Flocculation: Processes and Applications

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CHEMISTRY RESEARCH AND APPLICATIONS

FLOCCULATION PROCESSES AND APPLICATIONS

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CHEMISTRY RESEARCH AND APPLICATIONS

FLOCCULATION PROCESSES AND APPLICATIONS

ELEONORA VOLLAN EDITOR

Copyright © 2019 by Nova Science Publishers, Inc. All rights reserved. No part of this book may be reproduced, stored in a retrieval system or transmitted in any form or by any means: electronic, electrostatic, magnetic, tape, mechanical photocopying, recording or otherwise without the written permission of the Publisher. We have partnered with Copyright Clearance Center to make it easy for you to obtain permissions to reuse content from this publication. Simply navigate to this publication’s page on Nova’s website and locate the “Get Permission” button below the title description. This button is linked directly to the title’s permission page on copyright.com. Alternatively, you can visit copyright.com and search by title, ISBN, or ISSN. For further questions about using the service on copyright.com, please contact: Copyright Clearance Center Phone: +1-(978) 750-8400 Fax: +1-(978) 750-4470 E-mail: [email protected]. NOTICE TO THE READER The Publisher has taken reasonable care in the preparation of this book, but makes no expressed or implied warranty of any kind and assumes no responsibility for any errors or omissions. No liability is assumed for incidental or consequential damages in connection with or arising out of information contained in this book. The Publisher shall not be liable for any special, consequential, or exemplary damages resulting, in whole or in part, from the readers’ use of, or reliance upon, this material. Any parts of this book based on government reports are so indicated and copyright is claimed for those parts to the extent applicable to compilations of such works. Independent verification should be sought for any data, advice or recommendations contained in this book. In addition, no responsibility is assumed by the publisher for any injury and/or damage to persons or property arising from any methods, products, instructions, ideas or otherwise contained in this publication. This publication is designed to provide accurate and authoritative information with regard to the subject matter covered herein. It is sold with the clear understanding that the Publisher is not engaged in rendering legal or any other professional services. If legal or any other expert assistance is required, the services of a competent person should be sought. FROM A DECLARATION OF PARTICIPANTS JOINTLY ADOPTED BY A COMMITTEE OF THE AMERICAN BAR ASSOCIATION AND A COMMITTEE OF PUBLISHERS. Additional color graphics may be available in the e-book version of this book.

Library of Congress Cataloging-in-Publication Data ISBN: H%RRN

Published by Nova Science Publishers, Inc. † New York

CONTENTS Preface

vii

Chapter 1

Flocculant Polysaccharides Mainly from Plants Priscilla B. S. Albuquerque, Weslley F. Oliveira, Priscila M. S. Silva, Maria T. S. Correia and Luana C. B. B. Coelho

Chapter 2

Coagulation and Flocculation with Plant Extracts Jesús Manuel Epalza Contreras and Johan Jaramillo Peralta

Chapter 3

The Process of Water Treatment with Aluminum Sulphate Associated with the Application of the Cactus Opuntia Cochenillifera Higgor Henrique Dias Goes, Rita de Cássia Pereira de Souza and Joseane Débora Peruço Theodoro

Chapter 4

Flocculation: Mechanisms and Applications for Wastewater Treatment Elvis Carissimi, Cristiane Oliveira Rodrigues, Dounia Elkhatib and Vinka Oyanedel-Craver

Chapter 5

Flocculation of AOM in Water Treatment Martin Pivokonský, Jana Načeradská, Kateřina Novotná, Lenka Čermáková and Petra Vašatová

Chapter 6

Comparison of Natural Coagulant and Chemistry in Tanning Wastewater Treatment Using the Flocculation Process Edilaine Regina Pereira, Gustavo da Silva Souza and Joseane Débora Peruço Theodoro

1

47

69

81

107

143

vi Chapter 7

Chapter 8

Chapter 9

Chapter 10

Chapter 11

Chapter 12

Chapter 13

Chapter 14

Chapter 15

Index

Contents Moringa oleifera Seed Use in Salina Solution in Water Treatment in Lentic Bodies João Carlos Belisário Junior, Edilaine Regina Pereira and Joseane Débora Peruço Theodoro

155

Evaluating New Biopolyelectrolytes for the Meat Processing Wastewater Treatment via Coagulation-Flocculation E. A. López-Maldonado and M. T. Oropeza-Guzmán

169

Treatment of Residual Waters of the Brewery Industry through the Flocculation Process with the Use of Inorganic and Organic Coagulants Fellipe Jhordã Ladeia Janz, Edilaine Regina Pereira, Thaís Ribeiro, Dandley Vizibelli and Julio Cesar Angelo Borges

179

Application of Electrocoagulation with Voltage Variation to Obtain Potable Water Ingrid Cardozo Botelho, Thiago Andre Bezerra Higuchi and Joseane Débora Peruço Theodoro An Evaluation of the Performance of the Coagulation/Flocculation Process with Aluminum and Ferric Salts on the Removal of Algal Toxins Ayşe Büşra Şengül Treatment of Leachate from the Ouled Berjal Landfill in Morocco by Coagulation Flocculation: A Study of the Effect of Order for Reagent Introduction Hajar Bakraouy, Salah Souabi, Khalid Digua and Levent Yilmaz

187

197

217

OMW Pretreatment by Assisted Sedimentation Methods: Coagulation/Flocculation Gassan Hodaifa and Cristina Agabo García

259

Chitosan Based Flocculants for the Removal of Heavy Metal Ions Sayaka Fujita and Nobuo Sakairi

277

Determination of the Kinetic Coefficient of Aggregation and the Kinetic Coefficient of Rupture in the Turbidity Removal Process Joseane Debora Peruço Theodoro, Paulo Sergio Theodoro and Rosangela Bergamasco

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PREFACE Flocculation: Processes and Applications opens by approaching current trends in preparation and chemical modification of flocculant polysaccharides derived from plants and their flocculation performance. In addition, aspects including mechanisms of flocculation, chemical modification, the effect of physicochemical factors on flocculating activity, and recent applications of flocculant polysaccharides are reviewed. The authors go on to propose plant extracts which can efficiently perform coagulation and flocculation operations without the environmental risk of residual sludge with high concentrations of aluminum or iron. A separate study aimed to use the organic polymer from Opuntia cochenillifera cactus associated with the addition of aluminum sulfate to treat the water of a lentic body applying coagulation, flocculation, sedimentation and filtration processes. The authors propose that the design and operation of flocculators is crucial for the process efficiency and largely dependent on the following features: floc characteristics, flocculation kinetics, and engineering aspects of flocculation. This compilation also discusses current knowledge on algal organic matter (AOM) flocculation, the impact of AOM on the removal of other compounds and links AOM composition and character to the efficiency of flocculation, the reaction conditions and mechanisms and finally, to the properties of flocs. Additionally, the performance of natural coagulant tanin compared to chemical coagulants aluminium sulphate and ferric chloride commonly used in the treatment of raw wastewater from tannery, by means of the physicochemical processes of coagulation, flocculation and sedimentation are examined. Through physical and chemical parameters, the efficiency of the coagulation/ flocculation/sedimentation/filtration processes using organic coagulants in the treatment of water from a lentic system in Brazil are examined as well.

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Later, the physicochemical performance of chitosan and mesquite gum as coagulant flocculent agent for the treatment of residual water of the cutting and packing of meat products factory is presented. The brewing industry generates effluent that can cause serious environmental impacts when not treated properly due to high loads of organic matter in its composition. Thus, in view of the growing emergence of breweries in Brazil and consequent increase in effluent production, alternatives are sought for the auxiliary treatment using coagulants and their efficiency is analyzed. Urban development also contributes to increasing water pollution, therefore the authors perform water treatment (through the electrocoagulation process) to calculate the cost of the operation. Eutrophication is one of the most prevalent water quality problems in the United States as well as other parts of the world. It has led to excessive growth of algal blooms, which not only cause the death of aquatic plants and animals, but also produce high levels of toxins and odorous compounds. The authors examine the performance of the coagulation/flocculation process using aluminum and ferric salt coagulants for the removal of microcystins. One study focuses on the coagulation flocculation of young leachate from the Kenitra city landfill. Tests were carried out by adding ferric chloride mixed with three flocculants, namely: the chitosan, the Superfloc SD2065 and the Himoloc. The authors outline researches about combining assisted sedimentation with other operations such as oxidation processes in order to evaluate the solids removal of the complete designed wastewater treatment focusing on OMW treatment. The penultimate chapter focuses on the preparation and characterization of the chitosan based flocculant for removal of heavy metal ion prepared from chitosan by Nacylation with ethylenediaminetetraacetic acid monoanhydride. The concluding study aims to apply the Bratby method in the characterization of the turbidity removal process, through the determination of the kinetic aggregation coefficient (KA) of the flocs and the kinetic coefficient of rupture (KB) of the flocs. Chapter 1 - Natural polymers are biocompatible, low-cost, and easily available materials of innate origin. These polymers are increasingly preferred over synthetic materials for industrial applications due to their intrinsic properties; they also are alternative sources of raw materials with characteristics of biodegradability, biosafety, and sustainability. Polysaccharides are polymers extracted from plants, algae, animals, fungi or obtained via fermentation, applied on a wide range of uses, from food to biomedical industries. Nowadays, they have been attracting considerable attention as viable alternatives to harmful synthetic flocculating agents for the removal of contaminants from water and wastewater. Then, a great deal of dedicated effort improved the production and performance of natural flocculants based on polysaccharides. The aim of this chapter is to approach current trends in preparation and chemical modification of

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flocculant polysaccharides derived from plants and their flocculation performance. In addition, aspects including mechanisms of flocculation, chemical modification, the effect of physicochemical factors on flocculating activity, and recent applications of flocculant polysaccharides, also derived from non-plant sources are reviewed. Chapter 2 - The treatment of water in a conventional way includes the operations of coagulation and flocculation as a fundamental part in the removal of solids and other substances that are mixed with water, especially organic and inorganic solids with sizes less than 0.2 mm and densities similar to those of water. This forms a perfect mixture difficult to separate by natural sedimentation; in these cases the addition of coagulants is needed, which breaks the stability of the mixture and segregates the particles in the form of flocs, so that they can be separated by density difference. Reactive substances are used for this reason, such as aluminum sulfate, ferric chloride and aluminum polychloride; these substances are derived from industrial chemical reactions, which entail the use of natural resources and energy to obtain them. In addition to the environmental cost of the production processes, there is the problem of the final disposal of the thickened sludge, because due to its aluminum or iron content, the sludge can be harmful to the environment, especially for plants and animals. To reduce this impact, it is necessary to carry out these operations with substances that do not represent a danger to the environment; in this case, it has been proven that there are plant extracts that can generate the same reaction of segregating the solids and other substances of the water, by means of the reaction of the natural biopolymers of some plants, within which the Moringa oleifera, Melocactus sp, Opuntia sp, Cicer arietinum L, Aloe sp and others with destabilizing activity of particles can generate turbidity and color in water. These plant extracts can efficiently perform the coagulation and flocculation operations without the environmental risk of residual sludge with high concentrations of aluminum or iron. Chapter 3 - The present study aimed to use the organic polymer from Opuntia cochenillifera cactus associated with the addtion of aluminum sulfate to treat the water of a lentic body (Igapó II Lake - Located in Londrina in the state of Paraná and Brazil) applying coagulation, flocculation, sedimentation and filtration processes. The tests were performed with static a Jar-test reactor, aiming to evaluate the removal of parameters of turbidity and of apparent color, besides monitoring the pH variation. Regarding the physico-chemical characteristics, there was little influence of the Opuntia cochenillifera cactus in the pH parameter tending to neutrality. Therefore, the study showed that the use of an organic coagulant together with aluminum sulphate is effective for the removal of parameters of apparent color and of turbidity (95 and 94%, respectively). Chapter 4 - Flocculation is considered the main physico-chemical treatment prior any solid-liquid separation unit in water and wastewater treatment plants. Suspended particles, algae, microorganisms are aggregated in order to increase their density for a subsequent step of sedimention or flotation (in case of injection of air bubbles) and/or filtration. Design and operation of flocculators are crucial for the process efficiency, and

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are largely dependent on the following features: floc characteristics, flocculation kinetics, and engineering aspects of flocculation. Finally, examples of engineering applications using flocculation are described. Chapter 5 - Global proliferation of algal blooms and subsequent deterioration of water quality by organic compounds that are being produced (algal organic matter – AOM) pose new challenges to water treatment technologies. Flocculation/coagulation using primarily Al- and Fe-based coagulants is widely employed as an essential process in removal of various impurities at drinking water treatment plants and is also irreplaceable in the case of AOM elimination. This review chapter discusses current knowledge on AOM flocculation, the impact of AOM on the removal of other compounds and links AOM composition and character to the efficiency of flocculation, the reaction conditions and mechanisms and finally, to the properties of flocs. In general, the removal efficiencies of dissolved AOM are lower compared to intact phytoplankton cells and usually reach maximum under slightly acidic pH values. The strong pHdependence of flocculation is attributed to the fact that the involved mechanisms are to a great extent determined by the charge ratios in the coagulating system. Furthermore, substantial differences in flocculation behaviour were observed between diverse AOM constituents, i.e., between peptides/proteins versus non-proteinaceous matter and high versus low molecular weight organics. The latter (specifically AOM < 10 kDa) are reluctant to flocculate and would therefore require other treatment techniques. AOM has also been reported to influence flocculation of other common impurities, both of organic and inorganic nature. Mutual interactions have been proven, while their influence on flocculation efficiency can be either positive or negative, depending on the AOM character, pH conditions and on the ratio between AOM, the other polluting agents and coagulants. Finally, AOM also appeared to alter the properties of flocs, with an impact on the subsequent separation steps. In further research, a particular emphasis should be put on AOM components that are difficult to coagulate, the interactions of AOM with other impurities and on elucidation of the relationship between AOM and floc properties. Chapter 6 - The leather tanning industry uses a large amount of toxic substances and water. Thus, it generates effluents with high polluting load. Due to the large amount of effluent generated by tanneries and the difficulty in their treatment, several studies have been proposed to minimize the environmental impacts caused by inappropriate disposal of this effluent. This study investigated the performance of natural coagulants Tanin compared to chemical coagulants aluminium sulphate and ferric chloride commonly used in the treatment of raw wastewater from tannery, by means of the physicochemical processes of coagulation, flocculation and sedimentation. Using jar tests methods, different concentrations for the coagulants (chemical and natural) were applied to the concerned effluent and it was assessed their efficiency in removing certain parameters such as apparent color COD, and turbity besides the behavior of electrical conductivity and pH. The results showed that for pH and electrical conductivity parameters, there was

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no significant variation after application of coagulant in relation to the raw effluent. By comparing the coagulants for colour parameter it was observed that the natural coagulant tanin had greater efficiency compared to the chemical ones, reaching 56.9% of removal, however, the aluminium sulphate was more efficient at removing COD, with 95% of removal. Therefore, it is noticed that the chemical coagulant aluminium sulphate was more successful for the majority of the analysed parameters in comparison to other coagulants. Chapter 7 - The proposal of this paper was to evaluate through physical and chemical parameters the efficiency of the coagulation/flocculation/ sedimentation/filtration processes using organic coagulant (Moringa oleifera) in the treatment of water from a lentic system (Igapó II Lake), located in Londrina – Paraná - Brasil. It was made the water collection at two points of the lake, in the entrance (point 1) and at the exit (point 2). The treatment occurred using the jar-test equipment with the same conditions of fast mixing and slow mixing used in the Water Treatment Station (ETA). The sedimentation time was 30 minutes. The granulometry of the sand used in the filters was the same, in the range of 0.600 to 0.850 mm. The concentrations of saline solution of the organic coagulant to be applied were: C1 = 3 mg.L-1, C2 = 6 mg.L-1 and C3 = 9 mg.L-1. In addition, it was necessary to correct the pH of the samples in order to evaluate the behavior of the organic coagulant in different pH levels. After the assays, a study was carried out on the removal of turbidity and apparent color after the coagulation / flocculation / sedimentation processes and after the filtration process. It was verified for the parameters of turbidity and of apparent color, the concentration C2 (6 mg.L-1) and the pH around 7 (neutral) presented the highest removal efficiency, being it above 99%. For the pH, all concentrations did not present great variations when compared to the crude sample, in addition the results prove the efficiency of the coagulant in different pH levels. Only assay 2 in the entrance point, did not meet the maximum values allowed by the potability ordinance 2,914/11 of the ministry of health for parameters of apparent color and of turbidity, all other assays are in accordance. The results proved the efficiency of the organic coagulant extracted from Moringa oleifera seeds for the treatment of water in lentic systems. Chapter 8 - The solid-liquid separation processes are of great scientific and technological relevance in the area of food, beverages, agrochemicals, drugs, mineral extraction, ceramics and wastewater treatment. Nowadays, various chemical substances are used that act as destabilizing agents or stabilizers according to their field of application. One of the strategies to understand the coagulation-flocculation processes is to use the zeta potential measurements as an electrochemical tool to approximate the interface phenomena and establish the mechanisms that predominate at the molecular level. One of the trends is the use of various biopolyelectrolytes (BPE) that can be obtained, modified and applied strategically in various fields of study. In this chapter, the physicochemical performance of six biopolyelectrolytes in the coagulation of flocculation

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of wastewater with a high content of solids and fats and oils was evaluated. The ones that presented a better performance for this type of wastewater are mesquite gum and chitosan. The BPE that showed a better performance in the coagulation-flocculation test of the wastewater with high content of fats and oils at pH 5.2, was the chitosan, with a dose of 68 mg/L of chitosan the treated water has the following values of BOD5 = 30 mg O2/L, fats and oil = 1 mg/L, turbidity = 2 FAU, TSS = 2 mg/L and COD = 50 mg/L. Chapter 9 - The brewing industry presents a great generation of effluent that can cause serious environmental impacts when not treated in a regular way since it has a high load of organic matter in its composition. Thus, in view of the growing emergence of breweries in Brazil and consequent increase in effluent production, alternatives are sought for the auxiliary treatment of this effluent using coagulants. In this way, the paper aimed to analyze the efficiency the usage of two organic and one inorganic coagulant in the treatment of effluent from the brewing industry. The assay was performed in Jar Test, thus simulating the coagulation, flocculation and sedimentation processes, and in sequence the filtration process was carried out. During this process the parameters of apparent color, electrical conductivity, pH and turbidity were monitored. Three different treatments were used: Aluminum Sulfate (T1), Tannin (T2) and Moringa oleifera (T3). The results showed values of apparent color removal and turbidity of more than 90% for all treatments, but the treatment with Tanino presented the highest values of removal, being 98.8% for turbidity removal and 99.6% for removal of apparent color. The pH parameter showed a rise throughout the test for all treatments presenting final values close to the neutral value, demonstrating compliance with CONAMA Resolution No. 430/2011. The electrical conductivity showed a decrease in all treatments especially in the treatment where Tanino was used being 0.32μS.m-1 the lowest value obtained. The use of the coagulants in question showed positive responses in the analyzed parameters in the treatment of the effluent of the brewing industry, showing more emphasis for the Tanino that obtained the best values. It’s an option sustainable and is possible to mix this process with the comum process that there are in brewing industry. Chapter 10 - Urban development contributes to increasing water pollution, so we must develop alternative ways to treat water. Therefore, the objective of this paper was to perform the water treatment - through the electrocoagulation process - and to calculate the cost of the operation. The paper was done according to predefined experimental planning that has nine samples with duplicate plus a pair of samples in central point. The assays were carried out using a bench-level acrylic reactor (2 liters), a magnetic stirrer, a voltage source and a monopolar electrode system arranged by means of 4 equidistantly connected aluminum plates in parallel. The studied parameters were final pH and electric conductivity, tested in two different voltages (5V and 11V). Sampling time were 40, 60 and 80 minutes. At the end of the trials, treatment costs were calculated to ensure that it was applicable. The analysis of the results concluded that the electrocoagulation process assists in the neutrality of the solution, brings the acid and basic samples near to the

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neutral pH (7) and the electric conductivity does not have significant change. Through the work it was possible to observe that the eletrocoagulation process accomplished with the continuous voltage of 5V was the one that presented the lowest cost, considering that the energy consumption and the use of the electrode were smaller 0.03325kWh and 1.23949µg respectively. Chapter 11 - Eutrophication, or the excessive richness of nutrients in a lake or other body of water, is one of the most prevalent water quality problems in the United States as well as other parts of the world. It has led to excessive growth of algal blooms, which not only cause the death of aquatic plants and animals, but also produce high levels of toxins and odorous compounds, thereby posing serious risks to safe drinking water and human health. Microcystis aeruginosa is well known to be one of the most dangerous and most common bloom-forming cyanobacteria that produces hepatotoxic microcystins. This study evaluated the performance of the coagulation/flocculation process using aluminum and ferric salt coagulants for the removal of both microcystins (intracellular and extracellular) and turbidity. The effects of coagulant dosage, pH, and coagulant-aid dosage on microcystins and turbidity removal were also evaluated. All results demonstrated that the optimum dosage of aluminum sulphate, ferric chloride, and ferrous sulphate for the removal of both microcystins and turbidity was found to be 60, 60, and 20 mg/L, respectively. With optimized coagulant dosages, the optimum pH value for both microcystins and turbidity removal occurred with a pH of 7, 6, and 7 for aluminum sulphate, ferric chloride, and ferrous sulphate, respectively. On the other hand, for all coagulants, the optimum polyelectrolyte dosage for the removal of both microcystins and turbidity was found to be 0.2 mg/L. Among these coagulants, aluminum sulphate (65.2%) was found to be more effective for both microcystins and turbidity removal compared to ferric chloride (56.3%) and ferrous sulphate (30.9%). Last, the concentration of turbidity decreased to below 5 NTU, which is the maximum turbidity level in drinking water determined by the World Health Organization (WHO). After coagulation/flocculation, the total microcystin concentration (4.09 µg/L) in the water remained above the WHO guideline value of 1 µg/L for drinking water, but the release of toxins in the water was not observed. Therefore, both intracellular microcystin and turbidity could be removed through the coagulation/flocculation process, whereas extracellular microcystin is still of particular concern in drinking water treatment due to its difficult removal. Chapter 12 - In Morocco, like all the countries of the world, socio-economic activities coupled with population growth and changes in consumption patterns generate a significant production of municipal solid waste. This is accompanied by a significant increase in leachates produced during the fermentation of waste. These leachates have a considerable impact on the environment. Moroccan regulations require leachate treatment to reduce environmental impacts. Several techniques are currently used for the decontamination of leachate such as (coagulation flocculation, biological treatment, filtration, oxidation, ...). Indeed, the majority of the physicochemical treatments used for

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the purification of the leachates intervenes as pretreatment or finishing stage to complete the treatment chain, or to eliminate a specific pollutant. The addition of a polymer as a flocculant improves the effectiveness of coagulation by inorganic coagulants. In fact, these flocculants make it possible to obtain large flocs, which settle rapidly and which resist shear forces (Bratby, 2006). According to Bratby (2006), when a liquid is already destabilized after the addition of an inorganic coagulant, the polymers increase the rate of orthokinetic flocculation by the formation of larger flocs. This is done through a sufficient absorption affinity between the polymers and the flocs. The choice of polymers must be made judiciously because their effectiveness depends on several parameters, namely: the nature of the polymer, the pH, the temperature, the type of inorganic coagulant, the nature and size of the pollutant to be eliminated, the concentration of the coagulant and flocculant (Zemaitaitiene et al., 2003, Bolto and Gregory, 2007). The first part of this work concerns the coagulation flocculation of young leachate from the Kenitra city landfill. The tests were carried out by adding ferric chloride mixed with three flocculants, namely: the chitosan, the Superfloc SD2065 and the Himoloc. The dose of coagulant was fixed at 6 g/L (determined from preliminary tests), while the doses of flocculants ranged from 3,3 to 20 mL/L. The evaluation of treatment efficiency as well as the optimal doses of the flocculants was determined by the monitoring of the removal of turbidity, COD, phenol, color, Absorbance at 254 nm and the volume of sludge collected after 24 hours. The purpose of the second part reveals the effect of the order of introduction of the reagents on the efficiency of leachate treatment by coagulation flocculation. The reagents used are ferric chloride and the three flocculants previously mentioned. The authors varied the order of introduction by adding:   

Ferric chloride first followed by flocculant. The flocculant first followed by the coagulant; The coagulant and the flocculant at the same time.

The effect of the order of introduction of the reagents was evaluated in terms of elimination of turbidity, COD, color, Abs at 254 nm, phenol, detergents, ammonium ions, nitrite, nitrate and total phosphorus. Chapter 13 - Natural and assisted particles sedimentation are crucial operations during the treatment of wastewater generated in many industrial processes, above all in the wastewater treatment field. This operation is usually used as an effluent pretreatment; normally essential for reducing suspended solids, organic load, turbidity and colour so as to achieve the correct clarification of wastewater. This chapter introduce the coagulation and flocculation concepts as well as the influence of operational conditions on assisted sedimentation. At industrial level, the factual use of both processes has been proved on different wastewater. In this sense, this chapter outline researches about combining or comparing assisted sedimentation (coagulation, electrocoagulation,

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neutralization, etc.) with other operations such as oxidation processes in order to evaluate the solids removal of the complete designed wastewater treatment focusing on OMW treatment. In addition, in this work new trends about multifunctional and novel ecofriendly bio-degradable flocculants and coagulants were reviewed and suggested for OMW pretreatment. Chapter 14 - This chapter focuses on the preparation and characterization of the chitosan based flocculant for removal of heavy metal ion prepared from chitosan by Nacylation with ethylenediaminetetraacetic acid monoanhydride (EDTAM). In this study, a series of chitosan flocculants with various degree of substitution were prepared by changing the molar ratio of EDTAM to chitosan in the preparation. The structural characterization of the chitosan flocculants by FTIR and 13C NMR spectroscopy were performed. The newly introduced functional group provided properties such as being a strong chelating reagent and an amphoteric polyelectrolyte. It was found that chitosan flocculants had good water solubility in both acidic and basic regions and precipitated in a narrow pH region, which is close to its isoelectric point. The chitosan flocculants has an ability to remove heavy metal ion from aqueous solution by controlling pH or initial concentration of the flocculant, and removed Cu(II) almost completely. The flocculation mechanism was investigated using Cu(II) and found that flocculation occurred by charge neutralization was sensitive both pH conditions and amount of chelated Cu(II) on chitosan flocculants. The complexation stoichiometry of Cu(II) and the EDTA residues of chitosan flocculant determined by UV-vis titration. As a result, the chitosan flocculants can easily remove Cu(II) from aqueous solution by only flocculation/precipitation process, which indicated that the chitosan flocculants could be applicable for remediation and treatment system of wastewater.

In: Flocculation: Processes and Applications Editor: Eleonora Vollan

ISBN: 978-1-53614-339-3 © 2019 Nova Science Publishers, Inc.

Chapter 1

FLOCCULANT POLYSACCHARIDES MAINLY FROM PLANTS Priscilla B. S. Albuquerque*, Weslley F. Oliveira2, Priscila M. S. Silva2, Maria T. S. Correia2 and Luana C. B. B. Coelho2,* 1

Centro de Tecnologias Estratégicas do Nordeste-CETENE, Recife, PE, Brazil 2 Departamento de Bioquímica, Centro de Biociências, Universidade Federal de Pernambuco, Recife, PE, Brazil

ABSTRACT Natural polymers are biocompatible, low-cost, and easily available materials of innate origin. These polymers are increasingly preferred over synthetic materials for industrial applications due to their intrinsic properties; they also are alternative sources of raw materials with characteristics of biodegradability, biosafety, and sustainability. Polysaccharides are polymers extracted from plants, algae, animals, fungi or obtained via fermentation, applied on a wide range of uses, from food to biomedical industries. Nowadays, they have been attracting considerable attention as viable alternatives to harmful synthetic flocculating agents for the removal of contaminants from water and wastewater. Then, a great deal of dedicated effort improved the production and performance of natural flocculants based on polysaccharides. The aim of this chapter is to approach current trends in preparation and chemical modification of flocculant polysaccharides derived from plants and their flocculation performance. In addition, aspects including mechanisms of flocculation, chemical modification, the effect of *

Corresponding Author Email: [email protected].

2

P. B. S. Albuquerque, W. F. Oliveira, P. M. dos Santos Silva et al. physicochemical factors on flocculating activity, and recent applications of flocculant polysaccharides, also derived from non-plant sources are reviewed.

Keywords: agglomeration, aggregation, coagulation, contamination, flocculation, grafting, polymerization, polysaccharide, wastewater treatment

1. INTRODUCTION The flocculation phenomenon is related to the clumping of particles with consequent destabilization and coming out of the aggregates from suspension. In a chemical perspective, the flocculation process is essentially physical, occurring due to the contact and adhesion of aggregates by the formation of large-size clusters called flocs, which are excluded of the suspension. Commonly, one can observe flocculation being widely used as synonymous of agglomeration, aggregation, and coagulation (Santos et al., 2014). Flocculating agents are useful in different industrial fields, such as tapwater and wastewater treatment, dredging, textile, mining, cosmetology, pharmacology, food and fermentation industries and downstream processes (Salehizadeh, Yan and Farnood, 2017). Especially in food and beverage industries, flocculant agents are widely used with the important aim to remove microscopic particles that affect water taste, appearance and texture (Santos et al., 2014). Flocculants are generally classified into three groups: inorganic flocculants, organic synthetic flocculants, and natural flocculants (or bioflocculants). Although the first two groups are most commonly used due to their effective flocculating performance and low cost, they could be associated to serious environmental and health problems. In order to circumvent the above concerns, natural flocculants have been attracting more attention in utilization (Salehizadeh and Yan, 2014). Polysaccharides are biopolymers and particularly attractive as natural flocculants due to their inherent properties; they represent one of the most abundant industrial biomaterials usually reported by several studies due to their sustainability, biodegradability and biosafety. Even more, polysaccharides are abundant in nature and commonly found in many higher plants, being frequently produced as a protection mechanism following plant injury (Albuquerque et al., 2017; Rana et al., 2011). The most common polysaccharide bio-based flocculants are alginate, chitosan, cellulose, and starch; however, microorganisms could also be used as source of raw material (Lin et al., 2014; Teh et al., 2016; Yang et al., 2016). Moreover, polysaccharides may be chemically modified to improve their flocculation performance (Liu et al., 2017b; Lou et al., 2017). Broad industrial application of bioflocculants based on polysaccharides depends on the use of low-cost substrates and the development of more efficient fermentation and recovery processes, as well as the application of cost-effective chemical

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modification of the extracted polysaccharides for improved performance (Salehizadeh, Yan and Farnood, 2017). This chapter describes the progress in polysaccharide flocculants with special emphasis for those derived from plants. In particular, aspects summarized include extraction, purification, modification, characterization, and the broad range of applications in industry.

2. SHORT SUMMARY ON POLYSACCHARIDES The polysaccharide term gathers collectively quite diverse large carbohydrates composed by monosaccharides, being named homopolysaccharides if they have only one kind of repeating units (for example starch and cellulose), or formed by two or more different monomeric units, named heteropolysaccharides and exemplified as agar, alginate, and carrageenan. Polysaccharides are considered neutral, anionic or cationic depending on its electric charge; in addition, the conformation of the polymer chains is markedly dependent not only on the ionic strength of the medium, but also on the pH, particularly in the case of the polyelectrolytes, and the temperature and the concentration of certain molecules. Several anionic and cationic polysaccharides are widely available in nature and have gained keen interest in food and pharmaceutical fields (Prajapati et al., 2014). Gums and mucilages are the constituents of polysaccharides, possessing natural source and particular differences: gums readily dissolve in water, while mucilages form viscous masses; in addition, their similarities are related to their broad range of physicochemical properties, which are widely used for applications in cosmetics, paper, pharmacy, textile, adhesive, inks, lithography, paint, explosive, and smoking products (Albuquerque et al., 2017). The preference of polysaccharides when compared to synthetic materials is closely related to their biological and chemical properties, including biocompatibility, biodegradability, polyfunctionality, high chemical reactivity, chirality, chelation and adsorption capacities (Hossain and Mondal, 2014). Regarding the excellent adsorption behaviour of polysaccharides, it is important to point out characteristics such as high hydrophilicity (due to hydroxyl groups of the monomeric units), presence of a vast number of functional groups (acetamide, primary amino, and/or hydroxyl groups) with high chemical reactivity, and flexible structure of the polymer chain. In what concerns these advantageous characteristics, the development of new products based on polysaccharides is an attempt to circumvent the issues associated to synthetic polymers and a better way of, rationally, using renewable bioresources (Hossain and Mondal, 2014; Oladoja et al., 2017). The global awareness of the society for minimizing the use of synthetic polymers has been growing and gaining special attention in important environmental campaigns

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because of the increasing environmental damage of this century. In addition, the scientific community try to develop technological alternatives for this issue. The last two decades have been marked by a crescent interest in public and scientific communities about the use and development of biopolymers, which can be obtained from renewable sources, displaying the important characteristic of biodegradability, with the desired physicochemical properties of conventional synthetic materials (Albuquerque and Malafaia, 2017; Rhim, Park and Ha, 2013). The majority of biopolymers have rather low activity under environmental conditions. The primary task for scientific researches, in what concerns the polysaccharides, is to create a methodology for the synthesis of functional materials derived from them, which have significant properties for the enhancement of their utilization on a practical scale. This is expected to open the possibility of a real knowledge of the nature of intermolecular interactions in aqueous solutions of biopolymers (Oladoja et al., 2017). The optimal choice of a particular technology for engineering of polysaccharides can be either by chemical, physical or biological modifications. Physical (ultrasonic disruption and microwave exposure) and biological (enzymatic degradation) changes allow modifications of the polysaccharide molecular mass, while the chemical-one could change the substituent types of groups, number and position (Ghimici and Nichifor, 2018). Polysaccharide bio-based flocculants contain natural polysaccharides that are suspected to exhibit excellent selectivity towards aromatic compounds and metals in the absorption of particles, for example pollutants found in wastewaters (Crini, 2005). However, it is well known that their feasibility is restricted by their physicochemical properties, moderate flocculating activity and short shelf life. In recent years, grafted bioflocculants have been developed and claimed due to their remarkable flocculating ability and biodegradability. They are covalently modified by inclusion of synthetic monomers onto their backbone to synthesise the high molecular weight grafted copolymers that exhibit improved flocculating properties (Crini, 2005; Lee et al., 2014; Lee et al., 2012). The main methods for polysaccharide modification in aqueous solution can be categorized in: (1) conventional method, (2) microwave initiated grafting method, and (3) microwave assisted grafting method. In the conventional method, a chemical-free radical initiator is added under an inert atmosphere to produce free radical sites on the polymer in order to allow the addition of monomer to form the graft chain. This method is not suitable for an industrial scale of polysaccharide production due to its low reproducibility. The use of microwave irradiation emerges as a promising alternative; in the microwave assisted grafting method, ions are produced by the addition of external redox initiators to the reduction mixture, thus, the free radical initiators facilitates the grafting reaction. In microwave initiated grafting reactions, in turn, no initiators are

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added and a small amount of hydroquinone is required to inhibit the grafting reactions. It is important to mention that factors including pH, reaction temperature, reaction time, and reactants/initiator/crosslinker dosages and ratios influence the flocculation performance of the modified polysaccharide bio-based flocculants (Kumar, Setia and Mahadevan, 2012; Salehizadeh, Yan and Farnood, 2017; Sen et al., 2009).

3. GENERAL ASPECTS OF THE FLOCCULATION PROCESS The most commonly used flocculants in industry today are inorganic and synthetic organic flocculants; their effective flocculation activity and low cost are still preferable over the bioflocculants, however, the question of their toxicity to human health and environmental pollution has been a major concern (Okaiyeto et al., 2016). Inorganic flocculants include alum, polyaluminium chloride (PAC), aluminium chloride, aluminium sulfate, ferric chloride, ferrous sulfates or composites obtained by the mixture of these salts. The flocculation process occurs between the salt of these metals and the negatively charged suspended particles in a solution. This interaction leads to a reduction in surface charge and the formation of microflocs, which in turn aggregates to form larger flocs that can easily settle out of solution (Figure 1). Besides, its application has caused problems of increased metal concentration or residual aluminium in treated water, which may presents human health implications and produces large quantity of sludge whose disposal is another problem (Lee et al., 2014).

Figure 1. Flocculation mechanism by charge neutralization.

Synthetic organic flocculants include polyacrylamide (PAA), polyethylene amine, and poly(diallyl dimethyl ammonium chloride) (DADMAC). They are commonly derived from oil-based or non-renewable raw materials, usually have a high molecular weight,

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and present polyelectrolytes in their molecular chain, which enhance their flocculating effectiveness (Lee, Robinson and Chong, 2014; Okaiyeto et al., 2016; Suopajärvi et al., 2013). However, problems associated to Alzheimer´s disease (Campbell, 2002) and carcinogenic and neurotoxic risks (Rudén, 2004) to humans were already reported for aluminium and acrylamide salt flocculants, respectively. In addition, these type of flocculants have other limitations related to their relatively high dosage requirement, high pH sensitivity, and poor efficiency for the coagulation of very fine particles (Sharma, Dhuldhoya and Merchant, 2006).

3.1. Mechanisms of Polysaccharide Bio-Based Flocculant Bio-based flocculants (bioflocculants) are natural organic flocculants, i.e., products based on natural polymers considered of great interest due to their environmentally friendly behaviour and the promise alternative to replace conventional flocculants (Lee, Robinson and Chong, 2014). Natural polysaccharides from different sources have long been described and widely applied in different fields. In recent decades, there has been an increased interest in the utilization of these biomolecules, particularly the bioactive ones, for various novel applications owing to their inherent properties. In fact, they have high potential to be applied not only in food and fermentation processes, pharmaceutical, cosmetic, downstream processing, but also in water and wastewater treatment (Liu, Willför and Xu, 2015). The kinetics of flocculation by polymeric flocculants starts with a suitable concentration of the flocculant, which is fed into the suspension; then, the macromolecular flocculant makes contact with the suspended colloids by adsorption through electrostatic interactions, hydrogen bonding, van der Waals forces, etc. This leads to a rearrangement of the conformation of the adsorbed polymer such that the adsorbed suspended particles aggregate to form large flocs that finally settle down effectively (Bolto and Gregory, 2007; Yang et al., 2016). The flocculation mechanisms that direct the activities of various polymeric flocculants, including polysaccharides, can be categorized as charge neutralization, charge patching, bridging, and sweeping. Acting as bioflocculants, polysaccharides could destabilise the colloidal particles by increasing the ionic strength and giving some reduction in the zeta potential and thus a decreased thickness of the diffuse part of the electrical double layer. In the other hand, they could specifically adsorb counterions to neutralise the particle charge because they have particular macromolecular structures with a variety of functional groups, such as carboxyl, hydroxyl, amino, and sulphate, which can interact with contaminants. For many years, chitosan, tannins, cellulose,

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alginate, gums and mucilage have been basing flocculants and attracting wide interest of researchers (Lee, Robinson and Chong, 2014). It is predicted that some of the active ingredients in the mucilage are responsible for the flocculating property. Therefore, extraction becomes the essential step to isolate the active components that exhibit the flocculating activity from the plants. There are two methods for the production of plant-derived bioflocculants: (1) solvent extraction and precipitation and (2) drying and grinding. Briefly, the solvent extraction and precipitation method starts with the cleaning of the plant materials and then extraction with distilled water overnight, followed by filtration of the mucilaginous extract and precipitation using alcohol. In turn, the drying and grinding method starts with the cleaned materials being dried at high temperature and then grounded and sieved to obtain the bioflocculants. Bioflocculants prepared under solvent extraction and precipitation conditions displayed excellent flocculating ability in the treatment of wastewater with direct flocculation process where no coagulant and pH adjustment are required. Thus, these results suggest that the extraction step is closely related with flocculating efficiency and plays the major role to extract the active constituents with high flocculating activity from the plant materials. In addition, the method used to evaluate the flocculating efficiency of the plant-derived bioflocculants and optimise the flocculation process is called Jar Test (Lee, Robinson and Chong, 2014; Salehizadeh, Yan and Farnood, 2017). The most common flocculation mechanisms related for polysaccharide plant-derived bioflocculants are charge neutralization (including electrostatic patch effects) and polymer bridging. These mechanisms are intrinsically dependent on the adsorption of flocculants on particle surfaces; if there is some affinity between polymer segments and a particle surface, the adsorption process occurs (Bolto and Gregory, 2007; Lee, Robinson and Chong, 2014; Salehizadeh, Yan and Farnood, 2017). As already mentioned in section 3, the flocculation mechanism of charge neutralisation is only applicable when the colloid suspended particles and the added flocculants are of opposite charge. In this case, the particle surface charge density is reduced by adsorption of the flocculant polysaccharide; the electrostatic repulsions are reduced to a minimum. This mechanism has been found to be quite effective for low molecular weight polysaccharide flocculants that tend to adsorb and neutralize the opposite charges on the particles (Yang et al., 2016). Considering the great number of neutral polysaccharides acting as bioflocculants, it is suggested that charge neutralisation is not the mechanism responsible for flocculation. In fact, bridging is the major mechanism in like-charged or neutral polysaccharide flocculants, especially when they extends from the particle's surface into the solution for a distance greater than the distance over which the interparticle repulsion occurs. In this case, segments of the polysaccharide flocculant are adsorbed onto the particle surface resulting in loops and tails extending into solution with the possibility of attachment of dangling polysaccharide segments onto other adjacent particles to form flocs. Bridging could be due to van der Waals force, static, hydrogen bonds or even chemical reaction

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between some radical groups of the polysaccharide molecule and the particle; in addition, this mechanism is known to be especially effective for high molecular weight polysaccharide flocculants (Salehizadeh, Yan and Farnood, 2017). Electrostatic patch and sweeping are mechanisms that contribute to the process of flocculation. The first one is caused by polymer flocculants of high charge density interacting with oppositely charged colloidal particles of low charge density. The net residual charge of the polymer patch on one colloidal particle surface can adsorb onto the oppositely charged colloidal particle. The second one forms a bulky precipitate that enmeshed the colloidal particles, which are then either settled out or flocculate together with the precipitate (Salehizadeh, Yan and Farnood, 2017). Without doubts, flocculation is one of the most important and widely used treatment process of industrial wastewaters. Many authors already highlighted the simplicity and effectiveness of flocculation-coagulation processes (Lee, Robinson and Chong, 2014; Okaiyeto et al., 2016; Salehizadeh, Yan and Farnood, 2017; Teh et al., 2016). In what concerns the use of polysaccharides as bioflocculants, some characteristics could limit their application for certain purposes. For example, chitosan is soluble in acidic media and most of polysaccharides are water-soluble in their native form, therefore they cannot be used as insoluble sorbents (Crini, 2005). In the flocculation process, the polysaccharide biodegradability can lead to the loss of flocs stability and strength (Singh et al., 2000). Also, some polysaccharides have reduced/or no bioactivity in certain conditions (Salehizadeh, Yan and Farnood, 2017). During the time, much attention has been paid to overcome these disadvantages by modifications of polysaccharides.

3.2. The Effect of Physical-Chemical Factors on Flocculating Activity The chemical composition, physicochemical properties and flocculation activity of flocculants depend on the source of the flocculant and its production method. Characteristics such as charge density and grafting ratio are important in determining the flocculant performance of the substance; even more, earlier studies indicate that flocculation efficiency could be enhanced by optimizing the grafting ratio (Salehizadeh, Yan and Farnood, 2017). Besides the flocculant charge density, the flocculation mechanism can be mainly affected by other properties, including dosage, biopolymer molecular weight, the nature of the colloids and aspects such as concentration, pH, ionic strength, composition of culture media, and temperature, especially for production of bioflocculants from bacteria (Chaisorn et al., 2016; Salehizadeh and Yan, 2014). The effect of pH on flocculating activity is one of the most important external factors affecting bioflocculant production. Several works reported the flocculating activity of different bioflocculants being pH-stable in a wide range of pH values, usually from 3 to

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10 (Aljuboori et al., 2013; Huang et al., 2015; Li et al., 2013; Li et al., 2014; Liu et al., 2014b). The metabolism of microorganisms has direct relationship with cultivating temperature. Maximum enzymatic activation can be obtained at optimal temperatures (Zhang et al., 2007). In this way, temperature is an important parameter for bioflocculant production and cell growth, especially considering bacteria and fungi sources. Thermotolerant microorganisms have an optimum temperature for growth below 45 ºC, but ability to grow at higher temperatures; they are also defined as microorganisms able to grow at 60 ºC and below 30 ºC (Chaisorn et al., 2016). The flocculant dosage of the polysaccharide is a main aspect for the determination of the flocculating activity of a colloid system. When the polysaccharide dosage is lower than the optimum, the degree of flocculation is insufficient in a colloid system that results in stabilization and charge reversal of the colloidal particles. Thus, there is no bioflocculant enough to adsorb onto the colloidal particle surfaces to bridge between these particles. An overloaded dosage of the polysaccharide flocculants increases the electrostatic repulsion forces between the colloidal particles and increases the distance between the particles to inhibit floc formation and precipitation (Salehizadeh, Yan and Farnood, 2017).

Figure 2. Percentage of publication in the last 10 years about the scientific literature dealing with polysaccharides and flocculants.

4. PLANT FLOCCULANT POLYSACCHARIDES Polysaccharide flocculants can be classified into three main groups based on their source: marine, microbial, and plant flocculant polysaccharides. Their natural origin could be related to crustacean shell wastes, seaweeds, agricultural/forestry feedstocks,

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and microorganisms including bacteria, yeast, fungi, and algae. Figure 2 depicts the percentage of published articles reporting polysaccharides and flocculants in the last 10 years. Considering the main flocculants derived from plant-polysaccharides, we summarized below their properties and the current researches about them.

4.1. Cellulose Cellulose is a linear polysaccharide consisting of β (1→4) D-glucose; it represents the most abundant biopolymer on earth, with a global economic importance. The annual production rate of cellulose is estimated at 1011–1012 ton/year, being this polysaccharide the major structural constituent of the cell wall of plants, but also derived from different origins, such as animals and microorganisms. Cellulose has many advantages, including superior thermal and mechanical properties, in addition to biocompatibility, biodegradability, and cost-effectiveness (Albuquerque et al., 2017; Salehizadeh, Yan and Farnood, 2017). In what concerns the different pathways to obtain cellulose, it is possible to highlight four: the first one is the most popular and industrially important pathway for isolating cellulose from plants, which includes chemical pulping, separation, and purification processes to remove lignin and hemicelluloses. The second pathway is related to the biosynthesis of cellulose by different types of microorganisms, such as unicellular algae, fungi, and bacteria. The third pathway is the enzymatic in vitro synthesis starting from materials such as cellobiosyl fluoride, while the last one is a chemical synthesis, whose production of cellulose occurs through a ring-opening polymerization of the benzylated and pivaloylated derivatives (Chen, Cho and Jin, 2010). The polymeric structure of cellulose was first demonstrated by Staudinger in 1920. In fact, cellulose is a simple polysaccharide with no branching or substituents in its homogeneous backbone. The morphological hierarchy of this biopolymer is composed by elementary fibrils, packaged into microfibrils, and finally assembled into fibres. Within the cellulose fibrils, there are regions of crystallites, where the cellulose chains are arranged in a highly ordered structure, and amorphous regions of disordering. Five allomorphic forms of cellulose have been known based on the location of hydrogen bonds between and within strands. Natural cellulose, called cellulose I, has two different crystalline structures (Iα and Iβ). Cellulose may be also found with other crystal structures including cellulose II, III and IV, being cellulose II the most stable structure, which can be obtained by alkali treatment of cellulose I (Brinchi et al., 2013; Moon et al., 2011; Roy et al., 2009). Cellulose obtained from plants are usually composed of hemicellulose, pectin, lignin, and other substances, while bacterial cellulose is completely pure with much higher water

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content and higher tensile strength (Klemm et al., 2005). The hydroxyl groups are the most targeted reactive groups on the cellulose main chain, which can fully or partially react with chemical agents to obtain various derivatives with different substitution degrees. The obtained derivatives of cellulose are been applied in food, cosmetic, biomedical, and pharmaceutical industries, however, the application of cellulosic material is limited due to the difficulty in processing. The high crystallinity degree and rigid intra/intermolecular hydrogen bonds result in its insolubility in water and most organic solvents. In addition, cellulose becomes amorphous in water at 320 °C and 25 MPa and can be converted chemically into its monomeric units by reacting with concentrated acids at high temperatures (Deguchi, Tsujii and Horikoshi, 2006; Liu, Willför and Xu, 2014; Zhang, Lin and Yao, 2015). Problems associated to processing cellulose and its limited solubility are observed for other natural polymers since they present increasingly application in the industrial technology. Most polymers do not present biological activity until modifications are made, so it is important to mention that numerous attempts are being performed to minimize these certain drawbacks with chemical modifications in the polymeric structure (Albuquerque et al., 2017). Cellulose can be considered an efficient alternative to produce environmentally friendly functional materials and chemicals such as bioflocculants due to its inherent physicochemical characteristics, which are improved by chemical modifications (Salehizadeh, Yan and Farnood, 2017). The most recent researches on bioflocculant production are reporting isolated strains (Lee and Chang, 2018; Shahadat et al., 2017). The unique potential of bioflocculants produced from microorganisms was first investigated in Levure casseeuse yeast by Louis Pasteur, and a similar trend in bacterial culture was also observed by Bordet in 1899 (Shahadat et al., 2017). More recently, it was reported that some bacteria can produce bioflocculants by utilizing biomass from raw materials: a lignocellulose-degrading strain Cellulosimicrobium cellulans L804 isolated from corn farmland soil presented the ability to produce bioflocculants by the degradation of lignocellulosic biomass (Liu et al., 2015). Liu et al. (2017a) reported an alkaliphilic strain Bacillus agaradhaerens C9 bioflocculant producer by using untreated rice bran as carbon source, and Guo et al. (2018) reported a novel cellulase-free xylanase-producing bacterium G22 with the potential ability to directly convert various biomasses to bioflocculants. The scientific literature dealing with polysaccharide flocculants derived from plants is still scarce when compared to the works reporting bioflocculants produced from microorganisms, or even those one reporting commercial polysaccharide bioflocculants. However, the importance of these kind of studies rises with the increasingly serious environmental problems especially associated to the discharge of effluents. For example, Liu et al. (2014a) developed an efficient and eco-friendly flocculant from Phyllostachys heterocycle bamboo pulp cellulose grafted with polyacrylamide for an effluent from paper mill. After that, Zhu et al. (2016) optimized the method and employed the co-

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polymer with the metal ions Fe3+, Al3+ or Ca2+ to treat the effluent from a surfactant manufacturer. Liimatainen et al. (2012) evaluated the effectiveness of a flocculation treatment based on alum and soluble or nanoparticular anionic derivatives of dialdehyde cellulose derived from the bleached birch chemical wood pulp obtained in dry sheets of Betula verrucosa and B. pendula, by studying the removal of colloidal material in a model suspension containing kaolin.

4.2. Starch Starch is a linear, biodegradable, inexpensive polysaccharide synthesized in a granular form by green plants for energy storage over long periods. Starch granules consist of two major components called amylopectin and amylose, which are composed of α-D-glucopyranose residues, forming α-1,4-glucosidic bonds in linear structure of amylose and additional α-1,6-glycosydic branches in amylopectin molecules. Minor constituents such as lipids, proteins, and minerals are present in starch and the levels vary with the origin, whose botanical sources include wheat, rice, corn, barley, sorghum, millet, rye, legumes, banana, mango, potato, cassava and so on. Cassava and maize were known as the major sources of starch on a commercial scale for a long time (Albuquerque et al., 2017; Ashogbon and Akintayo, 2014; Salehizadeh, Yan and Farnood, 2017). Starch is soluble in hot water, but insoluble in cold water, alcohol, or other solvents. The differences between amylose and amylopectin structures have indeed significant variance in their properties. Amylose is much more prone to crystallization process, called retrogradation, and can produce tough gels and strong films, while amylopectin retrogrades much slower due to its dispersion in water, which results in soft gels and weak films (Liu, Willför and Xu, 2015; Pérez and Bertoft, 2010). Starch is an excellent material for biotechnological applications due to its biodegradable, available, low cost, and versatile characteristics; however, its direct applications are limited by its poor processability and intrinsic properties, such as thermal, mechanical, and biological properties. Thus, various chemical, physical, and enzymatic modifications or blending with other materials has supplied solutions to achieve properties that are more desirable (Albuquerque et al., 2017). Comparing starch and other high-performance natural-polymeric material, it is much cheaper than chitosan (Liu et al., 2017b). Similar to the cellulose, conventional chemical modifications of starch could be performed based on its primary and secondary hydroxyl groups, and can be obtained by esterification, etherification, oxidation, and graft copolymerization (Liu, Willför and Xu, 2015). Considering that cationic moieties aid flocculation and sterilization through effective charge attractions, various cationic starch-based flocculants have been developed using different modification methods and even considering the lack of commercial synthesis

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methods and high cost of the cationic monomers. For example, three different starchbased flocculants, all of them containing the strongly cationic quaternary ammonium salt groups but at different positions, have been designed and prepared through etherification, graft copolymerization, or their combination. The effects of chain architectures and charge properties on flocculation of humic acid (HA) and its floc properties have been investigated in terms of several environmental parameters including pH, dose, and initial HA concentration (Wu et al., 2016). Posteriorly, authors obtained four variations with different cationic contents of two versions of the starch-based flocculants reported in the previous work. The environmental parameters pH and flocculant dose were evaluated with the effects of structural factors, i.e., cationic group contents and distributions, on the flocculation of the hairwork effluents (Du et al., 2017). These starch-based flocculants were also evaluated by the efficient flocculation of real secondary textile dyeing effluents. Starch-graft-poly[(2-methacryloyloxyethyl) trimethyl ammonium chloride] (STC-g-PDMC) and starch-3-chloro-2-hydroxypropyl trimethyl ammonium chloride (STC-CTA) have been systematically investigated and compared with that of the traditional inorganic coagulant polyaluminum chloride, and the obtained results are of significance in guiding the design and selection of a suitable polymeric flocculant in treating target wastewater (Wu et al., 2017a). Liu et al. (2017b) prepared a series of cationized starch-based flocculants (ST-CTA) containing various quaternary ammonium salt groups on the starch backbone by using a simple etherification reaction. They observed an effective performance for the flocculation of kaolin suspension, two bacterial suspensions (of Escherichia coli and Staphylococcus aureus), and two contaminant mixtures (kaolin and each bacterium) under most pH conditions. Wang et al. (2013) prepared a cationic grafted starch (ST-gPDMC) with high flocculation performance for kaolin suspensions and efficient dewatering of anaerobic sludge. More recently, Huang et al. (2017) reported that the St-gPDMC was efficient for the flocculation of kaolin suspensions and for the inhibition of E. coli by introducing new quaternary ammonium groups. A grafted amphoteric starchbased flocculant (carboxymethyl-starch-graft-aminomethylated-polyacrylamide, CMS-gAPAM) was efficiently developed by Huang et al. (2016), in which the cationic groups were randomly distributed on the polyacrylamide branched chains using Mannich reaction. A series of cationic starches were developed by incorporating a cationic moiety (STC-CTA) onto the backbone of starch in presence of NaOH. The flocculation characteristics of these starches were evaluated in silica suspension and compared with various commercially available flocculants by jar test (Pal, Mal and Singh, 2005). It is important to mention that the majority of researches about starch flocculants deal with the commercial presentation of the polysaccharide. Well-prepared natural flocculants, with or without chemical modifications, owing to their superior performance and environmental friendliness, have wide-ranging uses in wastewater treatment, especially when more effective production techniques are developed and optimized in the

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near future. Additionally, it is important to highlight the volume of the sludge produced from the treatment associated to them and the considerable reduction in the cost of sludge disposal.

4.3. Pectin Pectins are ubiquitous plant polysaccharides. They are present in the cell walls located in the middle lamella, and primary and secondary cell wall. The chemical structure of this water-soluble gum is heterogeneous, depending on the origin, location in the plant and extraction method, being composed at least of 65% of galacturonic acid units plus rhamnose, arabinan, galactan and arabinogalactan (Müller-Maatsch et al., 2016; Tamnak et al., 2016). Actually, the uronic acid residues linked through a-1-4glycosidic bonds make the main structural polysaccharide motif, while there exist three pectin’s domains: α-(1-4)-linked linear homogalacturonic backbone (HG) alternating with two types of highly branched rhamnogalacturonans regions called RG-I and RG-II. The first region (RG-I) is substituted with side chains of arabinose and galactose units, while the second one (RG-II) has a highly conserved structure, consisting of the HG backbone branched with eleven different monosaccharides, including some rare sugars such as apiose, aceric acid, 2-O-methylxylose, 2-O-methylfucose, 2-keto-3-deoxy-dmanno-octulosonic acid, and 3-deoxy-d-lyxo-2-heptulosaric acid. In all natural pectins, some of the carboxyl groups exist in the methyl ester form (Albuquerque et al., 2017; Liu, Willför and Xu, 2015). Pectin can be categorized as anionic polysaccharides mainly derived from the cell wall of plants, and also from food-industrial wastes of fruits, whose main sources are citrus peels (e.g., lemon, lime, orange, and grapefruit), apple pomace, and sugar beet pulp (Babbar et al., 2015; Marić et al., 2018). Moreover, pectin from non-conventional sources has been evaluated, for example, from cocoa husks (Chan and Choo, 2013), mulberry branch bark (Liu, Jiang and Yao, 2011), jackfruit peel (Xu et al., 2018), faba bean hulls (Korish, 2015), sisal waste (Yang et al., 2018), watermelon rind (Maran et al., 2014), pomegranate peels (Pereira et al., 2016), potato pulp (Yang, Mu and Ma, 2018), Ubá mango peel (Oliveira et al., 2018), pistachio green hull (Chaharbaghi, Khodaiyan and Hosseini, 2017), pequi peel (Leão et al., 2018), and banana peel (OLiveira et al., 2016). In the industry, the major pectin component (homogalacturonan) can be obtained using hot water or chemically by acid extraction, but some innovative extraction approaches have been developed to improve extraction process and pectin quality (Salehizadeh, Yan and Farnood, 2017). Pectin structure determines in a great manner its physicochemical properties and applications; for example, pectin is efficiently used by the food industry due to their ability to form gels under certain circumstances and to increase the viscosity of drinks. It

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is also widely applied as stabilizers in acid milk products, and some may have other pharmaceutical uses (Müller-Maatsch et al., 2016). Pectin has many applications because of its low-cost, read availability, harmless and green nature. However, it may not provide the proper emulsifying activity because of its hydrophilicity. The following modification techniques have been recommended for the improvement of pectin physicochemical and functional properties: chemical modification (such as saponification, distillation, and esterification), enzymatic modification (by pectin methylesterases), and physical modification (by heat treatment and microwave) (Tamnak et al., 2016). Yokoi et al. (2002) were one of the first authors reporting pectin as an efficient flocculant for various suspensions. They found that pectin had a flocculating activity, however, in that time; there has so far been no report about flocculating activity of pectin and its applicability as a flocculating agent. Their results demonstrated that pectin had flocculating activity in a kaolin suspension, and this activity was enhanced by the addition of Al3+ and Fe3+ to the suspension; in relation to organic suspensions such as cellulose and yeast, pectin acted as flocculant when 0.1–0.2 mM Fe3+ was present in the suspensions. Other inorganic suspensions of activated carbon and acid clay were flocculated by pectin in the presence of Al3+ or Fe3+. A commercial citrus pectin with 60% esterification and the common organic synthetic flocculant polyacrylamide were characterized and used to optimize the treatment processes of both flocculants in synthetic turbid waste water. The results reported by Ho et al. (2010) were important for the industrial application of pectins since the main concern for industry is to use low flocculant concentrations to achieve maximum results. In this case, the usage of pectin achieved that goal and proved to be effective at a low concentration of 3 mg/L. The influence of four commercial citrus pectins, with different degrees of esterification, and pectin extracted from pomelo (Citrus maxima) on the stability of indomethacin suspension was extensively investigated by Piriyaprasarth and Sriamornsak (2011). The results demonstrated that the extracted pectin had comparable activity to the commercial ones. Moreover, the use of low concentration of pectin and ferric ions allowed obtaining indomethacin suspensions with suitable stability and redispersibility. More recently, pectin extracted from Nopal (Opuntia ficusindica) was tested to treat synthetic waste water contaminated with metallic ions (IbarraRodríguez et al., 2017). Authors well-characterized the pectin and then demonstrated its effectiveness in the removal of the heavy metals by coagulation-flocculation treatment. It is possible to observe that flocculation properties of pectin have been confirmed by the scientific literature. In fact, pectin can be utilized as a harmless bioflocculant, since it is biodegradable, and edible and non-toxic toward humans and the environment; however, the publications are still discreet when compared to the most popular polysaccharide bio-based flocculants.

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4.4. Other Polysaccharide´ Flocculants Derived from Plants Other polysaccharide bio-based flocculants derived from different and non-traditional plant sources have been reported by the scientific literature (Lee et al., 2014) reported that all of them have mucilaginous texture, due to the main polysaccharide composition, and a neutral pH. Plantago psyllium seed husk is known as Isabgol husk in India and widely used as laxative. This anionic polysaccharide is extensively studied due to its easy availability and a very economical cost. Mishra et al. (2002) reported for the first time the flocculation efficiency of this polysaccharide with different effluents. Their results demonstrated that this mucilage was found to be a very effective flocculant, capable of removing almost 85 and 95 percentages of suspended solid (SS) from sewage and tannery wastewater samples, respectively. The chemical modification of P. psyllium was done by grafting polyacrylamide (PAM), resulting in a graft-copolymer (Psy-g-PAM) and very effective flocculant, capable of removing more than 93% of SS, 72% of total dissolved solids (TDS) and 15.24% of colour from a textile waste water (Mishra et al. 2004a). The same group (Mishra and Bajpai, 2005) assessed P. psyllium for the removal of dyes from model textile wastewater containing golden yellow (C.I. Vat Yellow 4) and reactive black (C.I. Reactive Black 5). The mucilage reduced dye concentration by flocculation and settling, suggesting a preference of this bioflocculant for colour removal because of its low capital cost, as well as the lower operating costs when compared to other technologies (Al-Hamadani et al., 2011) evaluating the psyllium husk from seeds of P. ovata plant. Psyllium was more effective as coagulant aid when used with aluminum chloride for the treatment of landfill leachate. The mucilage extracted from tamarind (Tamarindus indica) seeds was used for the removal of vat and direct dye in aqueous solution (Mishra and Bajpai, 2006). After the promising results obtained in this study, Mishra et al. (2006) used ceric ion used initiated polymerization to obtain a grafted mucilage with acrylamide. The grafted copolymer (Tam-G-PAM) showed better results for dye removal. The optimal flocculant concentration was independent of dye concentration within the concentration range examined. Both the grafted and ungrafted flocculants were more efficient for removal of azo dyes than for reactive and basic dyes. The application of tamarind seed kernel powder for the sedimentation of clay slurry was examined in association or not with starch. Initial qualitative results indicated that tamarind can be successfully used to reduce the turbidity of clay slurry (Chakrabarti et al., 2008). Naturally occurring Cassia angustifolia (CA) seed gum was evaluated against polyaluminium chloride for its coagulation-flocculation ability to remove colour from synthetic dye solutions. The results demonstrated that the gum was found to be a good working substitute alone or in conjunction with a very low dose of polyaluminium chloride for decolourization of acid and direct, but not for reactive dye solutions (Sanghi, Bhatttacharya and Singh, 2002).

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Fenugreek, botanically known as Trigonella foenumgraecum, is a leguminous plant found in long pods and used for various medicinal purposes. This mucilage was reported for the very first time by (Mishra, Agarwal and Yadav, 2003), proving to be a very effective flocculant for sewage treatment and capable of removing almost 97% of SS and 20% of TDS. The flocculation efficiency of this mucilage was also reported as an efficient flocculant for tannery effluent treatment (Mishra et al., 2004b). Anastasakis, Kalderis and Diamadopoulos (2009) studied optimal dose, contact time and flocculation efficiency of Malva sylvestris (mallow) and Hibiscus esculentus (Okra) mucilages to remove turbidity from synthetic wastewater and biologically-treated effluent. In the pharmaceutical field, tablets prepared using the mucilages of Hibiscus rosasinensis Linn. and Abelmoschus esculentus Linn. (Okra). Authors observed that the higher concentration level of Okra mucilage show a slow and sustained release, and can be considered as an alternative natural excipient in the modified drug delivery systems. They also reported that Hibiscus mucilage could be used as a platform for prolonged release if its binder concentrations are increased (Ameena et al., 2010). Fenugreek (from T. foenumgraecum) and okra (from H. esculentus) were tested as flocculants for treatment of textile wastewater. Results showed that the mucilages were capable of removing more than 90% of SS, 30% of TDS, and 30% of dye using a very low concentration of polysaccharide (Srinivasan and Mishra, 2008).

5. FLOCCULANT POLYSACCHARIDES OF NON-PLANT SOURCED Despite the considerable number of polysaccharide bio-based flocculants derived from plants, especially cellulose and starch, other sources of polysaccharides could be derived from seaweeds, arthropods, and microorganisms, which might be chemically modified to improve their flocculation performance. Natural flocculant polysaccharides from microorganisms, microalgae, seaweeds and animals (Table 1) are also attractive substitutes for synthetic flocculants due to their ecofriendly nature, biodegradability, stability, cost-effective production process, and large availability and yield (Salehizadeh, Yan and Farnood 2017). Microorganisms such as bacteria and fungi are able to produce extracellular polymeric substances (EPS) with flocculating activity, including polysaccharides, proteins and glycoproteins. Bioflocculants from these sources are also potent alternatives for usage in wastewater treatment, textile, pharmacology and cosmetology industries. This section focuses in recent advances in polysaccharides bioflocculants from marine and microbial origins, considering their features, production, flocculant mechanisms and emerging applications.

Table 1. List of flocculant polysaccharides from bacteria, fungi, marine sources and arthropods Species Bacteria Alcaligenes aquatilis AP4

Source

Structure

Reference

Palm-oil mill efluent

Glycoprotein

Bacillus cereus SK Bacillus subtilis F9 Bacillus subtilis WD161 Bacillus thuringiensis

Wastewater treatment plant Wastewater sludge Recycled activated sludge of a seafood processing plant Aquaculture and Nutritional Laboratory, Pearl River Fishery Research Institute, Chinese Academy of Fishery Sciences, Guangzhou, China Fungal Culture Collection of Lublin

Glycoprotein Polysaccharide and protein Glycoprotein Polysaccharide

Adebayo-Tayo and Adebami, 2017. Busi et al., 2016 Giri et al., 2015 Chaisorn et al., 2016 Wu et al., 2017b

Polysaccharide and protein

Czemierska et al., 2017

Paper mill sludge

Polysaccharide, protein and nucleic acid Polysaccharide and protein

Guo et al., 2017

Polysaccharide Polysaccharide Polysaccharide, protein and nucleic acids Polysaccharide Glycoprotein

Li et al., 2013 Tang et al., 2015 Liu et al., 2014b

Water

Polysaccharide and protein

Microbial Culture Collection Unit (UNiCC), Laboratory of Industrial Biotechnology, Institute of Bioscience, University, Putra Malaysia White rot Soil surface

Polysaccharide and protein

Abu-Elreesh and Abd-ElHaleem, 2014 Aljuboori et al., 2013

Polysaccharides Polysaccharide

Patel et al., 2014 Pu et al., 2018

Rhodococcus rhodochrous R202 Pseudomonas sp. GO2. Anabaena sp. BTA992

Paenibacillus elgii B69 Paenibacillus mucilaginosus Klebsiella sp. Streptomyces sp. MBRC-91 Achromobacter xylosoxidans Fungi Curvularia sp. DFH1 Aspergillus flavus S44-1

SGMP1 and SGMP2 Aspergillus niger

National repository for cyanobacteria and microgreen algae (freshwater) of the Institute of Bioresources and Sustainable Development, Imphal, Manipur, India Soil Soil Activated sludge of a secondary sedimentation tank in a wastewater treatment plant (WWTP) Marine sediment Activated sludge of Bongaigaon oil refinery

Khangembam et al., 2016

Manivasagan et al., 2015 Subudhi et al., 2016

Species Microalgae/Seaweeds Scenedesmus obliquus AS-61 Seaweed Brown seaweed

Source

Structure

Reference

Water

Polysaccharide

Guo et al., 2013

Commercial Agar bacteriological Commercial sodium alginate

Prado et al., 2011 Rani et al., 2013

Brown seaweed

Commercial sodium alginate

Gyrodinium impudicum KG03 Animals Brachyura Animal source

Seawater

Cationized agarose Polymethyl methacrylate grafted sodium alginate Alginate graft polyacrylonitrile beads Sulfated polysaccharide

Xu et al., 2013 Agbovi and Wilson, 2018

Animal source

Commercial chitosan

Chitosan 3-chloro-2-hydroxypropyl trimethylammonium chloride grafted onto carboxymethyl chitosan Phenylalanine-modified-chitosan

Commercial chitosan powder from crab shells Commercial chitosan

Salisu et al., 2016 Yim et al., 2007

Du et al., 2018

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5.1. Flocculant Polysaccharides in Bacteria Bacteria have been reported to produce polymeric bioflocculants such as glycoproteins and exopolysaccharides, as metabolites. Bioflocculants with varied sugar composition have been isolated from bacteria and they have showed strong flocculating activity to kaolin clay, sewage water and heavy metals, being a promise for industrial and biotechnological applications The bacterium Alcaligenes aquatilis AP4 produces a flocculant glycoprotein which was isolated by first time from Palm-oil mill effluent (Adebayo-Tayo and Adebami, 2017). The isolated bioflocculant showed a high flocculating activity of approximately 90% and potential for large-scale production. An exopolysaccharide produced by Bacillus cereus SK showed flocculating activity to kaolin of 83.4% at 12 mg, and no considerable toxicity to zebra fish in vivo, revealing the potential of this EPS as a bioflocculant in industrial and biotechnological field (Busi et al., 2016). Other study revealed a flocculant glycoprotein produced by B. subtilis WD161, composed of mainly protein and sugar, with flocculating activity to precipitate suspended solid in palm-oil mill effluent increased by 35% (Chaisorn et al., 2016). A potent bioflocculant was also purified from B. subtilis F9, showing a composition of protein and mainly sugar (88.3%). The bioflocculant was able to flocculate small particles, although its low molecular weight, being considerate an excellent bioflocculant for industrial applications (Giri et al., 2015). A strain of B. thuringiensis highly-producer of flocculant was isolated from the biofloc in aquaculture waters. The bioflocculant was a solid substance with white colour and composition mainly of polysaccharides (Wu et al., 2017b). The flocculation potential of the exopolymer R-202 produced by Rhodococcus rhodochrous was investigated (Czemierska et al., 2017). With a composition of polysaccharides and proteins, and negatively charged, the exopolymer R-202 promoted the flocculation of a kaolin suspension with and without the addition of cations, being a promise for applications in flocculation industrial process. An exopolysaccharide composed of glucose, glucuronic acid, mannose and xylose isolated from bacterium Paenibacillus elgii B69 showed high flocculant activity when tested with kaolin clay, dyeing pigment, heavy metal ion and real wastewater (Li et al., 2013). A study about polysaccharide-based flocculants (PSBs) produced by P. mucilaginosus GIM1.16 revealed that the production and feasibility of these bioflocculants can be improved with the presence of metal ions in culture medium. The presence of Ca2+, Mg2+ and Fe3+ increased the production and flocculating activity of PSBs (Tang et al., 2015). M-C11 is a bioflocculant isolated from Klebsiella sp., composed of sugar (91.2%), protein (4.6%) and nucleic acids (3.9%). This bioflocculant showed high pH and thermal stability in kaolin suspension in the pH range of 4.0 to 8.0 and temperature of 20 to 60°C,

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and a sludge dewatering performance more efficient than inorganic flocculants (Liu et al., 2014b). An exopolysaccharide produced by cianobacterium Anabaena sp. BTA992 during its photoautotrophic growth was evaluated and it was observed bioflocculant activity with potential properties for commercial production and industrial applications (Khangembam et al., 2016). A biomass-degrading bacterium Pseudomonas sp. GO2 was able to produce a lowcost bioflocculant from untreated corn stover through directly hydrolyzing biomasses. Biochemical analysis showed a composition of polysaccharides (59%) with uronic acid (34.2%), protein (32.1%) and nucleic acid (6.1%), and a high flocculation potential flocculating to harvest the green microalgae Chlorella zofingiensis and Neochloris oleoabundans (Guo et al., 2017). Achromobacter xylosoxidans TERI L1 isolated from oil refinery waste produces an exopolysaccharide bioflocculant encompassed of various functional charged groups with flocculating activity for dispersed kaolin clay particles in suspension and to adsorption of multi metals from environment (Subudhi et al., 2016). Thus, this flocculant is a good candidate for heavy metal removal in contaminated waste-water. Green synthesis of silver nanoparticles was a method developed based in a polysaccharide flocculant produced by the marine actinobacterium Streptomyces sp. MBRC-91. The biosynthesized silver nanoparticles showed strong antibacterial potential in sewage water, being useful for wastewater treatment (Manivasagan et al., 2015). A flocculant exopolysaccharide from Arthrobacter sp. B4 was also used for green synthesis of silver nanoparticles, resulting in nanoparticles highly stable, with antimicrobial activity and low phytotoxicity (Yumei et al., 2017). This represents the use of microbial flocculants as a potential tool in many fields, including the medical therapies.

5.2. Flocculant Polysaccharides in Fungi Conventionally, fungi play valuable roles in environment and are involved in global biotechnological processes, including the production of enzymes, polysaccharides, lipids and pigments. Some fungal species have been reported as bioflocculant polysaccharide producers with high flocculating activities. An oleaginous fungal Curvularia sp. strain DFH1 demonstrated its potential to coproduce lipids and an exopolymer with a powerful flocculant activity of 95% (AbulElreesh and Abd-El-Haleem, 2014). The chemical analysis of the exopolymer shows a composition of protein and polysaccharide. An analysis of infrared spectrum indicates the presence of carboxyl and hydroxyl groups, typical in sugar derivatives. A polysaccharide bioflocculant named IH-7 was produced and isolated from Aspergillus flavus fermentation medium (Aljuboori et al., 2013). The bioflocculant

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consisted basically of protein (28,5%) and sugar (69,7%), including neutral sugar, uronic acid and amino sugar, and showed a good flocculating activity in kaolin suspension without cation addition. Two bioflocculant exopolysaccharides were isolated from fungal cultures named SGMP1 and SGMP2 found in soil samples collected from New Vallabh Vidyanagar, Gujarat (India). The flocculating activity was 99%, and the fungal isolates could remove the cations Al3+ and Fe3+ in ideal concentrations for application in bioremediation of heavy metals (Patel et al., 2014). A bioflocculant (MBFA18) produced by Aspergillus niger (A18) isolated from soil sample using potato starch wastewater as nutrients showed strong flocculant efficiency, less dosage, sludge amount and moderate treating condition comparable to the chemical flocculants. A flocculating rate of approximately 90% was achieved for kaolin clay under optimal cultivation condition (Pu et al., 2018).

5.3. Flocculant Polysaccharides in Algae Exopolysaccharides from marine algae have been explored due to their potential applications, including as bioflocculant agent, considered more efficient that commercial flocculants. Alginates are polysaccharides firstly isolated from brown seaweeds (Phaeophyta), and recently identified as produced also by two genera of soil bacteria, Pseudomonas and Azotobacter (Hay et al., 2013). This polysaccharide is constituted to over than 200 different types varying in length and array of β-D-mannuronic acid (M) and α-Lguluronic acid (G) monomer units (Albuquerque et al., 2017). Alginates are biocompatible, biodegradable, and non-immunogenic biopolymer polyelectrolytes (Yang, Xie and He, 2011). The physical properties in aqueous medium for alginates depend not only on the M/G ratio, but also on the distribution of M and G units along the chain. At this moment, it is important to highlight that the main property of alginates is their ability to retain water. Because of their linear structure, and high molecular weight, alginates form strong films and good fibres in the solid state. Their gelling and stabilizing properties are also very important characteristics for alginates; the stiffness of the alginate chains and the complex with counterions could be attributed to the composition (M/G ratio) and distribution of M and G units in the chains. The higher content of G units form stable crosslinked junctions with divalent counter ions (for example, Ca, Ba, and Sr, unless Mg), so the crosslinked network can be considered a gel. In addition, the low pH also forms acidic gels stabilized by hydrogen bonds (Albuquerque et al., 2017; Rinaudo, 2008; Yang, Xie and He, 2011).

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As an anionic polymer, alginate forms electrostatic complex when mixed with a cationic polymer. The stability of the formed complex depends on the pH and salt concentration, but even in the best conditions, the complex is insoluble and thus allows the formation of fibres, films, and capsules. They have been applied widely in biomedical, pharmaceutical and biotechnology fields due to its desirable characteristics, versatility and biocompatibility (Albuquerque et al., 2017; Hay et al., 2013; Salehizadeh, Yan and Farnood, 2017). Several studies already reported the excellent flocculation and decolourization capabilities of alginates (Dao, Cameron and Saito, 2016; Rani, Mishra and Sen, 2013; Salisu et al., 2016; Yuan and Jia, 2013). Considering the use of alginates for copolymerization, many works described the preparation and characterization of these complexes, also proposing many applications to them, especially for the most investigated polyelectrolyte complex based on alginate and chitosan (Ortiz et al., 2018; Yang et al., 2016). The sulfated exopolysaccharide p-KG03 produced by the red-tide marine microalga Gyrodinium impudicum KG03 showed bioflocculant activity more than 90% in kaolin suspension, and a flocculation rate higher than commercial flocculants as polyacrylamide and zooglan (Yim et al., 2007). The microalga Scenedesmus obliquus AS-6-1 is able to carry out flocculation and self-flocculation due to its cell wall-associated polysaccharides, composed by glucose, galactose, rhamnose and fructose with molar ration of 8:5:3:2:1. Fast flocculating action was observed on suspended cells of S. obliquus and Chlorella vulgaris in the presence of 0.6 mg/L flocculating agent (Guo et al., 2013). Agarose is a polysaccharide obtained of certain red seaweed of easy availability. Cationized agaroses were synthesized through the reaction of agarose with 3-chloro-2hydroxypropyltrimethylammonium chloride in alkaline medium, and showed flocculation activity in assays with colloid kaolin suspensions comparable with commercial cationic polyacrylamides, representing an alternative for water treatment (Prado et al., 2011).

5.4. Flocculant Polysaccharides in Animals 5.4.1. Chitosan According to Wu et al. (2012), chitin is the second most abundant polymer after cellulose. It is widely synthesized by many living organisms such as fungi, yeasts, algae and squid pen, being found in exoskeletons of crabs, lobsters, shrimp and crab shells, as well as insect cuticles. Depending on its source, chitin occurs mainly as two allomorphs, namely α (the most abundant) and β forms. The chemical structure (poly-β-(1→4)-Nacetyl-D-glucosamine) of chitin can be partially degraded by acid to obtain a series of

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oligomers namely oligochitins. Under alkaline conditions, a partial deacetylation of chitin results in one of the most chitin derivative in terms of applications: chitosan, biobased polymer with many bioactivities, including antitumoral, antimicrobial, fungicidal and immunotherapeutic properties, eliciting chitinase, and regulating organism growth (Albuquerque et al., 2017; Salehizadeh, Yan and Farnood, 2017). Chitosan is a linear, cationic polysaccharide composed of randomly repeating units of β(1→4)-linked 2-acetamido-2-deoxy-D-glucopyranose (A-unit; the neutral sugar unit GlcNAc) and 2-amino-2-deoxy-D-glucopyranose (D-unit, the positively charged sugar unit GlcN). The amount of D-units in chitosan is often more than 60%. It shows different degrees of deacetylation (DD) between 40–90% and is available commercially in various molecular weights ranging from 50,000 to 2,000,000 Da. The contents of the A-units in chitosan can vary from 0.7 (70% acetylated) to 0 (0% acetylated, all units charged). Therefore, chitosan can be considered as ampholyte (enriched in A-units) or polyelectrolyte (enriched in D-units). Chitosan is the only commercially available watersoluble cationic polymer, property that emerges as an advantage when compared to the marked insolubility of chitin in all usual solvents. The water solubility of chitosan is related to the positive charges on its primary amino groups, which allows the interaction of this cationic biopolymer with anionic molecules such as glycosaminoglycans (GAG) and proteoglycans (Albuquerque et al., 2017). Moreover, chitosan may be considered one of the most promising natural substitutes for commercial synthetic polymer flocculants due to its unique flocculation properties, also associated to the presence of these primary amino groups, as well as the potential to employ chemical modifications in this carbohydrate polymer. Chitosan was used as flocculant agent for harvesting of the microalga Chlorella sorokiniana, with flocculation efficiency reaching over 99% at dosage of 10 mg chitosan per gram algal biomass and reducing the volume by 20-50 folds (Xu et al., 2013). Recent studies reported by the scientific literature show the production, characterization, and application of microwaves (Cui et al., 2017), grafted-copolymers (Wang et al., 2016) and other hibrids (Dharani and Balasubramanian, 2015; Jia et al. 2016; Sun et al., 2017) of chitosan and, for example, lignin, ions, antibiotics, acrylamide. Chitosan was functionalized by graft with 3-chloro-2-hydroxypropyl trimethylammonium chloride, generating a new flocculant agent with potential for wastewater treatment (Agbovi and Wilson, 2018). Other chitosan-based flocculant denominated phenylalanine-modified chitosan showed higher removal potential of the antibiotics norfloxacin and tylosin in turbid water than commercial flocculants, being a potent contaminant removal (Du et al., 2018). Great flocculant activity was reported to a terpolymer based on chitosan and lignin (chitosan-acrylamide-lignin), which showed maximum percentage removal of 99.3% and 67.0% for the dyes reactive orange C-3R and methyl orange, respectively (Lou et al., 2018; Lu et al., 2017).

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6. POLYSACCHARIDE FLOCCULANTS FOR WASTEWATER APPLICATIONS Wastewater from different sources can be treated with flocculating polysaccharides, as shown in Figure 3. Contaminant particles dispersed in wastewater, such as dye molecules, can form flocs with these polysaccharides.

Figure 3. Flocs formation in wastewater by flocculant polysaccharide.

6.1. Dyes Removal Different types of industries, such as textiles and plastic, use dyes to colouring their products, generating large volumes of colored wastewater. However, dyes are substances capable of absorbing ultraviolet light and consequently decrease this absorption by photosynthetic organisms and reduce dissolved oxygen content of aquatic environment; characterizing, thus, a serious environmental pollutant (Rangabhashiyam et al., 2013; Bello et al., 2017). Coagulation-flocculation has been considered a cost effective technology with excellent color removal ability (Verma et al., 2012). A polysaccharide with cationic behaviour that is widely used for removal of negatively charged dyes in wastewater is the chitosan; anionic dyes can be adsorbed electrostatically with the protonated amine groups of chitosan (Lee et al., 2014; Vakili et al., 2014). For example, about 99% of the acid blue 92 dye was removed by chitosan, allowing recovery of the biopolymer from formed flocs with the dye using 0.1 M NaOH and with subsequent reuse of chitosan in acetic acid solution (Szygula et al., 2009). Additionally, modifications in chitosan structure as well as its association with other polymers have been increasingly studied to improve flocculant action in dye removal. A chitosan-based cationic polymer was elaborated through the modification of this polysaccharide by (3-chloro-2-hydroxypropyl) trimethylammonium chloride; such

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chitosan modification was useful for dye melanoidin removal from industrial wastewater (Momeni et al., 2018). In an attempt to elaborate amphoteric flocculants, capable of eliminating both anionic and cationic dyes, Yang et al. (2013) prepared grafting flocculants, formed by carboxymethyl chitosan-graft-polyacrylamide (CMC-g-PAM). These authors have found that the ability to remove methyl orange (anionic dye) and basic bright yellow (cationic dye) initially occurs by charge neutralization between produced flocculant and dyes, but flexibility of PAM graft chains allowed formation of large and insoluble flocs with net-like structure, allowing an easy sedimentation in water treatment (Yang et al., 2013). The synthetic monomer of acrylamide was used to graft chitosan and lignin (CAMCL) forming a ternary graft copolymer, since these two polymers together provide more functional groups to attract dyes, such as orange C-3R, methyl orange and acid black-172. In addition, flocculating mechanism of CAMCL occurred by the charge neutralization, bridging and sweeping effects (Cui et al., 2017; Lou et al., 2018). Cellulose has a regular structure and matrix formed by hydroxyl groups presenting a high degree of polymerization and susceptible to undergo chemical modifications making it a relevant flocculant (Kono and Kusumoto, 2015; Ferreira et al., 2016). Quaternized celluloses and ampholytes of this polysaccharide in different degree of cationic substitution, for example, had flocculating capacity against anionic dyes, such as acid red 13 and acid blue 92 (Kono and Kusumoto, 2015; Kono, 2017). However, carboxymethyl cellulose undergoing the grafting process with hydrolyzed polyacrylamide, generating CMC-g-HPAM, was able to remove the methylene blue cationic dye. The highest removal efficiency occurred under alkaline conditions where the carboxyl groups of CMC-g-HPAM were deprotonized, forming -COO- groups, allowing electrostatic interactions with methylene blue, favoring such flocculation (Cai et al., 2013). Gum polysaccharides also went through the grafting process, such as the ghatticrosslinked-polyacrylamide (Gg-cl-PAAM) hydrogel synthesized capable of adsorbing and removing cationic (rhodamine B and brilliant green) and anionic (methyl orange and congo red) dyes (Mittal et al., 2018). Xylan, a xylose polymer, is another polysaccharide which, when phosphorylated, acted as a flocculant removing more than 95% of cationic ethyl violet dye (Liu et al., 2018). A macromolecule originated using corn ethanol wastewater, named compound biopolymer flocculant (CBF), has in its composition more than 80% polysaccharide; CBF presented methylene blue removal, whose flocculation process occurs primarily by adsorption bridging and charge neutralization by its polar functional groups (Xia et al., 2018). The exopolysaccharide (EPS) produced and purified from Paenibacillus elgii B69, was able to promote high rate of decolourization for methylene blue and red X-GRL positive dyes, while less than 50% for anionic and neutral dyes (Li et al., 2013).

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6.2. Cleaning of Heavy Metal Ions Heavy metal ions, such as lead, copper and zinc, can contaminate water due to natural processes, since such elements can be stored in the soil and transported by surface waters. In addition, anthropogenic sources contribute to this type of pollution, such as industrial activities including mining and coal combustion (Kobielska et al., 2018). These ions are extremely toxic and can cause serious human health problems, such as damage to the neurological system, blood disorders, toxicity in different organs and even death (Shtenberg et al., 2015). In front of this serious scenario of contamination with heavy metal ions, to remove these contaminants in wastewater is very important to leave it free or in non-toxic concentrations of these ions; such removal can be carried out through bioflocculants, which include polysaccharides (Salehizadeh and Yan, 2014). Some polysaccharides, such as xanthan gum and starch, possess many –OH groups and act as metal ion coordination sites; while other polysaccharides, for example, chitosan with –NH2 groups and sodium alginate apart from –OH groups –COO- can bind to the metal ions (Kolya and Tripathy, 2013). Chitosan, for example, promoted simultaneous adsorption of heavy metal ions (iron, nickel and copper) and salt anion (sulfate). At pH range 5 to 6, chitosan has protonated and unprotonated amine groups, in which the latter group form chelate complexes with salt cations and salt anions are adsorbed through electrostatic interaction on chitosan (Mende et al., 2016). Polysaccharide inulin underwent a carboxymethylation process to synthesize carboxymethyl inulin (MIC), which removed metal ions in a kaolin suspension, reducing the total iron, chromium VI and manganese (II) content. The mechanism proposed for this chelation is the interaction with the cations by oxygen of the ether linkage and by oxygen of the carboxylate group through five membered ring formation (Rahul et al., 2014). A pectin, extracted from O. ficus-indica had affinity to the different metallic ions (Ca2+, Cu2+, Zn2+, Cr3+, Ni2+, Pb2+ and Cd2+); since pectin is a linear molecule composed of galacturonic acid, whose hydroxyl and carboxylic groups can be responsible for this affinity with the metal ions studied (Ibarra-Rodríguez et al., 2017). Flocculating power of polysaccharides produced by different bacteria also has been determined. EPS produced by bacteria, such as cyanobacteria, has negative charges and can act as a chelating agent of heavy metal ions with positive charge (Bhunia et al., 2018). The EPS bioflocculant purified from P. elgii B69 also had high capacity to adsorb Al3+, followed by Pb2+, Cu2+ and Co2+ (Li et al.; 2013). A flocculant system was made using EPS from Rhizobium sp. and polyethyleneimine (PEI), which was able to remove Cu2+. It was proposed that such process occurred firstly by binding Cu2+ to negativelycharged groups, mainly carboxylate, of the EPS followed by link of the EPS-Cu2+ complex with PEI resulting in firm and large flocs with easy removal (Escobar et al., 2015). While more than 90% of heavy metals (Zn2+, Cd2+, Pb2+, Cu2+ and Ni2+) were adsorbed to the EPS of glycoprotein nature produced by Achromobacter xylosoxidans

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when grown in culture medium supplemented with these ions (Subudhi et al., 2016). A polysaccharide molecule (MSI021) was purified from Bacillus cereus; and characterized as a bioflocculant heavy metal remover. A solution containing heavy metal salts (HgCl2, ZnCl2 and CuSO4) with a bioluminescent bacterium, Vibrio harveyi, was treated with MSI021. The presence of MSI021 in the solution allowed the V. harveyi growth, which continued with its luminescent phenotypic expression, differently from the absence of MSI021, in which there was a decrease in the luminescence of this bacterium; such phenomenon was possible due to this bioflocculant molecule that mitigated heavy metal toxicity (Sajayan et al., 2017).

6.3. Treatment of Pulp and Paper Industry Effluents About 42% of global industrial wastewater is produced by pulp and paper industry. The processes in the paper manufacturing involve pulping, bleaching and papermaking; in fact, in all these steps effluents composed of different chemical species are generated (Toczyłowska-Mamińska, 2017). Wastewater from pulp and paper industry have a diversity of organic and inorganic contaminants, such as resin acids, fatty acids, adsorbable organic halide (AOX) and total suspended solids (TSS) besides being able to have high content of biological oxygen demand (BOD) and chemical oxygen demand (COD) (Ashrafi et al., 2015; Kumar et al., 2015). These undiluted untreated effluents are toxic to aquatic organisms and their treatment can be carried through the flocculation physicochemical method, which includes the flocculating polysaccharides (Kumar et al., 2015). Thus, a copolymer flocculant prepared by grafting (2-methacryl-oyloxyethyl) trimethyl ammonium chloride onto chitosan (chitosan-g-PDMC) has been used to treat pulp mill wastewater. This novel cationic chitosan-based flocculant promoted efficient removal of COD, turbidity and lignin as well as water recovery. Grafting of chitosan showed in favour of the double electric layer compression, charge neutralization and improved the sweep-floc effects (Wang et al., 2009). In another work, raw and undiluted pulp and paper mill effluent was treated with Cassia obtusifolia seed gum, which removed COD and TSS an up to 36.2 and 86.9%, respectively; and the flocs formed after the treatment had a morphology highly fibrous-like and aggregate (Subramonian et al., 2014). Polysaccharides from potato starch have been modified by benzylation and insertion of hydroxypropyl-trimethyl ammonium (HPMA) moieties of different substitution degrees, generating benzyl 2-hydroxypropyl-trimethylammonium starch chloride (BnHPMAS). Flocculation performance was tested for BnHPMAS in a model of paper industry wastewater; these amphiphilic starch derivatives removed contaminants from recycled paper processing, so named stickies, including total organic carbon (TOC) (Genest et al., 2015). A cationic bioflocculant has been produced through polymerizing

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(2-methacryloyloxyethyl) trimethyl ammonium chloride and xylan, generating xylanDMC, removed COD, lignin, sugar, BOD and turbidity from pulp mill wastewater; the flocculation of particles occurred by bridging mechanism (Chen et al., 2018). Natural dicarboxyl cellulose flocculant (DCC) has been synthesized and presented great flocculation activity to the effluent from paper mill; DCC combined with CaCl2 reduced turbidity, COD and BOD through the process coagulation-flocculation of the effluent suspensions (Zhu et al., 2015). Turbidity reduction from paper mill effluent can allow the recovery of cellulose fibers. Mukherjee et al. (2014) tested flocculant action of guar gum, xanthan gum and locust bean gum polysaccharides and found that guar gum reduced the turbidity and recovered more fibers than the other carbohydrates of a synthetic effluent. In addition, guar gum-based nanocomposite, so called g-GG/SiO2, has been synthesized by grafting polyacrylamide chains on a guar gum (g-GG) followed by in situ nano silica incorporation on g-GG surface. This nanocomposite was able to reduce pollutant contents of paper industry, such as TSS and turbidity, and the flocculation in acidic environment occurs due to electrostatic and patching mechanism; under alkaline conditions the flocculation process happens mainly by bridging (Pal et al., 2015).

6.4. Removal of Agricultural and Food Contaminants More than 300 million ton of organic waste are produced each year by agricultural and food processing industries in the United States; sustainable treatment of such waste has become a worldwide challenge (Sheets et al., 2015). These organic substances found in wastewater from such industries comprise TSS, COD, organic colloids, sludge, oil/grease, beyond dissolved inorganics (Teh et al., 2016). In addition, nitrogenous compounds, especially ammonium nitrogen, can be present in large quantities in food industry wastewater (Zhukova et al., 2011). Phosphate is a common constituent of agricultural fertilizers and such chemical specie can contaminate effluents; excess of phosphorus in the aquatic environment can contribute to the process of eutrophication (Adesoye et al., 2014). Therefore, agricultural and food contaminants in wastewater need to be removed, and such process can be performed by flocculant polysaccharides. Wastewater is generated in potato starch process that is considered one of the most polluted in food industry. Potato starch wastewater (PSW) has been treated with a bioflocculat complex denominated MBF917, produced by Rhizopus sp. M9 and M17, such macromolecule is composed of more polysaccharide than protein. MBF917 removed the turbidity and COD from the PSW (Pu et al., 2014). A bioflocculant has been extracted from Paenibacillus polymyxa, and such compound showed to be thermostable with indicative of its main backbone being formed by polysaccharide; this bioflocculant was still used to treat PSW by reducing COD and turbidity efficiently (Guo et al., 2015a; Guo et al., 2015b). Another bioflocculant of polysaccharide nature has been produced

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and isolated in the fermentation liquor of Rhodococcus erythropolis. This bioflocculant was able to reduce COD, ammonium and total phosphorus concentrations of the PSW medium (Guo et al., 2018). Rice starch has been used to perform the treatment of agroindustrial wastewater from palm oil mill; this carbohydrate (at dosage 0.55 g/L) promoted removal of almost 90% TSS from palm oil mill effluent. Flocs produced with this treatment had a compact structure with smoother surface, designating formation of denser and larger flocs by bridging flocculation mechanism (Teh et al., 2014). Removal of orthophosphate (Pi), a very common contaminant in water bodies by agriculture, was obtained using the carboxymethyl chitosan grafted with 3-chloro-2-hydroxypropyl trimethylammonium chloride, CMC-CTA. The CMC-CTA flocculant efficiently removed Pi and the turbidity under acidic conditions of a simulated wastewater (Agbovi and Wilson, 2018). Therefore, it can be inferred that different polysaccharides are been used for a great versatility in wastewater applications. The composition of EPS molecules produced by microorganisms has been revealed which usually are of glycoprotein nature, and had their flocculating performance well established. While polysaccharides with structure already characterized have undergone chemical changes to improve their flocculant capacity.

CONCLUSION The purpose of this review was to approach scientific literature dealing with polysaccharide bio-based flocculants with special emphasis for those derived from plants. Moreover, this review emphasized aspects such as extraction, purification, modification, characterization, and the broad range of applications of natural flocculants in industry. The most current scientific publications demonstrate the industrial concern for the use of new substrates, besides the reduction in the costs of bioflocculants´ production and the constant awareness about the substitution of inorganic flocculants for the innovative ones. It was remarkable to note the preference of bioflocculants in comparison with inorganic flocculants due to their low cost, availability, biodegradability and biosafety; in addition, they can be obtained from renewable resources and their application is directly related to the improvement of quality of life. Several studies investigated the flocculating activity of polysaccharide bio-based flocculants in wastewater treatment; they are technically promising as flocculants with high removal efficiency of suspended solids, total dissolved solids, turbidity, colour and dye. However, its development is limited with variation of flocculating efficiency, short shelf life, and high production cost. The scientific literature dealing with flocculants polysaccharides derived from plants is still scarce when compared to bioflocculants produced from microorganisms, or even those reporting commercial polysaccharide bioflocculants. Regarding issues such as

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biosafety and the sake of ecology, more qualitative and quantitative research are necessary for further exploitation and applications of polysaccharide bio-based flocculants in different industries.

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BIOGRAPHICAL SKETCH Name: Priscilla Barbosa Sales de Albuquerque Affiliation: Centro de Tecnologias Estratégicas do Nordeste (CETENE), Recife, PE, Brazil. Education: PhD Research and Professional Experience: Biochemistry and Biotechnology

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Professional Appointments: Extraction and characterization of biomolecules derived from natural sources; experience with polysaccharides, immobilization of biomolecules, drug delivery systems and potential applications in pharmaceutical, food and cosmetic fields. Publications from the Last 3 Years: 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11.

https://www.sciencedirect.com/science/article/pii/S0141813016324394 https://www.ncbi.nlm.nih.gov/pubmed/28433769 https://www.ncbi.nlm.nih.gov/pubmed/28916381 https://www.ncbi.nlm.nih.gov/pubmed/28987799 https://www.ncbi.nlm.nih.gov/pubmed/28545372 https://www.ncbi.nlm.nih.gov/pubmed/26840177 https://www.ncbi.nlm.nih.gov/pubmed/29632933 https://www.ncbi.nlm.nih.gov/pubmed/26428171 http://www.journals.ufrpe.br/index.php/JEAP/article/view/1701 http://www.sciencedomain.org/abstract/13497 http://www.aimspress.com/article/10.3934/molsci.2016.3.386

In: Flocculation: Processes and Applications Editor: Eleonora Vollan

ISBN: 978-1-53614-339-3 © 2019 Nova Science Publishers, Inc.

Chapter 2

COAGULATION AND FLOCCULATION WITH PLANT EXTRACTS Jesús Manuel Epalza Contreras1 and Johan Jaramillo Peralta2 1

Environmental Engineering, Universidad de Santander, Bucaramanga, Colombia 2 Universidad de Valladolid, Valladolid, España

ABSTRACT The treatment of water in a conventional way includes the operations of coagulation and flocculation as a fundamental part in the removal of solids and other substances that are mixed with water, especially organic and inorganic solids with sizes less than 0.2 mm and densities similar to those of water. This forms a perfect mixture difficult to separate by natural sedimentation; in these cases the addition of coagulants is needed, which breaks the stability of the mixture and segregates the particles in the form of flocs, so that they can be separated by density difference. Reactive substances are used for this reason, such as aluminum sulfate, ferric chloride and aluminum polychloride; these substances are derived from industrial chemical reactions, which entail the use of natural resources and energy to obtain them. In addition to the environmental cost of the production processes, there is the problem of the final disposal of the thickened sludge, because due to its aluminum or iron content, the sludge can be harmful to the environment, especially for plants and animals. To reduce this impact, it is necessary to carry out these operations with substances that do not represent a danger to the environment; in this case, it has been proven that there are plant extracts that can generate the same reaction of segregating the solids and other substances of the water, by means of the reaction of the natural biopolymers of some plants, within which the Moringa oleifera, Melocactus sp, Opuntia sp, Cicer arietinum L, Aloe sp and others with destabilizing activity of particles can generate turbidity and color in water. These plant extracts can efficiently perform the coagulation and flocculation operations without the environmental risk of residual sludge with high concentrations of aluminum or iron.

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Jesús Manuel Epalza Contreras and Johan Jaramillo Peralta

Keywords: biopolymer, coagulation, flocculation, water treatment

INTRODUCTION The coagulation and flocculation processes are decisive in the treatment of water, both in purification and in wastewater, due to their efficiency of removing suspended particles from the water. To carry out the coagulation, it is necessary to add substances called coagulants, which come from chemical reactions that have been industrialized. The most important task is to generate drinking water, which can help the inhabitants of underdeveloped countries to improve their living conditions, as it is established in the main policies of the United Nations; but reducing the environmental impact of these activities and improving the coagulation and flocculation processes with coagulants of organic origin are easy to produce in agriculture and without metals that can affect the ecosystem from the ground. This document shows in a general way the advances in the processes of coagulation and flocculation with plants, and an emphasis is made on showing those made in recent years. The presented study is based on experiences with biopolymers derived from plants, especially from Melocactus sp, Opuntia sp, Stenocereus griseus, Cereus forbesii, Aloe arborescens, Aloe vera and Cicer arietinum. Melocactus sp, Stenocereus griseus, and Cereus forbesii have not been studied very much by other authors. Conventional water treatment processes include coagulation and flocculation, especially that which is chemically assisted, for both drinking water and wastewater; the removal capacity of these operations are effective and possess a speed that could have been used, especially with waters that have high concentrations of organic matter, and for this purpose reagents have been used such as aluminum sulfate, which is usually obtained from the reaction of aluminum hydroxide with sulfuric acid. Another reagent used is ferric chloride, which is obtained via the reaction of chlorine gas on heated iron, and an additional reagent that has been used in recent years is the aluminum polychloride that is obtained through a reaction of aluminum with hydrochloric acid in an aqueous solution. The reactions associated with the coagulants are determined by some parameters such as the pH, the temperature of the water, and the concentrations of the solids that are going to be complexed to form flocs that can be separated by density difference inside the mixture. When the flocs are separated from the mixture, sludge is generated that must be thickened and then disposed of within the parameters of a waste management plan. These residues will have a high concentration of aluminum and iron, respectively, according to the type of coagulant used, whether it be aluminum sulfate, aluminum polychloride or ferric chloride. The final disposal of this sludge usually comes with some difficulties,

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because due to their load of aluminum or iron they are considered toxic for soil in high concentrations. The disposal problems of this sludge, which generally has a high concentration of organic matter, generates environmental impacts when they are discharged into soils or bodies of water, changing the natural microbiota and affecting the species that have contact with these high concentrations of aluminum and iron. Because of this, different products of vegetable origin have been studied, which have properties similar to those of aluminum or iron compounds and generate coagulation and flocculation with organic compounds. Some examples of these cases include Melocactus sp, Opuntia dilleni, Stenocereus griseus, Cereus forbesii, Aloe arborescens, Aloe vera and the Kabuli Chickpea (Cicer arietinum L); these plants have shown activity for the flocculation of substances with small particle sizes (below 0.2 mm), which generally cannot be separated by natural sedimentation. The sludge derived from the coagulation and flocculation processes with plant extracts has a completely organic composition, which means that they can be digested by microorganisms and transformed into carbon, nitrogen and phosphorus substances that can be incorporated into the corresponding biogeochemical cycles, along with the absence of toxic metals for the soil, or with safe concentrations for this vital resource; this technological alternative transforms water treatment into a less aggressive process with the environment, taking into account that most of the waste generated in drinking water and domestic waste treatment is sludge. The extraction systems of plant biopolymers have different methodologies, which are easy to apply, proven and are part of already standardized unit operations. Taking into account that different parts are harvested from each plant, we must understand that for most of the plants their use concerns the majority of the biomass, whereas when we speak of Cicer arietinum, we are using only their seeds. This diminishes its use, taking into account the weight ratio of the plant and the mass used for the preparation of the coagulant. The operations developed to determine the efficiency of each plant extract in the coagulation and flocculation operations are defined within the established jar tests, and some of them have Z potential measurements (a measure of the magnitude of the repulsion or attraction between the particles).

CONVENTIONAL COAGULANTS Coagulants are substances with the capacity to break the stability of aqueous mixtures, causing suspended particles to be grouped in flocs, to be later segregated by gravity or by air injection separators.

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Coagulation is a process that allows us to separate a quantity of microorganisms in water due to the agglomeration in the flocculation process, which attracts bacteria and protozoa, agglomerates them and precipitates them in the process of sedimentation. The substances commonly used to perform coagulation are aluminum sulfate, ferric chloride and aluminum polychloride, which are the results of different reactions. 





Aluminum sulfate [Al2 (SO4) 3.x18 H2O]: This substance is an inorganic salt resulting from the controlled mixing of sulfuric acid and aluminum or bauxite, according to the purity and concentration desired for the final product. Ferric chloride [FeCl3. x6 H2O]: It is an inorganic salt, which is a product of the reaction between metallic iron and dilute commercial hydrochloric acid; this reaction is generally carried out with the industrial leftovers of hydrochloric acid, resulting in a high concentration ferric chloride. Aluminum Chloride [Al2 (OH) 3Cl or Al2 (OH) 3Cl3]: This salt is the result of the reaction of aluminum, bauxite or other minerals with high concentrations of aluminum and hydrochloric acid; from which different types of aluminum polychloride are produced, such as those that are named as PAC or PAFC, depending on their specification. Their alumina content may be between 13% and 17%.

The use of these salts has an environmental impact, especially regarding the generation of large quantities of sewage sludge with high concentrations of metals, usually either aluminum or iron. The final disposal of this sewage sludge is complicated, as their high aluminum content makes them toxic to the soil and plants that will grow in this site (Casierra Posada Fanor, 2007). Less commonly, other coagulating substances may be used, such as:    

Ferric sulfate [Fe2 (SO4) 3.x H2O]. Ferrous sulfate [FeSO4.x 7 H2O]. Magnesium carbonate [MgCO3 x 3H2O]. Aluminate of sodium [NaAlO3].

PLANTS WITH COAGULATION CAPACITIES Production of coagulants with plants is a technique used in a traditional way (Moa Megersa, 2014), but the possibility has recently been raised of using several plant species

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to extract the coagulant biopolymer, preferably in a similar way to the one that performs with conventional coagulants. The plants studied for the raw material of this process are diverse; within them, we have Moringa oleifera, Opuntia spp, Jatropha curcas, Cicer arietinum, Melocactus spp, Stenocereus griseus, Cereus forbesii, Aloe arborescens, Aloe vera, Cicer arietinum and Coccinia indica; these plants have presented good performance to coagulate and flocculate raw water, leading to better sanitary conditions. In the case of this text, we explored the species Melocactus sp, Opuntia sp, Stenocereus griseus, Brain forbesii, Aloe arborescens, Aloe vera and Cicer arietinum L, which were tested in their efficiency for coagulation and flocculation with raw water.

SELECTION OF PLANTS WITH THE POTENTIAL TO PRODUCE BIOPOLYMERS FOR COAGULATION AND WATER FLOCCULATION Plants with the capacity to generate biopolymers with coagulants and flocculants have been studied over the last few decades, especially Moringa olerifera, Opuntia spp, Cicer arietinum, and others that have demonstrated coagulant capacity as part of the traditional empirical knowledge of indigenous communities.

Source: http://cactiguide.com/cactus/?genus=Stenocereus&species=griseus. Figure 1. Stenocereus griseus.

The selected plants took coincided with those referenced and others present in semiarid regions in Colombia, such as La Guajira in northern Colombia and the banks of the Chicamocha River in the northeastern region; the species not studied are Stenocereus griseus (Figure 1), Cereus forbesii (Figure 2), Aloe arborescens, and Aloe vera; and the one already studied was Cicer arietinum (Moa Megersa, 2014). In the case of Opintia sp, they are present in the Colombian regions already named and sufficiently studied, in the same way Aloe vera and Aloe arborecens were selected

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(Figure 3); the Kabuli Chickpea (Cicer arietinum) is reviewed with studies already elaborated on by other authors (Hildebrando Ramírez Arcila, 2015). It should be noted that some species of Opuntia spp are used as part of the animal and human diet in communities of northeastern Colombia in semi-desert areas (Fernández, 2002).

Source: http://www.kakteensammlungholzheu.de/en/cereus_forbesii.html. Figure 2. Cereus forbesii.

Figure 3. Aloe arborescens.

To have a better selection, we reviewed the massive presence of these plants and they were not part of the list of plants in danger of extinction.

BIOPOLYMER EXTRACTION METHODOLOGIES Extraction of the Plants Melocactus sp, Opuntia dilleni, Stenocereus griseus, Cereus forbesii, Aloe arborescens and Aloe vera The extractions of each plant have particularities, taking into account the usable parts in the search of their coagulating capacity; the extractions are segregated into two types: The plants that are used in all their foliage are Melocactus sp (Figure 6), Opuntia dilleni

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(Figure 4), Stenocereus griseus, and Cereus forbesii, which belong to the family Cactaceae while the other part corresponds to Aloe arborescens, and Aloe vera, which belongs to the Xanthorrhoeaceae family, with superior Aloe classification. For the cactus and aloe species, an extraction methodology was used with different operations that are: 



The selection of parts of the plant for cutting: The operation of cutting parts of the plant is done by taking into account the mature parts, with the presence of thorns in the case of cacti and a hard external surface, similar to the criteria used for the animal or human consumption of Opuntia spp species. In the case of the Aloe species, the maturity of the leaves is considered, with the presence of perimeter spines, as this shows the possibility of isolating the crystals of the plant. Figure 4 shows a part of the penca or cladodes of a catus Opuntia sp with skin and thorns, but the part to be used is the vascular tissue of the plant, eliminating the skin and spines. For the sampling of the species of Aloe (Figure 5) garden plants were considered, which are cultivated in a homemade way, taking into account the age of the plant, as it must have enough leaves with enough crystals, and it must not present any evidence of contamination or parasites, especially the characteristics of the green color of the leaves, absence of external insects and total absence of organisms associated with diseases of the plant. Cut and transport to the laboratory. The cutting of the parts of the plant takes measurements (Figure 7) for transportation to the site of the coagulant; the transport must be carried out in refrigeration to avoid possible contamination with environmental fungi or other organisms that can significantly change the composition of the parts obtained.

Source: http://www.fichas.suculentas.es/Almacenfichas/903/903.html Figure 4. Opuntia sp.

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Source: http://www.fichas.suculentas.es/Almacenfichas/903/903.html. Figure 5. Aloe vera.





Weighing of the gross material. The weighing of the material is carried out on a 25 kg scale to determine the weight of the sample taken and then determine its performance according to its humidity. Cutting of thorns and removal of the bark. To perform the extraction of the coagulant, the cut parts are taken and the thorns are removed (Figure 8) along with the skin of the cacti, also called the epidermis, which is the external hard part of the pads or cladodes in the case of cacti and leaves in the case of Aloe species.

Source: http://www.tephroweb.ch/kuas/melo.htm. Figure 6. Melocactus sp.





Cutting of clean material. In order to follow the extraction process, the tissue of the plants is cut; this is done to improve the loss of moisture in the plant, increasing the contact surface with the atmosphere. Drying the pieces. The drying of the material is carried out outdoors (Figure 10), and it is important to note that the region in which these operations are carried out are from a warm tropical climate with low humidity. In these areas, the

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temperature ranges between 20°C and 35°C with relative humidity between 50% and 70% on average.

Source: authors. Figure 7. Opuntia sp and Cereus forbesi samples.

Source: authors. Figure 8. Removal of thorns.

Source: authors. Figure 9. Cutting of the plants.

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Jesús Manuel Epalza Contreras and Johan Jaramillo Peralta 







Weighing of dehydrated material. The material is kept outdoors, taking care that it is not hydrated by rain, and the drying time is between 48 and 96 hours depending on the temperature and relative humidity of the place where they are dried. Grinding of the material. The grinding of the dried material is done with a food processing device (Photo 1) and then it is passed through a mill that pulverizes the material. The final characteristics of the material are similar to the raw materials used in the coagulation and flocculation process, that is, a presentation similar to the presentation of type A and B aluminum sulfate and aluminum polychloride in their solid presentations. The liquid presentation is not sought because it is an organic material with nutritional characteristics for filamentous fungi and bacteria, which would require a procedure for its sterilization. For any application of excessive heat, a degradation of the biopolymers will be carried out, which is a condition that impairs its performance in coagulation. Material screening. The material after being macerated is taken to a 1 mm sieve (Figure 11), which separates the thick parts that cannot be diluted efficiently in an aqueous solution; this characteristic is based on the solubility of complex organic substances, such as the vascular tissue of these cacti and Aloe plants. Weighing of the material of interest. The material obtained from the plants Melocactus sp, Opuntia dilleni, Stenocereus griseus, Cereus forbesii, Aloe arborescens and Aloe vera is weighed to have a reference of its performance in relation to the weight, with respect to its use.

Source: authors. Figure 10. Desiccation of the specimens.

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Figure 11. Material screening.

EXTRACTION OF CICER ARIETINUM COAGULANT The seeds of the anionic coagulant Kabuli Garbanzo (Cicer arietinum L) were selected with the following procedures being performed. 

 

Washed. The seeds selected without evidence of the presence of fungi or yeasts were washed with large amounts of water to eliminate impurities related to bulk handling. In terms of their fractionation and packaging, they can take other materials such as small sand stones or other grain waste. Drying. After washing, they were dried for two days in the sun, taking into account that they cannot be wetted by rain or other water sources. Crushed. The material was crushed using a mixer (Oster) and the resulting powder was sieved with a No. 200 sieve to obtain a very fine powder for storage in plastic containers to avoid hydration and subsequent use in the preparation of the solutions of the coagulant.

TESTS OF THE BIOPOLYMERS OBTAINED After obtaining the biopolymers, we proceed to prepare solutions of these extracts, to perform jar tests and thus determine the coagulant and flocculant capacity of natural biopolymers. The tests are carried out with water of natural characteristics with different types of solids, which include natural tannins, solids smaller than 0.2 mm, organic matter and other substances typical of raw or residual waters.

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Preparation of the Solutions for Coagulation and Flocculation of Melocactus sp, Opuntia dilleni, Stenocereus griseus, Cereus forbesii, Aloe arborescens and Aloe vera After obtaining the biopolymers of the plants Melocactus sp, Opuntia dilleni, Stenocereus griseus, Cereus forbesii, Aloe arborescens and Aloe vera, the preparation of the solutions is carried out to realize the tests of the jars, which prove the action of the coagulants and flocculants. The flocculant preparation process was weighed for 1 gram of a biopolymer; then, 1000 ml of distilled water was added and manual agitation was carried out until it was completely diluted.

Preparation of Coagulation Solutions of Cicer arietinum L 1% of the solutions was prepared by adding 10 g of the anionic coagulant in 1000 ml with Milli-Q® water, obtaining a solution of 10,000 mg / l, after which stirring was carried out for one hour to homogenize the mixture. In this solution, the tests were carried out to know the adequate doses to treat the synthetic water prepared in the laboratory. To prepare the synthetic water, laboratory clay was used for the preparation of samples of turbid water for all the experiments. Twenty grams of clay were added to one liter of distilled water. The suspension was gently stirred for 1 hour on a magnetic stirrer in order to achieve a uniform dispersion of the clay particles. The suspension was allowed to stand for 24 hours to achieve complete hydration of the clay. This clay suspension served as a stock solution using distilled water to prepare water samples with a turbidity of 200 NTU.

Control Parameters in Rockrose Tests To test the coagulating and flocculating effect of the biopolymers of Melocactus sp, Opuntia dilleni, Stenocereus griseus, Cereus forbesii, Aloe arborescens, Aloe vera and the Kabuli Chickpea (Cicer arietinum L), jug tests were performed as provided in ASTM D2035: 08 The control parameters normally used in the efficiency of a coagulant are pH, turbidity and color, which are governed by standardized methodologies and which determine the ability to remove solids from water based on their behavior. pH and its spectrophotometric absorbance in the case of turbidity and color at different wavelengths were studied.

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In accordance with the regulations in force in Colombia, the tests were carried out taking into account the technical standards adopted by the country for each test. The removal obtained is processed in terms of percentages for the comparison of pH. It is observed that it complies with the provisions of the national standard for this parameter; and in the case of turbidity and color, the percentage of removal is taken into account, which is directly proportional to the decrease in absorbance in each test.

RESULTS OF JAR TESTS WITH NATURAL COAGULANT BIOPOLYMERS For the results of the tests of the biopolymers, natural coagulants are collected in 4 main tests: The first ones refer to the pH, the turbidity and the color, and the last one takes the coagulants with good performance and measures the Z potential. Turbidity and color in water is related to the presence of substances or microorganisms, which is directly related to its quality to be consumed or used in other ways; the results offer an overview of the potentialities of all the plants for the coagulation and flocculation processes, with different degrees of efficiency. To control the efficiency of coagulation and flocculation as a function of pH, the pH was taken after coagulation, taking into account that the initial pH of the water is 7.2. The pH results are shown in Graph 1, showing that the coagulant that most affected the final pH was the biopolymer of Melocactus sp, which brought the pH up to 6.2. The data show a standard deviation of 0.3 Graph 1 shows that the only one that did not affect the pH in the jar test was Stenocereus spp, while the others lowered the pH moderately to values of 7 or 6.8. The turbidity results (Graph 2) showed that the best biopolymers to remove these solids associated with turbidity were Melocactus spp and Cicer arietinum, which showed turbidity removals greater than 95% and 97% respectively. The data show a standard deviation of 3.1. The results of the other biopolymers showed a removal capacity greater than 88% and up to 92%, which shows the effectiveness of these biopolymers with water that has a neutral pH. All the biopolymers tested showed effective action in the removal of turbidity, in a range between 88% and 97%, with some differences and affectations to the pH of the sample at the final moment of the jar test. For the case of the color results (Graph 3), we can see a good activity of all the biopolymers, taking into account that the one that showed the best performance in the removal of the color was the biopolymer of Melocactus spp, with a performance greater than 96%, which was then appreciated for the two species of Aloe sp with a removal greater than 95%. Opuntia sp, Stenocereus sp and the Kabuli Chickpea (Cicer arietinum L) displayed performances greater than 94%, and the last one was evidenced

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by Cereus forbesi with a performance greater than 92%. The data show a standard deviation of 1.4.

Source: authors. Graph 1. Results of the pH test for studied coagulants.

Source: authors. Graph 2. Turbidity removal with each coagulant studied.

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Source: authors. Graph 3. Color removal with each coagulant studied.

Table 1. Potential Z of Melocactus sp and Kabuli Chickpea (Cicer arietinum L) pH

Zeta Potential (mv) Melocactus sp

3 4 5 6 7 8 9 10

-1,7 -3,9 -12,9 -19,6 -22,9 -22,9 -27,1 -29,4

Zeta potential (mV) Kabuli Chickpea 15,1 -2,5 -11,8 -19,8 -21,9 -21,9 -24,5 -27,1

Source: authors.

The results show a greater efficiency in the removal of color; the best performance of these tests lies in the Melocactus, which was the best in removing both turbidity and color, but also had the highest incidence of pH. The other biopolymer with a high performance is the Kabuli Chickpea (Cicer arietinum L), whichshowed a good turbidity and color removal capacity with very little pH affectation. The zeta potential of the biopolymers shows similar values in the range of pH 4 and pH 10, which may indicate a similar activity with solid particles of a small size, such as those that generate turbidity and color in the water.

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The zeta potential measurements were made for the biopolymers with better performance, which showed the following results. Table 1 shows the results of the Z potential of Melocactus sp and the Kabuli Chickpea (Cicer arietinum L), with a pH between 3 and 10. It is important to note that all plants used have the potential to treat water; the efficiency differences can be associated with the affinity for different particles and their extraction form.

CONCLUSION All the extracts showed turbidity and color removal with efficiencies higher than 88%, which indicates that the extraction methodologies conserve the coagulant and flocculant capacity of each plant. The biopolymers of Melocactus sp, Opuntia sp, Stenocereus griseus, Cereus forbesii, Aloe arborescens, Aloe vera and Cicer arietinum have an activity for coagulation and water flocculation. The plants with the best performance in the removal of turbidity and color were Melocactus sp and Cicer arietinum, with the best percentages of elimination for solids of small size in water. The potential zeta measurements for the extracts of Melocactus sp and Cicer arietinum have similar values in the range of pH 4 to 10, which shows a similar activity for the suspended particles of the water used in the tests. The biopolymers of the plants Melocactus sp, Opuntia sp, Stenocereus griseus, Cereus forbesii, Aloe arborescens, Aloe vera and Cicer arietinum can be a viable alternative for the treatment of drinking and residual water, in terms of the replacement of sulfate for aluminum, aluminum polychloride and ferric chloride; this would allow for decreasing the amounts of dissolved metals in the drinking water of humans and animals, especially with the aluminum residues associated with diseases such as autism and Alzheimer’s.

ACKNOWLEDGMENTS We are very grateful to the University of Santander in Colombia, which granted a large part of its resources to complete this book chapter. Additionally, we give thanks to the University of Valladolid, Spain, for allowing one of our authors to help create this chapter. We also would like to thank all the people of the universities involved who personally helped by committing to this work and research.

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CONFLICT OF INTEREST The authors declare that there is no conflict of interest regarding the publication of this document.

REFERENCES American Public Health Association. (1995). Standard Methods. Washington, D.C.: American Public Health Association. American Water Works Association. (2006). Microbiology for drinking water personnel: American Water Works 2006. New York: American Water Works Association. Asrafuzzaman M., F. A. (2011). Reduction of turbidity of water using locally available natural coagulants. ISRN Microbiology, 1(1), 1-6. ASTM. (2008). Standard Practice for Coagulation-Flocculation Jar Test Water. New York: ASTM. Betancourt, W. Q. (2004). Drinking water treatment processes for removal of Cryptosporidium and Giardia. Veterinary Parasitology, 219-234. Bruce Rittman, E. M. (2001). Biotecnología del Medio Ambiente, Principios y Aplicaciones [Biotechnology of the Environment, Principles and Applications]. Madrid: Mc Graw Hill/Interamericana. Casierra PosadaFanor, A. A. (2007). Estrés por aluminio en plantas: reacciones en el suelo, síntomas en vegetales y posibilidades de corrección. Una revisión. Revista colombiana de ciencias hortícolas [Stress for aluminum in plants: reactions in the soil, symptoms in plants and correction possibilities. A review. Colombian magazine of horticultural sciences], 1(2), 246-257. Daza Rina, B. A. (2016). Evaluation of the efficiency of bio-polymers derived from desertic plants as flocculation agents. Chemical Engineering Transactions, 234-239. De Souza Aloisyo, B. E. (1999). Nocoes gerais de tratamento e disposicao final de lodos de estacoes de tratamento de agua. Rio de Janeiro [General walnuts for treatment and final disposition of sewage sludge for water treatment. Rio de Janeiro]: RECOPE (Rede Cooperativa de Pesquisas). Decreto 3930 Republica de Colombia. (2010). Decreto 3930 de 2010. [Decree 3930 of 2010.] Bogotá: Gaceta oficial. Doka, G., Life, D., & Assessments, C. (2007). Wastewater Treatment. Metal Finishing. New York: Prentice-Hall. Fernández, J. X. (2002). Novedades taxonómicas y sinopsis del género melocactus link y Otto (cactaceae) en Colombia. Revista de la academia colombiana de ciencias exactas, físicas y naturales, [Taxonomic news and synopsis of the melocactus link

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and Otto (cactaceae) genus in Colombia. Magazine of the Colombian academy of exact, physical and natural sciences,] 353-365. G. Jayalakshmi, V. S. (2017). A Review on Native Plant Based Coagulants for Water Purification. International Journal of Applied Environmental Sciences, 12(3), 469487. Guzmán Luis, V. Á. (2013). Reduction of water turbidity using natural coagulants: a review. Revista U.D.C.A Actualidad & Divulgación Científica, 253-262. Hildebrando Ramírez Arcila, J. J. (2015). Agentes naturales como alternativa para el tratamiento del agua. Revista de Facultad de Ciencias Básicas [Natural agents as an alternative for water treatment. Journal of the Faculty of Basic Sciences], 11(2), 136153. Ibarra Nailea, J. J. (2018). Comparison of the Efficiency of Biopolymer Derived from Melocactus Sp and Aluminum Polichloride (PAC) in the Process of Crude Water Flocculation. Chemical Engineering Transactions, 157 - 162. ICONTEC. (2010). NTC 3903 Procedimiento para el ensayo de coagulación-floculación en un recipiente con agua o método de jarras [Procedure for the coagulationflocculation test in a container with water or jars method]. Bogotá: ICONTEC. M. Pritchard a, T. M. (2009). Potential of using plant extracts for purification of shallow well water in Malawi. Physics and Chemistry of the Earth, 799 - 805. Martínez Damarys, C. M. (30 de Abril de 2003). Performance of cactus lefaria to use like coagulating in the water clarification. Revista Técnica de la Facultad de Ingeniería Universidad del Zulia, 26(1), 76-82. Matthew Mold, D. U. (2018). Aluminium in Brain tissue in autism. Journal of Trace Elements in Medicine and Biology, 46(1), 76-82. Md. Asrafuzzaman, A. N. (2011). Reduction of Turbidity of Water Using Locally Available Natural Coagulants. International Scholarly Research Network, 1-6. Medina-Torresa L., B.-D. L.-S. (2000). Rheological properties of the mucilage gum (Opuntia ficus indica). Food Hydrocolloids, 417-424. Metcalf & Eddy Inc. (1979). Wastewater Engineering Treatment Disposal Reuse, 2nd ed. New York: McGraw-Hill International Editions. Moa Megersa, A. B. (2014). The use of indigenous plant species for drinking water treatment in developing countries: A review. Journal of Biodiversity and Environmental Sciences, 5(3), 269-281. Nishi Leticia, M. G. (2011). Cyanobacteria Removal by Coagulation/ Floculation with Seeds of the Natural Coagulant Moringa oleifera Lam. Chemical Engineering Transactions, 1129-1134. Ospina O., R. H. (2011). “Tratamiento casero alternativo de agua para consumo humano por medio de fitoquímicos [Alternative home treatment of water for human consumption through phytochemicals].” Escuela Colombiana de Ingeniería, 84(1), 717.

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Ramirez Arcilla, H. J. (Julio de 2015). Agentes naturales como alternativa para el tratamiento del agua [Natural agents as an alternative for water treatment]. Universidad Militar Nueva Granada, 11(2), 136-153. S.M. Miller, E. J. (2008). Toward Understanding the Efficacy and Mechanism of Opuntia spp. as a Natural Coagulant for Potential Application in Water Treatment. Environmental Science & Technology, 4274 - 4279. Torres Bustillos Luis G., C.-U. S. (2013). Production and characterization of Opuntia ficus-indica mucilage and its use as coagulant-flocculant aid for industrial wastewaters. International Journal of Biotechnology Research, 38-45. United Nations. (2016). Informe 2015 del Programa Conjunto de Monitoreo para los Objetivos del Milenio [of the Joint Monitoring Program for the Millennium Development Goals]. New York: Organización Mundial de la Salud. V. Petale, J. P. (2012). Mucilage extract of Coccinia indica fruit as coagulant-flocculent for turbid water treatment. Asian Journal of Plant Science and Research, 442-445. Vijayaraghavan G., S. T. (2011). Application of plant based coagulants for waste water treatment. International Journal of Advanced Engineering Research and Studies, 8892. Villabona Angel, P. I. (2013). Caracterización de la Opuntia ficus-indica para uso como coagulante natural. Revista colombiana de biotecnología [Characterization of Opuntia ficus-indica for use as a natural coagulant. Colombian biotechnology magazine], XV(1), 137-144. Wang L.K., H. Y. (2005). Physicochemical Treatment Processes. Vol 3 Handbook of Environmental Engineering. New Yersey: Humana Press. Water Environment Federation. (2009). Design of Municipal Wastewater Treatment Plants. New York: McGraw-Hill Professional. Wilkinson, C. y. (1998). Advanced Inorganic Chemical. New York: Interscience Publishers. Yin, C.-Y. (2010). Emerging usage of plant-based coagulants for water and wastewater treatment. Process Biochemistry, 1437-1444.

BIOGRAPHICAL SKETCH Jesús Manuel Epalza Contreras Affiliation: He has developed as a professor at different universities in the region, such as the Industrial University of Santander in the Chair of Biotechnology and Industrial Microbiology and the Antonio Nariño University; He is currently Associate Professor of the University of Santander UDES - Bucaramanga Colombia, and is in

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charge of the subjects of Water Purification, Environmental Remediation and Ecotechnology, in the Environmental Engineering career. Education: Microbiologist, from the University of Pamplona, Colombia, MSc Advanced Energy Systems of the University of Santander UDES, and candidate for MSc in Science Management, Technology and Scientific Policy with the University of Seville, Spain Research and Professional Experience: Recognized by COLCIENCIAS as Associated Researcher, in the 2017 national call. Inventor of “System and Method of Wastewater Treatment in Nucleos Decentralizados” patented in Colombia and recognized with the resolution number 52486 of December 2012, of the Superintendence of Industry and Commerce of Colombia. Inventor of “System that includes drinking water treatment plant, autonomous, compact, automated and assisted with photovoltaic solar energy and said plant” filed with the number 15-196159, of December 21, 2015. In his professional beginnings, he worked as an analyst of potable and residual water in different accredited laboratories and has worked as a soil analysis consultant for the determination of biocorrosion in the petroleum industry. He has developed work with water treatment, since 2002, being a participant in different designs of drinking water treatment plants and wastewater treatment plants, especially in physical, chemical and biological treatment operations, designing anaerobic and aerobic bioreactors, with the respective culture of microorganisms for the start of the bioreactors; to making improvements of coagulation, flocculation and sedimentation systems, of potable and residual water treatment plants in populations of Colombia and in food industries. It has also developed wastewater treatment works with anaerobic digestion, with biogas production, and its use; He has also worked as a consultant and researcher of residual biosolids in wastewater treatment of the food industry, testing different technologies for their energy use and also in the improvement of biosolids to be used as raw material in agriculture and livestock. He has developed different technological development projects at the University of Santander, especially in the treatment of drinking and residual water, combining different disciplines; At the moment, it is differencing projects of masters, the ones that stands out the development of guidelines of public policy for the recovery of the Simití swamp in the department of Bolivar, and the provision of the service of potable water in the municipality of Los Santos in the Santander department, with a Master’s degree in Public Management and Government from the University of Santander.

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Professional Appointments: He is part of the Environmental Research Group GAIA-UDES, as a researcher in the drinking water and basic sanitation line since 2010. He is part of the group of research professors of Environmental Engineering at the University of Santander UDES since 2008 Honors: Graduated Distinguished from the Master in Advanced Energy Systems in 2016 by the University of Santander. Recognized by the University of Santander in 2018, due to the results of the call for researchers in Colombia of Colciencias in 2017. Publications from the Last 3 Years: Evaluation of the efficiency of bio-polimers derived from Desertic plants as flocculation agents. Chemical Engineering Transactions, 2016. Obtaining a Cementitious Geopolymer from Gold Mining Tailings with Possible Use in Engineering Applications. American Journal of Engineering Research (AJER), 2018. Comparison of the Efficiency of Biopolymer Derived from Melocactus Sp and Aluminum polichloride (PAC) in the Process of Crude Water Flocculation. Chemical engineering transactions, 2018.

In: Flocculation: Processes and Applications Editor: Eleonora Vollan

ISBN: 978-1-53614-339-3 © 2019 Nova Science Publishers, Inc.

Chapter 3

THE PROCESS OF WATER TREATMENT WITH ALUMINUM SULPHATE ASSOCIATED WITH THE APPLICATION OF THE CACTUS OPUNTIA COCHENILLIFERA Higgor Henrique Dias Goes1, Rita de Cássia Pereira de Souza1 and Joseane Débora Peruço Theodoro2 1

Environmental Engineering Student - UTFPR- Londrina, Londrina, Brazil 2 Department of Environmental Academic, Federal Technological University of Paraná, Londrina, Paraná, Brazil

ABSTRACT The present study aimed to use the organic polymer from Opuntia cochenillifera cactus associated with the addtion of aluminum sulfate to treat the water of a lentic body (Igapó II Lake - Located in Londrina in the state of Paraná and Brazil) applying coagulation, flocculation, sedimentation and filtration processes. The tests were performed with static a Jar-test reactor, aiming to evaluate the removal of parameters of turbidity and of apparent color, besides monitoring the pH variation. Regarding the physico-chemical characteristics, there was little influence of the Opuntia cochenillifera cactus in the pH parameter tending to neutrality. Therefore, the study showed that the use of an organic coagulant together with aluminum sulphate is effective for the removal of parameters of apparent color and of turbidity (95 and 94%, respectively).

Keywords: organic coagulant, aluminum sulfate, water treatment

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1. INTRODUCTION Water intended for human consumption must be available in a potable way, in which it does not present health risks and denote the control and monitoring of its quality, according to the drinking standard established by the Ministry of Health Ordinance No. 2,914/2011 (Brazil 2011). In order to reach the standards established through the water regulatory agencies and to distribute it to a community, it is necessary to carry out its treatment (Howe et al. 2016). In a conventional manner, the water treatment consists of the following steps, which are shown in Figure 1. The clarification of the raw water occurs in the removal of solids present and associated with the parameter of turbidity, being removed by operations and processes as: coagulation, flocculation, sedimentation and filtration. At the beginning of the coagulation process, the coagulant is added under intense stirring in the water to be treated, ensuring uniform distribution of the product. This phase has the objective of destabilizing the impurities present in the medium, with the addition of a coagulant, capable of minimizing or eliminating the repulsive forces present between them. The most commonly used coagulants are metal salts based on aluminum or iron (COMUSA 2017; SANEP 2018). In order to replace or reduce the use of conventional coagulants, the natural agents with equal or superior efficiency when compared to metallic ones, generating a sludge with less toxicity, have a lower cost and greater abundance of plants as a source of extraction available (Yin 2010; Theodoro et al. 2013).

Sorce: SANEP 2018. Figure 1. Representative scheme of water treatment.

Derived from a renewable resource and its arrangement promotes simple organic degradation, mucilage of cacti for extraction of polymers is used to eliminate water turbidity (Pichler; Alcantar, 2012).

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The forage cactus Opuntia cochenillifera, originating in Mexico and spread in the northeast of Brazil, has several uses, ranging from animal and human feeding, to landscaping projects and dye extraction. Among its characteristics, it has the xeromorphic form with a cylindrical stem and its branches known as palms. Thus, the objective of this chapter was to analyze the water quality of Lake Igapó II, found in the city of Londrina-PR, according to the parameters of apparent color, of turbidity and of pH, and then to perform the treatment of these waters through the coagulation/flocculation/ sedimentation/filtration process using the organic polymer from the Opuntia cochenillifera cactus associated with the addition of Aluminum Sulphate, verifying the possibility use of these lentic waters for urban supply.

2. METHODOLOGY The water samples were taken from a lentic system from Lake Igapó II, located in the city of Londrina, state of Paraná, Brazil.

Fonte: Goes et al., 2017. Figure 2. Spatial location of the collection point in Lake Igapó II.

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Situated at 550 meters above sea level, one has the coordinates of the collection point are 23°19'42'' S and 51°10'11'' W. Figure 2 spatially represents the location of the highlighted point for sample collection. To perform the tests, 72 liters of Lake Igapó II water were collected and stored in previously sanitized plastic gallons. The methodology for the extraction of the polymer present in the cactus occurred in two stages: The first consisted in the removal of the spines and the bark, and thus cuts were made to reduce the size of the cactus to be used in the liquidification of the contents inside the palms ("pulp"). In the second, two liters of the extraction solution (required to extract the polymer from the viscous solution formed after liquefying) were prepared by the attachment of one liter of distilled water with 4g of 1% sodium chloride solutions and one liter of distilled water with 10g sodium hydroxide 0.10mol L-1 (Zara et al. 2012). The ratio was one ml of cactus prepared to 2.5 mL of the extraction solution, the mixture of which was homogenized on magnetic stirrer Nova Ethics, model 114, for 40 minutes. The resulting viscous complex was packed in glass sanitized vials and stored under refrigeration at 5°C until assays were performed on the JarTest equipment (Goes et al. 2017). Some of these steps are shown in Figure 3. The amount of water collected was divided into three gallons with the same volume, to carry out the tests at different pH values, being basic, neutral and acidic sample in order to work with the parameters of color and of turbidity after the operations and processes in the three tracks. To adjust the pH values with the purpose of making it acidic, the hydrochloric acid solution (HCl) with1 M concentration was used. For the basic pH sample, the sodium hydroxide solution (NaOH) with 1 M concentration. The neutral pH value of the crude sample was also measured. For the experiment, the dosages of coagulant cacti (Opuntia cochenillifera) were 1mg -1 L , 4mg L-1 and 7mg L-1 with the addition of Aluminum Sulphate in 1mg L-1, 4mg L-1 and 7mg L-1, respectively.

Source: Goes et al. 2017. Figura 3. a) Opuntia cochenillifera Palm; b) Removing the shell; c) Cut for further liquefaction; d) Storage of viscous complex.

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Table 1. Gradient of rotation of the mixing rods and time of action Quick Mix Gradient (s-1)

Slow Mix 1 Gradient (s-1)

Slow Mix 2 Gradient (s-1)

Slow Mix 3 Gradient (s-1)

Slow Mix 4 Gradient (s-1)

450 Time (mim) 00:10

90 Time (mim) 02:00

52 Time (mim) 02:35

40 Time (mim) 02:40

30 Time (mim) 05:40

Source: Higashi (2016).

In the water treatment trials by the coagulation/flocculation/ sedimentation processes, the six-proof jar-test equipment was used with a rotating regulator of the mixing rods. Table 1 shows the parameters used in coagulation/flocculation processes. For coagulation/flocculation/sedimentation assays, a sedimentation time of 10 minutes was adopted. At the end of the set time for sedimentation, all the samples were collected and the parameters of apparent color, of turbidity and of pH were measured. For the filtration test an iron structure adapted to fix the sand filters below the jar-test was used so that the water leaves the apparatus directly to the filters. The filter beds are made of Polyethylene Terephthalate (PET) of approximately 10 cm of internal diameter, forming a fixed bed model with downward flow, with six columns in parallel (Goes et al. 2017), as observed in Figure 4.

Source: Goes et al. 2017. Figure 4. Filtration process.

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The tubes are 25cm long with 15cm filled by sand, 3cm filled with crushed stone and 2cm filled with cotton. The granulometric of the sand used in the 6 filters were the same, in the range of 0.60 to 0.85mm. The slope used at the exit of the jar-test was 70º for two minutes, followed by another two minutes with the angulation of 60º and another two minutes with 50º (Di Bernardo et al. 2003). The water to be treated entered the top of the column and its supernatant was removed from the side. The grains of the filter bed were retained by a coffee filter together with the cotton and stone, present at the lower end of the column. For all variations of cactus concentrations and pH, the parameters of apparent color and of turbidity were determined according to the Standard Methods of Examination of Water and Wastewater (APHA 2012). In this work we used a statistical planning with two factors (independent variables), the concentration of coagulant cacti and three parameters responses (apparent color, turbidity and pH), the tests were performed in duplicates.

3. RESULTS The collected raw water had a neutral pH of 7.65. For acid pH and base, we have the values obtained of 4.87 and 9.08 respectively. After the treatment, the calculations were performed to remove the parameters apparent color and turbidity, thus obtaining data after the coagulation/flocculation/ sedimentation operation/filtration process and the overall process/global operation (coagulation/flocculation/sedimentation/ filtration), besides the monitoring of pH. The values found are shown in Table 2. Figures 5, 6 and 7 show the removal of the parameter apparent color and turbidity for the coagulation/flocculation/sedimentation processes, only filtration and for the complete process (coagulation/flocculation/ sedimentation/filtration), respectively. Analyzing Figure 5, it can be seen that the best results presented are associated with the neutral pH values (tests 2, 5, 8, 11, 14 and 17), removing around 30% of the color and turbidity. It is possible to verify that in tests 1, 3, 4, 6, 9, 10, 12, 15 and 18 the dissolution of the organic coagulant cactus occurred in the solution, causing the increase of the dissolved solids and, thus, and, thus, justify the negative values of percentage of removal of the color parameter.

Table 2. Numerical organization of the tests for different levels of coagulant concentration and pH with real values and results of parameters color, turbidity and pH Assay

pH

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

Cactus (mgL-1) 1 1 1 4 4 4 7 7 7 1 1 1 4

4,87 7,85 9,08 4,87 7,85 9,08 4,87 7,85 9,08 4,87 7,85 9,08 4,87

Color (C/F/S) % -7,0 32,6 -19,4 -11,0 29,6 -21,4 14,5 38,3 -14,2 -7,2 32,9 -8,5 -0,6

Color (Fi) % 77,6 66,1 68,4 93,7 76,5 84,1 91,2 82,2 79,5 91,4 89,6 78,1 95,0

Color (C/F/S/Fi) % 76,1 77,2 62,3 93,0 83,4 80,7 92,5 89,0 76,6 90,8 93,0 76,3 95,0

T (C/F/S) % 17,2 32,5 2,1 9,3 31,3 6,2 24,0 37,4 5,4 5,7 30,8 4,6 15,4

T (Fi) % 74,8 62,8 65,5 93,1 72,4 81,0 91,1 79,1 78,1 89,8 85,1 78,9 92,6

T (C/F/S/Fi) % 79,5 75,1 66,6 94,0 81,2 82,4 93,4 87,0 79,6 90,6 89,8 80,1 94,0

pH (C/F/S) 6,5 7,5 6,92 7,27 7,12 7,59 7,86 7,68 7,24 6,35 7,46 7,5 6,97

pH (C/F/S/Fi) 7,51 7,95 7,88 7,54 7,97 7,71 7,43 7,97 7,78 7,58 7,95 7,93 7,6

14 15 16 17 18

4 4 7 7 7

7,85 9,08 4,87 7,85 9,08

33,0 -22,1 22,3 75,0 -20,2

87,2 89,1 89,6 63,4 80,7

91,4 86,6 91,9 90,9 76,9

33,5 -0,8 31,2 70,6 3,8

83,4 86,2 89,3 62,5 77,7

89,1 86,3 92,9 89,1 78,8

7,74 7,59 6,1 7,42 7,65

7,8 7,82 7,53 7,84 7,85

OBS: C / F / S = coagulation / flocculation / sedimentation; Fi = filtration; C / F / S / Fi = coagulation / flocculation / sedimentation / filtration. Source: Own authorship.

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Figure 5. Removal of apparent color and turbidity after Coagulation/Flocculation/ Sedimentation process.

Figure 6. Removal of apparent color and turbidity in the filtration process.

The filtration process was more efficient for the basic and acid pH values, allowing a removal of more than 80% in the two analyzed parameters. With the completion of the complete process, it was noticed that in general the tests obtained values of color removal and turbidity above 80%. Thus, by analyzing the presented results, it can be concluded that both the coagulation/flocculation/sedimentation processes (Figure 5) and the filtration process (Figure 6) are important for the removal of color and of turbidity present in the raw water. Comparing the values obtained with those required by Ordinance 2,914/2011 of the Ministry of Health (Brazil 2011), the tests did not meet the VMP (maximum allowed value) of apparent color and of turbidity. The results of pH

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variation after coagulation/flocculation/ sedimentation processes and after the coagulation/flocculation/ sedimentation/ filtration process using cactus (Opuntia cochenillifera) are presented in Figures 8 and 9.

Figure 7. Removal of apparent color and of turbidity after Coagulation/Flocculation/ Sedimentation/Filtration process.

Figure 8 demonstrates that after coagulation/flocculation/sedimentation the pH of the acid and basic assays tend to reach neutrality during the process and the assays that were in this range remain.

Figure 8. pH after the coagulation/flocculation/sedimentation process.

After also passing through the filtration (Figure 9), the water tends to obtain values closer to the neutrality. This occurs due to the ability of the sand particles to adsorb the components present in the water, neutralizing the pH. Comparing the values obtained with those required by

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Portaria 2,914 / 2011 (Brazil 2011) of the Ministry of Health, all the tests met the pH VMP (6 to 9).

Figure 9. pH after the coagulation/flocculation/sedimentation/filtration process.

CONCLUSION According to the tests carried out in the study, the coagulant solution obtained from the Opuntia cochenillifera cactus associated with the addition of aluminum sulphate was efficient in the treatment of water from the Lake Igapó lentic system, tending to maintain its pH close to neutrality. The results for color removal and turbidity were promising, but did not reach compliance with the values required by the Ministry of Health Ordinance 2,914/2011 (Brazil 2011), not meeting the VMP (maximum value allowed) for both parameters.

REFERENCES APHA – American Public Health Association. Standard Methods for the Examination of Water and Wastewater. 22 ed. Washington, 2012. Brazil, Ministry of Health. 2,914, dated December 12, 2011. Available at: . Accessed on: January, 2018. COMUSA, Water and Sewage Service of Novo Hamburgo. Water treatment, 2017. Available at: http://www.comusa.rs.gov.br/index.php/saneamento/tratamentoagua. Accessed on: Feb. 2017.

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Di Bernardo, L.; Mendes, C. G. N.; Brandão, C. C. S.; Sens, M. L.; Pádua, V. L. Water Treatment for Direct Filtration. Di Bernardo, Luiz (coordinator) - Rio de Janeiro: ABES, RiMa, 2003. Project PROSAB 498 p. Goes, H. H. D.; Souza, R. C. P.; Melo, J. M.; Theodoro, J. D. P.; Study of the application of Opuntia cochenillifera cactus in water treatment. Encyclopedia Biosphere, Knowing Scientific Center - Goiânia, v.14 n.25; P. 554-563. 2017. Higashi, V. Y.; Theodoro, J. D. P.; Pereira, E. R.; Theodoro, P. S.; Use Of Chemical Coagulants (Ferric Chloride) And Organic (Moringa Oleifera) In Treatment Of Waters Derived From The Lentic System. Technical Scientific Congress of Engineering and Agronomy - CONTECC'2016, August 29 to September 2, 2016 Foz do Iguaçu, Brazil. Available at: . Accessed in Feb. 2018. Howe, K. J.; Hand, D. W.; Crittenden, J. C.; Trussell, R. R.; Tchobanoglous, G.; Principles of water treatment, São Paulo, SP: Cengrage, 2016. 624 p. Pichler, T., Young, K.; Alcantar, N. Eliminating turbidity in drinking water using the mucilage of a common cactus. Water Science and Technology: Water Supply, v. 12, n.2, 179-186, 2012. SANEP, Autonomous Service of saniamento of Pelotas. Treatment, 2018. Available at: . Accessed on: Feb. 2018. Theodoro, J. D. P.; Lenz, G. F.; Zara, R. F.; Bergamasco, R.. Coagulants and Natural Polymers: Perspectives for the Treatment of Water. Plastic and Polymer Technology (PAPT), v. 2, Issue 3, September 2013. Yin, C. Emerging usage of plant0based coagulants for water na wastewater treatment. Process Biochemistry, v. 45, 2010. Zara, R. F.; Thomazini, M. H.; Lenz, G. F. Study of the efficiency of natural polymer extracted from the mandacaru cactus (Cereus jamacaru) as an aid in the coagulation and flocculation processes in water treatment. Journal of Environmental Studies (Online), v.14, n.2 esp, p.75-83, 2012.

In: Flocculation: Processes and Applications Editor: Eleonora Vollan

ISBN: 978-1-53614-339-3 © 2019 Nova Science Publishers, Inc.

Chapter 4

FLOCCULATION: MECHANISMS AND APPLICATIONS FOR WASTEWATER TREATMENT Elvis Carissimi1,*, PhD, Cristiane Oliveira Rodrigues2, PhD, Dounia Elkhatib3 and Vinka Oyanedel-Craver3, PhD 1

Department of Sanitary and Environment Engineering, Federal University of Santa Maria, Santa Maria-Brazil 2 Department of Nutrition, Federal University of Health Sciences of Porto Alegre, Porto Alegre, Brazil 3 Department of Civil and Environment Engineering, University of Rhode Island, Kingston, Rhode Island, US

ABSTRACT Flocculation is considered the main physico-chemical treatment prior any solidliquid separation unit in water and wastewater treatment plants. Suspended particles, algae, microorganisms are aggregated in order to increase their density for a subsequent step of sedimention or flotation (in case of injection of air bubbles) and/or filtration. Design and operation of flocculators are crucial for the process efficiency, and are largely dependent on the following features: floc characteristics, flocculation kinetics, and engineering aspects of flocculation. Finally, examples of engineering applications using flocculation are described.

*

Corresponding Author Email: [email protected].

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Keywords: water treatment, wastewater treatment, flocculation, aggregation

1. INTRODUCTION A comparison of source water quality and the desired finished water quality is essential for any treatment process selection. However, flocculation is one of the most common unit operations and is frequently employed for water and wastewater treatment. Water treatment includes essentially three separated and sequential steps: coagulation formation, particle destabilization, and interparticle interactions. It is an important step for the removal of organic (viruses, bacteria, algae, protozoan cysts and oocysts, microplastics, humic acids, particulate and dissolved organic matter that may be present as natural organic matter - NOM) and inorganic particles (clay, silt, mineral oxides, and erosion particles). The removal of particles is very important because they cause turbidity (reduce water transparency and fotosintetic activities), may increase color to water; promote infectious agents (microorganisms), and have toxic compounds adsorbed to their external surfaces. NOM removal is quite important due the possibility of desinfection byproducts formation when chlorine is used for disinfection. Ferric iron and aluminum salts are the most common salts used to promote the coagulation and have been largely used in water and wastewater treatment plants. Polymers may be or not associated in order to increase floc density and floc strength and improve solid-liquid separation rates. Besides the addition of chemicals flocs formation are extremely dependent on the hydrodynamic conditions. The understanding of all the phenomena and mechanisms involved during flocculation is crucial to design efficient flocculation units that may be applied to water or wastewater treatment. Thus, the main goal of this chapter is to describe these mechanisms and applications of new flocculation units for water and wastewater treatment.

2. STABILITY OF PARTICLES IN WATER The stability of the colloidal systems can be explained in part by the balance between the London and van-der-Waals forces and the electric forces between the double layer of particles (repulsion energy) known as DLVO theory, in honor of Derjaguin-Landau and Verwey-Overbeek, a pair of Russian and Dutch scientists, respectively, who in the 1940s independently developed this theory. However, from the 1980s onwards, with the development of more advanced techniques (atomic force microscopy, for example), it was possible to obtain results of the surface forces in aqueous medium, which demonstrated (verified and proved the existing theoretical models) the existence of

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additional forces of hydration (repulsive force) and hydrophobic forces (attractive force much greater than the van der der Waals forces), which were not predicted by the classical theory. The inclusion of energy due to these forces, also known as structural forces, resulted in a more modern concept named extended DLVO theory, or, simply, XDLVO (Yoon and Ravishankar, 1994; Israelachvili, 1992; Lins and Adamian, 2000; Bratby, 2006; Bolto and Gregory, 2007; Vincent, 2012). The particles generally have surface charge in aqueous media, which may originate from the ionization of surface groups or sites, imperfection of the crystalline structure of the solid surface, specific adsorption of ions and/or differentiated solubilization between cations and anions. The surface potential of the colloids, the distribution of ions in solution and the thermal effects lead to the formation of the double electric layer, shown in Figure 1. The double electric layer is modeled as being composed of two regions separated by the Stern Layer (SL). The inner layer is known as the Stern Layer and the outer layer as Gouy-Chapman or diffuse layer. In the presence of ions that are adsorbed specifically by the chemical mechanism, the presence of two other planes is defined: the Internal Helmholtz Layer (IHL), with potential I, and the External Helmholtz Layer (EHL), with potential E. In the IHL the specific adsorption of ions by the chemical mechanism occurs. The adsorption of co-ions, with charge of equal signal to that of the surface of the particle, promotes an increase of the potential of the double electric layer. The adsorption of positive ions, more common case, promotes a decrease of the electric potential or even the reversion of the charge of the particle. On the other hand, in the EHL the ions are adsorbed by the physical or electrostatic mechanism, which, at the most, promote neutralization of the electrokinetic potential of the colloid (). Because of the difficulty of determining the surface electric potential of the particle, it is common practice to measure the potential in the shear plane between the moving particle and the surrounding liquid. The potential in this plane is known as Zeta Potential () or electrokinetic potential.

3. PRINCIPLES OF FLOCCULATION The destabilization of colloidal systems can be accomplished by the addition of inorganic electrolytes, flocculating polymers, surfactants and oils, and the aggregation or agglomeration (in the case of oils) of the ultrafine or colloidal particles (< 1μm) occurring in larger units.

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Elvis Carissimi, Cristiane Oliveira Rodrigues, Dounia Elkhatib et al. Negative ion

Positive ion

Negatively charged particle surface

Stern Layer Diffuse Layer Ions in equilibrium with bulk solution Figure 1. Schematic representation of the electric double layer model.

Destabilization with Inorganic Salts Inorganic salt destabilization, also known as homocoagulation or coagulation, occurs by the compression of the electric double layer that surrounds all the colloidal particles by the addition of inorganic salts (Weber, 1972). The adsorption of these inorganic ions occurs in the shear planer (Zeta), neutralizing the potential in this plane and reducing the energy of repulsion, allowing the attraction forces to act and the aggregation of the particles. This term is also applied for destabilization by the addition of hydrolyzable electrolytes, such as Fe+3 and Al+3. The mechanism that occurs with the addition of salts of the sulfate type or chloride of iron or aluminum differs from the monovalent salts, because in addition to reducing the double electric layer, these salts form hydrolysis products that polymerize forming large three-dimensional molecules with active ends. These chains form spongy masses which, when sedimented, entrain new particles, causing a sweeping effect. The empirical relationship of Schulze-Hardy expresses the ratio between the molar concentration of monovalent, divalent and trivalent ions for the coagulation of the colloids of a system stabilized by the electrostatic mechanism as: 1: (1/2) 6: (1/3) 6 or 100: 1.6: 0.13. Higher-valence ions have a greater tendency for specific adsorption, improving coagulation efficiency. The order of effectiveness for ions of the same valence follows the Hoffmeister series, in which coagulation varies directly with the hydrated ion radius (Adamson and Gast, 1997; Dobiás e Stechemesser, 2005; Bratby, 2006; Bolto and Gregory, 2007). Heterocoagulation is an aggregation process that also involves the interaction between double electric layers and van der Waals forces, and occurs between particles of

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different potential, being more complex than homocoagulation, especially when the particles have negative surface charge. Thus, electrostatic interaction is the main aggregative force acting on heterocoagulation.

Destabilization with Surfactants The destabilization results from the adsorption of surfactants at the solid-liquid interface making the colloidal particles hydrophobic. The aggregation by surfactants may be due to one of the following mechanisms: (a) Hydrophobic effect and hemimicle formation: in which the adsorption of surfactant reagents at the solid-liquid interface occurs mainly through electrostatic, chemical interactions (between the polar part and the superficial sites) and hydrophobic forces, with a decrease in the entropy of the system (surfactant molecules). When adsorbed the molecules orient themselves in the form of doublet/triplet, etc. with the tails interacting by hydrophobic forces, these conformations being known as hemimicles, and the phenomena that operate are given by the molecular recognition of the hydrophobic fractions; (b) Neutralization of charges and hydrophobic effect: neutralization of the surface charge of the dispersed particles can occur producing destabilization by the action of attraction forces (London, van der Waals and hydrophobic). The process is spontaneous, reducing the Gibbs free energy of the system by reducing the solid-solution surface area and the hydrophobic effect; (c) Shear aggregation or shear aggregation: shear aggregation occurs when hydrophobicized particles interact with surfactants in a turbulent hydrodynamic regime through the hydrophobic effect. This phenomenon of shear aggregation is due to the low energy involved in this interaction, and to aggregate the particles need to collide with a minimum energy for these hydrophobic forces to operate.

Destabilization by Oily Agglomeration When aggregation occurs with oils the process is known as agglomeration and, because the agglomerates acquire spherical shape, it is also termed spherical agglomeration. Through this mechanism hydrophobic particles present in water or hydrophobized with residual surfactants may be agglomerated by the addition of a nonpolar oil. This process consists of two stages:

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Elvis Carissimi, Cristiane Oliveira Rodrigues, Dounia Elkhatib et al. (a) Oil-particle interaction: being the oil little soluble in water, the interaction occurs between the droplets dispersed in water and the surface of the particles. If the particles are hydrophobic, the oil spreads initially forming a lens and then a liquid film that recovers its surface, making them more hydrophobic. Therefore, the interaction is of hydrophobic character (hydrophobic forces) (Israelachvili, 1992); (b) Capillary effect: when the oil concentration is high, the droplets occupy the entire internal area available between the particles. At this stage, the capillary effect is maximal and defines the spherical shape of the agglomerate with the particles being held together by oily bridges. The formation of oil capillaries between the particles promotes bonding and an increase in the hydrophobicity of the flocs.

Destabilization with Aquasoluble Polymers The use of synthetic polymers in the solid-liquid separation rather than the coagulant electrolytes allows a more effective process, providing more resistant aggregates (flocs), higher sedimentation rates and more permeable filtration pans (Metcalf and Eddy, 2003; Sincero et al., 2003; Fleer, 2010). The flocculating polymers employed for colloidal destabilization include natural and synthetic products. Among the natural ones are polyacrylamides, starches, proteins, tannins, biopolymers, guar gums and derivatives of natural products, such as dextrin and sodium alginate (Metcalf and Eddy, 2003; Schwoyer, 1981; Bratby, 1980). Most commercial polymers fits as synthetic polymers, such as, for example, polyacrylamides and polyamides, or nonionic polymers such as ethylene polyoxide (POE) and polyvinyl alcohol (PVA). As for the charge, the flocculating polymers may be cationic (radical - NH3+), anionic (-COOH- radical), nonionic (such as ethylene polyoxide), or amphoteric (semi-hydrolyzed polyacrylamides which have negative and positive charges in the same jail). Most polymers are hydrophilic, however, the presence of hydrophobic polymers (such as polyethylene oxide and polyvinyl alcohol) may occur. The polymers may be low (10,000-100,000) and high (> 100,000) molecular weight, reaching a molecular length of up to 1000 Å (Schwoyer, 1981; Bratby, 2006; Bolto and Gregory, 2007; Fleer, 2010). The aggregation of the particles by polymeric bridges is called flocculation. The polymer adsorb at the solid-liquid interface (hydrogen bonds, hydrophobic forces and electrostatic attraction) by the electrostatic attraction mechanisms, polymer bridges or the entrapment of the particles in polymer networks. The kinetics of the formation of the flocs depends on the following steps: (a) Diffusion of the polymer under turbulent conditions, followed by adsorption at the solid-liquid interface. The molecule adsorbs on the surface of the particle at

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one or more active sites, leaving the rest of the chain free, extended in the solution; (b) Conformation of the polymer forming loops, tails and trains. The conformation of the adsorbed polymers depends on chain size (molecular weight), chain flexibility, charge density (% hydrolysis), interaction energy between the polymer and the colloid, the chemical and physical nature of the superficial sites of the particles and competition between the polymer and other molecules present in the solution; (c) Adsorption of loops and tails and formation of polymer bridges. The strength of the flocs depends on the number of bridges formed, and hence on the number of loops and tails available. A factor of crucial importance is the availability of sites in the particles to accommodate the bonds of neighboring particles; (d) Growth of the flocs under slow stirring. According to some authors (Arboleda, 1973; Bratby, 1980; Metcalf and Eddy, 2003; Bratby, 2006), after addition of the destabilizing agent, rapid mixing is required for diffusion to take place in the solid-liquid suspension and formation of the primary flocs. After the appearance of the primary flocs, a slow mixing stage is usually required for growth and formation of larger flocs and subsequent sedimentation. However, flotation separation does not require the formation of large flocs. The energy for the aggregation process is provided by the induction of velocity gradients within the system (orthokinetic aggregation). The main parameters involved in orthokinetic energy are the velocity gradient applied and the stirring time. The main mechanisms involved in flocculation aggregation are shown in Figure 2.

4. PRINCIPLES OF FLOCCULATION HYDRODYNAMIC MIXING The effect of hydrodynamic conditions is another relevant factor in the destabilization of colloidal systems through hydrolyzable electrolytes and/ or flocculating polymers. In the aggregation of the particles, two processes must occur sequentially. First, the particles must collide with each other, and then, under the influence of the colloidal forces, they must be grouped into aggregates. Thus, the global aggregation equation is given by Equation (1):

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(a)

(d)

(c)

Figure 2. Schematic description of the mechanisms of adsorption and flocculation by bridges: conformation of the polymer in trains, tails and loops after adsorption at the particle/solution interface. (a) diffusion of macromolecules; (b) adsorption and conformation of the chains; (c) formation of primary flakes; (d) growth of the flakes (Kitchener, 1972; Rodrigues, 2010).

−

𝑑𝑁 𝑑𝑡

= {𝐶𝑜𝑙𝑙𝑖𝑠𝑖𝑜𝑛 𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦}𝑥{𝐶𝑜𝑙𝑙𝑖𝑠𝑖𝑜𝑛 𝑓𝑟𝑒𝑞𝑢𝑒𝑛𝑐𝑦} = 𝛼 𝑥 𝐽

(1)

In equation (1) N represents the concentration of particles at a given time t. Also, J is the collision frequency and represents the number of collisions that occur per unit time. Finally, the collision efficiency, α, reflects the fraction of the total number of collisions that result in the formation of aggregates. Conventionally (especially in flocculation), after the addition of the destabilizing agent of a system, there follows a rapid mixing step and a slow stirring step. In rapid mixing, in addition to the diffusion of the reactants, the breakdown of the repulsive energy barrier between reagents and particles and between particles and particles occurs. The primary flocs originate, which will have significant importance on the kinetics of the subsequent processes. After the appearance of the primary flocs in the fast mixing stage, a slow stirring stage allows the formation of larger flocs. According to Metcalf and Eddy (2003) the energy for the process of colloid aggregation is provided by two types of aggregation:  

microflocculation or pericinetic flocculation, and macroflocculation or orthokinetic flocculation.

Microflocculation is the term used to denote particle aggregation due to the random motion of molecules in the fluid. This random spatial motion of the molecules in the fluid is also known as Brownian motion. The pericinetic aggregation starts immediately after

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destabilization and stabilizes within seconds, since it is significant for particles in the range of 0.001 to 1 μm. Macroflocculation is the term that refers to the aggregation of particles larger than 1 or 2 μm. Macroflocculation may occur due to the induced velocity gradient or differential sedimentation. The energy imposed by a mixer is dissipated through velocity gradients and the energy rate introduced is proportional to the set velocity gradient. The velocity gradient is symbolized by G and is used to measure the mixing intensity. A high value of G means an intense mixture, and a low value of G denotes a slow mixture. According to Thomas et al. (1999), for a given value of G, orthokinetic aggregation is the predominant mechanism when the particles exhibit uniformity of size, whereas the differential sedimentation predominates when the particles present significant disparity of sizes. The balance between the G employed and the mixing time can be expressed by the Camp number (G.t). In any unstable state, the composition of the liquid mass varies with time. This is the case of most reactors used in treatment plants (mixers, flocculators, decanters, etc.) where at any point it is found that both the velocity and the composition change constantly because the water does not flow homogeneously, from the inlet to the outlet, i.e., not all the flow entering the initial time reaches the outlet, exactly at the nominal holding time td (Arboleda, 1973). According to Bratby (1980); Bratby (2006) and Bolto and Gregory, 2007, the ideal mixing type is the plug flow type, where all particles have the same residence time. In mixers of the full mix type, some particles are short-circuited and others have very long residence times. Such distribution of residence times is not desirable in the use of hydrolyzable salts or polymers. In the case of the hydrolyzable salts, a short residence time does not allow the complete adsorption of the hydrolyzed species on the surface of the particles. The same occurs in the adsorption of polymers. On the other hand, intense mixing for a very long time can break the polymer bridges between the particles and even the polymer.

5. FLOCCULATION PROCESSES Usually, three types of flocculators are employed in water and wastewater treatment: hydraulic, mechanical, and pneumatic (Sincero et al., 2003). Hydraulic flocculators take advantage of the energy that the flow acquires when flowing through a conduit to agitate the liquid mass. Also, according to the direction of the liquid stream, inside the chambers, hydraulic flocculators are divided into: horizontal flow, vertical flow and helical flow.The mechanical flocculators are classified according to the type of movement of the agitators, and can be alternating or rotating (Arboleda, 1973). Pneumatic flocculators employ air to promote agitation. Table 1 shows the main classification of flocculators.

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Hydraulic Flocculators Hydraulic flocculators utilize the kinetic energy that the flow acquires when flowing through a conduit to agitate the liquid mass. The most commonly hydraulic flocculator models are the baffles (Arboleda, 1973; Sincero, et al. 2003).

Baffled Flocculators The baffle flocculators consist of tanks, provided with internal channels, in which water flows at a fixed velocity, producing some turbulence, at each change of flow direction, making a 180° turn at the end of each channel, shown in Figure 3. The most common are horizontal flow and vertical flow. A head loss occurs mainly because: (a) Change of direction and turbulence; (b) By enlargement and contraction of the section; (c) By friction in the straight stretches. However, baffle flocculators present some disadvantages, such as: (i) greater head loss (greater velocity gradient) in the 180° flow turns compared to the straight stretches; (ii) in the case of fixed baffles, the velocity is constant for each flow. In case of variations in flow rate, the speed also changes, being very high or very low.

Outlet Inlet

Figure 3. Baffled Flocculator unit (http://www.nzdl.org).

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Table 1. Usual classification of the flocculators Type Hydraulic

Mechanical

Classification Horizontal Vertical Helical Rotating Alternates

Pneumatic

Example Baffles interspersed transversely of the tank Baffles interspersed above and below the tank Tanks with input and output devices in opposite directions Vertical or horizontal axis rotary vane Alternating vanes Air diffusers

Helical Flow Flocculators In this type of flocculator (also called tangential flow or spiral flow) the hydraulic energy is used to generate a helical movement to the water through inlet and outlet devices located in opposite directions, creating a mechanical torque and imparting a movement of rotation of the net mass (Arboleda, 1973; Richter and Netto, 1991). Figure 4 shows the design of a helical flow flocculator. Hydraulic flocculating flocculators are not as widespread as mechanical flocculators and wall flocculators. Arboleda (1973) cites that the Engineering Institute of the National Autonomous University of Mexico (UNAM) has developed studies in units of this type, with the objective of establishing parameters for such flocculators. Oliveira (1979, 1981) evaluated the performance and orthokinetic characteristics of the helical stream using this type of flocculator with a cylindrical chamber (avoiding dead zones) in the water treatment plant of the city of Atlântida (Southern Brazil) and verified the flocculation efficiency, in terms of turbidity removal, being technically feasible for small treatment plants (low velocity gradient). Both studies verified the limitation that occurs with the use of this type of flocculator for relatively large flow rates, and it is necessary to increase the number of chambers too much, resulting in loss of simplicity and structure savings.

Figure 4. Helical flocculator unit (Richer and Netto (1991)).

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Alabama Flocculator The Alabama Flocculator is made up of compartments interconnected by the bottom through 90° curves facing upwards. The flow can be up and down inside the same compartment. Removable nozzles installed at the exit of the reactor allow adjusting the speed to the conditions of calculation or operation (Richter and Netto, 1991). According to Vianna (1997), the flocs brought by the upstream tributary current collide with those carried by the effluent stream, descending, resulting in the growth of the flocs. Thus, according to the same author, it allows the existence of fewer chambers than vertical baffle flocculators. Figure 5 illustrates an Alabama flocculator.

Figure 5. Alabama flocculator unit (Source: Richer and Netto (1991)).

Cox Flocculator This flocculator was developed by Cox for the Public Health Services Foundation of Brazil (Richter and Netto, 1991). According to Vianna (1997), this type of flocculator has a small number of chambers, and the interconnections between the chambers alternate upper and lower positions, as shown in Figure 6. The main advantage of this type of flocculator is the small number of compartments and as the main disadvantage, there is cited the unevenness of the degree of agitation conferred on the liquid mass. Table 2 summarizes the major advantages and disadvantages of hydraulic flocculators.

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Inlet

Treatment Flux Outlet

Figure 6. Cox Flocculator (Source: Richer and Netto (1991)).

Table 2. Main advantages and disadvantages of hydraulic flocculators Advantages  Flow close to plug flow  Does not require complementary devices  It does not require electrical energy  Ideal for small installations

Disadvantages  There is no flexibility in changing G  Usually occupies a large space

Mechanical Flocculators Mechanical flocculators require an external power source to move an agitator in a tank or series of tanks, in which the suspension remains for a theoretical holding time td. According to the movement of the agitator are classified in rotary or alternating. The first can be of low speed of rotation (vane) or of high speed of rotation (turbines and propeller), being able to be of vertical or horizontal axis. The second consists of wooden beams that move vertically and alternately (walking beams) or oscillating systems like ribbons (flocculator) that move horizontally inside the tank. In both cases the energy transferred to the liquid mass is directly proportional to the energy with which the mechanical element moves within it (Arboleda, 1973).

Vanes These rotating flocculators have a system of vanes adhered by a horizontal or vertical axis, which rotates by an electric motor, displacing the water and producing work. These stirrers may have two, three or four arms, and, on each arm may have two or more vanes or impellers joined by a central axis, as shown in Figure 7.

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Figure 7. Rotating vanes (Source: Richer and Netto (1991)).

Impellers (Turbine and Propeller) Turbine and propeller type flocculators are typically more compact and can generate more energy when operated at high speed. Essentially, turbine-type flocculators consist of a central axis in which one or more discs with fins are assigned, as shown in Figure 8 (Metcalf and Eddy, 2003). The propeller-type flocculators have fins attached directly to the central axis of rotation. The speed of rotation of these agitators is greater than in the vane flocculators. In some plants, turbine or propeller flocculators are employed for the first tanks (which require a higher velocity gradient) and for vats for the tanks that will promote the slow stirring stage.

Figure 8. Impellers (http://www.solidscontrolsystem.com/four-mud-agitator-impeller-type/).

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Table 3. Main advantages and disadvantages of mechanical flocculators Advantages Formation of dense flocs Possibility of changing the speed of agitation according to the need of treatment Constant and homogeneous agitation

Disadvantages Production of short circuits or dead zones Equipment dependency Electric power consumption Need for electro-mechanical maintenance.

Table 3 presents the main advantages and disadvantages of mechanical flocculators. According to Hudson and Wolfman (1957) cited by Arboleda (1973), the problem of short circuits generated in flocculators by mechanical agitation is the main impediment in the comparison of flocculation results obtained in jar tests with the data obtained in the treatment plants. This is because in the jars test the water and the reactants are retained in their entirety in the cells during the test time, with no short circuits occurring. And the opposite occurs in the flocculation chambers, where part of the water passes quickly while another is held for longer periods.

6. PNEUMATIC FLOCCULATORS OR AIR-ASSISTED FLOCULATION The necessary stirring for flocs formation can be accomplished by the introduction of air into the system. The difference in density between the air bubbles and the water causes the bubbles to rise to the surface. As the bubbles rise, they cause the water to move, and consequently the mixture required for flocculation. In this case, the velocity gradient reached can be controlled by adjusting the airflow. In published pneumatic flocculation studies, chambers or columns are usually used where air is injected through a diffuser (McConnachie, 1984; Sincero et al., 2003). The in-line pneumatic flocculation of a biphasic flow (air-water), promoted by mixers, can be explained by mechanisms similar to those of pneumatic flocculation in chambers. In this process, the agitation necessary to promote flocculation is increased by the injection of air through diffusers into the stream containing the effluent to be treated and the destabilizing agent. In this way, the air released in the form of bubbles, in addition to promoting a piston-type mixing in in-line mixers, has a high flocculation efficiency for the removal of impurities that are suspended (Sholji and Kazi, 1997). Through the principles of pneumatic flocculation, many authors have suggested a new proposal for the generation of aerated flocs, in which dispersion of the air injected in the form of small bubbles that adhere and/or trapped themselves to the flocs during its formation (Owen et al., 1999; Fan et al., 2000; Da Rosa, 2002; Jameson, 1999; Zhao, 2002). In this way, aerated flocs “float” and are more easily separated later in a

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separation tank. These aerated flocs are structures composed of particles or colloids flocculated by high molecular weight cationic polymers containing trapped air in the form of microbubbles. The aerated flocs normally formed are of the order of centimeters, whose rise rate is significantly greater than the velocity of independent air bubbles. Bratby (1980) cites the generation of a local velocity gradient much larger than the mean gradient as one of the disadvantages of diffused air flocculation. This depends on the bubble size that is generated by the available diffusers. According to the same author, the maximum speed gradient generated is given by Equation (2). 𝐺𝑚𝑎𝑥 =

𝑔.𝐷𝑏(𝜌𝑙 −𝜌) 6.𝜇

(2)

where: ρ = density of the liquid (kg.m-3); ρ1 = density of the liquid; ρ = air in the bubble (kg.m-3); Db = bubble diameter (m); g = acceleration of gravity (9.81 m /s2); μ = absolute viscosity (10-3 N.s.m-2, for water at 20 ° C). Table 4 shows the Gmax values for a bubble size range. Table 4. Gmax values generated by a range of bubble diameters (water at 20°C) Gmax (s-1) 16 82 163 245 816 1633 3265

Bubble Diameter (mm) 0.01 0.05 0.1 0.15 0.5 1.0 2.0 Source: Bratby, J. Coagulation and Flocculation, p. 226, 1980

Table 5. Main advantages and disadvantages of pneumatic flocculators Advantages Possibility of formation of aerated flocs, assisting later separation Adjusting the stirring by controlling the flow of air.

Disadvantages Need for energy and specific equipment for air dispersion

However, according to Masschelein (1992) cited by Metcalf and Eddy (2003) the mean bubble diameter formed in this process is 5 mm, in a mean air flow of 10 percent of the liquid flow. The velocity gradient due to the formation of bubbles in this range ranges from 200 to 8200 s-1. In the case of extremely small bubbles of the order of micrometers, the value of Gmax will also be small, becoming practically negligible. Table 5 presents the main advantages and disadvantages of pneumatic flocculation.

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7. FLOCCULATION APPLICATIONS Considerations about the main applications of the flocculation considering water and wastewater treatment are discussed considering a compact helical unit named here as Flocs Generator Reactor that may be applied for water and wastewater treatment (emphasis is given for physicochemical processes) and a biological process application for sewage treatment named here as bioflocculation for nitrogen uptake.

Flocs Generator Reactor (FGR) Curved configurations of circular tubes are widely used in heat exchangers, chemical reactors, reverse osmosis units, blood oxygenation membranes, enzyme polymerization, etc. These helical mixing units present enormous advantages over straight-line systems or mechanical mixers, mainly due to hydrodynamic characteristics (higher Reynolds numbers and higher velocity gradients) and secondary flow. This flow presents an action of centripetal forces, with a movement along the walls and near the center of the tube, increasing the resistance to the flow (Streeter, 1961; Berger et al., 1983, Agrawal and Nigam, 2001; Elmaleh and Jabbouri, 1991; Ødegaard et al., 1992; Buchanan et al., 1998; Carissimi and Rubio, 2005; Carissimi et al., 2007, Carissimi and Rubio, 2015; Carissimi et al., 2018). The evaluation of curved systems employed industrially and the analysis of the different aggregation equipment used in the water and effluent treatment plants cited by Carissimi and Rubio (2005) allowed the design and the design of a hydraulic aggregation system in line with a piston regime, called Reactor Generator - RGF. Figure 9 shows the response curve generated by the instant introduction of a tracer (methylene blue) for determining the axial flow rate of the RGF. The pulse shown shows a slow tracer spreading at the feed rate of 3 Lmin-1, and the time of 25 seconds denotes the tracer residence time inside the RGF. The FGR consists of an in-line helical mixing reactor for the solid-liquid aggregation and separation of suspended particles, with a Brazilian Patent (INPI PI 0406106-3). The necessary stirring for dispersion of the destabilizing agent and generation of the aggregates is carried out by exploiting the kinetic energy of the hydraulic flow along the helical tubular reactor.

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Figure 9. Curve of the tracer response along the FGR. Conditions: feed flow = 3 Lmin-1, [AM] = 10000 mgL-1; FGR with a length of 12 m and a diameter of 2.5 cm. Length comprimento

microbolhas Air de ar microbubbles

Outer diâmetro diameter externo

Inlet entrada

saída Outlet

efluente + polímero Water/wastewater + polymer direção do fluxo Flow direction Figure 10. Flocs Generator Reactor (FGR).

One (semi-pilot) unit of the FGR is shown in Figure 10; consisting of a transparent polyurethane tube with internal diameter of 0.0125 m wrapped in the outside of a fixed polyvinyl chloride (PVC) column, with an internal radius of 0,05 m, consisting of 32 rings, 12 m volume of 1.2 L, occupying a surface area of 0.60 mx 0.13 m. This model has the alternative of injecting air microbubbles, generated through an air depressurising system (such as in the dissolved air flotation process), making the reactor as an aerated float floater (detailed later). The use of online aggregation (pipelines, ducts, pipes) is not a common practice, however, already existing in some industrial plants, either by the practical necessity of operators, space optimization or by commercialization by companies specialized in water and effluent treatment.

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Bioflocculation in Wastewater Treatment Plants Bioflocculation combines the primary influent of wastewater and the return activated sludge from the secondary treatment in order to improve the nitrogen removal efficiency as well as the nitrogen recovery. Excess Nitrogen in rivers and streams causes water pollution and hence affects the public health (Manuel, 2014). Nitrogen effluent discharge from wastewater treatment plants are therefore becoming increasingly strict (Agency, 2018). The need for effective nitrogen removal strategies to meet the nitrogen effluent limits while maintaining minimal operating Wastewater Treatment Plants (WWTP) costs is therefore increasing (Stare, Vrečko, Hvala, & Strmčnik, 2007). Conventional biological nitrogen removal processes are usually conducted in a series of anoxic/aerobic reactor (Metcalf Eddy, 2014). The biological processes that remove nitrogen are nitrification and denitrification. During the nitrification stage, high energy use for aeration is required to oxidize the ammonia to nitrite then nitrate, making it a cost burden to WWTP. Nitrogen removal requires 12 kWhel per person per year and significantly contributes to the overall wastewater energy budget (Verstraete & Vlaeminck, 2011). Nitrous oxide (N2O), which is a potent greenhouse gas, contributing for 5.3% of the global anthropogenic greenhouse gas emissions in 2013 (EPA, 2014), can be emitted during the nitrogen removal process in wastewater treatment. During the biological nitrogen removal process, N2O is produced by nitrite reduction in the aerated compartments (Toyoda et al., 2011) and during the anoxic stages as an intermediate product (Colliver & Stephenson, 2000). The Environmental Protection Agency of the United States reported that N2O from the wastewater sector accounts for about 3 per cent of N2O emissions from all sources and ranks as the sixth largest contributor in the United States (EPA, 2014). The increased presence of this gas in the atmosphere causes a rise in the equilibrium temperature of the earth, thus arousing climate change. Therefore, the need of an efficient nitrogen removal system that achieves low N2O emissions while maintaining the nitrogen removal standards, is required. The bioflocculation process is a proposed application, where the waste activated sludge from the secondary treatment is used as flocculent. This process has proven to enhance the nitrogen removal and recovery during the primary treatment stage. The removal of nitrogen and organics from the primary effluent could reduce the energy requirements in the activated sludge process and also reduce the N2O emissions produced during the nitrogen removal processes. The biogas and the residual solids from the facility’s anaerobic digester will increase upon digestion of primary sludge, which has high energy and nitrogen content. The bioflocculation application was tested using the influent wastewater and the activated sludge obtained from the Narragansett Bay Commission Wastewater Treatment Facility, located at Field’s Point in Providence, Rhode Island. The facility has an average

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daily flow of 40 MGD providing services to about 226,000 people. This plant uses the Integrated Fixed Film Activated Sludge (IFAS) process for the secondary treatment to promote nitrification. The influent wastewater used in this experiment was obtained from the outlet of the primary treatment, while the activated sludge was obtained from the Return Activated Sludge (RAS), which should have the same characteristics of the waste activated sludge. The collected samples were tested and analyzed at the environmental engineering laboratory located at the University of Rhode Island.

Figure 11. Diagram flow for the proposed treatment system.

Table 6. Mixture Conditions used during the Experiment Volume of Sludge [mL] 0 250 500 1000

Volume of Sewage [mL] 1000 750 500 0

In order to apply the concept of bio flocculation process at this existing wastewater facility with minimal investment costs, a pipe and a pump have to be installed to deliver the secondary activated sludge back into the primary clarifier. Figure 11 shows a schematic drawing of the proposed treatment system. The recirculation of the activated sludge to the inlet primary treatment is shown in red. The tests were conducted in sealed 1000 mL graduated cylinder. Influent wastewater (or sewage) and activated sludge were mixed in the cylinders according to the test conditions summarized in Table 6. The graduated cylinders were shaken to assure a good mixing of the components, followed by 30 minutes of contact time between the two materials. Bioflocculation efficiency was determined by the removal percentages of nitrogen from the influent. The removal percentage of organic matter takes into account the removal mechanisms from both the influent and the activated sludge. This method was based on a research study where settleable solids removal from bioflocculation was assessed

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(Araneda, Pavez, Luza, & Jeison, 2017). However, this method was modified for the purpose of this application to calculate the total removal organic matter from the influent. The results show that there is a considerable removal efficiency of respectively 59%, 47% and 25% for COD, TKN and NH3 concentrations in the second mixture (500:500), where the sludge and sewage are mixed in the same ratio. The N2O emissions at the NBC Field’s Point plant were found to be reduced by 1.4 µmol N2O/m2.s. Anaerobic digesters are one of the most common waste sludge treatment. In this process, the biosolids are broken down in the absence of oxygen, and partially converted into gases, while the remainder is dried and becomes a residual soil-like material (Metcalf Eddy, 2014). The treated sludge contains useful concentrations of nitrogen, phosphorus and organic material. When applying the suggested enhanced primary treatment using the bioflocculation, the total nitrogen removed from the primary effluent will be transferred to the primary sludge. The increase of the nitrogen availability in the primary sludge by 47% will increase the benefits of the treated sludge, as it will have higher nitrogen contents, and hence more beneficial to the grassland. The organic matter in sludge can also improve the water retaining capacity and structure of some soils, especially when applied in the form of dewatered sludge cake (Natural Resources Management and Environment Department). The nitrogen being transferred to the primary sludge, is hence recovered to a more useful way than being consumed by microorganisms in the secondary treatment, which requires high amounts of energy too. Anaerobic digestion reduces the volume of sludge and produces methane containing biogas, a renewable energy, as a by-product. Collecting the energy from the biogas through an efficient combustion process is both economically and environmentally beneficial. Based on the results of the bioflocculation application, the percent of COD concentrations in the influent that is transferred to the primary sludge was found to be 59%. The methane production achieved by primary sludge was found by (Mahdy, Mendez, Ballesteros, & González-Fernández, 2015) to be 266 mL per gram of COD. And, the methane has a calorific potential of 6.22E-3 kW.h/L CH4 (Metcalf Eddy, 2014). By using these information, the amount of CH4 produced per day will increase by 76,021 cubic feet, which is around 51% increase of the usual methane production at the NBC facility. The bioflocculation application of the influent sewage can be advanced primary treatment process. Its mechanism for the removal of organics, without any addition of chemicals, enhances the nitrogen removal and recovery from wastewater treatment plants. The experiments showed that TKN in the influent was reduced by 46% and the NH3-N was reduced by 24% as a result of mixing the activated sludge from secondary treatment with the primary influent, for a flocculation time of 30 min. The removal performance of the bio flocculation in the primary treatment, has also shown some energy consumption savings in the treatment aeration process. For the same

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removal percentages mentioned above, the expected reduction in the aeration process was about 18% for the cost and 36% for the air requirements. Another main advantage of the bio flocculation process is the recovery of nitrogen and organics in the primary sludge. The primary sludge, which is rich in nitrogen content, can be used as fertilizer to supply agriculture soils instead of chemical fertilizers that require large amounts of energy to produce. Also, the primary sludge which has a higher energy content than the sludge removed at the secondary treatment due to the high organics content, produce more biogas during digestion. Finally, the calculations from the bio flocculation process have proven a reduction of the nitrous oxide emissions from wastewater treatment due to the reduction of Nitrogen content. In the enhanced primary treatment where the bio flocculation was applied, the N2O emissions were reduced by 27%. In conclusion, the Bio flocculation process has proven to be a new approach in primary treatment of wastewater that leads to an energy efficient and improved process design in wastewater treatment sector.

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Buchanan, I. D., Nicell, J. A. and Wagner, M. (1998). Reactor models for horseradish peroxidase-catalysed aromatic removal. Journal of Environmental Engineering, 794-802. Carissimi, E., Miller, J. D. and Rubio, J. (2007). Characterization of the high kinetic energy dissipation of the Flocs Generator Reactor (FGR). International Journal of Mineral Processing, v. 85, 41-49. Carissimi, E. and Rubio, J. (2005). The flocs generator reactor-FGR: a new basis for flocculation and solid-liquid separation. International Journal of Mineral Processing, 75 (3-4), p. 237-247. Carissimi, E. and Rubio, J. (2015). Polymer-bridging flocculation performance using turbulent pipe flow. Minerals Engineering, 70, 20-25. Carissimi, E., Sanagiotto, D. G., Camaño-Schettini, E. B. and Rubio, J. (2018). Revisiting Coiled Flocculator Performance for Particle Aggregation. Water Environment Research, v. 90, 322-328. Colliver, B. B. and Stephenson, T. (2000). Production of nitrogen oxide and dinitrogen oxide by autotrophic nitrifiers. Biotechnology Advances, 18(3), 219-232. doi:10.1016/S0734-9750(00)00035-5. Dobiás, B. and e Stechemesser, H. (2005). Coagulation and flocculation. Marcel Dekker Inc, New York, 882 pp. Elmaleh, J. and Jabbouri, A. (1991). Flocculation energy requirement. Water Research, 25 (8), p. 939-943. EPA, U. S. E. P. A. (2014). Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2012. The Air Pollution Consultant, 24 (3), 1_17. Fleer, G. J. (2010). Polymers at interfaces and in colloidal dispersions. Advances in Colloid and Interface Science, 159(2), 99-116. Israelachvili, J. N. (1992). Intermolecular and surface forces. Academic Press, University of California, 2nd Edition, 450 p. Lins, F. F. and Adamian, R. (2000). Minerais coloidais, teoria DLVO estendida e forças estruturais [Colloidal minerals, extended DLVO theory and structural forces]. Rio de Janeiro, CETEM/MCT, 29 p. (In Portuguese). Mahdy, A., Mendez, L., Ballesteros, M. and González-Fernández, C. (2015). Algaculture integration in conventional wastewater treatment plants: Anaerobic digestion comparison of primary and secondary sludge with microalgae biomass. Bioresource Technology, 184, 236-244. doi:10.1016/j.biortech.2014.09.145. Manuel, J. (2014). Nutrient pollution: a persistent threat to waterways. Environmental health perspectives, 122(11), A304. doi:10.1289/ehp. 122-A304. Metcalf, e Eddy. (2003). Wastewater engineering: treatment and reuse. Editores: Tchobanoglous, G.; Burton, F. L.; Stensel, H. D. Metcalf e Eddy, Inc., McGraw Hill, 4th Edition, 1819 p.

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Metcalf Eddy, I. T., Burton, G. and Stensel, F. H. D. (Ed.) (2014). Wastewater Engineering: Treatment and Resource Recovery. 2 Penn Plaza, New York, NY 10121: McGraw-Hill Education. Ødegaard, H., Grutle, S. and Ratnaweera, H. (1992). An analysis of floc separation characteristics in chemical wastewater treatment. Chemical Water and Wastewater Treatment II. 5th Gothenburg Symposium, Nice – França. Eds. R. Klute and H. H. Hahn, 247-262. Oliveira, A. S. D. (1979). Floculadores hidráulicos de fluxo helicoidal em tratamento de água [Hydraulic flocculating flocculators in water treatment]. Dissertação de mestrado pelo Instituto de Pesquisas Hidráulicas da UFRGS, 94. (In Portuguese). Oliveira, A. S. D. (1981). Freitas, A. F. R. Floculador hidráulico cilíndrico de fluxo helicoidal em tratamento de água [Helical flow cylindrical flocculator in water treatment]. Engenharia Sanitária [Sanitary Engineering], 20 (2), 212-217. (In Portuguese). Richter, C. A. and Netto, J. M. D. A. (1991). Tratamento de água. Ed. Edgard Blücher Ltda, São Paulo-SP, 332 p. [Water treatment] Rodrigues, C. O. (2010). Mecanismos de floculação com polímeros hidrossolúveis, geração de flocos aerados, floculação em núcleos de bolhas floculantes e aplicações na separação de partículas modelos por flotação [Mechanisms of flocculation with water-soluble polymers, generation of aerated flocs, flocculation in flocculant bubble cores and applications in particle separation by flotation]. Tese de Doutorado UFRGS, 242. (In Portuguese). Schwoyer, W. L. K. (1981). Polyelectrolytes for water and wastewater treatment. CRC Press Inc., Boca Raton, Florida, 275 p. Sincero, A. P. and Sincero, G. A. (2003). Physical-chemical treatment of water and wastewater. IWA, USA, 832 p. Stare, A., Vrečko, D., Hvala, N. and Strmčnik, S. (2007). Comparison of control strategies for nitrogen removal in an activated sludge process in terms of operating costs: A simulation study. Water Research, 41(9), 2004-2014. doi:10.1016/ j.watres.2007.01.029. Streeter, V. L. (1961). Handbook of fluid dynamics. McGraw-Hill Book Company, Inc., New York, 1st Edition. Thomas, D. N., Judd, S. J. and Fawcett, N. (1999). Flocculation modelling: a review. Water Research, 33 (7), 1579-1592. Toyoda, S., Suzuki, Y., Hattori, S., Yamada, K., Fujii, A., Yoshida, N. and Shiomi, H. (2011). Isotopomer Analysis of Production and Consumption Mechanisms of N^sub 2^O and CH^sub 4^ in an Advanced Wastewater Treatment System. Environmental science and technology, 45(3), 917. doi:10.1021/es102985u. Verstraete, W. and Vlaeminck, S. E. (2011). ZeroWasteWater: short- cycling of wastewater resources for sustainable cities of the future. International Journal of

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Sustainable Development and World Ecology, 18(3), 253-264. doi:10.1080/13504 509.2011.570804. Vincent, B. (2012). Early (pre-DLVO) studies of particle aggregation. Advances in Colloid and Interface Science, 170 (1-2), 56-67. Weber, J. (1972). Physicochemical processes for water quality control. WileyInterscience, New York-USA. John Wiley and Sons, Inc, 640 p. Yoon, R. H. and Ravishankar, S. A. (1994). Application of extended DLVO theory III. effect of octanol on the long-range hydrophobic forces between dodecylamine-coated mica surfaces. Journal of Colloid Interface Science, 166 (1), 215-224.

In: Flocculation: Processes and Applications Editor: Eleonora Vollan

ISBN: 978-1-53614-339-3 © 2019 Nova Science Publishers, Inc.

Chapter 5

FLOCCULATION OF AOM IN WATER TREATMENT Martin Pivokonský*, Jana Načeradská, Kateřina Novotná, Lenka Čermáková and Petra Vašatová Institute of Hydrodynamics of the Czech Academy of Sciences, Prague, Czech Republic

ABSTRACT Global proliferation of algal blooms and subsequent deterioration of water quality by organic compounds that are being produced (algal organic matter – AOM) pose new challenges to water treatment technologies. Flocculation/coagulation using primarily Aland Fe-based coagulants is widely employed as an essential process in removal of various impurities at drinking water treatment plants and is also irreplaceable in the case of AOM elimination. This review chapter discusses current knowledge on AOM flocculation, the impact of AOM on the removal of other compounds and links AOM composition and character to the efficiency of flocculation, the reaction conditions and mechanisms and finally, to the properties of flocs. In general, the removal efficiencies of dissolved AOM are lower compared to intact phytoplankton cells and usually reach maximum under slightly acidic pH values. The strong pH-dependence of flocculation is attributed to the fact that the involved mechanisms are to a great extent determined by the charge ratios in the coagulating system. Furthermore, substantial differences in flocculation behaviour were observed between diverse AOM constituents, i.e., between peptides/proteins versus non-proteinaceous matter and high versus low molecular weight organics. The latter (specifically AOM < 10 kDa) are reluctant to flocculate and would therefore require other treatment techniques. AOM has also been reported to influence flocculation of other

*

Corresponding Author Email: [email protected].

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Martin Pivokonský, Jana Načeradská, Kateřina Novotná et al. common impurities, both of organic and inorganic nature. Mutual interactions have been proven, while their influence on flocculation efficiency can be either positive or negative, depending on the AOM character, pH conditions and on the ratio between AOM, the other polluting agents and coagulants. Finally, AOM also appeared to alter the properties of flocs, with an impact on the subsequent separation steps. In further research, a particular emphasis should be put on AOM components that are difficult to coagulate, the interactions of AOM with other impurities and on elucidation of the relationship between AOM and floc properties.

Keywords: algae, algal organic matter, AOM characterization, coagulation, coagulation mechanism, flocculation, floc properties, water treatment

1. INTRODUCTION Increasing worldwide occurrence of algal blooms in surface waters is an ongoing challenge in water treatment. In addition to the presence of algal and cyanobacterial cells, these are sources of a wide range of dissolved organic compounds, recognized as algal organic matter (AOM). AOM often comprises a substantial part of natural organic matter (NOM) occurring in water bodies that supply water treatment plants, where it adversely affects water quality and subsequent treatment processes (Zhang et al., 2010; Pivokonsky et al., 2016). AOM has gained a great attention due to the possible content of harmful cyanobacterial toxins (Carmichael, 1992; Dixon et al., 2011; Pearson et al., 2016) and compounds that give undesirable tastes and odours (Paerl et al., 2001; Huang et al., 2007; Zhang et al., 2010; Li et al., 2012). Further, AOM also serves as precursors of hazardous disinfection by-products (DBPs) that are being formed as a result of chlorination or chloramination of organic compounds (Nguyen et al., 2005; Fang et al., 2010; Li et al., 2012; Goslan et al., 2017). For example, trihalomethanes (THMs; e.g., trichloromethane (chloroform), dichlorobromomethan, dibromochloromethane or tribromomethane) and halogenated acetic acids (HAAs; e.g., monochloroacetic acid, monobromoacetic acid, dichloracetic acid or bromochloroacetic acid) are among the most pronounced DBPs (Fang et al., 2010; Li et al., 2012; Goslan et al., 2017). Apparently, AOM needs to be effectively removed in order to produce safe drinking water of satisfactory quality. Nevertheless, diverse AOM components act dissimilarly during water treatment processes and might pose specific complications in the treatment technology, such as interference with flocculation/coagulation1, membrane fouling or 1

The terms ‘flocculation’ and ‘coagulation’ commonly appear in the field of water treatment. These processes result in clumping of particles/molecules and subsequent formation of flocs, while ‘coagulation’ rather stands for the destabilization of particles (involving charge neutralization) and ‘flocculation’ for the aggregate (floc) formation. However, the terminology is not consistent among different studies and the terms are being used in

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competing with target pollutants regarding adsorption onto activated carbon (Pivokonsky et al., 2016). Flocculation followed by separation of the formed aggregates (sedimentation, flotation, filtration) is a fundamental step in water treatment. It is extensively employed at many drinking water treatment plants worldwide and is irreplaceable due to its operational benefits and cost-effectiveness. It also improves performance of potential downstream treatment processes, such as membrane filtration or adsorption onto activated carbon (Zhang et al., 2014). Flocculation has a potential to remove different polluting agents. Good removal efficiencies (94-99%) of algal and cyanobacterial cells were obtained under optimized flocculation conditions (Henderson et al., 2010; Baresova et al., 2017). However, AOM is generally much more difficult to coagulate, and additionally, AOM also influences flocculation of other compounds (Bernhardt et al., 1985; Henderson et al., 2010; Safarikova et al., 2013; Pivokonsky et al., 2015, 2016; Baresova et al., 2017).

2. WHAT IS AOM 2.1. Origin of AOM Algal blooms are formed by various phytoplankton species, belonging to cyanobacteria, green algae, diatoms, dinoflagellates or cryptophytes (Paerl et al., 2001). The concentrations of algal/cyanobacterial cells within the algal bloom have been reported to reach up to the millions of cells per mL in natural surface waters (Dixon et al., 2011). Consequently, considerable amounts of AOM are being produced. A part of the AOM is generated extracellularly, resulting from the metabolic processes of living algal/cyanobacterial cells, and is referred to as extracellular organic matter (EOM). For example, in laboratory cultures, EOM concentrations in a stationary growth phase reached approximately 20, 40 and 60 mg L-1 DOC (dissolved organic carbon2) for cell concentrations of 12·106, 12·104, and 18·106 mL-1 (different species), respectively (Pivokonsky et al., 2014). Furthermore, when the phytoplankton cells die and decompose, a mixture of compounds named cellular organic matter (COM3) is being formed. Especially when phytoplankton blooms decay, a sudden release of large amounts of COM may rapidly similar meaning. Thus, the terms ‘flocculation’ and ‘coagulation’ are considered equal in this chapter and the term ‘flocculation’ is preferred. 2 As AOM is a mixture of various organic compounds, its concentrations are commonly being expressed as DOC (dissolved organic carbon) in mg L-1 DOC. 3 Also the term ‘IOM – intracellular organic matter’ is sometimes being used in this sense (Pivokonsky et al., 2006; Fang et al., 2010; Li et al., 2012). Additionally, ‘SOM – surface-retained organic matter’ is distinguished in some studies (Takaara et al., 2010).

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alter overall water quality (Zhang et al., 2010). Additionally, COM can also occur as a result of water treatment processes that induce cell rupture, e.g., pre-oxidation (Ma et al., 2012b; Coral et al., 2013).

2.2. Composition of AOM Algal organic matter contains a wide range of organic compounds, including proteins, peptides, amino acids, mono-, di-, oligo-, and polysaccharides, lipids, fatty acids, nucleic acids, amino sugars, lipopolysaccharides, aldehydes, etc. (Bertocchi et al., 1990; Myklestad, 1995; Paerl et al., 2001; Her et al., 2004; Nguyen et al., 2005; Pivokonsky et al., 2006, 2014; Huang et al., 2007; Henderson et al., 2008a; Markou et al., 2012; Laurens et al., 2014; Villacorte et al., 2015). AOM might also comprise highly undesirable compounds such as harmful toxins, e.g., hepatotoxic microcystins, nodularins and cylindrospermopsins, or neurotoxic anatoxins and saxitoxins (Carmichael, 1992; Dixon et al., 2010; Pearson et al., 2016). Additionally, substances that deteriorate organoleptic properties of water (taste and odour compounds) can be also present, e.g., geosmin or 2-methylisoborneol (Paerl et al., 2001; Huang et al., 2007; Zhang et al., 2010; Li et al., 2012). An exact composition of both COM and EOM is species-dependent and is also given by a growth stage of the phytoplankton (Pivokonsky et al., 2006, 2014; Henderson et al., 2008a). In laboratory cultures, four growth phases are being distinguished, i.e., lag, logarithmic/exponential (exp), stationary (stat) and decline phase, where the amounts and character of AOM evolve as the growth proceeds (Pivokonsky et al., 2006, 2014; Baresova et al., 2017). Additionally, environmental conditions, such as nutrient status (Myklestad, 1995), temperature or light intensity (van der Westhuizen and Eloff, 1985) affect the production and properties of AOM. The composition and character of AOM significantly influence its appearance in the drinking water treatment processes. For example, peptide/protein and non-proteinaceous fraction of AOM have been proven to behave differently in flocculation experiments (Pivokonsky et al., 2009b, 2016), as described in detail in section 3.

2.2.1. AOM Peptides/Proteins Peptides and proteins often form a substantial part of AOM, comprising up to 6070% (Pivokonsky et al., 2006, 2009b). In laboratory cultures, the relative portion of peptides/proteins in EOM was observed to increase during the cultivation of different phytoplankton species (cyanobacteria Anabaena flos-aquae4 and Microcystis aeruginosa,

4

recognized as Dolichospermum flos-aquae since 2009

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diatom Fragilaria crotonensis, green algae Chlamydomonas geitleri and Scenedesmus quadricauda). DOCP (DOC constituted by peptides/proteins) in the stationary growth phase was the highest for cyanobacteria (up to 47%) and the lowest for green algae (max 28%) (Pivokonsky et al., 2006, 2014). However, the greatest content of peptides/proteins was determined as a part of COM, of which DOCP accounted for 60-66% for M. aeruginosa (Pivokonsky et al., 2006, 2009b, 2012, 2014; Safarikova et al., 2013), 53% for F. crotonensis (Pivokonsky et al., 2014), 51% for A. flos-aquae (Pivokonsky et al., 2006), 43% for Merismopedia tenuissima (Baresova et al., 2017), 33% for C. geitleri (Pivokonsky et al., 2014) and 29% for S. quadricauda (Pivokonsky et al., 2006).

2.2.2. AOM Carbohydrates Besides peptides/proteins, carbohydrates are also often contained in AOM in significant amounts (Myklestad, 1974, 1995; Laurens et al., 2014; Villacorte et al., 2015). For example, the carbohydrate proportion of AOM dry weight was reported to be up to 90% in case of marine diatoms (Myklestad, 1974) and up to approximately 50% in green algae (Chlorella sp., Scenedesmus sp.). Similar to the content of peptides/proteins, the carbohydrate content of AOM has been observed to change during the growth of the culture (Laurens et al., 2014). AOM carbohydrates are usually composed of mainly arabinose, fucose, galactose, glucose, mannose, rhamnose, ribose, or xylose (Bertocchi et al., 1990; Myklestad, 1995; Nicolaus et al., 1999; Huang et al., 2007; Markou et al., 2012). Additionally, uronic acids (glucuronic acid, galacturonic acid), aminosugars (glucosamine, galactosamine, mannosamine) or methyl-sugars might be also present (Bertocchi et al., 1990; Nicolaus et al., 1999). A substantial part of algal carbohydrates is often comprised of polysaccharides formed by some of these subunits (Myklestad, 1995). The polysaccharides are species-specific, including e.g., glycogen in cyanobacteria or starch in green and red algae (Markou et al., 2012).

2.3. Properties of AOM Related to Water Treatment Due to its varying compositions, algal organic matter differs in several characteristics that alter its flocculation behaviour. Apart from the division into peptides/proteins and non-proteinaceous matter, properties of AOM that are substantially important from the perspective of water treatment include (1) the degree of hydrophilicity/hydrophobicity, (2) molecular weight (MW) distribution and (3) surface charge (Pivokonsky et al., 2016).

2.3.1. Hydrophilicity/Hydrophobicity Algal organic matter is usually divided into three groups according to the level of its hydrophobicity, i.e., into hydrophilic (HPI), hydrophobic (HPO) and transphilic (TPI) fraction (Her et al., 2004; Henderson et al., 2008a; Pivokonsky et al., 2014; Baresova et

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al., 2017). Additionally, HPI compounds can be further distinguished as neutral hydrophilic (NHPI) and charged hydrophilic (CHPI) (Li et al., 2012). It was revealed that AOM is predominantly hydrophilic, with the HPI fraction ranging from 54-90% among various species (Anabaena flos-aquae, Aphanizomenon flos-aquae, Asterionella formosa, Chlamydomonas geitleri, Chlorella vulgaris, Fragilaria crotonensis, Merismopedia tenuissima, Microcystis aeruginosa, Scenedesmus subspicatus). Besides the species-dependence, the portion of HPI material was found to differ in EOM versus COM, while the cellular material was determined to be more hydrophilic. Small variations in the HPI/HPO/TPI proportions were also observed between EOM acquired in exponential and stationary growth phases (Her et al., 2004; Henderson et al., 2008a; Li et al., 2012; Pivokonsky et al., 2014; Baresova et al., 2017; Goslan et al., 2017). Percentage representation of hydrophilic, hydrophobic and transphilic fractions in EOM and COM of selected species is shown in Table 1. The highly hydrophilic nature of AOM is supported by low SUVA5 values (ranging from 0.34-1.7 L m-1 mg-1) ascertained for organic matter produced by a number of species (Her et al., 2004; Henderson et al., 2008a; Fang et al., 2010; Li et al., 2012; Goslan et al., 2017). Table 1. Percentage representation of hydrophilic (HPI), hydrophobic (HPO) and transphilic (TPI) material in exponential-phase EOM (EOMexp), stationary-phase EOM (EOMstat) and COM of different phytoplankton species. Species A. flos-aquaea Aph. flos-aquaea A. formosab C. geitleric C. vulgarisb F. crotonensisc Melosira sp.b M. tenuissimad M. aeruginosac S. subspicatusa a

EOMexp proportion (%) HPI HPO TPI 73 14 13 71 21 8 63 24 13 74 17 9 69 27 4 -

EOMstat proportion (%) HPI HPO TPI 81 8 63 18 68 19 13 73 22 5 72 11 17 74 19 7 60 32 8 69 28 3 54 26 -

COM proportion (%) HPI HPO TPI 89 10 1 90 8 2 77 7 16 87 12 1 -

Goslan et al., 2017; bHenderson et al., 2008a; cPivokonsky et al., 2014; dBaresova et al., 2017.

The HPI fraction of organic matter include carbohydrates, amino acids and other organic acids, aldehydes, ketones, etc. (Edzwald, 1993). HPO compounds (determined to form approximately 8-32% of EOM and 7-12% of COM) include humic and fulvic acids, aromatic acids and amines, and high-MW alkyl carboxylic acids (Edzwald, 1993; 5

SUVA (specific UV absorbance) corresponds to the aromaticity of a sample. It is defined as the UV absorbance at a given wavelength (254 nm) normalized for DOC concentration.

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Pivokonsky et al., 2014; Baresova et al., 2017; Goslan et al., 2017). AOM peptides/proteins contain both HPI and HPO parts because they are composed of hydrophilic as well as hydrophobic amino acids. However, in aqueous solutions, the HPO segments tend to cluster together, leading to protein folding, while the HPI regions are exposed to the surroundings (Creighton, 1993).

2.3.2. Molecular Weight Distribution AOM contains components of molecular weights (MW) ranging from several hundred daltons to hundreds of kilodaltons (Pivokonsky et al., 2006, 2014; Henderson et al., 2008a; Fang et al., 2010; Li et al., 2012). Low-MW fractions (< 10 kDa) include substances such as aldehydes, amines, amino acids, peptides, and mono-, di- and oligosaccharides (Nguyen et al., 2005; Huang et al., 2007). Compounds with medium MW (10-100 kDa) are, for example, polypeptide molecules, such as enzymes and their components (Pivokonsky et al., 2014) and high-MW fraction (> 100 kDa) comprises of biopolymers like proteins and polysaccharides. These polymers can form a significant portion of AOM (Myklestad, 1995; Henderson et al., 2008a; Pivokonsky et al., 2014). For example, proteins > 100 kDa accounted for 25 and 22% of EOM and COM, resp., for Microcystis aeruginosa stationary-phase peptide/protein fraction. Non-proteinaceous matter of several species (Chlamydomonas geitleri, Fragilaria crotonensis, M. aeruginosa) contained 20-27% (EOM) and 22-35% (COM) with MWs of > 100 kDa (Pivokonsky et al., 2014). Henderson et al. (2008a) quantified even AOM fraction > 500 kDa in M. aeruginosa and determined it to reach 25%.

Figure 1. Molecular weight fractionation of (a) COM peptides/proteins and (b) non-proteinaceous cellular organic matter of different phytoplankton species (Chlamydomonas geitleri, Chlorella vulgaris, Fragilaria crotonensis, Merismopedia tenuissima and Microcystis aeruginosa). Adapted from Pivokonsky et al. (2014), Baresova et al. (2017) and Naceradska et al. (2018).

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By contrast, substances with very low MW can also form a substantial part of AOM (Hoyer et al., 1985; Henderson et al., 2008a). E.g., 30% of Chlorella vulgaris AOM, 38% of M. aeruginosa AOM, 53% of Melosira sp. AOM and even 81% of Asterionella formosa AOM was determined to be < 1 kDa (Henderson et al., 2008a). More information on the proportion of high- and low-MW organics in AOM of different species is shown in Figure 1, where the difference between AOM peptides/proteins and non-proteinaceous matter is emphasized.

Figure 2. Molecular weight distributions of EOM and COM peptides/proteins of (a) Chlamydomonas geitleri, (b) Fragilaria crotonensis, (c) Merismopedia tenuissima and (d) Microcystis aeruginosa. EOM MWs were determined at exponential and stationary growth phases (EOMexp, EOMstat, resp.), COM was obtained at the stationary growth phase. Adapted from Pivokonsky et al. (2014) and Baresova et al. (2017).

The MW distribution differs not only between the diverse phytoplankton species, but also depends on the age of the culture and AOM fraction (i.e., EOM vs. COM). When the MWs of AOM peptides/proteins were analysed, COM was found to contain a much

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broader range of MW values compared to EOM in case of several phytoplankton species (Anabaena flos-aquae, C. geitleri, F. crotonensis, M. aeruginosa, Scenedesmus quadricauda), while some of the peptides/proteins were COM-specific (Pivokonsky et al., 2006, 2014). Additionally, changes in MW distribution were observed between exp and stat EOM, where the proportion of higher MW compounds usually increased with time, due to the exclusion of low-MW substances (Pivokonsky et al., 2014). Examples of AOM MW distribution of four different species are depicted in Figure 2.

2.3.3. Charge The charge of AOM is strongly pH dependent and is attributable to the presence of diverse functional groups that can release or accept proton, depending on the pH conditions (Creighton, 1993). It was found that AOM is negatively charged throughout a wide range of pH values (Bernhardt et al., 1985; Henderson et al., 2008a), e.g., Henderson et al. (2008a) determined negative zeta potential values of EOM derived from various species in the pH range 2-10. Nevertheless, the charge density varies among the species and their growth stage (Bernhardt et al., 1985; Paralkar and Edzwald, 1996; Henderson et al., 2008a). For example, the charge density of M. aeruginosa EOM at pH 7 decreased from 0.2 meq per 1 g DOC at the exponential growth phase to 0.1 meq per 1 g DOC at the stationary growth phase. On the contrary, the charge density of C. vulgaris at pH 7 increased from 0.9 to 3.2 meq per 1 g DOC from exp to stat phases (Henderson et al., 2008a). Additionally, distinct AOM constituents differ in their charge properties. AOM peptides/proteins are amphoteric due to the content of diverse functional groups (both acidic and basic, i.e., -OH, -COOH, -SH, -NH3+, =NH2+) (Creighton, 1993). Peptides/proteins with isoelectric points (pI) ranging from 4.8-8.1 were identified in COM of M. aeruginosa (Pivokonsky et al., 2012; Safarikova et al., 2013). Nevertheless, negative charge of peptides/proteins prevails within pH ranges relevant for water treatment (Pivokonsky et al., 2012). The charge of polysaccharides stems from the presence of uronic acids, containing weakly acidic -COOH groups (Hoyer et al., 1985). However, the non-proteinaceous fraction is generally considered to bear less ionisable groups and thus is less charged. For example, COM peptides/proteins produced by M. aeruginosa were reported to contain 100 mmol titratable functional groups per 1 g DOC (Safarikova et al., 2013), while non-proteinaceous COM of Chlorella vulgaris possessed about 14 mmol titratable functional groups per 1 g DOC (Naceradska et al., 2018). Similarly, alginate, an anionic polysaccharide, appeared to involve approx. 10 mmol COOH groups per 1 g DOC (Gregor et al., 1996).

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3. FLOCCULATION OF AOM A variety of chemicals have been trialled for coagulating algae and AOM including traditional metal coagulants aluminium sulphate (alum), ferric sulphate (FS), ferric chloride (FC) and inorganic polymers, for example polyaluminium chloride (PACl) and polyferric sulphate (PFS). Natural polymers, such as chitosan or cationic starch, have also been tested for coagulation of cell + AOM mixtures (Cheng et al., 2011; Vandamme et al., 2012, 2014; Garzon-Sanabria et al., 2013). In addition, alkaline flocculation, i.e., by chemical co-precipitation with calcium and magnesium salts of the culture medium under alkaline pH values, is used for algal biomass harvesting for biofuel production (Vandamme et al., 2012; González-Fernándes and Ballesteros, 2013; Vandamme et al., 2016; Branyikova et al., 2018). Most of the investigations into the flocculation of algae-laden waters have focused on algal and cyanobacterial cells (Henderson et al., 2008b, 2010; Cheng et al., 2011; Vandamme et al., 2012; Wyatt et al., 2012; Garzon-Sanabria et al., 2013; GonzalezTorres et al., 2014; Baresova et al., 2017). They found that algal cells easily combine with commonly used Al-based or Fe-based coagulants through electrostatic bridging between negatively charged algal cell surface and positively charged coagulant hydroxide precipitates at about neutral pH values (Henderson et al., 2008b; Wyatt et al., 2012; Gonzalez-Torres et al., 2014; Baresova et al., 2017; see Figure 3). At higher coagulant doses, sweep flocculation has also been reported to be influential (Wyatt et al., 2012; Gonzalez-Torres et al., 2014).

Figure 3. Flocculation mechanism of cells and coagulant.

The negative surface charge of algal cells arises from deprotonation of acidic groups (mostly -COOH) present at the cell surface or in EOM attached at the cell surface (Henderson et al., 2008b; Wyatt et al., 2012; González-Fernándes and Ballesteros, 2013). Wyatt et al. (2012) observed efficient flocculation of Chlorella zofingiensis cells even at alkaline pH values, which may be attributed to interactions between cationic amine

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groups on the cell surface with anionic coagulant precipitates, or when using sweep coagulation at higher coagulant doses (Duan and Gregory, 2003) or co-precipitation with calcium and magnesium salts. When natural polymers are used as coagulants, different coagulation mechanisms may be expected, as shown by Cheng et al. (2011) for flocculation of cells of Chlorella variabilis by chitosan. In this study, flocculation of Chlorella cells improved at pH 8.5 compared to pH 5.5 and 7, suggesting that hydrogen bonds between chitosan (a poly-glucosamine polymer with an isoelectric point around 6.5) and cell wall polysaccharides may be more important than electrostatic interactions. Several studies (Bernhardt and Clasen, 1991; Henderson et al., 2008b, 2010; Wyatt et al., 2012; Zhang et al., 2012) revealed a strong stoichiometric relationship between cell surface area and coagulant demand for spherical cells. The presence of EOM usually leads to the higher coagulant demand (Henderson et al., 2010; Ma et al., 2012b; Zhang et al., 2012), which is further elaborated in section 4.3. Compared to algal cells, flocculation of AOM is markedly less investigated and provides substantially lower removal efficiencies (Bernhardt et al., 1985, 1986, 1991; Widrig et al., 1996; Pivokonsky et al., 2009a, b; Henderson et al., 2010; Safarikova et al., 2013; Pivokonsky et al., 2012, 2015, 2016; Baresova et al., 2017; Naceradska et al., 2017; Tang et al., 2017; Naceradska et al., 2018). Henderson et al. (2010), for example, observed good cell removal (94-99%) for Microcystis aeruginosa, Chlorella vulgaris, Asterionella formosa and Melosira sp. by alum, while their EOM removal efficiency was 46-71%. Tang et al. (2017) recorded high removal efficiencies (> 90%) for cells of cyanobacterium Microcystis aeruginosa coagulating with PACl, but low removals for dissolved EOM (< 10%) and for cell-bound EOM (< 40%). Similarly, Baresova et al. (2017) obtained 99% cell removal efficiencies for cyanobacterium Merismopedia tenuissima and ferric sulphate, while its COM was reduced by 43-53% depending on the initial COM concentration. Similar to cell removal, AOM surface charge that is closely related to pH value is crucial for flocculation. AOM is usually removed at acidic pH values, at which AOM negatively charged functional groups interact with positively charged coagulant hydroxopolymers (Widrig et al., 1996; Hu et al., 2006; Pivokonsky et al., 2009a, b). To illustrate, Widrig et al. (1996), who examined the removal of EOM derived from green algae Scenedesmus quadricauda and Dictyosphaerium pulchellum and cyanobacterium Microcystis aeruginosa by alum and ferric chloride at two pH values, 5 and 8, showed that overall removals were improved at pH 5 (M. aeruginosa – 20%, S. quadricauda – 25%, and D. pulchellum – 50%) compared to pH 8 (5-10%). Likewise, Baresova et al. (2017) obtained the highest coagulation efficiencies for M. tenuissima COM at pH ranging between 5-6.5, while cells were preferably removed at pH 6-7.7, suggesting that different coagulation mechanisms were employed. Cells probably interacted through

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adsorption onto Fe-precipitates, whereas COM preferred charge neutralisation by Fehydroxopolymers. Pivokonsky et al. (2009a), who coagulated COM of M. aeruginosa by ferric sulphate and alum, recorded the highest removals, 50% for ferric sulphate and 40% for alum, at pH 4.5-6.5. However, the lowest coagulant residual concentrations, which must also be taken into consideration, were observed in different pH range for alum (pH 6.5-7) and narrower pH range for ferric sulphate (pH 6-6.5). Unsurprisingly, these pH ranges correspond to the lowest solubility of aluminium and ferric hydroxide precipitates (Stumm and Morgan, 1996). Furthermore, the study demonstrated higher removal efficiencies for proteinaceous (74% and 50%, respectively) than non-proteinaceous compounds (12% and 22%, respectively), for ferric sulphate and alum. Higher removal efficiencies for proteins (75% and 69%, respectively) than for saccharides (30% and 40%, respectively) were achieved also by Cui et al. (2016), who coagulated effluent organic matter from wastewater treatment plant by aluminium chloride and polyaluminium chloride (PACl). Several studies have, therefore, focused on coagulation behaviour of proteinaceous and non-proteinaceous compounds separately (Pivokonsky et al., 2012, 2015; Safarikova et al., 2013; Naceradska et al., 2018). The study on coagulation of peptides/proteins contained in COM of Microcystis aeruginosa showed that peptides/proteins were removed by ferric sulphate in the pH range of 4-6 owing to charge neutralization of peptide/protein negative surface (given by the presence of COOH groups) by positively charged hydrolysis products of ferric coagulant (Figure 4a). Moreover, adsorption of peptides/proteins onto ferric precipitates at pH 6-8 was observed at low COM/Fe ratio (COM/Fe < 0.33, Figure 4b). By contrast, at higher COM/Fe ratio (COM/Fe > 0.33), charge stabilization of Fe precipitates by peptides/proteins bound to its surface hindered flocculation at pH 6-8 (Figure 4c). In addition, peptide/protein flocculation was disturbed at pH of about 6.2 as a consequence of formation of dissolved Fe-peptide/protein complexes. However, this can be avoided by consistent optimization of pH conditions. The study by Pivokonsky et al. (2015) indicated that alum coagulates COM peptides/proteins of M. aeruginosa at pH values slightly higher (5-6.5) than in the case of ferric coagulant (Pivokonsky et al., 2012). Peptide/protein flocculation was also disturbed by formation of complexes between coagulant and peptides-proteins at pH of about 7 during the flocculation by alum. The difference in the pH values effective for coagulation using alum and ferric sulphate is attributed to a difference in the hydrolysis product distributions of Al and Fe (Stumm and Morgan, 1996). The only study investigating the flocculation of non-proteinaceous AOM was undertaken by Naceradska et al. (2018). Non-proteinaceous COM was gained from Chlorella vulgaris through protein precipitation. Only up to 25% of non-proteinaceous COM (mostly carbohydrates) was removed by flocculation by either alum or PACl in the optimized pH ranges 6.6-7.5 for alum and 7.5-9 for PACl. These pH values indicated that the prevailing coagulation mechanism was adsorption of non-proteinaceous COM onto aluminium hydroxide precipitates (Figure 5) rather than charge neutralization as stated

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for COM peptides/proteins (Pivokonsky et al., 2012). The low removals were attributed to high content of low-MW organics (< 10 kDa) in non-proteinaceous COM, which were disinclined to flocculate.

Figure 4. Flocculation mechanisms of COM proteins and coagulant: (a) pH = 4-6, (b) pH = 6-8, low COM/Fe ratio and (c) pH = 6-8, high COM/Fe ratio. Adapted from Pivokonsky et al. (2012).

Figure 5. Flocculation mechanisms of non-proteinaceous COM and coagulant.

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The reluctance of low-MW organics to flocculate was also ascertained for COM peptides/proteins (< 10 kDa) (Pivokonsky et al., 2012, 2015) and low-MW humic substances as a part of natural organic matter commonly occurring in surface water sources (Sillanpää et al., 2017). It should be noted that most cyanobacterial toxins are of low-MW, for instance microcystins have MW around 1 kDa, and therefore coagulation is largely ineffective for their removal (de Figueiredo et al., 2004). When flocculation performance of the most used coagulants is compared, it can be concluded that aluminium-based and ferric-based coagulants perform very similarly in AOM coagulation in terms of removal efficiencies under slightly shifted optimum pH values, given by different distribution diagrams of their hydrolysis products (Widrig et al., 1996; Pivokonsky et al., 2009a; Safarikova et al., 2013).

4. IMPACT OF AOM ON COAGULATION OF OTHER IMPURITIES 4.1. Inorganic Particles Studies that dealt with the impact of AOM on coagulation of inorganic particles showed that the AOM interacted with the inorganic particles and that the presence of AOM substantially changed the optimum pH for effective flocculation by ferric or aluminium coagulants (Bernhardt et al., 1985, 1986, 1991; Safarikova et al., 2013). Inorganic particles are often present in raw water, where they cause high turbidity, and they usually bear a negative charge in a wide range of pH values. The interactions between clay surfaces and organics were demonstrated in soils for lots of organic compounds, such as mono- and polysaccharides, amino acids, proteins, nucleic acids and humic substances (Goring and Bartholomew, 1952; Greenland, 1956; Pinck, 1962; Parfit and Greenland, 1970; Labille et al., 2005). Organic compounds that bear a charge (e.g., acidic polysaccharides, proteins) can interact with the negative charge of clays by electrostatic interactions. These are affected by pH of the solution, which governs dissociation constants of polar functional groups and thus the amount of charged groups in both clays and organic compounds (Pinck, 1962). For neutral compounds, several molecular mechanisms for adsorption via weak bonds were proposed: (1) substitution of interlayer water molecules solvating exchangeable cations (Parfit and Greenland, 1970), (2) hydrogen bonds between macromolecule hydroxyl and clay surface oxygens, or (3) hydrogen bonds between hydroxyl groups on sheet edges and macromolecule (Labille et al., 2005). Clay-organic interactions were ascertained also in cases of water treatment. For instance, Bernhardt and co-workers (Bernhardt et al., 1985, 1986, 1991), who investigated the effect of EOM of MW > 2 kDa excreted by several algal species on the

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coagulation of inorganic quartz particles, concluded that EOM polymers (neutral and acidic polysaccharides) were able to attach to the negatively charged surface of quartz particles by means of hydrogen and covalent bonds. Likewise, a study by Safarikova et al. (2013) suggested that cellular peptides/proteins of M. aeruginosa interact electrostatically (though -NH3+ and =NH2+ groups) with the negatively charged surface of kaolin particles. In both cases, AOM and inorganic particles formed negatively charged clusters, which were then removable by both ferric and aluminium coagulants in the pH range, where Fe/Al formed hydrolytic products bearing a positive charge, i.e., at pH ranges of 4-6.5 in the case of Fe and 4.5-7 in the case of Al (Figure 6).

Figure 6. Flocculation mechanism of kaolin, COM proteins and coagulant. Adapted from Safarikova et al. (2013).

By comparison, in the absence of AOM, inorganic particles are flocculated at higher pH values through adsorption onto Fe/Al hydroxide precipitates provided by electrostatic interactions, exchanging reactions and hydrogen bonds (Shin et al., 2008). For instance, optimum pH values for kaolin removal are between 6 and 8 for ferric coagulants and between 7 and 8.5 for aluminium ones. It should be noted that kaolin interacted with Fe/Al hydroxopolymers also at lower pH values, but flocculation efficiency was low (Ching et al, 1994; Kim and Kang, 1998; Safarikova et al., 2013). In the presence of AOM, the negative charge in the system increased with increasing pH to alkaline values and electrostatic repulsions between negatively charged particles led to system stabilization. The key factor for flocculation of inorganic particles and AOM is the ratio of coagulant to organic matter or more precisely, the ratio of charges in the system (Bernhardt et al., 1985, 1991; Safarikova et al., 2013). Bernhardt et al. (1991) found that a critical mass Fe/DOC ratio for EOM removal was within the range of 2-3 mg (0.0360.054 mmol) Fe per 1 mg DOC depending on species. Above this ratio, a partial coating of the quartz particles surface by EOM polymers can lead to particle aggregation through polymer bridging and aid flocculation. Below this ratio, large coverage of quartz particles

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by EOM polymers enhances the stability of the dispersed system by steric and charge stabilization (Bache and Gregory, 2007) and impairs flocculation. Similar results were obtained also in the case of alginic acid, an polyuronic acid composed of two uronic acids (poly-D-mannuronic acid and L-guluronic acid), which was used as a model compound for EOM acidic polysaccharides (Bernhardt et al., 1985, 1986, 1991). Similar to the flocculation of AOM solely (section 3.), Safarikova et al. (2013) ascertained that highMW peptides/proteins were removed by flocculation, while low-MW ones were reluctant to flocculate.

4.2. Humic Substances In many regions, humic substances (HS), comprising humic and fulvic acids (HA and FA), constitute the majority of natural organic matter in surface waters and may also occur together with AOM (Knauer and Buffle, 2001). While a lot of emphasis has been put on removal of HS, very little attention has been paid to possible HS-AOM interactions and their simultaneous removal by flocculation. One of the rare investigations was done by Jiang et al. (1993) who flocculated cells of diatom Asterionella formosa and AOM excreted during its growth by four different inorganic coagulants (polyferric sulphate, ferric sulphate, aluminium sulphate, polyaluminium chloride) in the presence of HS. They ascertained that the addition of HS to the algae + AOM solutions lead to a reduction of flocculation performance with increasing concentration of HS. With a greater HS concentration, higher doses of coagulants were required to achieve overall charge neutralization and removals comparable to those in the absence of HS. On the other hand, several studies have demonstrated that HS is able to adsorb onto the surfaces of freshwater phytoplankton cells and that the HS-cell interactions are strongly dependent on pH value (Campbell et al., 1997; Vigneault et al., 2000; Knauer and Buffle, 2001). Campbell et al. (1997) have proposed two mechanisms for the adsorption of HS onto the phytoplankton cell surfaces: (1) hydrogen bonds and (2) the formation of hydrophobic bonds between the cell surface and the hydrophobic domain of the HS. Interactions between HS and microbial products, such as polysaccharides and proteins, were also observed during membrane filtration (Myat et al., 2014). Myat et al. (2014) investigated the impact of interactions between model compounds, sodium alginate and bovine serum albumin (BSA) as representative biopolymers, with humic acid on membrane fouling. They detected formation of aggregates between sodium alginate and BSA with humic acid by liquid chromatography and they also employed molecular dynamics simulations to provide insights into the interaction mechanisms. For the BSA-humic acid system, they showed that electrostatic, hydrophobic and hydrogen bonding were the dominant types of interactions predicted. For the alginate-

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humic acid system, the interactions predicted were divalent ion-mediated interactions only. The existence of interactions between HS and BSA was confirmed by Pivokonsky et al. (2015). Moreover, they found that HS interact also with cellular proteins of M. aeruginosa (MA) and that interactions between HS-BSA and HS-MA proteins have very similar consequences for flocculation. In both cases, the clusters of HS-BSA and HS-MA proteins were flocculated by alum with DOC removals of 83% and 80%, respectively, in the pH range 5.5-6.2 through a charge neutralization mechanism, i.e., positively charged Al-hydroxopolymers interacted with negatively charged functional groups of BSA/MA proteins and HS (Figure 7).

Figure 7. Flocculation mechanism of humic substances, COM proteins and coagulant. Adapted from Pivokonsky et al. (2015).

Interestingly, protein-HS interactions lead to significant reductions in coagulant dose. While optimized coagulant doses were 0.25, 0.40 and 1.10 mg Al mg-1 DOC for BSA, MA proteins and HS, respectively, Al doses of 0.16 and 0.28 mg Al mg-1 DOC were sufficient for flocculation of HS-BSA and HS-MA proteins mixtures. Similar to flocculation of single AOM (section 3.) and AOM together with inorganic particles (section 4.1.), high-MW proteins underwent flocculation, while peptides of MW < 10 kDa formed residual organics after flocculation.

4.3. Algal Cells Most studies that dealt with the simultaneous flocculation of AOM and algal cells, have focused on the flocculation of algal cells in the presence of extracellular organic matter, either produced by cells during their growth into cultivation media in water treatment or during the harvest of algal biomass (Bernhardt and Clasen, 1991; Henderson et al., 2010; Vandamme et al., 2012; Garzon-Sanabria et al., 2013; Wu et al., 2012;

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González-Fernándes and Ballesteros, 2013; Branyikova et al., 2018), or EOM/COM released by oxidation processes employed prior to flocculation in water treatment (Ma and Liu, 2002; Plummer and Edzwald, 2002; Henderson et al., 2008b; Ma et al., 2012a, b; Wang et al., 2013). It was found that the presence of EOM increased the amount of required coagulant (Henderson et al., 2010; Vandamme et al., 2012; Garzon-Sanabria et al., 2013). For example, Garzon-Sanabria et al. (2013) reported that during flocculation of Nannochloropsis salina, EOM increased demand of various coagulants. For 90% flocculation efficacies, a 3-fold more of aluminium chloride, a 7-fold dose of synthetic cationic polymers and almost a 10-fold more of chitosan was needed. Similarly, Vandamme et al. (2012) showed that a 6-fold dose of aluminium sulphate, a 9-fold dose of chitosan and about a 4.5-fold dose of cationic starch was required for 85% removals of Chlorella vulgaris cells in the presence of EOM carbohydrates compared to flocculation of cells in the absence of EOM carbohydrates. Moreover, Wu et al. (2012) ascertained that the release of algal polysaccharides reduced alkaline flocculation efficiencies for algal cells of five species, but this could be mitigated by a further increase in pH values. On the other hand, Branyikova et al. (2018) reported that COM isolated from C. vulgaris, which contained a large proportion of non-peptide fractions (95%), showed little interference in alkaline flocculation of C. vulgaris cells. The study by Henderson et al. (2010) revealed the stoichiometric relationship between coagulant demand and charge density of algae + EOM system and further reported that coagulant demand decreased as molecular mass of EOM increased. Moreover, they pointed out that, in the case of some algal species (e.g., C. vulgaris), charge density is predominantly associated with the EOM component. On the other hand, some studies observed a positive influence due to the presence of high-MW EOM and/or COM released after pre-oxidation on the flocculation of algal cells, since algal biopolymers acted as a polymer coagulant aid (Ma and Liu, 2002; Henderson et al., 2010; Ma et al., 2012a; Wang et al., 2013). High-MW compounds easily combine with coagulants, promote flocculation and cell removal, most likely through adsorptive bridging. However, the release of COM and degradation of EOM/COM may have not only beneficial but also detrimental effects on flocculation, depending on oxidizer dose, pH value and the properties of EOM/COM (Hoyer et al., 1987; Paralkar and Edzwald, 1996; Henderson et al., 2008b; Ma et al., 2012a, b; Coral et al., 2013; Wang et al., 2013). Overdosing of pre-oxidant leads to cell lysis, releasing undesirable toxins or taste and odour compounds, and to EOM/COM degradation to lowMW compounds which may then be difficult to flocculate (Hoyer et al., 1987; Henderson et al., 2008b; Ma et al., 2012a, b). The positive impact of COM compounds on flocculation of algal cells was also observed by Baresova et al. (2017). In their study, COM did not originate from pre-oxidation, but was extracted from cells and then dosed into cell suspensions. They found that during flocculation of Merismopedia tenuissima

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cells, COM served as a cationic polymer coagulation aid and that the presence of COM shifted the optimum pH values for flocculation. While the cells were removed by adsorption onto coagulant precipitates (Fe-oxide-hydroxides) at around neutral pH, the COM + cell mixtures underwent charge neutralisation by Fe-hydroxopolymers within moderately acidic pH (5-6.5). Furthermore, coagulant doses for COM + cell mixtures were even slightly lower than those for single COM flocculation and the achieved DOC removals for COM + cell mixtures (37-57%) were comparable to the single COM flocculation (43-53%, rising with the increasing initial COM concentration). The high cell removals (up to 99%) were obtained in both the presence and absence of COM. The beneficial effect of COM on flocculation of M. tenuissima cells stemmed from bridging cells by high-MW COM, mainly on basis of hydrogen bonds and electrostatic interactions (Figure 8).

Figure 8. Flocculation mechanism of cells, COM and coagulant. Adapted from Baresova et al. (2017).

5. AOM AS A COAGULANT Natural polymeric materials are increasingly used in water and wastewater treatment as a coagulant or coagulant aid. The primary flocculation mechanism is ‘bridging’ which involves adsorption of the polyelectrolyte molecule from solution onto the surface of suspended particles. The most commonly used natural polymers are chitosan, alginate, starch and extract from seeds of Moringa oleifera. Since alginates bear a strong resemblance to algal products, it can be assumed that some compounds contained in AOM may also serve as coagulants. For instance, Devrimci et al. (2012) showed that calcium alginate proved to be a successful coagulant for turbid waters containing clay (predominantly smectite) and that calcium ions eased alginate-clay interaction.

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As stated in section 4.1., many studies, investigating the processes in soils, demonstrated that natural organic compounds, such as mono- and polysaccharides, amino acids, proteins, nucleic acids and humic substances adsorb onto clay surfaces by a range of mechanisms. To illustrate, Labille et al. (2005) ascertained that bacterial polysaccharides (dextran, succinoglycan, YAS34, xanthan, MWAP71, rhamsan, RMDP17) are able to attach to and subsequently flocculate Na-montmorillonite particles in the presence of CaCl2, which screened electrostatic repulsions between polysaccharides and Na-montmorillonite. The study further showed that flocculation of charged polysaccharide succinoglycan, which carries negative charge due to acidic moieties, was favoured at pH values below 6 due to electrostatic interactions between polysaccharide carboxyl groups and positively charged sheet edges of clay. At higher pH values, deprotonated sheet edges of Na-montmorillonite prevented such interactions and decreased flocculation efficiency was observed. Only a handful of studies on the effect of AOM as a coagulant have been conducted (Paralkar and Edzwald, 1996; Safarikova et al., 2013; Pivokonsky et al., 2015; Baresova et al., 2017). Several studies suggest that autoflocculation of algal cells in algal biomass harvesting for biofuel may be induced by extracellular polymeric substances (EPS) as reviewed by González-Fernándes and Ballesteros (2013). Carbohydrates are the main constituents of EPS, together with proteins in a lesser extent. Regarding drinking water treatment, a study by Paralkar and Edzwald (1996) pointed out that EOM produced by diatom Cyclotella sp., green algae Scenedesmus quadricauda and Chlorella vulgaris can interact with positively charged latex particles during experiments conducted at pH 7. Nevertheless, only EOM of Cyclotella sp., which contained the highest percentage of high-MW material, flocculated latex particles into aggregates that underwent sedimentation. As stated in section 4.1., Safarikova et al. (2013) observed electrostatic interactions between M. aeruginosa cellular peptides/proteins and kaolin particles. At pH values above 4.5, these interactions did not lead to aggregate formation due to electrostatic repulsions between peptide/protein-kaolin clusters and the addition of positively charged Al/Fe coagulant was necessary to induce flocculation. Nevertheless, at pH < 4.5, the negative charge of both kaolin and peptides/proteins was suppressed by protonation of their functional groups (especially -COOH groups of peptides/proteins), which enabled more peptide/protein-kaolin interactions and subsequent flocculation (Figure 9a). The turbidity removal efficiencies remained equal to those in the presence of coagulant, while DOC removal efficiencies decreased from 7080% to 45%. Similarly, Pivokonsky et al. (2015) ascertained that protonation of functional groups relating to a reduction in negative charge resulted in the flocculation of M. aeruginosa cellular peptides/proteins and humic substances at pH < 4 in the absence of coagulant (Figure 9b). DOC reductions of 55-69% were recorded, increasing with higher protein/humic ratio.

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Figure 9. Flocculation mechanisms of (a) kaolin and COM proteins (adapted from Safarikova et al., 2013), (b) humic substances and COM (adapted from Pivokonsky et al., 2015) and (c) cells and COM proteins (adapted from Baresova et al., 2017).

Furthermore, Baresova et al. (2017) found that the interactions of COM of Merismopedia tenuissima with its cells (mentioned in section 4.3.) resulted in flocculation at a pH range 3.5-4.5 with DOC and cell removal efficiencies comparable to those achieved in the presence of Fe coagulant. COM-cell flocculation was also attributed to protonation of -COOH groups of both COM and cell surface at low pH values and the attachment of COM to cells via hydrogen bonds and attractive electrostatic interactions (Figure 9c).

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6. INFLUENCE OF AOM ON FLOC PROPERTIES Floc properties, such as size, structure, shape, strength or settling velocity, are important parameters for the downstream treatment processes, i.e., separation by sedimentation, flotation and filtration. Each of these technological steps requires different flocs for their successful separation. Small (generally < 50-60 µm) and dense flocs are suitable for a single-stage separation by sand filtration (Ngo et al., 1995; Bubakova and Pivokonsky, 2012). For DAF (dissolved air flotation), Edzwald (1995) recommended producing strong flocs with particle size distributions in the range 10-30 µm (or 25-50 µm in Edzwald, 2010); however, Vlaški et al. (1997) reported that larger flocs (> 50 µm) formed by very low shear rate (G = 10 s-1) and hence having low density, resulted in efficient DAF as well. Finally, sedimentation is generally considered to be suitable for removal of large (> 100 µm) and dense flocs which have high settling velocities (e.g., Edzwald, 1995). Generally, floc properties are influenced by several basic parameters: the composition (type) and concentration of floc components, i.e., impurities to be removed and the coagulant; the shear rate (velocity gradient, G) and the time of its action (flocculation time). The properties of algal/cellular organic matter flocs have only been examined marginally thus far; however, some works concerning AOM, sometimes together with algal/cyanobacterial cells, have been published in recent years (Henderson et al., 2006; Pivokonsky et al., 2009a, b; Gonzalez-Torres et al., 2014, 2017; Vandamme et al., 2014; Jiao et al., 2015; Chekli et al., 2017; Filipenska et al., 2018). Some of them examined either the influence of coagulant dose and type, or pH value on AOM floc properties. To illustrate, Chekli et al. (2017) evaluated the performance of TiCl4 and polytitanium tetrachloride (PTC) for the removal of AOM from a marine diatom Chaetoceros muelleri in comparison with conventional FeCl3 treatment. They found that PTC and TiCl4 reached higher removal efficiencies (in terms of turbidity, DOC and UV254) and made larger, stronger and more compact flocs than FeCl3. Gonzalez-Torres et al. (2014) examined the properties of flocs made of M. aeruginosa cells and its AOM using Al2(SO4)3 or FeCl3 as coagulants at pH 6 (lower coagulant dose, charge neutralisation mechanism) and 7 (higher coagulant dose, sweep flocculation mechanism). Ferric flocs were confirmed to be larger than alum flocs regardless of the pH value or coagulant dose. Within one coagulant type, the coagulant dose was another factor influencing the floc size, since a higher dose produced larger flocs. In the case of the constant both coagulant type and dose, the pH values also affected the size of flocs. Specifically, pH 7 resulted in larger flocs than pH 6. Floc strength was determined primarily by the coagulant dose, irrespective of coagulant type. Higher coagulant doses produced stronger flocs, the strongest of which being produced at the higher dose of Fe at pH 6.

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The others evaluated the influence of AOM on the properties of flocs made of other impurities, such as clay minerals or cells. Unfortunately, a direct comparison of floc properties reported by different researchers is made difficult because of the varying experimental conditions (different/unknown shear rates, different coagulant doses or various AOM compositions and concentrations). Yet some general conclusions can be made. The principal finding is that the presence of AOM increases the floc size (Vandamme et al., 2014; Filipenska et al., 2018). For instance, Vandamme et al. (2014) coagulated Chlorella vulgaris cells with and without AOM using alum, chitosan and cationic starch as coagulants, electro-coagulation and alkaline flocculation. Generally, AOM increased the floc size (up to ten times for chitosan). However, flocs formed using cationic starch remained of the same size irrespective of the AOM presence. A clear trend was observed by Filipenska et al. (2018) who coagulated kaolinite and COM proteins of M. aeruginosa (separately and together) using Al and Fe salts as coagulants. In all cases COM proteins definitely caused the floc size to increase. However, the structure of flocs was more influenced by the coagulant type than by the presence of COM as the most compact and regular (in shape) flocs were Al-kaolinite and Al-COM flocs. Henderson et al. (2006) reported that flocs created from C. vulgaris cells and EOM were larger, but weaker, than flocs formed by inorganic particles (kaolin) or NOM (humic matter). Unfortunately, the tests with single cells without EOM have not been made, therefore it is not possible to evaluate the specific EOM contribution to the resulting floc size. Moreover, Pivokonsky et al. (2009b), who coagulated COM of M. aeruginosa with ferric sulphate, reported that COM concentration considerably affected the floc size, with lower COM concentration producing smaller flocs. The influence of the origin and composition of AOM on the floc characteristics can be demonstrated by research conducted by Gonzalez-Torres et al. (2017). They coagulated cells and associated EOM of C. vulgaris and M. aeruginosa by alum and used reflectance Fourier transform infrared (FTIR) imaging for biochemical characterisation of the associated flocs. M. aeruginosa flocs were measurably more uniform and smaller than C. vulgaris flocs and visibly more dense, which was attributed to the difference in AOM concentration and composition. The large flocs of C. vulgaris were characterized by a homogenous distribution of proteins and polysaccharides across the floc, indicative of high glycoprotein content. In contrast, the smaller but stronger flocs of M. aeruginosa had localized areas of increased protein concentration at the edge of regions which were absent of proteins and polysaccharides (and thus potentially comprising coagulant). Flocculation mechanisms and inter-particle interactions (mentioned in previous sections) acting within flocs also seem to influence the floc properties. Filipenska et al. (2018) pointed out an interesting phenomenon. When floc size

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and shear rate were plotted in a log-log plot6, a change in γ constant at approximately G ~ 120 s-1 for all types of flocs and an additional change in γ for COM flocs, between G of 40 to 50 s-1 and 60 to 70 s-1 for Al and Fe, respectively, could be observed (Figure 10).

Figure 10. Floc size vs. shear rate log-log plots of six different types of flocs. A change in γ constant at approximately G ~ 120 s-1 for all types of flocs and an additional change in γ for COM flocs, between G of 40 to 50 s-1 and 60 to 70 s-1 for Al and Fe, respectively, can be observed. Adapted from Filipenska et al. (2018).

The authors attributed these changes to different intermolecular interactions (hydrogen bonding or hydrophobic interaction) that are not able to withstand the hydrodynamic force when shear rate is increased above certain levels.

CONCLUSION This review shows that flocculation is a useful technology for the treatment of algaeladen waters. Specific outcomes and further research needs can be summarized as follows: 6

The dependence of the floc size on the shear rate is described by a decreasing power function (e.g., Parker et al., 1972) dav/max = CG-2γ, where dav/max is the average or maximal diameter of flocs in the system, G is the shear rate (global, average, mean) and C and γ are constants that include parameters such as the composition and concentration of contaminants, type and dose of coagulant and reaction pH (determining the attractive forces between individual floc components) and the type of flow or energy dissipation (the effect of hydrodynamics).

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AOM is a mixture of various organic compounds (e.g., peptides/proteins, carbohydrates, etc.) that behave differently during flocculation due to their diverse properties, such as the degree of hydrophobicity, MW distribution and charge. Determination of these characteristics can contribute to optimizing removal of AOM and to elucidating the involved mechanisms. Flocculation effectively removes algal cells and algae-derived organic substances of higher molecular weights, but is ineffective in removing those of low-MWs (including cyanobacterial toxins) and thus other treatment needs to be employed for their removal. Flocculation seems to be an effective pre-treatment to improve the performance and reduce the cost of downstream processes, such as adsorption onto activated carbon or membrane filtration, which are susceptible to the presence of biopolymers in source water. Optimization of flocculation pH is crucial for efficient AOM removal. For removal of algal cells and whole COM, suitable pH values lie in the range 6-8 and 5-6.5, respectively, for Al-based or Fe-based coagulants. The latter is similar to COM proteins (pH 4-6.5). For non-proteinaceous matter, the optimum pH lies in the alkaline range due to a different flocculation mechanism (see Figure 11). Higher removal efficiencies (70-80%) are achieved for peptides/proteins than for non-proteinaceous organics (< 25%). Flocculation of non-proteinaceous COM and also species-specific differences in flocculation behaviour require further investigation. Polymers contained in algal organic matter can act as polymer aids and enhance the removal of other impurities (inorganic particles, humic substances, cells). However, at this time studies are limited to a few algal/cyanobacterial species and extension of this research on more species would be helpful. Floc size decreases and density increases with increasing shear rate, ferric flocs being larger than alum flocs. The presence of AOM results in an increase of the floc size, where COM concentration has a proportional relationship to floc size. The floc properties also depend on the AOM origin (e.g., microorganism species), and are influenced by the intermolecular interactions acting within flocs. However, very few studies concerning properties of AOM flocs have been published thus far and it is almost impossible to compare their results because of diverse input parameters, such as coagulant/AOM concentration ratio. Therefore, comparative studies would substantially advance the knowledge on AOM floc properties.

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Removal efficiencies correspond to reductions in AOM concentration (expressed as dissolved organic carbon concentration). *Algal cells removal efficiencies correspond to reductions in optical densities. Figure 11. Optimal pH ranges for efficient removal of AOM, AOM together with other impurities and AOM removal efficiencies. Based on Pivokonsky et al. (2012, 2015), Safarikova et al. (2013), Baresova et al. (2017) and Naceradska et al. (2018).

ACKNOWLEDGMENTS The research project was funded by the Czech Science Foundation under the Project No. 18-14445S with institutional support RVO: 67985874. The authors acknowledge the financial assistance on this project.

REFERENCES Bache, D. H. & Gregory, R. (2007). Flocs in Water Treatment (1st). London, UK: IWA Publishing. Baresova, M., Pivokonsky, M., Novotna, K., Naceradska, J. & Branyik, T. (2017). An application of cellular organic matter to coagulation of cyanobacterial cells (Merismopedia tenuissima). Water Research, 122, 70-77. Bernhardt, H. & Clasen, J. (1991). Flocculation of microorganisms. Journal of Water Supply: Research and Technology – AQUA, 40(2), 76-87.

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Vandamme, D., Beuckels, A., Vadelius, E., Depraetere, O., Noppe, W., Dutta, A., Foubert, I., Laurens, L. & Muylaert, K. (2016). Inhibition of alkaline flocculation by algal organic matter for Chlorella vulgaris. Water Research, 88, 301-307. Vandamme, D., Foubert, I., Fraeye, I. & Muylaert, K. (2012). Influence of organic matter generated by Chlorella vulgaris on five different modes of flocculation. Bioresource Technology, 124, 508-511. Vandamme, D., Muylaert, K., Fraeye, I. & Foubert, I. (2014). Floc characteristics of Chlorella vulgaris: Influence of flocculation mode and presence of organic matter. Bioresource Technology, 151, 383-387. Vigneault, B., Percot, A., Lafleur, M. & Campbell, P. G. C. (2000). Permeability changes in model and phytoplankton membranes in the presence of aquatic humic substances. Environmental Science and Technology, 34(18), 3907-3913. Villacorte, L. O., Ekowati, Y., Neu, T. R., Kleijn, J. M., Winters, H., Amy, G., Schippers, J. C. & Kennedy, M. D. (2015). Characterisation of algal organic matter produced by bloom-forming marine and freshwater algae. Water Research, 73, 216-230. Vlaški, A., van Breemen, A. N. & Alaerts, G. J. (1997). The role of particle size and density in dissolved air flotation and sedimentation. Water Science and Technology, 36(4), 177-189. Wang, L., Qiao, J., Hu, Y., Wang, L., Zhang, L., Zhou, Q. & Gao, N. (2013). Preoxidation with KMnO4 changes extra-cellular organic matter's secretion characteristics to improve algal removal by coagulation with a low dosage of polyaluminium chloride. Journal of Environmental Sciences, 25(3), 452-459. Widrig, D. L., Gray, K. A. & McAuliffe, K. S. (1996). Removal of algal-derived organic material by preozonation and coagulation: Monitoring changes in organic quality by pyrolysis-GC-MS. Water Research, 30(11), 2621-2632. Wu, Z., Zhu, Y., Huang, W., Zhang, C., Li, T., Zhang, Y. & Li, A. (2012). Evaluation of flocculation induced by pH increase for harvesting microalgae and reuse of flocculated medium. Bioresource Technology, 110, 496-502. Wyatt, N. B., Gloe, L. M., Brady, P. V., Hewson, J. C., Grillet, A. M., Hankins, M. G. & Pohl, P. I. (2012). Critical Conditions for Ferric Chloride-Induced Flocculation of Freshwater Algae. Biotechnology and Bioengineering, 109(2), 493-501. Zhang, X., Amendola, P., Hewson, J. C., Sommerfeld, M. & Hu, Q. (2012). Influence of growth phase on harvesting of Chlorella zofingiensis by dissolved air flotation. Bioresource Technology, 116, 477-484. Zhang, X., Fan, L. & Roddick, F. A. (2014). Feedwater coagulation to mitigate the fouling of a ceramic MF membrane caused by soluble algal organic matter. Separation and Purification Technology, 133, 221-226. Zhang, X. J., Chen, C., Ding, J. Q., Hou, A., Li, Y., Niu, Z. B., Su, X. Y., Xu, Y. J. & Laws, E. A. (2010). The 2007 water crisis in Wuxi, China: Analysis of the origin. Journal of Hazardous Materials, 182, 130-135.

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BIOGRAPHICAL SKETCH Martin Pivokonský Affiliation: Institute of Hydrodynamics of the Czech Academy of Sciences, Prague, Czech Republic Education: Institute for Environmental Studies, Faculty of Science, Charles University, Prague, Czech Republic 2016

2002

1999

Associate Professor in Environmental sciences Inaugural thesis: “Characterisation of algal organic matter and its influence on water treatment processes” Ph.D. degree in Environmental engineering Ph.D. thesis: “Influence of the velocity gradient and time of its application on the size characteristics of the aggregates formed during water treatment” M.S. degree in Environmental engineering

Research and Professional Experience: Scientific management of the departments at the Institute of Hydrodynamics; coordination and management of the research in the field of water treatment, coagulation, flocculation, hydrodynamics, filtration, sedimentation, adsorption, natural organic matter (NOM), algal organic matter (AOM) Supervision and guidance of the M.S. and Ph.D. students of the Institute for Environmental Studies, Faculty of Science, Charles University, Prague and the Department of Water Technology and Environment Engineering, Faculty of Environmental Technology, University of Chemistry and Technology, Prague Expertise and consultancy activity in the field of the drinking water treatment and technological audits of the waterworks, design of new technologies for suspension formation and separation, e.g., PP&A Water Consulting (Pretoria, South Africa); Sv. Trojice, Želivka, Kouty and Světlá nad Sázavou waterworks; AquaServis, Ltd.; Česká voda – Czech Water, Ltd. (Czech Republic), EMBA spol. inc. Professional Appointments: 06/2017 – Present Director Institute of Hydrodynamics of the Czech Academy of Sciences, Prague, Czech Republic 01/2014 – 05/2017 Deputy Director

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Institute of Hydrodynamics of the Czech Academy of Sciences, Prague, Czech Republic 2010 – Present Scientist – Associate Professor (10/2016 – present), Research Assistant (2010 – 9/2016) Institute for Environmental Studies, Faculty of Science, Charles University, Prague, Czech Republic 2007 – 12/2013 Head of Department of Mechanics of Fluids and Disperse Systems Institute of Hydrodynamics of the Czech Academy of Sciences, Prague, Czech Republic 2005 – Present Scientist Institute of Hydrodynamics of the Czech Academy of Sciences, Department of Mechanics of Fluids and Disperse Systems, Prague, Czech Republic Publications from the Last 3 Years: Naceradska, J., Novotna, K., Cermakova, L., Cajthaml, T. & Pivokonsky, M. (2018). Investigating the coagulation of non-proteinaceous algal organic matter: optimization of coagulation performance and identification of removal mechanisms. Journal of Environmental Sciences (submitted). Filipenska, M., Vasatova, P., Pivokonska, L., Cermakova, L., Naceradska, J. & Pivokonsky, M. (2018). Influence of COM-peptides/proteins on floc properties coagulated by metal salts at different shear rate. Langmuir (submitted). Branyikova, I., Filipenska, M., Urbanova, K., Ruzicka, M. C., Pivokonsky, M. & Branyik, T. (2018). Physicochemical approach to alkaline flocculation of Chlorella vulgaris induced by calcium phosphate precipitates. Colloids and Surfaces B: Biointerfaces, 166, 54-60. Angst, G., Mueller, C.W., Angst, Š., Pivokonský, M., Franklin, J., Stahl, P.D. & Frouz, J. (2018). Fast accrual of C and N in soil organic matter fractions following postmining reclamation across the USA. Journal of Environmental Management, 209, 216-226. Cermakova, L., Kopecka, I., Pivokonsky, M., Pivokonska, L. & Janda, V. (2017). Removal of cyanobacterial amino acids in water treatment by activated carbon adsorption. Separation and Purification Technology, 173, 330-338. Baresova, M., Pivokonsky, M., Novotna, K., Naceradska, J. & Branyik, T. (2017). An application of cellular organic matter to coagulation of cyanobacterial cells (Merismopedia tenuissima). Water Research, 122, 70-77. Naceradska, J., Pivokonsky, M., Pivokonska, L., Baresova, M., Henderson, R. K., Zamyadi, A. & Janda, V. (2017). The impact of pre-oxidation with potassium

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permanganate on cyanobacterial organic matter removal by coagulation. Water Research, 114, 42-49. Pivokonsky, M., Naceradska, J., Kopecka, I., Baresova, M., Jefferson, B., Li, X. & Henderson, R. K. (2016). The impact of algogenic organic matter on water treatment plant operation and water quality: A review. Critical Reviews in Environmental Science and Technology, 46(4), 291-335. Novotná, K., Barešová, M., Čermáková, L., Načeradská, J. & Pivokonský, M. (2016). Effect of cyanobacterial peptides and proteins on coagulation of kaolinite. European Journal of Environmental Sciences, 6(2), 83-89. Pivokonsky, M., Naceradska, J., Brabenec, T., Novotna, K., Baresova, M. & Janda, V. (2015). The impact of interactions between algal organic matter and humic substances on coagulation. Water Research, 84(1), 278-285.

In: Flocculation: Processes and Applications Editor: Eleonora Vollan

ISBN: 978-1-53614-339-3 © 2019 Nova Science Publishers, Inc.

Chapter 6

COMPARISON OF NATURAL COAGULANT AND CHEMISTRY IN TANNING WASTEWATER TREATMENT USING THE FLOCCULATION PROCESS Edilaine Regina Pereira1, Gustavo da Silva Souza2 and Joseane Débora Peruço Theodoro1 1

Department of Environmental Academic, Federal Technological University of Paraná, Londrina, Paraná, Brazil 2 Environmental Engineer - UTFPR- Londrina, Londrina, Brazil

ABSTRACT The leather tanning industry uses a large amount of toxic substances and water. Thus, it generates effluents with high polluting load. Due to the large amount of effluent generated by tanneries and the difficulty in their treatment, several studies have been proposed to minimize the environmental impacts caused by inappropriate disposal of this effluent. This study investigated the performance of natural coagulants Tanin compared to chemical coagulants aluminium sulphate and ferric chloride commonly used in the treatment of raw wastewater from tannery, by means of the physicochemical processes of coagulation, flocculation and sedimentation. Using jar tests methods, different concentrations for the coagulants (chemical and natural) were applied to the concerned effluent and it was assessed their efficiency in removing certain parameters such as apparent color COD, and turbity besides the behavior of electrical conductivity and pH. The results showed that for pH and electrical conductivity parameters, there was no significant variation after application of coagulant in relation to the raw effluent. By comparing the coagulants for colour parameter it was observed that the natural coagulant

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E. R. Pereira, G. da Silva Souza and J. D. P. Theodoro tanin had greater efficiency compared to the chemical ones, reaching 56.9% of removal, however, the aluminium sulphate was more efficient at removing COD, with 95% of removal. Therefore, it is noticed that the chemical coagulant aluminium sulphate was more successful for the majority of the analysed parameters in comparison to other coagulants.

Keywords: water treatment, organic coagulants, inorganic coagulants

1. INTRODUCTION In developed and developing countries, most of the environmental impacts generated are in the industrial sector. The industrial sector consumes a large part of natural resources and also generates many types of wastes that are normally dumped into the environment, more specifically into aquatic ecosystems, with or without adequate treatment. One of the productive processes that generate a considerable volume of liquid effluents is the leather tanning industry. These industries have a great potential for pollution, since the entire productive process of leather tanning consumes a large amount of water, and the current average total consumption of the Brazilian sector is estimated at 25-30 m3 of water/ton of salty skin, about of 630 liters of water/salt skin on average (PACHECO, 2005). As a consequence, a quantity of liquid effluents similar to the total water withdrawn, as well as solid waste, and the use of certain substances, such as sodium sulphide, hydrated lime, inorganic acids, aluminum, titanium and chromium, the latter being the main pollutant in tannery, used as a tanning agent in about 90% of the industry (BAYER, 2005). In view of the problem of the treatment and inadequate disposal of effluents, which may leave the quality of river water compromised since this is the destination of the treated effluents of the industries, an efficient treatment in the stations of the industry is necessary. An alternative currently under study is the substitution of chemical coagulants used in the treatment of effluents by natural coagulants, as a way of minimizing the impacts generated and modifies the composition of the sludge presented, making proposals more sustainable and efficient. The tannin has as one of its main advantages to present a reduction of contaminants present in the treated effluent through the performance in the clarification of effluents. Therefore, the objective of this research is to make a comparative application of the efficiency of the natural coagulant tannin and the chemical coagulants aluminum sulphate and ferric chloride already used in the industry for the treatment of tannery effluent.

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2. METHODOLOGY The effluent used in this research came from a leather tanning industry, industry located in the city of Ibiporã – PR, Brazil. The effluent was collected in the treatment system of the still raw industry, before the application of the coagulant used by the industry. After being collected, the effluent was sent for testing and experimental analysis at the Sanitation Laboratory of the Federal Technological University of Paraná - Campus Londrina. A pre-test was performed first, aiming at defining the most appropriate concentrations of the chemical and natural coagulants used. Thus, the following concentrations were obtained: for Tannin C1 3mgL-1, C2 6mgL-1, C3 9mgL-1; for aluminum sulfate C1 15mgL-1, C2 20mgL-1, C3 25mgL-1; and for ferric chloride C1 15mgL-1, C2 21mgL-1, C3 28mgL-1. Table 1. Parameters, equipment and methodology used in this research Parameters Apparent color pH Electric conductivity Solid series Chemical Oxygen Demand

Equipments Spectrophotometer HACH 4000 pH monitor mPA-210 Conductivity Meter Mca 150 Greenhouse SL 100, Muffle MA 385, Balance AW 220 Biodigestor Thermo Digestor 462, Spectrophotometer HACH 4000

Methodology* 2120 C 4500-H+ B 2510 A 2540 A 5220 A

To prepare the coagulants 100 g of each coagulant were weighed and diluted in 1 L of distilled water using a volumetric flask. After the concentrations of each coagulant were defined in the pre-test, these concentrations were added to the effluent in a coagulation/flocculation/sedimentation test using the Jar-test equipment. The methodology for the test in the Jar Test was adapted from Theodoro (2012). The parameters analyzed are described in Table 1 and are in accordance with APHA (2012). The statistical model used to perform the analysis of the values resulting from the four trials was the completely randomized design, in a factorial scheme. The statistical model considered the effect of the interaction between Coagulant and Concentration factors in addition to the effect of the Coagulant factor (in three levels) and the factor Concentration (in three levels). Thus, the multiplicative statistical model is given by equation 1:

Yijk    i   j  ij  eijk

(1)

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E. R. Pereira, G. da Silva Souza and J. D. P. Theodoro On what:      

Yijk = observation corresponding to the kth experimental unit submitted to the i-th level of the Coagulant factor and the jth level of the factor Concentration; : overall average common to all observations; i : effect of the ith level of the coagulant factor; j : effect of the jth level of the factor Concentration; ij: is the interaction effect between the i-th level of the Coagulant factor and the j-th level of the factor Concentration; eijk: component of the random error associated with observation Yijk.

For the analysis of variance and comparison of the means of the three variables, a level of significance of 10% was considered. The results of the analysis of variance were grouped in Table 2 as proposed by Martins (2006). Table 2. Model adopted to organize the results obtained with the analysis of variance Source of variation Coagulant Concentration Coagulant X Concentration Residue

GL

SQ

QM

FC

P-value

3. RESULTS The Table 3 shows the values with pH variation during sedimentation times. For the coagulant Tannin, it was observed that there was not a very significant variation in relation to the initial pH (12.97), and the greatest variation occurred in the time of 30 minutes, when the lowest concentration of 300 mgL-1 reached the value of 12.90. The three concentrations obtained similar values and a little below the initial one, varying from 12.90 to 12.92. The pH can be adjusted for an application of the Aluminum Sulphate, in this way, the pH must be improved to be removed. When analyzing the coagulant Ferric Chloride, it was observed that there was the greatest reduction in the pH value with the highest coagulant concentration, reaching 12.53. After this, it can be observed that there was an increase in pH values for all concentrations. When comparing the data obtained with CONAMA Resolution 430 (CONAMA, 2011), it is observed that even after the treatment done in the effluent, it does not fit into

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the standards of release standard in relation to pH, since the Resolution requires that the pH value is maintained between 5 and 9 to be released into a receiving body. In this case, the pH of the tannery effluent should be corrected so that its value becomes less alkaline and falls within the parameters required by the law for the pH parameter. There was no significant variation in the pH values for tannery effluent with both natural and chemical coagulants.

FeCl3

Al2(SO4)3

Tanin

Table 3. pH variation as a function of coagulant versus time Time (min) 10 20 30 40 Time (min) 10 20 30 40 Time (min) 10 20 30 40

[Tanin] = 3 mgL-1 R1 R2 Average 12.93 12.91 12.92 12.93 12.9 12.91 12.91 12.89 12.9 12.91 12.93 12.92 Al2(SO4)3 = 15 mgL-1 R1 R2 Average 12.67 12.67 12.67 12.63 12.66 12.65 12.69 12.69 12.69 12.69 12.67 12.68 [FeCl3] = 15 mgL-1 R1 R2 Average 12.66 12.62 12.64 12.67 12.67 12.67 12.65 12.69 12.67 12.69 12.69 12.69

[Tanin] = 6 mgL-1 R1 R2 Average 12.91 12.91 12.91 12.91 12.91 12.91 12.91 12.92 12.91 12.92 12.92 12.92 Al2(SO4)3 = 20 mgL-1 R1 R2 Average 12.66 12.68 12.67 12.68 12.66 12.67 12.7 12.69 12.69 12.69 12.69 12.69 [FeCl3] = 21 mgL-1 R1 R2 Average 12.65 12.67 12.66 12.65 12.68 12.66 12.66 12.67 12.66 12.67 12.68 12.67

[Tanin] = 9 mgL-1 R1 R2 Average 12.91 12.94 12.92 12.91 12.9 12.90 12.92 12.91 12.91 12.92 12.93 12.92 Al2(SO4)3 = 25 mgL-1 R1 R2 Average 12.66 12.68 12.67 12.68 12.67 12.67 12.68 12.68 12.68 12.7 12.69 12.69 [FeCl3] = 28 mgL-1 R1 R2 Average 12.63 12.63 12.63 12.63 12.65 12.64 12.65 12.65 12.65 12.63 12.67 12.65

Figure 1 shows the behavior of the coagulants adopted in the work for the percentage of removal vesus time of the apparent color. The effluent collected in crude form had a color value of 96.800 mgPtCo L-1. Figure 1a shows that for the tannin all the concentrations used reached an apparent color removal greater than 56%. When analyzing the efficiency of the Coagulant Aluminum Sulphate (Figure 1b) it is observed that the largest removal was 36%. It is noted that the removal of the chemical coagulant Aluminum Sulphate was lower than the percentage of removal of the natural coagulant Tanino which demonstrates the viability of the organic coagulant for the effluent in question. In Figure 1c when looking at the Ferric Chloride as a coagulant agent in the removal of apparent color, it was observed that it is not a promising agent in the removal of color, because there was an increase in the parameter in all the concentrations used.

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(a)

(b)

(c) Figure 1. Percentages of removal of the apparent color parameter as a function of time for the coagulants Tanino (a), Aluminum Sulphate (b) and Ferric Chloride (c).

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In a study carried out by Vaz (2010), a similar result was obtained concluding the author that when the ferric chloride is added with some excess to the effluent, part of it does not participate in the coagulation/flocculation reaction, being this in solution having an increase of the values of the apparent color parameter. Table 4. Comparisons of means by the Tukey’s test for the apparent color Time 1

2

3

4

Coagulant FeCl3 Al2 (SO4)3 Tanin FeCl3 Al2 (SO4)3 Tanin FeCl3 Al2 (SO4)3 Tanin FeCl3 Al2 (SO4)3 Tanin

Média 430,500 402,333 227,500 382,667 357,333 185,333 356,500 340,500 161,667 364,333 354,500 139,667

Tukey (α=10%) a a b a a b a a b a a b

Statistical analysis showed a P-value of 0.841 > 0.1, indicating that the interaction between the Coagulant and Concentration factors is not significant, at 10% significance and it is also noted that the Concentration is not significant (value- P = 0.928 > 0.1), but the effect of Coagulant was significant (P-value = 0.000 < 0.1). The same occurred for the second, third and fourth sedimentation times, thus, mean comparisons were performed only for Coagulant and are presented in Table 4, using the Tukey test. The organic coagulant Tanino presented in all times of sedimentation statistically different averages and values statistically smaller than the other coagulants, thus confirming its greater efficiency in the removal of apparent color in comparison with the other coagulants. The Table 5 shows the behavior of the electrical conductivity during the sedimentation process in the assays for each coagulant. The effluent of tannery had an electrical conductivity of 21.84 mScm-1 before the treatment done in this work. For the coagulant Tannin, it is possible to observe that in all the concentrations used in the test, an increase occurred in the electrical conductivity, where in the time of sedimentation of 40 minutes the highest value was observed, reaching this 22.57 mScm-1 using the lowest concentration of the coagulant.

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FeCl3

Al2(SO4)3

Tanin

Table 5. Behavior of the electrical conductivity as a function of time for the coagulants Time (min) 10 20 30 40 Time (min) 10 20 30 40 Time (min) 10 20 30 40

[Tanin] = 3 mgL-1 R1 R2 Average 22.27 21.98 22.12 22.46 22.55 22.50 22.51 22.59 22.55 22.55 22.59 22.57 [Al2(SO4)3] = 15 mgL-1 R1 R2 Average 22.50 21.65 22.07 21.32 22.18 21.75 21.26 20.96 21.11 21.28 22.18 21.73 [FeCl3] = 15 mgL-1 R1 R2 Average 21.50 21.40 21.45 21.64 21.54 21.59 21.60 21.52 21.56 21.68 21.55 21.61

[Tanin] = 6 mgL-1 R1 R2 Average 22.33 21.79 22.06 22.51 22.52 22.51 22.47 22.52 22.49 22.54 22.58 22.56 [Al2(SO4)3] = 20 mgL-1 R1 R2 Average 21.51 21.56 21.53 21.31 21.10 21.20 21.20 21.21 21.20 21.16 22.20 21.68 [FeCl3] = 21 mgL-1 R1 R2 Average 21.85 21.74 21.8 21.87 21.69 21.78 21.91 21.74 21.82 22.08 21.80 21.94

[Tanin] = 9 mgL-1 R1 R2 Average 21.73 22.12 21.92 21.63 22.53 22.08 22.06 22.56 22.31 22.53 22.53 22.53 [Al2(SO4)3] = 25 mgL-1 R1 R2 Average 21.38 21.30 21.34 21.25 21.06 21.15 20.97 22.23 21.60 20.98 20.97 20.97 [FeCl3] = 28 mgL-1 R1 R2 Average 22.00 22.00 22.00 22.14 22.12 22.13 22.22 21.97 22.10 22.33 22.27 22.3

When analyzing the results of the electrical conductivity for the Coagulant Aluminum Sulphate, it can be said that there was an insignificant variation. For the coagulant Ferric Chloride, it was observed that there was an increase in the electric conductivity for the highest concentration of coagulant used. At the lower concentration, there was a decrease in conductivity values. In general, it is noticed that there was not a significant change in the electric conductivity after the coagulants application and, in this way, in relation to the parameter the coagulants do not have any variation of the same. Figure 2 shows the behavior of fixed and volatile solids in the treatment of tannery effluent. The crude effluent values for fixed solids and for volatile solids are 60,430 and 38,200 mgL-1, respectively. For the natural coagulant Tanino, it is observed in Figure 2 that the intermediate concentration of 6 mgL-1 was the one that best behaved in the removal of the solids, reaching a 48% removal for the fixed solids and 59% for the volatile solids. By observing the behavior of the chemical coagulant Aluminum Sulphate in the removal of solids, it was observed that it was efficient reaching values above 70% in all concentrations. The highest removal of fixed solids was 75% and occurred at the intermediate concentration of 20 mgL-1, the highest removal of volatile solids was 83% and occurred at the concentration of 28 mgL-1. In relation to the chemical coagulant Ferric Chloride, as well as the natural coagulant Tanino, the greatest removal of the solids occurred for the intermediate concentration. At the concentration of 21 mgL-1 there was a 51% removal of fixed solids and 59% of volatile solids, indicating values similar to Tannin and a similar behavior for solids

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removal, however, the chemical coagulant uses a higher concentration to obtain this removal.

Figure 2. Solids series for the coagulants Tannin (a), Aluminum Sulphate (b) and Ferric Chloride (c), in percentage values. TC1 = Tannin 3 mgL-1; TC2 = Tannin 6 mgL-1; TC3 = Tannin 9 mgL-1; SC1 = Aluminum Sulfate 15 mgL-1; SC2 = Aluminum Sulphate 20 mgL-1; SC3 = Aluminum Sulphate 25 mgL-1; CCl = Ferric Chloride 15 mgL-1; CC2 = Ferric Chloride 21 mgL-1; CC3 = Ferric Chloride 28 mgL-1.

(a)

(b)

(c) Figure 3. Removal percentage of the Chemical Oxygen Demand parameter for the coagulants Tanino (a), Aluminum Sulphate (b), and Ferric Chloride (c).

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Figure 3 shows the percentage of COD removal obtained for the coagulants used in the assay. The raw effluent collected at the company had a COD value of 79.850 mgL-1. For the parameter COD, it is possible to infer that the best results were obtained with the chemical coagulants, reaching values higher than 90% of COD removal, since no natural coagulant did not obtain values higher than 80%. Although the coagulants, especially the chemical ones, present great removal, the effluent still could not be released in the water body, since it does not meet the standards established by CEMA no. 70/2009 (CEMA, 2009) in annex 7, exceeding the limit value for COD, which is 350 mgL-1 for tanneries.

CONCLUSION Based on this research, it was verified that the chemical coagulant aluminum sulphate presented better efficiency in relation to the coagulant tannin. Therefore, the application of aluminum sulphate would be more feasible with regard to the physical-chemical treatment of the tanning effluent.

REFERENCES APHA – American Public Health Association. Standard Methods for the Examination of Water and Wastewater. 22 ed. Washington, 2012. Bayer, V. Study of the extraction of hexavalent chromium, by the technique of surfactant liquid membranes, aiming the treatment of liquid effluents of Tanneries. 2005. 126f. Dissertation (Master’s Degree in Chemical Engineering - Post-Graduation Program in Chemical Engineering, Federal University of Minas Gerais, Belo Horizonte, 2012. Brazil. National Environment Council - Conama. Resolution No. 357, dated March 17, 2005. Provides for the classification of water bodies and environmental guidelines for their classification, as well as establishing the conditions and standards for effluent discharge, and other measures. Official Gazette of the Union. Executive Power, Brasilia, DF, March 18. 2005. Available at: . Accessed on: May 25th. 2014. Brazil. National Environment Council - Conama. Resolution no. 430, dated May 13, 2011. Provides for conditions and standards for the discharge of effluents, complements and amends Resolution 357 of March 17, 2005, of the National Council for the Environment - CONAMA. Official Journal of the Union. Executive Branch,

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Brasília, DF, May 16, 2011. Available at: . Accessed on: May 25, 2014. Martins, G. A. General and Applied Statistics. 3 ed. São Paulo: Editora Atlas S. A, p. 237- 238, 2006. Theodoro, J. D. P. Study of Coagulation/Flocculation Mechanisms for Obtaining Supply Water for Human Consumption. 2012. 184f. Thesis (Doctorate in Chemical Engineering, area of process development) - State University of Maringá, Maringá, 2012. Vaz, L. G. De L.; Klen, M. R. F.; Veit, M. T.; Silva, E. A. Da; Barbiero, T. A.; Bergamasco, R. Evaluation of the efficiency of different coagulating agents in the removal of color and turbidity in electroplating effluent. Eclética Química, São Paulo, v. 35, n. 4, p. 14-22, 2012. Available at: . Accessed on: 3 nov. 2014.

In: Flocculation: Processes and Applications Editor: Eleonora Vollan

ISBN: 978-1-53614-339-3 © 2019 Nova Science Publishers, Inc.

Chapter 7

MORINGA OLEIFERA SEED USE IN SALINA SOLUTION IN WATER TREATMENT IN LENTIC BODIES João Carlos Belisário Junior1, Edilaine Regina Pereira2 and Joseane Débora Peruço Theodoro2 1

Environmental Engineer - UTFPR- Londrina, Londrina, Brazil 2 Department of Environmental Academic, Federal Technological University of Paraná, Londrina, Paraná, Brazil

ABSTRACT The proposal of this paper was to evaluate through physical and chemical parameters the efficiency of the coagulation/flocculation/ sedimentation/filtration processes using organic coagulant (Moringa oleifera) in the treatment of water from a lentic system (Igapó II Lake), located in Londrina – Paraná - Brasil. It was made the water collection at two points of the lake, in the entrance (point 1) and at the exit (point 2). The treatment occurred using the jar-test equipment with the same conditions of fast mixing and slow mixing used in the Water Treatment Station (ETA). The sedimentation time was 30 minutes. The granulometry of the sand used in the filters was the same, in the range of 0.600 to 0.850 mm. The concentrations of saline solution of the organic coagulant to be applied were: C1 = 3 mg.L-1, C2 = 6 mg.L-1 and C3 = 9 mg.L-1. In addition, it was necessary to correct the pH of the samples in order to evaluate the behavior of the organic coagulant in different pH levels. After the assays, a study was carried out on the removal of turbidity and apparent color after the coagulation / flocculation / sedimentation processes and after the filtration process. It was verified for the parameters of turbidity and of apparent color, the concentration C2 (6 mg.L-1) and the pH around 7 (neutral) presented the highest removal efficiency, being it above 99%. For the pH, all

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J. C. Belisário Junior, E. R. Pereira and J. D. Peruço Theodoro concentrations did not present great variations when compared to the crude sample, in addition the results prove the efficiency of the coagulant in different pH levels. Only assay 2 in the entrance point, did not meet the maximum values allowed by the potability ordinance 2,914/11 of the ministry of health for parameters of apparent color and of turbidity, all other assays are in accordance. The results proved the efficiency of the organic coagulant extracted from Moringa oleifera seeds for the treatment of water in lentic systems.

Keywords: Moringa oleifera, water treatment, lentic systems

INTRODUCTION The fresh water is divided into lentic ecosystems, lotic ecosystems and flooded ecosystem. The lentic systems are characterized by low flow or absence of hydrological flow, being represented by lakes, ponds and tanks. The lotic systems are characterized by the presence of water flow, such as rivers, streams and springs, on the other hand flooded systems, have water levels floating up and down during the year, being represented by swamps and marshes (Soares, 2005). According to the World Health Organization, about 80% of all diseases that spread in developing countries come from poor water. Diseases such as typhoid fever, cholera, diarrhea among others (Richter; Netto, 1991). The treatment of water aims to reduce impurities and/or correct some aspects of raw water with the possibility of reuse, or make it drinkable (Freitas, 2011). Vanacor (2005) states that in addition to making it drinkable, water treatment must meet the community’s need to have good quality water from a chemical, physical and bacteriological point of view, and may also serve hygienic purposes (removal of bacteria, viruses, microorganisms, algae, undesirable substances), aesthetics (color correction, turbidity, odor and taste) and economic (reduction of corrosivity, hardness, iron, manganese, etc.). Coagulation is one of the fundamental processes in surface water treatment systems for public supply purposes, as it is responsible for water clarification, removal of most heavy metals, and chemical and microbiological agents (Macedo, 2007). Coagulation and flocculation are practically simultaneous and interdependent, to the point that they can be considered a single step: coagulation / flocculation. Coagulation / flocculation is the process in which the particles agglutinate into small masses (flakes) with a specific weight higher than that of water. The transport of these particles into the liquid causes contact, establishing bridges between the particles and forming a threedimensional mesh of porous clots (Vanacor, 2005).

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Sedimentation is the physical phenomenon in which, as a result of the gravity action, the suspended particles present a downward movement in a liquid medium with a lower specific mass. The occurrence of sedimentation of the suspended particles is no more than the separation of liquid and solid phase, this phenomenon provides clarification of the water while the particles in the bottom form a layer of mud (Di Bernardo; Dantas, 2005). Filtration is a solid-liquid separation process, involving physical, chemical, and sometimes biological phenomena. It aims to remove impurities from the water by passing through a porous medium. When the velocity at which the water crosses the filter bed is low, the filter is called the slow filter, when it is high; it is called a fast filter (Ritcher; Netto, 1991). The Moringa oleifera`s seed contains the presence of a high molecular weight dimeric cationic protein, which destabilizes the particles contained in the water through a process of neutralization and adsorption. Its water-soluble powder acquires positive charges that attract negatively charged particles such as clays and silts, forming dense sedimentary flakes (Ndabigengesere, A., Narasiah, K. S.; Talbot, 1995). According to Arantes et al., (2015), the use of this organic coagulant combined with filtration in the treatment of water shows good results, reaching 99.0% turbidity in water. He further states that the filtration step is necessary for the removal of the organic matter introduced by the coagulant. With this, the present work aims to evaluate, from Ordinance 2,914 / 11 updated to consolidation ordinance nº5, from September 28, 2018 both from the ministry of health (Brazil, 2011, Brazil 2017), according to the parameters color and turbidity, previously determined, in addition to performing the treatment of these water through the coagulation / flocculation / sedimentation / filtration process using the saline solution extracted from the Moringa oleifera seed.

METHODOLOGY The water samples were taken from a lentic system from Lake Igapó II, located in the city of Londrina, state of Paraná, Brazil. Water samples of entry (Point 1) and exit (Point 2) were used. Figure 1 spatially represents the location of the collection points of each sample. Sampling was carried out at the entrance (Point 1) and exit (Point 2) of Lake Igapó II, highlighted according to Figure 1 and conditioned in plastic gallons of 50 liters each, previously sanitized.

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Figure 1. Scheme of the satellite view of the location of Lake Igapó II.

For the preparation of the Moringa oleifera organic coagulant solution, first the Moringa oleifera seed was peeled and 10g of it was weighed. Also weighed 58.44 g of NaCl and added to 1 L of distilled water, the solution was stirred well for the salt to dissolve completely, the salt solution being 1M NaCl. Finally, the 10 g of the seeds were ground together with the saline solution in the blender. The solution was then filtered using a cloth strainer and the Moringa oleifera coagulant saline at a concentration of 10 g.L-1 was obtained. To adjust the pH values to make it acidic, the solution of hydrochloric acid (HCl), concentration 1 M was used. It was necessary to add 20 mL of HCl to the volume used in order to achieve the acidic pH set. Meanwhile, the sodium hydroxide solution (NaOH), at 1 M concentration, was used for the basic pH sample. It was necessary to add 20 mL of the basic solution to achieve the set basic pH. Table 1. pH values used in the assays Samples Acid Natural Basic

pH Point 1 4.5 6.8 10.13

pH Point 2 4.3 6.8 10.8

Table 2. Mixing rod rotation gradient and time of action Fast Mixing

Slow Mixing

Slow Mixing

Slow Mixing

Slow Mixing

Gradient (s-1)

540

90

52

40

30

Time (min)

00:10

02:00

02:35

02:40

05:40

Source. (Trevisan et al. (2014); Higashi (2016); Goes et al., (2017))

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The final pH values applied in the samples are shown in Table 1. For the experiment, the dosages found for coagulant at both points were varied following the concentrations 3 mg.L-1, 6 mg.L-1 and 9 mg.L-1. The assays were carried out in the Jar-test equipment of six tests with regulator of rotation of the mixer rods. Placing in each compartment of the 2L water equipment with different pH and its respective concentration of extraction solution and natural coagulant. After it was held equipment rotation process at different rates (Table 2) for that to happen the coagulation and flocculation processes. For the filtration assay an iron structure adapted to fix the sand filters below the jartest was used so that the water exited the jar-test directly into the filters. The filter beds are made of Polyethylene Tereftalo (PET) of approximately 10 cm of internal diameter configuring a model of fixed bed with downward flow, with six columns in parallel, as observed in Figure 2. It was recommended by Di Bernardo et al., (2003) the tubes are 25 cm long with 15 cm filled by sand, 3 cm filled with crushed stone and 2 cm filled with cotton. The granulometric values of the sand used in the 6 filters were the same, in the range of 0.600 to 0.850 mm. The slope used at the exit of the test jar was 70 ° for 2 minutes, followed by an additional 2 minutes at an angle of 60 ° and a further 2 minutes at 50 °. A model of the filter layers is shown in Figure 3.

Figure 2. Filtration columns used in the assay.

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Figure 3. Representative model of filter layers.

The water to be treated entered through the top of the column and was withdrawn from the bottom. The grains of the filter bed were retained by a coffee filter together with the cotton and crust layer present at the lower end of the column. After this process, all parameters were measured. It is important to say that the assays were performed in duplicate for each pH value and concentration. For all variations of Moringa oleifera and pH concentrations the parameters of apparent color, turbidity and pH were determined (Table 3) according to the Standard Methods of Examination of Water and Wastewater (APHA, 2012). Table 3. Equipment and methodology for the test battery Parameter Apparent Color Turbidity pH

Equipment Spectrophotometer HACH DR-5000 Policontrol Turbidimeter AP-2000 pH-meter mPA-210

Methodology 2120 C 2030 B 4500 H+ B

Source: APHA, 2012.

Table 4. Permissible values of some water parameters according to the ministry of health ordinance 2,914/11 and consilidation ordinance no5, of September 28, 2018 Parameter Apparent color Turbidity pH

Pattern 15 mgPtCo.L-1 5 NTU 6.0 a 9.0

Source: Ministry of Health, Ordinance 2914/11 PRC September 20, 2017 and consilidation ordinance no5, of September 28, 2018.

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The results were evaluated and compared with the standard allowed by ordinance 2,914/11 updated to consolidation ordinance no5, of September 28, 2018 both from the ministry of health (Table 4) and can indicate if the experimental procedure was satisfactory. In this work, statistical analysis was used with two factors (independent variables), the concentration of the Moringa oleifera coagulant, and pH. The assays had a repeat, thus, performed in duplicate in Table 5 it is possible to verify these assay values. Table 5. Numerical organization of the assays for different levels of coagulant concentration and pH with coded and real values of point 1 and point 2 Assay

Duplicate

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

1 1 1 1 2 2 1 1 2 2 2 2 2 1 1 2 2 1

Concentration of Coagulant (mg.L-1) 3 3 3 6 6 6 9 9 9 3 3 3 6 6 6 9 9 9

pH Point 1 4.5 6.8 10.13 4.5 6.8 10.13 4.5 6.8 10.13 4.5 6.8 10.13 4.5 6.8 10.13 4.5 6.8 10.13

pH Point 2 4.3 6.8 10.8 4.3 6.8 10.8 4.3 6.8 10.8 4.3 6.8 10.8 4.3 6.8 10.8 4.3 6.8 10.8

RESULTS Figures 4, 5 and 6 show the removals of the apparent color parameter for the coagulation / flocculation / sedimentation processes (Figure 4), for the filtration process (Figure 5) and for the complete process, coagulation / flocculation / sedimentation / filtration (Figure 6) with the use of Moringa oleifera in different values of concentration and pH. Analyzing the presented results, it can be concluded that both the coagulation / flocculation / sedimentation processes (Figure 4) and the filtration process (Figure 5) are

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of great importance for the removal of color in the water treatment, both reached removal values above 80%. The processes together (complete treatment) demonstrated in almost all tests percent removal of color close to 100% as can be seen in Figure 6.

Figure 4. Removal of the apparent color parameter after the coagulation / flocculation / sedimentation processes.

Figure 5. Removal of the apparent color parameter after the filtration process.

Figure 6. Removal of the apparent color parameter after the coagulation / flocculation / sedimentation / filtration process.

In Figure 4 it is possible to verify the assay 2 as the assays with the lowest percentage of color removal, that is, a concentration of 3 mg.L-1 and a neutral pH of 6.8. However,

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its replica at the same point was the one with the highest removal value, besides that in point 2 the values of color removal with these same variables were also satisfactory. Also in Figure 4, assays 9 and 18 in point 2 were the assays with the lowest percentage of color removal at this point, these assays were replicates of each other, that is, concentration of 18 mg.L-1 and basic pH equal to 10.8. Comparing with the assays of point 1 it is verified that for point 1 these tests were also the ones with lower percentages of removal. With this we conclude that for color removal this combination was the worst. The other assays are ranging from 81% to 91% color removal after coagulation / flocculation / sedimentation processes. In the filtration process (Figure 5) it is also possible to verify a small variation of the percentages of color removal between 85% and 97%, except test 11 of item 1, which had removal value of 70%. Its replica at the same point also had below-average value, so it is understood that for such pH value and concentration the filtration process is slightly affected. In general, very satisfactory results were obtained, as can be seen in Figure 6, the complete treatment provided a reduction of the parameter apparent color of almost 100% in all the tests, it can be concluded that the processes are complementary and very efficient for the removal of color in the treatment of water. According to studies by Okuda et al., (1999), which demonstrate that the percentage of color removal using both the seed and the aqueous extract of Moringa oleifera was 80 to 99%. It is also possible to verify that the coagulant Moringa oleifera can be effective in a wide range of pH and concentration in this case, without significantly altering its results of color removal with the variation of these variables. According to studies conducted by Vaz (2009), Moringa oleifera can be used in a pH range between 4.0 and 12.0. Comparing the values obtained with those required by ordinance 2,914/2011 of the ministry of health 2017 and consilidation ordinance no5, of September 28, 2018, only one assay did not meet the VMP of apparent color, assay 2 of point 1. All others are in accordance with the amount required for the use of water for urban supply.

Figure 7. Removal of the turbidity parameter after the coagulation / flocculation / sedimentation process.

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Figure 8. Removal of the turbidity parameter after the filtration process.

Figure 9. Removal of the turbidity parameter after the coagulation / flocculation / sedimentation / filtration process.

Figures 7, 8 and 9 show the removals of the turbidity parameter for the coagulation / flocculation / sedimentation processes (Figure 7), for the filtration process (Figure 8) and for the complete process, coagulation / flocculation / sedimentation / filtration (Figure 9) with the use of Moringa oleifera in different values of concentration and pH. Analyzing the results presented in Figures 7 and 8, it is possible to verify that both the coagulation / flocculation / sedimentation processes and the filtration process had a high percentage of turbidity parameter removal, around 80% in Figure 7 and around 90% in Figure 8. With this it is possible to understand that the processes together are of extreme importance for the removal of turbidity in the treatment of water. Confirming the data presented in Figure 9 where the processes together (complete treatment) demonstrated in almost all the tests percentage of turbidity removal close to 100%. This confirms studies carried out by Higashi (2015), where after the treatment of Lake Igapó II water through the coagulation / flocculation / sedimentation processes with the use of organic coagulant Moringa oleifera obtained removal results above 80%. All other assays are ranging from 77% to 88% turbidity removal after coagulation / flocculation / sedimentation processes.

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In the filtration process (Figure 8) it is also possible to verify a small variation of turbidity removal percentages between 89% and 95%, except for assays 2 and 11 of point 1 and point 2, which are replicates of each other. These had removal value between 78% and 84%. Thus it is understood that for such pH value and concentration the filtration process is slightly affected. With the data of Figures 7, 8 and 9 it is possible to understand that the Moringa oleifera coagulant is effective over a wide pH range and also concentration, in this case, not significantly altering its turbidity removal results with the variation of these variables. Confirming studies by Cardoso et. al (2008) where the results indicate that the organic coagulant Moringa oleifera can be used in a wide range of pH. Comparing the values obtained with those required by ordinance 2,914/2011 of the ministry of health and consilidation ordinance no5, of September 28, 2018, only one assay did not meet the turbidity VMP, assay 2 of point 1. All others are in accordance with the value required for the use of water for supply.

CONCLUSION The results of the present paper showed that the use of organic coagulant from the Moringa oleifera seed used in a saline solution (NaCl, 1M) was very efficient in the removal of the parameters apparent color and turbidity. For the parameters of apparent color and turbidity, all the assays, at the end of the complete treatment, showed almost 100% removals.

REFERENCES APHA – American Public Health Association. Standard Methods for the Examination of Water and Wastewater. 22 ed. Washington, 2012. Arantes, C. C. et al. Different forms of Moringa oleifera seed in water treatment. Brazilian Journal of Agricultural and Environmental Engineering. v.19, n.3, p.266272, 2015. Brazil, Ministry of Health. 2,914, dated December 12, 2011. Available at: . Accessed on: January, 2018. Brazil, Ministry of Health. Consolidation Ordinance No. 5 of September 28, 2017. Available at: Accessed: April 11 2018.

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Di Bernardo, L.; Mendes, C. G. N.; Brandão, C. C. S.; Sens, M. L.; Pádua, V. L. Water Treatment for Direct Filtration. Di Bernardo, Luiz (coordinator) - Rio de Janeiro: ABES, RiMa, 2003. Project PROSAB 498 p. Di Bernardo, L.; Dantas, A.D. B. Methods and Techniques of Water Treatment. 2nd Edition. São Carlos: Rima, 2005. Freitas, D. B. Study of improvements in the chlorination systems of the water supply in the corsan by the installation of chlorine evaporators and gas scrubbers. Porto Alegre. 2011. Diploma in Chemical Engineering. Federal University of Rio Grande do Sul. Goes, H. H. D.; Souza, R. C. P.; Melo, J. M.; Theodoro, J. D. P.; Study of the application of Opuntia cochenillifera cactus in water treatment. Encyclopedia Biosphere, Knowing Scientific Center - Goiânia, v.14 n.25; P. 554-563. 2017. Higashi, V. Y.; Theodoro, J. D. P.; Pereira, E. R.; Theodoro, P. S.; Use Of Chemical Coagulants (Ferric Chloride) and Organic (Moringa Oleifera) In Treatment Of Waters Derived From The Lentic System. Technical Scientific Congress of Engineering and Agronomy – CONTECC’2016, August 29 to September 2, 2016 Foz do Iguaçu, Brazil. Available at: . Accessed in Feb. 2018. Macêdo, J. A. B. Waters & Waters: 3 ed. Belo Horizonte. MG: CRQ-MG, 2007. 1048p. Ndabigengesere, A.; Narasiah, K. S.; Talbot, B. G. Active agents and mechanism of coagulation of turbid water using Moringa oleifera. Water Research. V.29, p.703710, 1995. Okuda, T. et al. Improvement of extraction method of coagulation active components from Moringa oleifera seed. Water Res. V.33, n.15, p.3373-3378. 1999. Pichler, T., Young, K.; Alcantar, N. Eliminating turbidity in drinking water using the mucilage of a common cactus. Water Science and Technology: Water Supply, v. 12, n.2, 179-186, 2012. Richter, C. A.; Netto, J. M. A. Water treatment: Upgraded technology. São Paulo: BLUCHER, 1991. 332p. Soares, D. H. G. Ecosystems in the ecological context. Pernambuco. Monography (Undergraduate). Center for Higher Education Arcoverde, 2005. Theodoro, J. D. P.; Lenz, G. F.; Zara, R. F.; Bergamasco, R.. Coagulants and Natural Polymers: Perspectives for the Treatment of Water. Plastic and Polymer Technology (PAPT), v. 2, Issue 3, September 2013. Trevisan, Thales S. Coagulant Tanfloc SG as an alternative to the use of chemical coagulants in the treatment of water in ETA Cafezal. 2014. 106 f. Course Completion Work (Undergraduate) - Superior Course in Environmental Engineering. Federal Technological University of Paraná, Londrina, 2014.

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Vanacôr, R. N. Evaluation of the Organic Organic Coagulant used in a water treatment plant for public supply. Porto Alegre. 2005. Master’s Degree in Water Resources Engineering and Environmental Sanitation at the Federal University of Rio Grande do Sul. Vaz, L. G. Performance of the coagulation / flocculation process in the treatment of the liquid effluent generated in electroplating. 2009. 100f. Dissertation (Master in Chemical Engineering) - Center for Engineering and Exact Sciences, State University of Western Paraná, Toledo, 2009.

In: Flocculation: Processes and Applications Editor: Eleonora Vollan

ISBN: 978-1-53614-339-3 © 2019 Nova Science Publishers, Inc.

Chapter 8

EVALUATING NEW BIOPOLYELECTROLYTES FOR THE MEAT PROCESSING WASTEWATER TREATMENT VIA COAGULATION-FLOCCULATION E. A. López-Maldonado1,* and M. T. Oropeza-Guzmán2 1

Faculty of Chemical Sciences and Engineering, Autonomous University of Baja California, Tijuana, Mexico 2 Center for Graduates and Research in Chemistry, Technological Institute of Tijuana, Tijuana, Mexico

ABSTRACT The solid-liquid separation processes are of great scientific and technological relevance in the area of food, beverages, agrochemicals, drugs, mineral extraction, ceramics and wastewater treatment. Nowadays, various chemical substances are used that act as destabilizing agents or stabilizers according to their field of application. One of the strategies to understand the coagulation-flocculation processes is to use the zeta potential measurements as an electrochemical tool to approximate the interface phenomena and establish the mechanisms that predominate at the molecular level. One of the trends is the use of various biopolyelectrolytes (BPE) that can be obtained, modified and applied strategically in various fields of study. In this chapter, the physicochemical performance of six biopolyelectrolytes in the coagulation of flocculation of wastewater with a high content of solids and fats and oils was evaluated. The ones that presented a better performance for this type of wastewater are mesquite gum and chitosan. The BPE that showed a better performance in the coagulation-flocculation test of the wastewater with high content of fats and oils at pH 5.2, was the chitosan, with a dose of 68 mg/L of *

Corresponding Author Email: [email protected].

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Keywords: wastewater, zeta potential, coagulation-flocculation, biopolyelectrolytes, fats and oil

1. INTRODUCTION One of the issues of greatest scientific and technological interest is the quality and use of water, derived from the problems of scarcity and water contamination. The interaction of water with the environment is influenced by the water quality that both society and the industrial sector confer on water. Each type of industry has a particular interest in the care of water quality and its reuse, which is why day by day, they require new strategies to treat and recycle the wastewater they generate in the different production processes [1]. Water quality is affected by various chemical substances that dissolve in water used in each stage of the manufacturing process. In general, the main pollutants that are identified in the industrial wastewater are suspended particles, organic matter, drugs, dyes, heavy metals, agrochemicals, the hardness of the water and fats and oils [2]. The levels of concentration in which these contaminants or undesirable substances are present in the wastewater are directly related to the operating conditions of the productive processes. The presence of these pollutants in the water causes an impact on the efficiency of the production processes, limits the reuse of water, increases the consumption of clean water, the discharge of the wastewater generated contaminates the water bodies, and this implies sanctions to the industry for exceeding the maximum permissible limits at the effluent discharge point [3]. Currently, there are different technologies to perform the treatment of wastewater, including adsorption using various adsorbent materials (polymers, carbon, nanomaterials, clays, zeolites), electrodeposition, membrane filtration (ultrafiltration, nanofiltration and reverse osmosis), coagulation-flocculation, chemical precipitation with hydroxides, sulfides and chelating precipitations, advanced oxidation processes, electrocoagulation, electrodialysis, ion exchange, biological treatment, photocatalysis, and electroflotation. Each technology has certain advantages and disadvantages. Considering the most demanding environmental legislation, industries need more efficient wastewater treatments to eliminate suspended or dissolved metals [5-20]. In the case of coagulation-flocculation process, a very simplest equipment is required

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thus remains among the most popular process for the separation of various types of contaminants, in which chemical substances are used as synthetic coagulantflocculating agents, for example, alum, ferric chloride, polyaluminum chloride and synthetic organic polymer. The synthetic polyelectrolytes (PE) have also been reported to pose a number of environmental problems since some of the derivatives and intermediates are non-biodegradable and reported as hazardous to human health (their monomers are neurotoxins and carcinogens). One of the promising alternatives is the use of biopolyelectrolytes (BPE) as flocculating coagulants, which can be extracted from various sources such as residues from the food industry and agriculture. One of the most appreciated characteristics of PE is its efficiency and effectiveness in the destabilization of colloidal systems or dispersion of particles. In a colloidal system the suspended particles have a surface charge density, which causes that by electrostatic interactions the particles repel, preventing their sedimentation by gravity forces. Such is the case of the wastewater generated by the factory for cutting and packing of meat products, which consists of a dispersion of particles of fats and oils from animal origin. In this chapter, the physico-chemical characterization of meat processing wastewater is presented. The coagulation-flocculation performance in the wastewater treatment was evaluated using the two natural biopolyelectrolyte extracted from the shrimp husks (chitosan) and mesquite gum. The zeta potential was used as a key electrochemical tool to strategically dose the BPE allowing the destabilization of the contaminants present in the wastewater.

2. EXPERIMENTAL 2.1. Wastewater Sampling In this chapter, presents the physicochemical characterization of meat processing wastewater and how to develop a treatment strategy for water recovery and add value to the byproducts formed. The wastewater sampling protocol was followed as recommended by Mexican sampling standard (NMX-AA-003-1980). Residual water samples were taken from a factory for cutting and packing meat products. Tested parameters were: total solids (TS), total dissolved solids (TDS), total suspended solids (TSS), turbidity, color, particle size, electrical conductivity (EC), zeta potential (), total phosphorous (TP), biological oxygen demand (BOD5), chemical oxygen demand (COD), total organic carbon (TOC), fats and oils and total nitrogen (TN). Tests were carried out following the current Mexican standard procedures that are equivalent to those published by EPA (AWWA standard methods respectively).

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2.2. Zeta Potential f (pH) Profiles of the Industrial Wastewater and BPE Zeta Potential from wastewater and biopolyelectrolyte data was recorded on a Stabino Particle Charge Mapping (Microtrac). The measurements were done at ambient temperature in Teflon cuvettes. Influence of pH on the zeta potential behavior of each biopolyelectrolytes was studied within a pH range of 2-11 with 0.1 M NaOH and 0.1 M HCl [20].

2.3. Wastewater Coagulation-Flocculation Tests Using BPE The performance of cationic chitosan biopolyelectrolyte in the coagulationflocculation of meat processing wastewater was carried out using 20mL of residual water at pH 5.2, and in different doses of chitosan extracted from the shrimp shells. After each addition of chitosan, the mixture of residual water with chitosan was stirred at 200rpm for 2min, and subsequently at 50rpm for 20min. For the evaluation of the quality of the treated water, a sample of the supernatant was extracted [21].

3. RESULTS AND DISCUSSION 3.1. Meat Processing Wastewater Tables 1 show the physicochemical characterization of meat processing wastewater. The values of the main residual water quality parameters such as BOD5, COD, alkalinity, hardness, pH, electrical conductivity, fats and oils, content of dissolved and suspended solids, settleable solids, temperature, turbidity, nitrogen and total phosphorus are shown. Of these normative parameters the environmental legislation dictates which ones must comply, considering the type of industry and body of discharge of residual water. Additionally, other non-regulated parameters, which are fundamental to understand and operate the coagulation-flocculation process, such as particle size, turbidity, total organic carbon, biodegradability and zeta potential [21]. The measurement of these parameters is key to implement the design and sequence of an industrial wastewater treatment train to achieve the best quality of treated water. In all the regulated parameters exceed the maximum permissible limits, both for their discharge to the water receiving bodies and for their reuse. Considering the main interactions that occur between the suspended particles and the coagulant-flocculant agents, the zeta potential is a key parameter to determine the surface charge density of the

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suspended particles and the biopolyelectrolytes, as well as the optimum dose to perform the solid-liquid separation of the suspended particles. Table 1. Physicochemical characterization of Meat Processing Wastewater Parameter

Meat Processing Wastewater

Temperature (oC) Alkalinity (mg/L CaCO3) Fats and oils (mg/L) TSS (mg/L) TDS (mg/L) SS (mL/L) Turbidity (FAU) EC (mS/cm)

28 98 15,732 20,000 3,500 900 750 2.00 -20

 (mV) Particle size (nm) Color (Pt-Co) pH COD (mg O2/L) TOC (mg C/L) BOD5 (mg O2/L) Biodegradability (BOD5/COD)

750 35,083 6.8 60,587 53,45 40,250 0.67

3.2. f (pH) Profiles of the BPE Figure 1 the = f (pH) plot shows the charge density variation the BPE of maiz gum (GMZ), chitosan (Ch), mesquite gum (GMT), guar gum (GG), Tule lignin (LT) and Coffe lignin (LC) with respect to pH. The change in pH had a distinct effect with each BPE, because of the difference between the functional groups present in the chains of the iomacromolecules. Considering the zeta potential value (= -20 mV) of the wastewater at pH 5.2, the biopolyelectrolyte of chitosan and mesquite gum having positive surface charge density, were selected to carry out the strategic dosing in the wastewater with a high content of fats and oils and to evaluate their performance in coagulationflocculation.

3.3. Coagulation-Flocculation Tests with Biopolyelectrolytes Figure 2 shows the variation of zeta potential with respect to the pH of the meat processing wastewater and chitosan.

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BPE-GMZ

0

BPE-Ch

-10  (mV)

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-30 -40

BPE-LT

-50 -60 -70

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-80 -90 2

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Figure 1. = f (pH) profiles of GMZ, Ch, GMT, GG, LT and LC.

The zeta potential value of the wastewater shows that the suspended particles have a negative surface charge density at pH 4-12, while at pH