shows that the chronic toxicity threshold for these species occurs for TDS concentration of over 40 ppt. An acute toxicity test completed using another standard WET species, the topsmelt (Atherinops affinis), indicates that the salinity in the discharge can reach over 50 ppt on a short-term basis (1 day or more) without impacting this otherwise salinitysensitive species. The results of the STE completed for the CDP were well accepted by the state and local regulatory agencies (San Diego Water Quality Control Boards responsible for permitting of the desalination project discharge for this project). These results were also used for the environmental review and permitting of the 190,000 m3/day Huntington Beach desalination project, which was planned in parallel with the Carlsbad project. In August 2006 both projects received regulatory permits to discharge their concentrate to ocean.

4.2.8.7 Permit compliance observations A 2018 study (Petersen et al., 2019) has completed a thorough evaluation of the impact of the desalination plant operations on the aquatic environment in the vicinity of the discharge. The study team has collected in situ measurements of water chemistry and biological indicators in coastal waters (up to B2 km from

4.2 Surface water discharge case studies

Table 4.9 Overall condition of biometrics test species.

Scientific name Paralichthys californicus Paralabrax clathratus Paralabrax nebulifer Hypsoblennius gentilis Strongylocentrotus franciscanus Strongylocentrotus purpuratus Pisaster ochraceus Asterina miniata Parastichopus californicus Haliotis fulgens Megathura crenulata Lithopoma undosum Cypraea spadicea Anthropleura elegantissima Haliotis rufescens Dendraster excentricus

Common name California halibut Kelp bass Barred sand bass Bay blenny Red sea urchin Purple sea urchin Ochre sea star Bat star Sea cucumber Green abalone Giant keyhole limpet Wavy turban snail Chestnut cowrie Aggregating anemone Red abalone Sand dollar

Average weight change (grams)

Control group weight change

Sig.

Appearance and feeding

91.3

96.9

n/s

Strong

114.3

104.8

n/s

Strong

106.8

113.5

n/s

Strong

120.0

107.1

n/s

Strong

2.8

2.4

n/s

Strong

7.9

7.2

n/s

Strong

3.8

4.6

n/s

Strong

2.8 -2.2

3.1 2.3

n/s n/s

Strong Strong

9.6

7.7

n/s

Strong

5.1

4.7

n/s

Strong

3.9

2.4

n/s

Strong

0.6

1.0

n/s

Strong

115.9

48.9

n/s

Strong

9.2 3.5

7.8 4.5

n/s n/s

Strong Strong

n/s, Not significant; Sig., statistical significance.

shore) before and after the desalination plant began operations. A bottom water salinity anomaly was identified, which indicates that the spatial footprint of the brine discharge plume extended about 600 m offshore with salinity up to 2.7 ppt above ambient (33.2 ppt). This salinity is well within the limit of 40 ppt defined in the plant discharge permit. The study indicates that there are no significant changes in the assessed biological indicators (benthic macrofauna, BOPA-index, brittle-star survival, and growth) in the discharge area.

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Table 4.10 Results of Carlsbad desalination project salinity tolerance test. Species observed Red abalone Red abalone Red abalone Red abalone Red abalone Sand dollars Sand dollars Sand dollars Sand dollars Sand dollars Purple sea urchins Purple sea urchins Purple sea urchins Purple sea urchins Purple sea urchins

Salinity (ppt)

Mortality

Elapsed time to first mortality (days)

33.5 (Control tank) 37 38 39 40 33.5 (Control tank) 37 38 39 40 33.5 (Control tank) 37

0

N/A

0 0 0 0 0

N/A N/A N/A N/A N/A

0 0 0 0 1

N/A N/A N/A N/A 1

1

1

38

1

4

39

1

4

40

1

6

N/A, Not applicable.

4.2.9 United States: Tampa Bay desalination plant (collocated) 4.2.9.1 Tampa Bay facility description Colocation with a power station was first used for the Tampa Bay Seawater Desalination Project, and since then has been considered and used for siting numerous plants in the United States and worldwide. The intake and discharge of the Tampa Bay Seawater Desalination Plant are connected directly to the cooling water discharge outfalls of the Tampa Electric’s (TECO’s) Big Bend Power Station (Fig. 4.34). The TECO power generation station discharges up to 5.3 million cubic meters of cooling water per day depending on the load and the generating units in operation. The desalination plant takes an average of 166,540 m3/day from the cooling water discharge to produce 95,000 m3/day of fresh drinking water. The desalination plant concentrate is discharged to the same TECO cooling water outfalls downstream from the point of seawater desalination plant intake connection. The source seawater is treated through fine screens, coagulation and flocculation chambers, sand media, and diatomaceous filters in series, and SWRO system

4.2 Surface water discharge case studies

FIGURE 4.33 Carlsbad desalination project test tank.

FIGURE 4.34 Tampa Bay SWRO plant colocation schematic: daily water volumes.

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with partial second pass. The spent filter backwash water from the desalination plant is processed through lamella settlers. The solids produced are dewatered using a belt filter press. Treated backwash water and concentrate are blended and disposed through the power plant outfalls. The environmental monitoring program in the area of the desalination plant discharge is implemented by Tampa Bay Water independently from the desalination plant operator, American Water-Acciona Agua, in fulfillment of the plant’s discharge permit requirements. Overall objectives for the monitoring program are to detect and evaluate effects of discharge through comparison to a control area and time periods defined by facility operation (preoperational, operational, and offline periods). The plant discharge permit requires additional supplemental sampling to be performed as part of Tampa Bay Water’s hydrobiological monitoring program. Water quality and benthic invertebrate monitoring includes fixed and random sites, and is focused on areas most likely to be affected by the discharge including the power plant discharge canal and areas of Hillsborough Bay and middle Tampa Bay near the mouth of the canal (Fig. 4.35). A small embayment adjacent to the discharge canal is also monitored. The letters “I” and “D” on Fig. 4.35

FIGURE 4.35 Monitoring areas of Tampa Bay desalination plant discharge.

4.2 Surface water discharge case studies

indicate TECO intake and discharge canals, Letter “A” stands for Apollo Bay, a shallow embayment in the vicinity of the discharge. Areas designated by rectangular areas A, B, and C, are the prime sampling areas while D and northeast of Apollo Beach (NAB) zones have been added for supplemental monitoring. The NAB zone is the embayment NAB. A control area considered representative of ambient background bay water quality conditions has been used for comparison. For fish and seagrass, data collected by other government agencies monitoring in the vicinity of the Desal facility have been used to evaluate potential changes. In addition, the discharge permit also requires monitoring of chemical constituents to ensure that water quality in Tampa Bay is protected. Monitoring of the desalination facility began in April of 2002. The desalination facility first began operation in 2003 and since then it operated at varying production levels until being taken offline for remediation in May 2005. The facility came back online in March 2007.

4.2.9.2 Tampa Bay receiving water characterization The combined power plant cooling water and concentrate from the desalination plant are discharged into an artificially built open canal, which conveys the discharge to Hillsborough Bay. This bay is a subembayment of Tampa Bay on the west-central coast of Florida. The TECO power plant is near the mouth of Hillsborough Bay. Tidal action is the dominant force affecting water transport in lower Hillsborough Bay. With each tide reversal, more than 25 times as much water enters or leaves Hillsborough Bay and more than 200 times as much water enters or leaves Tampa Bay than is circulated through the power station (Levesque and Hammett, 1997). The canal has limited aquatic vegetation and due to the relatively high temperature of the power plant discharge the TECO discharge canal attracts manatees that bring their calves to the canal for the winter (Baysoundings, 2015; Savethemanatee, 2015).

4.2.9.3 Description of Tampa Bay discharge streams The discharge stream consists of concentrate, treated filter backwash (lamella clarifier supernatant) from the granular media filters, and membrane cleaning rinse water.

4.2.9.4 Description of Tampa Bay plant outfall The TECO power generation station discharges a maximum and average of 8,327,000 and 5,300,000 m3/day of cooling water per day depending on the load and the generating units in operation. From this cooling water (which averages 5,299,000 m3/day, the desalination plant takes an average of 166,540 m3/day) to produce 95,000 m3/day of fresh drinking water. The desalination plant concentrate is discharged to the same TECO cooling water outfalls approximately 21 m downstream from the point of seawater desalination plant intake connection.

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At full capacity, the RO process leaves about 71,915 m3/day of 2.3 times-assalty seawater, which is returned to TECO’s cooling water stream and blended with up to 15,299,000 m3/day of cooling water, achieving a blending ratio of up to 70:1. At this point, before entering and mixing with any bay water, the salinity is already only 1.0% 1.5% higher, on average, than the ambient water salinity in Tampa Bay. This slight increase falls within Tampa Bay’s normal, seasonal fluctuations in salinity. Tampa Bay Water plant recovery rate is 57% and thus slightly higher than the typical recovery rates of all other SWRO plants under construction and development in the United States, which have a typical recovery rate of 50%. The slightly higher recovery rate of this project is mainly due to the relatively lower average salinity of Tampa Bay (average of 26 ppt) as compared to that in the Gulf of Mexico (38 ppt) or that along the Pacific coast of the United States (33.5 ppt). The cooling water mixture moves through a discharge canal, blending with more seawater, diluting the discharge even further. By the time the discharged water reaches Tampa Bay, its salinity is nearly the same as the Bay’s. The large volume of water that naturally flows in and out of Tampa Bay near Big Bend provides more dilution, preventing any long-term build-up of salinity in the bay. At present the desalination plant is operated in a hot standby mode for 6 months per year and for the remainder of the time it operates at between 40% and 100% of its design freshwater production capacity. During hot standby mode the plant runs on a number of days per week and produces water for service purposes only—to maintain the readiness of the desalination plant for full capacity production. The pretreatment system of the plant operates at all times but during the hot standby period no coagulants are added to the processed feed water except during the days where service water is produced. Due to the continuous operation of the seawater pretreatment system the plant has a continuous discharge to Tampa Bay.

4.2.9.5 Tampa Bay key discharge permits and permit requirements Numerical effluent limitations from the Tampa Bay Water NPDES Permit FL0186813-006 are shown in Table 4.11. Most of the numerical limitations apply to the combined discharge. There are several monitoring sites for taking samples for reporting only.

4.2.9.6 Tampa Bay permit compliance observations Long-term monitoring of the plant discharge indicates that the plant has been consistently and continuously in compliance with its NPDES permit requirements. Environmental monitoring of the desalination plant discharge has been ongoing since the plant first began operation in 2003 (McConnell et al., 2009). Since then it operated at varying production levels until being taken offline for remediation in May 2005. The facility came back online in March 2007. The desalination plant discharges 72,000 m3/day of concentrate of salinity of 54,000 62,000 mg/L when the product water is 95,000 m3/day. The concentrate is blended with the remainder of the power plant cooling water prior to its disposal to Tampa Bay.

4.2 Surface water discharge case studies

Table 4.11 Numerical discharge limitations for Tampa Bay desalination. Effluent limitations (numerical) Parameter

Unit

Chronic WET, 7-day IC25 mysidopsis bahia RO facility discharge flow Dilution ratio

%

Max/ min

Statistical basis

Frequency of analysis

Sample type

100

Single sample

Quarterly

Grab

Daily maximum Single sample Single sample Annual total

Continuous

Recorder

Continuous

Calculated

Continuous

Calculated

Hourly

Calculated

Weekly

4 grabs/ day

Weekly Daily

4 grabs/ day Calculated

Daily

Calculated

Monthly

Calculated

Monthly

Calculated

Monthly

Calculated

Monthly

Calculated

Continuously

Meter

Continuously

Meter

Monthly

Calculated

Limit

MLD

MAX

104

ratio

MAX

N/A

MIN

28

h

MAX

N/A

mg/L

MIN

Report

mg/L

MIN

Report

Chloride (as Cl)

mg/L

MAX

0

Salinity

ppt

MAX

35.8

Copper, total recoverable Iron, total recoverable Radium 226 1 228, total Alpha, gross particle activity pH

µg/L

MAX

0

mg/L

MAX

0

pCi/L

MAX

5

pCi/L

MAX

15

MIN

6.5

MAX

8.5

MAX

0

Time dilution ratio , 28 h Oxygen (DO)

Mercury

µg/L

Monitoring requirements

Single sample (Grab) Single sample (24 h) Daily maximum Daily maximum Daily maximum Daily maximum Daily maximum Daily maximum Daily minimum Daily maximum Daily maximum

Because of the large dilution volume of the cooling water, the blend of concentrate and cooling water has salinity well within 2000 mg/L of the ambient bay water salinity (Mickley & Voutchkov, 2016). The discharge biomonitoring of the host community is a requirement under an Environmental Resource Permit that was issued by the local county

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CHAPTER 4 Case studies for surface water discharge

environmental agency. Environmental monitoring program in the area of the desalination plant discharge is implemented by Tampa Bay Water independently from the desalination plant operator. Overall objectives for the monitoring program are to detect and evaluate effects of discharge through comparison to a control area and time periods defined by facility operation (preoperational, operational, and offline periods). The plant discharge permit requires additional supplemental sampling to be performed as part of Tampa Bay Water’s hydrobiological monitoring program. Water quality and benthic invertebrate monitoring includes fixed and random sites, and is focused on areas most likely to be affected by the discharge. A control area considered representative of ambient background bay water quality conditions are used for comparison. For fish and seagrass, data collected by other government agencies monitoring in the vicinity of the desalination facility are used to evaluate potential changes. Evaluation of monitoring data from the period of 2002 2008 shows that even during periods of maximum water production, changes in salinity in the vicinity of the discharge were within or below the maximum thresholds (less than 2000 mg/L increase over background) predicted by the hydrodynamic model developed during the design and permitting phases of the plant. Review of monitoring data to date indicates that the plant operation does not have any observable adverse impacts on Tampa Bay’s water quality and abundance, and diversity of the biological resources near the facility discharge. While benthic assemblages varied spatially in terms of dominant taxa, diversity, and community structure, the salinity did not vary among monitoring strata, and the observed spatial heterogeneity of marine life distribution has been found to be caused by variables not related to the discharge from the desalination facility (i.e., temperature and substrate). Patterns in fish community diversity in the vicinity of the facility were similar to those occurring elsewhere in Tampa Bay, and no differences between operational and nonoperational periods have been observed.

4.2.9.7 Tampa Bay permitting support studies The key environmental studies completed for the permitting of the Tampa Bay SWRO desalination project included:

• Pilot study to generate concentrate, spent filter backwash, and spent • • •

membrane cleaning solutions which was used for discharge water quality characterization. One-year source water quality characterization study. Concentrate, spent filter backwash water and cleaning solutions chemical characterization study for compliance with all parameters regulated by the CWA and the Florida Department of Environmental Protection. WET study of the concentrate and various blends of concentrate and spent filter backwash water.

References

• Desk-top salinity tolerance study for marine species inhabiting the area of the discharge.

• Near and far-field hydrodynamic modeling studies to determine the zone of •

initial mixing and dilution ratios near the area of the discharge and within Tampa Bay. Environmental Impact Assessment of the desalination project, including product water delivery pipeline and offsite drinking water storage tanks.

References Baysoundings, 2015. ,http://baysoundings.com/the-state-of-tampa-bay/. (accessed November 2019.). Cannesson, N., 2009. Community, environmental and marine impact minimization at the Gold Coast desalination plant. In: International Desalination Association, Biennial Conference, IDAWC/DB09 242, Dubai, UAE, November 7 12. Christie, S., Bonnelye, V., 2009. Perth, Australia: two-year feed back on operation and environmental impact. In: IDA International Desalination Association, Biennial Conference, Dubai WC/DB09-278, Dubai, UAE, November 7 12. Drami, D., Yacobi, Y.Z., Stambler, N., Kress, N., 2011. Seawater quality and microbial communities at a desalination marine outfall. A field study at the Israeli Mediterranean Coast. Water Res. 45, 5449 5462. Frank, H., Fussmann, K.E., Rahav, E., Bar Zeev, E., 2019. Chronic effects of brine discharge from large-scale seawater reverse osmosis desalination facilities on benthic bacteria. Water Res. 151, 478 487. Kit, E., Levin, A., Gluzman, M., Sladkevich, M., Drimer, N., 2011. Engineering Opinion Regarding Brine Spreading from the Sorek Desalination Plant, CAMERI Report P.N. 726/11, Technion City, Israel. Le Page, S., 2004. Salinity Tolerance Investigations: A Supplemental Report for the Carlsbad, CA Desalination Project, M-Rep Consulting, Environmental Impact Report for Carlsbad Seawater Desalination Plant, City of Carlsbad. Levesque, V., Hammett, K.M., 1997. Water Transport in Lower Hillsborough Bay, Florida, 1995 96, U.S. Geological Survey Open-File Report 97 416, Prepared in Cooperation with the Southwest Florida Water Management District, Tallahassee, Florida. McConnell, R., 2009. Tampa Bay Seawater desalination facility environmental impact monitoring. In: Proceedings of 2009 Annual WateReuse Conference, Seattle, September. Mickley, M.C., Voutchkov, N., 2016. Database of Permitting Practices for Seawater Concentrate Disposal. Water Environment and Reuse Research Foundation Alexandria, Alexandria, VA. Oceanica Consulting, 2009. Perth Metropolitan Desalination Plant Cockburn Sound Benthic Macrofouna Community and Sediment Habitat, Repeat Macrobenthic Survey. Okel, P.N., Antenucci, J.P., Imberger, J., 2007. Field Investigation of the Impact of the Perth Seawater Desalination Plant Discharge on Cockburn Sound During Summer. Cente for Water Research, University of Western Australia, Perth.

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Petersen, K.L., Heck, N., Reguero, B.G., Potts, D., Hovagimian, A., Payton, A., 2019. Biological and physical effects of brine discharge from the Carlsbad desalination plant and implications for future desalination plant constructions. Water 11 (2), 208 226. Safrai, I., Zask, A., 2008. Reverse osmosis desalination plants marine environmentalist regulator point of view. Desalination 220, 72 84. Sauvet-Goichon, B., 2007. Ashkelon desalination plant a successful challenge. Desalination 203, 75 81. Savethemanatee, 2015. ,http://www.savethemanatee.org/info_manatee_migration.htm. (accessed November 2019.). Sladkevich, M., Levin, A., Kroszynski, U., Kit, E., Drimer, N., 2011. Numerical Simulations of Brine Spreading Discharged from the Proposed Sorek Desalination Plant Field Simulations, P. N. 726/11, Technion City, Israel. Talavera, J.L., Ruiz, J.J.Q., 2001. Identification of the mixing process in brine discharges carried out in Barranco del Toro Beach, South Gran Canarias (Canary Island). Desalination 139, 277 286. Torquemada, F.Y., 2009. Dispersion of brine discharge from seawater reverse osmosis desalination plants. J. Desalin. Water Treat. 5, 137 145. Vargas, C., Viskovich, P., Gordon, H., Walker, T., 2011. The Challenge of Managing Reverse Osmosis Brine disposal: Experience at QLD, IDA World Congress, Perth Australia, Ref. IDAWC/PER11-075, September 4-9. Voutchkov, N., 2012. Desalination Engineering: Planning and Design. McGraw Hill Companies, New York. WDR (Water Desalination Report)., 2011. SWRO Falls Victim to Politics. Water Desalination Report, 47. Weber, C.I., Horning, W.B., Klemm, D.J., Nieheisel, T.W., Lewis, P.A., Robinson, E.L., et al., 1998. Short-Term Methods for Estimating the Chronic Toxicity of Effluents and Receiving Waters to Marine and Estuarine Organisms, EPA/600/4-87/028, National Information Service, Springfield, Virginia.

CHAPTER

Discharge to sanitary sewer

5

5.1 Description Worldwide, concentrate from small seawater and brackish desalination plants is most commonly disposed of to nearby wastewater collection system (Mickley, 2006, 2018). In the United States, approximately 25% of desalination plants discharge their concentrate to the sanitary sewer. It deserves emphasis that only very small volumes of concentrate can be disposed of in this manner, and that the receiving wastewater treatment plant (WWTP) has to have a large enough capacity to process the concentrate as it has a very different composition to municipal wastewater. In the United States, sewer discharge is most common for desalination plants with production of 4 m3/day or less (Mickley, 2018). In most countries, discharge to sanitary sewer is regulated by requirements and discharge limitations which apply to industrial discharges, and managed by the utility responsible for wastewater collection system operation and maintenance (Voutchkov, 2011a).

5.2 Potential environmental impacts If the volume of discharged concentrate is one to two orders of magnitude smaller than the existing influent flow of the WWTP the impact of the concentrate discharge on the final effluent quality will be only a slight increase in salinity. The impact on the receiving water body of saline discharge will be similar to that of the effluent generated by codisposal with a WWTP as described in Section 3.2 (Voutchkov, 2011a).

5.3 Effect on sanitary sewer operations Usually, concentrate water quality is compliant with the typical requirements for discharging wastewater to sanitary sewers. Therefore the application of this concentrate disposal method is not anticipated to have significant impacts on the sanitary sewer system’s integrity and condition.

Management of Concentrate from Desalination Plants. DOI: https://doi.org/10.1016/B978-0-12-818045-7.00005-1 © 2020 Elsevier Inc. All rights reserved.

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The salinity of the concentrate is typically an order of magnitude higher than that of municipal wastewater, while the turbidity is several times lower. The BOD5 of the concentrate is well below 5 mg/L, that is, concentrate has low organic content as compared to municipal wastewater which usually has BOD5 of 150 250 mg/L. Since the discharges from desalination plants usually contain spent coagulant in the form of ferric hydroxide, this coagulant is likely to settle and deposit at the bottom of sewer lines if the pipeline velocity is lower than 0.5 m/s. The pH of the concentrate is usually well within the acceptable range of 6 9. Discharges from desalination plants with open ocean intakes typically have an oxygen content which is several times higher than that of municipal wastewater (5 8 mg/L vs 1 2 mg/L). However, concentrate generated by brackish desalination plants using saline aquifers as source water is often anaerobic and could reduce the overall concentration of oxygen in the wastewater or increase wastewater septicity. Antiscalant used in desalination plant treatment processes retards the rate of mineral scale formation on the surface of the membranes. However, most antiscalants have scale prevention effect that is limited to between 30 minutes and 2 hours after their introduction in the saline source water only. Therefore if the concentrate retention period in the wastewater collection system exceeds this time, calcium, magnesium, barium, strontium, and/or other scaling minerals could precipitate on the walls of the wastewater collection system pipelines and equipment, and impact sewer conveyance capacity and operation. Concentrate from seawater desalination plants is typically odorless and colorless if it does not contain filter backwash or spent membrane cleaning solutions, which may give it slightly reddish discoloration. Therefore its discharge will usually not cause significant alteration of the appearance of the wastewater in the sewer. Because of its high salinity, concentrate may suppress nitrification and reduce formation of hydrogen sulfide in the wastewater collection system if it exceeds over 20% of the total volume of the wastewater with which it is mixed. Such effect will be beneficial for the integrity of the wastewater collection system and the receiving WWTP.

5.4 Effect on wastewater treatment plant operations This method of disposal can only be considered if the existing WWTP has sufficient hydraulic capacity to accept the concentrate generated by the desalination plant. The biological treatment process of a WWTP is generally inhibited by high salinity when the plant influent TDS concentration exceeds 3000 mg/L. The threshold of salinity for impact on the nitrification process is even lower, at 1000 mg/L. The impact of the elevated salinity of the desalination plant

5.5 Effect on water reuse

concentrate on the biological treatment system needs to be assessed prior to this method of discharge being accepted as a viable concentrate disposal option (Voutchkov, 2011b). A rule of thumb on feasibility of this method of discharge can be determined based on the individual plant capacities of the desalination plant and the WWTP. Typical influent TDS to a municipal WWTP is in a range of 100 1000 mg/L. Seawater desalination plant concentrate usually has a TDS in excess of 65,000 mg/L. The capacity of the WWTP has to be between 30 and 35 times higher than the concentrate inflow to maintain a TDS below 3000 mg/L. For example, if an 80,000 m3/day WWTP has spare hydraulic processing capacity, it could accept up to 2000 m3/day of concentrate and maintain TDS below 3000 mg/L. At desalination plant recovery rate of 50%, this translates to a desalination plant producing 2000 m3/day of fresh water (Voutchkov, 2011b). More detailed analyses of the potential impacts of concentrate discharge on specific WWTP treatment processes is provided elsewhere (Rimmer et al., 2008).

5.5 Effect on water reuse With growing water scarcity worldwide, reusing water is becoming more common and gaining popularity. Treated effluent is widely used in industrial applications and for irrigation. Specific care needs to be taken if effluent from the WWTP considered for accepting desalination concentrate is being reused, together with the type of reuse application. For example, effluent can be reused for irrigation from a plant with typical processes of sedimentation, activated sludge treatment and sand filtration. Where concentrate is added to the inflow of a plant with effluent reused for irrigation, not only will salinity increase and thereby limit the effluent suitability for reuse, but if the sodium, chloride, boron or bromide levels are increased above the maximum tolerance thresholds of the irrigated plants, concentrate discharge to the sewer system could also result in the effluent no longer being suitable for such reuse. This is due to these compounds not typically being present in large quantities in typical municipal wastewater and the fact that WWTPs are therefore not designed to remove these dissolved salts. Some crops are very sensitive not only to salinity, but also to the minerals listed above. Wastewater effluent has typical chloride levels of approximately 60 150 mg/L, while most commonly planted flowers, trees, and grass are not able to survive if chloride levels in the irrigation water exceed 250 mg/L. In contrast, seawater desalination concentrate has chloride levels in excess of 40,000 mg/L. If its effluent is to be applied for irrigation, the 80 MLD WWTP used in the example above will not be able to process more than 160 m3/day of seawater concentrate, if the chloride level in the WWTP effluent has to be maintained below this threshold.

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Ornamental plants and some fruits and vegetables such as strawberries and avocado have lower tolerance levels: sodium of # 80 mg/L, chloride of # 120 mg/L, and boron in the region of 0.75 1 mg/L. Citrus fruits (e.g., lemons, limes, tangerines, oranges) have an even lower boron threshold level (0.5 mg/L) and production yield of these citrus trees is reduced significantly at higher levels. Fruit may also be discolored, which also reduces their commercial value and customer appeal (Voutchkov, 2011b). Some palm trees also have low tolerance to boron. It is therefore imperative to determine the concentration of key minerals in the blend of desalination plant discharge and wastewater entering the wastewater plant where WWTP effluent is reused for irrigation of salinity sensitive crops, flowers, and trees.

5.6 Design and configuration guidelines Municipal WWTP inflows typically have diurnal peak and off-peak periods and significant seasonal variations, while concentrate from the desalination plant is generated continuously at approximately the same hourly, daily and seasonal flow rates, and mineral content. To ensure that the combined salinity after concentrate discharge into the sanitary sewer remains at less than 3000 mg/L at all times, the concentrate may need to be stored in an equalization tank, as influent salinity above 3000 mg/L is likely to interfere with the biological activated sludge process and WWTP effluent quality. The equalization tank(s) could be located either at the desalination plant or at the WWTP. Recovery of the activated sludge system after exposure to high salinity wastewater is a slow process and typically extends over a period of 4 6 weeks and is thus best avoided (Voutchkov, 2011a). Other issues, such as periodic discharges of membrane cleaning solutions will need to be considered, if relevant and not equalized and treated at the desalination plant. Wastewater collection systems can sustain structural integrity and normal operation and maintenance if the discharges to the system have pH between 6 and 9. Usually desalination plant concentrate and spent filter backwash water are within this pH at all times. However, the spent membrane cleaning solutions could have pH as low as 2 3 and as high as 10 11. If the desalination plant discharge has levels outside of the 6 9 pH range, either the membrane cleaning solution or the entire discharge will need to be neutralized prior to blending with the wastewater in the receiving collection system. This pH control of the desalination plant discharge is typically done in a neutralization tank constructed for this purpose, with the necessary mixing and monitoring equipment to ensure appropriate pH in the final discharge. The concentrate will need to be conveyed from the desalination plant to the WWTP or to the closest receiving wastewater collection system. Pipeline design will be similar to that for conveyance of municipal wastewater, with a minimum

5.7 Costs for sanitary sewer discharge

velocity of 0.7 m/s to prevent sedimentation specifically of spent coagulant and mineral deposits. It is important that the conveyance time between the desalination plant and the receiving point of the WWTP is selected to be shorter than the time for which the antiscalant added at the desalination plant discharge can delay the formation of mineral scale—30 minutes to 2 hours. Plant concentrate can generally be safely disposed of with wastewater thus treatment prior to conveyance is not necessary. However, if antiscalant is added at the desalination plant and the time for conveyance exceeds 2 hours, it is advisable to consider injection of antiscalant to the desalination plant discharge at the desalination plant or along the pipeline route to prevent mineral scale formation in the discharge pipeline and associated obstruction of discharge flow. Materials such as HDPE, GRP, and PVC are suitable and widely used for pipelines conveying desalination plant discharge.

5.7 Costs for sanitary sewer discharge Where a nearby WWTP has the capacity to accept desalination concentrate without any negative impact on processes or reuse, this method of concentrate disposal has the lowest cost: US$0.32/m3 US$0.66/m3 of discharged concentrate (Ziolkowska and Reyes, 2016; Arafat, 2017). As has been shown in this chapter, the conditions and costs for discharge to sanitary sewers are site-specific. Costs of conveyance will depend on the distance to the receiving wastewater collection system or WWTP, as well as whether or not pumping is required. To protect the WWTP processes, construction of an equalization tank may also be necessary (Voutchkov, 2011a). To prevent scale formation and discharge pipeline obstruction, antiscalant addition at the desalination plant or along the pipeline route may be needed if the travel time of the concentrate to the receiving point of the wastewater collection system is longer than the time for which the antiscalant used at the desalination plant can prevent scale formation. Utilities may require substantial fees for connecting to sanitary sewers and/or discharging to existing WWTP plants or plant outfalls as such discharge would reduce the available capacity of the existing facilities to receive additional wastewater flows in the future. Sewer connection fees are known to vary considerably depending on the capacity and condition of the existing collection system and WWTP infrastructure. As a minimum, the fees will be related to available capacity and operational costs at the WWTP. The costs of increased risk of impacting the existing WWTP processes, compliance with WWTP effluent discharge permit (license) requirements, or additional treatment costs for salinity reduction at the WWTP via installation of reverse osmosis system if the plant effluent is reused, as well as penalty agreements may also be raised by the utility. Where spare capacity is taken up by concentrate in both conveyance and wastewater treatment

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processes, the opportunity cost of other developments generating sewage needs to be considered. In areas of high demand growth, the opportunity cost may be significant.

References Arafat, H., 2017. Desalination Sustainability: A Technical, Socioeconomic, and Environmental Approach. Elsevier. Mickley, M.C., 2006. Membrane Concentrate Disposal: Practices and Regulation, Desalination and Water Purification Research and Development Program Report N. 123, second ed. U.S. Department of Interior, Bureau of Reclamation. Mickley, M.C., 2018. Updated and Extended Survey of US Municipal Desalination Plants, Desalination and Water Purification Research and Development Program Report No. 207. U.S. Department of Interior, Bureau of Reclamation. Rimmer, A.E., Kobylinski, E.A., Hunter, G.L., DiGiano, F.A., Bierick, B., 2008. The Impacts of Membrane Process Residuals on Wastewater Treatment. Guidance Manual, WateReuse Foundation, Alexandria, VA. Voutchkov, N., 2011a. Desalination Plant Concentrate Management. Water Treatment Academy. Voutchkov, N., 2011b. Overview of seawater concentrate disposal alternatives. Desalination 273, 1. Ziolkowska, J., Reyes, R., 2016. Prospects for desalination in the United States experiences from California, Florida, and Texas. In: Ziolkowska, J.R., Peterson, J.M. (Eds.), Competition for Water Resources. Experiences and Management Approaches in theUS and Europe. Elsevier, p. 478.

CHAPTER

Deep well injection

6

6.1 Description Deep well injection of concentrate requires an appropriate aquifer located in close proximity of the desalination plant, which is confined, deep, and not connected to any adjacent fresh or brackish water aquifers. Disposal to deep wells is typically completed using wells of a depth between 500 and 1500 m or sometimes far deeper, which comprise of inner casing, surface casing, and injection tube. A pump may be required at the well head. Typical components of a deep well for concentrate injection is shown in Fig. 6.1 (Corollo, 2009). Current UIC regulations (40 CFR y144.12) for well disposal identify five classes of wells, three of which could be used for concentrate disposal. These are:

• Class I hazardous and nonhazardous waste injection wells; • Class II enhanced oil recovery (EOR) injection wells; and • Class V injection wells. The technical recommendations for injection wells adopted by the US Environmental Protection Agency (USEPA) are comprehensive in scope and detail the requirements for each class of well. Class I wells are specified for injecting industrial waste streams or municipal wastewater to underground aquifers located below any underground sources of drinking water (USDW). Concentrate is not typically considered hazardous, but disposal of concentrate as hazardous waste is a conservative option to follow. Class II wells are located in oil fields no longer used for production of oil. The USEPA requirements for Class II wells are very similar to those for Class I, with injection below the lowest USDW. Injecting concentrate into oil fields has the benefit of aiding oil field recovery. Class V injection wells are not appropriate for hazardous waste, with many providing for injection above USDW. Class V could be used for concentrate injection but below the lowest USDW to prevent endangerment (Frazier et al., 2006). While the requirements for the various classes of injection wells may differ, protecting USDW is paramount in the requirements for planning, siting, construction, and operation of wells. For example, where hazardous fluid is injected, the operator has to prove that any hazardous components will remain in the injection zone for either as long as they remain hazardous, or 10,000 years. Once the wells are operational, monitoring is continuous with various annual performance Management of Concentrate from Desalination Plants. DOI: https://doi.org/10.1016/B978-0-12-818045-7.00006-3 © 2020 Elsevier Inc. All rights reserved.

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FIGURE 6.1 Schematic of deep injection well.

requirements assuring mechanical integrity, annulus pressure in the well system, etc. Where well systems are not physically manned, procedures for remote monitoring and reporting and automatic shut-off systems have to be in place. Once a well is no longer required for injection, it needs to be plugged to prevent migration of contaminants. Regulatory authorities typically specify reporting requirements for the life of operation of the wells in license conditions. Where country-specific regulations are not available, the technical recommendations developed in the United States for injection wells provide comprehensive guidance on how to approach the design and operation of deep well injection as a method of concentrate disposal (Frazier et al., 2006).

6.1.1 Selection of geological formation Deep injection wells should be designed to deliver concentrate only where geological formations have suitable configuration and geology. The receiving aquifer must have capacity to store the entire volume of concentrate released over the useful life of the desalination plant—25
30 years (Ga´lvez et al., 2010; Olabarria, 2015). A thorough geological study of the target site has to be undertaken to determine the suitability of the area. In many regions, groundwater has been extensively studied and data made publicly available, but where more detail is required to reduce risk of negative environmental impacts, such studies take many years to complete, and well performance monitoring has to be completed for the entire project lifespan.

6.1 Description

The capacity of the aquifer can be estimated from the lateral extent and thickness of the aquifer, while the porosity and permeability are important to determine the safe injection rate which does not cause displacement of concentrate beyond the injection zone. Sandstone geological formations are highly porous and are very suitable for retention of liquids thus ideal for this application (Voutchkov, 2011). Above the injection zone, at least one layer of impermeable rock has to be present to contain the concentrate within the permeable rock layer, thereby preventing concentrate from moving toward any adjacent freshwater aquifers that are used as sources of drinking water. Such geological configuration is known as the confining zone, which is typically constituted of clay or shale rather than more brittle rocks such as sandstone or fractured geological formations. Groundwater conditions are well documented in the United States, and suitable aquifers have been identified in the Gulf Coast, Texas, Great Lakes, and Florida. The depth of wells vary from area to area, ranging from 500 to 1800 m in the Great Lakes region, and between 600 and 3600 m in the Gulf Coast. Florida is known to have geological formations particularly suitable for deep well injection, with five injection zones identified ranging in depth between 200 and 2500 m. In southeastern Florida, a zone known as the Boulder Zone is practically ideal for brine concentrate disposal because it has water quality similar to seawater, and depth between 550 and 1200 m. The confining zone protecting drinking water sources is constituted of deep, well-compacted layers of dolomite and sandstone. Elsewhere in Florida, injection well depth varies greatly: from a shallow maximum depth of 500 m along the west coast to wells between 1800 and 2400 m deep in the panhandle area. At such great depths, liquids move through aquifers extremely slowly—a few meters or less over hundreds of years. The result is that concentrate injected into such deep wells will be confined for a very long time. Arguably, the most critical factor for selection of a deep well aquifer is the long-term environmental sustainability of the aquifer’s water quality. It is critical that the aquifer has salinity higher than that of the concentrate to ensure that the aquifer water quality is not degraded over time. Given that saline water moves so slowly underground, degradation of aquifer water quality over time can be avoided by only recharging the aquifer with concentrate of better quality than the original water quality of the aquifer. Often, such deep aquifers are sufficiently saline to meet this requirement for concentrate from brackish desalination plants, and sometimes even from seawater desalination plants (Voutchkov, 2011).

6.1.2 Injection well shaft Injection wells are constructed in the same manner as extraction wells, using the same drilling equipment, casing type, and cement grouting required to meet designed flows and pressures. As concentrate is corrosive, the shaft design has to specify appropriate materials for the inner lining such as fiberglass, plastic or stainless steel of grade commensurate with the concentrate corrosivity.

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6.1.3 Casing Casings provide structural stability to the borehole to prevent it from collapse. Depending on the depth of the well and the surrounding geological environment, injection wells usually have three to four staged casings to protect upper freshwater zones from possible contamination. Casing materials are selected to suit both the hydrogeological characteristics of the site as well as the composition of the concentrate. With the corrosive nature of concentrate, casings are constructed from corrosion resistant materials such as stainless steel or fiberglass-reinforced plastic (FRP). The casing is usually sealed with latex cement, mineral blends, or epoxy to ensure integrity. The surface casing is the outermost protective layer, extending from the surface to the lowest level where drinking water may be sourced. The inner (or longstring) casing runs from the surface all the way to the injection zone. As the inner casing is continuously in contact with concentrate, the casing material needs to be designed not to deteriorate over time. Materials considered for injection casings include FRP, coated or lined alloy steel, or more costly materials such as zirconium, tantalum, or titanium. The number and length of additional casings depend on the depth of the well. The inner casing terminates either into open discharge into the aquifer, or can be screened with a perforated screen (Voutchkov, 2011).

6.1.4 Grouting Cement grouting protects groundwater by sealing the casing to prevent the injected liquid from penetrating zones above the injection zone, while also increasing the casings’ strength and serving as a barrier to corrosion from groundwater. Materials suitable for cement grouting are likely to be specified by the regulatory authority that issues the license for installation and use (Voutchkov, 2011).

6.1.5 Injection zone The geology of the injection zone determines how the innermost casing terminates. Open-hole completion is suitable for consolidated rock layers such as sandstone or limestone, while screen or perforated completion is necessary for loose sands and gravels. The circular space between the tubing and casing is sealed by the well head at the surface, and by a packer at termination. A packer is a device that mechanically seals the outside of the tubing to the inside of the inner casing, installed directly above the injection zone. Depending on the application, the complexity of the packer varies from a rubber device to a complex concentric seal assembly. Pressure must be constantly monitored in the circular space and maintained at a constant level to ensure the integrity of the injection operations (Voutchkov, 2011).

6.1.6 Pumping In most instances concentrate discharge pressure will obviate pumping into the injection well. Where pumping is required, care needs to be taken in specifying appropriate injection pump materials that are resistant to the corrosive effect of concentrate.

6.2 Potential environmental impacts

6.1.7 Storage and alternative disposal Unless redundancy has been provided in the well injection system, storage facilities will be required to temporarily retain concentrate at times when the wells cannot be used. Occasional maintenance and repairs will be required, for example if monitoring systems indicate possible leakage. An alternative concentrate disposal method may be required should on-site storage not be possible, but this will be determined by the specific site conditions. For well injection sites located close to the coast, surface water discharge may be the least costly option through a discharge pipeline or canal. An example of this is a BWRO desalination plant situated in Englewood in Florida with deep well injection of concentrate. When required, concentrate is discharged to the Gulf of Mexico via disposal pipeline just over 3 km in length. To accelerate recovery of oil and gas fields, concentrate can be injected into these wells. As long as suitably sized aquifers of appropriate salinity are available, deep well injection is a suitable form of concentrate disposal for various sizes of brackish water desalination plants. For small and medium SWRO desalination concentrate disposal, in some instances concentrate discharge to shallow beach wells may be possible. Such disposal involves injection of the concentrate into shallow unconfined coastal aquifers that eventually drain into the ocean.

6.2 Potential environmental impacts Deep injection wells have been extensively used in the United States over many years and is deemed to be reliable with relatively low probability of adverse impacts on the environment (Mickley, 2006). Under certain conditions, there is a clear risk of contamination of shallow aquifers by upward migration of concentrate which needs to be properly accounted for and managed. Such potential conditions are:

• Injection well casing failure: that could be due to corrosion of the casing or • • •

feed pressure being too high, allowing concentrate to migrate upwards through the well bore; Seal failure: if the seal at the injection zone allows concentrate to migrate upwards into shallow groundwater; Confining zone failure: where well infrastructure is sound but concentrate migrates through the confining zone as this zone is more permeable, jointed or fractured than designed for; and Breach of integrity of the confined aquifer: other wells tapped into the injection aquifer may not be properly plugged or have casings that have lost integrity or have not been appropriately designed, allowing upward migration of the concentrate and thereby contaminating groundwater.

Following construction of the well system, ongoing detailed hydrogeological studies, drilling and operation of test wells are recommended in order to minimize environmental risks and performance challenges (Mickley, 2018). Before start-up,

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the integrity of the well needs to be verified, often with closed-circuit camera inspection or radioactive tracer survey. Once operational, continuous monitoring of well head pressure and concentrate flow is required to prevent contamination. Where gradual increase in pressure is identified, the infrastructure should be checked for clogging. Sudden drop in pressure means that there is a leak in the system, either through the grout, casing, or seal. Operations should be as regular and smooth as possible without large variations in pressure or concentrate flow rate, thereby avoiding contamination and plugging. Bacteria, precipitation of suspended solids, and entrained air in the system can cause plugging. Monitoring wells are always required as part of a well injection system to provide assurance that adjacent aquifers are not contaminated by migration of concentrate. Monitoring wells should be tested monthly to ascertain that water quality has not deteriorated.

6.3 Criteria and methods for feasibility assessment Deep well injection has proven to be feasible for brackish desalination plants of wide range of salinities and flows in the United States. Several high-level, sitespecific considerations indicative of likely feasibility of well injection for concentrate disposal include:

• presence of confined aquifers with good soil transmissivity and sufficient storage capacity;

• absence of any seismic activity or geological faults; and • naturally occurring confining layer of sufficient depth and integrity. Other variables are controllable through proper design and operation, such as:

• leakage potential from the wells; and • decrease in discharge capacity over time due to scaling. Deep well injection has relatively high construction, operational, and monitoring costs. The necessity for an alternative disposal method as back-up can also significantly add to the cost. Groundwater is usually well regulated to protect drinking water as a scarce resource. Compliance with regulations and license conditions can be costly but critical to ensuring sustainable water augmentation through desalination. In the United States, regulations dictate specifications including transmissivity, TDS, and geological conditions to protect any underground water source with TDS below 10,000 mg/L.

6.4 Design and configuration guidelines 6.4.1 Site selection Once a suitable saline source water aquifer for the desalination has been identified, the best location for injection wells has to be identified. In the United States,

6.4 Design and configuration guidelines

regulations require injection wells to be situated at least 400 m away of the well site, with actual distance further determined by the proximity of acceptable injection zone and the hydrogeological characteristics of the receiving aquifer (Voutchkov, 2011). The injection zone needs to have at least the following characteristics:

• • • • •

TDS . 10,000 mg/L; high permeability and high transmissivity; geologically stability; absence of abandoned wells; and suitability of a confining rock layer.

All groundwater in the vicinity of the site needs to be well mapped with existing uses of water supply, aquifer recharge, wastewater disposal, etc. Artificial pathways for concentrate migration such as abandoned wells have to be identified as these may result in contamination by creating conditions for concentrate to contaminate USDWs.

6.4.2 Sizing of injection wells Injection wells need to be sized to accommodate the volume of concentrate to be disposed of, and is a function of the number of wells, their depth, and diameter. Well Depth. The well depth depends on the depth of the receiving aquifer suitable for discharging concentrate into. Groundwater aquifer characteristics are well documented in many parts of the world and information on aquifers is typically readily available from government authorities that regulate and monitor underground water basins in the area of the desalination plant. These authorities could provide information such as depth, capacity, and water quality of the aquifers and their transmissivity and potential areas of contamination or environmental sensitivity. Where groundwater information is not available, the design process needs to include a thorough hydrogeological investigation of the underlaying aquifers where concentrate is planned to be disposed of, which will determine the depth and capacity of suitable confined aquifers. Gathering the required data is likely to take several years, a consideration which should be highlighted during project feasibility. Well depth varies from a shallow, several hundred of meters to several kilometers underground. Well Diameter and Number. The total number of wells depends the maximum and average volumes of concentrate to be disposed of, and often is selected by the project designer to match the number of RO trains in a desalination plant. Redundancy is usually designed for by providing for an additional 20%
30% in standby wells. This enables planned well maintenance as well as provides additional capacity since well capacity could potentially decrease over time. Well diameter is also a function of the volume of concentrate and number of wells to allow a maximum tubing velocity of 3 m/s. A velocity range between 1.5 and 3.0 m/s is commonly used for design based on experience, and is prescribed by some regulators in the United States, for example the state of Florida. Fig. 6.2 presents injection well discharge capacity as a function of well diameter and tubular velocity. This graph can be used for determining the size of individual injection wells.

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FIGURE 6.2 Injection well discharge capacity as function of diameter.

Example For the example of a BWRO desalination plant with freshwater production capacity of 100,000 m3/day designed at 80% recovery, 25,000 m3/day of concentrate will be generated. The example BWRO plant has ten 10,000 m3/day RO trains and is designed to operate at a minimum capacity of 25% of the total plant production capacity with one RO train in service. The concentrate can be disposed of using deep injection wells to a confined aquifer at a depth of 800 m. (Continued)

6.5 Injection well costs

Example (Continued) The number of wells is assumed to be the same as the number of RO trains (i.e., 10) so at minimum production capacity the plant will have one RO train and one discharge well in operation. From the earlier assumptions, a single-duty well has to be designed to discharge a unit capacity of 25,000 m3/day / 10 5 2500 m3/day per well. Using Fig. 6.2, for this size injection well with a well velocity of 2.5 m/s, the well diameter is selected to be 150 mm (6 in.). At average velocity of 2.5 m/s, this well can discharge 3900 m3/ day, which is well above its average design capacity of 2500 m3/day. With 3.0 m/s as maximum well velocity, up to 5000 m3/day of concentrate can be disposed of in such a well. If 10 duty 150-mm diameter wells are provided, additional standby wells may not be required as the installed capacity is higher than required. Conservatively, a 20% safety margin will require two additional wells. Standby wells are, however, useful, and should be considered particularly if the scaling potential of the source brackish water and the water quality of the receiving aquifer are not well known. A conservatively designed injection well system for concentrate disposal of the reference 100,000 m3/day desalination plant will have 10 duty and 2 standby wells, each of 150 mm diameter and 800 m depth.

6.5 Injection well costs Concentrate disposal using injection wells is relatively costly as compared to other alternatives—US$ 0.54 to US$ 2.65/m3 of disposed concentrate (Ziolkowska and Reyes, 2016; Arafat, 2017). Well depth and diameter have the largest impact on the cost of injection wells. Table 6.1 presents construction costs (Voutchkov, 2019) for deep injection wells with diameters ranging between 100 and 500 mm as a function of concentrate discharge flow (in m3/day) and well depth (in meters). Table 6.1 Construction costs of concentrate injection wells. Well diameter (mm)

Typical well concentrate discharge capacity (m3/day)

Construction costs in 2020 US$ as a function of concentrate flow, Q (m3/ day) and well depth, H (m)

100 150 200 250 300 400

1000
2000 2000
4500 4500
6500 6500
10,000 10,000
15,000 15,000
30,000

42 52 68 80 88 94

Q 1 730 H 1 26,000 Q 1 900 H 1 52,000 Q 1 1150 H 1 80,000 Q 1 2100 H 1 155,000 Q 1 2200 H 1 200,000 Q 1 3400 H 1 270,000

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Cost Example Construction cost of injection wells. For the example 100,000 m3/day BWRO desalination plant described in the previous section, with 10 duty 1 2 standby 150-mm diameter wells of 800-m depth, using Table 6.1 the construction cost can be determined as follows: 5 Number of wells 3 ð52 Q 1 900 H 1 52; 000Þ
5 ð10 1 2 wellsÞ 3 ½52 3 25; 000 m3 =day=10 duty wells 1 ð900 3 800 m depthÞ 1 52; 000 5 12 3 ð130; 000 1 720; 000 1 52; 000Þ 5 US$ 10; 824; 000 This excludes cost of any pretreatment, storage or pumping that may be required, The cost of monitoring wells must also be added in determining the overall cost of a deep well injection system. Concentrate pretreatment. If concentrate is chemically incompatible with the receiving water quality, plugging is likely to occur, In this case it is necessary to pretreat the concentrate prior to injection. Typical pretreatment required is the removal of suspended solids, and adjusting of pH to prevent scaling. Suspended solids can be removed using simple systems such as bag or cartridge filters, or more sophisticated processes such as contact clarifiers or lamella settlers. The content of scale-forming compounds in the concentrate will determine its scaling potential. Such compounds include calcium sulfate, barium sulfate, strontium sulfate, calcium fluoride and iron, manganese, and aluminum salts. If the concentrate contains fine sand, silt, suspended solids it will need to be pretreated by a suitable filtration process such as microscreening, sand separation, dual media or cartridge filtration. The costs of such pretreatment are likely to vary between US$ 20 and US$ 50/m3/day of plant production capacity. This would mean a cost in the region of US$ 2,125,000 for the 100,000 m3/ day reference example. Concentrate pumping. Usually pumping is not required when disposing concentrate to deep injection wells, as many operate successfully below 1 bar and reverse osmosis systems typically release concentrate at 1.2
1.8 bars. Where the depth of the well and geological conditions are such that feed pressure of 2
4 bar is required, concentrate would need to be pumped. The estimated cost of pumping is in the range of US$ 2000
US$ 2500/hp. For the current example, assuming well feed pressure of 3 bars is required, the cost of pumping 25,000 m3/day of concentrate into the wells will be approximately US$ 325,000. Environmental monitoring well system. Both deep and shallow monitoring wells are required in the vicinity of the deep well discharge system. Costs of wells vary with depth and diameter, but typically, for wells less than 1 km deep, costs vary between US$ 600 and US$ 800/m and for deeper than 1 km, between US$ 400 and US$ 600/m. For the previously described example, assume that both a deep and shallow monitoring well are required at the discharge well and extraction well, respectively. The deep well with depth of 1200 m will cost approximately of US$ 588,000 and construction cost of a shallow well of 100 m depth will be approximately US$ 70,000, for a total cost of US$ 658,000. Summary of costs. When the costs of the well construction are added to the additional concentrate disposal costs, the total cost of the deep well discharge system is: 5 Injection wells 1 Pretreatment 1 Pumps 1 Monitoring wells 5 US$ 10; 824; 000 1 US$ 2; 125; 000 1 US$ 325; 000 1 US$ 658; 000 5 US$ 13; 932; 000: Taking under consideration that the total construction cost of 100,000 m3/day BWRO plant will be in a range of US$ 125 million to US$ 150 million, the use of deep injection wells will encompass 9%
11% of this cost.

6.6 Deep well injection case study

6.6 Deep well injection case study 6.6.1 Kay Bailey Hutchison desalination plant in El Paso, Texas 6.6.1.1 El Paso facility description The Kay Bailey Hutchinson plant is the largest BWRO desalination plant in the United States, located in El Paso, Texas, and operational since 2007. The plant design capacity is approximately 100,000 m3/day MLD, consisting of 55,000 m3/ day of permeate and 45,000 m3/day of blending water. Water is obtained from 32 wells (16 production and 16 blending water) from the Hueco Bolson Aquifer. The pretreatment design includes sand strainers, cartridge filters, and feed system for antiscalant. The plant has five BWRO trains with two-stage configuration. Each train is designed for 82.5% recovery, to produce 11,000 m3/day.

6.6.1.2 Description of El Paso concentrate well injection system Concentrate is disposed of at a remote site, approximately 35 km away, through three injection wells, 1150, 1228, and 1134 m in depth (see Fig. 6.3). The system is designed to dispose of approximately 11,000 m3/day of concentrate of salinity of 6000
8000 mg/L. Initially, three methods of concentrate disposal were considered: passive evaporation, enhanced evaporation, and deep well injection. Passive evaporation for 11,000 m3/day of concentrate would require a 280 hectare double-lined pond. The required pond size would be reduced if evaporation was to be increased through

FIGURE 6.3 Key Bailey Hutchinson desalination plant location.

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mechanical sprayers. Comparison of implementation and operating costs of the three alternatives explored indicated that deep well injection would be significantly cheaper. A detailed investigation into deep well disposal including test drilling, geological and geophysical studies, hydraulic modeling, and pilot test well was undertaken between 2002 and 2004 (Hutchinson, 2008). The initial hydrogeological study identified the Silurian Fusselman formation, a fractured dolomite suitable for injection, near the Texas
New Mexico border. Four test holes were drilled and profiled indicating geology of alluvial and lacustrine sediments, underlain by a thick layer of Paleozoic shale and limestone (ideal confining layer), which was underlain by the fractured dolomite at a depth between 700 and 880 m. Once high-level suitability had been confirmed, the first pilot well was constructed to a depth of 1150 m. The 230 mm diameter well has an open-hole completion in the injection zone and was constructed to Class I injection well standards. Several pump tests were undertaken and the propensity for mineral precipitation given the concentrate composition was evaluated between 2005 and 2007. Late in 2006 the second and third injection wells were constructed, also to Class I standards. The results of well tests showed that any two of the three wells could be used to dispose of the 11,000 m3/day of concentrate. Infrastructure was constructed at the well sites, including tanks, pipes, valves, and communication systems, as well as solar photovoltaic systems to provide power given the sites’ remote locations. Injection testing commenced in May 2007, initially with groundwater, and then gradually with diluted concentrate, until testing with undiluted concentrate indicated no detrimental impact. Testing was short-term in duration over a couple of months. The concentrate did not receive pretreatment during the pilot testing but no mineral precipitation was observed. The total deep well injection concentrate disposal cost amounted to BUS$ 19 million, including all conveyance costs. The BWRO desalination total plant capital cost was US$ 91 million. The annual concentrate disposal operating cost is US $ 200,000 of the total operating cost of US$ 4.8 million per year. At 80% rated capacity, approximately 10% or 4 US cents per cubic meter of produced freshwater can be attributed to deep well injection in this project (Hutchinson, 2008).

References Arafat, H., 2017. Desalination Sustainability: A Technical, Socioeconomic, and Environmental Approach. Elsevier. Carollo Engineers, 2009. Water Desalination Management and Piloting. South Florida Water Management District, Sunrise, Florida. Frazier, M., Platt, S., Codrington, A., Heare, S.F., 2006. Drinking Water Treatment Residual Injection Wells. Technical Recommendations. Technical Report. Environmental Protection Agency (EPA), Underground injection Control (UIC), National Technical Workgroup (NTW).

References

Ga´lvez, J.B., Rodr´ıguez, S.M., Delyannis, E., Belessiotis, V.G., Bhattacharya, S.C., Kumar, S., 2010. Solar Energy Conversion and Photoenergy Systems: Thermal Systems and Desalination Plants, vol. IV. EOLSS Publications. Hutchinson, W.R., 2008. Deep well injection of desalination concentrate in El Paso, Texas. Southwest Hydrology. March/April 28
30. Mickley, M.C., 2006. Membrane Concentrate Disposal: Practices and Regulation, Desalination and Water Purification Research and Development Program Report N. 123, second ed. U.S. Department of Interior, Bureau of Reclamation. Mickley, M.C., 2018. Updated and Extended Survey of U.S. Municipal Desalination Plants. Bureau of Reclamation, Denver, CO. Olabarria, P.M., 2015. Constructive Engineering of Large Reverse Osmosis Desalination Plants. Chemical Publishing Company. Voutchkov, N., 2011. Desalination Plant Concentrate Management. Water Treatment Academy. Voutchkov, N., 2019. Desalination Project Cost Estimating and Management. CRC Press. Ziolkowska, J., Reyes, R., 2016. Prospects for desalination in the United States experiences from California, Florida, and Texas. In: Ziolkowska, J.R., Peterson, J.M. (Eds.), Competition for Water Resources. Experiences and Management Approaches in the US and Europe. Elsevier, p. 478.

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Land application

7

7.1 Description Disposal of concentrate to land application is suitable only for small desalination plants, located in low humidity, arid climates, where land is available for infiltration, or where salt-tolerant plants are naturally abundant or can be grown and harvested economically and sustainably. Furthermore, water quality impacts on underlying groundwater aquifers in the areas of the land application would need to be assessed as a result of potential concentrate infiltration. This analysis is of critical importance if such groundwater aquifers are used for drinking water supply or for agricultural irrigation of salinity-sensitive crops.

7.1.1 Irrigation 7.1.1.1 Irrigation methods Irrigation with concentrate is applied in a similar fashion to conventional agricultural irrigation: concentrate is circulated and delivered to the surface and excess runoff is collected in a drainage system. Concentrate for irrigation can be applied in a number of methods, such as through sprinkler systems, application directly onto the surface, and drip irrigation. Sprinkler systems are most common, with mobile spray nozzles that move across the land to be irrigated (see Fig. 7.1; Voutchkov, 2011). Both soil condition and crop tolerance require thorough investigation before concluding that this method of disposal is viable. Environmental characteristics, which eliminate unsuitable soil types, include rolling terrain, erosion-prone soil, shallow soil profiles, variable soils, and high water tables. Where the characteristics can accommodate concentrate disposal, other considerations of feasibility are high capital cost of irrigation systems, high operational costs due to mechanical failure, the impact of wind, evaporation loss, and high energy costs. As for crop tolerance, over and above tolerance to salts in the soil, waxy leaves reject direct saline application, whereas nonwaxy leaves absorb salts directly. For similar reasons, the wetting and drying cycle should be maximized so that evaporation does not result in higher concentrations of salt on the vegetation. Slowly rotating sprinklers are thus not ideal. Sprinkling either at night or very early in the day is recommended to reduce evaporation rates. Management of Concentrate from Desalination Plants. DOI: https://doi.org/10.1016/B978-0-12-818045-7.00007-5 © 2020 Elsevier Inc. All rights reserved.

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FIGURE 7.1 Spray irrigation system.

Surface irrigation is usually more suitable than spray irrigation as water is delivered to the soil and roots, avoiding most of the impact of saline evaporation on foliage. Irrigation is provided either in narrow furrows of less than 5 m apart, or wide-graded with borders spaced at around 30 m or more. Drip-irrigation systems are even more suitable as evaporation plays no part in contact of saline solution with the plant foliage, as water is delivered directly to the roots. The main drawback with drip-irrigation systems is that system emitters clog easily due to high salinity. Of the types of irrigation introduced earlier, only surface systems produce notable volumes of runoff which require management. For surface systems, drainage canals are constructed to retain runoff. As alternative, a tailwater return system can be used: this consists of a sump (or reservoir), pump, and return pipeline. Pumps are usually designed to service approximately 25% of the volume of the distribution system.

7.1.1.2 Sprinkler systems Sprinkler systems are usually solid set, consisting of a mainline, with several lateral pipes equipped with sprinklers covering the field. To obtain sufficient pressure to reach all the sprinkler heads, pumping is commonly required. Such system is shown in Fig. 7.2 (Voutchkov, 2011). Solid-set systems, as implied by their name are fixed into position and thus do not move during concentrate delivery, This has advantages in reduced operational costs although initial capital costs are relatively high. A typical configuration of a solid-set sprinkler system is shown in Fig. 7.3 (USEPA, 1984). Both the recommended and ineffective methods for sprinkler

7.1 Description

FIGURE 7.2 Solid-set sprinkler irrigation systems.

configurations on a terrace are shown in Fig. 7.3. Configurations shown in (A), (C) and (E) will result in effective distribution. The use of part or half-circle sprinklers shown in (B) and (F) is not recommended as the concentrate will tend to drift back untreated. Concentrate from the adjacent terrace will thus accumulate in the collection channel in (B) or the road in (F). Half-circle sprinklers furthermore have a tendency to rotate out of their specific part-circle pattern. In the case shown in (D), minor wind may result in spray from a full-circle sprinkler onto a single terrace resulting in overloading and unbalanced treatment.

7.1.1.3 Concentrate storage Additional to irrigation infrastructure, storage facilities are required to retain concentrate when irrigation is not possible, such as during periods of heavy rainfall. Storage facilities generally comprise of earthen holding tanks, which are lined with concrete. Alternatively, depending on the storage volume required, steel structures with protective coating may be used. Where land conditions allow, percolation ponds or earthen storage lagoons can be constructed as temporary storage facilities, which has the advantage of reducing the volume of concentrate via evaporation and ground percolation (Voutchkov, 2011).

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FIGURE 7.3 Sprinkler system configuration.

7.1.1.4 Subsurface drainage Where application of irrigation is in an area with a water table of less than 3 m from the ground surface, the irrigation system needs to be designed with subsurface drainage. This provides the zone in which the roots are located to flourish, and improves absorption of concentrates and growth. As groundwater aquifers may be hydraulically connected, adjacent water bodies need to be considered in the design to eliminate cross-seepage. A subsurface drainage system is simply a network of perforated drainage pipes, buried below the upper layer of soil. These pipes collect unretained concentrate, and reticulate it to a container for reuse in irrigation or disposal, should a suitable water body be available (Voutchkov, 2011).

7.2 Potential environmental impacts

7.1.2 Rapid infiltration basins Rapid infiltration basins provide a method of concentrate disposal into underlying soil layers, through a series of porous, highly permeable earthen basins (Fig. 7.4). The infrastructure required includes pipeline(s) for conveyance, suitably sized earthen basins, inlet and outlet structures with flow control devices, and equipment to measure depth automatically. Large basins may be prone to erosion and require a distribution system for the concentrate within each basin. Smaller basins generally need only a splash block at the discharge point to ensure the earthen floor is not eroded (Mickley, 2006).

7.2 Potential environmental impacts 7.2.1 Irrigation Groundwater may be negatively impacted by intrusion of saline concentrate where a shallow aquifer underlies the irrigated area. Unless the irrigation area is in a close proximity to the coast, it is likely that shallow aquifers will be less saline than concentrate. Where aquifers are deep and confined, infiltration of irrigated concentrate is unlikely to impact aquifer water quality. Regulatory authorities responsible for groundwater aquifer management will require the project developer to implement measures for mitigating the risk of potential negative impact of concentrate disposal on groundwater quality (Voutchkov, 2011).

FIGURE 7.4 Rapid infiltration basins.

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7.2.2 Rapid infiltration A groundwater discharge permit is required for the use of infiltration basins, issued by the relevant body responsible for groundwater quality management. Environmental regulations often determine the chosen concentrate disposal alternative, and need to be assessed as early as possible to ascertain the feasibility of concentrate disposal by rapid infiltration. The concentrate may contain elements which obviate disposal in the vicinity of drinking water aquifers. Dilution of concentrate prior to disposal may sometimes be allowed. Monitoring wells are essential to continuously assess the impact of concentrate discharge on groundwater quality where relevant. It is important to note that the percolated concentrate has to meet both primary and secondary drinking water standards, and any other water quality requirements applicable to the site-specific environment (Voutchkov, 2011).

7.3 Criteria and methods for feasibility assessment Land application can be considered for disposal of concentrate of small desalination plants and where a suitable and environmentally sustainable receiving environment exists. The most important consideration is compliance with regulatory requirements and groundwater quality standards. If it appears that these can be met, then additional requirements for cost viability and environmental sustainability of long-term land application will need to be assessed. Project friendly environment would have adequate available and reasonably priced land, a dry climate, suitable soils and salinetolerant vegetation, deep water table, and underground water sources contained in confined aquifers that are not hydraulically connected to the land application area. As concentrate will be generated all year round, inland, desert-like conditions are most suitable for this method of disposal. Where colder or wet weather is likely to be encountered during the year, storage facilities may be needed to retain concentrate in periods when land application is not possible. Should these periods last extensively (e.g., for more than several weeks), an alternative disposal method may be required, since storage of such large volumes may not be feasible. High salinity concentrate limits the feasibility of land application. Where no other disposal options are available, it may be possible to dilute concentrate sufficiently to meet groundwater regulations and salinity tolerance thresholds of the selected vegetation. Sources of water that may be available for dilution include groundwater from shallow aquifers and treated effluent from WWTP. To avoid excessive runoff, relatively flat sites with slopes of not more than 20% are suitable. Water table need to be at least 2 m below surface, and areas with water table shallower than 3 m are likely to require subsurface drainage. Land application requires sandy or loamy soils for successful disposal of concentrate. Acidic soils are not ideal, while neutral and alkaline soils will both inhibit trace metal leaching.

7.3 Criteria and methods for feasibility assessment

7.3.1 Irrigation Salinity is the main determinant in the viability of concentrate irrigation and selection of vegetation. Only halophytes (salt-tolerant plants which grow in the world’s salt marshes and deserts) can commonly withstand salinity far above 1000 mg/L, while most plants can only tolerate salinity below 500 gm/L. As seawater has salinity in a typical range of 35,000
44,000 mg/L, and brackish water of 800
4000 mg/L, the difficulty with using concentrates from these desalination plants is obvious. Compatibility with the vegetation must be assessed not only in terms of TDS but also trace mineral uptake, vegetative percolation factors and maximum sodium absorption ratio (SAR) (Voutchkov, 2011). Irrigation potential can be significantly improved to include irrigation of lawns, sports fields, golf courses etc. where concentrate can be diluted to have a TDS below 1000 mg/L by the addition of treated effluent from WWTPs or lowsalinity groundwater. The SAR is used to determine the maximum content of sodium in the concentrate that could be safely applied to a soil without adverse long-term impact on soil structure and permeability. SAR can be calculated by the following formula (Voutchkov, 2011): SAR 5 Na=½ðCa1MgÞ=21=2

(7.1)

where: Na 5 sodium concentration in milliequivalent per liter (meq/L); Ca 5 calcium concentration (meq/L); Mg 5 magnesium concentration in (meq/L). Concentrate with high value of SAR may not be viable to dispose of by land application: soils can be negatively affected by values of 9 and above, while most vegetation with low-salinity tolerance require levels to be maintained below 6 (Voutchkov, 2011).

7.3.1.1 TDS The osmotic potential in soil is reduced and plants take on less water when the salinity of the soils and the irrigation water is high. The rate of flow of water through the soil is also reduced by the presence of salts, and as a result, the productivity of plant growth is negatively affected by salinity increase (Fig. 7.5). Some salinity-sensitive species (including beans, strawberries, almonds, carrots, onions, avocado, mango, and most golf-course grasses) can thrive in salinities between 500 and 1000 mg/L. A more selected group of crops including sugar beet, sugar cane, dates, cotton, and barley can tolerate salinities of 2000 mg/L. Halophytes have the capability of extracting salt from water and storing it in their plant tissue. These plants can tolerate salinity in excess of 2000 mg/L (Panta et al., 2016).

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FIGURE 7.5 Salinity impact on plant yield (example of Kale Plant).

Most desalination plants generate concentrate with salinity far in excess of 2000 mg/L. As a result it can be anticipated that only in rare cases, irrigation will be a feasible method of disposal for all the concentrate generated and such disposal option will mainly be possible to implement for concentrate of brackish desalination plants. As concentrate is continuously added via irrigation, salinity accumulation in both the soil and vegetation becomes problematic unless it is monitored and managed. The accumulation rate is a factor of the salinity of the concentrate as well as the leaching rate which removes salts. To avoid shallow water tables which could further add to salinity, adequate subsurface drainage is required (Voutchkov, 2011).

7.3.1.2 Trace metals Plant growth is also negatively impacted by mineral ions. Plants suffer from toxicity when ions are absorbed and accumulated in the plant tissue. Limits of key trace metals in irrigation concentrate over both the short- and long-term have been determined as shown in Table 7.1 (adapted from USEPA, 2004; Voutchkov, 2011).

7.3.1.3 pH To avoid leaching of trace metals, a pH not higher than 6 is recommended in concentrate used for irrigation. In summary, for irrigation to be considered as a viable concentration disposal method, a number of conditions need to be met related to prevailing groundwater conditions and environmental regulations, concentrate composition and

7.3 Criteria and methods for feasibility assessment

Table 7.1 Recommended limits for trace metal constituents. Constituent

Short-term use (mg/L)

Long-term use (mg/L)

Aluminum

2.0

5.0

Arsenic

2.0

0.1

Beryllium

0.5

0.1

Boron

2.0

0.75

Cadmium

0.05

0.01

Cobalt

5.00

0.05

Copper

5.0

0.2

Iron

20.0

5.0

Lead Manganese Nickel

10.0 10.0 2.0

5.0 5.0 0.2

Selenium

0.02

0.02

Vanadium

1.0

0.1

Zinc

10.0

2.0

Notes Can cause nonproductivity in acidic soils Toxicity threshold varies. Sudan grass limit 5 12 mg/L Toxicity threshold varies. Kale limit 5 5 mg/L Most grasses tolerant at 2
10 mg/L Toxic to beans and beets at 0.1 mg/L Toxicity inactivated in neutral and alkaline soils Toxic to a number of plants at 0.1
1.0 mg/L Could contribute to soil acidification, reduction of pH Can inhibit plant growth Can inhibit plant growth Reduced toxicity in neutral and alkaline soils Toxic to many plants at relatively low concentrations Toxic to many plants at relatively low concentrations Reduced toxicity in soils with pH above 6

availability of land and saline-tolerant vegetation in need of year-round irrigation. Over and above these, an alternative disposal mechanism will be required to manage disposal during wet periods, and such duplication is likely to have significant cost implications.

7.3.2 Rapid infiltration Similar to the requirements for irrigation, the necessary conditions for rapid infiltration to be feasible include the availability of adequate amount of land in the vicinity of the desalination plant, suitable groundwater conditions and environmental regulatory requirements, high permeability soil profile, and site with minimal flooding potential located outside of the 100-year flood line. Ideally the topography should be relatively fiat to obviate the need for cut-and-fill.

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Detailed hydrogeological surveys will indicate whether soils are suitable for rapid infiltration, determining characteristics of soil permeability, and hydrogeological conditions. Soil conditions determine how water flows within the soil, both vertically and horizontally, referred to as percolation. In coarse-textured soils such as sandy soils and loams, water percolates freely, which is a condition ideal for this method of disposal (Voutchkov, 2011).

7.4 Design and configuration guidelines 7.4.1 Sizing of irrigation systems 7.4.1.1 Selection of vegetation type Most commercially cultivated trees, fruits, and vegetables are not suitable for irrigation due to their low-salinity tolerance levels, compared to the very high salinity of the desalination concentrate. To offset the cost of the system for concentrate disposal, it is preferred to irrigate crops that can provide an income stream and fulfill a need in areas of irrigation water shortage. Table 7.2 provides guidelines for the TDS threshold of various salttolerant crops (Svensson, 2005) but it must be emphasized that site-specific conditions play a significant role; thus, these should be seen only as guidelines. At the top of the table of crop tolerance are Rye and Rapeseed, which can tolerate salinity above 7000 mg/L. Some grains such as Barley and Sorghum also do well with saline water irrigation at levels above 4000 mg/L (Voutchkov, 2011). Table 7.2 Guideline for salinity tolerance of common crops. Crops

TDS threshold (mg/L)

TDS at which yield declines with 25% (mg/L)

Rye Rapeseed (Brass. Napus) Guar Kenaf Barleya Guayule Cotton Sugar Beetb Sorghum Triticale Date Palm Mango

7300 7000 5600 5200 5100 5000 4900 4500 4350 3900 2550 800

8800 8250 6550 6600 8300 6500 8000 7200 5350 10,300 7000 1000

a

Sensitive during seeding stage (max salinity 2600 mg/L) Less tolerant during germination (max salinity 2000 mg/L)

b

7.4 Design and configuration guidelines

Table 7.3 Annual productivity of halophytes irrigated with 40,000 mg/L seawater. Plant species

Productivity grams DW/m2. year

Atriplex lentiformis Batis maritima Atriplex canescens Salicornia europea Atriplex barclayana Atriplex nummularia

1794 1738 1723 1539 863 801

FIGURE 7.6 Blue-green saltbush (Atriplex nummularia).

The commercial crops in Table 7.2 show tolerance in the range of 800
7300 mg/L. Notably other halophytes can tolerate salinities of up to 40,000 mg/L (O’Leary et al., 1985). Table 7.3 presents the sustainable yield of highproductivity halophytes. These halophytes have productivity with a maximum of 1794 g of dry weight (DW) per square meter per year. This translates to an equivalent mass of dry matter of between 8 and 17 t/ha. In contrast, a freshwater crop such as alfalfa has an annual yield of between 5 and 20 t/ha. It has been known for decades that Bluegreen saltbush (Atriplex nummularia) (shown in Fig. 7.6) can be used as forage crop on marginal lands (O’Leary et al., 1985). Experience has proved that this species of halophyte can be irrigated for

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multiyear periods at loading rates between 2.1 and 2.8 m of water per year and a salinity of up to 41,000 mg/L under low leaching fraction (,10%) without reaching the threshold salinity for yield reduction (Voutchkov, 2011). Due to salinization of the root zone, use of concentrate for irrigation will require periodic application of fresh water for irrigation. Usually, the higher the salinity of the irrigation water the greater the need for periodic freshwater irrigation and drainage. A successful solution to the high salinity challenges associated with golfcourse irrigation with brackish water concentrate is its dilution with reclaimed water in a 30%
70% ratio (Messmer et al., 1999).

7.4.1.2 Irrigation area The amount of land required for spray irrigation of concentrate is substantial and unlikely to be readily available in the vicinity of the desalination plant. The area for irrigation depends on the application rate of concentrate, where the application rate in turn is a function of the salinity of the concentrate as well as the type of soil and vegetation. Application rates vary widely, typically in the range between 0.5 and 5 m/year.

Example For the example of a 100,000 m3/day hypothetical BWRO desalination plant using a spray irrigation system on A. nummularia as forage crop, the assumed concentrate application rate is 2 m/year, and concentrate is applied 365 days per year. With the desalination plant generating concentrate of 25,000 m3/day, the minimum land requirement can be calculated as:
365 days 3 25; 000 m3 =day =ð2 m=yearÞ 2 5 4; 562; 500 m ð456:25 haÞ To accommodate service roads, buffer zones, storage zones, and concentrate storage lagoons, at least 30% additional land will be required. Resulting in a land need of at least 590 ha (1450 acres).

7.4.1.3 Concentrate storage Storage facilities are required to provide backup in the event that concentrate cannot be used for irrigation for a period. Lined ponds, plastic, or concrete tanks are usually constructed for this purpose. The size of storage depends on the period for which the plant will be generating concentrate while it is not possible to irrigate. To provide flexibility in operating the irrigation system, between 2 and 5 days of storage is recommended, but this will need to be increased if rainfall at the site is likely to be higher. Specifically to the United States, USEPA has determined a guideline to the number of days of storage required as reflected in Fig. 7.7 (USEPA, 1984).

7.4 Design and configuration guidelines

FIGURE 7.7 Recommended concentrate storage time.

Additional detailed recommendations for the design of spray irrigation systems for concentrate disposal are presented elsewhere (Mickley, 2006).

7.4.2 Sizing of rapid infiltration systems 7.4.2.1 Site selection A critical success factor for rapid infiltration of the desalination plant concentrate is the selection of the basin site. Potential sites need to be of adequate size, with reasonably flat topography, and suitable soils of high percolation rate to a depth of 3 m below the basin, lithology of the vadose zone, aquifer quality and gradient, existing vegetation, and distance to nearest seeps and surface waters (Voutchkov, 2011). Exploration for RIB disposal requires hydrogeological conditions to be well documented, and installing and operating a number of boreholes to establish the groundwater profile to a maximum depth of 50 m. The geological profile of underlying soils must be determined in terms of permeability and infiltration to a depth of at least 4 m to establish the depth at which concentrate can most effectively be applied (Voutchkov, 2011).

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7.4.2.2 RIB area The size of the concentrate application surface area is determined from the hydraulic surface loading rate which depends on the effective soil conductivity. The total area is larger as the basins are supported by access roads, transmission pipe lines, buffer zones, storage facilities, maintenance buildings and space for future expansion (Voutchkov, 2011). The relationship between hydraulic loading and soil conductivity is shown in Fig. 7.8, to assist in determination of hydraulic surface loading rate of the basins (USEPA, 1984). Hydraulic conductivity (Kv) is defined as the amount of water that can pass through a unit cross-section in the soil, at unit gradient and under saturated conditions (Voutchkov, 2011).

FIGURE 7.8 RIB Loading rate as a function of soil conductivity.

7.4 Design and configuration guidelines

Example To calculate how much water can be transmitted through every square meter of horizontal area per year, for a soil with vertical conductivity of 5 cm/h: For Kv 5 5 cm/h, the hydraulic surface loading rate (HLR) is calculated as follows:


HLRcv 5 fð5 cm=hÞ 24 h=day 365 days=year 1 m2 g=ð100 cm=mÞ 3 5 438 m This rate can also be expressed as depth of water on a unit surface area:  HLRcv 5 438 m3 =year =1 m2 5 438 m=year

Hydraulic conductivity of clean water (Kv) can be determined based on a basin flooding test. This test requires construction of a small pilot scale test cell on the selected site (or potential sites). The test needs to be conducted for a period of between 2 and 4 months, applying water to the test site daily. The hydraulic conductivity designed for the concentrate is between 5% and 15% of the conductivity measured from the clean water test. Thus the actual annual design concentrate load can be calculated using the clear water rate established in the test site, adjusted by a factor that considers water quality on long-term application rate (Voutchkov, 2011). If we assume an adjustment factor of 9%, then the annual concentrate loading rate will be: LRconc

5 ð9%ÞðHLRcv Þ 5 ð0:09Þð438Þ 5 39 m=year:

This is premised on year-round operation. As basins will not be operational every day of the year, the rate will need to be decreased proportionally in anticipation of actual operational days. Regular drying is essential for the successful operation of RIB systems. Cycles of application or loading to drying periods depend on water quality and vary seasonally. For concentrate the loading to drying ratio is typically between 0.5 and 1. If other waste streams such as backwash water is blended in the concentrate, the ratio of loading to drying is a maximum of 0.2. The loading rate in all cases should not exceed 2 days. As a guideline, a typical cycle for a mix of concentrate and pretreatment backwash water during the summer period is 2 days of concentrate application followed by 7 days of drying, resulting in a cycle length of 9 days. For this same mix, during winter 2 days of application is likely to require 12 days of infiltration, yielding a 2 week cycle length. To ensure that the area is sufficient, conductivity of the least permeable soil should be used, together with worst-case weather conditions to be anticipated.

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Example The calculation of the RIB area is illustrated for a BWRO desalination plant with total concentrate discharge flow of 25,000 m3/day, soil hydraulic conductivity, Kv of 5 cm/h and summer and winter application cycle lengths of 9 days and 14 days respectively. For these assumptions and northern hemisphere location, the number of summer application cycles (i.e., April through October has 214 days) is 214/9 5 24 cycles. The number of application cycles in the winter (November through March has 151 days) is 151/14 5 11 cycles. As a result, the total annual number of concentrate application cycles is: 24 1 11 5 35. For concentrate hydraulic loading rate of 39 m/year, the RIB surface loading rate per cycle is: (39 m/year)/(35 cycles/year) 5 1.1 m/cycle. As a result, the application rate (R) during a typical 2day wet period is: R

5 1:1 m=cycle=2 days=cycle 5 0:56 m=day

The RIB areas needed for concentrate disposal during the summer and winter period are as follows:

Summer 2 Area 5 25; 000 m3 =day 3 ð214 daysÞ=ð1:1 m=cycleÞ 3 ð24 cyclesÞ 3 10; 000 m2 =ha 5 20:25 ha

Winter 2 Area 5 25; 000 m3 =day 3 ð151 daysÞ=ð1:1 m=cycleÞ 3 ð11 cyclesÞ 3 10; 000 m2 =ha 5 31:25 ha As the area needed for concentrate application in the winter is larger (31.25 vs 20.25 ha), this is the total active filtration area needed for the RIB system. The RIB system will need to include a circulation area for servicing of the ponds and for the concentrate distribution system. Therefore, the total RIB system area is typically increased with 40%
60% to accommodate these service needs—that is, the total amount of land needed for the example RIB system: 5 1:6 3 31:25 ha 5 50 ha: This area compares favorably to the area needed for the example of the spray irrigation project which requires 590 ha for disposal of the same amount of concentrate (Voutchkov, 2011).

7.4.2.3 Other key RIB design criteria Further design recommendations for infiltration basins are listed below:

• • • • • • • •

Minimum Number of RIBs 5 3; Minimum Basin Depth 5 1.5 m; Minimum Distance from RIBs to Site Boundary 5 150 m; Minimum Basin Bottom Permeability at 30 cm 5 1.4 cm/s; Maximum Depth of Ground Water Below Basin Bottom 5 3 m; Minimum Depth of Impermeable Layer Below Basin Bottom 5 10 m; Minimum Distance from Water Supply Wells 5 300 m; Minimum Number of Monitoring Wells 5 3 of which at least one should be located upstream and one downstream of the basin.

7.5 Land application costs

Groundwater mounding can be reduced in locating basins perpendicular to the direction of groundwater flow. RIBs are mostly used for small to medium BWRO plants, and usually contain less than 20 basins. Individual basins are typically less than 2 ha for small projects, and up to 5 ha for large projects.

7.4.2.4 Dikes Dikes separate basins from one another, with a width of approximately 6 m to allow vehicle access. Dikes need to be properly compacted to accommodate vehicles with load of at least 5 tons and to prevent seepage. Dikes are typically between 1 and 1.5 m high, and need to be at least half a meter higher than the maximum water level, but not much higher than this. Typically, a porous barrier such as a silt fence is provided at the toe of dikes to prevent soil fines washing out. Additional design details for RIB systems are provided elsewhere (US EPA, 1984; Mickley, 2006).

7.4.2.5 Concentrate storage Similar to land application systems for concentrate disposal rapid infiltration basin systems should be designed with between 2 and 5 days of concentrate storage facilities to provide sufficient operational flexibility. Local conditions may predicate more storage to be provided (see Fig. 7.7) (Voutchkov, 2011).

7.5 Land application costs In general, the total cost of concentrate disposal by land application varies in a range of US$0.74/m3
US$1.95/m3 of concentrate (Ziolkowska and Reyes, 2016; Arafat, 2017).

7.5.1 Spray irrigation system costs The main parameters which influence the cost of spray irrigation systems are concentrate flow rate, hydraulic loading rate, distance to the irrigation site, irrigation land cost, size of storage tank and the need/size of the subsurface drainage (Voutchkov, 2011). Given the high salinity of concentrate, spray irrigation is only likely to be feasible where fresh water sources are available for blending prior to application, and where suitable soils and salt-resistant vegetation is to be found. The construction cost of land irrigation systems as a function of the concentrate flow rate and the annual hydraulic loading rate (LRconc) is presented in Fig. 7.9 (Voutchkov, 2011). Over and above the costs shown in Fig. 7.9, there are site-specific costs which will vary, depending for example on land cost, the needed additional storage capacity, and cost of reticulating concentrate to the irrigation site (Voutchkov, 2011).

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FIGURE 7.9 Construction costs of spray irrigation system.

Cost Example A planning-level cost estimate of a spray irrigation system for the hypothetical brackish desalination plant with freshwater production capacity of 100,000 m3/day designed at 80% recovery with concentrate generated of 25,000 m3/day, is provided below. This concentrate is to be disposed of using a spray irrigation system applied to the halophyte A. nummularia, at a loading rate of 2.0 m of water per year, then from Fig. 7.9, the construction cost for the spray irrigation system is US$9161 million. (Continued)

7.5 Land application costs

Cost Example (Continued) Under the assumption that the desalination plant concentrate can be applied 365 days per year, and that an earthen storage lagoon with a retention time of 2 days (50,000 m3) is constructed at a unit storage lagoon cost of US$0.0625 million per 1000 m3, the expenditures for concentrate storage are: 5 ð50; 000 m3 3 US$ 0:0625 million=1000 m3 5 US$ 3; 125; 000 As calculated previously, for a year-around application rate of 2 m/year, the land area needed for this project is 590 ha (1450 acres). If a unit cost of land of US$5000/acre is assumed, the land acquisition cost is calculated at: 1450 acres 3 US$ 5000=acre 5 US$ 7; 250; 000 In addition to the costs listed above, the operation of the spray irrigation system will require installation of a groundwater monitoring well system to ascertain that the irrigation system does not have negative environmental impacts such as groundwater aquifer salinity increase. Such system typically has a unit cost of between US$3000 and 5000/ha, which for this example would result in additional construction cost expenditures of US$2,360,000: ð590 ha 3 US$ 4000=ha 5 US$ 2; 360; 000Þ: As a result, the total construction costs for the spray irrigation system for disposal of 25,000 m3/day of concentrate for the reference 100,000 m3/day BWRO project is a sum of the costs of the spray irrigation system 1 storage lagoon 1 land acquisition 1 monitoring system 5 US$ 9; 161; 000 1 US$ 3; 125; 000 1 US$ 7; 250; 000 1 US$ 2; 360; 000 5 US$ 21; 896; 000 ðVoutchkov; 2011Þ

In Section 6.5, the estimated cost for deep-well injection was shown to be US$13.9 million, which is lower than that calculated for spray irrigation. If however, areas such as golf courses or forage crops are available in close proximity to the desalination plant, some of the costs would not be incurred, which should be considered during selection of the most viable concentrate disposal alternative. The presented cost estimate encompasses only the capital expenditure required, while operating costs are likely to be significant as irrigation is a more labor intensive concentrate management solution that most others. Maintenance and energy costs need to be considered in producing lifecycle cost estimates. Where vegetation is irrigated, crops would need to be harvested, unless used as forage. For example, Table 7.3 indicates that the blue-green saltbush can 801 g DW/m2 of vegetation mass per year. For the specific conditions of the cost example, 4,562,500 m2 of land irrigated with concentrate will produce 3650 DW tons {[0.801 kg/m2. year 3 4,562,500 m2]/1000 kg/t} of vegetation mass per year, or approximately 37,500 tons of green vegetation mass. This crop would need to be

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FIGURE 7.10 Construction costs for RIB system.

harvested, stored and delivered for use as a forage crop or ultimately disposed to a landfill. The costs for these O&M related activities is estimated to be US $1.25 M/year (Voutchkov, 2011).

7.5.1.1 Rapid infiltration system costs Rapid infiltration basins are usually only feasible where soils have high infiltration rates, and hydraulic loading rate is likely to be higher than that of spray irrigation systems. Planning level construction costs for infiltration basins are presented in Fig. 7.10 as a function of concentrate flow and land application rates (Voutchkov, 2011).

References

Cost Example For the RIB example presented in Section 6.4 (a 100,000 m3/day BRWRO desalination plant with concentrate discharge flow of 25,000 m3/day and loading rate of 39 m/year), the construction cost of RIB system for disposal of the plant concentrate is US$22 million (from Fig. 7.10). This cost excludes storage, costs of land acquisition, delivery of the concentrate to the RIB site and for the ground water monitoring system, which are site specific. With the same assumptions as for spray irrigation (including a 2-day storage tank, with a unit storage tank cost of $0.625million/1000 m3 and unit land cost of US$5000/acre), the additional costs are: 1. storage tank construction cost: 5 ð50; 000 m3 3 US$ 0:0625 million=1000 m3 5 US$ 3:125; 000 2. cost for acquisition of 50 ha of land 5 124 acres: 5 ð124 acres 3 US$ 5000=acre 5 US$ 625; 000 3. cost for installation of groundwater monitoring system: 5 ð50 ha 3 US$ 4000=ha 5 US$ 200; 000Þ In summary, the total construction cost for RIB disposal of the plant concentrate (excluding concentrate conveyance to the site) is: 5 RIB system 1 storage tank 1 land acquisition 1 monitoring 5 US$ 22; 000; 000 1 US$ 3; 125; 000 1 US$ 625; 000 1 US$ 200; 000 5 US$ 25; 950; 000 For comparison, this cost is 18% higher than the expenditures for construction of a spray irrigation system for disposal of the same quantity of concentrate (US$21.896 million).

References Arafat, H., 2017. Desalination Sustainability: A Technical, Socioeconomic, and Environmental Approach. Elsevier. Messmer, S., Hart, G., Netzel, J., Dietrich, J., 1999. Membrane concentrate reuse by controlled blending. Florida Water Resour. J. 23, 28. Mickley, M.C., 2006. Membrane Concentrate Disposal: Practices and Regulation, Desalination and Water Purification Research and Development Program Report N. 123, second ed U.S. Department of Interior, Bureau of Reclamation. O’Leary, J.W., Glenn, E.P., Watson, M.C., 1985. Agricultural production of halophytes irrigated with seawater. Plant Soil 89, 311
321. Panta, S., Lane, P., Doyle, R., Hardie,M., Haros, G., Shabala, S., 2016. Halophytes as a possible alternative to desalination plants. Halophytes for Food Security in Dry Lands. Elsevier, New York, pp. 317
329. Svensson, M., 2005. Desalination and the Environment: Options and Considerations for Brine Disposal in Inland and Coastal Locations. SLU, Department of Biometry and Engineering, Uppsala.

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USEPA, 1984. Process Design Manual for Land Treatment of Municipal Wastewater, Supplement on Rapid Infiltration and Overland Flow. EPA 625/1-81-013a. USEPA, Cincinnati, OH. Voutchkov, N., 2011. Desalination Plant Concentrate Management. Water Treatment Academy. Ziolkowska, J., Reyes, R., 2016. Prospects for desalination in the United States experiences from California, Florida, and Texas. In: Ziolkowska, J.R., Peterson, J.M. (Eds.), Competition for Water Resources. Experiences and Management Approaches in the US and Europe. Elsevier, p. 478.

CHAPTER

Evaporation ponds

8

8.1 Description Compared to land application where concentrate is discharged into basins to infiltrate the underlaying soils or is used for irrigation of salinity tolerant vegetation, evaporation ponds are constructed to contain a discharge of concentrate in a shallow contained area from which the water in the concentrate evaporates and leaves behind the minerals, precipitated as salt crystals. These crystals are considerably less voluminous than the concentrate and can be more economically disposed of off-site or beneficially used. There are two main types of evaporation ponds: conventional ponds and salinity gradient solar ponds. The first type simply facilitates evaporation of concentrate, while the second type (solar ponds) is mainly designed to generate electricity, harvesting solar energy accumulated in the pond in the form of heat.

8.1.1 Conventional evaporation ponds Evaporation ponds can be lined or unlined earthen or concrete structures which are designed to maximize water evaporation (Fig. 8.1). These ponds have found application for seawater concentrate disposal in many arid and semi-arid areas with high evaporation rates (Rodriguez et al., 2012). Operation of evaporation ponds is simple: concentrate is periodically fed into the basins where natural solar evaporation turns water into vapor, leaving salts behind. The feed of concentrate needs to be such that a high level of salinity is achieved to optimize evaporation, thus creating the need for storage ponds to hold concentrate prior to application. Evaporation pond design needs to consider the local evaporation rate, the volume of concentrate to be disposed of daily, the number and length of days with sunshine of adequate intensity, and the life span of the desalination plant and associated period for which its concentrate is to be disposed using the ponds, as well as to make allowance for reduction in volume due to accumulation of salts at the bottom of the ponds. Alternatively, these precipitated salts may be removed periodically and either disposed of to landfill or used in a beneficial manner. (Fig. 8.2). For safety and prevention of animals or people straying into ponds, the pond site should be fenced (Voutchkov, 2011).

Management of Concentrate from Desalination Plants. DOI: https://doi.org/10.1016/B978-0-12-818045-7.00008-7 © 2020 Elsevier Inc. All rights reserved.

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FIGURE 8.1 Conventional evaporation ponds.

FIGURE 8.2 Salt crystals removed from the bottom of evaporation pond.

8.1 Description

8.1.2 Evaporation pond performance enhancements To reduce the area required and concomitant costs of evaporation, efforts have been made to improve evaporation rates through

• spray evaporation (see Fig. 8.3); • pond aeration (see Fig. 8.4); and • addition of dye to elevate pond water temperature.

8.1.2.1 Spray evaporation Mechanical spray evaporators are used in spray evaporation to disperse concentrate over the surface of the pond in a fine mist, which can increase evaporation rates by more than 20%. The drawback of spray irrigation is the energy required, which can be costly and a deterrent in locations where electricity is in short supply.

8.1.2.2 Pond aeration Aeration of ponds provide for increased contact surface with air and thus accelerates evaporation. Aerators can be submerged or floating to achieve the purpose of increased evaporation. Fig. 8.4 presents a schematic of a pond with submerged coarse bubble aeration system. Circulating concentrate to draw higher salinity concentrate to the surface has been shown to increase evaporation. The system shown in Fig. 8.5 was tested in

FIGURE 8.3 Spray evaporation ponds.

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FIGURE 8.4 Evaporation pond with submerged aeration system.

FIGURE 8.5 Solar bee pond aeration system.

Salton Sea, California, and proved to increase the evaporation rate by an average of 30%. The aeration system is solar powered and thus has low operational costs. The concentration TDS was 45,000 mg/L (Carollo, 2009).

8.1.2.3 Use of dye for enhanced evaporation Adding dye to evaporation ponds has been shown to increase the rate of evaporation. Naphthol green dye was distributed over the top 0.2 m of a 500 m2 pond, at a concentration rate of 2 mg/L. The evaporation rate increased by 13% (Ahmed et al., 2000). The cost of application of dye can be substantial in larger ponds and needs to be assessed against the gains in evaporation rate (Voutchkov, 2011).

8.1 Description

8.1.3 Solar ponds The aim of solar ponds is not only to dispose of concentrate, but also to generate electricity. The concentrate is thus put to beneficial use at the expense of evaporation efficiency. Evaporation ponds are designed to maximize the rate of evaporation while solar ponds are designed to retain heat. Solar ponds are therefore much deeper earthen lined lagoons which convert solar energy into electricity (see Fig. 8.6). Stratification happens naturally in solar ponds with distinctive layers of varying salinity forming. The surface zone typically forms at a depth between 0.3 and 0.5 m from the surface, has low-salt content and is cooler than the other two; it is also known as the upper convective zone (Walton and Swift, 2001). The salt-gradient layer forms below the surface zone with higher salinity and temperature, to a depth of between 1 and 2 m. Temperature and salinity both increase from top to bottom in the salt-gradient layer. The third and final layer has a salt content close to saturation: around 250,000 mg/L. If the salinity gradient in the salt-gradient layer is large enough, no convection occurs in the gradient zone even when heat is absorbed in the lower zone and on the bottom. This is due to the fact that higher temperature and higher salinity water at the bottom of the gradient remains denser than the colder, lower salinity water above it (Voutchkov, 2011).

FIGURE 8.6 Solar pond schematic.

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Thermal electricity is generated from the bottom layer when temperature reaches 85
C. This temperature can be achieved as the sunlight which penetrates to the bottom layer is trapped: water is invisible to visible light but opaque to infrared radiation. The heat can only escape through convection, and with concentrate having low heat conductivity, the middle layer acts as insulation (Voutchkov, 2011). Practically, solar ponds have been used in El Paso, Texas, and in Australia. A 10,000 m2 solar pond in Victoria, Australia, was tested and produced 200,000 kWh/ year of electricity (Arakel et al., 2001). Another 5000 m2 solar pond system in Australia has been documented to produce electricity of 130,000 kWh/year at power generation cost of US$ 0.12/kWh (Hignett et al., 2002).

8.2 Potential environmental impacts Evaporation ponds are designed to dispose of concentrate through evaporation rather than percolation, and ponds thus generally need to be lined. Groundwater regulations may require double lining should concentrate contain hazardous trace metals. Especially where geomembrane liners are used, leak-detection systems must be installed beneath the liner to protect groundwater. Where regulations do not require lining, and soil conditions are favorable, groundwater monitoring systems need to be in place to ensure that underlying aquifers are not affected in terms of deterioration of groundwater quality (Roychoudhury and Petersen, 2014). To effectively monitor groundwater, at least three monitoring wells are required: one in the center of the pond system and one each up- and downgradient. Groundwater quality in the wells should be monitored monthly.

8.3 Criteria and methods for feasibility assessment Similar to the requirements for land application, the feasibility of evaporation and solar ponds is predicated on suitable local conditions: arid climate enabling high evaporation rate, flat terrain, low land cost, and low precipitation and humidity (Voutchkov, 2011). Evaporation rate is influenced by the salinity of concentrate, but mostly by climatic conditions such as wind, rainfall, humidity, temperature, and solar irradiation intensity. Dry equatorial regions are likely to be most suitable for construction of evaporation ponds. As a rule of thumb, evaporation ponds may be potentially feasible if the annual rainfall is less than 0.3 m/year; the humidity is lower than 60%; and the evaporation rate of at least 1 m/year. Fig. 8.7 presents a map of the solar irradiation intensity in the United States. Arizona, Nevada, and New Mexico as well as parts of Texas and Southern California are conducive to the use of solar evaporation ponds (Voutchkov, 2011).

8.3 Criteria and methods for feasibility assessment

FIGURE 8.7 Map of solar irradiation intensity in the United States.

The pond evaporation rate is the difference between the annual ambient evaporation rate and the actual amount of annual rainfall. This difference is also known as the evapotranspiration potential. In practice, then, high rainfall often renders evaporation ponds not to be feasible. An example of this can be seen in South Florida, which has high rainfall and standard evaporation rate between 1 and 2 m/year. Adjusted for annual rainfall, this reduces the pond evaporation rate to 0.6 m/year (Carollo, 2009). The impact of this reduction is a significant increase in land needed for construction of evaporation ponds: for example more than 70 ha of evaporation ponds will be required to dispose of each 1000 m3/day of concentrate (Voutchkov, 2011). While wind has less of an impact, winds of high speed and long duration can also significantly increase evaporation rates and thus increase site suitability for ponds. In such conditions, impact of fine solids carried into the evaporation ponds during sandstorms on pond capacity and performance need to be considered in the design and operation of the pond system. An increase in salinity leads to a decrease in evaporation rate. Notwithstanding, it is generally less costly to evaporate smaller volumes of concentrate with higher salinity, as much of the evaporation pond cost is related to the volume to be disposed of. Reducing the volume of concentrate has cost benefits when it is disposed using evaporation ponds.

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8.4 Design and configuration guidelines Evaporation ponds are designed as a function of the volume of concentrate disposed, the evaporation rate, and the annual rainfall. Basic design guidelines for evaporation ponds encompass building at least two rectangular or square ponds with a minimum depth of 2.5 m, separated by dikes, and removing precipitated salts from the pond bottom approximately once every 2 years. In areas of high wind, a higher number of smaller ponds is preferred as it decreases the risk of wave damage to the dikes in high winds. Usually ponds are designed to accommodate not only the maximum operating volume of concentrate but also a 24 hour, 1-in-100 year storm event applicable to the area. The pond depth is calculated to hold this volume plus an additional 0.5 m of freeboard (Voutchkov, 2011).

8.4.1 Sizing of conventional evaporation ponds 8.4.1.1 Pond depth While evaporation rate is positively impacted upon by shallow depth, such pond configuration requires a larger surface area to dispose of the same volume of concentrate and thus it is likely to increase cost. Practical experience shows that the reduction in evaporation rate does not increase very much with depth, and that deeper ponds are indeed more cost effective. Based on an evaporation pond study, an increase in depth from 0.1 to 2.5 m had only a 4% decrease in evaporation rate (Mickley, 2006), and the optimal depth for evaporation was found to be approximately 0.5 m. Ponds are commonly between 2.5 and 5 m deep, which is efficient in terms of construction cost, and also provides area for salt accumulation on the pond floor, contingency water storage, and rainwater retention capacity.

8.4.1.2 Pond dikes Ponds are separated by dikes, where dikes are earthen structures compacted to not less than 90% of Proctor density. Dikes are typically in the region of 6 m wide for vehicular access, with side slopes between 2:1 and 4:1, and height determined based on by the storage required.

8.4.1.3 Pond liner To prevent entrance of concentrate into the underlying aquifer, evaporation pond floor and dikes are covered with low conductivity liners at least 2 m beyond the dike walls toward the access road. Naturally available clay is sometimes applied or mixed with bentonite to line the ponds. Alternatively, plastic liners such as PVC, HDPE, or Hypalon can be used (see Fig. 8.8). Liners must have hydraulic conductivity of less than 1027 cm/s and seepage rate of less than 5 mm/day. Design requirements should specify liner durability to meet at least a 20-year project life, considering both contact with high salinity concentrate and exposure to UV light.

8.4 Design and configuration guidelines

FIGURE 8.8 Lined evaporation ponds.

Pond liner material dictates the required minimum liner thickness:

• • • • •

In-situ clay: 1 m Compacted clay: 0.5 m Soil and Bentonite mix: 0.1 m Geomembrane liner: 30 mil (0.76 mm) HDPE Liner: 60 mil (1.52 mm)

Construction of clay liners that prevent seepage require careful execution and must meet a number of requirements:

• clay material must have 30% passing #200 sieve (0.074 mm); • clay must have a liquid limit minimum of 30% and plasticity index of at least 15%;

• clay liners must be compacted in at least four layers, of maximum thickness 200 mm each;

• compacted to 95% of Proctor maximum dry density. If concentrate pH falls outside of the 69 range, which is the range of tolerance of most pond liners, the pH has to be properly adjusted prior to discharge into the ponds (Voutchkov, 2011). Care should be exercised in the operation of shallow ponds, which dry more quickly, leading to extended liner exposure to sunlight, heat and potential damage. Clay liners are prone to cracking when repeatedly exposed to wetting and drying cycles.

8.4.1.4 Pond area The required pond surface area is a function of local climatic conditions, which determine the evaporation rate. Evaporation rate is measured in meters per year, for freshwater 1 m/year is equivalent to 27.4 m3/day ha (Voutchkov, 2011). In the United States, the most favorable areas for evaporation rates are to be found in Southern Arizona, Western Texas, and Southern California. As shown on Fig. 8.9, the average annual evaporation rates in these regions vary between

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FIGURE 8.9 Average evaporation rates in arid regions across the world.

0.7 and 1.5 m/year (which translates to 19.8 and 40.7 m3/day ha). For comparison, in the Middle East (e.g., Saudi Araba and Oman) evaporation rates along the Persian Gulf coast typically vary in a range of 1.52.5 m/year and average 2.1 m/year, while in the desert regions of these countries they can reach 4.04.5 m/year. In Egypt, the average and maximum evaporation rates along the Mediterranean coast are 2.7 and 3.9 m/year respectively (Hassan, 2013), while in the desert areas they reach 5 m/year (Svensson, 2005). In Eastern Australia (Sydney) and Western Australia (Perth) the average/ maximum evaporation rates are 1.3/1.6 and 1.5/1.9 m/year, respectively. With the current trend of worldwide global warming, these rates are expected to increase with 6%8% over the next 10 years (20202030)—for example with an average of 0.7% per year. As salinity decreases evaporation rate, the average evaporation rates published in technical literature should be reduced for TDS level in the concentrate to compensate for salinity. Site-specific pilot testing using freshwater and concentrate will provide the actual reduction ratio to apply. Where it is not possible to establish a site-specific factor, it is suggested that concentrate evaporation rate can be assumed to be 70% of the freshwater evaporation rate for the same location (Mickley, 2006). For BWRO concentrate, the evaporation rate is between 80% and 90% of the freshwater evaporation rate in the same location (Voutchkov, 2011).

8.5 Evaporation pond costs

A factor of safety of 20%25% is often applied to the calculated pond capacity, to allow for fluctuations in volume of concentrate generated as well as unseasonal rain events. The total evaporation pond surface area can be calculated as a function of the freshwater evaporation rate using the following formula: Ap 5

ðQconc 3 CF Þ ðSF 3 SERÞ

(8.1)

where Ap is the active evaporative pond area, ha; Qconc is the concentrate flowrate in m3/day; SER is the standard evaporation rate for freshwater, m3/day ha; CF is the contingency factor; SF is the factor for conversion of freshwater evaporation rate to concentrate evaporation rate.

Example For 100,000 m3/day BWRO plant which generates 25,000 m3/day of concentrate and is located in Southern Arizona, with local freshwater evaporation rate of 40.70 m3/day ha, the active area of the evaporation pond can be calculated as follows: Adding 20% contingency, CF is 1.2, and assume SF at 0.8 for BWRO. Then the active evaporation pond area needed is calculated as:

 Aep active 5 25; 000 m3 =day ð1:2Þ=ð0:8Þ 40:70 m3 =day ha 5 921 ha The area estimate assumes: 20% contingency (i.e., CF of 1.2), and conversion factor SF of 0.8 for BWRO. Taking into consideration that evaporation pond systems also have dikes, the total pond area, including the dikes, could be determined using the following formula (Mickley, 2006): h
n
1=2 io (8.2) Aep total 5 Aep active 1 1 0:325ðHdike Þ= Aep active where Hdike is the height of the dikes in meters and Aep total and Aep active are in hectares. For the example earlier and dike height of 2.5 m: n o Aep total 5 ð921 haÞ 1 1 ½0:325ð2:5 mÞ=ð1052Þ1=2  5 943 hað2330 acresÞ

For the aforementioned reference example, the land requirement is 1.6 times higher than that needed for spray irrigation (590 ha) and 19 times higher than that for rapid infiltration basins (50 ha) (see Section 7.4). While other factors would effect land requirements of concentrate disposal methods, the example emphasizes that evaporation pond disposal of concentrate has by far the largest land requirement.

8.5 Evaporation pond costs The principle construction cost factor for evaporation ponds is its surface area which depends on the evaporation rate, which, in turn, is determined by the local

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climate conditions—humidity and solar irradiation intensity. Other evaporation system components which have significant contribution to the construction costs include the pond liners, and the earthworks. The cost of concentrate disposal using evaporation ponds ranges from US$ 3.3/m3 to US$ 10.0/m3 of processed concentrate which renders it one of the costliest methods for brine management (Ziolkowska and Reyes, 2016; Arafat, 2017). Fig. 8.10 graphically represents the construction cost of evaporation pond systems as a function of the evaporation rate and the concentrate flow. This representation is premised on the use of geocomposite liner, which typically contributes 25%30% of the total construction cost.

FIGURE 8.10 Construction cost for evaporation pond system.

References

Cost Example The construction cost of an evaporation pond system for disposal of 25,000 m3/day of concentrate generated by 100,000 m3/day brackish water desalination plant estimated for an evaporation rate of 1.5 m/year (i.e., Southern Arizona), using Fig. 8.10 is US$ 87,320,000. This cost excludes the expenditures for land acquisition, delivery of the concentrate to the pond site and the cost of installation of a leak-detection system. Land cost: Assuming unit land cost of US$ 5000/acre the expenditure for land acquisition is: 5 2664 acres 3 US$ 5000=acre 5 US$ 13; 320; 000 Leak-detection system cost: The expenditure for the leak-detection system, needed for groundwater quality monitoring is projected using a unit cost of US$ 8500/acre (Nicot et al., 2007): 5 2664 acres 3 US$ 8500=acre 5 US$ 22; 644; 000 As a result, the construction cost excluding concentrate delivery to the site, for the construction of evaporation pond system for disposal of the BWRO plant concentrate is: 5 Evaporation pond system cost 1 Land cost 1 Leak detection system cost: 5 US$ 87; 320; 000 1 US$ 13; 320; 000 1 US$ 22; 644; 000 5 US$ 123; 284; 000 The evaporation pond system cost is approximately 5.6 times higher than that for construction of a spray irrigation system (US$ 21,896,000) and 4.7 times higher than that for RIB system (US$ 25,950,000) for disposal of the same quantity of concentrate.

The order of magnitude difference in land area required can be attributed to the evaporation rates being very much lower than soil uptake rates: therefore the disposal of the same volume of concentrate requires much more land. Pond liners also add significantly to the cost of evaporation ponds, and these liners are obviously not required for land application (Voutchkov, 2011).

References Ahmed, M., Shays, W.H., Hoey, D., Mahendran, A., Morris, R., Al-Handaly, J., 2000. Use of evaporation ponds for brine disposal in desalination plants. Desalination 130, 155168. Arafat, H., 2017. Desalination Sustainability: A Technical, Socioeconomic, and Environmental Approach. Elsevier. Arakel, A.M., Hoey, D., Coleman, M., 2001. Integrated power, water and salt generation: a discussion paper. Desalination 134, 3745. Carollo Engineers, 2009. Water Desalination Management and Piloting, South Florida Water Management District, Sunrise, Florida. Hassan, M., 2013. Evaporation estimation for Lake Nasser based on remote sensing technology. Ain Shams Eng. J. 4 (4), 593604.

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Hignett, C., White, R., Rechten, H., 2002. Solar ponds  technology and economics. ,http://soilwater.com.au/solarponds/. (accessed November 2019). Mickley, M.C., 2006. Membrane Concentrate Disposal: Practices and Regulation, Desalination and Water Purification Research and Development Program Report N. 123, second ed. U.S. Department of Interior, Bureau of Reclamation. Nicot, J.-P., Gross, B., Walden, S., Baier, R., 2007. Self-sealing Evaporation Ponds for Desalination Facilities in Texas. Texas Water Development Board, Austin, Texas. Rodriguez, F.A., Santiago, D.E., Franquiz Soarez, N., Ortega Mendez, J.A., Veza, J.M., 2012. Comparison of evaporation rates for seawater and brine from reverse osmosis in traditional saltworks: empirical correlations. Water Sci. Technol., Water Supply 12 (2), 234240. Roychoudhury, A.N., Petersen, J., 2014. Geochemical evaluation of soils and groundwater affected by infiltrating effluent from evaporation ponds of a heavy mineral processing facility, West Coast, South Africa. J. Geochem. Explor. 144, 478491. Svensson, M., 2005. Desalination and the Environment: Options and Considerations for Brine Disposal in Inland and Coastal Locations, SLU, Department of Biometry and Engineering, Sweden. Voutchkov, N., 2011. Desalination Plant Concentrate Management, Water Treatment Academy. Walton, L.H., Swift, J.C., 2001. Desalination coupled with salinity-gradient solar ponds. Desalination 136, 1323. Ziolkowska, J., Reyes, R., 2016. Prospects for desalination in the United States experiences from California, Florida, and Texas. In: Ziolkowska, J.R., Peterson, J.M. (Eds.), Competition for Water Resources. Experiences and Management Approaches in the US and Europe. Elsevier, p. 478.

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9

9.1 Overview Zero-liquid discharge (ZLD) is an alternative to traditional concentrate disposal methods and aims to eliminate the need for disposal of concentrate thereby achieving the environmental principles of sustainability and resilience. No single concentrate treatment process is currently available to achieve ZLD or near-ZLD, though a combination of processes can be applied. The cost of new technologies, market value and energy requirements are likely to limit the implementation of large scale ZLD systems, but it is recognized that reducing concentrate volume is beneficial and is likely to be more widely practiced in the future (Subramani and Jacangelo, 2014; Morillo et al, 2014). Key drivers for the expanding use of ZLD systems in recent years include stricter regulations for concentrate disposal, water scarcity, increasing costs of conventional concentrate disposal methods, environmental, physical and cost constraints for release of large volumes of concentrate, especially in inland desalination plants and public environmental awareness (Tong and Elimelech, 2016). ZLD technologies combine thermal or membrane brine concentrators and thermal crystallizers that convert concentrate into highly purified water and solid dry product suitable for landfill disposal or for recovery of useful salts or beneficial reuse. These systems typically consist of concentrate conveyance pipelines to and from the equipment, thermal or membrane concentration system, crystallizer towers, heat exchangers, de-aerators, seed slurry storage and delivery system as well as vapor compressors and recirculation pumps. In addition, the crystallizer system contains concentrate slurry dewatering equipment. While thermal evaporator/crystallizer systems are the most commonly used ZLD technologies, other brine concentration technologies, high recovery processes, and their combination into cost-competitive concentrate management systems are discussed in detail elsewhere (Mickley, 2008; USBR, 2009; Tong and Elimelech, 2016; Panagopoulos et al., 2019).

Management of Concentrate from Desalination Plants. DOI: https://doi.org/10.1016/B978-0-12-818045-7.00009-9 © 2020 Elsevier Inc. All rights reserved.

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9.2 Disposal system technologies 9.2.1 Thermal brine concentrators Conventional ZLD systems deploy thermal brine concentration technology to increase the concentration of the desalination plant brine to a level that could be further used to crystalize the salts in the brine and produce a dry residual. Thermal brine concentrators are single-effect thermal evaporator systems which convert concentrate from a liquid phase into a dense slurry by boiling it in a tall vertical packed tower. In these mechanical vacuum compression (MVC) systems, the vapor produced from boiling of concentrate is pressurized by the compressor and is then recirculated for more vapor production (Fig. 9.1). Before entering the evaporator, the feed concentrate passes through a heat exchanger with the distillate and through a de-aerator that removes noncondensable gases such as carbon dioxide and oxygen. A scale inhibitor is typically added to the feed concentrate to prevent scaling of the evaporator and heat exchanger chambers.

FIGURE 9.1 Schematic of thermal brine concentrator.

9.2 Disposal system technologies

The conditioned concentrate is pumped to the top of the evaporator and distributed over the surface of the evaporation chamber heat transfer tubes (heating element) in the form of a thin film which travels by gravity to the bottom of the evaporator chamber. A portion of this traveling thin film of concentrate is evaporated, and the rest is collected at the bottom of the evaporator to be recirculated for another evaporation cycle. The vapor generated in the evaporator is evacuated from the evaporator chamber and is pressurized by a vapor compressor. This superheated vapor condenses on the outside surface of the heat transfer tubes and the condensate (distillate) formed on the tube surface is collected and evacuated from the evaporator. It is used to preheat the incoming feed concentrate and then collected as distillate. Usually distillate TDS concentration is lower than 10 mg/L. With every cycle, a small portion of the concentrated saline stream is removed from the reactor in the form of slurry. The high-salinity slurry generated in the brine evaporator could be either solidified in an evaporation pond or crystalized by mechanical drying equipment (crystallizer or drier). The highly concentrated brine slurry can then be dewatered to a solid earth-like material by centrifuge and thereafter it can be disposed of to a landfill in a solid form as dry residual. Alternatively, the concentrated salt product could be used for commercial applications. Usually, existing thermal concentrator technology can evaporate between 90% and 98% of the concentrate (i.e., can reduce concentrate volume by between 10 and 50 times). As a result, TDS content of the high-salinity concentrate produced by these systems can reach 20,000 250,000 mg/L. The maximum salinity that can be achieved by evaporators is limited by the formation of precipitates of various mineral salts such as glauberite (Na2Ca(SO4)2), sodium chloride (NaCl), and sodium sulfate (Na2SO4). Vapor compression driven concentrators are very energy efficient, using approximately 10 times less energy than single-effect steam-driven evaporators. Typically, energy for the concentrators is supplied by a mechanical vacuum compression system. Both capital and operations and maintenance (O&M) costs associated with the use of thermal brine concentrators are directly dependent on the volume of the concentrate processed by these systems. Since the expenditures for preconcentration of brine before thermal evaporation are usually lower than the costs of providing additional evaporator capacity, concentrate volume minimization processes are commonly used in such systems. Thermal brine concentrators rely on highly energy intensive technology that consumes 7 10 times more energy than the SWRO system generating concentrate (Mickley, 2008; Burbano and Brankhuber, 2012). These concentrators are also capital cost intensive as they require expensive high-quality stainless steel or titanium to prevent corrosion from the high-salinity concentrate they process.

9.2.2 Membrane brine concentrators It is apparent that conventional thermal brine concentration is highly energy intensive and costly in terms of capital investment. In response, the desalination

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industry has developed another class of technologies which rely on membrane separation rather than evaporation for brine concentration. The four most widely applied membrane brine concentration systems are based on the following processes: osmotically assisted reverse osmosis (OARO); electrodialysis (ED); forward osmosis (FO); and membrane distillation (MD). Osmotic pressure of sodium chloride solution increases from 59 bars at 70,000 mg/L to 211 bars at salinity of 250,000 mg/L. The existing standard SWRO membranes available on the market are designed to withstand up to 83 bars and typically produce concentrate of up to 70,000 mg/L, operating at maximum recovery of 50% 55%. In addition, to the practical pressure limits, recovery that can be obtained using standard commercially available RO elements is also limited by the high risk of scaling and membrane fouling. However, over the last 10 years, a number of membrane manufacturers have introduced ultrahigh pressure RO membrane elements, which can operate at up to 120 150 bars and concentrate brine up to 130,000 mg/L of total suspended solids.

9.2.3 Osmotically assisted reverse osmosis OARO is a pressure driven membrane technology which combines the principle of reverse osmosis and FO to concentrate brine while producing a low salinity stream. Similar to RO, the OARO applies hydraulic pressure to transport water through RO membranes but the osmotic pressure needed for water transport is reduced by adding water of salinity higher than the feed water to the permeate side of the membranes in order to minimize the pressure applied on the highsalinity side of the membrane to less than the maximum pressure that the conventional membranes can handle (83 bars). Such high-salinity water is typically referred to as a “sweep solution” and its purpose is to create osmotic draw (FO movement) of water from the high-pressure side of the membrane to the low pressure side of the membrane. The OARO systems have found commercial implementation in various configurations such as the CounterFlow Reverse Osmosis (CFRO) system developed by the Massachusetts Institute of Technology (MIT) and commercialized by Gradient (Chung et al., 2017) and the Cascading Osmotically Mediated Reverse Osmosis (COMRO) system created by the Columbia University (Chen and Yip, 2018). Alternative OARO configurations are discussed in detail by Peters and Hankins (2019). While the SWRO membranes which are part of the OARO system are conventional RO elements, the OARO membranes technically operate as FO membranes with draw solution being the sweep solution. The most widely used in practice OARO membranes to date are hollow fiber SWRO membranes, in which the back (tail) side of the hollow fibers is fed with sweep solution while the front side is used to evacuate low salinity permeate. The feed direction of the sweep solution is opposite to the feed direction of the brine that would need to be concentrated. This feed brine that is being concentrated is applied on the high-pressure (outer) side of the hollow fibers. Most recently, hollow fiber manufacturers have

9.2 Disposal system technologies

developed OARO elements which have an FO design that is more closely tailored to their use in brine concentration system configuration. However, the next generation of OARO elements is expected to be FO elements of spiral-wound configuration. The existing OARO processes can concentrate brine to levels of 120 250 ppt and yield water recovery of 35% 50%. The energy use of these processes is typically between 7 and 15 kWh/m3 and is proportional to the target TDS level of the concentrated brine. The cost per cubic meter of concentrated brine varies between US$1.5 and 2.5/m3. However, such cost is expected to be reduced as the OARO technology is advanced. Fig. 9.2 illustrates a hypothetical CFRO system: The lefthand-side box is fed with brine (at 90 g/L) from the desalination plant which is targeted for achieving concentration of up to 150 g/L. The box on the righthand-side consists of a conventional SWRO component that generates sweeping solution of 90 grams per liter (g/L). This SWRO concentrate is fed as a sweep solution to the back end of the permeate side of the upstream OARO system (middle box) and moves in a direction counter to that of the feed water. The feed water from the lefthand-side to the middle box is shown to have salinity of 60 g/L. Since the 60 g/L feed water is pressurized to overcome the osmotic pressure of the difference between the feed water and the sweep solution, fresh water moves from the high-pressure side to the low pressure side of the OARO membrane thereby diluting the sweep solution from 90 to 30 mg/L. As a result, the concentration of the feed water on the high-pressure side of the OARO membrane (middle box) is concentrated from 60 to 120 g/L. In turn, this 120 g/L concentrate is used as a sweep solution to the lefthand-side box. As a result, the CFRO system concentrates brine from 90 to 150 g/L while producing freshwater from the SWRO component of this system (depicted as B0 g/L on Fig. 9.2). Another OARO membrane technology at advanced stage is developed by Hyrec (Panagopoulos et al., 2019). This technology utilizes two feed streams: the first feed stream is the same desalination plant feed stream, processed through the

FIGURE 9.2 Process schematic of CFRO brine concentration system.

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FIGURE 9.3 Process schematic of hyrec brine concentration system.

RO membranes and leaving the module with increased concentration. Some of this concentrated RO stream is recycled back to the opposite side of the membranes as a second feed stream; it is diluted through the membranes and leaves the module with decreased concentration. The reduced osmotic-pressure difference between the feed and the permeate sides allows the treatment of ultrasaline feeds at pressures as low as 70 bars as shown in Fig. 9.3. The Desalination Technology Research Institute of the Saline Water Conversion Corporation (SWCC) of Saudi Arabia has recently developed and patented a dual brine concentration technology (Dual Concentrator) that allows generation of two high mineral content streams from seawater, depicted in Fig. 9.4. Fig. 9.4 schematically shows a membrane dual concentrator. The dual concentrator has a nanofiltration (NF) system to separate divalent ions from the seawater. As the NF permeate has a very low divalent ion content, scale deposition on the downstream SWRO membranes is minimized, and thus the downstream twostage SWRO system has significantly higher recovery (55% 65%) than conventional SWRO systems (40% 45%) (Al-Amoudi et al., 2019). To make the NF reject stream suitable for beneficial use, this reject is further concentrated using hollow fine fiber (HFF) FO membrane system, shown as Concentrator 2. A small portion of NF reject flows through the bore-side of the HFF-FO membrane, and the rest of NF reject is pressurized and flows through the shell-side. For a typical SWRO system which desalinates Red Sea seawater of 42 46 ppt, approximately 7% of NF reject is considered as the bore-side flow to optimize the osmotic pressure difference below the membrane busting pressure.

9.2 Disposal system technologies

FIGURE 9.4 Schematic of membrane dual brine concentrator.

The bore-side flow is diluted while receiving fresh water from the pressurized shell-side, and this product from the bore-side of HFF-FO is blended with the mainstream of NF permeate prior to being directed for further processing through the downstream SWRO system. The reject stream of HFF-FO (shell side) is of very high concentration of divalent calcium and magnesium salts, so these divalent minerals can be cost effectively extracted and applied for production of various beneficial commercial products or reused in the production of desalinated water as a source of minerals for posttreatment of the SWRO permeate. After NF treatment, the saline water fed to the SWRO system has a lower TDS concentration which allows an increase in the recovery of the SWRO system. Pilot testing at the Umm Lujj desalination plant in Saudi Arabia shows that for a typical salinity of Red Sea seawater of 44 ppt, the SWRO system recovery is 58% for the first-stage SWRO and 20% for the second-stage SWRO. The content of divalent ions in the SWRO brine is limited and scaling is thereby mitigated. The only remaining obstacle for further concentration of the brine is the need to apply feed pressure to the SWRO elements that is higher than their bursting pressure. In order to overcome this challenge, a counter-current flow HFF-FO is included again as a membrane brine concentrator (Concentrator 1 in Fig. 9.4). For the first stage of Concentrator 1, the bore-side diluted stream is designed to have similar TDS as that of the first-stage SWRO feed. For the second stage of Concentrator 1, the bore-side diluted stream is designed to have TDS concentration similar to that of the second-stage SWRO feed. Under this configuration, all the diluted steams are recycled, and the only brine discharge is the highest concentration brine from the last stage. Note that both Concentrators 1 and 2 are designed to use the minimum number of pumps required, and energy recovery devices are utilized in the final reject streams for efficient energy use. The prototype dual brine concentrator was tested for six months at the Umm Lujj SWRO plant in Saudi Arabia. The key test results are summarized in Tables 9.1 and 9.2.

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Table 9.1 Energy use for SWRO desalination and brine concentration. Desalination system component

Overall recovery

SEC

Energy recovery device

1. Pump 1 SWRO only 2. Dual brine concentrator (Fig. 9.1) 3. Brine concentrator—total energy use

50.0% 61.3%

2.91 kWh/m3 4.56 kWh/m3

95% efficiency 80% efficiency

Δ11.3%

11.85 kWh/m3

Notes: Feed seawater TDS 5 45,000 ppm, T 5 25 C, product water TDS 5 300 ppm, back pressure on SWRO permeate and final brine discharge 5 2 bar, pump 3 motor efficiency 5 85%.

Table 9.2 Ion concentrations (ppm) of seawater and the two brine rejects of dual brine concentrator. Ions

Seawater

Brine reject 1

Brine reject 2

Cl 2 Na 1 SO422 Mg11 Ca11 K1 HCO3 2 TDS

24,904 13,863 3414 1657 502 482 171 45,000

86,417 50,602 6434 3486 1183 1,738 391 150,279

42,835 21,331 11,321 5128 1426 764 496 83,300

Notes: Ion rejections of NF are based on pilot test.

Review of the information in Table 9.1 indicates that the dual brine concentrator uses less than 12 kWh/m3 of energy. Table 9.2 shows that a two-stage brine concentrator system can concentrate the NaCl enriched Brine Reject 1 to 150,000 ppm at which concentration the brine can find various industrial uses. Review of the Brine Reject 2’s mineral content reveals that the concentration of divalent ions in this brine is approximately three times higher than that in seawater and could be a valuable product. This brine can be applied for the remineralization of desalinated water, adding both calcium and magnesium hardness, and can be used as liquid fertilizer of high-magnesium demanding crops such as mangos. Using calcium and magnesium extracted from desalination brine is a step forward toward elimination of the use of commercial chemicals in the production of desalinated water. Further concentrated, the magnesium rich NF brine can also be processed for extraction of solid magnesium via ion-selective resins, which then can be used as raw material for the automotive and other high-tech industries. The brine from a reverse osmosis system which is downstream from a NF system is of very high sodium chloride content which can be used as source material

9.2 Disposal system technologies

by the chloralkaline industry. This industry cannot use brine with high calcium and magnesium content, but after NF desalination, the SWRO brine contains a low-enough content of these minerals to be suitable for the chloralkaline industry.

9.2.4 Forward osmosis FO is a membrane-based technology which uses osmotic pressure gradient rather than hydraulic pressure to convey fresh water through the membrane thereby leaving concentrated brine on the feed side. In the FO, a special solution that can cause very high osmotic pressure (referred to as the “draw solution”) is used to produce an osmotic pressure gradient across the semipermeable FO membrane as shown in Fig. 9.5. At the end of the FO process the draw solution is separated from the fresh water: usually by reverse osmosis or low-temperature distillation and recycled back to the FO system. If the FO is operated without draw solution recovery (also referred to as “regeneration”) this process is more energy efficient since no external pressure is required to overcome osmotic pressure. The only pressure applied is to convey the concentrated brine and the draw solution through the FO system and to overcome the transmembrane pressure of the FO membranes. Although early studies indicated that FO membranes were low-fouling, recent studies where FO was operated at flux comparable to that of SWRO membranes (e.g., 15 20 L/m2
h) revealed that fouling is also an issue in FO (Bell et al., 2017). The draw solution has a key function in creating the osmotic pressure

FIGURE 9.5 Schematic of forward osmosis system.

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gradient and therefore the concentration and type of draw solution have significant impact on the efficiency of the FO technology. A number of different draw solutions have been tested in recent FO brine concentration systems, including organic solutes, inorganic salts, nanoparticle-based solutes, and volatile solutes. However, none of them have been found to be “ideal” for brine concentration. In addition to the lack of cost-attractive, easy to regenerate draw solutions, challenges to the use of FO technology for brine concentration has been the limited commercial availability of appropriate FO membranes. These are required to operate at a flux comparable to SWRO elements, have low transmembrane pressure, have minimal reverse salt flux and which do not exhibit significant concentration polarization. Therefore at present there is a limited number of commercially available FO systems that can be used for cost-effective brine concentration. Compared to RO or OARO, the specific energy consumption of FO systems without draw solution recovery (e.g., systems where the draw solution and permeate are directed to an evaporation pond) are significantly lower (0.2 0.9 kWh/m3). However, when the draw solution regeneration is included, the energy use of existing FO systems usually exceeds that of OARO and is in a range of 10 14 kWh/m3. While the annualized capital cost of the FO system itself is comparable to that of OARO (US$ 0.5 0.7/m3 of fresh water produced), the cost of draw solution recovery usually increases this cost significantly. An example of a FO-based ZLD system is the 650 m3/day brine concentration facility for the Chagxing power plant in Zhejiang Province in China (Oasys Water, 2014). This system treats a mixture of flue gas desulfurization (FGD) wastewater and cooling water blowdown. The feed water to the FO brine concentrator is first concentrated to 60,000 mg/L by the RO system. The brine concentrator uses ammonium/carbon dioxide draw solution and concentrates the brine to 220,000 mg/L. As a final step the FO brine is fed to a crystallizer and the FO permeate which has a TDS of 100 mg/L or less is processed through the secondary RO system and used as a boiler makeup water.

9.2.5 Crystallizers In order to achieve ZLD, the high-salinity brine produced by the thermal or membrane concentrators is further processed in brine crystallizers. Crystallizers precipitate highly soluble salts from concentrate such as sodium carbonate, sodium sulfate, and sodium chloride into solid residuals. Similar to brine concentrators, this technology applies vacuum compression and produces salt crystals and distilled water by forced circulation of slurry or dense concentrate in tall cylindrical reactors (crystallization vessels). The crystallization vessels are vertical units operated using steam supplied by a boiler or heat provided by vacuum compressors for evaporation (Fig. 9.6). Vapor compressor driven crystallizers are typically operated in a forced circulation mode. The viscous brine is pumped through submerged heat exchanger tubes under pressure thereby preventing boiling and scaling inside the heater tubes. Concentrate or concentrate slurry from the evaporator is fed to the

9.2 Disposal system technologies

FIGURE 9.6 Schematic of concentrate crystallizer.

crystallizer vessel, passed through shell-and-tube heat exchanger and heated by vapor introduced by the vacuum compressor. The heated concentrate then enters the crystallizer where it is rotated in a vortex. Concentrate crystals are formed in the vessel and the crystalline mineral mass is fed to a centrifuge or a filter press to be dewatered to a solid state. The mineral cake removed from the concentrate contains 85% solids and is the only waste stream produced by the crystallizer. The low salinity water separated from the concentrate is collected as distillate at the condenser. The filtrate from the filter press or centrate from the dewatering centrifuge is typically blended with the RO feed or permeate. The recovery of salts and reuse of the liquid separated from the concentrate is practically 100%. Usually, for small volumes of concentrate (10 50 m3/day), steam-driven evaporators are used. Steam can either be produced using a standard boiler system or it could be supplied by a nearby industry that generates steam for their main production processes. Usually steam for larger crystallizer systems is produced by electrically driven vacuum compressors or supplied by industrial installations in the vicinity of the desalination plant. Similar to brine concentrators, crystallizers are made of corrosion-resistant materials and therefore are very costly. They consume approximately three times more energy per unit of processed concentrate than concentrators as removing water from the concentrate by evaporation becomes more difficult with the increase in concentrate salinity.

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FIGURE 9.7 Schematic of evaporator-crystallizer system.

Commercially available crystallizers typically have unit processing capacity in a range of 50 500 m3/day and are available from the same manufacturers that offer thermal brine concentrator systems and driers.

9.2.6 Evaporator-crystallizer system Often brine concentrator and crystallizer systems are combined into one evaporator-crystallizer system. In this system, the brine slurry produced by the evaporator is fed into the crystallizer (see Fig. 9.7). Fig. 9.8 depicts an evaporator-crystallizer system designed to process 1000 m3/day of concentrate.

9.3 SWRO systems for increased recovery and brine concentration A recent trend aimed at the reduction of the brine volume and the cost for freshwater production is the use of SWRO system configurations that allow an increase in the overall recovery of seawater desalination plants from a typical range of 40% 45% to between 55% and 60%. Two recently developed highrecovery SWRO systems, which have significant potential for improving the overall plant recovery are: FEDCO’s Multistage Dual Turbocharger (MSDT) system and Hitachi’s E-REX system. Both system configurations aim at maximizing permeate recovery by uniform distribution of flux among all of the membrane elements within the SWRO vessels.

9.3 SWRO systems for increased recovery and brine concentration

FIGURE 9.8 1000 m3/day evaporator-crystallizer.

FIGURE 9.9 High recovery SWRO system with multistage dual turbochargers (MSDT).

9.3.1 Multistage dual turbocharger high recovery SWRO system The Multistage dual turbocharger (MSDT) system (see Figure 9.9), which incorporates one high-pressure feed pump (HPP) and two-stage SWRO configuration, which are designed to achieve uniform flux distribution of all seven elements within the membrane vessels by reducing the feed pressure to the first-stage SWRO elements and operating these elements at relatively low recovery and flux (Barrasi, 2018). The concentrate from the first-stage SWRO elements is then treated through a second set of SWRO elements to obtain a total SWRO system recovery of 55% 60%. Each of the two SWRO stages is equipped with highpressure boosters (HPB1 and HPB2).

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Based on full-scale testing of the high recovery system depicted earlier, the energy used by the SWRO system for seawater salinities of 35,000 and 43,000 mg/L was 2.1 and 2.9 kWh/m3, respectively. Such energy use is comparable to that of conventional SWRO systems with pressure exchangers operating at SWRO system recovery with the key difference that the sustainable recovery of the MSDT system is 30% 40% higher (e.g., 55% 60% vs 42% 45%). Designing the plant intake and pretreatment systems for such significantly higher recoveries allows one to achieve significant capital and cost of water production savings for new plants or to enhance the existing plant freshwater production capacity at relatively low capital investment.

9.3.2 E-REX high recovery SWRO system The E-REX system is an innovative reverse osmosis desalination technology, which uses a patented two-stage RO system configuration to significantly increase the recovery of this system and to thereby reduce the size, construction and operating costs of the desalination plant’s intake, pretreatment and discharge facilities by 30% 50% (Kitamura and Miyakawa, 2017). This system consists of three key components: 1. first-stage RO module, that contains only two elements per vessel and has feed flow that is typically 1.5 3 times smaller than the feed flow per vessel of a typical conventional SWRO system; 2. energy recovery turbine installed on the permeate line from the first-stage RO module, which creates 10 20 bars of backpressure on this permeate thereby reducing the flux, fouling and concentrate polarization of the first-stage RO elements; and 3. second-stage RO module which typically has only four membrane elements in series and processes the concentrate from the first-stage RO module. As shown on Fig. 9.10, similar to conventional SWRO systems, the feed flow to the first-stage RO module of the E-REX system is pumped by an HPP and the concentrate generated by the second-stage RO module is processed through an energy recovery device (ERD), which typically is a pressure exchanger type.

FIGURE 9.10 Process schematic of E-REX high recovery desalination system.

9.3 SWRO systems for increased recovery and brine concentration

The permeate from the first-stage RO module is directed to an energy recovery turbine (e.g., turbocharger, ERT) installed to operate in series with the high-pressure pump and to boost the pressure of this pump with 10 20 bars. The backpressure of the first-stage permeate line is controlled by a flow control valve. One of the unique features of this technology is the two-stage configuration of the SWRO treatment system. This allows the permeate back pressure on the membranes of the first stage of the SWRO system, which is generated by an ERD (turbocharger), to create an even distribution of feed and permeate production flows of all membrane elements included in the two stages of the system. In turn, this increases the overall membrane productivity and the recovery of the SWRO system, while reducing the total energy used for desalination. The E-REX system configuration allows reduction of the feed flow and permeate flux of the front two SWRO elements by two to three times compared to that in conventional SWRO systems. This reduces the fouling and concentration polarization of the front elements, which results in a beneficial decrease of the transmembrane pressure and increase in the overall productivity of the SWRO system. Depending on the source seawater salinity and temperature, as well as the configuration of the two stages of the SWRO system, the overall desalination system recovery can be significantly increased. For seawater of salinity up to 35,000 mg/L (i.e., typical Pacific and Atlantic Ocean waters) an increase from 45% 50% to 60% 65% and for the high-salinity waters of the Mediterranean sea (39,000 41,000 mg/L) and the Red Sea, Arabian Gulf (42,000 46,000 mg/L) from 40% 45% to 55% 60%. Despite the slight (4% 6%) increase in the capital costs of the SWRO desalination system due to the two-stage configuration of this system and the addition of an energy recovery turbine on the first-stage permeate line, the overall desalination plant construction costs are reduced due to the significant capital cost savings from the use and operation of smaller size intake, pretreatment and discharge facilities, and the SWRO energy recovery system. The capital cost savings stem from the fact that desalination plant, which has E-REX SWRO system is designed and operated at 30% 40% higher overall plant recovery than conventional reverse osmosis desalination plants. As a result, a desalination plant with E-REX SWRO system is 10% 20% more energy efficient, and 10% 20% less costly in terms of both capital investment as well as annual operation and maintenance expenditures than conventional SWRO desalination plants with the same freshwater production capacity. A significant additional benefit of the E-REX system is the reduced fouling rate of the SWRO membranes. The E-REX system configuration evens out the flux of all RO membrane elements in the first- and second-stage vessels; reduces by half the flux and fouling of the front elements and approximately doubles the productivity of the back (second-stage) elements. As a result, the EREX configuration increases the recovery of the SWRO system by approximately 1.5 times (from 40% to 60%) as compared to a conventional sevenelement configuration.

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Since the flux of the first-stage RO elements is proportional to the difference between the feed and the backpressures, for a typical feed pressure to the RO system of 68 bars for high-salinity ocean water (e.g., Arabian Gulf and Red sea) and backpressure of 20 bars, the flux of the first two elements is reduced by 1.45 times [68 bars/(68 bars 20 bars) 5 1.42] as compared to the flux of the first two elements in a conventional seven-element per vessel RO system. Because RO membrane fouling rate is exponentially related to flux, a 1.42times flux reduction would result in a decrease over fourfold of the membrane fouling rate. Such fouling rate decrease was clearly observed during the sixmonth side-by-side testing of conventional RO and E-REX RO systems on Red Sea water (Kitamura and Miyakawa, 2017).

9.3.3 High efficiency RO system High efficiency RO (HERO) technology is a proprietary pretreatment system that improves the recovery rate of RO systems. HERO is specifically designed to purify difficult to treat feed brackish waters, which can often pose problems to a conventional RO process (Subramani and Jacangelo, 2014; Mukhopadhyay, 2003). HERO in general can produce recovery of over 90% for brackish water, produces purer water than conventional RO, and the membrane flux for HERO is nearly double that of conventional RO. The HERO system employs a three-step process: 1. removal of dissolved solids (such as calcium and magnesium) by increasing the alkalinity of the feed water, which creates a cation exchange where hydrogen ions are exchanged with hardness ions, reducing the hardness of the water; 2. degasification that removes carbon dioxide gas created in the cation exchange process; and 3. acidification that decreases the pH above 10 to increase solubility of silica and inhibit silica fouling as well as to destroy biological growth. HERO system RO membranes are operated in a high pH environment that limits the potential foulants and substantially improves overall performance, producing higher quality permeate. An additional benefit can be the elimination of additional anti-scaling chemicals as the pretreatment process reduces hardness in the feed water, which in turn can reduce the cleaning and maintenance requirements compared to conventional RO systems.

9.4 Potential environmental impacts Despite one of the main goals of ZLD being to reduce water pollution and improve water sustainability, application of ZLD also results in unintended

9.5 Criteria and methods for feasibility assessment

environmental impacts. The evaporator-crystallizer system for ZLD management of concentrate has the highest energy use and carbon footprint of all concentrate management alternatives and often exceeds the total power demand for production of desalinated water by the plant generating concentrate. MVC brine concentrators would typically produce 19 23 kg of CO2/m3 of treated brine (Tong and Elimelech, 2016), which is significantly higher than the carbon footprint of production of desalinated water by reverse osmosis, which is 2.1 3.6 kg CO2/m3 of desalinated water (MIT, 2016). Using technologies with lower energy demand, such as the OARO, as well as using renewable energy (e.g., solar, wind, and geothermal energy) would enable further energy reduction. Brine concentrators increase the content of all constituents in the source saline water by 10% 100%, which depending on the quality of the source water may make the crystalline product from concentrate treatment a hazardous waste. The dry residuals generated by the crystallizer system which are typically disposed to landfills require such landfills to be lined and properly managed to avoid the leaching of chemicals into the groundwater (Younos, 2005).

9.5 Criteria and methods for feasibility assessment Usually, ZLD systems are used when other options for concentrate management are not feasible mainly due to their high construction and O&M costs. Since concentrate is very corrosive, all equipment used in this type of system is built from corrosion-resistant materials such as titanium, molybdenum, and super duplex stainless steel. This makes ZLD systems quite costly. The generation of steam for the concentrate evaporation process could also add significant expense to the ZLD system operation. Therefore most existing evaporator-crystallizer systems are operated using a waste stream from a nearby power plant or industrial facility that generates steam as a byproduct (e.g., oil refineries). While ZLD has received significant attention over the past 10 years, its cost challenges have not been successfully solved to date. Often, the total cost for construction of the zero-discharge concentrate processing system is comparable to or higher than the cost of the actual desalination facility. High cost and energy consumption will remain the main barriers to ZLD adoption in the near future. As the feedwater becomes more concentrated along the ZLD treatment train, its salinity and the minimum energy needed for desalination increase. Therefore the energy demand of ZLD, along with its associated costs, will still be higher than that of conventional wastewater treatment or disposal options. Future growth of the ZLD market will likely rely on regulatory incentives that outweigh its economic disadvantages. As the severe consequences of water pollution are increasingly recognized and attract more public attention, stricter

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environmental regulations on wastewater discharge are expected, which will push more high-polluting industries toward ZLD. Fresh water scarcity caused by both climate change and over-exploitation of existing freshwater will likely facilitate ZLD implementation. Resource recovery may provide an additional economic incentive for ZLD. Beneficial components in the feedwater (e.g., valuable salts, nutrients, rare metals, and elements) can precipitate or be largely enriched when the feedwater is concentrated.

9.6 Design and configuration guidelines Evaporator and crystallizer systems for concentrate management apply proprietary technologies and therefore the system manufacturer should be contacted to determine the design parameters and configuration of such systems. At present the three leading suppliers of concentrator and crystallizer systems are SUEZ (GEIonics-RCC), HPD, and Aquatech. Typically the size of brine concentrators and crystallizers is a function of the concentrate feed rate. Most commercially available thermal brine concentrator-based ZLD systems have unit concentrate processing capacity in the range of 500 4000 m3/day. Evaporator-crystallizer systems are usually much more space efficient than most of the other concentrate management methods. Typically, the land needed for the construction of such systems is 10% 20% of the total footprint of the desalination plant.

9.7 Zero-liquid discharge costs Typically, ZLD is the least cost-effective concentrate management method since it requires the use of costly mechanical equipment and large amount of energy for evaporation, crystallization, and dewatering of the salts in the concentrate. The construction cost of ZLD by the evaporator-crystallizer system is mainly a function of the flowrate of the processed concentrate (see Fig. 9.11). This figure should be used for order-of-magnitude cost estimates only as project specific factors such as concentrate salinity and availability of waste stream have measurable impact on these costs. The energy use of evaporator and crystallizer systems is usually an order of magnitude higher than that of any of the other concentrate management alternatives, and often exceeds the energy used for freshwater production by RO separation. The energy demand of brine concentrators is typically in a range of 16 26 kWh/m3 of processed concentrate (Suez, 2017). Crystallizers use 50 70 kWh/m3 of feed concentrate.

9.7 Zero-liquid discharge costs

FIGURE 9.11 Construction cost of evaporator: crystallizer system.

Cost Example The construction cost of evaporator-crystallizer system for disposal of 25,000 m3/day of brackish water concentrate can be determined using Fig. 9.11—US$165 million. This cost does not include the expenditures for land acquisition or for delivery of the brine to the concentrator. A land requirement for construction of the example ZLD system of 9 acres and assuming unit land cost of US$5000/acre, for the example referenced earlier, the land acquisition cost is: 9 acres 3 US$ 5000=acre 5 US$ 45; 000 In summary, the total construction cost for the implementation of this project (excluding concentrate delivery to the site) is: Brine concentrator=crystallizer system 1 land acquisition 5 US$ 165; 000; 000 1 US$ 45; 000 5 US$ 165; 045; 000 (Continued)

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Cost Example (Continued) The total expenditure for construction of brine concentrator/crystallizer system is higher than the construction cost for implementation of any of the other alternatives presented previously. This cost would be far higher than the cost for construction of 100,000 m3/day BWRO plant which would generate this concentrate (US$50 60 MM).

Due to the very high capital and O&M costs, zero-discharge technologies are not practical unless no other concentrate management alternatives are available or a reliable market for offtake from minerals and metals is established. Usually, zero-discharge concentrate management systems are justifiable for inland brackish water desalination plants where site-specific constraints limit the use of natural evaporation, deep well injection or evaporation ponds. The most commonly applied approach to reduce the overall costs of the ZLD system is to minimize the volume of concentrate delivered to the ZLD system by concentrate pretreatment in a high recovery desalination system.

9.8 Case studies 9.8.1 Thermal brine concentrator/evaporation pond -Tracy, California One of the largest evaporator systems for treatment of concentrate from a RO brackish water desalination plant providing drinking water supply in the US was installed in 2009 for the Deuel Vocational Institute (DVI) in Tracy, CA. This system uses a 30 m tall thermal brine concentrator (evaporator) to treat 1400 m3/day of brine from the groundwater BWRO system supplying water to DVI. The evaporator increases brine salinity to between 175 and 200 ppt and reduces concentrate volume by 97% and recycles high-quality drinking water back to the facility. The remaining 3% of concentrate slurry is disposed of to a 4-acre on-site evaporation pond for drying and ultimate disposal to a landfill to achieve ZLD. A mechanical vapor compression system drives the falling film evaporator to concentrate the brine. The unit power use of this system is 21 kWh/m3 of concentrate. The total capital cost of the combined BWRO desalination plant and ZLD system was US $26.5 million of which the BWRO desalination plant and 350 m pipeline costed US$9.8 million, the ZLD system cost was US$10.0 million and the expenditures for the evaporation pond was (year 2009 costs).

9.8.2 Thermal brine concentrator/crystallizer: Salt Lake City, Utah The largest ZLD system in the US is located at the 22,000 m3/day RO municipal brackish water desalination plant for Salt Lake City in Utah. This ZLD system

References

consists of evaporator and crystallizer. This ZLD system’s thermal brine concentrator (evaporator) processes 5500 m3/day of brine and reduces its volume by 97%. The downstream crystallizer has a capacity of 165 m3/day. The evaporator increases brine salinity to 200 ppt and the concentrated brine slurry is converted to salt crystals by the crystallizer and dewatering centrifuges. The capital cost of the entire ZLD system is US$129.8 million and the annual O&M cost for this system is US$0.63/m3 of processed concentrate. The energy use of the ZLD system is 21.5 kWh/m3. The cost of water production is US$1.54/m3 (year 2008 costs). The main project driver for the installation of this ZLD system was that this inland desalter does not have any suitable location for brine discharge as the nearby Jordan River was not an acceptable discharge location due to the high content of selenium in the brine.

References Al-Amoudi, A.S., Voutchkov, N., Ihm, S., Farooque, A.M., 2019. Desalination brine concentration system and method. US Patent Pending 16/371,816. Barrasi, G., 2018. High Recovery in SWRO Using a Multistage Turbocharger Configuration: Process Optimization and Cost Analysis, CaribDA 2018 Biennial Conference and Exposition, May 29 June 1, 2018, Curacao. Bell, E.A., Poynor, T.E., Newhart, K.B., Regnery, J., Coday, B.D., Cath, T.Y., 2017. Produced water treatment using forward osmosis membranes: evaluation of extendedtime performance and fouling. J. Membr. Sci. 525, 77 88. Burbano, A.; Brankhuber, P. (2012) Demonstration of Membrane Zero Liquid Discharge for Drinking Water Systems—A Literature Review, WERF5T10a; Water Environment Research Foundation: Alexandria, VA. Chen, X., Yip, N.Y., 2018. Unlocking high-salinity desalination with cascading osmotically mediated reverse osmosis: energy and operating pressure analysis. Environ. Sci. Technol. 52 (4), 2242 2250. Chung, H.W., Kishor, G.N., Jaichander, S., Karim, M.C., Lienhard, J.H.V., 2017. Thermodynamic analysis of brine management methods: zero discharge desalination and salinity-gradient power production. Desalination 404, 291 303. Kitamura, K., Miyakawa, H., 2017. Verification of Advanced Designed Seawater RO System for Low Energy And Operation Cost, The International Desalination Association World Congress—Sa˜o Paulo, Brazil, REF: IDA17WC-57963. Mukhopadhyay, D., 2003. Method and apparatus for high efficiency reverse osmosis operation. U.S. Patent 6537456 B2, March 25. MIT, 2016. Low Carbon Desalination—Status and Research, Development, and Demonstration Needs. Report of a workshop conducted at the Massachusetts Institute of Technology (MIT) in association with the Global Clean Water Desalination Alliance, October 17 18. Edited by: John H. Lienhard V, Gregory P. Thiel, David M. War singer and Leonardo D. Banchik. Mickley, M.C., 2008. Survey of High-Recovery and Zero Liquid Discharge Technologies for Water Utilities, WateReuse Research Foundation, Report WRF-02-006a.

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Morillo, J., Usero, J., Rosado, D., El Bakouri, H., Riaza, A., Bernaola, F., 2014. Comparative study of brine management technologies for desalination plants. Desalination 336, 32. Oasys Water, 2014. Oasys applies FO to treat wastewater from China’s growing power market. Memb. Tech. 11, 2 3. Panagopoulos, A., Haralambous, K.J., Loizidou, M., 2019. Desalination brine disposal methods and treatment technologies. Sci. Environ. 693, 133545. Peters, C.D., Hankins, N.P., 2019. Desalination. Osmotically assisted reverse osmosis (OARO): five approaches to dewatering saline brines using pressure-driven membrane processes. Desalination 458, 1 13. Subramani, A., Jacangelo, J.G., 2014. Treatment technologies for reverse osmosis concentrate volume minimization: a review. Sep. Purif. Technol. 122, 472. Suez, 2017. Using Evaporators to Achieve Zero Effluent at a BCTMP Pulp Mill. Suez Environment. Tong, T., Elimelech, M., 2016. The global rise of zero liquid discharge for wastewater management: drivers, technologies and future directions. Environ. Sci. Technol. 50, 6846 6855. USBR, 2009. Brine-Concentrate Treatment and Disposal Options Report, Southern California Regional Brine-Concentrate Management Study—Phase I, Lower Colorado Region, US Bureau of Reclamation, October 2009. Younos, T., 2005. Environmental issues of desalination. J. Contemp. Water Res. Educ. 132 (1), 11 18.

CHAPTER

Beneficial use of concentrate

10

10.1 Technology overview Concentrate from desalination plants contains large quantities of minerals naturally occurring in sea water that may have commercial value when extracted. Minerals found in highest concentration are chloride, sodium, magnesium, calcium and potassium. These have been commercially extracted as Cl2, SO422, and CO322 (Bardi, 2010) while magnesium has been extracted as MgO (Quist-Jensen et al., 2016). Extraction of rare metals and other mineral products from desalination plant concentrate has a number of potential advantages as compared to terrestrial mining of the same compounds. Much of the discovered shallow high-grade mineral ore worldwide has been mined over many decades leaving poorer quality, more difficult to access, and less mineral-enriched ores for future extraction. Mining operations have become progressively more costly over the past 15 years to mine ever deeper, mitigate environmental impacts, and process the poorer quality material extracted. With the reality of climate change, increased awareness of scarce resources such as fresh water has impacted on the costs of mining, and any energy intensive operations where renewable energy is not yet in use. Conventional mining often creates a multitude of environmental problems including the wastes generated, and pose significant health risk to miners. More stringent environmental regulations may well be imposed by governments in future, which would further restrict terrestrial mining. Ocean brine mining offers an alternative with numerous advantages: extraction and beneficiation require no additional energy, and concentrate provides a homogenous blend without mineralgrade difference. As technologies for seawater brine mining evolve, this source of minerals becomes more economically and environmentally viable. The economic gains obtained by extracting minerals is proportional to the increase in the concentration of minerals in the concentrate as well as the market price of these minerals. In this respect, mining of Mg, Na, Ca, K, Sr, Li, Br, B, and U could potentially be more economically attractive for harvesting from concentrate, if suitable methods of brine concentration and extraction are developed (Loganathan et al., 2017).

Management of Concentrate from Desalination Plants. DOI: https://doi.org/10.1016/B978-0-12-818045-7.00010-5 © 2020 Elsevier Inc. All rights reserved.

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The composition of brine from brackish- and seawater desalination plants differ, but minerals can be beneficially recovered from both. Research has been ongoing since the 1970s, but due to the low concentration of minerals in brackish and seawater, it has achieved little traction. Economically, the cost of extraction needs to be weighed against the revenue achievable, which relies on market fluctuations of commodity prices. Environmentally, extraction from brine is arguably less intrusive than conventional mining with the added benefit of reduction in brine volumes. Commercial viability has been assessed to be likely for a number of metals, including bromine, chlorine and sodium hydroxide, magnesium, potassium, sodium, and uranium. Process intensification is likely to result in further improvement in membrane technologies to sustainably recover minerals from concentrate (Quist-Jensen et al., 2018; Shahmansouri et al., 2015). A further benefit of extraction from brine is the likelihood of significant decrease in volume of concentrate to be transported and disposed of. Technologies currently emerging for beneficial reuse are summarized below.

10.1.1 Salt solidification and recovery The purpose of the process of salt solidification and recovery is to selectively recover high purity beneficial salts from the desalination plant concentrate. The effluent from salt processing is then further treated before end products are disposed of as shown schematically in Fig. 10.1. Technologies currently in use to extract salts are fractional crystallization and precipitation. Salts can presently be crystallized either through concentrate evaporation or via temperature control (Voutchkov, 2011). Minerals precipitate from seawater via evaporation in the order shown in Fig. 10.2. Calcium carbonate (or calcite) and calcium sulfate (or gypsum) are most easily extracted, followed by table salt. The remaining salts are precipitated

FIGURE 10.1 Schematic of salt solidification and recovery system.

10.1 Technology overview

FIGURE 10.2 Sequence of precipitation of minerals from concentrate.

in the last 2.5% of evaporation. Calcite is used in the production of lime and plastics, and gypsum has found broad application in the construction industry (Voutchkov, 2011). Addition of chemicals can result in fractional precipitation: selectively removing a specific mineral from the concentrate solution. For more than a decade magnesium and calcium salts have been readily extracted for beneficial production using several existing commercial technologies (Mickley, 2009). A further precipitation technology patented by GEO-Processors has found application in Australia and the United States. Through the SALPROC process, salts are precipitated through a combination of chemical reactions with repeated evaporation and cooling steps. In this way, salts such as magnesium carbonate, calcium carbonate and gypsum are recovered from concentrate (Svensson, 2005; Carollo Engineers, 2009). Chemical precipitation has been used to recover salts from seawater and RO reject brines using various precipitants (Sorour et al., 2014). Recovery rates vary depending on which chemical precipitants are applied. Salts have been recovered from seawater and desalination concentrate using sodium phosphate and carbonate

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as precipitants on the coasts of the Red and Mediterranean seas. In seawater, sodium phosphate led to 98% recovery of calcium, and 47% of magnesium. In concentrate, these rates were 75% and 24%, respectively (Giwa et al., 2016). The earlier-mentioned review of precipitation technologies shows that the addition of sodium carbonate to RO concentrate and seawater allows a reduction of calcium from 690 to 36 mg/L and 400 to 20 mg/L, respectively. In addition, magnesium concentration decreased from 2600 to 2375 mg/L and 1460 to 1250 mg/L for RO concentrate and seawater, respectively (Giwa et al., 2016). Approximately 2 kg/m3 of calcium and magnesium were precipitated from concentrate per 1 kg of sodium carbonate used. Similarly, 1.43 kg/m3 of calcium and magnesium were obtained from the seawater per 1 kg of sodium carbonate. Before chemical precipitation, membrane/thermal technologies and ion exchange were used as intermediate steps. The concentrate from the SWRO process can be decalcified in such a manner that ion exchange can subsequently be applied to remove magnesium from the decalcified stream. Calcium and magnesium byproducts from RO concentrate can also be precipitated using sodium carbonate and sodium hydroxide at 25 C and 65 C through another salt recovery technology (Casas et al., 2014). This research indicates that calcium removal is accelerated at 65 C while magnesium removal is unaffected at this temperature. In addition, it was also found that the recovery of calcium and magnesium was hindered by antiscalants and other metallic ions in the reject brine. To compensate for this, the reject brine was further concentrated through the use of ED, reducing the amount of antiscalants in the brine. A range of 0.35 14 g/L of sodium carbonate and 0.85 g/L of sodium hydroxide were used to maximize the removal of calcium and magnesium. The residual from the ED-RO process contained 10 mg/L of calcium and magnesium and the overall removal efficiency of these minerals from brine exceeded 95% (Giwa et al., 2016).

10.1.2 Disposal to saltwater wetlands Concentrate can in some cases be applied in support of wetlands, which are typically tolerant of TDS of less than 2500 mg/L. For short periods, wetlands could accept salinity of twice that (i.e., 5000 mg/L). This is feasible where trace elements are of no concern. In Oxnard, California, concentrate from a BWRO desalination plant with a TDS of 4500 mg/L has been used to restore a small coastal marsh. Salt grass yerba mansa (Anemopsis californica) and bulrush (Scirpus americanus and Scirpus californicus) were found to adapt to irrigation with concentrate (Voutchkov, 2011). In California, concentrate is seasonally discharged into saltwater wetlands to support healthy wetlands of marsh plants such as alkali brush, tulles, and salt grass. Wetlands are typically flooded up to half a meter in autumn through winter. Toward the end of winter, accumulated salts are released through pond drainage, where after the wetlands are again flooded with concentrate, and drained again 2

10.2 Extraction of minerals from concentrate

weeks later. This cycle is repeated up to three times in late winter. In spring, the ponds are drained to mudflat level. This enables the salt-tolerant plants to germinate and flourish. Where wetlands are connected with brackish or sea water bodies, such disposal is both beneficial as long as the concentrate can be tolerated by the local flora and fauna. An added benefit of such disposal to wetlands is the partial assimilation of contaminants such as nitrates and selenium, resulting in less contaminated brine entering water bodies. Part of the concentrate disposal design needs to include the occasional drainage of the wetland as the habitat is not sustainable without such periodic drainage. If a surface water body is available to safely accept such concentrate, this method of disposal is likely to be environmentally beneficial (Voutchkov, 2011).

10.1.3 Concentrate use for powerplant cooling Concentrate can be used beneficially to cool small powerplants where circumstances are suitable. Most importantly, as concentrate is highly corrosive and causes mineral deposits, the cooling towers have to be built of suitable material. The cost of such a cooling system is not insubstantial, given pumping and storage expenditures, and that the concentrate will still need to be disposed of as only between 2% and 10% is typically converted to vapor during the process. The main benefit of using concentrate for cooling is reducing environmental impact where seawater would be required for cooling. If collocated, the desalination plant can share the powerplant intake and outfall.

10.2 Extraction of minerals from concentrate The global economy relies in part on the sustainable supply of rare-earth metals and valuable minerals. The development and deployment of sustainable products to the advanced manufacturing industries of the 21st century will require large amounts of valuable metals such as lithium, copper, cobalt, silver, magnesium, and gold. Advances in resource recovery technology over the last 10 years have made extraction of minerals and metals from seawater brine cost competitive to terrestrial mining and have elevated seawater into an important and largely untapped source of valuable minerals (Bardi, 2010; Gilbert et al., 2010; Nakazawa et al., 2011; Diallo et al., 2015). Moreover, terrestrial mining has a significant detrimental environmental footprint and uses valuable and costly resources such as land, energy, and water. Furthermore, it generates large quantities of waste, often hazardous in nature. Table 10.1 presents typical market price range of sodium, calcium and magnesium salts that could be extracted from concentrate. In seawater and brine, valuable metals can exist as cationic or anionic species. Some of the high-value metals that are frequently present as cationic species in seawater and brine include copper, nickel, cobalt, and lithium. In contrast,

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Table 10.1 Typical market price range of Ca, Mg, and Na minerals. Mineral product

Chemical composition

Price US$/dry ton (2020)

Calcium—magnesium hydroxide (gypsum) Magnesium sulfate (epsomite) Magnesium hydroxide Calcium carbonate Calcium chloride Sodium sulfate Sodium chloride

CaSO4.2H2O 1 Mg (OH)2 MgSO4.7H2O Mg(OH)2 CaCO3 CaCl2 NaSO4 NaCl

150 250 500 350 600 200 150 100

600 550 800 300 250 180

Table 10.2 Rejection of high-value metals by NF and SWRO elements. High-value metal/salt in brine Barium (Ba)/ BaSO4 Cesium (Cs)/ CsCl Lithium (Li)/ LiCl Magnesium (Mg)/ MgSO4.7H2O Rubidium (Rb)/ RbCl Strontium (Sr)/ SrSO4 Uranium (U)/UCl Nickel (Ni)/ NiCl2

Seawater concentration (mg/L)

Rejection by NF membranes (%)

Rejection by SWRO membranes (%)

0.021 0.0003 0.17 1.290

87.7 87.7 26.7 87.7

99.6 99.6 99.6 99.6

0.12 8.1 0.0033 0.0066

26.7 87.7 40.0 87.7

99.6 99.6 99.6 99.6

uranium, platinum, molybdenum, and vanadium are present in brine as anionic species. Table 10.2 shows the concentration of key rare elements contained in seawater and the rejection of these elements by NF and SWRO membranes. As seen from this table, NF brine has high concentration of most key high-value metals except for lithium, rubidium, and uranium. However, these elements can be concentrated and collected in the brine of a subsequent SWRO system. Usually, NF membranes reject over 85% of the calcium and magnesium in the seawater and only 15% 20% of sodium and chloride. Several technologies can be applied to mine minerals from seawater (Loganathan et al., 2017). The four main technologies are solar evaporation, electrodialysis, membrane distillation, and subsequent crystallization (MDC), and adsorption/desorption/crystallization. In all these technologies, the concentration of the metal targeted for extraction is first increased to the level of supersaturation to enable their crystallization. In all the technologies mentioned barring the last,

10.2 Extraction of minerals from concentrate

recovery of minerals requires that the solubility product of the salt needs be less than the enriched ionic product of the constituent ions. Typically, CaCO3, NaCl, MgSO4, and Br are mined in this manner. The method of adsorption/desorption/ crystallization is suitable for minerals including Li, Sr, Rb, and U. By using adsorbents, these minerals can be adsorbed with other minerals and later quantitatively desorbed and crystallized (Voutchkov, 2011). Minerals can be mined using ED, RO, NF, and MF directly from seawater or from desalination concentrate. Brine can be further concentrated by membrane OARO when the concentrations of the minerals reach the saturation point of crystallization. The minerals’ concentrations in the brine are 1.5 2.5 times higher than that in the source seawater which favors their crystallization.

10.2.1 Solar evaporation Solar evaporation in ponds is the oldest method for extraction of minerals such as sodium chloride from seawater and desalination plant concentrate. As explained in Chapter 8, Evaporation Ponds are designed as a system of shallow ponds to concentrate and crystallize desalination plant brine. Evaporation pond systems are relatively easy to construct, require low maintenance and minimal mechanical equipment. Significant land area is, however, required, and the period for brine concentration and crystallization can be quite lengthy. To prevent groundwater pollution, the ponds have to be lined with clay, polyvinyl, and polyethylene materials. The main expenditure for solar evaporation ponds is the cost of land as such ponds are very land-intensive. Only minerals with high content (e.g., NaCl) can be economically recovered through this process.

10.2.2 Electrodialysis By applying selective monovalent cation and anion permeable membranes, electrodialysis can be used to separate the monovalent ions, Na1 and Cl2, from the divalent ions, Ca21, Mg21, and SO422 in the brine producing concentrated solutions of NaCl, which can be further crystallized by evaporation. The NaCl depleted ED concentrated solution would have Mg21 concentration which is four to six times higher than that in seawater. This allows Mg21 to be precipitated as Mg(OH)2 by increasing pH to 11 by the addition of NaOH. Ca can inhibit the precipitation of Mg but this can be avoided by pretreatment of brine, otherwise known as softening. Ca is removed from brine when pretreating with Na2CO3. The produced Mg(OH)2 typically has purity of 99% or more. Removal of Ca by softening or NF pretreatment will also help to prevent scaling of the ED membranes. Development of monovalent cationic and anionic permeable membranes which can separate Cl, Na and Br from Ca, SO4, and Mg has improved ED as a process for mineral recovery. Membrane research is expected to yield further improvements in permeable membranes, sensitive to specific individual metals, for example, Lithium.

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10.2.3 Membrane distillation crystallization MDC is a process of recovering minerals from seawater concentrate. MD, which acts as a preliminary process step prior to crystallization, is a thermally driven process where a hydrophobic microporous membrane separates pure water produced as distillate from the brine solution (Loganathan et al., 2017). An interface between vapor and liquid is created at the entrance to each pore, preventing movement of water, due to the polymeric membrane which is hydrophobic in nature. So when the water evaporates on the heated side of the membrane, vapor diffuses through the pores to condense as distillate on the membrane’s cold side. Supersaturation of salts is controlled by the hydrophobic hollow fibers so that crystallization can occur and salts recovered in the crystal recovery system. Crystal nucleation and growth take place due to the supersaturation which creates a metastable state. Tight control of supersaturation is a distinctive benefit of MDC in brine concentration, which enables higher quality crystals as output when compared to other techniques separating solids. To date, besides NaCl and MgSO4, no other compounds have been produced from seawater by using MDC. Even these compounds, so far, have only been produced in laboratory scale experiments and not on an industrial scale. Based on theoretical considerations, recent research indicates that there is potential for the recovery of minerals such as Ba, Sr, Li, Cu, and Ni from NF and RO seawater brines using MDC if water recovery of .99% is achieved (Quist-Jensen et al., 2018). Potential was proven through the study that NF reject could more easily yield Ba, Sr, and Mg. Further indicated in the research was that whereas Li was only possible from RO brine, Ni was from both NF reject and RO brine. Compared to pond evaporation and ED, MDC has the advantage that it simultaneously produces high quality fresh water while concentrating salts/minerals. Thus MDC would enable achievement of near zero liquid discharge for the desalination process while providing mineral concentration. While MDC has a greater thermal energy demand, this cost is balanced by the benefits of eliminating the need for disposal of brine and 100% water recovery as well as recovery of pure crystals as product with value. The energy demand may still lead to MDC being more competitive as the thermal requirement is low (less than 60 C) which could potentially be provided by solar energy, industrial waste heat, or other inexpensive renewable source. In terms of energy requirement, MDC shows promise to be competitive for extraction of NaCl and MgSO4 from NF and RO brines at scale. An economic analysis of the production of LiCl by MDS (Quist-Jensen et al., 2016) using a single salt aqueous LiCl feed solution shows that this mineral can be produced for US$2.18/kg which is competitive as compared to the cost for Li production from salt lake brines (around US$2/kg). The economics of minerals and water recoveries from NF and RO brines based on evaporation ponds, brine evaporator and MDC to produce NaCl, MgSO4
7H2O, CaCO3, and water were studied by Al Bazedi et al. (2014). The results indicate that brine mining using MDC is the most cost effective.

10.2 Extraction of minerals from concentrate

10.2.4 Adsorption/desorption Minerals are naturally found in low concentration in seawater, which may be why economics until recently favored land mining. Separating out individual minerals in low concentration is difficult and existing technologies cannot efficiently precipitate or crystallize these. Adsorbents have been developed to selectively adsorb minerals, even where they are in solution with other minerals. Once adsorption is complete, the selected mineral needs to be desorbed and precipitated to form the crystalized salt. The desorbed solution may contain other minerals which in turn need to be removed through applying adsorbents specifically to these minerals. High adsorption capacity may be particularly effective in brines which are between two and three times more concentrated, although the higher concentration will result in more significant competition for adsorption. Only four minerals have been extensively studied for potential recovery through adsorption/desorption. These are lithium, uranium, strontium, and rubidium (Loganathan et al., 2017). Only lithium appears to have been recovered in the pure crystalline form using the adsorption/desorption method. It is possible to concentrate minerals in raw seawater through adsorption/desorption to be able to crystallize through evaporation. Continuous recovery of suitable minerals is achieved through placement of adsorbents in containers directly into the ocean. Many of these minerals are difficult or impossible to crystallize using the other processes described previously due to their low concentrations. Branched polyethyleneimine (PEI) macromolecules embedded in highcapacity chelating resins and membrane absorbers have been studied for selective recovery of critical metals and valuable elements from seawater and brine (Mishra et al., 2012). The study proved that complex processes result in formation of high density resin which enables extraction of valuable elements including molybdenum, boron and vanadium. Mixed-matrix polyvinylidene fluoride membranes are being developed with PEI particles (Kotte et al., 2014). This new membrane development shows great promise for recovery of copper and uranium from seawater (Diallo et al., 2015). By exploiting the reactivity of branched PEI macromolecules, new types of UF membranes can be developed using a variety of base polymers and functional reagents as precursors with in situ synthesized supramolecular hosts for metal ions. There is potential that such new UF membrane absorbers could be configured into low-pressure and high-capacity regenerable modules for the selective extraction of cationic/anionic species of critical metals and valuable elements from the pretreated feedwater and desalination plant concentrate (Diallo et al., 2015).

10.2.5 Mineral recovery 10.2.5.1 Magnesium Magnesium compounds in seawater have a variety of useful applications in the agricultural, nutritional, chemical, construction and industrial industries.

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For example, calcium sulfate (gypsum) can be used as a construction material for wallboard, plaster, building cement, and road building and repair (Voutchkov, 2011). Besides sodium and chloride, magnesium is one of the most abundant minerals in seawater and many brackish waters. Magnesium is a low-density, and therefore lightweight metal that produces strong alloys which in recent years have replaced aluminum in many products in the cellular phone and computer industries. It is the lightest of the commonly used metals. Aluminum is more than 50% more dense than magnesium, for example, Magnesium is used in the production of alloys, fertilizer, refractories and flame retardants and for water purification. It is also essential for human health. Regarding the uses of magnesium metal, about 50% goes into alloys with aluminum. Aluminum-magnesium alloys are extensively used in the construction, automotive, railway, ship- and boat-building and pressure vessel industries. There are also magnesium, silicon and aluminum alloys, which are often used in complementary applications to aluminum-magnesium alloys. The aerospace industry appears to be migrating to more extensive use of magnesium alloys while magnesium is also an important component in the production of titanium and other metals. The use of magnesium by the automotive industry is increasing (Kotte et al., 2014). Although magnesium can be obtained from the minerals dolomite and carnallite, outside of China, its main source is seawater and briny lakes. Each cubic kilometer of seawater contains more than a million tons of magnesium compounds. In the United States, 63% of magnesium production came from seawater and brines during 2015. Salts are melted at very high temperature, where after electrolysis (passing an electric current through the molten salt) is used to extract magnesium metal.

10.2.5.2 Lithium Studies on extracting Li to date have focused on the use of MnO2-based adsorbent (Chitrakar et al., 2001; Nishihama et al., 2011; Nakazawa et al., 2011). It has been shown that the H-form of MnO2 had the highest adsorption capacity for Li from seawater among 12 inorganic adsorbents (Chitrakar et al., 2001). The ratio of metal ion uptake (mg g21) to metal ion in seawater (mg L21) for Li on H-MnO2 was 2.0 2.4 3 105 compared to 0.2 9.5 for Na, K, Mg, and Ca. Li has maximum adsorption capacity of 34 40 mg g21 compared to ,10 mg g21 for the other ions. Lithium’s small molecular size means it can penetrate the spinal structure of MnO2 and thus exhibit a higher selective adsorption on MnO2 (Chitrakar et al., 2001).

10.2.5.3 Strontium Studies of strontium recovery from brine is still in early stages. Sr recovery from synthetic seawater was studied using the Ca form of alginate microspheres and hydrothermally structured titanite nanotubes (Hong et al., 2016; Ryu et al., 2016).

10.2 Extraction of minerals from concentrate

In pure Sr solutions, such sorbents proved to have high sorbent capacities (110 mg g21 for alginate and 92 mg g21 for titanite nanotubes). Competition with other minerals such as Ca, Na, and Mg reduces adsorption of Sr in synthetic seawater. Such adsorption competition is caused by the high ionic strength of the seawater. Removal of calcium of seawater prior to strontium adsorption is expected to significantly improve Sr recovery.

10.2.5.4 Rubidium Recent studies of Rb recovery from synthetic seawater show that it could be costeffectively adsorbed using KCuFC (Naidu et al., 2016). While adsorption of Rb was affected only slightly by high concentrations of Ca, Na, and Mg, K significantly reduced sorption of Rb. To compensate, the column adsorptive removal of Rb was investigated with a polymer encapsulated KCuFC. Using 0.1 M KCl, the adsorbed Rb was desorbed. A solution of 68% pure Rb was produced through a resorcinol formaldehyde column and subsequently leaching with HCl which kinetically separated the Rb from the K. The sorption capacity decreases in order from Rb to Cs to Li, Na, Ca. BAMBP [4-tertbutyl-2-(a-methylbenzyl) phenol] or [4 sec-butyl-2-(a-methylbenzyl) phenol] to extract rubidium from brine obtained from a desalination plant with capacity of 100,000 m3/day was used in a similar study. Approximately 80% recovery of rubidium was reported (Jeppesen et al., 2009).

10.2.6 Other beneficial uses Where water is required for temporary uses, concentrate can be used for application in construction including dust suppression and roadbed stabilization, and operationally for deicing (Mickley, 2010). As these applications are occasional, they have to be viewed as supplementary beneficial use where a permanent primary concentrate disposal alternative has been implemented. Inactive salt mines in various states in the United States have been filled with solidified concentrate. This has provided structural integrity to underground caverns, reducing the risk of collapse and potential damage to infrastructure and other structures in proximity to the mines. As beneficial use, this would accommodate only a single application of concentrate and would also require a primary disposal alternative. Regeneration of wetlands and agricultural applications have potential both from BWRO located inland and coastal SWRO plants. Trials in modular farming have indicated that opportunities exist in use of saline brine for aquaculture (fish, brine shrimp). Modular farming is possible in both coastal areas and inland and includes production of halophytes (as explained in Chapter 7: Land application), specifically on degraded and barren land. This type of farming is beneficial to local communities while using reject brine as resource rather than waste (Giwa et al., 2016; ICBA, 2018).

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There is further scope for cultivation of species which are tolerant to concentrated brine and concentrated seawater, proving potential for beneficial use of desalination concentrate. The brine shrimp (Artemia) for example, can live in seawater but thrives in high-salinity waters of 70 340 g/L. Many young and adult species of shellfish and fish use this small crustacean (typically less than 20 mm long) as a food source. Another species with cultivation potential is Dunaliella salina, a microalgae, which due to its high glycerol content stores large quantities of up to 14% of dry mass of carotenoids (Rodr´ıguez-DeLaNuez et al., 2012; Zhuang et al., 2010).This can be used for making pharmaceutical or food products.

10.3 Feasibility of beneficial reuse Concentrate from desalination plants is still seen mainly as a waste product to be disposed of. The costs of beneficial uses remain high, adding to the overall cost of water produced. As climate change continues to encourage sustainable resource use, the beneficial technologies described in this chapter are likely to become more competitive. At present, conventional production of for example, construction materials is still financially far cheaper. With the increase in appeal of environmentally positive large-scale beneficial reuse of minerals produced from desalination plant concentrate, technologies are expected to evolve significantly.

References Al Bazedi, G., Ettouney, R.S., Tewfik, S.R., Sorour, S.H., El-Rifai, M.A., 2014. Salt recovery from brine generated by large-scale seawater desalination plants. Desalin. Water Treat. 52, 4689 4697. Bardi, U., 2010. Extracting minerals from seawater: an energy analysis. Sustainability 2, 980 992. Carollo Engineers, 2009. Water Desalination Management and Piloting. South Florida Water Management District, Sunrise, Florida. Casas, S., Aladjem, C., Larrotcha, E., Gibert, O., Valderrama, C., Cortina, J.L., 2014. Valorisation of Ca and Mg by-products from mining and seawater desalination brines for water treatment applications. J. Chem. Technol. Biotechnol. 89, 872 883. Chitrakar, R., Kanoh, H., Miyai, Y., Ooi, K., 2001. Recovery of lithium from seawater using manganese oxide adsorbent (H1.6Mn1.6O4) derived from Li1.6Mn1.6O4. Ind. Eng. Chem. Res. 40 (9), 2054 2058. Diallo, M.S., Madhusudhana, R.K., Manki, C., 2015. Mining critical metals and elements from seawater: opportunities and challenges. Environ. Sci. Technol. 2015 (49), 9390 9399.

References

Gilbert, O., Valderrama, C., Peterko´va, M., Cortina, J.L., 2010. Evaluation of selective sorbents for the extraction of valuable metal ions (Cs, Rb, Li, U) from reverse osmosis rejected brine. Solvent Extr. Ion. Exch. 28, 543 562. Giwa, A., Dufour, V., Al Marzooqi, F., Al Kaabi, M., Hasan, S.W., 2016. Brine management methods: recent innovations and current status. Desalination 407, 1. Hong, H., Ryu, J., Park, I., Ryu, T., Chung, K., Kim, B., 2016. Investigation of the strontium (Sr(II)) adsorption of an alginate microsphere as a low-cost adsorbent for removal and recovery from seawater. J. Environ. Manage. 165, 263 270. International Center for Biosaline Agriculture [ICBA] 2018. ICBA scientists manage to increase fish biomass by 300% using reject brine. ,https://www.biosaline.org/news/ 2018-06-07-6506. (accessed 08.02.18.). Jeppesen, T., Shu, L., Keir, G., Jegatheesan, V., 2009. Metal recovery from reverse osmosis concentrate. J. Clean. Prod. 17, 703 707. Kotte, M.R., Cho, M., Diallo, M.S., 2014. A facile route to the preparation of mixed matrix polyvinylidene fluoride membranes with in situ generated polyethyleneimine particles. J. Membr. Sci. 450, 93 102. Loganathan, P., Naidu, G., Vigneswaran, S., 2017. Mining valuable minerals from seawater: a critical review. Environ. Sci.: Water Res. Technol. 3, 37 53. Mickley, M.C., 2009. Treatment of Concentrate. US Department of the Interior, Bureau of Reclamation, Technical Service Center, Water Treatment and Research Group, Denver, Colorado. Mickley, M.C., 2010. Brackish Water Concentrate Management, State-of-the-Science White Paper Prepared for NMSU and CHIWAWA. Mishra, H., Yu, C., Chen, D.P., Dalleska, N.F., Hoffmann, M.R., Goddard, W.A., et al., 2012. Branched polymeric media: boron-chelating resins from hyperbranched polyethyleneimine. Environ. Sci. Technol. 46, 8998 9004. Naidu, G., Loganathan, P., Jeong, S., Johir, M.A.H., To, V.H.P., Kandasamy, Vigneswaran, J., 2016. Rubidium extraction using an organic polymer encapsulated potassium copper hexacyanoferrate sorbent. Chem. Eng. J. 306, 31 42. Nishihama, S., Onishi, K., Yoshizuka, K., 2011. Selective recovery process of lithium from seawater using integrated ion exchange methods. Solvent Extr. Ion. Exch. 2011 (29), 421 431. Nakazawa, N., Tamada, M., Ooi, K., Akagawa, S., 2011. Experimental studies on rare metal collection from seawater. In: Proceedings of the Ninth (2011) ISOPE Ocean Mining Symposium, Maui, Hawaii, June 19 2 24, ISBN 978-1-880653-95-1, 184 2 189. Quist-Jensen, C.A., Ali, A., Drioli, E., Macedonio, F., 2018. Perspectives on mining from sea and other alternative strategies for minerals and water recovery the development of novel membrane operations. J. Taiwan. Inst. Chem. Eng. 94, 129. Quist-Jensen, C.A., Macedonio, F., Drioli, E., 2016. Membrane crystallization for salts recovery from brine an experimental and theoretical analysis. Desalin. Water Treat. 57 (16), 7593 7603. Rodr´ıguez-DeLaNuez, F., Franquiz-Sua´rez, N., Santiago, D.E., Veza, J.M., Sadhwani, J.J., 2012. Reuse and minimization of desalination brines: a review of alternatives. Desalin. Water Treat. 39, 137 148. Ryu, J., Jung, J.,Yu, Y., Kweon, J., 2016. Evaluation of organic matter characteristics of FO and RO concentrates, Desalin. Water Treat. 57, 24606 24614.

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Shahmansouri, A., Min, J., Jin, L., Bellona, C., 2015. Feasibility of extracting valuable minerals from desalination concentrate: a comprehensive literature review. J. Clean. Prod. 100, 4. Sorour, M.H., Hani, H.A., Shaalan, H.F., Al-Bazedi, G.A., 2014. Schemes for salt recovery from seawater and RO brines using chemical precipitation. Desalin. Water. Treat. 1 10. Svensson, M., 2005. Desalination and the Environment: Options and Considerations for Brine Disposal in Inland and Coastal Locations, SLU. Department of Biometry and Engineering, Sweden. Voutchkov, N., 2011. Desalination Plant Concentrate Management. Water Treatment Academy. Zhuang, X., Han, Z., Bai, Z., Zhuang, G., Shim, H., 2010. Progress in decontamination by halophilic microorganisms in saline wastewater and soil. Environ. Pollut. 158, 1119 1126.

CHAPTER

Regional concentrate management

11

11.1 Types of regional concentrate management systems Resource constraints, political agendas, and administrative boundaries, inter alia, often result in project conception failing to consider benefits of synergizing with other projects regionally. Holistic water resource management within sensible regional or watershed boundaries can offer significant benefits to optimize all facets of project development and implementation. Regional concentrate management has direct benefit to both cost and environmental impact. Regional concentrate management approaches can be used separately or coimplemented at the same central facility. Where small desalination plants are geographically spread in fairly close proximity, concentrate can be conveyed to a suitable central location and disposed of by any of the methods described in preceding chapters. Concentrate generated by brackish desalination plants can be blended with source water for seawater desalination plants. Another possible input source for seawater desalination plants is effluent from advanced wastewater treatment plants. Brine can also be recovered from SWRO by reverse electrodialysis (RED) combined with joint disposal of wastewater plant effluent and seawater brine minerals. Conveying concentrate to a suitable central location has the advantage of providing economies of scale, and centralizing at a point most suitable to disposal of concentrate. A practical example is the Santa Ana regional interceptor in Southern California which collects concentrate from a number of brackish inland desalination plants and blends with effluent from a large existing wastewater treatment plant (WWTP) to an ocean outfall (Corollo Engineers, 2009). As surface water discharge and deep injection wells have the greatest potential to dispose of concentrate at scale, these options are likely to yield the greatest economy-of-scale benefits. The benefit of increased volume is highly unlikely in the case of land application and evaporation ponds: the same land area would be required while conveyance cost would need to be added. The nonavailability of land at some plants may however necessitate such solutions, despite an increase in cost (Voutchkov, 2011). Both brackish water plants and WWTP produce effluent of low salinity, which when blended with source water into seawater desalination plants result in overall reduction in salinity at the plant, and concomitant cost savings. Management of Concentrate from Desalination Plants. DOI: https://doi.org/10.1016/B978-0-12-818045-7.00011-7 © 2020 Elsevier Inc. All rights reserved.

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11.2 Use of brackish water concentrate in SWRO plants In many cases, the lack of access to suitable concentrate disposal options is a limiting constraint to the implementation of inland brackish water desalination plants. The most frequently used means of disposal currently is injection into deep saline aquifers or collection into regional conveyance pipeline to be discharged in ocean outfalls with regional WWTP effluent. Neither of these options are without compromise: suitable aquifers with adequate capacity to accept concentrate are not always readily available in close proximity to the desalination plant. Disposal with wastewater leads to a reduction in the effluent that can be generated by the WWTP and thus an opportunity cost which may impact on development. These methods of disposal require costs to be incurred while obtaining no benefit from accepting BWRO concentrate. Where it is locationally feasible, an innovative approach to regional concentrate management can be achieved by conveying concentrate generated by any number of BWRO desalination plants to a large coastal SWRO desalination plant. The concentrate is blended as supplemental feed with seawater collected from the ocean as a beneficial input source to the desalination process, as shown in Fig. 11.1. Pathogens such as bacteria, Giardia, Cryptosporidium, etc. are not usually found in brackish groundwater sources, thus requiring no further concentrate treatment prior to blending with seawater (Voutchkov, 2018).

Inland municipality

Inland municipality

Drin kin wate g r Brackish intake wells

Inland municipality

Drinki ng water

Drin kin wate g r

Inland brackish water desalination plant ctor colle rine ) nal b ish brine io g Re (brack

Coastal municipality

Coastal power plant

ctor colle rine ne) nal b bri Regio rackish (b Brac kish brine Intake

Power plant cooling water intake

Cooling water discharge king Drin r wate

Discharge Coastal seawater desalination plant

FIGURE 11.1 Integrated inland desalination brine disposal and seawater desalination.

11.2 Use of brackish water concentrate in SWRO plants

Fig. 11.1 includes collocation with a power plant, but this is not a requirement for use of brackish water concentrate. This regional concentrate management system requires only the BWRO plants, an interceptor or collector pipeline and a SWRO desalination plant. Such regional disposal has the added benefit that the plant capacity of the BWRO can be increased to maximize the volume of brackish water available as concentrate disposal is usually a limiting factor. Furthermore, the concentrate is used to produce drinking water instead of being disposed of as waste. Operational costs are likely to be reduced as the cost of conveyance is negligible compared to that of disposal via deep well injection. The capital costs will depend on the distance to the regional SWRO plant. Seawater typically has total dissolved solids (TDS) between 33,500 and 45,000 mg/L while BWRO concentrate is in the region of 2000 and 5000 mg/L, thus an order of magnitude less. The result of blending BWRO concentrate is lowering the feedwater salinity, which has the benefit of increasing the recovery rate and decreasing the total energy requirement in producing fresh water (Voutchkov, 2013). Higher recovery results in a reduction of both the volume and salinity of the SWRO concentrate with concomitant benefit to the environment. A further advantage in the use of brackish concentrate is the presence of antiscalants in the concentrate. This minimizes or eliminates the need for addition of such chemicals in the SWRO process, which results in an increase in overall recovery of the plant, increased production flow and reduction in unit production costs (Voutchkov, 2011). As a smaller volume of water will need to be extracted from the ocean, it can be anticipated that the environmental impact of the ocean water intake will be reduced corresponding to the volume of brine concentrate blended. Impingement and entrapment of organisms at the ocean water intake will be proportionally reduced. There are however some limitations to this type of regional concentrate management. If the brackish concentrate exhibits whole effluent toxicity, the SWRO desalination plant may not be allowed to dispose of concentrate to open water bodies. The concentrated brine toxicity is governed by the concentration ratio of one or more ions (any of calcium, magnesium, fluoride, strontium, sodium, chloride, potassium, sulfates, and bicarbonates) to the TDS (ion/TDS) (Mickley, 2000). This does not, however, provide an absolute barrier as the toxicity can be remedied by either removing the offending ion (via precipitation or absorption), or increasing the brine salinity (Voutchkov, 2011). Mycid shrimp are used in standard WET tests. A brackish concentrate with 500 mg/L of Ca ion and TDS of 10,000 mg/L results in a ratio of 500/ 10,000 5 0.05. This was found to cause 100% mortality rate in the mycid shrimp. Increasing the TDS to 20,000 mg/L halves the ratio to 0.025 where no mortality is observed. The threshold value for Ca ion ratio is 0.05; reducing it below this level neutralizes toxicity. Fortunately, TDS can be significantly increased to the desired level and thus detoxified by mixing the brackish concentrate with seawater (or SWRO concentrate) (Mickley, 2000).

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The mixing ratio will be site specific, depending on the composition of the brackish concentrate as well as the chosen mixing medium to increase TDS. Pilot testing is the simplest mechanism to establish the required mixing ratio which is not toxic.

11.3 Joint desalination and reuse 11.3.1 Hitachi’s Remix system for treatment of water reuse brine and seawater In a regional setting, the highly treated wastewater brine from the RO system of advanced water reclamation plants (AWRP) can be treated jointly with the source seawater of a desalination plant to eliminate or reduce the AWRP’s discharge. The AWRP discharge has far lower salinity than seawater—in the range of order of magnitude lower—which would result in significantly lowering the feedwater salinity. As with use of brackish concentrate described in Section 11.2, this results in significantly lower energy requirement. Such treatment process is referred to as joint desalination and water reuse (Voutchkov, 2018). An example of such joint desalination and water reuse facility is the Hitachi’s Remix system, which has been extensively tested at the 40,000 m3/day Water Plaza Advanced Treatment Plant in Japan (Kurihara and Takeuchi, 2018) as depicted in Fig. 11.2. At present, joint desalination and reuse is in its infancy and its practical implementation has been for industrial water supply. The use of joint desalination and water reuse systems for production of drinking water requires further research and development. Relevant regulations will also need to be developed in each applicable country if the product is to be used directly as potable water.

FIGURE 11.2 Water treatment system for joint desalination and reuse.

11.3 Joint desalination and reuse

It is anticipated that joint desalination and water reuse facilities will find traction over the next decade as climate change and environmental awareness influences the acceptability of potable water reuse. The lower energy requirement and circular use of water speaks directly to sustainability. Demonstration plants in Japan and South Africa are in operation and expected to provide useful data on efficiency, reliability, cost and water quality (Voutchkov, 2018).

11.3.2 Reverse electrodialysis system for SWRO brine recovery Brine from seawater desalination plants can be completely recovered and reused as feed water for the desalination plant, if it is jointly treated via RED with the secondary or tertiary effluent from a WWTP (Zhuang et al., 2019). Such joint treatment of SWRO brine and WWTP effluent appears to be viable in a regional setting if the two plants are in a close proximity (within 15 km). Applying two water streams of significant difference in their content of TDS, such as high-salinity seawater concentrate (brine) and low-salinity wastewater effluent on the two opposite sides of alternating cation and anion exchange membranes creates a process of RED which moves ions from the concentrated stream (brine) to the fresh water stream lowering the salinity of the brine as well as generating electricity as depicted in Fig. 11.3.

FIGURE 11.3 Principle of reverse electrodialysis (RED).

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CHAPTER 11 Regional concentrate management

The RED system consists of cells with several membranes separated by spacers which allow for flow of feed water. Cation exchange membranes (CEMs) are alternated with anion exchange membranes (AEMs). The presence of saltwater on one side and fresh water on the other side of the membrane creates a voltage over the membrane (as result of Donnan potential). When CEMs and AEMs are alternated with concentrate and low-salinity wastewater between the membranes as shown in Fig. 11.3, the voltage over each membrane increases. Using electrodes and redox reaction, the ionic current can be converted to electrical current to generate power. The rate of transport of ions from the concentrated stream (brine) to the lowsalinity stream (e.g., wastewater) can be accelerated if an external electric potential is applied. Such process is referenced as dRED. Applying the dRED process can facilitate near full recovery of the salts from brine and recycle the lowsalinity brine stream back to the desalination plant thereby nearly halving the intake volume of new ambient seawater collected for desalination (Fig. 11.4). The RED brine recovery system consists of multiple cell RED units configured in stages. Each stage completes stepwise exchange of salts between the high-salinity brine stream and the low-salinity wastewater as shown in Fig. 11.5. Fig. 11.5 illustrates the example where concentrate from SWRO desalination plant with salinity of 54,000 ppm is processed along with WWTP effluent with salinity of 900 ppm through a four-stage RED system. Each stage gradually reduces the salinity of the brine and transfers a portion of the brine salts to the WWTP effluent. The outcome of the four-stage RED treatment is a total

FIGURE 11.4 RED process application for brine recovery.

11.3 Joint desalination and reuse

FIGURE 11.5 Multistage RED system.

concentrate salinity reduction down to 30,000 ppm and increase in WWTP effluent salinity from 900 to 24,900 ppm. The final salinity of the brine and the WWTP discharge are comparable with the ambient seawater salinity. The highest application potential of the RED/dRED technology is for enhanced recovery (reduction of the salinity) of the concentrate generated by existing SWRO desalination plants, using the discharge of a nearby WWTP as a low-salinity stream to which salts removed from the brine are transferred. Under this application, the recovered brine would have salinity comparable to that of the ambient seawater and would be returned back to the desalination plant inlet and reused as source seawater for production of new fresh water. Most of the existing SWRO desalination plants are designed for 40% 50% recovery (e.g., 40% 50% of the source seawater is converted to fresh water and 50% 60% is converted to brine). Since the RED/dRED process can recover nearly 100% of the brine and convert it into saline source water for production of new fresh water by the desalination plant, under this application the actual volume of ambient seawater collected using the plant intake could be reduced by 50% 60%. This decreases the intake pumping energy costs as well as the environmental damage caused by impingement and entrainment of marine organisms contained in the ambient seawater collected at the intake by the same amount. Another benefit, which stems from the use of the RED/dRED technology is the elimination of the need for brine discharge into the ocean, which is usually one of the main environmental challenges associated with environmental permitting, construction and operation of SWRO desalination plants. For existing desalination plants, recovery by RED/dRED will negate the necessity for expansion of the existing intake and discharge outfall of the SWRO plant, should the desalination plant production capacity need to be upgraded. Since the construction costs for the plant intake and outfall facilities are typically between 10% 30% of the total capital costs for the desalination plant, the savings from eliminating the need of their construction will partially or fully offset the expenditures for the installation of the RED/dRED system.

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References Carollo Engineers, 2009. Water Desalination Management and Piloting. South Florida Water Management District, Sunrise, FL. Kurihara, M., Takeuchi, H., 2018. SWRO-PRO system in “Mega-ton Water System” for energy reduction and low environmental impact. Water 10, 48. Mickley, M.C., 2000. Major Ion Toxicity in Membrane Concentrate. AWWA Research Foundation, Denver, CO. Voutchkov, N., 2011. Desalination Plant Concentrate Management. Water Treatment Academy. Voutchkov, N., 2013. Seawater Desalination Costs and Technology Trends, Encyclopedia of Membrane Science and Technology. Wiley Online Library. Voutchkov, N., 2018. Energy use for membrane desalination current status and trends. Desalination. 431, 2 14. Zhuang, H., Moe, N., Lumibao, M., Zhao, Y., Kee, K.K., Barber, J., 2019. Pilot study of recovering seawater desalination brine by RED/DRED process. In: Proceedings of the IDA World Congress, Dubai, October 20 24.

CHAPTER

Nonconcentrate residuals management

12

Desalination plants generate three main types of waste streams: concentrate, spent pretreatment backwash water and spent membrane cleaning solutions. The previous sections of this book focused on concentrate management. This section addresses the disposal of the other two nonconcentrate residual streams. Besides these main waste streams, desalination plants also generate other solid and liquid waste streams in varying quantities. This includes screenings collected at the intake screens, not-to-specification filtered water generated for the first 15 30 minutes after the backwash of the individual filters cells (also referred to as “rinsing water”), sludge from lime clarifiers (or backwash water from the limestone contactors used for post-treatment of desalinated water) as well as spent cleaning solutions from the cleaning in place (CIP) systems of the pretreatment and RO membranes. The plants also release small amounts of service water from pumps and other equipment, and storm water surface runoff from the facility roofs, roads, process and parking areas. Spent pretreatment filter backwash water and membrane cleaning solutions are by far the two largest volumes of nonconcentrate waste streams generated by desalination plants. These usually account for 5% 10% of the total daily intake volume of saline source water processed by the desalination plant. All other plant waste streams collectively amount to less than 1% of the desalination plant’s daily intake volume of saline source water.

12.1 Spent pretreatment backwash water Types of waste streams (residuals) which are typically produced during desalination plant operation are indicated in Fig. 12.1. Table 12.1 describes the source of these residuals. The amount of residuals produced is primarily a function of the feed water quality relative to the constituents that must be removed prior to the membrane desalination process. Seawater collected from open ocean intakes for example, has measurable content of suspended solids. These solids must be removed prior to treatment with reverse osmosis, either in a backwash stream or as sludge (residuals). Other than the concentrate stream, these solids create the most significant residual stream from a desalination plant. Management of Concentrate from Desalination Plants. DOI: https://doi.org/10.1016/B978-0-12-818045-7.00012-9 © 2020 Elsevier Inc. All rights reserved.

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FIGURE 12.1 Key desalination plant waste streams.

Table 12.1 Key nonconcentrate residuals from membrane desalination processes. Residual

Source or cause

Backwash solids/sludge (residuals)

Suspended solids in the feed water removed from the spent filter backwash water after sedimentation and dewatering From backwashing of the filters for removal of suspended solids in the feed water at the end of the filtration cycle Filtered water that does not meet RO feed specification and which is produced by the pretreatment filter units for the first 15 30 min after backwash From cleaning in place (CIP) of pretreatment and/ or RO membranes Permeate generated by the RO system which does not meet target water quality Final fine filtration prior to RO, periodic replacement Membrane replacements

Backwash water from filters

Pretreatment filter rinsing water

Spent membrane cleaning solutions including membrane flush water RO permeate to drain Spent cartridge filters (solid waste) Spent MF/UF pretreatment membranes (solid waste) RO membranes (solid waste)

Membrane replacements

12.1 Spent pretreatment backwash water

Table 12.2 Comparison of waste streams from granular media and membrane pretreatment. Waste stream (% of feed volume)

Granular media filtration

Membrane filtration

Intake bar screens wash water Microscreen wash water Spent filter backwash water (reject) Chemically enhanced backwash Spent membrane cleaning chemicals Total (% of feed volume)

0.1 0.2 None (not needed) 2.0 6.0 None (not needed) None (not needed)

0.1 0.2 0.5 1.5 5.0 15.0 0.2 0.4 0.03 0.05

2.1 6.2

5.83 17.15

Spent filter backwash water is a waste stream produced by the desalination plant’s pretreatment filtration system. Depending on the type of the pretreatment system used (granular or membrane filters) the spent filter backwash water will vary in quantity and quality (see Table 12.2). Typically, granular media filtration systems generate only one large liquid waste stream: spent filter backwash. The volume of this stream in a well-designed plant varies between 2% and 6% of the total plant intake seawater volume. In addition to the particulate solids and colloids that are contained in the source seawater, this waste stream also contains coagulant (typically iron salt) and may have flocculant (polymer). Membrane pretreatment systems generate two large liquid residual streams: spent membrane backwash water (reject) and membrane cleaning solution from daily chemically enhanced backwash (CEB). The volume of the spent membrane filter backwash water is typically 5% 15% of the plant intake source volume, that is approximately twice as much as the spent filter backwash water volume of granular media pretreatment systems. The difference in total liquid residual volume generated by membrane pretreatment systems is even larger, taking into account that the microscreens protecting the membrane pretreatment filters are a source of additional waste discharge from intermittent cleaning. While conventional traveling fine bar screens use 0.1% 0.2% of the intake source water for cleaning, the microscreens generate waste screen-wash volume of 0.5% 1.5% of the intake flow. The relatively larger waste stream volume of the membrane pretreatment system requires proportionally larger intake seawater volume, which in turn results in increased size and construction cost for the desalination plant intake facilities, and pump station. This translates to higher O&M costs for source seawater pumping to the pretreatment facilities. In addition to the daily membrane washing and monthly membrane cleaning, operation of membrane pretreatment systems requires daily CEB using large dosage of chlorine (typically 20 200 mg/L) and strong base or/and acid over a short

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period of time. This performance enhancing CEB adds to the volume of the waste streams generated at the RO membrane plant and to the overall cost of source water pretreatment. The daily volume of waste stream generated during CEB is usually 0.2% 0.4% of the volume of the intake source seawater. Another waste stream that is associated only with membrane pretreatment is generated during the periodic chemical cleaning of the pretreatment membranes. Extended off-line chemical cleaning, often referred to as CIP, during which membranes are soaked in a solution of hydrochloric and/or citric acid, sodium hydroxide and surfactants, is critical for maintaining steady state membrane performance and productivity, and such cleaning is usually needed once every 1 3 months. The CIP cleaning generates an additional waste stream that is 0.03% 0.05% of the source seawater volume. One advantage of membrane pretreatment systems is that the waste filter backwash generated by these systems contains less source water conditioning chemicals (coagulant and polymer) and therefore, it is more environmentally friendly than the waste filter backwash stream generated by conventional pretreatment facilities. This benefit stems from granular media filtration typically requiring between two and three times higher coagulant dosage than membrane filtration (Voutchkov, 2017). In some cases, source seawater may not need conditioning with coagulant before membrane pretreatment, and this spent filter backwash could be disposed of along with the SWRO concentrate without further treatment. For comparison, due to the high content of iron, the spent filter backwash from granular media filtration pretreatment needs to be treated by sedimentation and the settled solids needs to be dewatered and disposed of to sanitary landfill. Otherwise, the high content of iron salt in the backwash water will cause the desalination plant discharge to have red color every time a pretreatment filter is backwashed, and the backwash discharged with the plant concentrate. The waste streams generated during the CEB and the CIP pretreatment membrane cleaning should be pretreated on-site in a neutralization tank prior to discharge. The additional treatment and disposal costs of the waste membrane cleaning chemicals must be taken into consideration when comparing membrane and granular media pretreatment systems. Spent filter backwash water is typically handled either by direct discharge to the ocean after blending with concentrate or by on-site treatment. Discharge to a surface water body along with plant concentrate without treatment has previously been the most widely practiced disposal method until 2010, especially for small and medium size SWRO desalination plants. Typically, this is the lowest cost disposal method as it does not involve any treatment prior to disposal except for dechlorination and pH neutralization (if needed). This disposal method is usually suitable for a deep discharge into large water bodies with good flushing—such as open oceans or large rivers. Because of the high content of ferric hydroxide in the spent filter backwash water, if this water is discharged in shallow water bodies, the area of the

12.1 Spent pretreatment backwash water

discharge often has reddish discoloration, especially if the discharge depth is less than 10 m and the spent backwash water is not equalized at the plant site prior to discharge. Since 2010, most environmental regulatory agencies worldwide have introduced requirements to prevent such discoloration, and to treat the spent filter backwash water by sedimentation to remove solids from the backwash. In this case the clarified water is blended with the concentrate and discharged through the plant outfall, while the backwash solids settled in the sedimentation basins are dewatered and removed as dry residuals.

12.1.1 Lamella sedimentation tanks for treatment of spent filter backwash At present, the most commonly used backwash treatment process is gravity settling in conventional or lamella plate sedimentation tanks. This is followed by solids thickening and mechanical dewatering (see Fig. 12.2). Lamella sedimentation tanks (also referred to as lamella clarifiers or settlers) usually have superior performance, three to four times smaller footprint than

FIGURE 12.2 Schematic of typical spent filter backwash treatment system.

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FIGURE 12.3 Schematic of lamella sedimentation tank.

conventional clarifiers and can handle up to four times higher source water turbidity (e.g., up to 200 NTU). Therefore, they have found a wider application for treatment of spent filter backwash water than conventional sedimentation basins. These clarifiers contain plastic lamella plate modules installed in the upper portion of the clarifier tanks (see Fig. 12.3), which enhance the sedimentation process by shortening the path of solid particles to the bottom of the clarifiers. Lamella clarifiers can be configured both as rectangular or circular structures. However, rectangular lamella clarifiers are most widely used for backwash sedimentation. Fig. 12.4 shows the lamella settlers of the 95,000 m3/day Tampa Bay Desalination Plant in Florida, United States. Typical design criteria are shown in Table 12.3. The spent filter backwash water is typically conditioned by anionic or nonionic polymer at a dosage of 3 5 mg/L before sedimentation. The polymer is mixed with the spent backwash water via in-line static mixers or in upstream coagulation tanks. Lamella modules used in these clarifiers are proprietary products and the design engineer should consult equipment manufacturers regarding lamella module configuration, the number and size of modules as well as design surface loading rate and depth of the sedimentation tank. The settled filter backwash water can either be disposed of with the desalination plant concentrate or recycled at the head of the pretreatment filtration system for reuse. It may be more cost-effective to recycle and reuse the settled filter backwash water rather than to dispose of it with the concentrate.

12.1 Spent pretreatment backwash water

FIGURE 12.4 Lamella sedimentation tank of Tampa Bay Desalination Plant, Florida.

Table 12.3 Design criteria for sedimentation tanks. Criteria

Value

Minimum number of tanks Water depth Mean flow velocity Detention time (in the lamella module) Surface loading rate (lamella module) Surface loading rate (clarifier area) Sludge collector speed

Two 3.5 0.3 0.2 1.0 4.0 0.4

5.0 m 1.1 m/min 0.4 h 2.0 m3/m2h 8.0 m3/m2h 0.8 m/min

The solid residuals (sludge) retained in the sedimentation basin typically have solids concentration of 0.5% 1.5% and are either discharged to the sanitary sewer in liquid form (typically practiced at small size plants) or processed on site in a solids-handling facility using mechanical dewatering equipment: belt filter presses, centrifuges, or plate-and-frame filter presses. Most regulations for sludge transportation worldwide require the sludge to be dry enough so that it does not cause liquid release on roads while transported. The sludge produced by mechanical dewatering of spent filter backwash solids and other desalination plant waste streams such as lime clarifier sludge has the same salinity as the source seawater and therefore cannot be applied as fertilizer to crops. This sludge also has low organic (,30% by weight) and nutrient content. However, the sludge generated at desalination plants is not toxic and can be disposed of to conventional lined or unlined sanitary landfills.

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FIGURE 12.5 Schematic of belt filter press.

FIGURE 12.6 Belt filter presses of Tampa Bay Desalination Plant, Florida.

12.1.2 Belt filter presses Belt filter presses use pressure to force water out of the residuals through the porous belt while retaining the separated solids on the belt as shown in Fig. 12.5. Fig. 12.6 shows the belt filter press of the 95,000 m3/day Tampa Bay Desalination Plant. Before sludge enters the press it is chemically conditioned for

12.1 Spent pretreatment backwash water

dewatering with an emulsion polymer flocculant that helps form stronger flocs. A transfer pump conveys the conditioned sludge onto a dewatering belt where free water separates by gravity and falls into a collection trough. As sludge is conveyed along the belt, ploughs roll it around to help water drain out. Before dropping down to the next stage, guide plates position the sludge toward the middle of the belt and ensure nothing is squeezed out the side of the filter. The process is repeated in a second gravity thickener before sludge is fed into a pressing zone. The remaining solids/water are sandwiched between two porous belts and passed over/under a series of different diameter rollers. The different rollers impart low and high pressure on the belts, squeezing the additional water from the solids and through the porous belt. The more extensive the belt travel, the drier the filter cake. Finally, the pressed sludge is scraped off the belt and collected in a bin. Using this technology, sludge from desalination plants can be dewatered to 20% 25% of dry solids.

12.1.3 Centrifuges In centrifuges, mechanical dewatering is accomplished by centrifugal force created by the rotation of the sludge at very high speed (2500 3000 rpm). The force applied and the centrifuging time determine separation effectiveness. The solid bowl centrifuge depicted on Fig. 12.7 is the principal type of centrifugal separator used to dewater residuals from desalination plants. This type of centrifuge has two moving parts: the bowl and the scroll. The sludge enters the centrifuge where the sludge is spun, separating the solids and liquid. As centrifugal force pushes the solids to the edge of the spinning bowl, a rotating scroll moves the dewatered solids along a horizontal axis to a collection point. Prior to feeding the residuals to the centrifuge, these residuals are conditioned with polymer at a dosage of 0.5 1.0 kg/kg of dry solids in the residuals.

FIGURE 12.7 Schematic of centrifuge.

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FIGURE 12.8 Centrifuge of Carlsbad Desalination Plant, California.

Centrifuges yield dewatered residuals of 28% 36% dry solids. Since these mechanical devices can produce 30% 40% drier sludge than belt filter presses, they are preferred in cases where transportation costs of the dry residuals are high. Typically, residual transportation and landfill disposal costs vary between US$15 and US$80/wet ton depending on the distance and capacity of the landfill to which they are disposed of. At disposal costs of less than US$25/wet ton, the belt filter presses are usually more cost competitive. At higher residual disposal cost, centrifuges are typically more advantageous on a life-cycle cost basis. While centrifuges produce drier sludge resulting in disposal cost savings, their capital cost is usually 1.8 2.5 times higher than that of belt filters presses. Fig. 12.8 depicts the centrifuge used at the 200,000 m3/day Carlsbad seawater desalination plant. This centrifuge dewaters the plant filter backwash sludge to 30% 35% of solids content.

12.1.4 Plate-and-frame filter presses Plate-and-frame filter press (shown in Figs. 12.9 and 12.10), also referred to as diaphragm filter press, applies very high feed pressure to the residuals and force the liquid out while retaining the solids. These presses have special compartments formed by the filter frames and the filter fabric that receive the pumped sludge at elevated pressure. The filter fabric covering the plates allows the water to escape while retaining the solids. This is a continuous process until the pressure drop across the filter equals the pumping pressure and the unit is shut down. The filter press is then opened and manually cleaned and returned to service. The-plate-and-frame filter presses are most costly and energy intensive, but they can produce dewatered sludge with solids content of 40% 60%, resulting in

12.1 Spent pretreatment backwash water

FIGURE 12.9 Schematic of plate-and-frame filter press.

FIGURE 12.10 Plate-and-frame filter press of Santa Barbara Desalination Plant, California.

2 3 times lower volume and disposal cost than that for dewatering the same sludge using belt filter press. Equipment cost of belt filter press systems are 30% 50% higher than that of centrifuges and 2.5 3 times higher than belt filter presses. Because of the very high capital and O&M costs associated with these systems, plate-and-frame presses are usually used only if the cost of sludge hauling and disposal exceeds US$80/wet ton.

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12.2 Chemical cleaning residuals The accumulation of silt or scale on membranes causes fouling which reduces membrane performance. Desalination system membranes must be cleaned periodically to remove foulants and extend the membrane useful life. Typical cleaning frequency of the membranes is two to four times per year. Membrane trains are usually cleaned sequentially. A chemical cleaning solution is circulated through the membrane train for a preset time. Usually, membranes are cleaned with low and high pH cleaning chemicals and commercial soaps and disinfected with sodium bisulfide cleaning solution between the low and high pH cleanings. After the cleaning solution circulation is completed, the spent cleaning solution is evacuated from the train to a storage tank and the membranes are flushed with permeate (flush water). The flush water is used to remove all the residual cleaning solution from the RO train to prepare the train for normal operation. The flush water is stored separately from the rest of the plant permeate in a flush tank. All the membrane cleaning streams listed above are typically conveyed to one wash-water tank often named the “scavenger tank” for waste cleaning solution retention and treatment. This tank should be sized to retain the waste cleaning solution from the simultaneous cleaning of a minimum of two membrane trains. The scavenger tank should be equipped with mixing and pH neutralization systems. The mixing system should be installed at the bottom of the tanks to provide complete mixing of all four cleaning solution streams listed above. After mixing with flush water, the concentration of the cleaning solution chemicals will be reduced significantly. The used cleaning solution should be neutralized to be pH compatible with the pH requirements for discharge to the wastewater collection system. At many plants, only the most concentrated first flush is discharged to the wastewater collection system. The rest of the flush water usually has only trace

FIGURE 12.11 Schematic of typical waste stream management system with buffer tank.

Reference

levels of contaminants and is most often suitable for surface water discharge (i.e., discharge to the ocean or other nearby water body). Often, desalination plants are provided with a buffer tank that receives and blends all plant waste streams prior to discharge (Fig. 12.11). The buffer tank is sometimes equipped with a pH adjustment system to control discharge pH, and an aeration system to mix tank content as well as boost the oxygen of the discharge. Such configuration is most common for ocean water discharges.

Reference Voutchkov, N., 2017. Pretreatment for Reverse Osmosis Desalination. Elsevier.

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13

13.1 Concentrate management alternatives With increased reliance on desalination as a source of potable bulk water, improved sustainability merits investigation to evaluate profitability and environmental concerns related to concentrate management. Comparative consideration of the most commonly used concentrate management alternatives presented in the previous sections of this book are summarized in Table 13.1. When conceptually planning a desalination project, there are usually project specific considerations present which eliminate at least some concentrate management alternatives. Geographic constraints and environmental legislation provide absolute barriers, while complexity, energy requirements, and cost are less rigid. Determination of the size of the plant depends on the water demand requirements. Plants could be designed in phases, to cater for future growth (especially when cost is a primary consideration) or constructed to provide sufficient water for a considerable future period. Whereas water resources such as dams are typically constructed to provide for decades of growth in demand, the considerable operational costs of desalination plants mean that construction is usually phased to provide supply aligned to the anticipated demand. Discharge to surface water bodies is the most used alternative for large plants. Zero liquid discharge can theoretically cater for unlimited concentrate volumes, as long as energy can be provided and costs covered. Deep well injection is reliant on the capacity of the aquifer, and thus constrained in volume. Land application and evaporation ponds require appropriate land available close to the plant, and are thus suitable only for smaller concentrate volumes, while sanitary sewers discharge is mainly viable for very small plants. Environmental permitting can provide an absolute barrier. For example in Cape Town, the Department of Environmental Affairs declared much of the coastline as Marine Protected Areas. There is no merit in exploring sites with such status, as environmental restrictions tend to become more stringent over time. The design and resultant cost of surface water discharge is affected by regulations, and with desalination providing a sustainable water supply option, it is beneficial

Management of Concentrate from Desalination Plants. DOI: https://doi.org/10.1016/B978-0-12-818045-7.00013-0 © 2020 Elsevier Inc. All rights reserved.

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Table 13.1 Comparative impact of concentrate management alternatives. Comparative impact Project size Construction cost Operating cost Environmental impact Permitting cost Complexity Geographic constraints Site footprint Energy requirement Beneficial use

Surface water discharge

Sanitary sewer discharge

Deep well injection

Land application

Evaporation ponds

Zero liquid discharge

All High

Small Low

Medium Medium

Small Medium

Small Medium

All High

Low Medium

Low Low

Medium Medium

Medium Medium

Medium Low

High Low

High

Low

Medium

Low

Low

Low

Medium Medium

Low High

Medium High

Low Medium

Low Medium

High Low

Small Low

Small Low

Small Medium

Large Low

Large Low

Small High

No

No

No

Yes

No

Yes

that such discharge is designed to have minimal negative impact on the receiving water body. Protection of groundwater is a primary consideration for inland plants. Deep well injection requires complete environmental information and monitoring to ensure damage to the environment is eliminated. Lining of evaporation ponds and monitoring of groundwater impacts for both land application and evaporation ponds is necessary. Environmental regulations are likely to continue evolving as new information becomes available and is more readily shared across borders. Energy requirements for desalination plants are considerable, and with zero discharge disposal, the energy requirement for the project is likely to more than double. The distance between the desalination plant and where concentrate is managed or disposed of also impacts on energy requirements as pumping costs can be considerable. While energy can be generated either as part of the desalination project or separate to it, this poses its own environmental and cost considerations, which are beyond the scope of this book. Locating desalination projects is a function of a variety of factors, of which land availability will be an important consideration. In an urban setting, land application and use of evaporation ponds are likely to be eliminated. Plant footprints are likely to become more compact and efficient over time as technology advances, such as that at Carlsbad. Finally, concentrate discharge cost is very much a part of the entire project of producing water via desalination, and needs to be considered holistically. Individual considerations will inform the most beneficial alternative for each location considered, and the project will then need to be fine-tuned to align with availability of electricity, funding and other relevant resources.

13.1 Concentrate management alternatives

FIGURE 13.1 Decision tree for desalination plant discharge management.

A general decision tree for selection of desalination plant discharge management alternatives is presented in Fig. 13.1 (AWWA, 2007). While concentrate water quality is of critical importance in the selection process, the criterion of highest significance which is most widely applied for selection of the most viable concentrate management alternative is the life-cycle project cost.

13.1.1 Costs The costs for the concentrate disposal methods listed above are impacted by a number of site-specific factors and therefore a general cost estimate analysis is difficult to complete. Table 13.2 presents the construction costs for an example concentrate disposal system for a 100,000 m3/day brackish and seawater desalination plants, respectively. The BWRO plant is assumed to operate at 80% recovery

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Table 13.2 Construction costs for key concentrate disposal methods of hypothetical 100,000 m3/day desalination plant. Concentrate disposal method

Desalination plant range in US$ M Brackish water Seawater

Surface water discharge Sanitary sewer discharge Deep well injection Spray irrigation Rapid infiltration Evaporation ponds Zero liquid discharge

2.5 10.0 0.5 2.0 4.0 8.0 8.0 10.0 15.0 20.0 30.0 50.0 50.0 70.0

6.5 30.0 1.5 6.0 15.0 25.0 30.0 40.0 60.0 100.0 140.0 180.0 160.0 200.0

and produce 10,000 m3/day of concentrate while the SWRO plant has 50% recovery and generates 40,000 m3/day of concentrate. Review of this table indicates that the sanitary sewer and surface water discharge are the two most costeffective methods for concentrate disposal, which explains their popularity. Note that it is highly unlikely that wastewater treatment plants would have sufficient capacity to process this amount of concentrate. Even if capacity was available, the externalized cost of the treatment plant should ideally be considered as part of the project. Depending on site-specific conditions, deep well injection, surface water discharge, and spray irrigation could be competitive concentrate disposal alternatives. Zero liquid discharge systems typically have highest construction and operation costs at present. However, under specific circumstances (such as cold climate, low evaporation and soil uptake rates, high land costs and low power costs) the zero liquid discharge systems could be cost competitive to evaporation pond and spray irrigation disposal alternatives. Competitiveness will further increase by consideration of externalities of the various processes. Since life-cycle costs are often the prime criterion for selection of concentrate management alternative, it is not surprising that concentrate disposal to sanitary sewer, which is usually the lowest-cost concentrate management method, is also the most widely used alternative for small volumes. Historically over 75% of the concentrate from brackish desalination plants in use is disposed to the sewer (Mickley, 2008). Considering only theoretical cost, this alternative is followed by surface water discharge, which has two key advantages over most of the other concentrate management methods—it is suitable for all sizes of desalination plants and it is not climate dependent.

13.1.2 Environmental impacts The environmental impacts of the various concentrate management alternatives are very much site-specific. Evaporation-crystallization typically has the lowest

13.1 Concentrate management alternatives

environmental impact in terms of waste stream volume and quality. However, this alternative typically has a carbon footprint more than 10 times higher than any other concentrate management scenario. When a suitable deep, high-salinity aquifer is available near the location of the desalination plant, well injection is an environmentally attractive alternative with reasonably low carbon footprint.

13.1.3 Regulatory acceptance Regulatory acceptance of a given concentrate disposal alternative can be evaluated based on:

• the number of permits or licenses needed to construct and operate the concentrate disposal system;

• the time needed to obtain the regulatory permits/licenses; • the complexity and length of the environmental studies required by the governing agencies in order to issue the permits/licenses;

• the environmental monitoring requirements associated with the operation of the concentrate disposal system; and

• the overall environmental and construction permitting costs. Concentrate discharge to sewer or to surface waters (sea, ocean, or river) are usually the most well understood disposal alternatives by environmental regulators worldwide as they are the most common. While discharge to sanitary sewer is usually easiest to receive approvals for, this concentrate management alternative is viable only for very small desalination plants. Construction of lined evaporation ponds with appropriate leakage monitoring system typically has wider regulatory acceptance than land application (RIB disposal and spray irrigation) as it is more protective of local groundwater resources.

13.1.4 Ease of implementation This criterion plays an important role in the selection of most viable concentrate management alternative specifically when time is of the essence for the implementation of the desalination project. The length of construction of some concentrate disposal systems, such as long ocean outfalls with complex diffuser structures, is often comparable to the time needed to build the desalination plant and involves prolonged environmental studies and regulatory review. Therefore in such projects the selection of a discharge management alternative is often driven by its ease of implementation and environmental review. Similarly, the construction of RIBs for concentrate disposal and deep injection wells involve detailed and lengthy (often 6 12 month or longer) studies of site suitability and constraints. Discharge to sanitary sewer is usually the easiest to implement alternative.

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Ideally, projects need to be planned and implemented in advance of the water supply being required. It is ironic that utilities that can least afford it often delay implementation decisions to the extent that sub-optimal solutions are chosen under emergency circumstances and additional costs incurred.

13.1.5 Site footprint The total area needed to implement alternative concentrate disposal methods varies significantly and could be an important constraint for selecting the most viable concentrate disposal alternative or combination of alternatives. The smallest site footprint alternative is usually concentrate discharge to the sanitary sewer. In contrast, construction of evaporation ponds is virtually always the alternative with the largest site requirements.

13.1.6 Reliability and operational constraints This selection criterion refers to the mechanical reliability of the equipment and performance reliability of the treatment technologies incorporated into a given disposal method as well as its dependency on natural changes in the surrounding environment. These include temperature, wind speed, humidity, precipitation, solar irradiation intensity, strength and direction of underwater currents, natural changes in source water salinity as well as exposure to storms, tornadoes, hurricanes, earthquakes, floods and other natural disasters. For example, deep injection wells are not suitable for discharge of concentrate in seismic zones and require the availability of very deep and highly-saline confined aquifers to be feasible. Similarly, shallow beach wells for concentrate disposal are not suitable for seashore locations exposed to significant beach erosion. Some of the concentrate management alternatives (i.e., evaporation ponds, land application) may be seasonal in nature and in this case, a backup alternative is needed to improve their reliability. If deep well injection is used, the injection wells will need to be inspected and maintained periodically, which requires either a backup disposal alternative or installation of backup wells to sustain continuous operation.

13.1.7 Energy use Energy use and carbon footprint associated with the construction and operation of concentrate disposal alternatives varies significantly. Usually energy use for concentrate disposal is 5% 20% of that for seawater desalination. However, achieving zero liquid discharge with evaporator-crystallizer concentrate treatment system, involves the use of electricity which could be larger than the electricity needed for RO desalination.

13.2 The future of concentrate management

13.2 The future of concentrate management 13.2.1 Chemical-free desalination Over the past 5 years, many countries with large desalination plants such as the Kingdom of Saudi Arabia, Australia, Israel, and Spain have initiated the implementation of comprehensive programs for green desalination, which aim to reduce both the amount and the types of chemicals used in the production of desalinated water. These programs are likely to ultimately convert all existing facilities into chemical-free seawater desalination plants by implementing the latest advancements of desalination technology and science. Chemical use has specifically been reduced. Desalination plants used to continuously chlorinate intake seawater using sodium hypochlorite to suppress the growth of marine life in both the intake piping and on the reverse osmosis membranes. Such practice was abandoned by most desalination plant operators close to a decade ago, and currently chlorination is used only once or twice a month for a period of 6 8 hours. In addition, some desalination plant operators do not apply any disinfectants to the intake seawater as they prefer to use the pretreatment system of the plant for control of biofouling. Currently ferric chloride and ferric sulfate are the most commonly used coagulants for pretreatment of seawater. In the past these chemicals were dosed at a constant rate and a relatively high dosage. Over the past decade, the desalination industry adopted automated monitoring of the content of solids in seawater and automated adjustment of the coagulant dosage proportional to the actual content of suspended solids in the water. Automated monitoring has now been introduced at most plants worldwide and has reduced the use of coagulant to less than half of what it once was. Acids and flocculants were used for optimization of the chemistry of water treatment in many desalination plants until a decade ago. Most advanced desalination plants and skilled plant operators today no longer use acids and flocculants for pretreatment, instead relying on optimized pretreatment system design and operation to manage water chemistry. Until 2010, antiscalants and sodium hydroxide were commonly applied in many desalination plants worldwide, mainly to prevent scaling associated with removal of boron from desalinated water. Since 2011, when the World Health Organization increased the drinking water guideline limit for boron from 0.5 to 2.4 mg/L, most desalination plants discontinued the addition of sodium hydroxide and antiscalants. The desalination industry is constantly evolving and adopting new chemicalfree, renewable energy-based technologies. The next step in this development process is to use calcium and magnesium extracted from brine for post-treatment of the desalinated water instead of using commercially supplied calcium compounds such as lime of limestone.

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13.2.2 Ocean brine mining The sustainable existence of closed systems such as planet earth depends on an efficient circular path when using resources like energy and water. A circular economy is the only path forward toward worldwide sustainability. For example, applying the circular economy model, brine generated from desalination plants can be used as a source of valuable minerals, such as calcium, magnesium and sodium chloride. Rare-earth elements can also be extracted from brine including lithium, strontium, thorium and rubidium. Recent stresses in the global market of rare-earth elements have brought the availability and supply of rare metals to the forefront of the sustainability debate and research agenda. These metals are used to fabricate critical components of numerous products, including airplanes, automobiles, smart phones, and biomedical devices. There is a growing realization that the development and deployment of clean energy technologies and sustainable products, processes and manufacturing industries of the 21st century will also require large amounts of rare metals and valuable elements including platinum group metals such as, lithium, copper, cobalt, silver, and gold. The latest technology trends indicate that magnesium may be replacing aluminum in the car, computer and cell phone industries as it is over 30% lighter. While the world’s mining sources of magnesium are fairly limited, seawater brine contains large quantities of magnesium which could be recovered by concentration of desalination brine followed by selective extraction by adsorption. In recent years, the desalination industry has developed a number of other brine concentration and mineral extraction technologies which enable the manufacture of commercially valuable products from the brine. Extracting minerals from seawater is a more environmentally friendly enterprise than terrestrial mining. Moreover, seawater extraction will not require fresh water for processing nor create volumes of contaminated water or tailings for disposal. In addition, these new brine concentration technologies enable dramatic reduction or complete elimination of brine discharge to the sea. Transitioning to a circular economy can achieve far more than reducing the negative impacts of the linear economy. Rather, it represents a systemic shift that builds long-term resilience, generates business and economic opportunities, and provides environmental and societal benefits. Beneficial reuse of brine could also be the key to solving the energy sustainability challenges of desalination. A type of next-generation nuclear power plant is likely to use thorium and rubidium as a power source instead of uranium. A plant with capacity of between 10 and 50 MW, small enough to fit in a trash can, could power a medium to large size desalination plant. The key advantage of this new energy source is that the building blocks can be directly extracted in adequate quantities from seawater desalination plant brine. Besides being readily extractible from the brine, a further advantage of these rare elements is that they cannot be used in atomic weapons.

13.3 Concluding remarks

13.3 Concluding remarks Desalination has developed rapidly over the past couple of decades, and the industry is actively addressing the misconceptions which have developed in public opinion. The myths and relevant facts concerning each misconception are summarized Table 13.3. While the water industry faces diverse challenges, over the last 20 years desalination technology has significantly progressed toward cost-effective and sustainable water management and environmentally safe disposal of concentrate and other byproducts from desalination processes. Disruptive technologies such as membrane brine concentration and mining, are expected to transform water management and to elevate its reliance on alternative water resources such as water reuse and desalination in the future. Water professionals worldwide are united in building a future where water is recognized and treated as a precious, highly valuable resource, and as a cornerstone of the circular economy. The transformational change in the water industry is premised on a new era of water management where old barriers to water and wastewater are slowly disappearing. Water in all of its states is now looked upon as a valuable commodity and precious resource that has to be valued, shared, monitored, accounted for, and reused rather than being considered a simple, abundant source of supply or waste that has to be disposed of. Table 13.3 Myths, misconception and facts. Myth/misconception

Facts

Concentrate generated from desalination plants is toxic and harms the marine environment.

1. Brine is .99.9% concentrated seawater which contains salts that originated from the ocean and does not harm the environment; 2. Concentrate is dispersed using natural mixing or outfalls with diffusers which usually bring its salinity to ambient conditions within 50 m from the point of discharge; 3. The outfall discharge area tends to be a very productive marine habitat due to the nutrients in the discharge; 4. The impact of concentrate discharge on the aquatic environment is strictly regulated and monitored; and 5. The thermal load of modern desalination plants is limited to match the natural variation in temperature and tolerance of marine life. (Continued)

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Table 13.3 Myths, misconception and facts. Continued Myth/misconception

Facts

Desalination plants use toxic chemicals and discharge them to the marine environment.

1. Desalination plants use exactly the same nontoxic chemicals that are used in conditioning the source water of conventional water treatment plants; 2. All chemicals used in desalination plants are: • Food grade quality; • Nontoxic and approved for production of drinking water; • Biodegradable. 3. Coagulant (Usually ferric salt): • Used to be discharged with the brine but this practice has been discontinued over 20 years ago; • The side-stream containing coagulant is processed in solids handling facilities and disposed to landfill. 4. Membrane chemical cleaning uses the same detergents contained in toothpaste and are nontoxic; 5. Chemicals used for membrane cleaning are not disposed into the ocean but are conveyed to WWTP for further treatment; 6. The desalination industry no longer uses acids and flocculants for seawater conditioning; 7. Antiscalant used for desalination is applied in small dosages and is biodegradable. Only antiscalants certified to be nontoxic by health authorities are used; 8. Industry no longer practices continuous chlorination—oxidant, such as sodium hypochlorite, is typically applied 4 6 times per month for 4 6 h only; and 9. Residual chlorine applied to source seawater is converted by sodium bisulfite to benign salts already contained in the ambient seawater: sodium, chloride, and sulfate. Comprehensive Studies at the large (200 MLD) Carlsbad intake show that the daily amount of impingement of fish is approximately 2 3 kg/ day (which is equal to the daily fish intake of two pelicans).

Intakes from desalination plants cause significant damage to the marine environment.

(Continued)

13.3 Concluding remarks

Table 13.3 Myths, misconception and facts. Continued Myth/misconception

Facts

Desalination is an enormous consumer of energy.

1. The energy needed to produce drinking water from seawater for an average family for a year is approximately equal to the power used by a standard refrigerator (2100 kW/year), and approximately half that used annually by a typical domestic water heater; 2. Energy for conveyance of water in California and Spain from their mountainous regions to coastal communities is comparable to energy for seawater desalination; 3. Power use for treatment of water ranges as follows: • Conventional surface water treatment power use: 0.4 0.6 kWh/m3; • Brackish Water desalination power use: 1.0 1.8 kWh/m3; • Reclamation of Municipal wastewater power use: 0.8 1.4 kWh/m3; • Seawater desalination power use: 2.8 4.5 kWh/m3. The carbon footprint of producing desalinated water for a single person is B0.11 tons CO2/ year, equivalent to 3.7% of the sustainable carbon footprint of one person (3 t/ CO2/year (UNDESA, 2011).

Desalination has a significant impact on climate change.

Traditionally water utilities have managed water supply and treatment of wastewater, minimizing the impact on the environment by removing nutrients and using the waste generated in a beneficial manner. To adapt to the challenges anticipated in the next 10 15 years, utilities have to develop a diversified portfolio of water supply in which conventional and direct potable water reuse and desalination have a comparable share to that of conventional water sources such as rivers, lakes and dams. Currently water and wastewater is regulated separately (e.g., in the United States they are regulated by the Safe Drinking Water Act and the Clean Water Act). For the essential transformation of the water industry to transpire by 2030, the fundamental legal framework has to be rewritten into a unified One-Water Act that recognizes water as a valuable resource in all of its forms and uses.

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CHAPTER 13 Selection of concentrate management approach

References American Water Works Association, 2007. Reverse Osmosis and Nanofiltration, Manual of Water Supply Practices, American Water Works Association, M46. Mickley, M.C., 2008. Survey of High-Recovery and Zero Liquid Discharge Technologies for Water Utilities, WateReuse Research Foundation, Report WRF-02-006a. UNDESA, 2011. United Nations Department of Economic and Social Affairs, World Economic and Social Survey 2011 The Great Green Technological Transformation, Chapter 2.

Appendix 1

Abbreviations AEM ANZECC AOR AWRP AWWA BMP BOD BOOT BWRO Ca CCC CDP CEB CEM CF Cf CFD CFRO CO2 CIP COMRO CWA DAF DBB DBO DEC DERM DO dRED DVI DWEER DW ED EES EIA EIR

anion exchange membranes Australian and New Zealand Environmental and Conservation Council area of review advanced water reclamation plants American Water Works Association best management practices biological oxygen demand build-own-operate-transfer brackish water reverse osmosis calcium California Coastal Commission Carlsbad Desalination Project chemically enhanced backwash cation exchange membranes concentration factor contingency factor computational fluid dynamics counter flow reverse osmosis carbon dioxide clean-in-place cascading osmotically mediated reverse osmosis clean water act dissolved air flotation design-bid-build design-build-operate Department of Environment and Conservation Department of Environment and Resource Management dissolved oxygen accelerated RED through external electric potential Deuel Vocational Institute double work exchanger energy recovery dry weight electrodialysis environment effects statement environmental impact assessment environmental impact report

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EMPCA EOR EPC EPS EQMF EQO ERA ERD ERS EV FGD FO FRP GCDP GRP HBMP HDPE HEPA HERO HFF HLR HPB HPP IEC IPP IX LBS LEPA LOEC MCRA MD MDC MEP MEPA MF Mg MI MIT MM MSDT MTBE Na NDMA NPDES NTU NSW

Environmental Management and Pollution Control Act 1994 enhanced oil recovery engineering, procurement, and construction Encina power station environmental quality management framework environmental quality objectives environmentally relevant activities energy recovery device energy recovery system environmental values flue gas desulfurization forward osmosis fiberglass reinforced plastic Gold Coast desalination plant glass reinforced plastic hydrobiological monitoring program high density polyethylene high ecological protection area high efficiency RO hollow fine fiber hydraulic surface loading rate high-pressure booster high-pressure feed pump Israeli electricity company industrial pretreatment program ion exchange land-based sources low ecological protection area lowest observed effect concentration marine contamination risk assessment membrane distillation membrane distillation crystallization Ministry of Environmental Protection medium ecological protection area microfiltration magnesium mechanical integrity mechanical integrity tests million multistage dual turbocharger methyl tertiary butyl ether (gasoline additive) sodium N-nitrosodimethylamine National Pollutant Discharge Elimination System nephelometric turbidity unit New South Wales

Appendix 1

NWQMS OARO OCSD OEPA O&M ORP P PDFB PEI PP PVC PVDF R RCRA RED RIB RO RWQCB S. AZ S. CA SAR SARI SDI SDWA SER SP STE SWWC SWRO TCLP NF TDS TECO TN TOC TP TSS UAE UF UIC US USDW USEPA UV W. TX WET

national water quality management strategy osmotically assisted reverse osmosis Orange County Sanitation District Office of Environmental Protection Authority (Australia) operation and maintenance oxidation-reduction potential of water phosphorus percent difference from balance polyethyleneimine polypropylene polyvinyl chloride polyvinylidene fluoride application rate Resource Recovery and Conservation Act reverse electrodialysis rapid infiltration basin reverse osmosis Regional Water Quality Control Board Southern Arizona Southern California sodium absorption ratio Santa Ana River Interceptor silt density index Safe Drinking Water Act (USA) standard evaporation rate salt passage salinity tolerance evaluation Saline Water Conversion Corporation of Saudi Arabia seawater reverse osmosis toxic characteristic leaching procedure nanofiltration total dissolved solids Tampa Electric Power Company total nitrogen total organic carbon total phosphorus total suspended solids United Arab Emirates ultrafiltration underground injection control United States of America underground source of drinking water United States of America’s Environmental Protection Agency ultraviolet radiation Western Texas whole effluent toxicity

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Appendix 1

WHO WTP WWTP Y ZID ZLD

World Health Organization water treatment plant wastewater treatment plant plant recovery, % zone of initial dilution zero liquid discharge

Appendix 2

Units cm  C day ha h Hp kg km kW kWh kWh/m3 l or L m m2 m3 m3/day MCM MGD mg/L MLD mm µ µg/L µS/cm ppb ppm psi psu ppt s year

centimeter degrees celsius: unit of temperature day hectare hour horsepower (unit of power) kilogram kilometer kilowatt (unit of power) kilowatt-hour (unit of energy) kilowatt hours per cubic meter (measure of energy used to produce or convey one cubic meter of fresh [desalinated] water) liter meter square meter cubic meter cubic meters per day million cubic meters million gallons per day milligrams per liter million liters per day millimeter µm or micrometer (one-millionth of a meter) microgram per liter micro-siemens per centimeter: unit of specific conduance of water parts per billion (1 ppb 5 1 µg/L) parts per million (1 ppm 5 1 mg/L) unit of pressure: pounds per square inch practical salinity units (1 psu 5 1000 mg/L) parts per thousand (1 ppt 5 1000 mg/L) second year

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Glossary Acidification reduction of pH in soil over time, resulting in reduced production due to changes in availability of soil nutrients Adsorption adhesion in an extremely thin layer of molecules onto the surface of solid or liquid bodies Desorption release of a substance from or through a surface Aeration process of air circulated, mixed, or dissolved in a liquid Aerobic containing oxygen Alginate a salt of insoluble colloidal acid abundant in cell walls of brown algae Alkaline having a pH of more than 7.0 Alloy substance created by combination of two or more elements, at least one of which is a metal Alluvial flat landform formed by sediment deposition over long time period as result of river(s) forming alluvial soil Ambient surrounding background Ambient seawater seawater in the open ocean used for desalination Anaerobic not containing oxygen Anthropogenic caused by human activity Antiscalant a chemical which inhibits scale formation on the SWRO membranes Aquifer underground formation that is saturated with water Backwash preventive maintenance on filter media, pumping water or air backwards through the filters media Bactericide a chemical capable of destroying bacteria Bathymetry survey study of the underwater topography of the sea or ocean bottoms Beneficiate processing of raw materials such as minerals to improve chemical properties in preparation for smelting Benthic habitat/organisms flora and fauna inhabiting the lowest level of an ocean or lake, including sediment and subsurface layers Bioaccumulation gradual accumulation of chemicals in a living organism Bioassay analytical method to determine impact of a substance on living cells or organisms Biochemical study study of chemical processes within and relating to living organisms Biocide chemical used to inactivate microbiological organisms (i.e., chlorine) Biodegradation breakdown of substances in the water by microorganisms Biodiversity a measure of variation at genetic, species, and ecosystem level determining variety and variability of life Biofouling membrane fouling caused by the excessive growth and accumulation of microorganisms and their secretions on the membrane surface Biomass living organic matter Brackish water water with total dissolved solids concentration of 1000 10,000 mg/L Brine the concentrated stream separated from the source seawater during the desalination process; usually the concentrate from SWRO desalination has 1.5 2.5-time higher TDS concentration than the source seawater Build-own-operate-transfer project implementation by concession from public sector to a private entity to finance, design, construct, own, and operate a facility (e.g., desalination plant)

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Glossary

for a contractually determined period (“concession period”) and to transfer the ownership of the facility to the public sector at the end of the concession period Buoyancy upward force exerted by a fluid that opposes the weight of an immersed object By-product secondary product from a treatment process or chemical reaction, traditionally put to waste Carcinogenic a substance, radionuclide, or radiation that promotes the formation of cancer Centrifugal moving outward from the center Chelating type of bonding of ions and molecules to metal ions Chloralkaline industrial electrolysis of sodium chloride solutions, producing chlorine and sodium hydroxide Chlorination adding chlorine to water to kill certain bacteria and microbes to produce germfree potable water Clean-in-place process of cleaning membranes used in desalination plants without disassembly Co-disposal two or more waste streams combined prior to disposal to exploit synergies and reduce environmental impacts and costs Coagulation a chemical process involving neutralization of charge to promote clumping of fines for easier separation from water Colloidal items of small size floating in a medium of air or liquid Collocation location of desalination plant on existing power generation station and connection of desalination plant intake and outfall to the cooling water discharge of the power generation station Concentrate same as brine Conductivity a measure of a solution’s ability to conduct electricity Corrosion a natural process that converts a refined metal into a more chemically-stable form such as oxide, hydroxide, or sulfide Contaminant an undesirable substance contained in the source seawater, permeate, or concentrate Crystallization a process in which a solid (e.g., brine salt) is formed by atoms/molecules highly organizing into a structure known as a crystal Degasification removal of dissolved gasses from liquids Desalination, desalting a process that removes dissolved solids (salts) from seawater Design-bid-build a method of project delivery where the client contracts with separate entities for design and construction of a project Design-build-operate a method of project delivery where a client contracts with a single entity to design and build a project (e.g., desalination plant) and then to operate this project for a contractually predetermined period of time Desorption an occurrence where a substance is released from or through a surface Desulfurization the removal of sulfur or sulfur compounds from liquids Dewatering removing water from a wet solid material (e.g., liquid sludge or residuals formed during the backwashing of pretreatment filters in desalination plants) Diffuser offshore end portion of outfall which consists of discharge ports configured to maximize the mixing of the desalination plant discharge with the ambient receiving waters by releasing the desalination plant concentrate at high velocity Dioxide an oxide containing two atoms of oxygen, each of which is bonded directly to an atom of a second element

Glossary

Dissipation transformation of energy from one form to another in an irreversible process (e.g., spreading of the high salinity brine into the ambient seawater in the area of discharge) Distillation purification of high salinity liquid (e.g., source seawater) through evaporation and collection of a low salinity liquid (e.g., distillate) by condensation Dodecyl a radical derived from dodecane (a colorless thick oily hydrocarbon) by removing one hydrogen atom Double-pass RO system a RO system that consists of two sets of RO trains (units) configured in series in which permeate from the first set of RO trains (units) is processed through the second set of RO trains Drought a long, usually multiyear, period of abnormally low rainfall Ecosystem a community of living organisms interacting with each other and with non-living components of the environment they inhabit Effective size the media grain diameter at which 10% of the media by weight is smaller than this diameter, as determined by sieve analysis (ASTM, 2001) Electrodialysis accelerated dialysis under applied electric potential difference with oppositely charged electrodes on either side of a membrane Entrainment injury or destruction of aquatic organisms by the water treatment facilities, equipment and processes located downstream of the water intake structure Evaporate to convert water from liquid phase to vapor phase Feed water influent water that is fed into a treatment process/system Filtrate the purified water that is produced by the membrane pretreatment system Flocculant a substance that can be added to a suspension to improve aggregation of suspended particles Flux the rate of water flow across a unit of membrane surface area expressed in liters per hour per square meter (L/h-m2 or Lmh) Fouling the gradual accumulation of contaminants on and/or within the RO or pretreatment membrane surface that inhibits the passage of water, thus decreasing membrane permeability and productivity Halophyte a plant adapted to live in a saline environment Hardness concentration of calcium and magnesium salts in water Hydrocarbons organic compounds containing only carbon and hydrogen Hydrodynamic study study of liquids in motion describing dissipation of the concentrate released from desalination plant diffusers into the ambient aquatic environment Hypoxia depletion of dissolved oxygen to an extent that is detrimental to aerobic organisms Impervious surface surface covered with water-resistant material Impingement injury or destruction of aquatic organisms entering water intake as a result of their pressing against the screens of the intake due to the high velocity of the flow through the screens Imposex the development of sex organs contrasting with their actual gender in marine gastropods Inert matter that does not dissolve in water, nor reacts chemically with water or other substances Injection zone geological formation receiving desalination plant discharge via deep injection well Inorganic commonly also referred to as mineral, includes all matter that does not originate from living organisms (animals, plants, bacteria, etc.)

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Glossary

Intake the facility through which source water is collected to produce fresh water in a desalination plant Ion an atom or group of atoms/molecules that has a positive charge (cation) or negative charge (anion) as a result of having lost or gained electrons Ion strength a measure of the overall electrolytic potential of a solution Lacustrine related to lakes, or in-land deep-water and wetland habitats Lamella thin plate, layer, scale or membrane Langelier saturation index (LSI) a parameter indicating the tendency of a water solution to precipitate or dissolve calcium carbonate Lithology study of rocks including color, texture, grain size and composition Mass transfer coefficient a coefficient quantifying material passage through a membrane Membrane a thin film of polymer material permeable to water and capable of separating contaminants from the source seawater as a function of their chemical and physical properties when a driving force is applied. Microfiltration and ultrafiltration membranes have measurable porous structures which physically remove particles and microorganisms larger than the size of the membrane pores. Ultrafiltration membranes also remove molecules larger than a specified molecular weight. Reverse osmosis membranes remove both soluble and particulate matter from the source water Membrane element an individual membrane unit of standard size and performance Membrane system a complete system of membrane elements, pumps, piping and other equipment that can treat feed water and produce filtrate (UF and MF systems) or permeate (RO systems) Microfiltration filtration through membranes of pore size between 0.1 and 0.5 µm Mitigation prevention of significant environmental impact and/or repair of such impact on aquatic habitat exposed to desalination plant discharge. Often mitigation involves restoration of existing habitat or creation of new habitat similar to the one that is impacted on the same or different location Nanofiltration type of membrane filtration for removal of organic matter Near-shore discharge disposal on the desalination plant waste streams through structure (channel, pipe, weir, etc.). Located on the shore or within several hundred meters from the shore in the tidal zone Nucleation first step in formation of a new structure through self-organization (e.g., formation of mineral scale on the surface of the reverse osmosis membranes) Offshore discharge disposal of desalination plant waste streams via long outfall structure extending beyond the tidal zone Open intake intake collecting source water directly from the water column of surface water body Organic organic matter is a broad category that includes both natural and man-made molecules containing carbon and hydrogen. All organisms living in water are made up of organic molecules Osmosis the naturally occurring transport of water or other solvent through a semipermeable membrane from a less concentrated solution to a more concentrated solution Osmotic pressure a pressure applied on the surface of semipermeable membrane as a result of the naturally occurring transport of water from the side of the membrane of lower salinity to the side of the membrane with higher salinity Outfall discharge structure (outlet, diffuser, pipe opening, weir) through which a waste stream (e.g., concentrate from desalination plant) enters the water body receiving the discharge

Glossary

Oxidation chemical reaction with oxygen involving moving of electrons Ozonation injection and distribution of ozone through water as a method of water purification Percent recovery the ratio of pure water (filtrate or permeate) flow to feed water flow of filtration system. In SWRO systems this is the ratio between permeate and feed water. In UF and MF systems it is the ratio of filtered water and feed water Percolation passing through a permeable substance to introduce water into groundwater aquifer Permeability the capacity of membrane material to transit flow. Expressed as the membrane flux normalized for temperature and pressure and expressed in liters per square meter per hour per bar (Lmh/bar); also named specific flux Permeate purified water of low mineral content produced during the reverse osmosis separation process. Permeate is the portion of the feed seawater which passes through the RO membranes Ph the negative logarithm of the hydrogen-ion concentration. A solution of a pH lower than 7 is acidic, while one with pH higher than 7 is alkaline Plume a body of one fluid moving through another Precipitate to form an insoluble compound either by reacting two salts or changing temperature to affect solubility of a compound Pressure filtration filtration aided by imposing pressure differential across an enclosed filter vessel Pressure vessel a housing containing membranes in a preset configuration which operates under pressure. For SWRO systems, pressure vessels are plastic or metal tube-shaped devices that house 6 8 SWRO elements Pretreatment process that includes one or more source water treatment technologies (e.g., screening, coagulation, sedimentation, filtration, chemical addition, etc.), which aim to remove foulants from the source seawater prior to SWRO separation in order to protect the membranes and improve desalination plant performance Product water low salinity (fresh) water usually with TDS concentration of 500 mg/L or less produced by the desalination plant and suitable for distribution system delivery. In order for the desalination plant permeate to be converted to product water it has to be disinfected and conditioned for corrosion and predetermined water quality requirements Reject same as brine (concentrate) or spent pretreatment filter backwash water Remineralization addition of mineral elements such as calcium and magnesium to the desalinated water to prevent corrosion of the piping and equipment pumping and conveying this water and to improve its drinking water quality and health value Resin solid or very viscous substance of either plant or synthetic origin that can be converted to polymers and that is used to extract minerals from water Reverse osmosis pressure-driven movement of water through a semipermeable membrane from the side of the membrane with more concentrated solution to that of a less concentrated solution Riparian located on the bank of a natural watercourse Salinity the concentration of total dissolved solids in water Salinity tolerance threshold the maximum TDS concentration of the desalination plant discharge at which the concentrate will not exhibit harmful effect on the aquatic environment. Salinity tolerance threshold usually is established based on the most-salinity sensitive species living in the discharge area

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Glossary

Salt passage the ratio of the concentration of salt/s (ion/s) in permeate and the concentration of the same salt/s (ion/s) in the feed seawater. Typically, salt passage is expressed as percent of the feed water concentration of the salt/s Salt rejection the ratio of salt/s (ion/s) removed (rejected) by the RO membrane to the salt/s (ion/s) of the source water. Salt rejection is equal to 100% minus the salt passage Saturation filling or dissolving a substance so that no more can be added Scale mineral deposits formed on the surface of membrane and/or membrane matrix as a result of concentration (saturation) of the mineral/s to a level at which they form insoluble amorphous or crystalline solids Scale inhibitor see antiscalant Scaling process of scale formation on the surface or in the matrix of RO membrane Semi-arid area an area characterized by very low rainfall, less than 500 mm per year Semi-permeable membrane membrane that has structure that allows small molecules, such as water, to pass while rejecting a large portion of the salts contained in the feed water Silt density index (SDI) a dimensionless parameter widely used to quantify the potential of seawater to cause particulate and colloidal fouling of RO membranes Sludge liquid, semisolid or solid residuals generated from the pretreatment of seawater by, sedimentation, dissolved air flotation, filtration, or other separation methods Slurry a thin watery mixture of insoluble materials (e.g., concentrated brine) Solute a substance dissolved in another substance (the component present in a lesser amount) Sorbent a material that absorbs or adsorbs liquids or gasses Spiral-wound element an RO or NF membrane element which consists of membrane leaves wound around a central permeate collection tube and including feed and permeate spacers, anti-telescoping devices and a brine seal Stage a set of pressure vessels installed and operated in parallel Supernatant the clear liquid overlying material deposited by precipitation, settling, or centrifugation Supersaturation a solution containing more dissolved material than could be dissolved under normal circumstances Subsurface intake intake located below the ground surface collecting source water from groundwater aquifer. Examples of subsurface intakes are vertical, horizontal and slant wells and infiltration galleries Suspended solids particulate solids suspended in the water Sustainable capable of being maintained and continued with minimal long-term effect on the environment Synthetic not of natural origin Terrestrial living or growing on land, not aquatic Total dissolved solids, salinity measure of the total mass of all dissolved solids contained in the water Total suspended solids the concentration of filterable particles in water (retained on a 0.45 µ filter) and reported by volume Train a membrane system which consists of rack housing a number of pressure vessels which have a common feed, permeate, and concentrate piping and control equipment, and can be operated independently. The RO system or pressure-driven MF or UF membrane system consists of multiple trains operating in parallel Transmissivity the rate at which groundwater flows horizontally through an aquifer

Glossary

Turbidity a measure of concentration of suspended solids in water which is determined by the amount of light scattered by these solids Ultrafiltration filtration through membranes of pore size between 0.01 and 0.05 µ Uniformity coefficient the ratio of the 60th percentile media grain diameter to the effective size of the filer media Vacuum filtration filtration through MF or UF membrane created in enclosed filter vessel by applying vacuum Viscosity a tendency of fluid to resist flow (movement) as a result of molecular attraction (cohesion) Zero liquid discharge (ZLD) concentrate management alternative in which the concentrate is converted from liquid phase to solid phase (salt residual) by evaporation, freezing or other means allowing to crystalize the salts contained in the concentrate Zone of initial dilution (ZID) area around the discharge of desalination plant at which boundary the concentration of the TDS of the mix between concentrate and ambient water reaches 10% of the TDS level

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Index Note: Page numbers followed by “f,” “t,” and “b” refer to figures, tables, and boxes, respectively.

A Acidification, 159t, 202 Adelaide, 41 42 Adsorption, 214 215, 217 219, 252 Advantages, 1, 25, 64, 72t, 107, 152 153, 209, 216, 223, 225, 234, 248, 252 Aeration, 55 56, 62 64, 175 176, 176f, 243 Agricultural, 103 104, 151, 217 219 Alginate, 218 219 Alicante 1 SWRO, 105 106 Alkaline, 14, 156, 159t Ambient water, 26 27, 30 31, 36, 51, 97t, 102t, 126 Anaerobic, 132 Analysis, 30 31, 33, 37 53, 66, 74 75, 102 103, 115, 127t, 151, 247 248 Anionic, 213 215, 217, 236 Anthropogenic, 94 Antigua desalination plant, 31 Antiscalant, 17, 51, 98 99, 132, 134 135, 147, 212, 225, 251, 253t Apoxia, 107 Aquatic habitat, 32, 53, 89, 102 103 Aquifer, 2, 138 140, 143, 151, 156, 224, 245, 250 Arizona, 178 Ashkelon SWRO Plant (Israel), 26, 26f, 98 99 Australia Gold Coast Desalination Plant, 88 93 Perth I Desalination Plant, 79 88 Sydney Water Desalination Plant, 41 Australian and New Zealand Environmental and Conservation Council (ANZECC), 40, 42, 44 45

B Backpressure, 200 202 Barcelona SWRO plant, 46 Bathymetric, 47 49 Belt filter press, 81, 87 89, 122 124, 237 241, 238f Beneficial use feasibility, 220 joint desalination and reuse, 226 229 Benthic, 30 31, 49 50, 65, 86, 93, 102 104, 107, 120 121, 124 125, 128 Bentonite, 180 181 Bio-accumulative, 32, 42 Bioassay, 32, 65

Biocide, 17, 19 Biodiversity, 44 45, 47 48 Biofouling, 72t, 251 Biological oxygen demand (BOD), 17, 23, 27, 96 Biomass, 31, 69 Biometrics test, 35, 114, 117, 120, 121t Brackish water reverse osmosis (BWRO), 54, 64, 66, 79, 97, 141, 144, 146 148, 162, 166 167, 169, 182 183, 185, 206, 212, 219, 224 225, 247 248 Brine, 1, 5, 17, 102 103, 188 191, 193 195, 198, 206 207, 210, 213 215, 228 229, 252, 253t Brine concentrator, 187, 188f, 189 190, 193 194, 193f, 194t, 196 198, 202 207 Build own operate transfer (BOOT), 6 Buoyant, 57, 99

C California, 10 11, 26, 37 39, 66, 112, 175 176, 206, 212 213, 240f, 253t Canary Islands, 45 46, 107 109 Carboneras SWRO Plant (Spain), 69 Carbon footprint, 1, 116, 202 203, 248 250, 253t Carcinogenic, 56 Carlsbad SWRO, California, 10 11 Cartridge filters, 71, 80, 94, 101, 103 104, 107, 146 147, 232t Case studies, 79, 206 207 Cationic, 213 215, 217 Centrifuge, 101, 104, 189, 196 197, 206 207, 237, 239 241, 239f, 240f Chemical cleaning residuals, 20 23, 242 243 quality, 22 23 quantity, 20 22 Chemically enhanced backwash (CEB), 233 234, 233t China, 3, 8, 196, 218 Chloralkaline, 194 195 Chlorophyll, 43t, 96, 98 99 Clay, 139, 180 181, 215 Cleaning solutions, 13 14, 21 23, 22t, 81, 89, 96, 98, 104, 107, 111 112, 114, 128, 132, 134, 231, 232t, 233, 242 Clean Water Act (CWA), 8 10, 44, 115, 128, 255 Clean-in-place (CIP), 13 14, 20 22, 20f, 115, 231, 232t, 234 Coagulation, 122 124, 236

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Index

Cockburn sound, 80 81, 84 85 Co-disposal with power plant cooling water cost factors and analysis description, 67 70 design and configuration guidelines, 72 74 potential environmental impacts, 70 source water treatment requirements, 70 72 Co-disposal with wastewater effluent cost factors and analysis, 66 description, 64 examples, 66 67 feasibility considerations, 65 66 potential environmental impacts, 64 65 Collocation, 68 70, 72 75, 72t, 225 Colloidal, 18, 20 Concentrate beneficial use, 209 conveyance, 58, 62, 171, 187 management, 1, 8 12, 169, 202 206, 231, 245, 251 252 power plant cooling, 65, 126 127 pretreatment, 146, 206 pumping, 146 quality, 15 17 quantity, 15 storage, 153, 162 163, 163f, 167, 169 surface water discharge, 25 treatment, 7 8, 54 56, 187, 202 203, 224, 250 Concentrate treatment requirements, 54 55, 55 56 Concentration factor (CF), 16 17 Concentrator/crystallizer, 206 207 Conductivity, 48 49, 52, 84t, 86, 86f, 164 166, 164f, 178, 180 Configuration, 1, 31, 60, 72 75, 134 135, 142 145, 152 153, 201, 204, 236, 243 Confined aquifer, 141 144, 156, 250 Construction costs, 8t, 31, 58, 60 64, 62f, 68, 75, 145 146, 145t, 167 171, 168f, 170f, 180, 184 185, 184f, 201, 204 206, 205f, 229, 233, 246t, 247 248, 248t Contaminant, 10, 13 14, 27, 44, 55 56, 65, 93, 137 138, 212 213, 242 243 Corrosion, 56 57, 140 141, 189, 197, 203 Cost examples, 63b, 146b, 168b, 169 170, 171b, 185b, 205b Cost factors and analysis, 66, 74 75 Costs construction, 8t, 31, 58, 60 64, 62f, 68, 75, 145 146, 145t, 167 171, 168f, 170f, 180, 184 185, 184f, 201, 204 206, 205f, 229, 233, 246t, 247 248, 248t

operations and maintenance, 189, 203, 206 207, 233, 240 241 of water production, 7, 56, 66, 74 75, 200, 206 207 Crop irrigation, 9 salinity tolerance, 160t Crystallizer, 187, 189, 196 198, 202 207, 205f

D De-aerator, 187 188 Deep well injection, 8 9, 137 139, 141 142, 146 148, 169, 206, 225, 245 246, 246t, 248, 248t, 250 Degasification, 202 Desalination plant cost, 2 3 discharge, 8 10, 13, 26, 30 34, 44 45, 50 53, 81, 86, 86f, 89, 96 99, 104 106, 109, 114 116, 120, 124, 126 128, 134 135, 234, 247, 247f recovery rate, 133 schematic, 14f waste streams, 13 14, 232f, 237 Description, 64, 67 70, 81 83, 89 91, 96, 101 102, 104 108, 125 126, 131, 137 141, 151 155, 173 178 Design example, 162b, 165b, 166b Design guidelines, 56 60, 180 Design bid build (DBB), 7 Design build operate (DBO), 6 Desorption, 214 215, 217 Desulfurization, 196 Detergents/surfactants, 14 Dewatered, 81, 87 89, 101, 104, 122 124, 189, 196 197, 234 235, 239 241 Diffuser design, 82 83 outfall, 25 27, 31, 59f, 85 86 ports, 58 59, 82, 91 structure, 60, 60f, 66, 249 Diffuser ports, 58 59, 82, 91 Dikes, 103 104, 167, 180, 183 Discharge characterization, 13 conductivity, 86f near-shore, 25, 26f, 62f, 63 64 Discharge impact on the environment, 51 Disinfection, 80, 88 89, 111 Dissipation, 35, 58 59, 64, 69 70, 72t, 109f Dissolved oxygen (DO), 28, 43t, 48 49, 52, 55 56, 81, 84 85, 87, 92t, 93, 94t, 96, 97t, 102t, 105t Distillation, 195

Index

Diurnal, 134 Divalent, 192 194, 215 Dose, 18 Double-lined, 147 148 Drought-proof, 1 4, 7 8, 10

E Earthen, 153, 155, 169, 173, 177, 180 Ease of implementation, 249 250 Ecological, 40, 42, 93 Economy, 2, 213, 252 253 Ecosystem, 51, 81 Effluent, 31 32, 38, 51, 66, 93, 131, 133, 223 224 Electrodialysis (ED), 3, 189 190, 214 215 Embayment, 124 125 Encina Power Plant, 109 Endangered, 29, 35, 47, 94, 101 Endocrine disruptor, 28, 56 End-of-pipe, 53 Energy costs, 58, 151, 169, 229 Energy recovery system (ERS), 7, 58, 99, 101, 201 Energy use, 8t, 116, 191, 193, 194t, 195 196, 200, 202 207, 250 Entrainment, 45, 47 48, 55, 69 70, 72t, 116, 229 Environmental impact, 12, 25 26, 29 31, 36 37, 42, 47, 65, 75, 79, 209, 248 249 Environmental monitoring well system, 146 Epifouna, 96 Equipment, 7, 13, 32 33, 57 58, 62 64, 99, 132, 134, 139, 155, 187, 189, 203 204, 215, 231, 236 237, 240 241, 250 E-REX, 198, 200 202 Europe, 3 4, 103, 112 Evaporation ponds conventional, 173 174, 174f, 180 183 costs, 184 185 description, 173 178 design and configuration guidelines, 180 183 feasibility assessment, 178 179 potential environmental impacts, 178 sizing, 180 183 solar, 178, 215 spray, 175, 175f Evaporator, 175, 188 189, 196 197, 204, 206 207, 216 Evaporator-crystallizer, 198, 199f, 202 205, 250

F Feasibility assessment, 30, 142, 156 160, 178 179, 203 204 Feasibility considerations, 65 66, 70, 72t Feed water, 13, 20, 101, 109, 126, 190 191, 196, 202, 227 228, 231, 232t

Ferric chloride, 18, 32 33, 93 94, 96, 101, 111 112, 251 Fertilizer, 194, 218, 237 Fiberglass-reinforced, 140 Filter press, 196 197, 240 Filtration, 7, 17 18, 55 56, 88 89, 93 94, 101, 105 106, 232t, 233, 236 Flocculation, 122 124 Flooding, 159, 165 Flow diagram, 61f Flowrate, 51, 60, 62, 65, 183, 204 Fluctuation, 33 35, 66, 126, 183, 210 Flux, 195 196, 198 202 Footprint, 1, 69 70, 101, 116, 120 121, 202 204, 213, 235 236, 246, 250 Forage, 161 162, 169 170 Foraminifera, 31 Fouling, 7, 20, 22 23, 195 196, 200 202, 242 Fujairah SWRO plant (United Arab Emirates), 26

G Geocomposite, 185 Geological formation, 138 139 Geomembrane, 178, 181 Germination, 85 Gladioferens, 85 Glass-reinforced plastic (GRP), 56 57, 57t, 82, 134 135, 140 Gold Coast SWRO, 42, 60, 92t, 93 Granular media filters, 13 14, 20, 125 Granulometry, 96 Groundwater monitoring, 169, 171, 178 Guidelines, 38 39, 42, 59, 160, 160t, 162, 165, 251 Gypsum, 210 211, 214t, 217 218

H Habitat, 29, 32 33, 45, 49 50, 104, 212 213 Halophytes, 157, 161 162, 161t, 219 Heavier, 58 59, 64 Hedionda, 109, 116 High density, 217 High-density polyethylene (HDPE), 56 57, 57t, 60 62, 64, 93 94, 134 135, 180 181 High-salinity, 109, 189 190, 196, 201 202, 220, 227 228, 249 High-value, 5, 213 214, 214t Homogenous, 209 Humidity, 151, 178, 184 185, 250 Huntington Beach, 38, 66, 112, 120 Hydraulic Surface Loading Rate (HLR), 164 165 Hydrobiological, 124 125, 128 Hydrocarbons, 48, 52

273

274

Index

Hydrodynamic, 11, 26 27, 31, 34 35, 49 50, 52, 65 66, 97, 99, 112, 115, 128 129 Hydrogeological, 140 143, 148, 160, 163 Hypalon liner, 180 Hypoxia, 84

I Impingement, 45, 47 48, 55, 69 70, 72t, 116, 225, 229, 253t Imposex, 45 Infouna, 96 Inhibitor, 36 37, 188 Injection well casing, 140 costs, 145 146 discharge capacity, 142 145, 144f, 145t grouting, 140 shaft, 139 sizing, 143 145 Injection zone, 137 143, 148 Inorganic, 14, 17, 22t, 43t, 195 196, 218 Intake open, 55, 80, 101, 103 104 subsurface, 55 Ion, 16 17, 31 32, 54, 194t, 228 Ion imbalance, 31 32, 54 55, 64 65 Iron, 17 19, 32 33, 49, 55 57, 70, 72t, 98 99, 102t, 105 106, 105t, 127t, 234 Irrigation system area, 162 costs, 167 171 rapid Infiltration, 156, 159 160 sizing, 160 163 Isochrysis, 85 Israel Ashkelon desalination plant, 93 99 Sorek desalination plant, 99 103

J Javea and San Pedro del Pinatar plants, 105 107 Javea SWRO, 105 107 Joint desalination and reuse, 226 229, 226f

K Kwinana SWRP Plant, Perth (Australia), 41

L Lacustrine, 148 Lamella, 44, 81, 87 89, 101, 104, 122 125, 146, 235 237, 237f, 237t Land application, 8 9, 151, 156, 167 171, 173, 178, 185, 223, 245 246, 249 250

Landfill, 56, 68, 81, 87 89, 101, 111 112, 114, 169 170, 173, 187, 189, 202 203, 206, 234, 240, 253t Land requirement, 162, 183, 205 Limestone, 94, 101, 140, 148, 231, 251 Limits effluent, 38 salinity, 39 40, 115 Liner, 178, 180 181, 185 Lithology, 163

M Macroalgal, 31, 34 Macrofauna, 31, 120 121 Macromolecules, 217 Manganese, 49, 55, 146, 159t Marine species, 11, 31 32, 35, 39, 49 50, 52, 101, 112, 114, 117, 118t, 129 Maspalomas II desalination plant, Canary Islands, 107 109 Mediterranean, 45, 46f, 47, 50 51, 101, 181 182, 201, 211 212 Membrane cleaning, 7, 13 14, 21 22, 22t, 28, 51, 96, 107, 111, 125, 128, 132, 134, 231, 233, 242, 253t Membrane configuration, 134 135 Membrane elements, 7, 198, 200 201 Membrane flux, 202 Metastable, 216 Mexico, 126, 141 Microalgae, 31, 220 Microfiltration (MF), 215, 232t Mineral content, 15 16, 134, 192, 194 Mitigation, 6, 12, 39, 47 48, 53, 116 Monitoring program, 1, 29, 51 52, 96, 124, 127 128 Monitoring well, 142, 146, 156, 166, 169, 178 Multistage, 198 200, 229f Multivalent, 17

N Nanofiltration (NF), 4, 17, 192 Nanoparticle, 5, 195 196 Near-shore discharge, 25, 26f, 62f, 63 64 New surface water discharge, 25 27, 60 64 Nitrates, 43t, 49, 52, 99, 212 213 Nonconcentrate residuals, 231, 232t Noncondensable, 188 Nonhazardous, 137 NPDES permit, 9 10, 38, 114 116, 126 127 Nucleation, 216 Nutrients, 23, 30, 45, 94, 96, 98 99, 204, 237, 253t, 255

Index

O Ochre, 118t, 121t Offshore discharge, 53 Onshore, 52, 96, 106, 109 Operations and maintenance (O&M), 6, 169 170, 189, 203, 206 207, 233, 240 241 Organic fouling, 20 Organics, 13 14, 17, 20, 22t, 44, 49, 51, 64, 132, 195 196, 237 Osmosis, 1 2, 5, 13, 54 55, 79, 135 136, 146, 195 196, 202 203, 231, 251 Osmotic, 17, 33, 69, 157, 190 193, 195 196 Osmotically assisted reverse osmosis (OARO), 189 196, 202 203, 215 Outfall costs, 63f diffuser design, 82 83 pipeline, 56 58 Overview, 1, 8, 25, 27 30, 105 107, 187 Oxidation, 55 56 Ozonation, 56

P Paleozoic, 148 Particulate fouling, 20 Particulates, 13, 20, 51, 111 112, 233 Pathogens, 2, 7, 64, 224 Pelagic, 31 Percolation ponds, 9, 153 Perforated, 26, 58, 140, 154 Perforations, 58 Permeability, 138 139, 143, 157, 159 160, 163 Permeate, 13 14, 17, 22, 57 58, 72t, 105 106, 147, 190 192, 195 198, 200 202, 232t, 242 Permitting agencies, 8 10, 47 48 Australia, 45 Israel, 50 53 limits, 38 practices, 10, 37 regulations, 39 regulatory bodies, 50 Spain, 45, 47 48 support studies, 47 48 USA, 37 40 Perth, Australia, 79 88 Perth I desalination plant, 79 88, 83f pH adjustment, 243 Phenolic, 117t Phytoplankton, 65 Plastic pipe, 56 57 Plate-and-frame filter press, 237, 240 241, 241f

Plume, 26 28, 30 31, 47 48, 58 59, 64, 69 70, 82 83, 85, 91, 98 99, 107, 120 121 Polychaetas, 31 Polyethylene, 215 Polyethyleneimine (PEI), 217 Polymer, 217, 219, 233 234, 236, 238 239 Polypropylene (PP), 56 57, 57t Pond area, 181 183 depth, 180 dykes, 180 liner, 180 181 Porous, 138 139, 155, 167, 238 239 Poseidon, 115 116 Poseidonia, 103 104 Post-treatment, 231, 251 Potential environmental impacts, 25, 27 53, 64 65, 70, 131, 141 142, 155 156, 178, 202 203 Power plant, 25, 32 33, 65 75, 72t, 96 99, 109, 110f, 115 116, 122 127, 203, 225, 252 Precipitation of minerals, 211f Pressure filtration, 105 106 Pretreatment conventional, 234 membrane, 7, 13 14, 20, 36, 233 234, 233t Process design, 143 Product water, 11, 13, 16, 22, 36, 58, 94, 111, 126 127, 129 Pumping, 57 58, 135, 140, 152, 213, 229, 233, 240, 246 Purification, 218 Pycnocline, 84

Q Quality, 2, 5, 15 19, 22 23, 49, 56, 70, 202 203, 233, 248 249 Quantity, 11, 15, 18, 20 22, 171, 185, 233 Queensland, 40 42

R Radioactivity, 33, 117t Radionuclide, 32 33 Rapid infiltration basin (RIB), 9, 155, 155f, 167, 170 171, 183 Rare-earth, 213, 252 Raw seawater, 217 Recirculation, 22, 30, 72, 187 Reclamation, 1, 28 29, 38 39, 253t Recovery, 15 16, 187, 193, 197, 200 202, 210 212, 216, 225, 247 248 Redundancy, 141, 143

275

276

Index

Regional Concentrate Management types, 223 use of Brackish water concentrate, 224 226 Regulations Australia, 42 Israel, 50 Spain, 47 49 USA, 39 Regulatory acceptance, 249 Regulatory requirement, 1, 4, 7, 10, 38 39, 44 45, 75, 156, 159 Reject, 192 193, 212, 219, 233, 233t Rejection, 7, 16 17, 213 214, 214t Reliability, 1, 5, 227, 250 Remediation, 42, 125 127 Remineralization, 194 Residual, 8 10, 13, 22, 28, 188, 196, 212, 231, 232t, 233, 237, 240, 242, 253t Resin, 194, 217 Reverse osmosis (RO), 1 2, 13, 54 55, 79, 135 136, 146, 195, 202 203, 231, 251 Riparian, 29

S Salinity tolerance evaluation (STE), 34 36, 116 120 Salt passage (SP), 16 17 Salt rejection, 16 17 Salt solidification and recovery, 210 212, 210f Salt-gradient, 177 Salt-tolerant crops, 160 Saltwater wetlands, 212 213 San Diego, 111, 115 116, 120 San Pedro de Pinatar SWRO, 105 106 Sand, 31 32, 49, 71, 101, 117, 118t, 121t, 122 124, 122t, 133, 146 147 Sanitary sewer discharge, 135 136, 246t, 248t Santa Ana river interceptor (SARI), 66 Santa Barbara, 65, 67, 241f Saturation, 43t, 177, 215 Saudi Arabia, 192 193, 251 Scaling, 13, 17, 36 37, 132, 142, 145, 188, 190, 193, 196 197, 215, 251 Scarcity, 1 3, 5, 29, 133, 187, 203 204 Schematic, 14f, 20, 138f, 188f, 193f, 195f, 197f, 198f, 210f, 235f, 236f, 238f, 239f, 241f, 242f Screening, 68, 71 72, 231 Sea urchin, 31 32, 65, 114 Sedimentation, 7, 36, 55, 111 112, 133 135, 232t, 234 237, 237t Selection of geological formation, 138 139 Semi-arid, 8, 173 Shallow beach well disposal, 141, 250

Silica, 22t, 49, 97, 202 Site footprint, 246t, 250 Sizing of injection wells, 143 145 Sludge, 9, 19, 44, 81, 88 89, 101, 111 112, 114, 133 134, 231, 237 241 Slurry, 187 189, 196 198, 206 207 Sodium absorption ratio (SAR), 157 Soil conductivity, 164 165, 164f Solutes, 195 196 Sorbents, 218 219 Sorek desalination plant, 99 103 Source seawater, 11, 15 16, 27, 55 56, 65, 72t, 74 75, 80, 93 94, 101, 103 104, 114 115, 122 124, 201, 215, 226, 229, 233 234, 237, 253t Spain Alicante 1, 105 107 Javea, 105 107 Maspalomas II, 107 109 San Pedro Del Pinatar, 105 107, 106f Torrevieja (Alicante), 103 105, 103f Spent pretreatment backwash water, 114, 231 241 Spray evaporation ponds, 175f Spray irrigation, 152, 152f, 162 163, 166 171, 175, 183, 185, 248 249, 248t Sprinkler system, 151 153, 154f Stabilization, 80, 88 89, 111, 219 Steady state, 234 Stratification, 177 Subsurface drainage, 154, 156, 158, 167 Subsurface intake, 55 Supernatant, 87, 111 112, 114, 125 Supersaturation, 214 216 Surface loading rate, 166, 236, 237t Surface systems, 152 Surface water discharge, 8 10, 19, 25 27, 54 64, 79 129, 141, 223, 245 246, 248 Sweep, 190 191 Sydney Water, 41, 60f Synthetic, 218 219

T Tampa Bay desalination plant, 38, 122 129, 124f, 236, 237f, 238 239, 238f Tampa Bay Water, 124 128 Tasmania, 42 Terrestrial, 209, 213, 252 Test biometrics, 34 35, 114, 120, 121t salinity range, 34 salinity tolerance, 35, 114, 117, 120, 122t species, 11, 34 35, 39 Test species, 11, 34 35, 39 Texas, 38 39, 139, 147 148, 178

Index

Thermal, 1 3, 36, 69 70, 116, 178, 187, 189, 196, 212, 216, 253t Threshold, 19, 26, 30, 32 33, 36 37, 54 55, 120, 128, 132 134, 156, 161 162, 225 Tidal, 25 27, 30, 94, 107, 125 Torrevieja (Alicante) desalination plant, 103 105 Total dissolved solids (TDS), 2, 15 16, 48, 52, 105t, 212, 225, 227 Total suspended solids (TSS), 18 19, 33, 51 52, 96, 105t, 190 Toxicity, 32, 42, 54, 65, 86, 93, 159t, 225 Trace metals, 156, 158, 159t, 178 Tracy, California, 206 Trans-membrane, 7, 195, 201 Transmissivity, 142 143 Treatment, 1, 19, 23, 36, 41, 55, 62 64, 79, 87, 107, 134 135, 191 192, 231, 234, 247 248, 250, 253t Trigger, 33 34, 42, 44, 51, 99 Tunnel, 57, 62, 64, 109 Turbidity, 17 18, 32 33, 36, 43t, 44, 51, 96, 99, 102t, 117t, 132, 235 236 Turbocharger, 201 Turbulent, 25 26, 58, 106 107 Turnkey, 6

U Ultrafiltration (UF), 217, 232t Ultraviolet radiation (UV), 56, 180 Underground injection control (UIC) program, 8 10 Underground source of drinking water (USDW), 137 138, 143 Unit cost, 64, 169, 185 United States of America’s Environmental Protection Agency (USEPA), 8 10, 32, 37 39, 44, 55 56, 137, 152 153, 158, 162, 164 165 USA Carlsbad, 38, 109 121

Huntington Beach, 38, 66 Tampa Bay, 38, 122 129 Utilities, 1, 135 136, 250, 255

V Vadose, 163 Vapor compression, 189, 206 Vessels, 20 21, 99, 196 197, 199, 218 Victoria, 40 42, 178 Viscous, 196 197 Vortex, 196 197

W Waste streams, 1, 13 14, 17, 19, 21 23, 44, 50, 64, 114, 137, 165, 203, 231, 233 234, 233t, 248 249 Wastewater effluent, 31 33, 54, 56, 64 67, 133, 227 Wastewater treatment plant (WWTP), 19, 25, 27 28, 31 32, 65 67, 70, 131, 133, 135 136, 156, 223 224, 228 229, 253t Water reuse, 4 5, 29, 46, 66, 133 134, 226 227, 253, 255 Well depth, 139, 143, 145 146, 145t Well diameter and number, 143 Well intake, 105 106 Wetland, 212 213, 219 Whole effluent toxicity (WET), 11, 30 32, 44, 84, 225

Z Zero liquid discharge (ZLD) costs, 204 206 description, 187 design and configuration guidelines, 204 feasibility assessment, 203 204 potential environmental impacts, 202 203 Zone of initial dilution (ZED), 30 31, 85 86, 102 103, 112

277