Environmental Pollution Control 9783110538311, 9783110537895

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Liu, Zhang, Liu Environmental Pollution Control

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Jingling Liu, Lulu Zhang, Zhijie Liu

Environmental Pollution Control

DE GRUYTER

China Environment Publishing Group

Authors Jingling Liu Beijing Normal University School of Environment Xin Jie Kou Wai Street No.19 100875 Beijing China [email protected] Lulu Zhang Hebei University of Science and Technology College of Environmental Science and Engineering Yuxiang Street No.26 050018 Shijiazhuang Hebei China Zhijie Liu Ministry of Environmental Protection of China Center for Environmental Education & Communications Yuhuinanlu 1 Chaoyang District 100084 Beijing China

ISBN 978-3-11-053789-5 e-ISBN (PDF) 978-3-11-053831-1 e-ISBN (EPUB) 978-3-11-053806-9 Set-ISBN 978-3-11-053832-8 Library of Congress Cataloging-in-Publication Data A CIP catalog record for this book has been applied for at the Library of Congress. Bibliographic information published by the Deutsche Nationalbibliothek The Deutsche Nationalbibliothek lists this publication in the Deutsche Nationalbibliografie; detailed bibliographic data are available on the Internet at http://dnb.dnb.de. © 2017 Walter de Gruyter GmbH, Berlin/Boston Typesetting: Compuscript Ltd., Shannon, Ireland Printing and binding: CPI books GmbH, Leck Cover image: RomoloTavani/iStock/Getty Images ∞ Printed on acid-free paper Printed in Germany www.degruyter.com

Preface Environment issues have become a complex issue involving many fields such as politics, economy, diplomacy, society, culture, science, and technology, with multiple dimensions. International negotiations on key environmental topics such as addressing climate change and conserving biodiversity have increasingly become the hot topic of foreign affairs and focus of interests of many countries in the world. This has something to do with deepening understanding of the international communities in the field of environment and development. In particular, there are four historic leaps of human understanding about eco-environment issues. The first leap happened at the First United Nations Conference on the Human Environment in Stockholm, Sweden, in June 1972. This conference gave a warning to the whole world that there is “Only One Earth.” The Declaration on the Human Development adopted by the conference stresses that “Man has constantly to sum up experience and go on discovering, inventing, creating and advancing.” The second leap happened at the United Nations Conference in Environment and Development held in Rio de Janeiro, Brazil, in June 1992. This meeting, for the first time, considered economic development in the context of environmental protection, identified the principle of “common but differentiated responsibilities,” and put forward sustainable development strategy. The third leap happened at the World Summit on Sustainable Development held in Johannesburg, South Africa, in August of 2002. This meeting identified that economic development, social progress, and environmental protection are the three pillars for sustainable development. The fourth leap occurred at the United Nations Conference on Sustainable Development held in Rio de Janeiro, Brazil, in June 2012. Targeting the themes of “Build Green Economy to Achieve Sustainable Development and Lift People out of Poverty” and “Institutional Framework for Sustainable Development,” this conference discussed and adopted the outcome document The Future We Want, centering on the three objectives of “Securing renewed political commitment for sustainable development,” “Assessing the progress and implementation gaps in meeting previous commitments,” and “Addressing new and emerging challenges.” It has decided to launch the process for achieving the objectives of sustainable development and help developing countries enhance their capacity in sustainable development. The commencement, growth, and development of environmental protection cause of China keep the same pace with that of the world. As the biggest developing country in the world, China makes active contributions to the four leaps in the field of global environment and development. In particular, the Central Committee of Communist Party of China and the State Council put forward a series of new concepts, such as the development of ecological civilization, ecological restoration of rivers and lakes, promotion of historic transformations of environmental protection, and exploration of new path to environmental protection that protects the environment in the process of development and development in the process of environmental protection, DOI 10.1515/9783110538311-202

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 Preface

and have released many major policy measures since the beginning of the “11th FiveYear Plan” period to facilitate important changes in environmental protection from understanding to practice. In view of the difficulties, such as still prominent imbalanced, uncoordinated, and unsustained development issues, inappropriate industrial structures, increasing resource and environment constraints and evidently more social contradictions in the development of our country, the 18th National Congress of Communist Party of China, closed in mid-November 2012, for the first time integrated the development of ecological civilization into the five overall arrangements for the cause of socialism with Chinese characteristics. This is a key innovation of the Chinese Government in both concept and practice of development; a strategic option complying with the new trend of green and low-carbon development of the world; and an effective approach to facilitate our economy and society following the path of comprehensive, coordinated, sustainable, and scientific development. The development of ecological civilization is both a key development issue and an important welfare issue. It is conducive to the improvement of eco-environment quality, promotion of social harmony and stability, and enhancement of sustainable development capacity. We must establish the idea of ecological civilization that respects and complies with and protects nature, put the development of ecological civilization at prominent position, and incorporate it into all aspects and whole process of economic, political, cultural, and social development; strive for developing beautiful China; march toward new era of socialist ecological civilization; achieve sustainable development of the Chinese nation; and make contributions to global ecological safety. The Chinese Government firmly adheres to the independent foreign policy of peace, unswervingly follows the path of peaceful development, and strives for developing a harmonious world of lasting peace and common prosperity. In international environment cooperation and exchanges, China firmly adheres to the principles of common but differentiated responsibilities, equity, and respective capability; proactively lends a helping hand to developing countries; shoulders the obligations and responsibility for foreign aid within our capacity; actively strengthens the unity and cooperation with developing countries; jointly safeguards legitimate rights and interests of developing countries; supports stronger representation and voice of developing countries in international affairs; and will always be a reliable friend and sincere partner of developing countries. With the Green Envoy Program of China South–the South Environment Cooperation, the Ministry of Environmental Protection has organized a range of environmental protection training courses for environmental officials and professionals of developing countries over the past few years, with participants from the countries of regions like Africa, West Asia, Oceania, Southeast Asia, Central Asia, and Latin America, which have facilitated bilateral and multilateral environmental cooperation and strengthened friendship and mutual understanding and obtained good achievement. To better standardize the management of international environmental training

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and exchange activities in the future, the Ministry of Environmental Protection has organized relevant experts to compile a series of books for environmental training under the Green Envoy Program of China South–South Environmental Cooperation. This series includes six books that systematically summarize typical policies, laws and regulations, management skills, and professional expertise in environmental protection field of China. With both professional theory and analysis on practical cases, this series of books fill the gap of the textbooks for training overseas participants in the field of environmental protection. I believe that the publication of this series of books will showcase and publicize new concepts and successful practice of environmental protection of our country, especially an important role in publicizing successful experience of our country in the development of ecological civilization and beautiful China.

Contents Preface 1 1.1 1.2 1.3 1.4

v The principle of environmental pollution control The basic theory 1 Environmental pollution control targets 4 Pollution control technology 8 High-technology outlook 13

17 2 Water pollution control technology 2.1 Introduction 17 2.2 Physical method 19 2.3 Chemical method 26 2.4 Physicochemical method 34 2.5 Biological method 51 2.6 Technique process and reuse of wastewater 2.7 Summary and outlook 72

1

64

73 3 Air pollution control technology 3.1 Introduction 73 3.2 Air pollution control technology for stationary source 75 3.3 Air pollution control technology of mobile source 86 3.4 Summary and outlook 96 99 4 Solid waste pollution control technology 4.1 Introduction 99 4.2 Solid waste treatment and disposal technologies 100 4.3 Industrial solid waste treatment and disposal technology 122 4.4 Hazardous waste treatment and disposal technology 124 4.5 Summary and outlook 136 139 5 Physical pollution control technology 5.1 Introduction 139 5.2 Sound source control technology 142 5.3 Noise control technology 169 5.4 Noise pollution control planning and management 5.5 Other physical pollution prevention technologies 5.6 Summary and outlook 187

177 181

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6 Ecological recovery technology 191 6.1 Introduction 191 6.2 Ecological engineering design 193 6.3 Ecological engineering technology 202 6.4 Ecological engineering technology optimization 6.5 Summary and outlook 245

222

247 7 Regional environmental systems engineering and technology 7.1 Introduction 247 7.2 Environmental system information technology and simulation model 247 7.3 Regional/watershed planning technology 271 7.4 Summary and outlook 285 287

Postscript

Acknowledgments

289

About the authors

291

Index

293

1 The principle of environmental pollution control 1.1 The basic theory The globality and complexity of environmental problems are new challenges faced by mankind; managers, experts, and the public around the world attach great­ importance to these. Environmental pollution control technology is the key ­technology for implementing sustainable development strategy. The principle of environmental pollution prevention and control is the optimization, application, and innovation of environmental pollution control technology and theoretical support. The types of environmental pollution could be classified in various ways. In accordance with environmental elements, it can be divided into air pollution, water pollution, soil pollution, and physical pollution. In accordance with anthropogenic activities, it can be divided into industrial pollution, cities pollution, and agricultural pollution. In accordance with the nature and sources of pollution, it can be divided into chemical pollution, biological pollution, physical pollution, solid waste pollution, and energy pollution. The features of environmental pollution are as follows: 1. Pollutants can enter the environment naturally or can be caused by human activities (for example from burning coal). Most pollution from anthropogenic activities occurs in or near urban and industrial areas, where pollutants are concentrated. Industrialized agriculture also is the major source of pollution. 2. Pollutants could transform, metabolize, degrade, or be enriched in the environment through biological, physical, or chemical reactions, which result in property and concentration change in pollutants and then cause different harmful effects. 3. Pollutants affect the human body in a long time through air, water, soil and food in various ways, for example, disruption of life-support systems for humans and other species; damage to wildlife, human health, and property; and nuisances such as noise and unpleasant smells, tastes, and sights. Two approaches are commonly used to deal with pollution: 1  preventing pollution that comes into the environment or 2 cleaning it up if it did. Pollution prevention or pollution source control can reduce or eliminate the generation of pollutants. Pollution can be prevented by the following “five Rs” of resource use: refuse, replace, reduce, reuse, and recycle. Theory is the foundation and precondition for technology and management innovation, which determines the development, practice, and integration of environmental pollution control. The theory of sustainable development requires legal protection, technical support, and management practice to build, in order to ultimately be built into national/regional environmental security and early warning system.

DOI 10.1515/9783110538311-001

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 1 The principle of environmental pollution control

1.1.1 Theory of circular economy Circular economy is a kind of ecological economy, which is the integration of cleaner production and comprehensive utilization of waste, in accordance with the material circulation of natural ecosystem and energy flow pattern reconstruction of the economic system; it is harmonious with the natural ecosystem material cycle. Circular economy is based on the basis of constant and circulatory use of resource, which requires the economic activities in accordance with the natural ­ecological system pattern, forming a “resource-product-renewable resource” such a closed-loop model of material cyclic flow. The important symbol of resource utilization is the comprehensive waste reutilization, reduction, and harmless. The main objective is to achieve the sustainable use of resources, such as the resources with “efficient use and low pollution emissions.” Circular economy will become the main mode in future development in developing countries. At present, the Guigang national ecological industry (sugar) demonstration zone and the South China Sea national ecological demonstration zone are carrying out cycle testing and pilot for the promotion of circular economy in China and have accumulated valuable experiences.

1.1.2 Life cycle theory The life cycle theory may be involved in various stages of the product system. It is an application of self-organization of ecosystem structure and function and the theory of ecological balance in the production and living. Life cycle is an important theoretical basis for clean production and aims at helping in environmental management. In the long-term, that is, the tools and techniques is very important in sustainable development. Life cycle assessment (LCA) includes the entire life cycle of the product or the production and living activities. LCA studies the environmental impact of the system from three areas: the ecosystem, human health, and resources consumption, but does not deal with the economic and social impact. In accordance with the ISO definition, LCA is a technique that researches the production, use, and disposal of the entire product life cycle from raw material (from the cradle-the grave-the cradle) and may be involved in the whole production process of the environmental aspects and potential impacts. LCA has 20 years of development history, known as “environmental management tools” in the 1990s; in the 21st century, it is the most important utility tool used at different levels of environmental protection and sustainable development and plays an important role in cleaner production and energy conservation.

1.1 The basic theory  

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1.1.3 Complex systems theory Complex systems theory is a front direction in system science, the most active fields of science and hotspot after combination with environmental sciences, which is the main task of complexity science. Its main purpose is to reveal the dynamic process of complex systems, which is difficult to explain through existing scientific methods. Compared with traditional reductionist approach, the difference is that the complex systems theory emphasizes combining holistic method with reductionist method to the analysis system. Living systems, social systems, and environmental systems are complex systems; the complex systems theory applied in large-scale integration and optimization of environmental technology, environmental simulation, and mathematical modeling has great significance. The main differences with the traditional control system are as follows: 1. Model: The system model is usually the subject and their interactions with the evolution of variable structure description. 2. Objectives: to the overall behavior of the system. 3. The law: to explore the general evolutionary dynamics law. In the process of national, regional/watershed, and urban environmental pollution control technology optimization and integrated prevention and control process, more and more applications of various types of environmental models and broad application prospects in environmental pollution control. 1.1.4 Ecosystem management theory Ecosystem management is driven by clear objectives and practical implementation under the supervision of policies and agreements, on the basis of ecological monitoring and ecological interactions, in accordance with the management to maintain the structure and function of the ecosystem. The purpose of ecosystem management is to overcome obstacles on the use of information obtained through adaptive management. Ecosystem management should apply ecological knowledge into natural resources management activities. The transfer from concept to practice needs to consider the sustainability, complexity, and relevance; the characteristics of ecosystem dynamics; and the relationship between human and ecological systems, adaptability, and interpretability. In recent years, sustainability has become the goal of natural resource management. In China, theory, technology innovation, and good experience have been made in natural resource management, industrial and agricultural ecological engineering, ecological city and new rural construction, and ecological restoration in the level of eco-city/community building and watershed/wetland restoration.

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 1 The principle of environmental pollution control

1.2 Environmental pollution control targets Environment problems, pollution features, and stages of development have differences in different countries/regions and scales, and environmental pollution control target should give full consideration to the particularity of environmental issues [1]. The main goals of environmental pollution control are as follows: 1. Pollution control: prevention and control of large quantities of pollutants entering into the water, air, and soil systems and ensuring the safety of environment and human health. 2. Ecological restoration: aims at regions with serious environmental pollution, to repair use functions of water, air, soil, and other environmental factors. 3. Environmental safety: plays the services function of ecosystem, provides a safe environment to sustainable production of human life. Aiming at the complexity, comprehensiveness, and lagging of environmental issues and guided by sustainable development theory, environmental pollution control targets have undergone great change, with trends from concentration control to total quantity control, from end treatment to the whole process, and from simple pollution control to environmental risk management [2].

1.2.1 Concentration control and total control Concentration control is the method of controlling the concentration of pollutants in the discharge port to protect environment quality. The emission concentration standards are based on the concentration of pollutants emission standards of the countries. In the past decades, China’s pollution control mainly according to the concentrations of pollutants emission standards. The implementation of concentration control is convenient in management, with lower request for managers; it is suitable for the actual situation of China’s economic development; and it has played a very important role in pollution control. With the continuous development of environmental issues, even if all sources of pollution are discharged according to standards, with the increasing number of pollution sources, the total discharge of pollutants will continue to increase; thus, those areas have serious environmental pollution. In pollutant emission control, according to the requirements of regional environmental objectives (environmental quality objectives or emission targets), the allowed maximum emissions of pollutants to achieve environmental objectives are precalculated, and then through optimum calculation, the emission targets in various of

1.2 Environmental pollution control targets 

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pollution sources are assigned; the allocation of emission targets should be based on different geographic locations, levels of technology, and economic affordability of pollution sources. The total amount control can be divided into “the capacity of total control” and “the goal of total control”. Environmental capacity refers to the maximum acceptance ability of the pollutants within a certain area and, based on environmental capacity, is the total amount of control, referred to as “the capacity of total control.” It is in accordance with the regional environmental quality objectives to calculate the environmental capacity and accordingly draw the maximum allowable volume of sewage, technical and economic feasibility, and the optimal allocation among the emissions of pollutant sources. Finally, the total capacity control scheme of environmental capacity is drawn up. The goal of total control is based on the total target or the reduction target in the regional pollutant emissions, starting from the levels of current emissions, through technical and economic feasibility analysis, to the emissions and reductions in the optimal allocation in the source of pollution, to develop a scheme of total control and to achieve the total targets of regional pollutant emissions and/or the reduction target of regional pollutant emissions. Concentration control and total amount control each has characteristics and are a kind of complement each other (Tab. 1.1); the relationship between the two cannot substitute each other. Selecting what kind of control method to use to solve the problem of pollution is based on the actual situation of the country and the region. In short, the pollutants has been changed from simple concentration control to a combination of total control in China. Tab. 1.1: Concentration control vs. total control of pollution sources.

Concentration control

Advantage

Disadvantage

Convenient, lower request for managers

Unable to guarantee the level of environmental quality Not take into account the disposal ability of pollutant sources Not related to the environmental capacity

Total control

Take into account of the environmental capacity

According to the status of China, there is still not related institution and standard to the total control.

Integrated control Source: Zhifeng Y, Jingling L, et al. Introduction to environmental science. 2nd ed. Higher Education Press 2010.

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 1 The principle of environmental pollution control

1.2.2 Decentralized control and centralized control Decentralized control, also known as “point source” control, is the method of controlling a single pollution source. Decentralized control has been a widely used control method and has played a role in pollution control. However, this control method has many disadvantages, such as disperse investments, hard management, short of economy benefits, and low comprehensive benefits. As opposed to decentralized control, centralized control of pollutants is also called “non-point source” control. Centralized control is established to protect the environment through centralized treatment facilities and management measures in a specific area and is an important approach to strengthen environmental management. The purpose of centralized control is to improve the environmental quality of the watershed, regional, and control units, in accordance with the pollution prevention plan, with central management according to the nature, the type, and the geographical location of wastewater and solid waste, with as small as possible inputs to obtain the greatest possible environmental, economic, and social benefits. Centralized control has directional strategic significance on environment management. With centralized control through a reasonable area, a focus on limited funds, and adopting relatively advanced technology for pollution concentration, it is possible to obtain larger benefits. Decentralized control requires each industry to separate the construction of pollution treatment facilities, which gives economic and management difficulties. Pollution of centralized control conforms to the international development trend. At present, the development of disposal of hazardous waste and facilities moves forward in a large-scale, centralized direction in industrialized countries. Although there are many advantages of centralized control, the implementation of centralized control requires a comprehensive urban infrastructure and reasonable industrial layout. The industrial layout of many cities in China is still relatively fragmented. Centralized control and decentralized control are indispensable in Chinese pollution control. The strategic change in China‘s pollution control aims to achieve the transition from decentralized control to centralized control.

1.2.3 Terminal control and whole process control In terminal control, also known as “tail control,” environmental management departments utilize various means to control/impose restrictions on the emissions of pollutants or the whereabouts. This control mode is carried out after human a ­ ctivity ­produces the consequences of pollution and damage to the environment. It is a primitive, traditional pollution control method. The terminal treatment is a stopgap measure, high investment, and poor effects control method.

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The whole process control, also known as “source control” method, is contraposed for terminal control. It mainly refers to the industrial production process control and management from source to final product; the substance of production system is a continuous, dynamic closed-loop control in order to achieve the maximization of resource utilization and minimization of waste. The main content of the whole process control is clean production, through the use of clean energy and raw materials and adopting clean production process to produce clean products, maximizing reduction of pollution sources. Therefore, the whole process control has significant economic, environmental, and social benefits, which belong to the active control. Terminal control is the traditional control method. However, as industrial development and environmental pollution problems have become increasingly prominent, the method of pollution control would be changed from terminal control to whole process control in China.

1.2.4 Pollution control and environmental risk management According to the latest research results on the theory of complex systems and ecosystem management, pollution control should be closely combined with environmental risk management, for early warning and forecasting of environmental safety, to minimize the impact of environmental risks to human life and production and to achieve pollution control and environmentally safe. Environmental risk is caused by human activities or by human activities and natural movement process, spread through environmental media. It has two characteristics, namely uncertainty and harmfulness. Environment risk assessment of a construction project is carried out through assessment, prevention, emergency response, and mitigation measures of toxic and hazardous substances, which is caused by the impact on personal safety and the environment impact and damage. The purpose of the environmental risk assessment is to analyze and forecast the potentially dangerous and harmful factors of construction projects, the process of construction projects and the degree of environment impact and damage, which are caused by toxic and hazardous substances such as leaks, so that the accident rate of construction projects decreases the degree of environmental impact to an acceptable level. The focus of an environmental risk assessment should include the degradation of environmental quality, and the forecasts and protection of the ecosystem. Condition permitting, you can use the safety evaluation data to carry out the environmental risk assessment. The main difference between environmental risk assessment and safety evaluation is the environmental risk assessment’s focus is on the environmental impact of the plant (field).

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1.3 Pollution control technology Environmental pollution control technology is an important technical support for the implementation of the basic national policy of environmental protection; the principle of environmental pollution control technology is the basics that environmental scientists must master. According to different classification standards, environmental pollution prevention and control technology can be divided into different types: according to environmental factors, it can be divided into water, air, and soil pollution control technology; according to the principle of the method, it can be divided into physical, physical chemical, chemical, biological, and ecological approach. 1.3.1 Control techniques based on pollutant Due to increasing pollution, many new pollutants such as Persistent organic pollutants (POPs) and Pharmaceutical and Personal Care Products (PPCPs) appear constantly; these pollutants usually have the characteristics of being degradation-resistant and having low concentrations. It is difficult for the technology of conventional biological and physical technology to effectively remove these pollutants. 1.3.1.1 Treatment technology of organic wastewater The removal effect of traditional technologies such as coagulation, sedimentation pretreatment, and biological treatment technology for pesticides, dye intermediates, and other degradation-resistant organic wastewater is low. Therefore, research on treatment technology in degradation-resistant organic wastewater is the focus of the wastewater treatment field. The pretreatment technology to improve wastewater biodegradability is the key of organic wastewater treatment. At present, a physical and chemical approach is used more often, which, based on the iron-carbon of the corrosion layer principle of electrolysis technology, is an application more effective than wastewater pretreatment; nitro compounds and organochlorine pollution wastewater can enhance the effect of biodegradability in wastewater. 1.3.1.2 Treatment technology of ammonia wastewater High concentrations of ammonia wastewater are common in chemical wastewater and landfill leachate. The high-concentration ammonia wastewater often leads to a biological treatment system that is difficult to run, and the degradation efficiency of organic wastewater is also greatly reduced. Wastewater treatment with highconcentration ammonia commonly uses the stripping-biological method, strippingbreakpoint chlorination method, and chemical precipitation-biological method.

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1.3.2 Control technology based on environmental factors According to environmental elements, environmental pollution prevention and control technology can be divided into water pollution control, air pollution control technology, and soil pollution control technologies [5]. 1.3.2.1  Water pollution control technology Wastewater treatment involves treatment through the use of various techniques to separate the pollutants from wastewater or transformation of the contaminants into harmless materials, so that the wastewater will be purified [3]. According to the technology principle and removal of the object, the method of wastewater treatment can be divided into physical treatment, physical and chemical treatment, chemical treatment, biological treatment, and ecological approach (Tab. 1.2).

Tab. 1.2: Main wastewater pollution control technology and the scope of processing object. Principle of method

Physical method

Physical method

Chemicalphysical method

Method of disposal

Object of disposal

Scope of application

Regulating reservoir

Balanced water quality and water yield

Pretreatment

Grating

Bulky suspended matter

Pretreatment

Screen

Small suspended matter

Pretreatment

Sedimentation

Gravity settling matters

Pretreatment

Flotation

Emulsified oil, close to water-density suspended matter

Pretreatment or intermediate treatment

Centrifuge

Emulsified oil, solid matter

Pretreatment or intermediate treatment

Blowoff stripping

Solubility gas

Pretreatment or intermediate treatment

Cyclone separator

Major-density suspended matter

Pretreatment

Filter

Small suspended matter

Intermediate or deep treatment

Membrane technology

Barbiturate, disintegrate pollutants

Deep treatment

Neutralization

Acid, alkali

Pretreatment

Coagulation

Colloform, small suspended matter Intermediate or deep treatment

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Tab. 1.2 (continued) Principle of method

Chemicalphysical method

Biological method

Ecological method

Method of disposal

Object of disposal

Scope of application

Chemical precipitation

Solubility harmful heavy metal

Intermediate or deep treatment

Redox

Solubility organic and inorganic pollutants

Intermediate or deep treatment

Extraction

Solubility organics

Pretreatment or intermediate treatment

Adsorption

Solubility organics

Intermediate or deep treatment

Ion exchange

Disintegrate pollutants

Deep treatment

Advanced oxidation technology

Difficult degradation organics

Pretreatment or deep treatment

Aerobic treatment

Colloform, Solubility organics

Intermediate treatment

Anaerobic treatment Macromolecule organics or Difficult degradation organics

Intermediate treatment

Biodenitrification

Ammonia nitrogen, total nitrogen

Intermediate treatment

Land treatment

Nitrogen, phosphorus, organic matter

Intermediate treatment

Stabilization pond

Nitrogen, phosphorus, organic matter

Intermediate treatment

1.3.2.2 Air pollution control technology On the basis of the physical form of atmospheric pollutants, air pollution control technology can be divided into particulate and gaseous pollutant control technology. These techniques are basically based on the physical and chemical methods (Tab. 1.3). Tab. 1.3: Main air pollution control technology. Atmospheric pollutant

Pollution control technology

Particulate pollutant

Gravitational dust collection, inertia force dust removal, centrifugal force dust removal, wet dust removal, electric precipitation

Gaseous pollutants

Absorption peak, adsorption process, catalytic combustion, condensation

1.3 Pollution control technology 

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1.3.2.3 Soil pollution remediation technology Heavy metals and organic pollutants (volatile, semivolatile, and difficult volatile organic compounds) are the main pollutants in soil. For different types and properties of pollutants, different soil remediation technologies are usually taken (Tab. 1.4). Tab. 1.4: Main soil pollution control technology. Pollutants

Restoration technology

Volatile/semivolatile organic pollutants

Soil replacement, microbial restoration, incineration, vapor stripping, heat desorption, chemistry redox

Difficult volatile organic compounds

Soil replacement, microbial restoration, incineration, multiphase extraction, chemical eluviation, immobilization, chemistry redox, immobilization

Heavy metal

Soil replacement, immobilization, chemical eluviation, plant absorption

1.3.2.4 Solid waste pollution control technology The key of solid waste pollution control is to solve waste treatment, disposal, and comprehensive utilization. The solid waste pollution control technology, which from the source of pollution, can be improved or applied new cleaner production process to strengthen the utilization of solid waste, to minimize the waste, for different types of solid waste generated in the process of the life and production, can be used reasonable disposal and processing technology. For industrial solid waste, using different methods of treatment and resource recovery is needed according to the nature of the solid waste. For toxic, hazardous waste and medical waste, disposal methods such as incineration and disinfection are needed (Tab. 1.5). Tab. 1.5: Main solid waste pollution control technology. Type

Disposal technology

Pretreatment

Consolidation, smash, separation, solidification, contraction

General treatment

Landfill, incineration

Resource utilization technology

Incineration generating, pyrolysis, aerobic compost, anaerobic fermentation

1.3.2.5 Physical pollutant control technology Noise, radiation, electromagnetic, thermal, and other physical pollution prevention controls are generally based on physical principles of technology (Tab. 1.6).

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Tab. 1.6: Main physical pollution control technology. Pollution type

Prevention technology

Noise pollution

Sound absorption, sound insulation, noise elimination, damp, vibration reduction

Radioactive contamination

Radioactive substances manage, work-yard ventilation, shielding protection

Electromagnetic pollution

Shielding protection, protection appliance, grounding protection, absorption protection

Thermal pollution

Improve thermal energy utilization efficiency, develop sunshine, geothermy, ocean, and wind energy, afforest

1.3.3 Control techniques based on regional environmental problems Compared to a global scale, the scope of a regional area is relatively small, but the environmental crisis is still there. Scales environmental crisis such as a large area of river basin water environment issues, land desertification, soil erosion, forest and wetlands shrink, scarcity of water resources, heat island effect, as well as smallerscale soil pollution and so on. 1.3.3.1 Technology to reduce carbon emissions Global warming has led to the greenhouse gas (carbon dioxide) control technology, which has become an important content of the air pollution control technology. Through utilization of natural photosynthesis to absorb carbon dioxide storage, the development of biotechnology and fuel cell energy can effectively control and reduce carbon dioxide emissions. Carbon dioxide pollution control technology included carbon dioxide capture and disposal technologies. For the capture of carbon dioxide pollution control, there are chemical absorption, frozen separation, membrane separation, and molecular sieve adsorption trapping method. More and more attention has been paid to geological disposal of carbon dioxide. Storing carbon dioxide in an oil gas well, underground aquifers, and the sea are three main ways of storing carbon. 1.3.3.2 Integrated control techniques of water pollution Taking water resource as an example, as essential resources for human survival and development, the development and utilization of water resources not only protect the domestic water needs but also promote social progress and economic development. In an industry such as agriculture, overexploitation of water resources and the destruction of manmade hydropower project pollution of water resources have caused

1.4 High-technology outlook  

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ecosystem changes. Wastewater treatment uses various techniques to separate the pollutants from wastewater or the contaminants into harmless material, so that the wastewater will be purified. Taking into consideration the role of technology principle and removal of the object, the method of wastewater treatment can be divided into physical treatment, physical and chemical treatment, chemical treatment, biological treatment, and ecological approach.

1.3.3.3 Integrated control technology of urban pollution At present, China is in a period of rapid industrialization and urbanization development. The urban ecosystem is a natural human-centered economic and social complex artificial ecosystem. The key of urban ecosystem function is the strength of the system self-regulating ability. The regulation of the urban ecosystem should rely on the decisions for urban planning, policies and regulations, public education, and management of human control. Urban ecological engineering is based on the basic principles of the regulation of an urban ecosystem, to create the eco-city goals, and on the use of biological, physical, chemical, social, political, and legal measures, to resolve a range of issues in the urban ecosystem [4].

1.4 High-technology outlook With the development of environmental science, increasing number and types of pollutants, and increasing challenges to the development of pollution control technology, current research and development of new pollution control technology are a hot research field in environmental science and engineering [6].

1.4.1 Energy-saving and emission-reduction technology The model of economic development in developing countries generally has a low labor cost and is resource-driven. From the model of resource consumption to the model of technological innovation, the core of the transition is to be closely linked to the major needs of energy saving in national and regional scales and to optimized key generic technologies to speed up technology promotion and application. Examples are using clean technology for renewable energy and fossil fuel efficiency; promoting the use of new-generation recycled steel production process technology in key areas such as steel, electricity, building materials, chemicals, and agriculture; using exhaust gas purification technology and wet flue gas desulfurization systems and equipment that meet the Euro III standards for diesel vehicles/motorcycles; and using low-carbon technologies.

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 1 The principle of environmental pollution control

1.4.2 Monitoring technology for ecological security Ecological monitoring is the use of living systems at all levels of the response to determine the quality of the environment caused by natural or manmade environmental changes. Ecological monitoring technology has irreplaceable advantages: It can reflect environmental quality, has a continuous monitoring function, monitoring with high sensitivity, and reflects the ecological security and prediction of environmental risk.

1.4.3 Ecological restoration technology The soil pollution and remediation technology of Europe and American developed countries has a history of 40 years; the pollution remediation of brownfields in the United States is under the protection of the Superfund Law, and to develop a series of repair techniques and standards, ecological restoration projects and technology have become a frontier of environmental science and engineering and have expanded from soil remediation to the serious pollution at different scales, regional and field. Examples are river ecological recovery technology, wetlands ecological restoration and reconstruction technology, vegetation restoration and reconstruction technology, mines ecological restoration technology, and heavy metal pollution restoration technology.

1.4.4 Environmental risk assessment and early warning In order to implement the “People’s Republic of China on Environmental Impact Assessment Law, Construction Project Environmental Management Ordinance, and Environmental Impact Assessment Technical Guidelines” for the construction project environmental risk assessment into environmental impact assessment management areas, to improve the quality and efficiency of environmental risk assessment and review, the Construction Project Environmental Risk Assessment Technical Guidelines (HJ/T 169–2004) has been approved, promulgated by the State Environmental Protection Administration of China in December 11, 2004. Environmental risk refers to the extent of harm on the environment caused by accident. Environmental risk assessment and early warning technology for construction projects occurring during the construction and operation of predictability accidents, the leakage of toxic and hazardous, flammable and explosive substances, or unexpected event caused by the impact and damage to personal safety and the environment impact, for scientific prediction and assessment, put forward the measures of prevention, emergency response, and mitigation.

References 

 15

1.4.5 Biological pollution prevention and control technology In water, air, soil, and solid waste pollutants, the main pollutants are chemical pollutants and biological contaminants. Bacteria, viruses, and other biological pollution and its prevention are the areas of preventive medicine; medical waste, algae, bacteria, viruses, and other biological pollution have also become important environmental pollutions.

References [1] Cheng F, Chang H. The basis of environmental protection. Beijing: Tsinghua University Press; 2002. (In Chinese) [2] Lu X, Chen G. The principle of environmental pollution control. Wuhan: Huazhong University of Science and Technology Press; 2010. (In Chinese) [3] Wu G. Water pollution monitoring and control. Beijing: Science Press; 2004. (In Chinese) [4] Zhu Y. Environmental pollution control technology. 3rd ed. Beijing: China Environmental Science Press; 2008. (In Chinese) [5] Yang Z, Liu J. Introduction to environmental science. 2nd ed. Beijing: Higher Education Press; 2010. (In Chinese) [6] Miller GT Jr, Spoolman SE. Living in the environment. 13th ed. Beijing: Higher Education Press; 2008.

2 Water pollution control technology 2.1 Introduction Water is the general term for oceans, lakes, rivers, swamps, reservoirs, and groundwater. Daily production and living activities discharge large amounts of wastewater and other pollutants into water bodies, which exceed the level of background concentration and the self-purification capacity of water bodies, resulting in water pollution. Water pollution source refers to the sites, equipments, and devices that discharge pollutants into water bodies, causing damage to the water quality. The pollutant sources can be divided into two major categories, including natural pollution source and anthropogenic pollution source. Natural pollution source is the release of hazardous substances or the harmful effects of nature to the water body, such as rock weathering and hydrolysis, volcanic eruption, water eroding land surface, atmospheric dust precipitation leaching, and biological (mainly green plants) release of substances in the geochemical cycle. Anthropogenic pollution source is the source of pollution caused by human activities, which is the main target of environmental protection and prevention. The system of anthropogenic source is very complex; the way of human activities can be divided into pollution sources such as industry, agriculture, transportation, residence, etc., based on human activities. Discharge pollutants according to different classifications can be divided into inorganic, organic, hot, radioactive, heavy metals, pathogens, and the mixture of many kinds of pollutant discharge and other pollution sources if based on the type of pollutants. It also can be divided into point source and nonpoint source based on the spatial distribution of the pollutants emissions [1]. Water pollution point source is a form of point-like emission. For example, general industrial wastewater and domestic sewage were discharged into water body through urban sewage treatment plants, which is the important point source of water pollution. Point source often contains pollutants with complex composition and changes seasonally and randomly based on the emission characteristics of industrial wastewater and domestic sewage. For water pollution nonpoint source, its characteristic is the formation of a large area of distribution and discharge of pollutants caused by water pollution sources. Runoff pollutants and irrigation water are the main nonpoint sources of water ­pollution. Water pollution sources mainly include the following three aspects [2]. Industrial wastewater Industrial wastewater contains wastewater, sewage and waste liquid produced during the industrial production process. Wastewater mainly refers to the industrial DOI 10.1515/9783110538311-002

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cooling water. Sewage refers to the drainage seriously contaminated through direct contact with contaminants. Wastes refer to the outflow of wastes during the production process. Industrial wastewater contains extremely complex compositions, and the quality of wastewater varies at different time periods due to the combined effects of the products, raw materials, pharmaceutical, process, equipment, construction, operating conditions, and other factors. Domestic sewage Domestic sewage refers to the sewage generated by human consumption and activities, including the sewage and pollutants discharged from places such as kitchens, bathrooms, and toilets. Based on the forms, pollutants in the domestic sewage can be divided into the following: 1) insoluble substances: accounting for 40% of the total pollutants, either precipitated at the bottom or suspended in water; 2) colloidal substances: about 10% of the total amount of pollutants; 3) dissolved substances: about 50% of the total amount of pollutants. The majority of these substances are nontoxic, containing inorganic salts such as chloride, sulfate, phosphate, sodium potassium, and calcium bicarbonate. Organic substances include cellulose, starch, sugar, fat, protein, urea, etc. In addition, it also contains a variety of trace metals, all kinds of detergents, and a variety of microorganisms. The common domestic sewage is quite turbid; organic substances account for about 60%, pH is above 7, and the BOD level is between 100 and 700 mg/L. Agricultural production sewage Agricultural production sewage refers to the sewage generated in the process of ­agricultural production. The basic task of water pollution control is to separate pollutants from w ­ astewater or to convert them into harmless substances. Water pollution control technologies can be divided into 1) physical method, 2) chemical method, 3) physiochemical method; 4) biological method, and 5) other combined technology (Tab. 2.1). Tab. 2.1: Basic methods for water pollution control. Classification Treatment methods

Targets of the treatment Main equipments Scope of ­application

Physical method

Equalizing water quality and volume Bulky suspended and floating substances Suspended matter Emulsified oil, solid substances Tiny suspended matter Emulsified oil

Adjustment Flow cut-off Sedimentation Centrifugation Filtration

Balance tank Grille and screen Sedimentation tank Centrifuge Filtration tank

Pretreatment Pretreatment Pretreatment Pre or intermediate treatment Intermediate or deep processing

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 19

Tab. 2.1 (continued) Classification Treatment methods

Targets of the treatment Main equipments Scope of ­application

Chemical method

Neutralization Coagulation Precipitation Redox Air stripping Extraction Electrolysis

Acid, alkali Colloform and tiny suspended matter Dissoluble hazardous heavy metals Dissoluble harmful substances Dissoluble gas Dissoluble organic substances Electrolytic substances

Physicalchemical method

Air floatation Adsorption Ion exchange Electroosmosis RO Ultrafiltration

Emulsified oil, Floatation pond suspended matter Absorption tower Dissoluble substances Ion exchanger Dissociatable substances Electrodialyzer Dissociatable substances RO Salt Ultrafilter Dissoluble matter

Biological method

Aerobic Colloid and dissoluble biotreatment organic substances Anaerobic biotreatment Land treatment Stablization pond

Reaction pond, sedimentation tank Coagulating pond, sedimentation tank, flotation tank Reaction pond Reaction pond Stripping tower Extraction tower Electrolyzer

Activated sludge reactor, biofilter Anaerobic digester and filtration pond, underground infiltration and slow filtration Aerobic and anaerobic pond

Pretreatment Intermediate or deep processing Intermediate or deep processing Intermediate or deep processing Pre or intermediate treatment Pre or intermediate treatment Intermediate or deep processing Pre or intermediate treatment Intermediate or deep processing Deep processing Deep processing Deep processing Intermediate treatment Intermediate treatment Deep processing Deep processing

2.2 Physical method There are often some insoluble suspended solids in the natural water body and ­wastewater discharged from human activities; they can usually be separated and recycled by physical and mechanical forces without changing the chemical properties in the process, which is known as physical method. Physical method for water treatment is divided into 1) magnetic separation technology, 2) precipitation, 3) filtration technology, and 4) centrifugal separation technology. The equipment for the water treatment with physical method mainly involve precipitation, grit, clarification, sludge removal,

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floating, flotation, sieving, coarse filtration, centrifugation, dehydration, evaporation, magnetic separation, etc., mainly used in urban water supply treatment, urban sewage treatment, and industrial wastewater treatment [3].

2.2.1 Magnetic separation technology Magnetic separation is the method using magnetic force to retain and separate the pollutants in wastewater. It is mainly used to remove magnetic and nonmagnetic suspended solids and heavy metal ions, organics, oil, the bacteria, virus, and other pollutants.

2.2.1.1 Basic principle The particulates in wastewater are affected by the force of attraction, external magnetic field, gravity, inertial force, viscous force, and the interactions of particulates when the treated wastewater passes through the magnetic field. The magnetic particles can be captured and separated from the water if the magnetic force is greater than the external force. Magnetic forces can also serve to promote flocculation, which we call the magnetic agglomeration. Magnetic condensation is a way to promote the separation of solids from liquids and is a pretreatment method to improve the efficiency of sedimentation separation or magnetic separation. Magnetic agglomeration involves making wastewater pass through a magnetic field when the magnetic particles in water are magnetized, forming the magnet with north and south poles. As the gradient of magnetic field is zero, therefore, the resultant force is zero, affected by the equal size and the opposite direction force. The particles are not captured by magnet. But the interaction between the particles forms large particles is easier to precipitate and to separate. Through this magnet pretreatment, the precipitation efficiency can be increased by 40%–80% for the wastewater from iron and steel manufacturing process.

2.2.1.2 Magnetic separation methods Magnetic agglomeration A magnetic agglomeration system consists of magnets and magnetic circuit. The magnets can be permanent magnets or electromagnets. Each side of the magnet with the polarity arranged to constitute a uniform magnetic field. In order to prevent the contamination of the magnet surface, the flow rate of wastewater passing through the magnetic field should be greater than 1 m/s. No chemical flocculants are needed

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 21

for magnetic cohesion method; it is stable, easy to manage, free from secondary ­pollution, and easy for sludge dewatering and recycling. Magnetic disk method The magnetic disk method is the use of the submerged part of the magnetic disk to absorb the particles in the wastewater onto the slowly rotating disk. With the rotation of the disk, the sludge moves away from the water surface and is scraped off. The disk is produced with nonmagnetic materials (stainless steel, aluminum, hard plastic, etc.), attached with hundreds of permanent magnet with staggered polarity. The structure of a magnetic disk device is simple, is highly efficient, and requires short processing time (only 2–5 s retention time in the work area for processing the wastewater from iron and steel manufacturing, with purification rate up to 94%– 99%). It requires a small floor area (about 5% of common sedimentation tanks), the water content in the sludge is low after being processed, and the dewatering procedure is easy, but the mud scraping method has yet to be improved. High-gradient magnetic separation Weak magnetic and diamagnetic substance can be separated by increasing the magnetic force through the improvement of magnetic field gradient, which is called highgradient magnetic separation method. Magnetic filter is the device commonly used for this method.

2.2.2 Sedimentation technique The sedimentation technique is one of the basic water treatment methods that use the settling property of suspended particles in water to produce sinking under gravity, in order to achieve a solid-liquid separation process in the sewage treatment process (Fig. 2.1). There are three common applications: 1) for the pretreatment of wastewater, which can remove sewage sediments (sand), such as grit chamber; 2) for preliminary treatment prior to biological treatment tank, for example, the preliminary sedimentation tank; and 3) for solid-liquid separation after biological treatment, such as the ­secondary sedimentation tank. 2.2.2.1 Types of sedimentation Sedimentation phenomenon of suspended solids in the wastewater can be divided into four types: free sedimentation, flocculation and sedimentation, layered sedimentation, and compression sedimentation.

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Fig. 2.1: Grille and sedimentation tank.

Free sedimentation Free sedimentation generally occurs where the content of the suspended solid is low and no mutual aggregation occurs among different types of suspended particles; instead, each suspended particle settles independently. The sedimentation trajectory is a linear shape. The shape, size, and density of the particles do not change during the sedimentation process. The sedimentation process involves sand and inorganic particles with higher density. Flocculation and sedimentation Flocculation and sedimentation is a flocculation of solid particles in dilute suspension sedimentation. Although the concentration of suspended solids is not high, particles collide in the settlement process, gathering into larger flocs through mutual contact, and thus, the particle size and sedimentation rate will increase with the continuation of the deposition time. In wastewater treatment, the later stage of sedimentation in the primary sedimentation and the early settlement of secondary sedimentation tank in the biochemical treatment fall into this category. Layered sedimentation This is the sedimentation where the solid particles (especially the strong flocculent particles) settle in the suspension with higher concentration. The higher concentration pulls the particles closely together and the adsorption force aggregates them as a whole, while they settle together, with each keeping its own relative position. At this point, a clear interface between the water and the particles forms, and the sedimentation process is the process when the interface moves down with the

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sedimentation. The late sedimentation of sludge in the secondary sedimentation tank in the biological treatment process and the primary sedimentation in the thickener fall into this category. Compression sedimentation Compression sedimentation occurs in high concentrations of suspended particles in the sedimentation process; the concentration of precipitation is higher than in crowded sedimentation. The particles have gathered a massive structure in the sedimentation, contacting and supporting one another, and the clump structure goes through further compression during sedimentation process. The gravity of the particles at the upper layer can squeeze the water out of the gap among the particles at a lower layer, thus compressing the particles. The thickening of activated sludge in the secondary sedimentation tank and the concentration in the sludge thickener in all belong to this type of sedimentation. 2.2.2.2 Factors affecting sedimentation The sedimentation efficiency of suspended particles in wastewater depends on the velocity of the sewage in the sedimentation tank, the sedimentation rate of ­suspended particles, the structure and size of sedimentation tank, and the hydraulic conditions, etc. 2.2.2.3 Sedimentation tank A sedimentation tank is a structure separating suspended particles, which can be divided into ordinary sedimentation tank and inclined plate sedimentation tank based on their structure. The former one is more widely used. These are briefly ­introduced here. Common sedimentation tank A sedimentation tank can be classified into three categories: horizontal, vertical, and radial flow sedimentation tank, based on the water flow direction in the tank.

Selection of sedimentation tank The following factors should be taken into account when selecting the sedimentation tank: 1 the volume of the wastewater flow, 2 the nature of the suspended solids in the ­ eological wastewater and the settlement characteristics, and 3 the overall layout and g conditions of wastewater treatment plant. The horizontal and radial flow sedimentation tanks are often used for a large volume of wastewater.

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Wastewater containing inorganic suspended solids settles faster. The slag humidity is low, hard to be removed, and requires mechanical sludge scraper; thus, the horizontal and radial flow sedimentation tank should be used. The water content of sludge containing organic suspended solids is higher, suitable for using hydrostatic pressure to eliminate the sludge. The vertical flow sedimentation tank can be used if the volume of the treated wastewater is not large. The horizontal or radial flow sedimentation tank should be used when the groundwater level of the treatment plant is high.

2.2.3 Filtration technique Filtering is a common method for the separation of heterogeneous mixtures. The basic procedure is the fluid from the mixture passes through the filter media (gravity, pressure, centrifugal force, etc.) under the driving force, to achieve the separation of fluid from particles. Filtering operation is widely applied in the industry; both can be used to s­ eparate mixtures of heterogeneous liquid and realize liquid-solid separation and can also be used to separate mixtures of heterogeneous gas and realize gas-solid separation. 2.2.3.1 Suspension filtration Filtration mechanism When water and wastewater pass through granular media, such as quartz sand, the suspended particles and colloids are retained in the filter surface and the internal space enables the separation of the insoluble contaminants from water. It can be used for the pretreatment prior to deep processing, such as activated carbon adsorption and ion exchange, and can also be used for postprocessing of chemical coagulation and biochemical treatment. The mechanism for granular media filter generally includes resistance interception, gravitational sedimentation, and contact flocculation. Resistance interception When the raw water flows through granular media top-down, the larger suspended particles are first trapped in the gap of the surface filter, so that the gap between this layer media gets smaller and smaller and the capacity of sewage interception gradually increases. There gradually forms the layer of filter cake, mainly constituted by solid particles, which mainly functions as a filter. Gravity sedimentation When the raw water passes through the filter layer, the large filter surface provides a huge area for sedimentation, forming numerous “small sedimentation tanks” suspended solids can easily settle down here.

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Contact flocculation Because the filter material has huge surface area, it has obvious physical ­adsorption with suspended solids. In addition, the sand in the water often carries negative surface charge and can be adsorbed on positively charged colloidal iron, aluminum, etc., forming a positively charged film on the filter surface, which then adsorbs ­negatively charged colloids such as clay and a variety of organic compounds, thus contacting and flocculating on the granular media. In the actual filtering process, the mechanism of these three often work at the same time, just have a primary and secondary.

2.2.3.2 Classification of filtration Classification by filtration mechanism For larger suspended particles, resistance interception is mainly used. As the process occurs mainly at the filtration surface, it is also known as surface filtration (or cake filtration). For small suspended solids, gravity sedimentation and contact flocculation are mainly used, also known as deep filtration.

Classification by fluid flow Filtration can be classified into gravity filtration, pressure filtration, and centrifugation based on the driving force. It can be classified into intermittent filtration and continuous filtration if based on the operation model.

2.2.3.3 Filtration equipment At present, many types of filters have been used; they can be classified into singlelayer filter, double-layer filter, and multilayer filter based on the type of filter material. It can be classified into gravity filter and pressure filter based on the role of waterhead. It can also be classified into ordinary rapid filter chamber, siphon filter chamber, and valveless filter chamber if based on the supply and elimination mode of influent, effluent, and backwash water.

2.2.4 Centrifugal separation technology 2.2.4.1 The principle of centrifugal separation When the water-containing suspended particles (emulsified oil) are rotating in high speed in water, because of the different mass of particles and water molecules, the centrifugal force is different. Particles with relatively larger mass are thrown to the external layer, while the particles with smaller mass are kept in the internal layer.

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Appropriate arrangements for the different outlets of particles and water can separate the particulate matter from water and purify the water quality. 2.2.4.2 Classification of centrifugal separation equipment Centrifugal separation equipments used for water treatment include hydrocyclones, spiral flow tank, centrifuge, etc. Hydrocyclone Hydrocyclone is also known as cyclone separator. The centrifugal force is generated by the rapid rotation after the wastewater enters into the equipments in tangent direction as the result of water pump pressure or the pressure difference between the inlet and outlet. According to the energy sources of flow rotation, it can be divided into pressure hydrocyclone and gravity hydrocyclone pool. Centrifuge Centrifuge is a kind of machinery that uses inertial centrifugal force to separate liquid heterogeneous mixture. The biggest difference between centrifuge and cyclone separator is that the latter does not have a rotating part, while the main component of the centrifuge is the high-speed rotating drum. A rotating drum is installed in the vertical or horizontal axis, driven by the motor rotation, while driving the waste liquid into rotation. The density difference between suspended solid particles and the liquid can help in achieving the separation. There are many types of centrifuges. According to the size of the centrifugal factor, they can be classified into the following categories: constant speed centrifuge (Kc < 3,000), which is mainly used for the separation of general suspension and the dewatering of sludge; high-speed centrifuge (Kc > 3,000) which is mainly used for separating fine granular suspension; and ultracentrifuge (Kc > 12,000) which is mainly used for separating emulsions and oils with very fine granular suspension.

2.3 Chemical method Chemical treatment method of wastewater involves using the principles and methods of chemical reaction to separate the contaminants in the recycled wastewater or change their nature, making it harmless. The main targets of the chemical treatment are soluble inorganic substances and organic or colloidal substances with poor biodegradable properties. The main technologies for chemical treatment of wastewater include 1 coagulation technology, 2 neutralization technology, 3 redox technology, and 3 electrolysis technology. The main equipment for chemical treatment involves

2.3 Chemical method 

 27

neutralization, redox, disinfection, coagulation, dosing, etc., mainly used for urban sewage treatment and industrial wastewater treatment [4].

2.3.1 Coagulation Chemical coagulation technology, briefly named as coagulation technology, can be applied at each stage of wastewater treatment, including pretreatment, intermediate treatment, and advanced treatment. Besides removing turbidity and color, it can also remove heavy metals to a certain extent, such as polymers, fiber materials of fauna and flora, some organic substances, oil substances, microorganisms, active substances, pesticides, mercury, cadmium, lead, etc., so it is widely used in wastewater treatment. The advantages of coagulation technology are low equipment cost, good effects, and simple operation and management. The disadvantages are higher operation costs, as the coagulants need to be continuously added to the wastewater. 2.3.1.1 Basic principles of coagulation It is difficult to remove tiny suspended solids and colloidal particles in wastewater by the sedimentation method. They can remain in the water for a long time in the form of scattered suspension without natural sedimentation and has a certain stability. The coagulation method involves adding coagulants to water to disrupt the stability of these small particles. At first, they contact with each other, and then form flocs and settle down, thus getting separated. The former is called cohesion, and the latter is known as flocculation; generally, these two processes are known as ­coagulation. Stability of colloidal particles The stability of the colloidal particles in water is mainly caused by three mechanisms: Brownian motion of the fine particles, electrostatic repulsion between the colloidal particles, and particle surface solvation. Colloidal stability is actually the combined effects of these three mechanisms; however, the main factors for stability vary slightly depending on the different types of colloids. The principle of coagulation Colloidal particles in wastewater are quite stable; the disruption of the stability is necessary in order to enable the large particles to aggregate and sink. Coagulation with added flocculants to the wastewater is a process disrupting the stability of colloidal particles. Coagulation is the result of combined processes of mixture, reaction, coagulation, flocculation, etc. It is a very complicated process. The chemical

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coagulation mechanism is not yet fully understood as there are many factors involved in the coagulation process. There are several explanations based on different coagulants, such as the function of compressed double electric layer, the function of adsorption bridge, and the function of sediments net. Factors affecting the coagulation effects pH value of wastewater: The pH of the water can affect the charge on the surface of the particles and flocs precipitation process; it is a very important parameter. Experiences have shown that each type of coagulant has a suitable pH range for a certain kind of wastewater. Within this range, the slag turbidity of the wastewater is the minimum after the mixture and cohesion; therefore, the effects of pH on coagulation vary depending on the types of coagulants. Water temperature: Water temperature has a significant effect on the coagulation effect. The hydrolysis of inorganic coagulants is endothermic reaction; the low temperature is not beneficial to hydrolysis, especially for aluminum sulfate. The speed of hydrolysis is very slow when the temperature is below 5°C. Meanwhile, the low temperature and high viscosity are not conducive to the mutual flocculation and the destabilization of colloidal particles, thus affecting the treatment effects. The polymer coagulants can be added to improve the treatment effect, or the flotation method for the follow-up treatment process can be used instead of the sedimentation method. The components, properties, and concentration of the impurities in the wastewater is complicated. The impact of the impurities in wastewater is very complicated. In practical application processes, the coagulant selection and the dosage used should be based on experimental results. Agitation: Agitation can affect each stage of the processing: mixture, reaction, and cohesion; therefore, agitation must be appropriate. Generally speaking, it should be rapid when mixing coagulants. Intense agitation can make the coagulants disperse fully in the water quickly and evenly, creating good conditions for hydrolysis and polymerization, to destabilize the colloids and aggregate through the Brownian motion of particles and water flow; the formation of large flocs is not required at this stage. In the coagulation stage, the formation of large flocs with good precipitation performance is required. The super intense agitation will break the aggregated sediments, unfavorable for coagulation and sedimentation. Therefore, the intensity of agitation and the water velocity should be reduced as the flocs get larger. Impact of coagulants: The impact of coagulant types: The selection of coagulants depends on the nature and the concentration of colloids and fine suspended solids.

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Inorganic coagulants should first be added to destabilize the cohesion if the main pollutants are colloidal and have higher potential. Polymer coagulants or active silicic acid and other coagulants should be added if the flocs are small. The impact of the dosage of added coagulants: The dosage is related to the type, nature, concentration of the particles in water, also related to the coagulant type, dosing method, and medium conditions. For coagulation treatment, the best coagulant and optimal dosage are the key and are usually generally determined through experiment. The impact of the sequence of coagulant addition: The optimum sequence for coagulant addition can be determined through experiments. Usually, inorganic coagulants are added prior to organic coagulants when they are used jointly. However, when the treated particles are larger than 50 μm, the organic coagulants are added first to absorb the bridge, followed by the inorganic coagulants to compress and ­disperse the colloids.

2.3.1.2 Coagulants Classification of coagulants Coagulants can be divided into inorganic coagulants, organic coagulants, and polymer coagulants. The main coagulants used in China are inorganic coagulant such as aluminum and iron salts. In recent years, the development of organic coagulants and polymer coagulants improved significantly; their performance far surpassed inorganic coagulants. Polymer coagulants in particular have been focused due to their advantages. Selection of coagulants and the prerequisites for application The selection and application amount of coagulants should be decided based on the specific nature of the wastewater. The general principle is that all the coagulants used must be inexpensive, be easy to get, require less for application, and be highly efficient. The flocs are easy to settle and be separated. Special attention should be given to the pH range for application when using inorganic coagulants. Usually, the pH regulators are added after the inorganic salt coagulants are applied. For polymer coagulants, those that can be evenly dispersed and dissolved and can absorb active genes, water-soluble polymer coagulants should be selected to give full play its role for chemical bridging in water. Usually, the solution is prepared consisting of pure water and soft water prior to its addition to the wastewater to be treated, in order to scatter the polymer coagulants. Because these polymer compounds are often subject to the impacts of water quality, molecular diffusion and ion-based dissociation are suppressed, and the effect of treatment is decreased.

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2.3.1.3 Process and equipments for coagulation technique The treatment process of coagulation is a comprehensive procedure, including the pharmaceutical preparation, dosing, coagulation, flocculation, and sedimentation separation. Preparation and dosing of pharmaceuticals The method of dosing can be subdivided into dry cast and wet cast. The dry cast method involves directly throwing the broken and dissolved pharmaceuticals into wastewater. It uses a small floor area, but the requirements for pharmaceuticals are more stringent. The dosage is difficult to control, the method has higher requirements for machines and equipments, and the working conditions are poor and thus rarely used. The wet cast method involves preparing the solution with coagulants and coagulant aids, then adding them to the wastewater based on the quantity of treated water. The process includes the preparation, measurement, and addition of pharmaceuticals. Mixing The purpose of mixing is to make the coagulant distribute in the wastewater quickly and evenly in order to facilitate coagulation and sedimentation. The speed of mixing should be as fast as possible, leading to the strong treading of water. Usually two modes are applied: mixing before and after pumps are used and mixing within trough. Flocculation reaction The mixed wastewater and the evenly mixed pharmaceuticals are put into the reactor for reaction. The reactor is designed in different sizes based on the flow rate: With a higher flow rate, the colloidal particles collide and absorb with one another in water; with a smaller flow rate, the absorbed particles form into larger flocs, easily settling down. The retention time of wastewater in the tank must be adequate in order to generate full reaction. Sedimentation The flocculants first generated in the reaction tanks enter into the sedimentation tank, are separated from water, and settle down in the sedimentation tank.

2.3.2 Neutralization technology Industrial wastewater often contains a certain amount of acid or alkaline substances; neutralization treatment should be conducted for those with 4% of acid or less and

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 31

those with 2% of alkaline or less, until effective recycling methods are developed. The pH of wastewater should be regulated to the discharge standard for industrial wastewater before they can be discharged. There are two kinds of neutralization methods commonly used for wastewater: 1) balance method and 2) pH value control method [5].

2.3.2.1 Basic principle The neutralization treatments of acidic wastewater and alkaline wastewater are both referred to as neutralization reaction, with the following, ionic equation: H+ + OH− → H2O 2.3.2.2 Balance method Balance refers to direct mixing of acidic wastewater with alkaline wastewater in the balancing tank, to make the pH value close to neutral. The equipment used should be based on the discharge conditions of acid-alkaline wastewater. No neutralization tank is required if the acid-alkaline wastewater is discharged evenly and can reach acid-alkaline balance, the reaction can occur in the pipeline. However, the neutralization tank needs to be set if the concentration and flow rate of the discharged acidalkaline water are constantly changing and fluctuating.

2.3.2.3 The pH value control method This method involves adding a neutralizer to neutralize acidic or alkaline wastewater, the most commonly used methods are the following: Acidic wastewater treatment It can be divided into two categories based on the handling methods and processing equipments: dosing neutralization and reactor neutralization. Dosing neutralization: Put lime, limestone, calcium carbide slag, caustic soda, soda, and other alkaline substances directly into the wastewater and neutralize it. This method can treat all the acidic wastewater of any property and concentration. Dosing methods can be divided into dry cast and wet cast; wet cast is widely used. The wet cast method is more effective than the dry cast method, and the dosage required is less (1.05–1.07 times the theoretical value), and lime milk is cheap, so it is widely used. However, the technique of the method is complicated, sediment volume is huge, and the dewatering process is difficult.

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Reactor neutralization: This is also known as filtration neutralization. The acidic wastewater is put through the reactor with alkaline filter layer (such as limestone, marble, dolomite, etc.) for neutralization reaction, and neutralization is achieved at the same time with filtration. The method is applicable for treating cleaner wastewater containing hydrochloric acid, nitric acid, or low-concentration sulfuric acid. The equipment of reactor for neutralization includes fixed bed, fluidized bed, and drum type. Alkaline wastewater treatment Alkaline wastewater can be neutralized with acid substances. The commonly used neutralizers include sulfuric acid, hydrochloric acid, acidic exhausts, etc. The acid containing wastewater from industrial production is a good neutralizer. The neutralization equipments for alkaline wastewater are same as those for acidic wastewater. The treatment facilities should usually include dosing device, mixing reaction tank, and sedimentation tank if sedimentation occurs during the reaction.

2.3.3 Redox technology For those toxic and hazardous pollutants with stable chemical properties and that are difficult to treat with biological or other methods, their properties of oxidation and reduction in chemical reaction can be utilized to change their form, turning them into nonharmful and nontoxic substances, or to convert them into other substances that are easy to handle – this method is called redox [6]. 2.3.3.1 Oxidation The oxidation method involves adding some kind of oxidants to the pollutants, turning the reductive toxic and hazardous substances into nontoxic or less toxic substances. Oxidants commonly used in environmental engineering mainly include oxygen in the air, pure oxygen, ozone, chlorine, bleach, hydrogen peroxide, etc. Their oxidative capacity can be identified based on the standard electrode and electric potential of these oxidants. 2.3.3.2 Chemical reduction method The chemical reduction method involves using some reducing agents to react with the pollutants in the wastewater, to turn the toxic substances into low-toxic, slightly toxic, or nontoxic substances. Because some metal ions in wastewater are more toxic when in the state of high valence, the chemical reduction method can be used to reduce them into low-valence state, then they are removed and eliminated. Some pollutants in wastewater, such as hexavalent chromium, can be reduced to less-toxic

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trivalent chromium with this method, and then it can be converted to Cr(OH)3 for precipitation and removal. Commonly used chemical reduction methods include 1 pharmaceutical reduction, 2 metal reduction, 3 catalytic reduction method, 4 nonselective catalytic reduction, and 5 selective catalytic reduction.

2.3.4 Electrolytic technology The electrolytic method, also known as electrochemical method, is the process of electrochemical reaction when the electrolyte in the wastewater responds to direct current (DC). The electrolysis process is carried out in the electrolytic tank. The electrode connected to the positive power is called anode, and the one connected to the negative power is called cathode. After being connected to the DC, under the electric force, the positive and negative ions in wastewater move to the two polars, respectively, and the oxidation reduction reaction takes place in the surface of electrode, resulting in water-insoluble sediments or gases from water, thus reducing the concentration of harmful substances or converting them into nontoxic or low-toxic substances in wastewater. The electrolytic method is mainly applied for the treatment of heavy metal ions and decolorization in oil contained wastewater. It began to be used for handling industrial organic wastewater in recent years. The electrochemical treatment of wastewater can be divided into four categories. 2.3.4.1 Electrode surface treatment process The soluble pollutants in the wastewater gain or lose electrons on the surface of the electrode, resulting in redox reactions, forming insoluble sediments, gases, or low-toxic and nontoxic compounds in the wastewater. The treatment of cyanide-­ containing wastewater is a typical example of electrochemical oxidation.

2.3.4.2 Electrolytic redox process The electrode used for electrolytic redox process is “soluble” electrode; the electrode generates oxidative or reductive products in the electrolysis process, which then go through redox process with the contaminants in the wastewater and purify the water. 2.3.4.3 Electrolytic flotation process The use of insoluble electrode in the electrolysis process can separate a large number of small bubbles on the electrodes. For example, water electrolysis can produce H2 and O2; the electrolytic oxidation of organic substances and chloride

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will produce gases such as CO2, N2, and Cl2, and they will form bubbles escaping from wastewater. These bubbles have very small diameters, are highly dispersed, and have strong capture capacity over the suspended solids and oils in the wastewater, which can then be carried out to the water surface and removed, resulting in good water quality after the treatment.

2.3.4.4 Electro-coagulation process The use of soluble anode (iron, aluminum) during the electrolysis process can produce Fe3+, Al3+, and other ions, which then can form a series of active aggregatesflocculants through hydrolysis and polymerization. The flocculants can aggregate and absorb the pollutants in the wastewater, forming floc particles, and sink and get separated; this method is called electrolysis coagulation. The first two categories are electrochemical-chemical method, while the latter two categories belong to electrochemical-physical method.

2.4 Physicochemical method The physicochemical method involves using the principle of physicochemistry and chemical unit operation to remove the impurities in wastewater. The c­ommonly used physicochemical methods include adsorption, flotation, ion exchange, ­membrane separation, extraction, air stripping, distillation, evaporation, freezing, ­crystallization, etc [7]. This section focuses on four commonly used physicochemical treatment methods: 1) flotation, 2) adsorption, 3) ion exchange, and 4) membrane separation.

2.4.1 Flotation Flotation is an effective solid-liquid and liquid-liquid separation method, commonly used for the separation of small particles with particle density close to or less than that of water. Air flotation is the process where air enters into the water in the form of tiny air bubbles, which then stick to the suspended particles in the water, forming a watergas-particle three-phase mixing system. After the particles adhere to the bubbles, they will float on the water surface if the density is smaller than that of water, separated from the water, forming scums. The flotation method has been widely used for oil-water separation in petroleum and chemical production and recycling of pulp fibers and fillers from the wastewater of paper and pulp plants.

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2.4.1.1 Flotation principle The molecular attraction undertaken by the molecules on the surface of liquid is different from that inside the liquid. The force undertaken by the surface molecule is unbalanced, which pulls the surface molecules into liquid internal, reducing the liquid surface area; this force is called the surface tension of fluid. The attraction of the liquid molecules internal should be resisted in order to prevent the surface molecules from moving toward the liquid internal. It can be seen that the molecules at liquid surface have more energy; this energy is called the surface energy.

2.4.1.2 Conditions for the adhesion of suspended particles with bubbles The suspended particles will strive to adhere to bubbles to reduce its interfacial energy when bubbles exist in the wastewater, but not all the particles can adhere. The effective adhesion mainly depends on the surface properties of particles, i.e. the wettability of water for particles. In chemistry, substances susceptible to water wetting are referred to as hydrophilic substances; on the contrary, those that have difficulty in water wetting are referred as hydrophobic substances. The general rule is that the hydrophobic particles tend to adhere to bubbles, while the hydrophilic particles are hard to adhere to bubbles.

2.4.1.3 Dispersion and stability of bubbles A large number of small and uniform bubbles are needed as the carrier during the flotation process. The effect of flotation depends largely on the amount of air dissolved in water, the saturation, the bubble dispersion, and stability. It has been proven that with the same amount of air, the smaller the bubble diameter, the more the dispersion, the larger the total surface area, and the more chances to adhere to suspended particles, the higher the flotation efficiency. Usually, a bubble diameter under 100 mm is the best. The bubbles should be quite stable. The amount, size, and uniformity of the bubbles are directly related to the saturation pressure – the higher the pressure, the greater the solubility of air in the water and the more bubble dispersion. 2.4.1.4 Process of flotation method According to the modes of bubble generation, the flotation method includes using an impeller or jet to disperse the air in the water into small bubbles (the former is called impeller flotation, the latter is called jet flotation); using pressurization to feed air into the water, saturated, then the water pressure is suddenly reduced, so that the air is separated from water in the form of tiny bubbles (this method is called dissolved air flotation); and using tiny air bubbles generated through the electrolysis process and conducting flotation, called electrolysis floatation.

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2.4.1.5 Device of flotation The flotation device is generally subdivided into pressure dissolved gas system, air release system, and the flotation.

2.4.2 Adsorption Adsorption refers to the phenomenon of gas or liquid molecules attaching on the surface of solid substances; it is a commonly seen pollutant purification method, especially suitable for treating low-concentration exhaust gases with high purification requirements. The substances adsorbed to the solid surface are called adsorbents. The advantages include high purification efficiency, recyclable useful components, simple equipments, easy to implement, automation, and control. The disadvantages are small adsorption capacity, bulky equipment, limited adsorbent capacity, requiring frequent regeneration, troublesome regeneration process for intermittent adsorption, and low equipment utilization rate. Adsorption was initially used for the separation of substances. In recent years, it has been widely used in the field of water treatment. The method is mainly used for removal of trace contaminants. The range of applications include bleaching, deodorizing, removal of heavy metals, a variety of dissolved organic substances, and radioactive elements.

2.4.2.1 Mechanism of adsorption The extra surface energy exists on the solid surface due to the uneven force imposed on molecules; the smaller the particles, the higher the surface energy. When certain substances collide with solid surface, they are attracted by these unbalanced forces and stay on the solid surface; the process is called adsorption. The porous solid material with adsorption capacity is called adsorbent. The substances adsorbed in the solid are known as the adsorbate. The result of adsorption is adsorbate enrichment on the adsorbent surface, which can reduce the surface energy of the adsorbent. Therefore, adsorption is an interface phenomenon, affecting two phase interfaces. In the system of water medium, adsorption is the result of the interaction of water, solutes, and solid particles. 2.4.2.2 Classification of adsorption Adsorption can be divided into physical adsorption, chemical adsorption, and ion exchange adsorption based on the force between adsorbents and adsorbates. Physical adsorption This is the adsorption caused by intermolecular forces (van der Waals force) between adsorbents and adsorbates. The character of physical adsorption is its

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nonselectivity – adsorbates are not fixed at a specific location on the adsorbent surface and can move within the interface, the degree of fastness for physical adsorption is less than chemical adsorption, and it is prone to surface displacement and easy desorption. Physical adsorption occurs mainly in low temperature; the heat of adsorption is small, similar to the liquefaction heat, about 42 kJ/mol or less, in a form of single molecule or multimolecular layer adsorption. Adsorption rate is faster and does not require activation energy, independent of temperature. The main factors are the specific surface area and pore distribution of adsorbents.

Chemical adsorption Adsorbents and adsorbates go through chemical reaction, forming a strong adsorption bond and surface complex. Adsorbate molecules cannot move freely on the surface. The heat of adsorption is large, similar to the heat of chemical reaction, about 84–420 kJ/mol, and is hard to desorb. The chemical adsorption is selective. That is, a type of adsorbent can only absorb certain types of substances; usually, it is monolayer adsorption. The rate of chemical absorption is smaller and requires activation energy, and the rate accelerates with the increase in temperature. Chemical adsorption is closely related to the surface chemical properties of adsorbents and the chemical properties of adsorbates. 2.4.2.3 Factors affecting adsorption For the same adsorption system, the greater the concentration of adsorbates and the faster the adsorption rate, the more the adsorption amount, extending to the saturated adsorption capacity. In addition, there are many factors affecting adsorption, mainly those that can affect the adsorption capacity, including the nature of adsorbents, the properties of adsorbates, the temperature of the solution, pH, other components of solution, mode of adsorption operation, contact time, etc. Adsorption isorhermal curve The adsorption process is usually studied through graphs known as adsorption ­isotherm. That is the amount of adsorbate on the adsorbent as a function if its pressure or concentration at constant temperature. The quantity adsorbed is nearly always normalized by the mass of the adsorbent to allow comparison of different ­materials.

Basic adsorption isotherm From the above, we can predict that after saturation pressure, Ps, adsorption does not occur anymore and that there are limited numbers of vacancies on the surface of the

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adsorbent. At high pressure, a stage is reached when all the sites are occupied and a further increase in pressure does not cause any difference in the adsorption process. At high pressure, adsorption is independent of pressure.

Types of adsorption isotherm Five different types of adsorption isotherm and their characteristics are explained below (Fig. 2.2):

Adsorption Amount (STP ml/g)

I

III

II

Weak Substrate

Micropores

IV

Nonporous V

Micropores Capillary Condensation

VI Weak Substrate

Layering

Relative Pressure P/P0 Fig 2.2: The period of adsorption process (source: http://arnrita. Vlab.co.in/?sub=z&brch=190&sim=606&cnt=1).

Type I adsorption isotherm The below graph depicts Monolayer adsorption. This graph can be easily explained using Langmuir adsorption isotherm. In the BET equation, when P/P0 > 1, then it leads to monolayer ­formation and Type I adsorption isotherm is obtained. Examples of Type I adsorption are adsorption of nitrogen (N2) or hydrogen (H) on charcoal at temperature near −1,800°C. Type II adsorption isotherm Type II adsorption isotherm shows a large deviation from the Langmuir model of adsorption. The intermediate flat region in the isotherm corresponds to monolayer formation. In BET equation, the value of C has to be very large in comparison to 1. Examples of Type II adsorption are nitrogen (N2 (g)) adsorbed at –1,950°C on iron (Fe) catalyst and nitrogen (N2 (g)) adsorbed at –1,950°C on silica gel.

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Type III adsorption isotherm Type III adsorption isotherm also shows large deviation from the Langmuir model. In the BET equation, if c