Green Adsorbents [1 ed.] 9781681081366, 9781681081373

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Green Adsorbents Authored By

George Z. Kyzas Technological Educational Insitute of Kavala Aristotle University of Thessaloniki Greece

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DEDICATED To… My adorable wife Vicky, My newborn child Zacharias, My lovely parents Zacharias and Elli, Memory of Lyda

CONTENTS About the Author Foreword Preface

i iii v

CHAPTERS 1.

Composition of Industrial Wastewaters

2.

Adsorption in Wastewater Treatment

35

3.

Synthesis of Green Adsorbents

55

4.

Pollutants Removed with Green Adsorbents

69

5.

Economic Perspectives and Future Trends

89

References

99

Subject Index

3

115

i

ABOUT THE AUTHOR Dr. George Z. Kyzas was born in Drama (North Greece). At the age of 18, he passed the entrance examination at the Department of Chemistry of Aristotle University of Thessaloniki. He followed the expertise of Environmental Chemical Technology in the last year of his under-graduate studies, where he completed a diploma work in the environmental field under the title: “Study of the reuse of flotated dye-samples to the textile dyeing”. After his B.Sc. graduation, he passed the postgraduate program (M.Sc.) from the Department of Chemistry (Aristotle University of Thessaloniki) in the Division of Chemical Technology. After successful completion of 4 semesters of M.Sc. diploma work (M.Sc. thesis: “Multiparametric study for the removal of environmental pollutants in sorptive beds”) he received his M.Sc. degree. His doctorate studies lasted for 3.5 years and his Ph.D. thesis was focused on adsorption process (Ph.D. thesis: “Dyes removal from aqueous systems with sorption process”). Research Committee of Aristotle University of Thessaloniki awarded him with the highest honor (full annual scholarship) named “Excellence Honour” as a great Ph.D. student of 2009 in the Department of Chemistry. Moreover, in 2013 the same Committee awarded him with another highest honor (full annual scholarship) named “Excellence Honour” as a great PostDoc researcher. The high-level of his research potential was confirmed with: (i) the publication of numerous papers in scientific journals; (ii) oral or poster presentations in national and international coferences; (iii) publication of chapters in scientific books; (iv) responsibility as Editor, Guest Editor and Reviewer in scientific journal. Dr. George Z. Kyzas is now a Lecturer at the Technological Educational Institute of Kavala (Greece) teaching lab and theory courses of “Physics”, “Physical Processes”, “Legislation of Wines and Drinks”, “Wastewater Management”, “Physical Chemistry I”, “Physical Chemistry II”, “Quantitative Chemical Analysis”, “General Inorganic Chemistry”. Furthermore, his lectures on Medical Wastewater Treatment were of significant importance. More info about Dr. Kyzas is found in http://georgekyzas.com

iii

FOREWORD When Dr. Kyzas asked me to write this preface, I was honored and thrilled to have the opportunity to introduce this outstanding work! I have been impressed with the promising career of Dr. Kyzas who has contributed enormously in the field of environmental technology and in particular adsorption phenomena. He has both published extensively on this subject and is well qualified to write and edit such books. Dr. Kyzas has made significant contributions in the synthesis and adsorptive evaluation of various materials during his early research career. The research potential of Dr. Kyzas is really impressive. The high-level of his research includes: (i) publication of many papers in highly Impact Factor scientific journals; (ii) oral or poster presentation in National and International Scientific Conferences; (iii) publication of many chapters in scientific books; (iv) editorship in Scientific journals; (v) reviewership in Scientific journals. However, the most impressive thing in his early scientific research career is that until the end of his Ph.D. he had published 6 papers, while the next 5 years took off his research capabilities, publishing 52 papers in high Impact Factor journals. Taking into account (i) his age; (ii) his teaching work (until now) as a.Lecturer at Technological Educational Institute of Kavala (Greece); (iii) the impressively rapid growth of his research career in a relatively young age, I can assure that Dr. Kyzas can be easily considered as one of the topranked young scientist of Greece. The book is very well organized in multiple short chapters that are beautifully illustrated both with ultrasound images and diagrams. Initially, they introduce the subject with a chapter on the different compositions of industrial wastewaters. Next, adsorption (as the major treatment of wastewater) is presented, which is a simple, rapid, and economic decontamination technique. This technique is also described in this eBook both in batch mode examples and fixed-bed ones. The following chapters introduce the synthesis of various materials used as adsorbents. These are environmental-friendly materials satisfying some basic standards of the general field of “green technology”. Examples of polluatnts removed from wastewaters with green adsorbents are then presented as dyes, heavy metals (ions), pesticides, phenols, insecticides etc. The last chapters report some useful information which can be characterized as real and practical regarding technoeconomical data for the use of green adsorbents. Industrial scaling and economic perspectives are posed along with the future trend of green adsorption technology. This book, while very comprehensive, remains simple in its approach. It makes a very complex and rather intimidating organ accessible to both the novice and the seasoned examiner. Furthermore, this book is presented as an eBook which is a very innovative format, awaited with great anticipation. Such novel media will challenge the primacy of bulky printed books. Many books will soon be available as eBooks and carried as a small discrete thumb-drive or even downloaded perhaps on an electronic device. Electronic versions of books are the future of our industry and Dr. Kyzas has stepped up in choosing such a modern and practical display for his book.

iv

In conclusion, I am very excited about this eBook, not only because it is superbly organized and is well illustrated, but also because as an eBook it can be carried and propagated throughout our community much more easily than a hard copy book. Dr. Kyzas has succeeded admirably in their endeavor to produce what promises to be an outstanding resource on “Green Adsorption” technology.

Athanassios Ch. Mitropoulos Technological Educational Institute of Kavala Petroleum and Natural Gas Technology Kavala, Greece

v

PREFACE One of the most recent trends in environmental technology is the research turn to green chemistry. It is generally accepted that one of the most promising techniques for wastewaters treatment is adsorption. On this basis, numerous adsorbent materials have been synthesized up to now. However, nowadays, there is a novel concept, which promotes the use of materials with the lowest possible cost. The economic crisis of the 2000s led researchers to turn their interest to adsorbent materials with lower cost. Attempts were already realized to use some low-cost adsorbent materials in order to initially treat synthetic aqueous solutions and then real industrial samples. In this eBook, the main scope is to describe these environmental-friendly materials namely “green adsorbents”, as I firstly introduce this term. With this term, it is meant the adsorption process using low-cost materials originated from: (i) agricultural sources and by-products (fruits, vegetables, foods); (ii) agricultural residues and wastes; (iii) low-cost sources from which most complex adsorbents will be produced (i.e., activated carbons after pyrolysis of agricultural sources). It is a fact that low-cost adsorbent materials belong to a hot-topic of recent literature given its economic perspective. Although they present a slightly lower adsorption capacity compared to more complex materials (i.e. polymers), their near zero cost of preparation makes them very attractive in chemical technology. In this field, some crucial factors will be developed regarding the removal of those environmental pollutants from aqueous systems with the aforementioned type of materials. Three main categories of environmental pollutants are discussed as: (i) dyes; (ii) heavy metals, and (iii) others (phenols, pesticides/insecticides etc). This category will be preferred to be presented as general category of “others”, because the number of published works for this type of pollutants is still limited compared to those of dyes or metals. Extensive comparison will be done for: (i) their adsorption capacity, showing the main models used up to now for the expression of their theoretical maximum capacity theoretically; (ii) their kinetic behavior, showing the main models used and some more specific kinetic simulations; (iii) parameters influenced by adsorption (salinity, particle size or mass of adsorbent etc); (iii) their reuse potential, given the ultimate goal of each adsorbent to be used in industrial/factorial design; (iv) fixed-bed columns; (v) the surface of those low-cost materials (comments about their characterization); (vi) economic perspectives; (vii) future trends and applicability. CONFLICT OF INTEREST The author confirms that he has no conflict of interest to declare for this publication. ACKNOWLEDGEMENTS Declared none.

George Z. Kyzas Technological Educational Insitute of Kavala Aristotle University of Thessaloniki Greece

Green Adsorbents, 2015, 3-34

3

CHAPTER 1

Composition of Industrial Wastewaters Abstract: The composition of industrial wastewaters is not the same for each type of effluents. Other compositions have dyeing effluents, and are drastically different from tanneries. Therefore, in this chapter a special mention is realized about the characteristics of wastewaters and various physic-chemical properties.

Keywords: BOD, COD, composition, dyeing effluents, industrial wastewaters, insecticides, ions, pesticides, phenols, phenols, SS, tannery effluents. 1. INTRODUCTION A human after its birth is certain to produce waste. Most of this waste ends up in the form of fluids or water. Waste water generally corresponds to waste in liquid form. But in environmental terminology it refers to aqueous phase waste. This is how the term waste water has been described. A huge difficulty in this time period is the lack of uniformity in quality and composition of waste water. The reason for this is a massive expansion in different industries which are producing effluents of varying types and varieties. The standard, concentration and amount of wastewater are found by many inter relating determinants. Every human and industry produces different amount of wastes. An occupant’s lifestyle, outlook of life, standard of living and the various mechanics of life and style determines the form and quantity of waste produced. In homes, generally, the type of waste produced is solid and liquid. These two states of waste can be altered in their constitution and amount significantly. The components of the waste water cannot be illustrated by constant values as there are significant differences and dissimilarities in the volume moving per unit time and concentration of the effluents. The effluent may be in the form of a solution, a suspension or a colloid with varying degrees of solids spread throughout the effluent. The acidity or basicity of the effluents and the intensity of the colour of the effluents are also important factors. Diseased bacteria and poisoned substances maybe a part of these wastes. However, less harmful substances such as unreactive chemicals or organic waste may also be present. These effluents might be released into the sewage system considering no negative effects on the treatment methods and sewer networks occur. It might be compulsory to treat waste before release into local system and to completely treat it before releasing it into the ground. George Z. Kyzas All rights reserved-© 2015 Bentham Science Publishers

4 Green Adsorbents

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2. INDUSTRIAL WASTEWATER CHARACTERISTICS Physical and chemical aspects mentioned below are for both industrial and municipal effluents. 2.1. Physical Characteristics Major physical constituents of effluents are colour, odour and temperature. 2.1.1. Total Solids The total amount of solids in effluents is made up of insoluble, suspended, and soluble solids. The amount of solid in the suspension is found by filtering, drying and weighing the residue removed from the sample. Volatile solids are combusted when residue is kindled. Some volatile solids are organic but some organic matter might not burn and some inorganic matter breaks down at high temperatures. The constituents of organic matter include proteins, carbohydrates and fats. In an average effluent 40 to 65% of the solid is suspended. Solids that settle to the bottom of the conduit can be separated from the effluent by the process of decanting or sedimentation. A unit of millimetres/litre is used to denote the amount of these solids in the effluent. Solids may also be divided into volatile solids (those that change their state at elevated temperatures) and fixed solids (those that do not do so). Most of the volatile solids are organic in nature. 2.1.2. Color Colour is a qualitative aspect that can be used to judge the general condition of effluent. Effluent that is light brown coloured is less than 6 hours old, while a light-to-medium grey colour is representative of the fact that the substance has undergone some degree of decolourisation or has been in the disposal system for some time. Dark grey or black coloured effluent is generally full of harmful chemicals, having undergone extensive bacterial decomposition under a lack of oxygen. The darkening of wastewater is generally due to the development of various sulphides such as ferrous sulphide. This happens as a result of combination of hydrogen sulphide with a divalent metal in the absence of oxygen. The divalent ion may be iron (Fe2+). Colour is measured by comparison with some standards. 2.1.3. Odour The evaluation of odour has become exponentially significant, as the general consensus towards the proper treatment of effluent in its facilities has changed.

Composition of Industrial Wastewaters

Green Adsorbents 5

The odour of fresh wastewater is generally not that bad. A combination of odour rich compounds forms when wastewater, in the absence of oxygen, is cleaned and purified. Table 1 shows the wide varieties of stinky odours that occur in effluents. Table 1. Unpleasant odours in some industries Industries

Origin of odours

Cement works, lime kilns

Acrolein, amines, mercaptans, dibutyl sulphide, H2S, SO2, etc.

Pharmaceutical industries

Fermentation produces

Food industries

Fermentation produces

Food industries (fish)

Amines, sulphides, mercaptans

Rubber industries

Sulphides, mercaptans

Textile industries

Phenolic compounds

Paper pulp industries

H2S, SO2

Organics compost

Ammonia, sulphur compounds

2.1.4. Temperature The temperature of effluent is generally greater than that of its source water. This is due to the induction of hot municipal water to it. The temperature of effluent should be noted regularly, because most treatment processes are biological in nature. Biological methods are extremely sensitive to temperature. Variation of temperature of effluent happens from time to time. This variation also occurs with a change in place. The limit of the temperature where cold is prevalent is between 7 to 18 degrees. The same limit for mildly hot locations is 13 to 24 °C. 2.2. Chemical Characteristics 2.2.1. Inorganic Chemicals Organic and inorganic phosphorus, nitrates, nitrites, nitrogen and free ammonia are the major chemical tests involved in this line of work. Nourishment for underwater flora generally involves the use of phosphorus and nitrogen. The importance of both these elements is due to this factor. Other tests, like pH alkalinity chloride, sulphate, are used to overview the varied treatment methods and to check whether the treated effluent can be reused or not. Trace elements, like heavy metals, are not normally measured, but they may be an important variable in the biological cleaning and purification of effluents. Every life (whether human, animal or plant) requires various degrees of trace elements, like

6 Green Adsorbents

George Z. Kyzas

iron, copper, zinc and cobalt, for better growth.Assessing the quantity of heavy metals is necessary where reuse of treated effluent or sludge is considered because of the production of toxic effects. Many metals are a classified as major pollutants like arsenic, cadmium, chromium, mercury, etc. For the system to be more efficient, gases like oxygen, hydrogen sulphide, methane and carbon dioxide are measured. The assessment of existence of hydrogen sulphide is not only significant because of its smell and poison ability but also because of its corrosive ability on elongated sewers on flat slopes. For checking and overseeing aerobic biological treatment processes measurements of dissolved oxygen is important. Amount of methane and carbon dioxide are noted in relation to the working of anaerobic digesters. 2.2.2. Organic Chemicals For determination of organic content in waste water various tests exist. Usually, the tests are divided either to measure total concentrations of organic matter greater than 1 mg/l or to calculate small concentrations in the range of 10-12 to 10-3 milligrams per litre. Processes mostly used these days for assessment of massive quantity of organic matter (greater than 1 mg/L) in effluents are the following: (i) chemical oxygen demand (COD) (ii) biochemical oxygen demand (BOD), and (iii) total organic carbon (TOC). Trace organics in the range of 10-12 to 10-3 mg/l are measured using processes like chromatography and gas mass spectroscopy. Definitive organic compounds are measured for determining the presence of major hazardous materials. The COD TOC BOD, tests are total measures of organic amount and are not a mirror to various biological analyses of the effluents. As a result, the division of effluents into various major types is useful. 2.2.3. Volatile Organic Carbons (VOC) On average hazardous material in soil contains Volatile organic compounds like xylenes, toluene, tri chloro ethane, and benzene, and trichloroethylene, dichloromethane in industrialized and commercialized areas. A major cause of these materials being in the soil is discharge from underground storage tanks. Prominent reason of soil VOCs are inappropriately thrown away solvents and depot built before availability of present day strict principles about the environment. Most of organic substances are considered as major hazardous materials. These include 1, 3-butadiene, polychlorinated biphenyls (PCBs), polycyclic aromatic, acetaldehyde, formaldehyde, dichloromethane polycyclic aromatic, 1, 2-dichloroethane and hexachlorobenzene (HCB). In Table 2, a list of unusually found inorganic and organic materials in industrial effluents is shown.

Composition of Industrial Wastewaters

Green Adsorbents 7

Table 2. Substances present in industrial effluents [1]. Substances

Present in Wastewaters from:

Acetic acid

Acetate rayon, beet root manufact

Acids

Chemical manufacture, mines, textiles manufact

Alkalies

Cotton and straw kiering, wool scouring

Ammonia

Gas and coke and chem. manufacture

Arsenic

Sheep dipping

Cadmium

Plating

Chromium

Plating, chrome tanning, alum anodizing

Citric acid

Soft drinks and citrus fruit processing

Copper

Copper plating, copper pickling

Cyanides

Gas manufacture, plating, metal cleaning

Fats, oils, grease

Wool scouring, laundries, textile industry

Fluorides

Scrubbing of flue gases, glass etching

Formaldehyde

Synthetic resins and penicillin manufacture

Free chlorine

Laundries, paper mills, textile bleaching

Hydrocarbons

Petrochemical and rubber factories

Free chlorine

Laundries, paper mills, textile bleaching

Mercaptans mills

Oil refining, pulp

Nickel

Plating

Nitro compounds

Explosives and chemical works

Organic acids

Distilleries and fermentation plants

Phenols

Gas and coke manufacture, chemical plants

Starch

Food processing, textile industries

Sugars

Dairies, breweries, sweet industry

Sulfides

Textile industry, tanneries, gas manufacture

Sulfites

Pulp processing, viscose film manufacture

Tannic acid

Tanning, sawmills

Tartaric acid

Dyeing, wine, leather, chemical manufacture

Zinc

Galvanizing zinc plating, rubber processing

3. HEAVY METALS Wastewater streams from factories containing heavy metals are created from several diverse commercial ventures. Electroplating and metal surface treatment techniques produce critical amounts of wastewaters containing the heavy metals: cadmium, zinc, lead, chromium, nickel, copper, vanadium, platinum, silver, and titanium.

8 Green Adsorbents

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These metals are formed from an assortment of uses. These uses incorporate electroplating, electro less testimonies, transformation covering, anodizing-cleaning, processing, and carving. An alternate huge point of supply of substantial metals remains results from printed circuit board (PCB) making. Tin, lead, and nickel bind plates are the most generally utilized safe over plates. Different hotspots for the metal squanders incorporate: the wood handling industry where arsenic rich wastes are developed by a chromated copper arsenate wood treatment; inorganic colour making which produces colours that contain chromium mixes and cadmium sulphide; petroleum refining which involves compounds tainted with nickel, vanadium, and chromium; and photographic operations creating film with high amounts of silver and Ferro cyanide. These generators deliver a huge amount of wastewaters, buildups, and ooze that can be labelled as a dangerous substance obliging an immediate and efficient waste removal process [2]. 3.1. Heavy Metals and Inorganic Species Chromium is not that harmful to humans, plants or animals. More dangerous than chromium are the metals cadmium, lead and mercury. They are strongly attracted to sulphur and interrupt and destroy enzyme function by reacting with sulphur groups. Carboxylic acid and amino groups in protein chains are also a group of compounds boundary by heavy metals such as lead or cadmium. The ions of these metals stick to the boundaries of cells and disrupt and interfere with various reactions happening in the cell. Phosphate bio compounds are also developed and/or destroyed by these metals. A list of these heavy metals is shown in the table below (Table 3). Table 3. Heavy metals found in major industries [1]. A

As

Cd

Cr

C

X

X

X

X

X

X

X

X

X

X

Pulp and paper mills Organic chem. Alkalis, Chlorine

Hg

Pb

Ni

X

X

X

X

X

X

X

X

Fertilizers

X

X

X

X

X

Petroleum refining

X

X

X

X

X

X

X

X

X

X

X

X

X

X

Steel works Aircraft plating, finishing

X

Flat glass, cement

X

Textile mills

X

Tanning

X

Power plants

X

X

Zn X

X

X

X

X

X

X

X

X

X

X

Composition of Industrial Wastewaters

Green Adsorbents 9

In water, hazardous material that is cadmium may result from industrial and mining effluents. Metal plating usually requires the use of cadmium. Cadmium and zinc are similar in chemical composition, and both change by going through geo chemical processes. In water their oxidation state is +2. The results of severe cadmium poisoning in humans are many including but not limited to: destruction of testicular tissue, high blood pressure, kidney damage, and destruction of red blood cells. The stereo-structure of the enzyme is changed when cadmium substitutes zinc causing its catalytic properties to diminish. Industrial areas usually contain Cadmium and zinc in underground water and residue effluents. Inorganic lead present in water is in the +2 oxidation, obtained from different industrial and mining sources. A massive contributor of atmospheric and earthly lead is Lead obtained from leaded gasoline that mostly becomes part of natural water systems. Strong lead poisoning in humans causes grave malfunction in the kidneys, reproductive system, liver, and nervous system. Many minerals contain mercury as trace elements, usually in continental rocks containing about 80 ppb (μg/L), or less, of it. Major commercial mercury ore is Cinnabar and red mercuric sulphide. In laboratory vacuum apparatuses requires Metallic mercury as an electrode in the electrolytic generation of chlorine gas. Organic mercury compounds were mostly used as pesticides, usually fungicides. Use of mercury by human is a major contributor to its presence in environment, for example; discarded laboratory chemicals, pharmaceutical products, batteries, broken thermometers, amalgam tooth fillings lawn fungicides. There is, occasionally, ten times more mercury in industrial waste water than in ordinary water. During 1953-1960, in the Mina Mata Bay (Japan) devastating effects of mercury poisoning were seen. Seafood eaten that originated from the contaminated bay resulted in 43 deaths. 111 other cases of mercury poisoning were also documented. Adverse effects of mercury poisoning include paralysis, neurological damage, irritability, chromosome breakage and birth defects, insanity and blindness. Cyanide ion, CN-, is most important inorganic molecule in effluent. Cyanide is a fatal toxin; it is present in water as HCN, a weak acid. It is strongly attracted to various metal ions, forming comparatively weaker poison Ferro cyanide, Fe(CN)64-, with Fe(II). HCN is deadly, unstable and has been used to implement the death penalty in America. Mostly Cyanide is used in cleaning and electroplating in industry. It is one of the major gas and coke scrubber effluents produced. Cyanide is commonly used in some mineral processing reactions.

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The decomposition of nitrogenous wastes produces ammonia initially which predicts the existence of such wastes. Some sources of underground water contain it normally. For the removal of taste and smell of unbounded chlorine, it is added in drinking water. Since the pKa (the negative log of the acid ionization constant) of the ammonium ion, NH4+, is 9.26, most type of ammonia in water is present as NH4+ ion rather than the NH3 molecule. Anaerobic decomposition of sulphur containing organic matter produces Hydrogen sulphide, H2S, as a by-product. It is also made by microorganisms in the anaerobic reduction of sulphate and as a toxic gas from geothermal waters. Effluents from various types of industrial mills and tanneries are also rich in the compound H2S. The transitional oxidation state of nitrogen is represented by the nitrite ion (NO2-). This nitrite ion is found in water. To prevent corrosion the nitrite ion is used in some industries. Its levels do not exceed over 0.1 mg/L in water that is used for drinking. The Sulphite ion, SO32-, is part of a few industrial effluents. A compound of this ion, Sodium sulphite, serves the function of an oxygen scavenger:

2SO32  O2  2SO42

(1)

3.2. Organic Pollutants Wastewater from industries contains a variation of pollutants. The majority of these pollutants are organic pollutants. Mostly oil, grease, solids and substances requiring oxygen are removed from Primary and secondary sewage treatment processes. Substances that are not satisfactorily removed include salts, heavy metals and refractory organics (which are mostly nitro compounds or organo chlorides). Organic pollutants are mostly caused by detergents, soaps and other similar chemicals. The most problem causing substance in the detergents is poly phosphates. These are mainly used to hold the detergent molecule rigidly. Contrary to popular belief, surface active agents are not the main reason for the harmful properties of the detergents. Aromatic and chlorinated hydrocarbons are a form of bio refractory organics and consist of several different molecules. These break down slowly and therefore remain in the ground for a long period of time. These bio refractory organics (e.g. bromo benzene and camphor) also occur in water that is used for hydration purposes. This water must then be purified with air stripping, solvent extraction, and ozonation and carbon adsorption methods to make it fit for drinking.

Composition of Industrial Wastewaters

Green Adsorbents 11

PCB compounds were first discovered to have a negative impact on the environment in 1966. These PCBs are found commonly around the globe inside birds, marine animals, and soil and in water. A replacement on the biphenyl aromatic structure of 10 chlorine atoms (at most) results in this family of pollutants. Around 209 new structures are formed of these PCBS when the Cl atoms are replaced with other atoms. 4. POLLUTION LOAD AND CONCENTRATION Following are the important factors that result in the birth of waste water effluents. 

Sanitation waste (from washing clothes, utensils, bathing, drinking, etc.)



Cooling (from radiation of excess heat to the environment through the use of water as a fluid that transmits energy)



Wastewater resulting from manufacturing processes ( this contains the water employed in the manufacture and cleaning of products and the water used in cleaning and transmission of the effluents)



Cleaning (wastewater from washing and service of factories)

Production of dirty water in metropolitan areas is composed of factory and local waste water in equal proportions. This does not include the huge amounts of waste water generated in power generation. The amount of waste water used in factory processes is different for each process. This amount can be reduced and large quantities of water saved by the implementation of several parameters. These parameters include plant changes and machinery modifications. The role of environmental commissions that oversee industrial pollution is also important in this regard. Strict and stringent quality control measures by the commission can save huge quantities of water. Where ever these measures have been implemented, a significant reduction in water usage has been seen. If these water saving measures are not put into effect, the cost of cleaning and purifying each litre of an effluent increases exponentially. The amounts and the concentrations of these effluents are not constant and vary as a result of several factors. Common effluents and a BOD limit for several of industrial wastes are provided in Table 4.

12 Green Adsorbents

George Z. Kyzas

Table 4. Wastewater characteristics for typical industries. Industry

Principal pollutants

BOD5 (mg/L)

Dairy, milk processing

Carbohydrates, fats, proteins

1000-2500

Meat processing

Suspended solids, proteins

200-250

Poultry processing

Suspended solids, proteins

100-2400

Bacon processing

Suspended solids, proteins

900-1800

Sugar refining

Suspended solids, carbohydrates

200-1700

Breweries

Carbohydrates, proteins

500-1300

Canning fruit etc

Suspended solids, carbohydrates

500-1200

Tanning

Suspended solids, protein, sulphide

250-1700

Electroplating

Heavy metals

minimal

Laundry

Suspended solids, carbohydrates, soaps

800-1200

Chemical plant

Suspended solids, acidity, alkalinity

25-1500

The values of typical concentration parameters (BOD5, COD, suspended solids) and pH for different industrial effluents are given in Table 5. Table 5. Comparative strengths of wastewaters from industry. Type of waste

BOD5 mg/l

COD mg/l

SS mg/l

pH

Cotton

200-1000

400-1800

200

8-12

Wool scouring

2000-5000

2000-5000 (a)

3000-30000

9-11

1

-

100

9-10

Tannery

1000-2000

2000-4000

2000-3000

11-12

Laundry

1600

2700

250-500

8-9

850

1700

90

4-8

Apparel

Wool composite

Food Brewery Distillery Dairy

7

10

Low

-

600-1000

-

200-400

Acid

2000

-

000

Acid

Cannery citrus pea

130

Acid

1500-2500

-

800

7

2000

3500

2500

11-13

Sugar beet

450-2000

600-3000

800-1500

7-8

Farm

1000-2000

-

1500-3000

7.5 8.5

500-800

600-1050

450-800

6.5-9

Slaughterhouse Potato processing

Poultry

570

Composition of Industrial Wastewaters

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Table 5: contd…

Materials Pulp; sulfite

1400-1700

-

Variable

Pulp; kraft

100-350

170-600

75-300

Paperboard

100-450

300-1400

40-100

7-9.5

Strawboard

950

-

1350

Coke oven

780

1650 (a)

70

7-11

Oil refinery

100-500

150-800

130-600

2-6

(a) = COD as KMnO4 mg O2/L

5. INDUSTRIAL WASTESTREAM VARIABLES The factors that affect the waste water produced by factories, their merits of grouping and the significance of the recurrence and treatment of effluents in discussed in this section of the report. 5.1. Compatible and Noncompatible Pollutants The definition of compatible pollutants extends to include all types and forms of pollutants (such as ammonia, oil, grease, suspended solids and biochemical oxygen demand) that are treated by POTW which is the publicly owned treatment works system. Cleaning household waste water and purifying the above mentioned effluents are the main tasks of this system. Pollutants that are not generally cleaned by POTW are known as non-compatible pollutants. They interfere with the treatment system by promoting flock formation and may not be generally detected by the system. These pollutants are also not feasible to be treated by a biological industrial waste water treatment system. Heavy metals which include lead and cadmium; organic compounds including 1, 1, 1-trichloroethylene, methyl ethyl ketone, acetone, gasoline and methylene chloride; and cooling oils are non-compatible pollutants. The properties of compatible and non-compatible pollutants interchange when a POTW system is used. The processes of stripping tower, nitrification and denitrification that happen in the POTW system are disturbed when ammonia is formed unexpectedly by making of fertilizers. This unexpected formation damages the backup POTW system and is the result of a soluble BOD. Bio degradable organic compounds which include but are not limited to alcohols and ketones are eliminated by the action of bacteria. The functions of other noncompatible compounds that include heavy and poisonous metals involve their use

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in the reduction of biological oxygen demand and in the making of bacterial matter as micronutrients. 5.2. Dilute Solutions Compatible and non-compatible effluents which are dilute in nature make up most of the industrial effluents. These effluents are transmitted without delay and without any initial tests into the POTW or into the factory’s pre-treatment systems. Crude oil dewatering, raw food cleaning and plating bath rinses are fabrication methods that may be categorized under dilute effluents of both compatible and incompatible nature. Increase in pollutant concentration in waste water will cause interferences in the fabrication methods. Uniform discharge of dilute effluents results from the water used in power generation processes. These processes include water used in washing and cleaning the boiler, water employed in cooling towers and waste water in pumps. Harmful chemicals that seep into the soil from their storage tanks and transmission mediums are another source of low concentration waste water. These chemicals are absorbed into the ground and mix with the underground water and water from rainfall. The low strength of the pollutant means that there is no pretreatment before it is flowed into the river. However this strength is greater than the standards set for the effluent emissions relating to surface fluids. Hydraulic capacity complications arise when the additional effluent is treated other than the normal flow to the pre-treatment system or to the POTW. This additional amount of effluent is stored in tanks and then slowly added to pre-treatment. Effluents that have seeped into the ground over the years are a priority today. These effluents are large in volume and contain high amounts of solvents, fuels, heavy metals and pesticides. The nature of these chemicals makes them quite dangerous and as public perception about the environment has developed, more stringent regulations have been put into place. As a result, these cleaning methods are employed the product of which is “cleaned industrial water”. 5.3. Concentrated Solutions Concentrated solutions are those substances or fluids made in industries and factories that cannot be put to use again in the same process that used them the first time. Concentrated solutions are not made each day but develop in fixed amounts spanning over week, months, years or more. These solutions have concentrations that are much, much more than the assorted ceiling or cap of the pre-treatment system or POTW. Since they are so strong, the recycling and

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cleaning processes are unable to purify these chemicals in one go. As a result, these substances are analysed and tested to see what purifying process would be more suitable for them so that they do not impair and render the treatment process useless. Industry standards and POTW standards differ in labelling some of these effluents “strong” or “concentrated”. A particular example can be taken of the chemical used in metal surface treatment processes. This chemical is usually sulphuric acid but other acids are also frequently used. Factories typically use around 50 % concentrated sulphuric acid that is degraded to about 10 % at the end of the process. After this process, the acid becomes useless and can no longer clean the surface to the same extent. This is when the cleaning and purification of the acid is required. However, the treatment principles still label this spent chemical (10%) as concentrated. This solution still has a pH of less than 1 and a heavy metal occurrence of 1000 milligrams per each litre of solution. Treatment principles require that for the chemical to label dilute, its pH should be between 1 and 4 and heavy metals should be present in an amount of 100 milligrams per each litre of solution. Fluids used to clean machine parts are also an origin for concentrated solutions. These are also considered ‘weak in strength’ by the industry but become concentrated once they reach the treatment area. The amount of harmful chemicals in these fluid are strongest in the beginning and are reduced each time they are used to clean the machine parts. This difference in concentration is not good for the treatment process and severely affects the IWTS system. The impact of these chemicals is increased quite greatly by the drains at the floor of the factory. Therefore, drains should not be put where these chemicals are frequently discharged. The existence of drains might cause irreversible damage to the treatment systems ahead. 5.4. Concentration versus Mass of the Pollution To plot and illustrate the ramifications of an effluent on the pre-treatment system of factories, the POTW, the IWTS and other purification methods, the amount and strength of the effluent has to be analysed and checked. The standard unit for the amount of the harmful substance in waste water is milligrams per litre (mg/L). This unit expresses the amount in grams of the harmful substance for each unit of volume of wastewater. The unit of the amount is ‘kilogram’, ‘gram’ or ‘pounds’. This is used to denote weight. Weight per unit time denotes the mass emission flow. This unit of mass emission flow is promoted to pounds or kilograms per day when used in the industry. Concentration is used in denoting metal finishing process while mass emission rates are used in other processes. The use of mass

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emission rates to express the amount of pollution has the advantage of prevention of falsifying the data. Industry owners typically add water to the pollutants in order to show that the concentration has decreased. This is prevented by using mass emission rates that increase when the quantity of water is increased. If we have the concentration of the pollutant and the quantity of effluent in which the pollutant has dissolved, then the mass emission rate can be calculated. The ramifications on IWTS and POTW are similar due to the amount and concentration of effluents. Pressure driven issues in any segment of the POTW frame work could result in effluents to pass through the POTW untreated. This is despite the fact that the amount of the effluent remained constant. On the off chance that the day by day mass stacking remains constant, and the real time mass outflow rate is exceptionally variable, the POTW's accumulation framework may not adjust the slug stacking of a strong effluent. This may cause impedance within the purification framework resulting in both effluent and sludge treatment cap to be greater than that allowed. 5.5. Frequency of Generation and Discharge The amount of industrial effluents produced and wasted is significant to the working of POTW and pre-treatment networks. The time period of flow of the effluents also affects the wastewater testing to explore process issues and consistence with the flow limitations. 5.5.1. Hours of Operation Versus Discharge Time of flow to the IWTS is equal to the time the treatment process runs. Therefore the effluent will arrive at the plant for purification running. On the off chance that the generation is consistent, the release volume and substance constituents will likewise be steady. A few normal circumstances where a modern waste must be dealt with after the typical generation hours are listed below: 1.

The "wet" methods run for one shift, yet the "dry" methodologies run for two. The dry techniques may use packed air or an evaporator. Both of these a wastewater release.

2.

In factories with long accumulation frameworks, creation and waste water stream to the framework may stop, however the IWTS may keep on operating and release until the wastewater in the gathering framework has been transformed.

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3.

The IWTS may operate more than the fixed time frame allotted to it due to the wastage, accidental discharges or storm water that flows into it.

4.

IN relation to the food processing factory, most of the waste is generated by scrubbing processes. This scrubbing and purification is done when the plant is not operating. The rest of the effluent (which is small in amount) is produced during the production of the plant.

5.

There is an equalization tank in the IWTS network. This tank is placed at the beginning or the cusp of the network. Release from the balance tank to whatever is left of the IWTS may proceed after generation stops on the grounds that it is customized to pump to the following unit process until it achieves its smallest elevation.

Equalization of the wastewater is a critical component influencing the time of wastewater release to the IWTS and sewer. So to convey a moderately steady stream and convergence of contaminations to the IWTS, huge wastewater accumulation areas, balance tanks or capacity tanks maybe utilized. These machines increase the period of flow past the working time of the factory. POTW also benefits from the equalization of industrial wastewater. By extending the hours of release of flow of the effluent, the diminished modern stream rates cause a powerful increment in the accessible pressure driven limit of the POTW accumulation framework. The typical diurnal variety in residential wastewater streams causes the water powered limit of a sewer to be increased if an extensive mechanical stream is permitted to be released to the sewer in a brief amount of time. In this manner, it might be vital for the factory to release the effluents just during the evening. Testing of this release of effluents would then be moved to the last portion of night. 5.5.2. Discharge Variations Commercial ventures that have every day, week after week, or occasional assembling cycles will indicate varieties in the waste water cycles. Business cycles for each of the different portions of the economy will have an impact on the making and transmission of wastewater. The edible food production industry gives a decent case study of major changes in release amount and quality. For instance, a citrus peel making factory which produces pectin is reliant on the time the raw peel is provided. This may mean anywhere in the range of three to six days every week. As the season advances, the kind of peel changes from orange to

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lemon, and the sugar substance also changes. This results in a somewhat diverse sort of wastewater. Once the citrus season ends, the factory is totally closed down. In some specific commercial enterprises, varieties in the amount of wastewater reflect the way of the enterprise or the cycle of operations of the specific enterprise section. In a little shop delivering printed circuit sheets, it is ordinary to have a 30-day turnaround with deals, requesting, and improvement occurring amid the first piece of the month. Generation is moderate while making test sheets, however once the board is created, creation moves ahead at a fast pace to create the sheets for shipment in the most recent week of the month. The printed circuit board industry faces both good times and bad times in the business. The real toxin from this line of work is copper. Thus, the amount of copper released to waste changes accordingly with the trends in manufacturing and economy. Changes in the nature of modern waste can also happen because of business powers or natural concerns which results in the invention of a new kind of item. In the metal polishing industry, for instance, organizations are moving from cadmium-plated metal (which is more dangerous and more difficult to release to the environment) to zinc-plated parts. Know how of the business, the assembling methodologies, and business sector factors are significant apparatuses required by the mechanical waste treatment plant administrators to cope with the changes in effluents. 5.5.3. Continuous and Intermittent Discharges Characteristics of effluents from the factories generally reflect the type of the assembling procedure of the factories. Uniform rate methods of manufacturing have a tendency to create wastewater nonstop. The volume and quality of the related effluent also remain the same. Batch manufacturing processes tend to deliver an irregular release. The bigger the assembling process, the more probability there is of a nonstop release of effluents. Illustrations of assembling procedures that have nonstop releases incorporate washing or cleaning of parts or nourishment, handling of unrefined petroleum, either at the wellhead or refinery, air or smoke scouring, papermaking, and cowhide tanning. Discontinuous releases of wastewater are portrayed by releases of a volume of wastewater divided by a period between releases. These commonly happen toward the starting or consummation of an assembling procedure or amid gear cleanup, a spill, substitution of used chemicals, or transfer of a poor quality item. Irregular releases additionally have a tendency to be more strong and of smaller amount than the regularly released waste water. For a

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modern pre-treatment factory, the irregular releases and the varieties in waste affect the build and the components of the treatment network. 5.5.4. Industrial Effluents Though the nature of the house hold waste water is moderately steady, the unpredictable qualities of modern effluents require an individual examination for each one kind of industry and frequently involve the utilization of particular treatment forms. In this manner, a careful understanding of the manufacturing methods and the framework association is a prerequisite. There are four sorts of modern effluents to be considered: 1.

Common effluents: Most procedures offer result in harmful effluents coming about because of the contact of water with vapours, fluids or solids. The effluents are either constant or irregular. They even may just be created a few months a year. Normally if creation is normal, contamination patterns is known. On the other hand, for commercial enterprises working in particular sectors such as manufactured sciences, pharmaceutical and para-chemical businesses, it is harder to dissect the effluents because of their constantly changing properties.

2.

Particular effluents: Some effluents are collected in large tanks for reconditioning at a calculated flow rate. This is done by placing them in to the treatment network again. Others are decanted into several components. Each of these components is then purified and cleaned.

3.

General effluents: Water that is discharged from households and water used in power generation utilities come under the banner of these effluents.

4.

Non constant effluents: These are very important and should not be sidelined. They may be produced during various industrial processes.

If an industrial effluent treatment plant is to work correctly and accurately, it must be made sure that the following points are implemented and followed strictly and promptly. 

Varieties of raw materials, cycles and production capacities used,



Constituents of the particles in the water used in factories,

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

Whether the effluents can be divided into constituent parts and cleaned,



Amount of each form of effluent that is produced each day,



Average and maximum flows in an hour (their duration and frequency by, variety),



Moderate and highest effluent flow (their frequency and span) for each variety of waste and effluent that is produced by the factory under examination.

The application of these parameters is extremely important since these parameters have a significant impact on the working of the plant and may very well cause damage to the machinery of the plant if not adhered to in a proper way. During the development and construction of a new industrial plant, these important factors are measured and/or calculated. Nearby industrial plants may also be utilized in this research and the data from these plants compared with that of the newly developed plant. Ultimately, it all comes down to the selection and frequency of the processes which have a final say in the extent of pollution. 6. EFFECTS OF INDUSTRIAL WASTEWATER The discussion done in this paper earlier was upon the effects of industrial waste water discharges on collection and treatment systems. The influences exerted on the operations and performances of IWTS and POTW by the industrial waste water will be discussed in detail in the following section. This section will also include details about the effects left on the receiving water by the direct discharges to the environment. Critical issues may arise by the discharging of industrial waste water to an IWTS that has not been designed with the capacity to handle such loads. This would result in the passing of untreated water to the POTW, further aggravating the situation, or it could also result in the interference with the IWTS processes. The POTW may suffer in a similar way. The discharge permit may be violated or the reuse or recycling of water may be not allowed. The industrial waste water sludge may also suffer contamination by the untreated industrial discharge or may lead to an air emission problem. The maintenance and production personnel engaged in activities in or around the industrial sewer or the treatment system may also face a health risk due to the toxic gases being produced.

Composition of Industrial Wastewaters

Green Adsorbents 21

The characteristics of the industrial waste streams, the size and design of the IWTS and the standards for discharge, recycle or disposal of waste water, sludge or air emissions will determine the criticality of the effects. In the same manner, the characteristics of the effluent, the type and size of the POTW system, the standards for sludge and waste water disposal or reuse will determine the effects of the discharging the effluent in the environment and the POTW. The compatibility of the waste water discharge with the IWTS must be calculated by evaluating the waste water characteristics such as temperature, pH, odor, toxicity, concentration and flow. The apparent effects on the POTW systems can be comprehended beforehand by evaluating the characteristics of the IWTS effluent. Industrial waste discharge may also leave some positive effects as well. High concerns are attached with the POTW collection systems in terms of small treatment system discharging to a trout stream, a continuous discharge of the boiler blow downs from a large power plant. Issues such as, accelerated biological degradation, slime growth, odor production from anaerobic decomposition and corrosion of concrete pipe and metal sewer parts can result from the high temperature discharges to the sewer. A shift in the bacterial population in the secondary treatment can result from the high temperature discharge waste water, which in turn can make BOD removal ineffective and create floating sludge. The treatment plant will fail to comply with the discharge permit limits and may also violate the allowed temperature standards to the trout stream, owing to the high temperature waste water. The secondary POTW treatment process removal efficiencies may be increased by the high temperature waste water discharge from the power plant in larger conveyance. The high temperature waste water will be beneficial in case of treatment plants situated in cold climate regions as the temperature of the waste water will be kept well above 65 F all year round. An understanding of the specific characteristics of the waste is important to evaluate the industrial waste water. In addition, the operators must be familiar with the effects of the discharge on each component of the IWTS and the effects on the conveyance, treatment, disposal and reuse of facilities of the POTW’s. 6.1. Effects on Collection System The transportation of the combined and the individual industrial waste water components is kept in mind when designing and constructing the IWTS collection system. Issues like plugging, odours, erosion, corrosion and explosions may arise as a result of a spill, leak or accidental discharge of the combined or the individual

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waste water components. These accidents may occur due to inadequate design or construction of the collection system. But some substances in the discharge have been observed to produce positive effects on the collection system. These positive effects cancel out the negative effects of the other components of the waste water discharge. In-line neutralization is among the positive effects. The waste water may be brought under the limits of treatability of the IWTS by the large flows that will produce huge velocities in low flow sewers and will also dilute the concentration of the spill. 6.1.1. Hydraulic Capacity Problems If a large slug of waste water or a continuous flow is discharged to the industrial sewer, then hydraulic overload issues may be created. A tank rupture or water line breakage can cause a slug discharge. A broken valve or a valve left open by mistake can lead to continuous large flow. A sewer back up or a pump station overflow may be the result in both the cases. The probability of the occurrence of these issues is more, when the capacity of the sewer is small and the contribution by the individual waste stream is larger. The solution lies in the detection of these risks through flow restrictions on water valves or tank levels switches to warn of high or low levels. The discharge may need to be equalized in order to restore the effluent for off-peak hour discharges, in case the condition is not improving. The introduction of new manufacturing processes may result in these situations owing to their discharge and may be dealt in the manner mentioned above. If similar processes are being used simultaneously on a site and are creating similar discharges, a hydraulic overload condition may result. For instance, there are two parts of a food processing plants. Both these plants may be carrying out the cleaning of tanks, reactors and cooking pots at the same time. A hydraulic overload may not result in case of one line of discharge, but if this line of discharge was doubled by another similar line of discharge happening at the same time, then hydraulic overload is probable. Equalization of the flow at the IWTS is the possible solution to this problem. The cleaning up process of both the lines can be avoided at the same time, by scheduling the cleaning up process. 6.1.2. Plugging The sewers may get plugged due to the presence of large amounts of fibrous or stringy materials, heavy solids, adhesives or grease in the discharged material. It is at the downstream of the discharge and at the pumping station that the plugging may occur. Rough surfaces may capture these fibrous or stringy materials, which will soon build up by entangling more solids. Pump failure may result due to the fibrous or the stringy materials getting caught around pump impellers or shafts. In

Composition of Industrial Wastewaters

Green Adsorbents 23

case of the problem persisting, the manufacturing process should be checked for faults. The discharges should also be treated before discharging to eliminate the problem. The need for any modifications in the process or disposal of wastes or the need to enlarge the sewers to give more room for the materials can be ascertained based on the review of the manufacturing process. The hydraulic capacity of a pumping station can be reduced by the accumulation of heavy solids such as sand, ceramic or porcelain solids in the sewer or the pump station wet well. When the waste water is not pre-treated to remove solids before discharge, the solids are discharged during peak waste water flows during the day and when the flow subsides, these solids may settle down in the pump station wet wells or oversized sewers downstream of the actual point of discharge. The solids may get compacted after settling and they will not resuspend, until the flow in the sewers return to their peak flow. Restrictions in the flow will be created due to the accumulation, settling and compaction of the solids in the cycle of transportation. When large objects are released to the sewer, the flow may get completely blocked. If the operator is not careful or the equipment is mal-functioning, there can be an accidental release of rags, tools or rejected food products in to the sewer. The sewer or the lift station pump can get completely blocked, if these large sized materials get wedged or entwined with other waste materials. 6.1.3. Odors Industrial waste discharged from the processes involving the process of petrochemical manufacturing, food processing and petroleum refining can normally be odorous. Compounds containing sulphur such as, Hydrogen sulphide and mercaptants produce strong odours. Residents and other industries usually complain about these odours. These odours can be calculated as parts per billion range (by volume) in the air. Industrial discharges are the main source if this problem, although this problem is airborne. The POTW system’s discharge usually contains this problem. The modification of the manufacturing process may be the first option to address this issue. Steam can be used to strip the waste water containing high concentrations of sulfide (sour water). The Klaus process can be used to reduce the elemental sulfur. The odor producing pollutants have been successfully reduced through this process and various other recovery processes. I return they have produced sulfur as a by produce, that can be sold in the market. In the other option, the pollutants can be oxidized through air, hydrogen peroxide or chlorine before discharge. The other option is not to discharge these pollutants at all. Incineration is also a solution. Odiferous substances are produced during the process of etherification reaction to make polyester. The waste product is incinerated at zero fuel cost, as it contains a high percentage of organics.

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Toxic and corrosive conditions can be created by the industrial discharge of sulfide. Hydrogen sulfide gas may be produced under anaerobic conditions in the sewer, when a biodegradable material is present with a source of bacteria and sulfide. In the presence of insufficient oxygen in the waste water, the inorganic sulfate is reduced to sulfide by the bacteria. Hydrogen sulfide gas is produced as a result. Other bacteria present in the waste water will oxidize the sulfide to sulfate under aerobic conditions thus producing sulfuric acid. The crown of the sewer pipes can be severely damaged by the sulphuric acid. The sewer maintenance staff is threatened by the présence of the hydrogen sulfide gas, which is toxic. If discharged to the sanitary sewer, the IWTS operator with the POTW collection system will also be under threat. Sulphurous and sulphuric acid will be produced, when hydrogen sulphide is dissolved in the waste water. The uncoated material and concrete surfaces will be easily corroded by the sulphuric acid. An active biological population is required for the anaerobic reduction process, plus this process is time consuming as well. Prior to discharge, the sources of sulphide and sulphate should be detected and recovered and treated. Oxygenation and chlorination can be tried as an option before discharge. The waste water in the collection system can be aerated. A slug loading of alkali or chlorine can be used to periodically remove the slime layer of anaerobic growth in the system or a high velocity cleaner or a pig can be used to periodically clean the sewer. Restrictions are applied on the industrial discharges to the POTW with a high concentration of sulphide with a total of 5mg/L of total sulphide and 0.5 mg/L of dissolved sulphide allowed. 6.1.4. Problems with pH It is during the designing phase that the pH of an industrial discharge or the amount of acids and alkalis discharged to an industrial sewer are considered in the calculations. Modern facilities are using plastic, fiberglass or other resin materials to construct the industrial waste water pipes and sewer systems. Earlier materials that were less resistant to corrosion were used by the petroleum, chemical and primary metal industries. Modifications in the processes can initially lead to problems. Sometimes the system is not compatible to the new chemicals introduced in the process, also causing problems. For instance, sulfuric acid is not dangerous in a system manufactured using fiberglass, but the introduction of hydrofluoric acid may cause damage in this system. Strong acids or alkalis may be handled by the industrial system that has been specifically designed for these chemicals. But these systems may not be equipped

Composition of Industrial Wastewaters

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to handle high temperatures resulting from reactions. The temperature may increase when a concentrated solution of sodium hydroxide is discharged to the sewer. The heat of the solution may go well beyond 104 degrees Fahrenheit, which is the temperature at which PVC will deform, if there is a small quantity of stagnant waste water in the sewer pump station. Steam can be produced due to a rise in temperature because of a spill of liquid chlorine, which in turn will lead to the production of toxic gas. Plastic is easily damaged by liquid chlorine. Concrete and cast iron sewers, concrete wet wells and tanks, trickling filters, aerators, the internal steel equipment in the primary and secondary clarifiers, and pumps are easily corrode by acids. The base metals are cleaned by using mineral acids such as, sulphuric acid, nitric acid, hydrochloric acid and phosphoric acid in the metal finishing industries. These acids are also used by the fertilizer, iron and steel mining industries in huge quantities. 6.1.5. Flammables The collection system is threatened the most by the discharge of flammables. Explosions have been caused by the gasoline, aviation fuel and hexane in the sewers used in the soybean extraction. These explosions have cost damages worth million dollars. People have lost their lives due to these explosions. The discharge of these materials has to be prevented by strictly monitoring and controlling the industries producing and distributing based on fuels and solvents. Fuels and solvents have a specific gravity less than water and are only slightly soluble in water. These fuels and solvents will float and will get collected in slow moving sewers and pump station wet wells, in case of an accidental discharge. Fire or explosions can be created in the presence of a source of ignition. A spark created while removing a manhole cover with a pick or tripping a breaker can create that ignition. Owing to the same reasons mentioned above, the discharge of flammables to the PORW sewer can also be dangerous. Explosions can be created, if the concentration of flammables is high enough. The usage of pure oxygen in the secondary treatment system can also be dangerous. If the secondary treatment system is not uncovered, then also it can be a serious threat. In a pure oxygen activated sludge system, any hydrocarbon may create a threat of fire or explosion. To prevent any possibility of explosion or fire, sensors and purge systems are installed. 6.1.6. Temperature The manufactured processes are controlled thus causing the production of heated industrial waste water. The production of energy in these processes will also

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create heated waste water. The rate of reaction is increased during the manufacturing processes through heat, which leads to a heated product or waste that must be cooled. The product or by-product is heated or cooled by a direct or an indirect usage of water. Water is also used to transport the product to the next step of the process. The processes solutions are heated through steam in the metal finishing industry. The boiler tubes and steam lines are protected from plugging by removing the solids collected in the pipes. This discharge is termed as boiler blow down. A heat load is added to the industrial and POTW system, in cooling systems, single pass cooling water and cooling tower blow down. IWTS collection and treatment systems also suffer from issues such as, gases, odours, pump overheating, rotation of equipment bearings, shift in the population of microorganisms used in the biological treatment of industrial waste water and sterilization, due to the heated industrial discharge. PVC cannot be used for transportation of hot water, as it has a temperature limitation of 40 degrees centigrade. Exfiltration or infiltration of the collection system may occur, due to the failure of the O-rings to tolerate constant high temperatures in the POTW sewer laterals. This is because; the O-rings have not been designed as such. A similar problem can occur in the POTW collection and treatment systems. The permit limit may be violated, if the POTW is discharging to a stream or a lake with a temperature limit and the discharge exceeds this limit. 6.2. Effects on the Treatment System The manner in which the collection system is damaged by the industrial waste discharges is the same for the treatment plant as well. The pumping capacities are well exceeded by the high volume discharges. High solid discharges can plug the mechanical equipment, such as bar screens or pumps. Metal parts will fail to function due to corrosion by the acids and the alkalis. The presence of flammables is the greatest threat of all, as explosions can instantaneously destroy the entire process. Other additional concerns are also attached with the discharge of industrial processes such as blinding of the filters with oil, reverse osmosis membranes, nanofiltration, plugging microfiltration, contamination of the byproduct through intrusion in the recovery processes and unnatural modifications in the aerobic and anaerobic biological treatment processes. 6.2.1. Hydraulic Overload It is under conditions of a constant flow and constant loadings applied that an optimum performance of unit processes such as neutralization, sedimentation, filtration and biological treatment can be obtained. The efficiency of these

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processes will be reduced after large changes in the volume of the flow or accelerated changes in the loadings. These accelerated variations are evident in the presence of hydraulic surges from an industrial process or utility discharges. A series of changes must be introduced in the plant operating conditions in order to deal with these inadequacies. The increase of the blower output, increase in the chemical addition rate, changes in the sludge removal rate is among the options that can be incorporated. If changes are not accommodates, the effluent limit will be violated. The hydraulic surges are best controlled by operating the treatment process at a constant or near constant flow rate, through equalization of the flow at the source or as part of the IWTS. 6.2.2. Interference A discharge that interrupts the POTW alone or in combination with other discharges from other sources has been termed as interference by EPA. This interference will also interfere with the treatment processes or operations, sludge processes, usage or disposal. The sludge is not disposed according to regulations, due to these interferences. Discharges by industrial processes to the IWTS also suffer the same case of interference, as explained above. The potential interference issues are detected by the IWTS operator while working in coordination with the manufacturing and utility operators. The sudden or gradual changes in the operation of the plant or quality of the effluent are best identified through good communication between the IWTS operator and the operators in the manufacturing facility. Interference is created with the POTW treatment processes due to the discharge of untreated wastes or even large quantities of treated waste. 6.2.3. Influent Variability The changes in the influent to the IWTS or POTW are identifiable through measurements of waste water flow, pH, temperature and conductivity. Major upsets may be created due to the hydraulic surges and the variability in the chemical composition of the influent waste water. The intensity of the problem will increase with the increase in the difference between the existing influent composition and the contribution from the industrial discharge. The concentration of the acid in the influent will increase by manifolds, due to the change in one pH unit. The pH of the waste water greatly affects the chemical reactions, precipitations, filtration ability and settlement ability. The accelerated in the environmental conditions will cause an interruption in the aerobic and the anaerobic treatment of the biological treatments. The toxicity level for the bacteria will be too much in operations outside of the pH range of 7.0 to 8.5. The microorganism can adapt to the pH levels slightly beyond this range, if the change

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is gradual. The increase or the decrease in the soluble salts, cyanide or metals is normally represented by the changes in the conductivity or ORP. The over loading of the chemical processes with the mass of metals or cyanide requiring treatment to prevent the biological reactions may cause a range if interferences and inhibitions. The rate of oxygen transfer through bacterial cell walls is modified by the changes in the soluble salt concentrations. This in turn will influence the health and performance of the micro-organisms. 6.2.4. Slug Loadings (Also Called Shock Loads) The treatment processes or passage of pollutants may be affected by the slug loadings or batch dumps of compatible or non-compatible pollutants from industrial processes, whether they are intentional or accidental. The mass of the discharge and the resultant concentration at the treatment plant need to be considered in order to analyse the effects of the slug loadings. For instance, a resultant concentration of 5 mg/L for a 5 minute will be obtained due to the discharge of a concentrated solution containing 45.3 g of copper. The effect on the activated sludge treatment system would be minimum, although this will be considered as a serious deviation from a 0.25 mg/g average influent concentration. If this deviation occurs only once, then it will not affect the sludge reuse potential. The biological treatment system will definitely be affected, if the concentration remains at 5.0 mg/L for a one hour period. The sludge would get contaminated as the biological treatment would be reduced or completely stopped. Both the examples showed the same measured concentration of sludge loadings at the treatment plant. A batch dump which was 12 times more in mass than the first was seen in the second example. Until the time that new bacteria are cultured to restore the process to their previous efficiency, the sludge would be contaminated, discharge limit would be exceeded and the efficiency of the biological treatment removal would be severely affected. The organisms in the activated sludge or the trickling filter process would collect and the effluent quality will remain unaffected by the daily discharge, if the slug loadings are continued every day. 6.3. Effects on Effluent and Sludge Disposal and Reuse The pass through discharges is a combination of the industrial discharges with the discharges from other sources that pass through the POTW’s facilities to waters that can be controlled. The pass through discharge will not comply with the discharge limit. When the POTW system is under stress, the pass-through of compatible and non-compatible pollutants may occur. The stresses may be caused by the hydraulic or compatible waste overloads or shock loadings of toxic

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pollutants. The effluent will contain components of the industrial discharge, when the pollutant removal efficiency declines. Small quantities of toxic organics that are miscible or immiscible will most likely pass through the IWTS. In addition, lipophilics, polychlorinated biphenyls and soluble heavy metals that are not used as micronutrients may also be found in the discharge. Small quantities of toxic organics that are miscible solvents or chelated metals will pass through a physical-chemical IWTS. The level of the toxic discharge in the sewer is reduced to the minimum extent by controlling the toxic constituents on site. The recycle and the reuse option of both the effluent and the sludge are optimized. The sludge can further undergo treatment to use it further. Agricultural lands can use sludge as fertilizers and if the sludge is not biological, it can be mixed with a bulking agent and converted into compost. The sludge can be refined or smelted to extract the ore, if it contains a high percentage of metal in it. The effluent and the sludge quality will eventually get affected, even if the industrial discharge is allowed to pass through the treatment system. The waste water has been contaminated by the industrial processes. The effluent and the sludge become a liability, instead of being used as a useful source. 6.4. Effects on the POTW The effects of the manufacturing process waste on the IWTS goes hand in hand with the effects of an industrial discharge on the POTW collection, treatment and the disposal system. Each system component suffers issues. The removal of toxic pollutants at the source was the main aim behind the Pre-treatment Regulations, which were put in place to protect the POTW’s collection, treatment and disposal system. The characteristics, the skill of the POTW inspectors, laboratory analysts and the POTW operators, the industrial flow and the flexibility of the system will determine the effects of an industrial discharge on the POTW. The manner in which the industrial discharge will affect the POTW collection system will also be governed by the size and length of the sewer system. The effect of s single discharge on the POTW will be minimized with the increase in the size of the system, irrespective of whether the industrial discharge is a slug loading or a constant discharge. The effects on the POTW facilities are reduced, as a larger system will naturally support equalization and dilution of the industrial discharge. The effect of an industrial discharge will increase with the increase in the complexity of the POTW treatment systems from primary to tertiary systems. Industrial discharges will more likely disturb the higher degree of treatment. The toxic ‘overdose’ of the heavy metals will destroy the secondary and tertiary processes such as, activated sludge, nitrification, denitrification and anaerobic digestion. The passing of oil or carryover gelatinous bacteria from a misbalanced

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biological process will leave a tertiary physical-chemical process such as sand filtration, completely useless. The effects of the industrial discharge can be controlled by modifying the configuration of the treatment system. The passing through of non-compatible pollutants or air strip volatile organic compounds can be prevented by the modifying the recycle ratio on a trickling filter or changing the concentration of biomass in an activated sludge system. The high loadings of the compatible pollutants can be removed from the system by changing a two unit process from parallel operations to a series operation. The industrial discharges will also affect the disposal of the POTW effluent and sludge. In comparison to the requirements for the discharge of the effluent to receiving waters, the requirements for the discharge of effluent for water reuse are stricter. This means that much severe requirements will be applied on the use of POTW sludge as a part of the compost for resale, while the requirements for sludge being land filled is more lenient. The recycle and the reuse are limited owing to the toxic components of the industrial discharge. The toxic components may get involved when the POTW is not properly protected from slug loadings or a certain level of contaminated concentration is attained which may pass through easily and become a part of the sludge or the effluent. The sludge will be deemed as hazardous, if certain metals reach dangerous concentration limits. 7. DYEING WASTEWATERS The wastewater discharged from the dyeing industry is also an important topic. Human health is endangered by the toxic, carcinogenic and hazardous chemicals of these factories. Pre-treatment, dyeing, printing and finishing are included in the process by the textile printing and dyeing industries. The pre-treatment process of pulp, cotton gum, cellulose, hemicelluloses and alkali produce organic matters as the primary pollutants. The printing processes are using additives and dyes that are also pollutants. The finishing process produces minimum pollutants, while 55% of the pollutants are contributed by the dyeing and the printing process, while 45% is contributed by the pre-treated waste water. About 69% of the pollutants are produced by the chemical fiber in China, out of which 80% is contributed by the polyester fibers. About 80% of the natural fiber production is based on cotton. The analysis of these two fibers will account for the analysis of the dyeing waste water and the pollutants produced. Desizing and scouring is a part of the pre-treatment process of cotton. The impurities present in the cotton, cotton gum, hemicelluloses, slurry and the alkali used in the weaving process account for the main pollutants. Currently, 3,000 mg/L of the COD concentrations are obtained in the pre-treatment waste water. The residual dyes and the

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auxiliaries from the dyeing and the printing processes make up the main pollutants of this system. After mixing, the average concentrations produced are 1000mg/L of COD and 2,000 mg/L of the total average concentrations. The reduction of the alkali includes the pre-treatment of polyester fibers. The reduction process is based on the treatment of the polyester fabric with 8% of sodium hydroxide at 90 degrees centigrade for about 45 minutes. Sometimes a thin polyester fabric is obtained after some of the polyester fabrics have peeled off and decomposed into terephthalic acid and ethylene glycol to obtain a silky texture. Continuous process can be conducted or it can be conducted in batches. The concentration of COD is about 20,000-60,000 mg/L in the batch type. About 5% of the volume of waste water is based on the waste water produced from the reduction process. In the conventional dyeing and finishing process, the COD accounts for 60% of the waste water. Chroma is the main concern. The average dyeing rate in the dyeing process is more than 90%, which implies that the remaining 10% is taken up by the residual dyes in finishing waste waters. This becomes the main factor behind contamination. The presence of chroma in the waste water has increased 200 to 500 times more than usual. The pH is another factor, as after the treatment of water with alkali at high temperatures around 90 degrees centigrade, the pH of the dyeing waste water stays between 10 to 11 after the treatment in the process of scouring, desizing and mercerization. Sodium hydroxide is used in the polyester based reduction processes. The total pH stays between 10 and 11. The pH value of the textile dyeing waste water needs to be adjusted, because most of the dyeing water is alkaline in nature. Dyes and raw materials produce up to 10 mg/L of the nitrogen and ammonia nitrogen present in the waste waters. Batik techniques are used, as the urea is required. The nitrogen through this is about 300 mg/L which is a hard to treat nitrogen. The phosphor detergents contribute the phosphorus in the waste water which will cause eutrophication of surface water and hence needs to be controlled. Trisodium phosphates are used in some industries to attain phosphorous levels around 10 mg/L. The pre-treatment process will remove the phosphorous. The fiber scrap and the undissolved raw materials lead to the suspended substances in the production process that can be removed through grille and grid. The secondary sedimentation tanks containing sludge that have not been separated completely, will result in the suspended solids reaching up to 10-100 mg/L. sulfur produces sulfide, which is a cheap dye. The developed countries have forbidden its usage due to its high toxicity level. In China, the sulfides have been included in the waste water standards, as some of the industries are using it in their processes. About 10 mg/L of sulfide is present in the waste water. Hexavalent chromium is produced from two main sources. Cylinder engraving and the usage of potassium

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dichromate additive in hair dyeing is another source. Cylinder engraving process is not used. Dyes also produce aniline. The chromophore produces the colour of the dye. Amino rings and benzene rings are also present in some dyes, which will be decomposed by the treatment of the waste water. Table 6 presents the potential specific pollutants produced by the textiles [3]. Table 6. Specific pollutants from textile and dyeing processing operations. Process

Compounds

Desizing

Sizes, enzymes, starch, waxes, ammonia

Scouring

Disinfectants and insecticides residues, NaOH, surfactants, soaps, fats, waxes, pectin, oils, sizes, anti-static agents, spent solvents, enzymes

Bleaching

H2O2, AOX, sodium silicate or organic stabiliser, high pH

Mercerizing

High pH, NaOH

Dyeing

Colour, metals, salts, surfactants, organic processing assistants, sulphide, acidity/alkalinity, formaldehyde

Printing

Urea, solvents, colour, metals

Finishing

Resins, waxes, chlorinated compounds, acetate, stearate, spent solvents, softeners

7.1. Textile Dyeing Wastewater Risk Environmental issues are being created by the discharged waste water of some industries that is being discharged uncontrolled and under inappropriate conditions. The future of the human race depends on the treatment and pollution control strategies. The natural water bodies and the land in the surrounding areas will get disturbed by the discharge of the waste water in the local environment by the textile mills. The dissolved oxygen sources in the water will get depleted by the high concentration of COD and BOD5, grease, oil and particulate matter in the effluent. The high concentrations of chromium discharged through the effluents from the textile industries may enter the food chain and cause threatening effects. The effluents are dark in colour owing to the presence of dyes and chemicals, which increases the turbidity of water. The photosynthesis process is destroyed thus affecting the entire food chain. 7.2. The Textile Industry Standards for Water Pollutants The various agencies have applied strict regulations in the disposal of waste water due to the presence of harmful pollutants in the waste water. The standards of the waste water have too much items, as there are huge variations in the raw materials, products, dyes, technology and the equipment. The local conditions and environmental protection requirements are considered by the national

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environment protection department in developing such standards. These standards are different from region to region. The nature of the emissions is a primary consideration. 8. RADIOACTIVE WASTEWATERS The scale of the applications and range of activity connected with the nuclear and the radioactive material usage in a certain country will determine the generation of radioactive wastes, which implies that the radioactive waste will differ from one country to another. The human health and the environment are at great risk due to these radioactive wastes and much debate is going on upon the proper disposal of these waste products. The processes of generation, collection, separation, treatment, storage, conditioning and transportation will become more convenient, when these waste a categorized into groups. The categorization can be derived on the basis of safety requirements, physical/chemical characteristics of the waste, process engineering or regulatory concerns [4]. The choice of the type of management will depend upon the radioactivity level of the waste. This due to the various shielding requirements imposed. The activity level and the half-life are being considered by the current internationally accepted classification system for the categorization. The categorization is done in a manner to eliminate the (EW), low- and intermediate-level wastes (LILW). These are further categorized into short-lived (LILW-SL), and long-lived (LILW-LL) wastes, and high-level wastes (HLW) [4]. The annual dose to members of the public of less than 0.01 mSv is used to determine the clearance levels. The EW will be according to the activity level at or below the clearance levels. The activity levels are above clearance levels and thermal power is below about 2 kW/m3 in case of LILW. There are restricted long lived radionuclide concentrations for LILW-SL, while for there is long lived radionuclide concentrations exceeding limitations for short lived waste in the case of LILW-LL. When thermal power above 2kW/m3 and long lived radionuclide concentrations exceed limitations for short lived waste, HLW applies the thermal power. The management of radioactive waste is dependent upon the treatment process s it reduces the volume of the generated waste. The reduction of waste means that the costs are reduced and the safety is enhanced. The waste is split into two parts. The concentrate containing the bulk of radionuclide forms the first part and is less in volume. This part is restricted to the management system. The low radioactivity material forms the second part and is more in volume. This portion is treated and then disposed of to the environment [5]. The liquid radioactive waste was categorized into aqueous and organic liquid wastes. This made the management of

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liquid wastes much easier. The fact that nuclear waste is hazardous to human life has been accepted as a terrifying truth and more attention is being paid to the proper disposal of these materials in order to protect the environment from the radiation released by these materials [6]. After consideration to the chemical and biological characteristics of the liquid radioactive wastes, conventional treatment methods are applied. New emerging trends in the selection and application of radioactive waste management strategies and technologies are being observed such as, new legislations and regulations, new waste reduction strategies, safety and risk analysis, incorporation of safety measures in the design and operation of waste management facilities, new technology and development of quality assurance steps.

Green Adsorbents, 2015, 35-53

35

CHAPTER 2

Adsorption in Wastewater Treatment Abstract: In this chapter, the process of adsorption is described and especially its use in wastewater treatment. Some literature reports of previous decades are given in order to compare the adsorption applicability in past and present, and the various isotherm models used are extensively described.

Keywords: Adsorption, Brunauer-Emmer-Teller (BET), Dubinin-Radushkevich, Flory-Huggins, Freundlich, Halsey, Langmuir, Redlich-Paterson, Sips, Temkin, Toth, Wastewater. 1. INTRODUCTION Among the decontamination techniques of waste water, absorption is an important process. A variety of the treatment technologies have been established that have fuelled the research of the scientific community in this respect. The main processes being the precipitation, coagulation-flocculation, sedimentation, flotation, filtration, membrane processes, electrochemical techniques, biological processes, chemical reactions, ion exchange and absorption process [7-17]. In the process of absorption, multi component fluid mixtures are attracted to the surface of a solid absorbent and form attachments through physical or chemical bonds. This is an effective process for the waste water treatment [18]. This process is economical, viable, technically feasible and socially acceptable [19]. 2. ADSORPTION FOR WASTEWATERS DURING PAST DECADES Adsorption technique for wastewater treatment has become more popular in recent years owing to its efficiency in the removal of pollutants too stable for biological methods. Dye adsorption is a result of two mechanisms (adsorption and ion exchange) and is influenced by many factors such as dye/adsorbent interaction, adsorbent’s surface area, particle size, temperature, pH and contact time. The main advantage of adsorption recently became the use of low-cost materials, which reduces the procedure cost. According to a brief screening in Scopus, numerous results were exported for the term “dye adsorption” (Fig. 1). The major peak for this process was observed in 21st century. The present review firstly introduced the technology process, research history and hotspot of adsorption. The application in dyeing wastewater was then described in details. Major conclusions for the differences of procedures were strongly influenced by George Z. Kyzas All rights reserved-© 2015 Bentham Science Publishers

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new trends and economic aspects of each time-period. All of these confirmed the sustainability of adsorption technique. Another point of interest is the different philosophy of adsorbent materials used during the last decades, making the turn to low-cost materials obvious. 1000 900

Adsorption

800

Papers

700 600 500 400 300 200

2011-2013

2001-2010

1991-2000

1981-1990

1971-1980

1961-1970

1951-1960

0

1910-1950

100

Fig. (1). Works published for “dye adsorption” terms (Data after search in Scopus).

2.1. First Attempts (1910-1950) It was 1912 that the first paper on dye absorption was published. The paper attempted the separation of particle dye molecules through the absorption techniques. This study was conducted by Chapman and Siebold [20] and was more of an analytical process with limited knowledge. The growing crystals of sodium nitrite were used to remove the dye materials such as lead nitrate and barium nitrate [21, 22]. The removal of wool violet 4BN from lead sulphate was studied, leading to acidity optimum conditions [23]. The absorption interactions of methylene blue, Congo red, Bordeaux extra, indigo carmine and Solway ultrablue were studied by Gibby and Argument [24]. The Gibb’s equation was used to calculate the absorption, as it showed the absorption passed through maximum with the increase in the concentration. 2.2. Initial Knowledge (1951-1970) Ewing and Liu also studied the absorption of crystal violet and orange II from aqueous solutions on anatase, rutile and zinc oxide [25]. Some of the oxides were encouraged in some processes and a variation in the nature of the absorbent material was evident. True equilibrium was obtained after 9 days of agitation. The

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process was further stimulated by high temperatures. The absorption was physical in nature. The importance of dye absorption in crystal habit modification phenomenon was studied by Whetstone [26]. Modified crystals were studied that showed various results indicating absorption of dyes with overgrowth of dye molecules. The specific absorption of the alkyl orange dyes on silica gels was observed by Haldeman and Emmett [27]. These gels were manufactured in the presence of these dyes. A specific absorptive capacity was observed in the results for the particular alky orange present during the gel preparation. When the gels were stored at a specific temperature, the specificity disappeared gradually. The heats of the absorption of Congo Red and Fuchsine were calculated by Prasad and Dey [28] to study the dynamics of the process. Various samples of hydrous thorium oxide were used for this purpose. The order of heat absorption conformed to the order of specific absorption of the dyes by the samples. Brooks presented an intense study in the dye absorption process [29] indicating the changes in the process since the last few years. The mechanism of Methylene blue absorption from aqueous solutions was explained by Brooks in relevance to a different absorbent system. This process used common siliceous materials found in the petroleum reservoirs formation. To cover all the cec sites on the mineral surfaces with sodium, three minerals montmorillonite, kaolinite, and silica-sand flour were used. These three minerals were used as a base for the measurement of the Methylene blue dye absorption isotherms. The isotherm of some cynanine dyes was observed in other studies to be absorbed on the surface of the silver halide precipitates [30, 31]. The measurements of the absorption of the argon and benzene vapor were used to derive the specific areas of precipitates. Absorption was not observed for the given cyanine dye in the same area per molecule under saturation conditions on each of the silver chloride, bromide and iodide surfaces. It was in 1969 that Davis et al. [32] made the first attempt to use porous and ceramic absorbent materials. The dye adsorbtion was seen on surfaces of untreated and pre-treated ceramic raw materials. The ceramic materials had never been in this capacity before. Specific surface area is a factor that determines the absorption of dyes on alumina, bone, ceramic colours and flint. A hysteresis effect is observed on the porous materials such as flint based on the difference of rate of absorption and desorption. 2.3. Economic Development (1971-2000) Many changes were accepted during this time period regarding the absorption of model dyes from aqueous solutions. This led to the development of new theories and materials. The results of an experimental study were presented by Iyer et al. [33] in

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which the effects of electrolytes in the aqueous dye bath according to various surfaces were observed. Samples of viscose rayon, amorphous titanium dioxide, silica (aerosil), Graphon, and activated charcoal were dyed using the anionic direct dye Chlorazol Sky blue FF. The sample’s absorption thermodynamic parameters were studied as a function of the electrolyte concentrations. Rock and Stevens conducted the first approach on dyeing waste waters [34]. A combined process based on absorption of synthetic polymers and ion exchange was studied. In comparison to the activated carbon absorption, this process had various operating and performance benefits. In 1975, the need for a more complete approach was realized by Sethuraman and Raymahashay [35]. The kinetics of absorption of two industrial dyes (Mythelene blue and Sulfur blue) was studied through an experiment involving kaolinite and montmorillonite clays. Montmorillonite was used to remove the cationic dye from the aqueous solutions at a constant decelerated rate from 10 to 0.07 mg/g min. The dye was absorbed at a constant and a faster rate of 16 mg/g min by the kaolinite. Kaolinite was used to remove the anionic dye at a uniform rate of 2.3 mg/g min and montmorillonite was used to remove it at 2.6 mg/g min. Besides the factors of pH, kinetics, capacity, etc., there were other parameters as well that were considered later on under the economic upheaval. The effectiveness of dye removal from textile waste waters through low cost activated carbons was studied by Mitchell et al. [36]. This was the first time low cost materials were preferred. The residual dyes could be effectively removed from waste waters through activated carbons produced from solid wastes. The quality of removal process varied from the type of carbon produced. For instance, carbon produced from peanuts gave a poor performance as compared to the carbon produced from pine bark. Activated carbon from the peanut hulls was used to reduce the carbons to less than 1 ppm concentration. The removal of organics, including dyes can be best done through the activated carbon. This method has proven to be economically viable as well. Agricultural, industrial and municipal solid waste is a potential source of carbon. McKay [37] did a further study into the real industrial dyeing waste waters. The ability of Fiktrasorb 400 activated carbon was studied in this process to absorb Astrazone Blue and Telon Blue dyes. The experiment was done on batch equilibria and fluidized beds. According to the dye stuff type and particle size of the absorbent, the carbon was absorbed between 30 and 80%. The fluidized beds were also used to study the effects of absorbent particle size and dye flow rates, while fixed beds were also used. The results from both the experiments were correlated into a design model using the bed depth service time (BDST) method of analysis [38]. The study of diffusion of dye

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molecules onto absorbents during the process was undertaken by many researchers during this era [39-42]. 2.4. 21st Century 2.4.1. Activated Carbon Activated carbon has proven to be the most useful material from the 21st century [43,44]. In comparison to other treatment methods, the activated carbon has been successfully used in the removal of a wide variety of dyes from the waste waters [44]. Activated carbon is considered the most effective material owing to its capacity to absorb pollutants. Their chemical properties can be further enhanced through chemical treatment and they have a larger surface area due to their structural characteristics and porous textures. Examples of waste water decolourization with activated carbon will be provided ahead. Surface area, adsorbate, solution pH and the presence of other ions in solution, pore size distribution and surface functional groups on the absorbent, polarity, solubility and molecular size will determine the capacity of the activated carbon to absorb. Microporous are the most frequently used activated carbon types. They have a high surface area and are highly efficient for the absorption of low molecular weight compounds and larger molecules. Methylene Blue was also studied in conjunction with the activated carbon fiber. Removal of noxious gases has been through it. It has proved itself through its large surface area, high absorption capacity, easy reproduction, processibility and well-developed micropores. The effects on the absorption rate in relevance to the initial MB concentrations and ACF mass were studied. The Freundlich isotherm equation was effectively used. The process recorded high speeds [45]. The porous properties and hydrophoicity of the activated carbon were calculated by Nakagawa et al. [46]. This activated carbon was extracted from PET waste, waste tires; refuse derived fuel and waste generated during lactic acid fermentation from garbage. The traditional steam activation process was used to extract activated carbon with varying pore size distributions. Pretreatment method using mixtures of raw materials with metal salts, acid treatment and carbonization was also used. To confirm the applicability of these carbons in practicality, the liquid-phase absorption characteristics of organic compounds from aqueous solutions were obtained. The representative adsorbate was used in the form of reactive dyes. The absorption capacity was found to be high for the activated carbons with numerous mesopores prepared from PET and waste tires. These activated carbons could absorb large molecules in larger capacity. These can prove to be specifically

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efficient in case of bulky absorbates during the waste water treatment. During the batch and continuous activated carbon absorption system, atrazine was displaced by strong portions of natural organic matter, as stated by Li et al. [47]. The type of PAC was found to determine the extent of atrazine displacement by NOM. The rate of function was dependent on the type of carbon dose and PAC. The absorption of three acidic dyes Acid Blue 80 (AB80), Acid Red 114 (AR114) and Acid Yellow 117 (AY117) was absorbed by the activated carbon. Absorption isotherms for three single components of (AB80, AR114, and AY117) and three binary components (AB80+AR114, AB80+AY117, AR114+AY117) were also reported for the same paper by Choy et al. [48]. For the prediction or correlation of the binary data, four models were introduced to determine the multi-component equilibrium sorption isotherms such as; extended Langmuir isotherm, simplified model based on single component equilibrium factors, a modified extended Langmuir isotherm with a surface coverage dependent interaction factor and a modified extended Langmuir isotherm with a constant interaction factor. Karanfil et al. [49] studied ACF10 for the adsorption of trichloroethylene (TCE) by two ACFs and two granular activated carbons pre-loaded with hydrophobic and transphilic fractions of NOM. Kannan et al. [50] studied the kinetics and mechanism of the MB adsorption by using the commercially activated carbon. Bamboo dust, coconut shell, groundnut shell, rice husk, and straw were used to indigenously prepare activated carbon for this study. The study of combined adsorption membrane process was done by Jirankova et al. [51] on the removal of organic dyes. Experiment was conducted in batches to study the Egacid red sorption on PAC. McKay et al. [52] conducted the removal of two organic pollutants, acid dye and parachlorophenol from aqueous effluent through tapered bed adsorption and activated carbon. To acquire the saturation capacity (Qe) for each pollutant, equilibrium isotherms were measured by using Chemviron Filtrasorb 400 carbon for the function of continuous adsorption columns. The sorption process of these organic pollutants is best described by the RedlichPeterson isotherm’s best fit model. Tapered beds have not been subjected to conventional bed depth service time (BDST) model before because of the continuously changing linear velocity of fluid along the column. The adsorption of various dyes has been tested by various other researchers as well [53, 54]. Chemical treatments have been used to modify the surface chemistry of selected activated carbons using HNO3, H2O2, NH3, and thermal treatments under a flow of H2 or N2 [55]. These treatments did not modify the textural properties but the dye adsorption was significantly affected by altering the surface chemistry. A positive effect has been indicated by the acid oxygen containing surface groups for cationic dyes. But a good performance was gained by the thermally treated

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samples, revealing the presence of two parallel adsorption mechanisms. These mechanisms involved electrostatic and dispersive interactions. The colour removal from real textile process effluent further confirmed the results for each dye. Agricultural waste is another source of activated carbon. Some detailed reviews on this area were made by Demirbas [56] and Sharma [57]. Cheap and renewable additional source of activated carbon was found in the agricultural waste and various unused plant parts. These waste materials are hard to dispose and are worthless, so instead, they can be used to remove dyes in both treated and untreated forms. Sharma [57] explained a wide range of agro-waste produced activated carbons such as, as pine wood, corn cob, fruit stones, nut shells, cassava peel, tapioca peel, bamboo, bagasse, rice husk, bark, leaves and used tea leaves. The removal of Malachite green was conducted through activated carbon prepared from rice husk, which proved to be an effective adsorbent. It proved to be better than the activated carbon prepared from banana peels [58], date pits [59], rice husk [50], wood saw dust [60], orange peel [58], and sugarcane dust [61]. In the removal of malachite green, sulfuric acid treated saw dust was better than formaldehyde treated saw dust in terms of adsorption capacity [62]. The ACR adsorption capacity was not influenced by the pH. Dye removal by SDC and SD was optimum when the pH was between 6 and 9. Ash prepared from rice husk had a high surface area and volume, which proved to be an efficient adsorbent. About 690 mg/g was estimated as the maximum monolayer capacity. Ash showed more adsorption than activated carbon prepared from rice husk after calcinations due to the silica and carbon present in it. The increase in the pH led to a decrease in the dye adsorption of direct red 23 on mangrove bark that has been treated with formaldehyde in acidic medium. These values were studied in relation to the ion exchange mechanism of the adsorption and maximum removal was observed at 2. The capacity of monolayer sorption of modified bark for Direct red 3 sorption was evaluated as 21.55 mg/g. Various issues are attached with the activated carbon [27]. The increase in quality of activated carbon means increase in costs as well, while it does not work on disperse and vat dyes. Regenerating saturated carbons is also expensive and complicated and leads to a loss in adsorbent. Restoration of adsorptive capacity of saturated activated carbons through desorbing adsorbed contaminants on the activated carbon surfaces is involved in the reactivation or the regeneration of activated carbons.

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Thermal reactivation is used in the regeneration techniques [63]. There are three steps in the process of thermal regeneration [64]; adsorbent drying at approximately 105 °C, high temperature desorption and decomposition under inert atmosphere and residual organic gasification by oxidizing gas at high temperatures. The exothermic nature of the adsorption is used in the heat treatment process and leads to desorption, partial cracking and polymerization of the organics adsorbed. The removal of charred organic residue formed in the porous structures is conducted in the final stage. The porous carbon structure regenerating its original surface characteristics will be revealed in this manner. The adsorption columns can be reused after treatment. The adsorptive capacity is reduced after the burning of the pre-adsorption thermal regeneration cycle between 5-15 wt% of the carbon bed [65]. High temperatures are required in the process of thermal regeneration, which means that the energies involved in this process are high. This process is hence energetically and commercially expensive [64]. Before it is feasible to have regeneration facilities on site, a certain size has to be attained for the plants based on thermal regeneration of activated carbon. Smaller waste treatment sites normally transport their activated carbon cores to specialized facilities for regeneration. This increases the footprint of the carbon [66]. Research into the alternative regeneration methods has been stimulated to reduce the environmental effects of these processes owing to the high energy costs of thermal regeneration. Industries have used some alternatives to the regeneration methods such as (i) chemical and solvent regeneration [67]; (ii) microbial regeneration [68]; (iii) electrochemical regeneration [69]; ultrasonic regeneration [70]; (iv) and wet air oxidation [71], while there are some alternative that have been restricted to the research area only. 2.4.2. Chitosan-Based Adsorbents The evaluation of adsorption performances of raw chitosan has been extensively studied with respect to the adsorption capacity or uptake. The equilibrium state of the adsorption systems determines the evaluation of the dye uptake rate by a chitosan based materials in a batch system. So far, 100 dyes have been studied, which mostly contain anionic dyes. Many classes of dyes concur an extremely high affinity of chitosan. Superb removal capacities for anionic dyes such as, acids, reactive and direct dyes have been revealed in this case. The unique polycationic structure is the reason behind it. Various researchers have studied the effectiveness of chitosan in its ability to react with dyes. The effectiveness of

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chitosan in the removal of reactive dyes has been demonstrated by Juang and his co-workers [72-74]. The maximum adsorption capacities of Chitosan were evaluated as 1653, 1009 and 885 mg/g, respectively [73] for RR 222, RB 222 and RY 145 by them. In terms of removal of effluent of textile mills, the chitosan proved to be a useful adsorbent because of its high adsorption capacity, stated Annadurai [75-77] and Crini et al. [78]. In comparison to other adsorbents, chitosan can be used in the studies of dyestuff adsorption, as stated by Uzun and Guzel [79-82]. In comparison to CAC and other cheap adsorbents, this polysaccharide revealed a greater capacity for adsorption of dyes, as stated by Crini [83]. In comparison to CAC, Kim and Cho [84] showed that chitosan beads adsorbed much greater RB5. In case of BB9, Lima et al. [85] came to similar conclusions. The ability of chitosan as an effective adsorbent for the removal of acid dye stuffs from aqueous solutions was demonstrated by McKay’s group in his recent publication [86-88]. The monolayer adsorption (saturation) capacities were calculated as 973.3, 922.9, 728.2 and 693.2 mg of dye per gram of chitosan for AO 12, AO 10, AR 73 and AR 18, respectively [86]. Guibal and his coworkers studied the interactions between chitosan and anionic dyes [89-92] and concluded that chitosan was effective for the treatment of waste water due to its natural selectivity for dye molecules. The adsorption capacities were calculated between 200 and 2000 mmol/g for chitosan and between 50 and 900 mmol/g for CAC [91]. When acids, direct, reactive and mordant dyes were used, the chitosan showed double the adsorption capacity than CAC. The dye determined better option between CAC and chitosan. The correlation between the chemical structure of the dye and the affinity to carbon or chitosan could not be determined. The modification ability of chitosan is a major benefit. Its properties can be enhanced by modifying the chitosan structure. To improve its adsorption capacity, researchers have suggested the modification in the Chitosan backbone. Grafting reactions further highlighted these modifications [78, 93]. Chitosan’s removal capacity can be increased with its other properties as well such as dyes selection through modifications. It can also help in modifying its physical and mechanical properties and its physical properties as well, while controlling its diffusion properties and reducing its sensitivity of adsorption to the environmental conditions. Chitosan has low affinity for basic cationic dyes. Chemical grafting of specific ligands was proposed by many scientists [94, 95]. To develop its cationic dye hydrophobic adsorbent properties and to improve its efficiency, the usage of N- benzyl mono- and disulfonate derivatives of chitosan is suggested [78,93]. In the absence of cross linking reactions, these derivatives could be used as hydrophobic adsorbents in acidic media. Addition of chemical substituents at a

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specific position in a controlled manner is required to develop high potentials of chitosans [96]. New adsorption properties are created towards basic dyes in acidic medium or reactive dyes in basic medium through chemical derivatization. The enzymatic grafting of carboxyl groups on chitosan was studied to determine the ability of chitosan in the adsorption of basic dyes on beads [96]. The surface polarity and the density of the adsorption sites increased in the presence of new functional groups on the surface of beads. This in turn improved the adsorption selectivity for the targeted dye. Chemical derivatizations were seen to enhance the ability of chitosan to selectively adsorb dyes, as evident through other studies. The reaction of the chitosan with high fatty acids and glycidyl moieties lead to the creation of chitosan based materials with long aliphatic chains [97]. In case of both anionic and cationic dyes, these products proved to be effective adsorption materials. The usage of cyclodextrin grafted chitosan derivatives was suggested as a new chitosan derivative for dye removal [98,99]. The rate of adsorption and a global efficiency greater than that of the parent chitosan polymer, would define these materials [96]. Some disadvantages are attached with the pure form of chitosan powders such as, unsatisfactory mechanical properties and poor heat resistance. The solubility of the pure form in the acidic media is another disadvantage, which prevents its usage as an insoluble adsorbent under these conditions. The transformation of the raw polymer into a form with more enhanced physical properties is another technique to deal with this problem. Cross-linked beads have been developed and proposed. These materials will not lose their original properties and original characteristics after cross linking [100]. This means that it will maintain its high adsorption capacity, but its density of free amine groups will be reduced at the surface of the adsorbent due to the chemical modifications. This will in turn reduce the polymer reactivity towards metal ions [89, 90]. The cross linking agent is significant. The chitosan behaviour was studied by many researchers that was manufactured with varying types of cross linkers such as, ethylene glycol diglycidyl ether (EGDE), glutaraldehyde (GLA), tripolyphosphate sodium (TPP), epichlorydrine (EPI), etc. [101-104]. According to the results, higher adsorption power was observed for the Chitosan-EPI beads than the GLA and EDGE [103, 104]. The removal of reactive, direct and acid dyes was confirmed by the results. About 2498, 2422, 2383 and 1954 mg of various reactive dyes (Reactive Blue 2, Reactive Red 2, Direct Red 81 and Acid Orange 12, respectively) were adsorbed by 1 g chitosan [102]. A variation in the adsorption capacities was observed from 280 to 720 mg/g in commercially activated carbon for reactive dyes. The cationic amine function of the polymer is retained by the EPI, which is an added advantage

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as it is a major adsorption site to attract the anionic dyes during the adsorption [103]. The availability of the amine function is reduced by the cross-linking with GLA or EGE for the complex dyes. The uptake capacity will also decline with a high cross-linking ratio. The chemical nature of the cross-linker and the extent of the reaction will have a great effect on the dye adsorption. The extent of crosslinking will determine the adsorption capacity, which will decline with the rise in the density of cross-linking. The saturation adsorption capacity of reactive dyes on cross-linked chitosan decreased exponentially from 200 to 50 mg/g after the cross-linking of the beads with GLA under heterogeneous conditions. The increase was observed when the cross-linking went from 0 to 1.5 mol GLA per mol of amine. The limited diffusion of molecules through the polymer network and its reduced polymer chain flexibility were the main reasons behind it. This decrease may also be attributed to the loss of amino binding sites after the reaction with aldehyde. To improve the mechanical resistance, it was important to improve the cross-linking as it would lead to an improvement of the material agent acid, alkali and chemicals and an increase in the adsorption capacities of chitosan. The adsorption capacity of non-cross-linked beads was more than the cross-linked beads under similar experimental conditions, states the literature [101-104]. Materials cross-linked with GLA have been observed to be effective dye adsorbents [98,100]. The imine groups are created as a result of the reaction with chitosan, which in turn causes a decline in the number of amine groups and reduced adsorption capacity. This behavior is specifically evident for the dyes adsorbed through ion-exchange mechanisms. As indicated by XRD diffractograms, the crystalline nature was also seen to be changed by the crosslinking. There was a small increase in the crystallinity and the accessibility of the chitosan to small pores, after the cross-linking reactions. The short literature survey clearly tells that due to its amazing adsorption capacity, chitosan can be used as a remarkable tool for the purification of dyecontaining wastewater. 3. ISOTHERM MODELS It is necessary to form the most appropriate adsorption equilibrium correlation in an attempt to discover innovative adsorbents in gain access to an ideal adsorption system [105], which is vital for consistent prediction of adsorption parameters and quantitative comparison of adsorbent behaviour for various adsorbent systems (or for varied experimental conditions) [106,107]. Adsorption isotherms, which are a common name of equilibrium relationships, are essential for optimization of the adsorption mechanism pathways, expression of the surface properties and

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capacities of adsorbents, and productive design of the adsorption systems since they explain how pollutants interrelate with the adsorbent materials [108,109]. Explaining the phenomenon through which the preservation (or release) or mobility of a substance from the aqueous porous media or aquatic environments to a solidphase at a persistent temperature and pH takes places, in broad-spectrum, an adsorption isotherm is an invaluable curve [110, 111]. The mathematical association which establishes a significant role towards the modelling analysis, operational design and applicable practice of the adsorption systems is normally represented by plotting a graph between solid-phase and its residual concentration [112]. When the concentration of the solute remains unchanged as a result of zero net transfer of solute adsorbed and desorbed from sorbent surface, a condition of equilibrium is achieved. These associations between the equilibrium concentration of the adsorbate in the solid and liquid phase at persistent temperature are defined by the equilibrium sorption isotherms. Linear, favourable, strongly favourable, irreversible and unfavourable are some of the isotherm shapes that may form (Fig. 2).

Fig. (2). Linear, favorable, strongly favorable, irreversible and unfavorable isotherms examples.

Understanding of the mechanism of adsorption, surface properties, along with the extent of affinity of the adsorbents are delivered by the physicochemical parameters accompanied by the fundamental thermodynamic suppositions [113]. In terms of three basic approaches, an extensive diversity of equilibrium isotherm models (Langmuir, Freundlich, Brunauer-Emmett-Teller, Redlich-Peterson,

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Dubinin-Radushkevich, Temkin, Toth, Koble-Corrigan, Sips, Khan, Hill, FloryHuggins and Radke-Prausnitz isotherm), has been framed in the past [114]. The first approach to be mentioned is kinetic consideration while thermodynamics being the second one. A state of dynamic equilibrium with both adsorption and desorption rates in a balance is an adsorption equilibrium and a framework of deriving numerous forms of adsorption isotherm models are given by thermodynamics [115, 116]. The key idea in the generation of characteristic curve is generally given by the third approach which is a potential theory [117]. The alteration in the physical interpretation of the model parameters compels us to follow an interesting trend in the isotherm modelling which is the derivation in more than a single approach [118]. 3.1. Langmuir Isotherm Model Tradition has been used to calculate and compare the performance of different bio-sorbents and formerly developed to describe gas-solid-phase adsorption onto activated carbon is the Langmuir adsorption isotherm [119]. This experimental model in its preparation presumes that the adsorption is monolayer (the adsorbed layer is only a single molecule thick) and can occur explicitly at a finite (fixed) number of specific localized sites, which without any lateral interaction and steric hindrance among the adsorbed molecules, even on head-to-head sites and are alike and correspondent [120]. Homogeneous adsorption in which every molecule has constant enthalpies and sorption activation energy (all sites possess equal affinity for the adsorbate) is basically represented by Langmuir isotherm in its derivation [121] with absolutely no traveling of the adsorbate in the plane of the surface [122]. A plateau is an equilibrium saturation point where once a molecule lodges a site and no more adsorption takes place. This plateau is shown graphically [110, 123]. Furthermore, to the rise of distance, Langmuir theory has characterized a quick decrease of the attractive forces between the molecules. Table 1 exemplifies the mathematical expression of Langmuir isotherm models. Webber and Chakkravorti defined a dimensionless constant, usually known as separation factor (RL) which can be denoted as [124]:

RL 

1 1  KL C0

(1)

where KL (L/mg) refers to the Langmuir constant and C0 is denoted to the adsorbate initial concentration (mg/L). In this context, lower RL value reflects that

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adsorption is more favorable. In a deeper explanation, RL value indicates the adsorption nature to be either unfavorable (RL > 1), linear (RL = 1), favorable (0 < RL < 1) or irreversible (RL = 0). 3.2. Freundlich Isotherm Model The most primitive known relationship explaining the non-ideal and reversible adsorption, not limited to the formation of monolayer is the Freundlich isotherm [125]. Multilayer adsorption with non-uniform spreading of adsorption heat and affinities over the heterogeneous surface can use the application of this experiential model [126]. Signifying that the proportion of the adsorbate onto a given mass of adsorbent to the solute was not constant at changed solution concentrations, traditionally, it was made for the adsorption of animal charcoal [127]. In this standpoint, until adsorption energy is exponentially decreased upon the conclusion of adsorption process, the quantity adsorbed is the sum of adsorption on all the sites (each having bond energy), with stronger binding sites being engaged first [128]. Freundlich isotherm right now is extensively applied in heterogeneous systems particularly for organic compounds or exceedingly reactive species on molecular sieves and activated carbon. A measure of the adsorption intensity or surface heterogeneity is the slope range between 0 and 1 and as its value gets nearer to zero, it becomes more heterogeneous while a value under 1 suggests chemisorptions process where 1/n above one refers to cooperative adsorption [129]. Table 1 enlists its linearized and non-linearized equations. Since it lacks a necessary thermodynamic basis, not approaching the Henry’s law at disappearing concentrations, Freundlich isotherm is currently being critiqued [107]. 3.3. Dubinin-Radushkevich Isotherm Model Following a pore filling process, Dubinin-Radushkevich isotherm [130] is an experimental model originally considered for the adsorption of subcritical vapours onto micropore solids. With a Gaussian energy dispersal onto a heterogeneous surface, adsorption mechanism is usually described by it [131]. It has disappointing asymptotic properties and does not forecast the Henry’s law when the pressure is low but the model has habitually effectively fitted high solute activities and intermediate range of concentrations data [132]. To differentiate the physical and chemical adsorption of metal ions with its mean free energy, this approach was frequently exercised [117]. The following relationship calculates the E per molecule of adsorbate (for removing a molecule from its site in the sorption space to the infinity) [133]:

Adsorption in Wastewater Treatment

 1 E  2k DR 

   

Green Adsorbents 49

(2)

where kDR is denoted as the isotherm constant. Meanwhile, the parameter ε can be correlated as:

 1    RT ln  1    Ce 

(3)

where R, T and Ce represent the gas constant (8.314 J/mol K), absolute temperature (K) and adsorbate equilibrium concentration (mg/L), respectively. This isotherm is temperature-dependent and when adsorption data at different temperatures are plotted as a function of logarithm of amount adsorbed vs. the potential energy’s square, the same curve called the characteristic curve will carry all appropriate data on it. This is one of the most interesting features of the Dubinin-Radushkevich isotherm model. 3.4. Temkin Isotherm Model

Showing the adsorption of hydrogen onto platinum electrodes within the acidic solutions, Temkin isotherm is one of the early models. A factor that especially considers adsorbent-adsorbate interactions is a part of this isotherm. The model by disregarding the tremendously low and large values of concentrations makes the assumption that instead of logarithmic coverage, heat of adsorption (function of temperature) of all molecules in the layer would decrease in a linear manner [134]. Its derivation is described by a uniform distribution of binding energies (up to some supreme binding energy) according to the equation. Complex adsorption systems like the liquid-phase adsorption isotherms are generally not suitable to be represented by Temkin equation but it is absolutely brilliant for making predictions regarding the gas phase equilibrium (when it is not necessary to organize in a firmly packed structure with alike orientation) [135]. 3.5. Flory-Huggins Isotherm Model

By intermittently deriving the intensity of surface coverage characteristics of adsorbate onto adsorbent, the viability and impulsive nature of an adsorption process can be expressed by Flory-Huggins isotherm model [136]. θ (in this framework) represents the degree of surface coverage while equilibrium constant and model exponent are denoted by KFH and nFH, respectively. The equation that is

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related with its equilibrium constant KFH for the calculation of spontaneity free Gibbs energy is as follows:

G 0  RT ln  K FH 

(4)

3.6. Hill Isotherm Model

Hill equation defined the binding of different species on homogeneous substrates [137], which initially came from the NICA model [138]. Adsorption, as assumed by this model, is an accommodating phenomenon with the ligand binding capability at one site on the macromolecule and the same macromolecule’s different binding sites may be influenced by it [139]. 3.7. Three Parameter Isotherms 3.7.1. Redlich-Peterson Isotherm Model

Including three parameters in an experimental equation, Redlich-Peterson isotherm [140] is a crossbreed isotherm presenting both Langmuir and Freundlich isotherms. To signify adsorption equilibrium over an extensive concentration range that can be applied either in homogeneous or heterogeneous systems on account of its flexibility [106], the model linearly relies upon an exponential function in the denominator and concentration in the numerator [141]. By maximizing the association co-efficient between the experimental data points and theoretical model assumptions with solver add-in function of the Microsoft excel, normally, a minimization procedure is implemented in resolving the equations [87]. Being in agreement with the low concentration perimeter of the perfect Langmuir condition (as the β values are all close to one) in the limit, it reaches up to Freundlich isotherm model at elevated concentration (as the exponent β tends to zero) [142]. 3.7.2. Sips Isotherm Model

For prediction of the heterogeneous adsorption systems, avoiding the drawback of the rising adsorbate concentration related with Freundlich isotherm model, Sips isotherm [143] is a collective form of Langmuir and Freundlich isotherms [131]. It shrinks to Freundlich isotherm at little adsorbate concentrations while it forecasts a monolayer adsorption capability characteristic of the Langmuir isotherm at elevated concentrations. Change in pH, temperature and concentration are the operating conditions under which the equation parameters work, as a general tenet [122].

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3.7.3. Toth Isotherm Model

Beneficial in explaining heterogeneous adsorption systems which have content of both low and high-end boundary of the concentration, Toth isotherm model [144] is another equation make better the Langmuir isotherm fittings (experimental data) [120]. Sips equation is unacceptable at the low-end as both forms are not reduced in the right Henry’s law type in the low concentration limit while Freundlich equation is unsuitable at low and high-end boundary of the concentration, so we can say that both of them have their respective limitations. The association assumes an asymmetrical quasi-Gaussian energy distribution, with most of its sites having an adsorption energy lower than the highest (maximum) or mean value making the Toth equation so prevalent [107]. 3.7.4. Koble-Corrigan Isotherm Model

Koble-Corrigan isotherm [145] is a three-parameter equation, which united both Langmuir and Freundlich isotherm models for demonstrating the equilibrium adsorption data, just like the Sips isotherm model. The linear plot using a test and error optimization is used to evaluate the isotherm constants, A, B and n. 3.7.5. Khan Isotherm Model

For pure solutions with bK and aK representing to the model constant and model exponent, the general model used is the Khan isotherm [146]. Its highest uptake values can be properly calculated at moderately elevated correlation coefficients and least ERRSQ or chi-square values [147]. 3.7.6. Radke-Prausnitz Isotherm Model

Generally anticipated well by the elevated RMSE and chi-square values is the association of Radke-Prausnitz isotherm. βR is the model exponent and model constants are represented by aR and rR [120]. 3.8. Multilayer Physisorption Isotherms

Very broadly applied in the gas-solid equilibrium systems and established to derive multilayer adsorption systems with relative pressure ranges from 0.05 to 0.30 analogous to a monolayer coverage lying between 0.50 and 1.50 is the Brunauer-Emmett-Teller (BET) [148] isotherm, which is basically a theoretical equation. The extinction model related to its liquid-solid interface is shown as:

qe 

q s CBET Ce  Cs  Ce  1   CBET  1 Ce / Cs  

(5)

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where CBET, Cs, qs and qe are the BET adsorption isotherm (L/mg), adsorbate monolayer saturation concentration (mg/L), theoretical isotherm saturation capacity (mg/g) and equilibrium adsorption capacity (mg/g), respectively. As CBET and CBET (Ce/Cs) are much greater than 1, the equation is simplified as:

qe 

qs 1   C e / Cs 

(6)

Meanwhile, another multilayer adsorption derivation from the potential theory, which is the Frenkel-Halsey-Hill (FHH) isotherm [149], may be transcribed as:

C ln  e  Cs

   qs     RT  q e d  

r

(7)

where d, α, and r are the signs of the interlayer spacing (m), isotherm constant (J mr/mole) and inverse power of distance from the surface (about 3), respectively. Correspondingly, an adsorption model interpreted from the inclusion of surface tension effects in the BET isotherm is MacMillan-Teller (MET) isotherm [150] written as: 1/3

  kC e qe  qs   ln  C  C   s e  

(8)

where k is an isotherm constant. When Cs/Ce is approaching unity, the logarithmic term can be approximated as: 1/3

 kC e  qe  qs    Cs  Ce 

(9)

For relative pressures more than 0.8 and around Brunauer-Emmett-Teller (BET) isotherm for relative pressures lower than 0.35, the experimental isotherm is best fit to Frenkel-Halsey-Hill (FHH) or MacMillan-Teller (MET) isotherms.

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Table 1. Lists of adsorption isotherms with their non-linear forms Isotherm

Non-linear form

Q0 bCe 1  bCe

Langmuir

qe 

Freundlich

q e  K F  Ce 

Dubinin-Radushkevic

qe   qs  e k DR 

Tempkin Flory-Huggins

[119] 1/ n

[125]

2

[130]

 RT  qe    ln  AT Ce   bT   n  K FH 1    FH C0

[151] [136]

qSH Cen H

Hill

qe 

Redlich-Peterson

qe 

Sips

qe 

Toth

qe 

Koble-Corrigan

qe 

Khan

qe 

Radke-Prausnitz

qe 

BET

qe 

FHH

C ln  e  Cs

MET

  kCe q e  qs   ln  C  C   s e  

[137]

K D  Cen H

K R Ce

[140]

1  a R Cge KSCeS

[143]

1  a SCe S K T Ce

[144]

 a T  C e 1/ t ACen

[145]-

1  BCen q s b K Ce

1  b

K Ce

Reference



[146]

aK

a RP rR Ce R

[120]

a RP  rR Ce R 1 q s C BET Ce

 Cs  Ce  1   CBET  1  Ce / Cs      qs     RT  qe d  

[148]

r

[149]

1/3



[150]

Green Adsorbents, 2015, 55-68

55

CHAPTER 3

Synthesis of Green Adsorbents Abstract: An extensive study on the use of different materials as green adsorbents for eliminating environmental pollutants from wastewaters is provided in this chapter. This chapter focuses on two topics i.e. synthesis of activated carbon from cost effective agricultural sources, which are environment friendly and use of agricultural wastes/residues, by-products, natural sources etc. for the production of green adsorbents. This classification helps study the synthesis of green adsorbents in detail.

Keywords: Agricultural wastes, agro-based activated carbon, fly ash, food residues, fruits, industrial wastes, municipal wastes, peels, preparation routes, vegetables. 1. INTRODUCTION According to former chapters, the method of adsorption using supplies that are not very expensive is represented by the term “green adsorbents” and it basically comes from three sources i.e. agricultural sources and by-products (fruits, vegetables, foodstuffs), agricultural residues and wastes; and inexpensive sources that form best complex adsorbents (viz., activated carbons after pyrolysis of agricultural sources etc.). Yet, the substrate is the biomass in relation to all the aforementioned cases. Biomass stands for (bio (in Greek language means “life”) and mass (or maza in Greek language) wood, short-rotation woody crops, agricultural wastes, shortrotation herbaceous species, wood wastes, bagasse, industrial residues, waste paper, municipal solid waste, sawdust, bio-solids, grass, food processing waste, water plants, algae animal wastes, and a host of other materials [152]. For all organic materials that originate from plants, trees, crops and algae, it is a relatively modest term. Cellulose and hemicelluloses (holocellulose) are two greater carbohydrate groups with substantial value. Non-sugar type molecules compose the lignin portion [153]. Detained together in a huge straight chain molecule, a pure organic polymer containing exclusively the units of anhydroglucose is cellulose [154]. β-(1,4)glycosidic linkages which form cellobiose as the repeat unit for cellulose chains bound these anhydroglucose units together. Before fermentation to ethanol, it is necessary for cellulose to hydrolyze to glucose. George Z. Kyzas All rights reserved-© 2015 Bentham Science Publishers

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The chains are likely to be arranged in a parallel fashion and form a crystalline supermolecular structure by establishing intramolecular and intermolecular hydrogen bonds between OH groups inside the same cellulose chain and the adjacent cellulose chains. Following this, microfibril which is oriented in the cell wall structure is formed by the bundles of linear cellulose chains (in the longitudinal direction) [155]. With little tendency to acid and enzymatic hydrolysis, cellulose is not soluble in most solvents. Different monosaccharide units combine to form a hemicellulose, unlike cellulose. The polymer chains of hemicelluloses have small branches and are amorphous and due to this, hemicelluloses are partly soluble or swell-able in water. Derived chiefly from chains of pentose sugars, and act as the adhesive material holding together the cellulose micells and fiber, hemicelluloses (arabinoglycuronoxylan and galactoglucomannans) are basically plant gums and they occur in much shorter molecule chains as compared to cellulose [156]. Xylose is one of the most important sugar of the hemicelluloses component and in hardwood xylan, the spine chain contains xylose units connected by β-(1,4)glycosidic bonds and divided by α-(1,2)-glycosidic bonds with 4-Omethylglucuronic acid groups [155]. Occasionally, OH groups in location C2 and C3 are substituted by O-acetyl groups though consisting of arabinofuranose units interconnected by α-(1,3)-glycosidic bonds to the spine, softwood xylan has extra branches. Hemicelluloses are more simply hydrolysed as they are highly soluble in alkali [157-159]. The chains are likely to be organized in a parallel fashion and form a crystalline supermolecular structure by establishing intramolecular and intermolecular hydrogen bonds between OH groups inside the same cellulose chain and the adjacent cellulose chains. Following this, a microfibril which is oriented in the cell wall structure is formed by bundles of linear cellulose chains (in the longitudinal direction). With little tendency to acid and enzymatic hydrolysis, cellulose is not soluble in most solvents. Due to the above listed reasons, the chapter is divided into two parts so as to make a comprehensive report about the production of green adsorbents and those parts are: (ii) activated carbon manufactured from agricultural inexpensive sources, which can be simply considered as materials that do not harm the environment, and (ii) green adsorbents from agricultural wastes/residues, by-products, natural sources etc.

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2. ACTIVATED CARBON FROM WASTES To substitute bone char in the sugar refining process in 1900-1901, the foundation for modern industrial manufacture of active carbons was established [160]. Consuming wood as a raw material in the early 19th century, ground activated carbon was first produced commercially in Europe. For the removal of taste and smell from polluted water in the United States, the usage of activated carbon for the treatment of water was first reported in 1930 [161]. With an irregular or amorphous structure, which is extremely porous, presenting a wide range of pore dimensions, from noticeable cracks, gaps and slits of molecular dimensions, activated carbon is a rough form of graphite [162]. Carbohydrates, cottonseed hulls, corn cobs, distillery waste, fuller's earth, fertilizer waste slurry, fish, fruit pits, graphite, human hairs, jute stick, kelp and seaweed, lignin, lignite, lampblack, leather waste, municipal waste, molasses, nut shells, newspaper, oil shale, olive stones, petroleum acid sludge, pulp-mill waste, palm tree cobs, petroleum coke, petroleum acid sludge, potassium ferrocynide residue, Rubber waste, rice hulls, refinery waste, reffination earth, scrap tires, sunflower seeds, spent fuller's earth, tea leaves, wheat straw and wood are all the sources from which activated carbon has been prepared [163,164]. Among these, the most ordinarily used are wood (130,000 tons/year), coal (100,000 tons/year), lignite (50,000 tons/year), coconut shell (35,000 tons/year), and peat (35,000 tons/year). Due to such factors like surface area, a micro-porous structure, and very high surface reactivity, activated carbon has an adsorptive nature. Surface functional groups are determined by the starting material and the activation method used. The carbon surface chemistry which has been thoroughly studied relies upon the conditions of activation and the temperatures provided. Mesopores, micropores and ultramicropores are formed giving huge surface areas up to 2,000 m2/g since the pore structure is also improved as a result of activation. 2.1. Activation of Carbon By elimination of comparatively less arranged sloppily bound carbonaceous material, the gaps between the elementary crystallites in the course of the activation process are cleared. A porous structure with huge internal surface area is formed by the resulting channels through the graphitic regions, the spaces between the elementary crystallites together with clefts within and parallel to the graphite planes [165]. A porous structure within a starting material of comparatively low surface area is imparted by two types of activation, thermal/physical or chemical activation.

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2.1.1. Physical (Thermal) Activation To remove the bulk of the volatile matter tailed by restricted gasification using mild oxidizing gas for example CO2, steam or fuel gas at 800-1000 °C to create the porosity and surface area, physical or thermal activation includes carbonization at 500-600 °C [163, 166]. The raw materials studied by this method were rice husk, corn cob, oak, corn hulls, corn stover, rice straw, rice hulls, pecan shells, peanut hulls and almond shells [167-176]. The activation temperature ranges between 600 and 900 °C while carbonization temperature ranges from 500 to 850 °C, and sometimes touches 1000 °C. 2.1.2. Chemical Activation The combination of inorganic additives, metallic chlorides such as zinc chloride or phosphoric acid into the precursor before the carbonization are all included in chemical activation [177]. ZnCl2 incorporation produces carbons with fine mesoand microporous structure. Active carbon surface area and pore volume were increased by KOH activation productively [178]. For activation, ammonium salts, borates, calcium oxide, ferric and ferrous compounds, manganese dioxide, nickel salts, hydrochloric acid, nitric acid and sulfuric acid have also been utilized. For corn cob, olive seeds, rice husks, rice straw, cassava peel, pecan shells, Macadamia nutshells, hazelnut shells, peanut hulls, apricot stones and almond shells [167,169,170,173,174,179-185] chemical activation was employed in most of the studies. ZnCl2, KOH, and H3PO4 are the most common chemical agents and while less K2CO3. For 2 h, a solution of ZnCl2 (30 wt%) at 750-800-850 °C was used to activate almond shells, hazelnut shells and apricot stones [180] and it was also consumed in Badie et al. study [170]. In this study, for 6h, a 50% solution was mixed with sample of peanut hulls at 300-750 °C. Furthermore, for Macadamia nutshells [179], and rice husks [174], at 500 °C for 1 h, and at 600 °C for 3 h in addition with CO2, respectively giving the best characteristics of the activated carbons than with any other agent (chemical or physical), ZnCl2 was used. KOH at 800 °C for 1 h and 500-700 °C for 3 h correspondingly was used to activate Carbons from Macadamia nutshells [179], and peanut hulls [170]. ACs produced did not have as good quality as the ones produced by utilizing ZnCl2. AC with such good SBET was not given by Corn cob char [185], which was activated with KOH at 500-800 °C for 1 h. ACs with high surface area and char

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yield were produced by the activation of olive seed carbons [181], at 800-900 °C for 1-2 h. The activation of rice straw char [173], continued firstly in one-stage at 500-900 °C for 1 h and then in two-stages at 700-1000 °C for 1 h (carbonization conditions) and then at 900 °C for the activation. The higher SBET was yielded in the second case. Cassava peel char [182] was activated at 650 and 750 °C. The better process according to the results was the two-stage process giving greater porosity ACs. Also, from all the studies being stated in the current review this method (two-step chemical activation process), gave greater surface area, too. For carbons from peanut hulls [170], corn cob [169], almond shells and pecan shells [167] activation with H3PO4 was used. 500 °C for 3 h and 500 °C for 2 h were the activating conditions for peanut hull chars and corn cob chars respectively. As compared to peanut hull, improved characteristics of the ACs in the respective research were given by corn cob. Carbons with slightly lower surface area than those mixed with ZnCl2 were gained from almond shell chars activated with H3PO4. K2CO3 at 500-800 °C for 1 h was the condition used to activate carbons from corn cob [185] and the ACs produced had a lower surface area and gave the maximum char yield as compared to those in which KOH was used. 2.1.3. Differences Between Physical and Chemical Activation The number of stages necessary for activation and activation temperature is the main dissimilarity between physical and chemical activation. Carbonization and activation are the two steps involved in physical activation while chemical activation concludes in only one step. Also chemical activation temperatures range between 200-800 °C while physical activation requires temperatures (8001000 °C) which are greater than the former. Acidic and basic activated carbons according to Steenberg's classification [186] exist:  Carbon activated at 200-400 °C, known as L carbons, usually develop acidic surface oxides and lower the solution pH values. They adsorb bases, are hydrophilic in nature, and display a negative zeta potential.  The carbons activated at 800-1000 °C are called as H carbons, develop basic surface oxides and increase pH of the solution. They adsorb acids and exhibit a positive zeta potential. Nevertheless, cooling H carbons in the presence of air alters the zeta potential to a negative value as acidic surface oxides are produced.

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Metal ions are absorbed by the acidic groups present on activated carbons [187]. H carbons are weaker solid acids hence L carbons adsorb metal ions more competently. For adsorption on activated carbon, surface area might not be a prime factor and high adsorption capacity isn’t caused as a result of high surface area [188] because:  Only the wetted surface adsorbs ions. The total surface area is rarely wetted.  Sometimes where the bulk of the surface area may exist, the material to be adsorbed is too large to enter the smallest pores.  Surface area, pore volume and surface chemistry are not typically connected with species adsorbed. Since ionic charges upset removal kinetics from solution, the adsorption of metal ions on carbon is more intricate in comparison to uptake of organic compounds. Activated carbon properties, adsorbate chemical properties, temperature, pH, ionic strength, etc. are properties on which the adsorption capacity relies. Being expensive, many activated carbons are accessible commercially but few are discriminatory for heavy metals. Carbon remains expensive necessitating massive quantities of activated carbon despite the fact that carbon is productively used in the treatment of wastewater. Better and ideal materials are needed and substitutes should be easily obtained, are cheap and, most of all, provide quantitative retrieval, be renewed eagerly. Activated carbons or inexpensive adsorbents can be formed from industrial or agricultural by-products. 2.2. Non-Conventional Wastes for Activated Carbons In literature, besides the aforementioned examples, non-conventional wastes (from municipal and industrial wastes) are reported. A pattern of mass production, mass consumption plus mass deposition [189] was progressively created from the economic activities in the modern society. An accumulation of numerous industrial and post-consumer waste products, by which their nature is hard or ill effective to be renewed into other materials and that presently wind up in fire plants or landfills, was a consequence. Restrictions on the use of such alternatives are extraordinarily increasing because of the more constrained environmental standards.

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A stern challenge for waste management policies is the release of plastic wastes, for example polyethylene terephthalate (PET) and polyvinyl chloride (PVC), industrial wastes, for example oil combustion residues and fabrics, plus the discharge of tires, sewage sludge, and fertilizers. Hence according to environmentally suitable measures, it is important to discover replacements by which such materials can be reprocessed or recycled [190]. For the elimination of contaminants from aqueous phase, there is a fairly abundant amount of fresh studies on the application of AC made from non-conventional waste materials [191-195]. Organic compounds of adaptable nature viz. phenol and its derivatives, and different types of dyes and heavy metals such as mercury, nickel, and copper are some of the pollutants that might be eradicated using these adsorbents. To prepare AC with antibacterial activity [196], the use of industrial wastes laden with chemicals like organometallics, could also be used. It is anticipated that prepared AC economically practical and the adsorption mechanism is, in numerous studies, basically pH reliant. Decent development of both chemical surface and porosity is usually presented by the adsorbents. Briefly presented in Table 1 are some of the pertinent issues regarding different fresh studies on the application of these materials in aqueous phase. Table 1. Aqueous-phase application of activated carbon prepared using non-conventional wastes as raw material [197]. Raw material PET

Sago waste

Pollutant removed

Issues

Reference

Dye (methylene blue)

High adsorption capacity of methylene blue (reaching 1 mmol/g).

[198]

Phenol, aniline

Adsorption was pH dependent, stronger for aniline than for phenol. Aniline had low water solubility which did not affect adsorption capacity. Adsorption interactions were mainly due to dispersion effect.

[199]

2,3,4-trichlorophenol

The adsorption capacities were comparable to commercial carbon. The adsorption mechanism depended fundamentally on the solution pH.

[200]

Dye (Rhodamine-B)

Ion exchange was the predominant dye adsorption mechanism. 100% removal was obtained when the pH increased to 7 (adsorbent dose of 275 mg/50 ml, 20 mg/l dye concentration).

[201]

AC was effective and economically attractive for the removal of Hg (II). Removal percentage increased with increasing pH from 2 to 10.

[202]

Mercury (II)

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Table 1: contd…

Heavy metal, dyes

Adsorption of all dyes and metal ions required a very short time leading to quantitative removal. AC are expected to be economically viable.

[202]

Coal tar pitch

Bacteria (Bacillus subtilis)

AC were prepared from pitch containing organometallics. The CaO, MgO, CoO, and ZnO dispersed AC exhibited antibacterial activity for B. subtilis both in solutions and agar.

[196]

Furfural residue (chemical)

Caramel, dye (Methylthionine chloride)

PAC showed excellent adsorption capacities for caramel and methylthionine chloride. Optimal conditions were: H3PO4 impregnation for 8-12 h, carbonization and activation at 450-500 °C for 1.5-2 h followed by soak washing (hot water) and drying.

[203]

AC with adsorption capacities of 6.24 mg/g at pH 3.5 were obtained The rate constant for removal of dye was 0.026 min-1. Adsorption capacities where greater than for commercial AC.

[204]

Prepared adsorbents showed good development of the chemical surface. The processes were endothermic and spontaneous.

[205]

Mercury (II)

AC prepared by chemical activation (H2SO4, H3PO4 and ZnCl2) might be effective to remove mercury from industrial wastewaters.

[206]

Copper ion, Phenol, dyes

AC allowed copper ion, phenol and dyes (Acid Red 18 and Basic Violet 4) to be removed from aqueous solution. The optimal preparation conditions were: 1.5 g of H2SO4 per g of sludge, 700 °C and 145 min.

[207]

Mercury (II) Mercury (0)

Combination of the AC and TiO2 (TiO2 modified sewage sludge carbon) and under ultraviolet irradiation doubled the adsorption capacity of mercury on the carbon (from 87 g/kg to151 g/kg).

[208]

Anionic dyes

Contrary to commercial carbons, for equilibrium pH values between 5 and 9, the adsorption capacity of the AC for dyes was altered (due to the presence of ionizable surface functional groups).

[209]

Dyes (Methylene blue, Saphranine)

The prepared adsorbents might be promising for dye removal from aqueous streams.

[210]

Buffing dust (leather industries)

Tires

Sewage sludge

Dye (Acid brown)

Dyes (methylene blue, brilliant red)

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Table 1: contd…

Fertilizer

Organics

AC showed great porosity and high surface area. Adsorption of crystal violet was higher and faster than indigo carmine or phenol. Prepared AC can be promising materials to remove organic pollutants from aqueous streams.

[211]

Mercury (II)

Adsorption of Hg (II) increased with increasing pH and the process was exothermic. Adsorption occurred through a film diffusion mechanism at low concentrations, and particle diffusion mechanism at higher concentrations.

[212]

3. AGRO-BASED WASTES – SOURCES 3.1. Rice and Wheat Waste One of the most cultivated crops all over the world is rice, is the seed of a monocot plant known as Oryza sativa. The majority of world’s population uses rice as a staple food as it is a cereal grain. Ever since 1960s the production of rice has increased rapidly, production of 200 million tonnes of paddy rice went up to 600 million tonnes in 2004, on a global level. Rice husk, rice hull, rice husk/hull ash, rice bran are the by-products produced by the rice industry. Nasir et al. studied the rice husks and tested them for removal of arsenic from water [213]. Khalid et al. explored the adsorption activity of rice husks for removal of antimony ions from aqueous solutions [214]. Kumar and Bandyopadhyay also studied the adsorption activity of rice husks for removal of Cd(II) from aqueous solutions [215]. 3.2. Tea and Coffee Waste The leaves, leaf buds, and internodes of the Camellia sinensis plant collectively produce tea. Various techniques are used for preparing and curing tea. Tea is recognized as the most consumed drink in all parts of the world. In 2003, the annual world tea production was recorded to be 3.15 million tonnes. Different studies have helped in identifying the role of used tea leaves as adsorbents for removing different pollutants from water. Ahluwalia and Goyal, (2005) used tea leaves from removing lead, iron, zinc and nickel from water [216]. Methylene Blue aka cationic dye was also removed by tea leaves waste by Hameed [217]. Coffee is also largely consumed across the globe. During 1998-2000 the annual production of coffee was recorded to be 6.7 million metric tons, globally. It was

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predicted to rise up to 7 million metric tons by 2010. The largest amount of green coffee is produced by Brazil, Vietnam and Colombia are second in coffee production. Studies have been carried out on coffee industry wastes for water treatment. Minamisawa et al. investigated the adsorption behaviour of arabica and robusta roasted coffee beans for heavy metals [218]. Powder activated carbon has been synthesized by coffee residue as raw material, this is done by chemical activation with zinc chloride for adsorption of Pb(II) ions from aqueous solutions [219]. 3.3. Coconut Waste The coconut (Cocos nucifera) produces coconuts, which has high nutrition value and a good source of fibre, vitamins, and minerals. Over 80 countries produce coconuts which sums up to a global production of 49 billion nuts very year. Apart from the edible part wastes like coir pith, coconut bunch waste, coconut husk, copra meal, male flowers of coconut tree, etc. are also produced, which have been studied for adsorbent activity in water treatment. Kadirvelu and Namasivayam, (2000) used coir pith waste to remove of Pb(II) from aqueous solution [220]. 3.4. Peanut (Groundnut) Waste Arachis hypogaea is a plant species in the legume family and produces peanuts (groundnut). During the production year 2008-09, 34.43 million metric tons were produced globally. Most of the world’s peanuts are produced in China and India. The husk/hull of this nut has also been used as absorbent for water treatment. Namasivayam and Periasamy, (1993) converted the peanut hull into an adsorbent by its treatment with concentrated sulfuric acid, then by carbonization in air and finally by treating it with 1% sodium bicarbonate for the night [221]. For removing chromium(VI) tests were ran on untreated and silver impregnated groundnut husk [222]. Oliveira et al., (2009) studied peanut hulls for removal of copper and lead from aqueous solutions 225]. At 295 K adsorption of Neutral Red (NR) onto peanut husk in aqueous solutions was studied [223]. 3.5. Peels (of Various Wastes) Peel or the outermost layer of a fruit or vegetable also called skin has been the focus of recent studies for adsorbent activity in water treatment. Orange, banana, watermelon, cassava, mango peels are being used for the removal of different pollutants from water. The adsorbent activity of orange peel is quite evident in removal of Ni(II) from electroplating wastewater [224].

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The adsorption of acid violet 17 dye by orange peel from aqueous solutions has been studied as a factor of adsorbent dosage, initial dye concentration, agitation time and pH [225]. Whereas Namasivayam et al., (1996) studied orange peels for removing congo red, procion orange and rhodamine B dyes [226]. Memon et al., (2009) investigated banana peels for removal of Cd(II) from environmental and industrial wastewater along with consuming thermally treated watermelon peels (TWMP) for the removal of methyl parathion (MP) pesticide from water [227, 228]. The removal of Cd2+ and Pb2+ from aqueous solution was studied by using mango peel waste (MPW) as a sorbent [229]. A batch process was used to evaluate the potency of garlic peel for removing methylene blue from water [230]. 3.6. Shells (of Various Wastes) Researchers have also been exploring the shells of different agricultural products for removing toxic pollutants from water. Activated carbon is produced by bael fruit shell and it acts as a cost-effective adsorbent for removing Cr(VI) from aqueous phase [231]. Shells from raw Brazil nut are studied for the adsorption of methylene blue and Indigo Carmine dyes [232]. Brazilian pine-fruit-shell (Araucaria angustifolia) is used for production of carbonaceous adsorbents i.e. activated (ACPW) and non-activated (C-PW), which are tested for the removal of Procion Red MX 3B dye (PR-3B) from aqueous effluents [233]. A batch adsorption technique was used to test the adsorption of basic dyes, methylene blue and crystal violet by wood apple shell (WAS) [234]. The shells of hazelnut (HNS) (Corylus avellana) and almond (AS) (Prunus dulcis) were tested for removing Pb2+ from aqueous solutions by batch experiments [235]. Efficient and cost effective adsorbents are prepared by hard shell of apricot stones selected from agricultural solid wastes, used for gold separation from gold-plating wastewater [236]. 3.7. Seed, Seed Coat, Stem and Stalk of Different Agricultural Products (of Various Wastes) The removal of toxins and pollutants from water has always remained a challenge. Researchers have been working on different methods and techniques for developing ways to make better anti-pollutants. Researchers have also studied the use of stem, stalk, seed and seed coat from different crops and cultivated products as substances for removing pollutants from water. The use of cultivated products is very inexpensive. For removing Methylene blue from aqueous solutions, the use of pineapple stem waste has been studied [217]. Rengaraj et al. investigated the prospective of palm seed coat for elimination of o-cresol [237]. Aqueous solutions also contain Cr(VI), for its removal the use of tamarind seeds has also been tested

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[238]. For eradicating two direct dyes (Diret blue 71 and Congo red) and two basic dyes (basic red 9 and methylene blue) the consumption of sunflower stalks has been considered by Sun and Xu [239]. Basic blue 3 (BB3) can be removed from aqueous solution by using rubber (Hevea brasiliensis) seed coat obtained from activated carbon [240]. Dyes and phenols can also be removed from aqueous solution by utilizing mango and guava seeds [241, 242]. The removal of methylene seeds by using papaya seeds have also been inspected [243]. 3.8. Miscellaneous Agricultural Wastes Other than the above mentioned agricultural products which are being used as adsorbents other agricultural wastes have also been looked upon by researchers. Almond husk has also been studied as an efficient adsorbent of toxins like Ni(II) ions by Hasar [244]. A few of other adsorbents have been discussed below. The use of Barley straw (BS) for eradicating Cu2+ and Pb2+ ions from aqueous solution has been studied [245]. For removing cadmium and zinc the exploitation of sugarcane bagasse after converting it to carbonaceous adsorbent has been studied [246]. The removal of ions is also possible by using black gram husk (BGH) and its use has been further investigated [247]. Farnella et al. [248] carried out research on using grape bagasse for eliminating Pb(II) and Cd(II) ions. McKay et al. [249] investigated the utilization of bagasse pith for removing two acidic dyes and two basic dyes. Bagasse pith is a waste obtained from the sugarcane industry. Copper(II) can be removed from the aqueous solution by using dried sugar beet pulp [250]. Use of palm fruit bunch and maize cob has been studied for adsorbing manganese and iron. Edgehill and Lu [251] studied one of the waste products obtained from the wood industry which is carbonized slash pine bark for eliminating phenol from waste water. 4. INDUSTRIAL AND MUNICIPAL WASTES 4.1. Fly Ash Fly ash is one of the major solid waste products obtained from thermal power plants after burning of coal. It is one of the most efficient products being used for adsorbing ions and phenols from waste water because of the abundant presence of alumina and silica. Other uses of fly ash include construction of bricks, cement, roads, etc.

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4.2. Steel Industry Wastes (Blast Furnace Slag, Sludge and Dust) Likewise, the waste products obtained from steel industry have also been studied for using them as adsorbents. The waste products that have been studied include dust, blast furnace slag and sludge, etc. Blast furnace slag has been investigated by Kanel et al. for eliminating As(III) [252]. This product has also been used by Dimitrova [253] for eradicating lead. The same product has also been studied by several researchers for removing dyes [254, 255] and phosphate [256-260]. Dimitrova [261] further researched on ungranulated blast furnace slag in order to get rid of Zn2+, Cu2+, and Ni2+ ions from water. It was also found out that the adsorption takes place through colloidal silicic acid particle and hydro complex formation because of the slag alkalizing activity. 4.3. Aluminium Industry Waste (Red Mud) The waste products from the aluminium industry have also been studied as adsorbents. The most useful waste product is red mud which is obtained after the treatment of bauxite. Çengeloğlu et al. [262] studied on using red mud for eliminating fluoride from aqueous solution. Lopez et al. investigated on using red mud for treating waste water [263]. The removal of arsenic from water has also been carried out using red mud [264]. 4.4. Fertilizer Industry Waste The by-products obtained from the fertilizer industry pose serious environmental threats and also have severe issues regarding their disposal because they are produced in very large amounts. To cater this issue and lessen the severity Namaivayam and Ranganthan used one of the waste products from this industryFe(III)/Cr(III) hydroxide for adsorbing Cr(VI) from aqueous solution [265]. Srivastava et al. [266] also used one of the waste products which is waste carbon slurry for getting rid of Cr6+, Cu2+, Pb2+ and Hg2+ from aqueous media. This waste product has also been used for eradicating anions, pesticides, phenols, dyes, etc. from water [267-271]. 4.5. Leather Industry Waste The waste obtained from leather industry has also been studied for exclusion of As(V) and Cr(VI) from aqueous solution [272]. 4.6. Paper Industry Wastes

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The waste products obtained from the paper industry are also in large quantities and have the same issue as that of fertilizer industry. Black liquor, a waste product originated from paper industry, was examined for the adsorption of Pb2+ and Zn2+ by Srivastava et al. [273]. Calce et al. investigated papermill sludges for adsorbing phenols [274]. It was also studied for being used in removing orange G dye (an anionic dye) [275]. Newspaper has been used for obtaining activated carbon by Shimada et al. [276]. 4.7. Miscellaneous Industrial Wastes as Adsorbents Bhatnagar et al. explored the use of waste from battery industry for eliminating metal ions like Cu, Zn, Pb and Cr from any aqueous media. In this study the sorption potential of the adsorbent material was of considerable value (33-64 mg/g) [277]. The side product of ammonia soda process- solid wastes obtained from distiller waste (DW) has been utilized for eliminating anionic dyes from aqueous solution [278]. Cr(III) can be eliminated from aqueous media by using waste biogas residual slurry as studied by Namaivayam and Yamuna [279].

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69

CHAPTER 4

Pollutants Removed with Green Adsorbents Abstract: The main pollutants studied for the treatment of industrial effluents are dyes, heavy metals and others (pesticides, phenols, drugs etc). In this chapter, two crucial adsorption parameters are investigated regarding the adsorption of those pollutants with green adsorbents; equilibrium (adsorption capacity) and kinetics. Many models are described and useful data are given.

Keywords: Adsorption, dyes, kinetics, metals, models, other pollutants. 1. INTRODUCTION Adsorption potential and kinetics are the paramount adsorption parameters. Therefore, the upcoming section consists of discussion about the adsorption kinetics and potential of the expulsion of ions, dyes, phenols, pesticides etc. 2. VARIOUS POLLUTANTS 2.1. Dyes The most frequently used colorant (dye stuff) for the staining or dyeing of silk and wool is Methylene blue (MB). Its use is harmful for human and animals eyes as it causes eye burn leading to the permanent damage to the eye. It can cause difficult or rapid breathing for short span in case it gets inbreathed whereas its mouth intake can be a source of burning sensation that results in vomiting, nausea, sweating, mental perplexity and methemoglobinemia [280, 281]. Thus, the sewage having such dyes must be properly treated as they have dangerous impacts on the receiving water. Barka et al. [282] made an important investigation about the biosorption of dyes like Eriochrome Black T (EBT), MB and AS Alizarin S as of the aqueous solution by means of cost effective, natural and environment friendly biosorbents like dehydrated prickly pear cactus cladodes. The value of Qm (Particularly of MB) was far higher than that of Chatterjee et al. [283]. 189.83 mg/g for MB, 118.35 mg/g for AS and 200.22 mg/g for EBT were the highest monolayer adsorption potentials. The expulsion of MB by a cost effective adsorbent made from Parthenium hysterophorus has been studied by Chatterjee et al. [280, 281]. The cost effective adsorbent is produced by the carbonization of Parthenium (an injurious weed) with the orthophosphoric acid working as activating agent. Freundlich (R2 = 0.95) and Langmuir George Z. Kyzas All rights reserved-© 2015 Bentham Science Publishers

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(R2 = 0.99) equations were used for fitting. The process had Qm having value of 98.06 mg/g, but the authors asserted this value to be closely related to other comparable adsorbents regarding the removal of MB as: Denix regia prepares 24 mg/g of adsorbent [284], Parthenium prepares 39.68 mg/g of adsorbent [285], morinda coreia buch-ham bark prepares 60.0 mg/g of acid activated carbon [286], 89.4 mg/g of rectorite [287]. Another investigation was made by Hameed on the likelihood of using papaya seeds for the adsorption of MB as they are abundantly found wastes in Malaysia, their adsorption capacity was found very high (556 mg/g) [243]. McKay et al. [288] used very inexpensive resources as green adsorbents like hair from parlours, waste cotton etc. and found high adsorption potentials for safrarine (common dye) and MB. The Qm found in case of safranine for rice husk, hair, tea wood bark, waste cotton and bituminous coal were 838, 190, 1119, 875, 120 mg/g respectively but the values were 312, 158, 914, 277 and 250 respectively for the case of MB. Similarly, another study was made by Ferrero [289] which was about MB adsorption on the ground hazelnut shells in contrast with different wood species sawdust so as to discover the use of this material as green adsorbent for dye house waste. The Qm (MB) for hazelnut shells was 41.3 mg/g for dp = 500 um. This was the most valuable result as it suggested Qm(MB) for normal hazelnut shells five times more than that reported for activated carbon obtained from the similar substance. The similar value with dp = 125 um was obtained to be 76.9 mg/g. The finding of Qm for the adsorption on charcoal (activated) was 0.179 mg/g according to Iqbal et al. [290]. This exceptionally low capacity was able to illustrate this material as entirely unsuitable. The value of Qm for the adsorption of MG onto bentonite clay was shown to be 7.72 mg/g by Tahir and co-workers [291]. Similarly low value of Qm (8.27 mg/g) [292] was showed by ACC (Activated carbons of commercial grade), Qm (26.1 mg/g) by hen feathers [298] and Qm (4.88 mg/g) was shown by sugar cane dust [293]. Some studies showed higher values of Qm like utilizing lemon peels for green adsorbents gives Qm (51.73 mg/g) [294] and coconut coir activated carbon gives (27.44 mg/g) [295]. Malachite Green (MG) is another majorly used cationic colorant of wastewaters. It is an organic colorant used for dyeing and is one of the disputable agents in aquaculture. Traditionally, for dyeing of materials like paper, leather and silk, MG is used [296]. Because of the examination of high deviation, many papers having uncertain and dissimilar capacities have been published. Hasnain Isa et al. [297] used palm ash to remove disperse dyes like Miketon Polyester Scarlet RCS and Begacron Blue BBLS 200% but they also concluded their study with lower values of Qm 61 and 49.5 mg/g, respectively. El-Haddad

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et al. used animal fillet meal as a green adsorbent for the adsorption exclusion of Rhodamine B from sewage water [298]. Nearly 65 mg/g capacities were obtained at various different temperatures. Doulati Ardejani and co-workers [299] examined orange peels as green adsorbents for DR23 that is Direct Red 23 and for DR80 that is Direct Red 80 but found to have low capacities of 10 and 21 mg/g respectively. Vijaya Kumar studied the use of musa spp adsorbent for the adsorption of violet 54 (V54) and found much lower Qm of 36.49 mg/g [300]. The research of El-Mekkawi and Galal [301] showed the adsorption capacity of Degussa P25 TiO2 as 144 mg/g and of rutile TiO2 as 144 mg/g for the expulsion of Direct fast Blue B2RL with optimum pH = 2. The first thing to be concluded from above discussion is the non-uniformity of adsorption capacities. The green adsorbents had high value of Qm that is about 150 mg/g but many others had low capacities even peanut husk charcoal (0.36 mg/g) > fly ash (0.18 mg/g). But all these values were neither suitable for batch experiments and nor for industrial use owing to their low Qm.

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Bhattacharya and co-workers [304] made investigation on the process of elimination of Cr (VI) from aqueous solution using various inexpensive absorbents and batch adsorption method. To find the Cr(VI) adsorption efficiency, he made use of low-priced adsorbents like rice husk ash, clarified sludge (Waste of steel industry), fuller’s earth, activated alumina, saw dust, fly ash and neem bark etc. The equilibrium data was perfectly fitted in Languir model as (R2~0.999) but it showed low adsorption potentials (19 – 31 mg/g) as: rice husk ash (25.64 mg/g), clarified sludge (Waste of steel industry) (26.31 mg/g), fuller’s earth (23.58 mg/g), activated alumina (25.57 mg/g), saw dust (20.70 mg/g), fly ash (23.58 mg/g) and neem bark (19.60 mg/g). For the elimination of heavy metals from aqueous solution, Kumar et al. [305] used an odd adsorbent material that is straw. For ATS and ISX both, the value of Qm for the expulsion of Cr(III) was found to be very low as 1.88 and 3.91 mg/g respectively. The cost of adsorbent was increased due to its modification to insoluble straw xanthate (ISX) and alkali-treated straw (ATS). Aziz et al. [306] studied the cadmium adsorption from TOS Treated olive stones and found Qm to be 49.3 mg/g by Langmuir model. Nasernejad et al. [307] study showed the possibility of metal ions adsorption onto carrot residues owing to the existence of phenolic and carboxylic groups having cation exchange characteristics. At high pH values of solutions like pH = 4 for Cr(III), pH = 5 for Zn(II) and Cu(II), further more metals were adsorbed. Cr(III), Zn(II) and Cu(II) had the highest adsorption potentials of 45.09, 29.61 and 32.74 mg/g respectively. HCl-treated carrot residues can be used for the exclusion of heavy metals like Cu(II), Zn(II) and Cr(III) from sewage water. To exclude resins, tannins, coloured materials and reducing sugars, acid action is performed. The 12 of the secondary products in the agriculture field were analysed and some deductions were made. Those 12 products include pecan shells, English walnut shells, sugarcane bagasse, peanut shell, rice hulls, black walnut shells, almond shells, soybean hulls, corn cob, cottonseed hulls, almond hulls and macadamia nut hulls. Along with reported deductions, a conclusion was made by Perez-Marin et al. that around 48.33 mg/g Cd(II) was absorbed by organic oranges waste [122]. The Wartelle and Marshall [308] findings showed direct relation over the amount of absorbing copper ion and the total negative charge of the byproducts after the treatment with citric acid. The low density materials became more negatively charged therefore the copper ions absorbed were the most. And also it was seen that modifying the by-product with (NaOH) or any base along with citric acid

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considerably increased the negative charge. In the experiment the least amount of copper ion absorbed were by high density nutshells like English walnut shells and black nutshells showing less number of carboxyl groups. This was due to the presence of lignin in nutshells that didn’t allow the penetration of citric acid to the reactive places and that leads to less intake of copper ion. While the low density material like soybeans hulls absorbed highest amount of copper intake which is the rise in carboxyl groups due to thermochemical reactions with citric acid. A small aquatic fern used by the rice fields and by botanical gardens is called Azolla. It participates in binding and transferring ions of heavy metals is possible due the charged carboxyl and phosphate groups. The ions exchange can be increased by presence MgCl2 and further increased by increasing concentration of MgCl2. The heavy metals absorbed by Azolla without MgCl2 were 33, 29, 40 and 24 of Pb, Cd, Cu and Zn [309]. While presence of H2O2 did not had much affect but combination of 2 M MgCl2 in the presence of 8 mM H2O2 helped in reaching the maximum absorption level that were 228, 86, 62, and 48 mg/g of Pb(II), Cd(II), Cu(II) and Zn(II). Annadurai and co-workers experimented on the power of absorption by alkali and acid treated banana and orange peels of metal ions especially Cu2+, Zn2+, Co2+, Ni2+ and Pb2+ [310]. The reports showed that peels could be used for abstracting, renewals and for retrieval of metal ions. The descending order of absorption capacity is as follow Pb2+> Ni2+> Zn2+> Cu2+> Co2+ for the absorbents, these absorbents abilities were improved using acid (HNO3) and alkali (NaOH) solutions. It was concluded that the absorption ability using banana peel was 6.88 (Ni), 4.75 (Cu), 7.97 (Pb), 5.80 (Zn) and 2.55 mg/g (Co) while the results using orange peel were 5.25 (Zn), 7.75 (Pb), 3.65 (Cu) 6.01 (Ni), and 1.82 mg/g (Co). Hence using the results it was finalized that banana peel have more absorption capability then orange peel. In comparison of treated peels acid treated peels showed best absorption against alkali and water treated peels. 2.3. Others The investigation of the level of phenols adsorption by coir pitch carbon of 2chlorophenal (2-CP) was carried out with Freundlich, Langmuir and DubininRadushkevich equations [311]. They carried the experiments with making slight differences like changing pH and temp or agitation time, absorption dosage or phenol’s concentration. In the whole experiment presented the balanced adsorption capacity that was (Oe) while not calculated highest value which was (Om).

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For the next experiment used green absorbents was made by coconut shells (CSAC) along with few chemical agents like CaCO3, H3PO4, KOH, ZnCl2 and NaOH for differing in activation methods and this type of adsorbents used activated carbon [312]. Radhika and Palanivelu worked on other king of phenols which include parachlorophenol (PCP) and 2,4,6-trichlorophenol (TCP). The capacity from CAC was approximately 150 mg/g but the Om for PCP was its half and was 72 mg/g. The respective value was more for TCP. In the experiment best fitting was awarded to Freundlich model. Freundlich, Langmuir, Sips and Redlich-Peterson isotherm models were exactly according to balanced data and also compared to results from commercial activated carbon (CAC). Jain and co-workers did a comparative study on the absorption of methylphenols on absorbents which are the products of some different industries [313]. The results concluded that carbonaceous adsorbent has the most adsorbent ability in comparison to other which are blast furnace sludge, dust and slag). The adsorption results on carbonaceous adsorbents from fertilizer industry waste was 37.3 for 2methylphenol, 40.5 for 4-methylphenol, 65.9 for 2,4-dimetylphenolol and 88.5 for 2,4,6-trimethylphenol. After the conduction of another similar study by Bhatnagar [314], it was concluded that carbonaceous adsorbents have larger surface area and larger absorbing ability. In the above mentioned study, the adsorbents for the removal of 2-bromophenol (2-BP), 4-bromophenol (4-BP) and 2,4-dibromophenol (2,4-BP) were studied that were prepared by few industrial wastes. The carbonaceous adsorbent has the most adsorbent ability than any other which include blast furnace sludge, slag, and dust as their absorbing limit of bromophenols is much smaller. The carbonaceous adsorbent which is made from fertilizer industry waste absorb 40.7 mg/g for 4-BP, 170.4 mg/g for 2-BP and 190.2mg/g for 2,4-BP. To separate out pyridine from industrial waste Mohan et al. [315] used activated carbon from coconut. Langmuir achieved the best fitting (R2>0.9553) after representing his isotherm by giving Om: SAC, 19.46 mg/g; ATSAC, 60.35 mg/g; FAC, 20.31 mg/g ATFAC; 54.63; ACF (activated carbon from fabric cloth), 161.40 mg/g. Following like SAC (activated carbon derived from coconut shell), ATFAC (activated carbon derived from acid treated coconut fibres) FAC (activated carbon derived from coconut fibers) and ATSAC (activated carbon derived from acid treated coconut shells) were prepared as adsorbents. Nitrobenze is another kind of pollutant that is removed from waste water with the help of maze and rice [316]. The maze stem showed Om equal to 10.40 mg/g while

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rich stem had much smaller value that is 1.31 mg/g. If it represents so much low absorption capacity it is not approved as green adsorbent. Due to this it won’t be further examined and will be rejected without considering it to be free of cost. In China latter are in abundant quantity and so they are present in low price. In the Langmuir and linearized Freundlich model the balanced data was best fitted. The saw dust produced by the saw mill in Farrokhi City (Iran) was manufactured as a probable green adsorbent. The sawdust/ Copper ferrous Oxide (CuFe2O4) nan-composite is used to remove Cyanine Acid Blue (CAB) [317]. In order to determine the extreme value for adsorption capability the Freundlich and Langmuir models were used. The result obtained from the tests showed that the sample of the mixture contained 178.56 mg/g of Qm. On the other hand, the sample containing only sawdust had 151.45 mg/g of Qm. From these results the observation seen was an improvement in the value of Qm, though it was not conclusive as to whether the composite was lucrative. Akhtar and his team studied and inspected the use of rice (Orzya sativa) bran (RB), Moringa oleifera pods (MOP), rice husk (RH) and bagasse fly ash (BFA) of sugar cane (Saccharum officinarum) as a possible adsorptive to remove methyl parathion pesticide (MP) from ground water and surfaces [318]. The highest possible sizes of BFA, RH, RB and MOP were 0.39, 0.35, 0.3p and 0.36 mol/gm respectively as calculated by using the equation of Langmuir isotherms. High value of Qm was observed when inexpensive adsorbents were used to remove pesticides from discharges. Different pesticides such as aldrin, dieldrin and endrin having Qm values 19.54, 23.74 and 43.71 mg/g respectively were removed using acidtreated olive stones as green adsorbents having a dosage of 0.1 g/L only by El-Bakouri and team [319]. 292.5 mg/g quantity of rice husk treated with meth-acrylic acid was used as adsorbent to remove parquet (pesticide) [320]. 3. KINETICS Whenever, we talk about modelling in physiochemical procedures it has a broadspectrum and incorporates extensive and lengthy models established using standardized principles [321] as well as, fitting of figures obtained from tests [322]. In this review we have assimilated a number of distinct models for the study of adsorption particularly those models which pertain to liquid-phase adsorption via inexpensive adsorbents. Thorough analysis of the models has been done in this sub-section and will be referred to during to the main discussion of the adsorbents based on them

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The typical experimental setup includes an initial concentration of adsorbate (C0), a beaker volume (V) and a mass of adsorbent (M). The amount of adsorbate adsorbed on the adsorbent (per unit adsorbent mass) is expressed as “Q” and evolves from Q = 0 to an equilibrium value Q = Qe, which corresponds to the Q thermodynamic equilibrium between Qe and Ce  C0  M   . The modeling V issue is focused on the quantitative description of the evolution curve Q(t), which is deduced by measuring experimentally the evolution of adsorbate concentration C(t) from C0 to Ce. The most extensively used models are typically those with the least physical background. The adsorption kinetic models which have been employed in green adsorption are: (i) The first model that has been employed is the pseudo- first order model which abbreviated is PS1. The Lagergren equation [323] that represents this model is given in differential form as: dQ  k1  Q  Q e  dt

(1)

After integration of Eq. (1):



Q  Qe 1  e k1t



(2)

The fitting to the experimental data can be performed using linear (i.e., using ln 1   Q / Qe    k1t ) or nonlinear (i.e., using directly Eq. (2)) techniques. The model is purely empirical and the only physical parameter used is the equilibrium value (Qe). The only fitting parameter is k1. Typically, instead of using the experimental value of Qe and find k1 from fitting, both k1 and Qe are found from fitting and then Qe is compared to the experimental one. (ii) The pseudo-second order abbreviated as PS2 is another model that has been used. It’s mainly experimental but gives more accurate fitting outcomes as compared to the first model. It is represented by following the derivative equation [324]: dQ 2  k 2  Q  Qe  dt

After integration of Eq. (3):

(3)

Pollutants Removed with Green Adsorbents

k 2 Qe 2 t Q 1  k 2 Qe t

Green Adsorbents 77

(4)

There are several ways to transform the relation to a linear one in order to use linear fitting techniques. The most usual is:

t 1 t   2 Q k 2 Qe Qe

(5)

As in the case of the first-order model, the fitting can be done either for k2 alone using the experimental value of Qe or for the pair (k2, Qe). The above models are used to find the coefficients k1 and k2, which are regarded as pure fitting parameters and subsequently depends on operational variables as C0. (iii) Elovich model is the third model which has been abbreviated as ELV [325]. In this model it has been assumed that for adsorbed species quantity there is logarithmic time dependence. The equation representing this model is gives as: Q

ln     ln  t  

(6)

where α, β are constants which are called initial adsorption and desorption rate, respectively. β is associated with surface coverage and α is linked with the rate of chemisorption [326]. Though this equation is used frequently in theoretical analysis but it does not easily incorporate the data. (iv) We also make use of INTD which is the intra-particle diffusion model for studying adsorbents. The basis of this approach is the supposition that intraparticle diffusion mechanism dominates the adsorption kinetics [327]. The equation that represents this model is basically used for constant adsorbate concentration and linear isotherm but theoretically it has also been used to make deductions for a wide-range of situations. The equation is given as:

 6 Q  Qe 1  2  

 i 2 2 D   1 exp t    2 2 i 1 i  R  

(7)

where D is the intraparticle diffusion coefficient, R is the particle radius and i is an integer that defines the infinite series solution.

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The procedure of fitting Eq. (7) to the kinetic experimental data can be found under the name Reichenberg [328] or Helffrich [329] model. For Q far from the equilibrium, the above relation can be simplified to Q  k1D t 0.5 (where k1D is the intraparticle diffusion constant [330] (abbreviated hereafter as INTD-1). In some cases, the alternative coefficient kin  k1D / M appears defined as the initial rate of intraparticle diffusion [302]. The last equation is actually more general than Eq. (7), since it is restricted only by the smallness of (Q/Qe) and not by the form of isotherm and the constancy of bulk concentration. The model is a phenomenological one, since includes parameters with physical 6 . The model is meaning. The relation between k1D and D is k1D  0.5 R  D /  better but it has its drawbacks since it cannot predict the long term equilibrium since it augments as a function of time. A constant value (p) is added to the right hand side of INTD-1 which aids in overall curve fitting procedure but this is an experimental addition and has not practical meaning. Another purely empirical extension of INTD-1 is the addition of a constant value (p) to its right hand side (abbreviated hereafter as INTD-2). This can help to the overall curve fitting process but is has no physical meaning since it implies that Q = p at t = 0, whereas the real value is Q = 0.

(v) The other model is the so-called McKay model [331] (abbreviated hereafter as MCK). This mass transfer model is phenomenological and was derived for the case of a linear isotherm and for mass transfer from the solution to the particle surface being the dominant (slowest) step of the adsorption process. The corresponding equation for the evolution of bulk concentration is (modified to admit use of linear fitting procedures):  C 1   KM   1  KM   ln    ln    hSt  1  KM   KM   C0 1  KM 

(8)

where S is the total adsorbent particles external area, h is the mass transfer coefficient and K is the linear isotherm constant. This model was derived in order to analyze the effect of stirring on adsorption kinetics and is meaningful only if the stirring is low enough to dominate the adsorption kinetics. Interestingly enough, the model is used to analyze typical adsorption experimental data taken using high stirring intensity needed for optimization of the global kinetics. Obviously the use of this model in those cases is quite erroneous.

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(vi) The chemical reaction engineering approach (abbreviated hereafter as GREA) to adsorption dynamics applies classical concept of chemical engineering to the adsorption process [321]. The key aspects are that (i) all parameters are of fundamental value, and (ii) these parameters characterize the adsorbate and the adsorbent separately. Unlike the previous models, the present model can be scaled-up in order to be used under different experimental conditions The adsorbate can be found in the adsorbent particle phase as solute in the liquid filling the pores of the particle (concentration C in kg/m3) and adsorbed on the solid phase (concentration q in kg adsorbate/kg adsorbent). The “homogeneous” equations for the evolution of C and Q inside a spherical adsorbent particle of radius R, are the following:

C 1   2 C    r Dp   p G  C,Q  t r 2 r  r 

(9)

Q 1   2 Q   2  r Ds   G  C, Q  t r r  r 

(10)

εp

where r is the radial direction, εp the porosity of the particle, ρp the density of the particle (kg adsorbent/m3), Dp is the liquid-phase diffusivity of the adsorbate and Ds is the corresponding surface diffusivity. The diffusivity Dp for a given pair of adsorbate-fluid depends only on the temperature, whereas the diffusivity Ds depends both on the type of adsorbent and on Q also (apart from their dependence on geometry). The function G(C,Q) denotes the intrinsic rate of the adsorptiondesorption process. The boundary conditions for the above set of equations are the mass transfer from the solution to the particle (where Cb is the concentration of the adsorbate in the bulk solution) (Eq. (11)) and spherical symmetry (Eq. (12))

 C  h  Cb  C    D p    r r R

(11)

 C   Q    0   r   r 

(12)

Having values for the initial concentrations of adsorbate in the particle and for the bulk concentration Cb, the above mathematical problem can be solved for the

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functions C(r,t) and Q(r,t). The above model is the so-called non-equilibrium adsorption model. In the case of adsorption by small particles, the adsorptiondesorption process is much faster than the diffusion, leading to an establishment of a local equilibrium (which can be found by setting G(C,Q) = 0 and corresponds to the adsorption isotherm Q = f(C)). In the limit of very fast adsorptiondesorption kinetics, it can be shown by a rigorous derivation that the mathematical problem can be transformed to the following:

Q  1   2 Q   2  r D C t  r  r r

(13)

 Q    0  r r 0

(14)

 Q  h  C b  C   p D p    r r R

(15)

An additional assumption considered in the above derivation is that the amount of the adsorbate found in the liquid phase in the pores of the particle is insignificant compared with the respective amount adsorbed on the solid phase (i.e. εpCACM. The situation in which both of the parameters are variable, the dominancy of green adsorbents can be observed clearly. 4. COMPARISON OF ECONOMICS IN REAL REGARDING INDUSTRIAL DATA The real situation can aid in estimation of adsorbents quantity in which the average industry treats and releases 1 MGD (megagallons per day) as effluents. The effluents may be dyes or metals. If the industry is textile, then concentrations of dyes used will be 0.01-0.25 g/dm3 (= 10-250 g of dye per m3 of effluent). This concentration of dye is used in dye house as cited, which depends on the process and dyes consumed [371]. Hence, the dyeing effluent should possess 37.85946.25 kg concentration of dye per day required to be removed or adsorbed. In

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order to make an effective effluent, Table 1 displays the example of concentrations of required constituents, which are 378.5-9462.5 kg of AW, 1263154 kg of ACM, and 189-4731 kg of AC. Conversely, the outcome cost for the production as mentioned previously for the AW is zero. Therefore, for all cases, this method can be considered as an adequate process. The similar procedure involving average metal (chromium) plating along with the effluent rate of 2 MGD is conducted by the use of 0.5-270,000 g per m3 concentration of chromium according to the cited material [372]. 5. FUTURE TRENDS Controversies lie for the use of adsorption methods in order to decontaminate the wastewaters. Considering this as an old and non-applicable procedure for industries, many researchers have denied its adaptation. On the other hand, some researchers object the use of this material only as adsorbent. The consumption of usual chemical as adsorbents which are formed following the complicated recipes, was common in past. The main issue is the scarcity of literature regarding green adsorbent as compared to the literature of complex and expensive adsorbents. The foremost beneficial fact related to the adsorbent is their use in industries. Consequently, several adsorption methods are taken into consideration for the development and have been patented. Among them, some have been developed for commercial uses. Table 1 displays some of the examples of such methods. In the USA and Canada, pilot installations and units are prepared commercially [373]. However, in the pilot installations, biosorption is the basic technique for sequestering or extracting the pollutants including uranium. This pilot installation is confirmed along with some restrictions which are inadequate in acquiring cheap and reliable raw biomass, difficult recycling, and biomass reuse, and the disadvantages pertaining to the adsorption capacity and co-existing ions [373]. Besides, some of these adsorbents are accepted commercially from sequestering and extracting metals from the aqueous solutions as mentioned in Table 2. However, with extent of our knowledge, no industry has been found using these adsorbents. Researches raise some questions now-a-days, which need to be evaluated before determination of the adsorbent potential for the extraction of dyes and metals from industrial aqueous solutions. The questions include: a) Effluent Characteristics: types of pollutants and contaminants, which are targeted, volume, solution chemistry involving pH, temperature, etc.

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b) Adsorbent Characteristics: the properties of adsorbents that comprise of production, cost, recycling, availability, pollutant specificity, capacity to adsorb, mechanical stability, rate, etc. c) Process Conditions: conditions of the process involving type of process can be batch or continuous, relation with other processes, skill of the operator, etc. d) Capital Cost: capital cost of land space, cost of operation, production cost, etc. e) Other Characteristics: other properties comprising of dumping of used adsorbent, recycling or reuse of metals extracted from effluents, etc. However, increase in commercialization is required for the aqueous wastes in particular. The data for gas adsorption indicated a success in commercialization of industrial tests and adsorbers. In this way, similar outcomes are not obtained for wastewaters. Table 2. Commercialized adsorbents [374]. Commercial product AlgaSORB

TM

Remarks/Comments Biosorbent manufactured from a fresh water alga, Chlorella vulgaris, by being immobilized on silica

B.V. Sorbex

Biosorbent manufactured from a variety of sources including the algae Sargassum natans, Ascophyllum nodosum, Halimeda opuntia, Palmyra pamada, Chondrus crispus, and Chlorella vulgaris

AMT-BioclaimTM

Biosorbent manufactured from Bacillus sp. by being immobilized with polyethyleneimine and glutaraldehyde

Bio-Fix

Algae and other various sources are used to extract biosorbents, which are immobilized via use of porous polypropylene beads

RAHCO bio-beads

Organic polymer are used to make the biosorbent immobile which are produced from peat moss and other different sources

Research should be continued in both fundamental forms so that the adsorption mechanisms are determined and for the evaluation of interactions between pollutants and cheap (green) materials. Industrial effluents possess various pollutants, which are not present in laboratory solutions. Hence, the extraction of pollutants which co-exists is required. Some researches have been conducted to evaluate extraction of co-existing pollutants [375]. However, these researches deal with effluents containing dyes and metals only and are devoid of any additives.

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On the other hand, a real effluent is composed of various materials as discussed in Chapter 1. Hence, the interaction between the materials will be different. Therefore, it is required to produce green adsorbents, which will serve purposes generally and carry out removal of various pollutants. To achieve the aim, one technique can be the combination of several costeffective materials as adsorbents. Thereby, the materials are functional in place of any modification hence, preventing increase in cost. Moreover, the mixing of materials from nature will help as they will be of no cost. Furthermore, by making the materials reusable can aid in achieving our goal. Subsequently, researchers are evaluating the adsorption capacities of the materials along with their desorption capacities. The preference is given to the material which is more capable of desorption from the pollutant than having high adsorption capacity as compared to the materials which are less desorptive but have high adsorptive properties. Consequently, several researches would be needed for the production of appropriate desorbers. For this, adsorption and desorption cycles in sequences can help in categorizing the materials with good capacity of desorption.

Fig. (2). Main future trends of green adsorbents.

In conclusion, the future perspective is clear which is to transform the adsorption process towards the industrial level. In the laboratory, the illustrations are not that difficult as compared to the illustrations on a pilot scale. Major financial and

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technical efforts will be required in order to level up the process for industrial scale. Scientific progress concerning the biosorption research and halt in the technology of industrial innovations does not match; therefore, the correction is required to move them along. This correction can be conducted by the research of translation and technology transmission along with the commercial research. In addition, universities can play their part in introducing better approach in technology transmission and protecting intellectuality [376, 377]. A useful scheme describing all the above is Fig. (2). DISCLOSURE Part of this article has been previously published in “Green Adsorbents for Wastewaters: A Critical Review”, Materials 7 (2014) 333-364, doi:10.3390/ma7010333 and “The Change from Past to Future for Adsorbent Materials in Treatment of Dyeing Wastewaters”, Materials 6 (2013) 5131-5158; doi:10.3390/ma6115131.

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115

Subject Index A Ability of chitosan 43, 44 Absorbate 82, 83 Absorbents 38, 39, 64, 73, 74, 82 Absorption process 35 Absorption rate 37, 39 Accidental discharges 17, 21, 25 Acidic dyes 66 Acidic media 43, 44 Acidic surface oxides 59 ACR adsorption capacity 41 Activated alumina 72 Activated carbon (AC) 38, 39, 40, 41, 42, 44, 47, 48, 53, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 68, 70, 71, 74, 83, 86, 87, 89, 90, 92, 93, 94 Activated carbon absorption 38 Activated carbon cores 42 Activated carbon costs 90 Activated carbon fiber 39 Activated carbon properties 60 Activated carbon surfaces 41 Activated carbon types 39 Activated sludge 28, 29 Activation process 57 Activation temperature 58, 59 Adjacent cellulose chains 56 Adsorbate 39, 46, 47, 48, 49, 60, 76, 79, 80, 81, 82, 83, 84, 85, 86, 87, 90 Adsorbate concentrations 50, 76, 85, 86, 87 Adsorbate equilibrium concentration 49 Adsorbate monolayer saturation concentration 52 Adsorbent ability 74 Adsorbent activity 64 Adsorbent-adsorbate interactions 49 Adsorbent-adsorbate pairs 84 Adsorbent behaviour 45 Adsorbent capability 91 Adsorbent characteristics 95 Adsorbent cost 92 Adsorbent dosages 65, 87 Adsorbent dose 61 Adsorbent drying 42 Adsorbent materials 36, 46, 68, 72, 89, 97 Adsorbent particle 81 Adsorbent particle phase 79 Adsorbent production 93 Adsorbent quantities 86 Adsorbents quantity 93 Adsorbent’s surface area 35 Adsorbent suspension 90 Adsorbent systems 45

Adsorbent water treatment cost 91 Adsorption activity of rice husks 63 Adsorption applicability 35 Adsorption behaviour 64 Adsorption capability 75 Adsorption capacities 41, 42, 43, 44, 45, 60, 61, 62, 69, 70, 71, 93, 94, 96 Adsorption columns 42 Adsorption cost 92 Adsorption data 49, 87 Adsorption-desorption process 79, 80 Adsorption/desorption revolution 89 Adsorption dynamics 79 Adsorption efficiency 72 Adsorption energy 48, 51 Adsorption equilibrium 47, 50 Adsorption equilibrium correlation 45 Adsorption equilibrium data 71 Adsorption exclusion 71 Adsorption heat 48 Adsorption intensity 48 Adsorption interactions 61 Adsorption isotherm models 47 Adsorption isotherms 45, 46, 53, 80 Adsorption kinetic models 76 Adsorption kinetics 69, 77, 78 Adsorption mechanism 48, 61, 95 Adsorption mechanism pathways 45 Adsorption nature 48 Adsorption of Cr 86 Adsorption parameters 45, 69, 71 Adsorption performances 42, 71 Adsorption properties 44 Adsorption results 74 Adsorption selectivity 44 Adsorption sites 44 Adsorption systems 42, 46 Adsorption technique 35, 36 Adsorptive capacity 41, 42 Adsorptive nature 57 Agricultural products 65, 66 Agricultural sources 55 Agricultural wastes 41, 55, 66, 92, 93 Agricultural wastes (AW) 55, 56, 66, 93, 94 Agricultural wastes/residues 55, 56 Agro-based activated carbon 55 Alkalis 8, 24, 26, 30, 31, 45, 56, 73 Alkali-treated straw (ATS) 72 Ammonia soda process 68 Anaerobic biological treatment processes 26

George Z. Kyzas All rights reserved-© 2015 Bentham Science Publishers

116 Green Adsorbents

Anaerobic reduction process 24 Analytical process 36 Anionic dyes 38, 42, 43, 45, 62, 68 Apricot stones 58, 65 Aqueous effluents 40, 65 Aqueous media 67, 68, 71 Aqueous phase 61, 65 Aqueous solutions 36, 37, 38, 39, 43, 62, 63, 64, 65, 66, 67, 68, 69, 72, 94 Aqueous streams 62, 63 Ash-based adsorbent 85 Assembling procedures 18 Azolla 73

B Bacon processing 12 Bagasse fly ash (BFA) 75 Bagasse pith 66 Balanced adsorption capacity 73 Balanced data 74, 75 Balance tanks 17 Banana peels 41, 73 Barley straw (BS) 66 Based materials 42, 44 Based reduction processes 31 Base solutions 90 Basic activated carbons 59 Basic cationic dyes 43 Basic dyes 44, 65, 66 Batch adsorption method 72 Batch adsorption technique 65 Batch manufacturing processes 18 Best complex adsorbents 55 Best fit model 40 Best fitting 74 BET adsorption isotherm 52 Biochemical oxygen demand (BOD) 3, 6, 13, 89 Biological processes 30, 35 Biological treatment 26, 28 Black coloured effluent 4 Black gram husk (BGH) 66 Blast furnace slag 67 Blast furnace sludge 74 Bound carbonaceous material 57 Breweries 7, 12 Brunauer-Emmer-Teller (BET) 35, 51, 52, 53 Bulk concentration 78

C Cadmium 6, 7, 8, 9, 13 Cadmium adsorption 72 Capital cost 95

George Z. Kyzas

Caramel 62 Carbohydrates 4, 12, 57 Carbonaceous adsorbents 65, 66, 74 Carbon adsorption methods 10 Carbon dioxide 6 Carbonization 39, 58, 59, 62, 64, 69 Carbonization and activation 59, 62 Carbonization temperature 58 Carboxyl groups 44, 73 Cationic dyes 38, 40, 44, 63 Cellulose 30, 55, 56 Cellulose chains 55, 56 Cell wall structure 56 Changed solution concentrations 48 Cheap activated carbon concentrations 86 Cheap adsorbents 43 Cheap carbonaceous adsorbents 86 Chemical activation 57, 58, 59, 62, 64 Chemical activation process 59 Chemical activation temperatures range 59 Chemical adsorption 48 Chemical derivatizations 44 Chemical manufacture 7 Chemical modifications 44, 93 Chemical oxygen demand (COD) 3, 6, 12, 13, 31, 32, 89 Chemical processes 9, 28 Chemical surface 61, 62 Chemisorptions process 48 Chi-square values 51 Chitosan 42, 43, 44, 45, 84, 87 Chitosan-Based Adsorbents 42 Chitosan’s removal capacity 43 Chlorella vulgaris 95 Citric acid 7, 72, 73, 90 Citrus fruit processing 7 Clarified sludge 72 Cleaned industrial water 14 Cleaning household waste water and purifying 13 Cleaning processes 15 Clearance levels 33 Coconut shell 40, 57, 74 Coke scrubber effluents 9 Collection system 21, 22, 24, 25, 26 Combined adsorption membrane process 40 Commercial activated carbon (CAC) 43, 74 Commercial carbons 61, 62 Commercialized adsorbents 95 Common adsorbents 89 Common effluents 11, 19 Compatible pollutants 13, 30 Complex adsorption systems 49 Complex dyes 45

Subject Index

Concentrated solutions 14, 15, 25, 28 Concentration of dye 61, 93 Concentrations of absorbate 82, 83 Constant adsorbate concentration 77 Constant effluents 19 Continuous activated carbon absorption system 40 Continuous adsorption columns 40 Cooperative adsorption 48 Copper ions 62, 71, 72, 73 Cost-effective adsorbents 65, 89 Cost-effective materials 96 Cotton gum 30 Crab carapace 71 Cross-linked beads 44, 45 Crystalline supermolecular structure 56 Crystal violet 36, 63, 65 Cultivated products 65 Curve fitting process 78 Cyanide 7, 9, 28 Cyanine acid adsorption 87 Cyanine acid blue (CAB) 75 Cylinder engraving process 32 Cynanine dyes 37

D Degrees centigrade 26, 31 Density 44, 45, 79 Design model 38 Diffusion coefficients 86, 87 Diffusion values 87 Direct blue dye adsorption 84 Direct dyes 42, 66 Discharged material 22 Discharged waste water 32 Discharge limit 28 Discharge of flammables 25 Discharges by industrial processes 27 Disperse dyes 70 Disposal system 4, 29 Distiller waste (DW) 68 Dubinin-Radushkevich isotherm model 48, 49 Dye absorption 36, 37 Dye absorption process 37 Dye/adsorbent interaction 35 Dye-adsorbent-temperature combinations 84 Dye adsorption 35, 40, 41, 43, 45 Dye adsorption terms 36 Dye-containing wastewater 45 Dyeing effluents 3, 89, 93 Dyeing industries 30 Dyeing process 31 Dyeing processing operations 32 Dyeing waste waters 30, 31, 38

Green Adsorbents 117

Dyeing Wastewaters 30, 35, 97 Dye removal 38, 41, 44, 62 Dyes and raw materials 31 Dyes concur 42 Dyes selection 43 Dyestuff adsorption 43

E Effective adsorbent 41, 43, 65, 69 Effective adsorption materials 44 Effective dye adsorbents 45 Effective effluent 94 Effects of industrial wastewater 20 Effects of mercury poisoning 9 Effects on effluent and sludge 28 Efficient adsorbent 41, 66 Efficient waste removal process 8 Effluent and sludge disposal and reuse 28 Effluent characteristics 18, 94 Effluent emissions 14 Effluent limit 27 Effluent quality 28 Effluent rate 94 Effluents results 14 Electroplating 8, 9, 12 Electroplating wastewater 64 Elementary crystallites 57 Elevated concentrations 50 Eliminating anionic dyes 68 Eliminating environmental pollutants 55 Empirical models 81 English walnut shells 72, 73 Enzymatic hydrolysis 56 Equilibrium adsorption capacity 52 Equilibrium adsorption data 51 Equilibrium isotherm models 46 Equilibrium value 76 Eriochrome black T (EBT) 69 Establishing intramolecular 56 Ethylene glycol diglycidyl ether (EGDE) 44

F Fabrication methods 14 Factory processes 11 Fast adsorption-desorption kinetics 80 Fertilizer industry 67, 68 Fertilizer industry waste 67, 74 Fiberglass 24 Finishing process 30, 31 Finishing waste waters 31 First-order model 77 Five adsorbents 85

118 Green Adsorbents

Five low-cost activated carbons 87 Flory-Huggins Isotherm Model 49 Fluidized beds 38 Fluorides adsorption 87 Food chain 32 Food industries 5 Food processing 7, 23 Food processing factory 17 Food processing plants 22 Food processing waste 55 Food residues 55 Formaldehyde 6, 7, 32, 41, 90 Free chlorine 7 Frenkel-Halsey-Hill (FHH) 52, 53 Fresh wastewater 5 Freundlich isotherm models 48, 50, 51 Freundlich isotherms 48, 50, 71 Freundlich model 74 Fuels and solvents 25 Fuller’s earth 57, 72

G Gas adsorption 95 Gas-solid-phase adsorption 47 Glycosidic bonds 56 Gold-plating wastewater 65 Granular activated carbons 40 GREA 79, 81, 82, 84, 87

H Harmful chemicals 4, 14, 15 Harmful effluents 19 Harmful substances 3, 15 Hazelnut shells 58, 70, 83 Heated industrial discharge 26 Heated industrial waste water 25 Heat treatment process 42 Heavy metals 5, 6, 7, 8, 10, 12, 13, 14, 15, 29, 60, 61, 62, 64, 69, 71, 72, 73, 85 Heavy solids 22, 23 Hemicelluloses 30, 55, 56 Henry’s law 48 Heterogeneous adsorption systems 50, 51 Heterogeneous surface 48 Heterogeneous systems 48, 50 High adsorption capacity 43, 44, 60, 61, 96 High adsorption potentials 70 High adsorptive properties 96 High-end boundary 51 Higher adsorption power 44 Highest adsorption potentials 72 Highest effluent flow 20

George Z. Kyzas

Highest monolayer adsorption potentials 69 High-level wastes (HLW) 33 High surface area 39, 41, 58, 60, 63 High temperature discharges 21 High temperature discharge waste water 21 High temperature waste water 21 High temperature waste water discharge 21 Hill isotherm model 50 Homogeneous adsorption 47 Hot water 26, 62 Huge wastewater accumulation areas 17 Hydraulic overload 22, 26 Hydraulic surges 27 Hydrogen sulfide gas 24 Hydrogen sulphide 4, 6, 10, 24 Hydrophobic adsorbents 43

I Ideal adsorption system 45 Indigo carmine 36, 63, 65 Individual industrial waste water components 21 Industrial aqueous solutions 94 Industrial discharges 23, 24, 27, 28, 29, 30 Industrial dyes 38 Industrial effluents 6, 7, 10, 12, 14, 16, 19, 69, 95 Industrial effluent treatment plant 19 Industrial processes 19, 26, 27, 28, 29 Industrial sewer 20, 22, 24 Industrial waste adsorbents 87 Industrial waste discharge 21, 23, 26 Industrial wastes 11, 55, 60, 61, 74 Industrial wastes laden 61 Industrial waste streams 21 Industrial wastestream variables 13 Industrial waste water 9, 20, 21, 26 Industrial wastewater characteristics 4 Industrial waste water discharges 20 Industrial waste water pipes 24 Industrial waste water sludge 20 Inexpensive adsorbents 60, 71, 75 Influent waste water 27 Initial adsorption 77 Initial concentrations 47, 76, 79 Initial concentrations of adsorbate 76, 79 Insoluble adsorbent 44 Insoluble straw xanthate (ISX) 72 Intermolecular hydrogen bonds 56 Intra-particle diffusion model 77 Ion exchange 35, 38, 61 Irreversible reaction model 81 Isotherm 37, 49, 51, 52, 53, 74, 78, 82, 91 Isotherm constant 49, 51, 52 Isotherm modelling 47

Subject Index

Isotherm models 35, 45 IWTS effluent 21 IWTS operator 24, 27 IWTS processes 20

K Kaolinite 37, 38 Khan Isotherm Model 51 Kinetic data 82, 83, 84, 85, 86, 87 Kinetic data sets 84, 86, 87 Kinetic modeling 88 Kinetic sets of data 82, 83, 84 Klaus process 23 Koble-corrigan isotherm model 51

L Langmuir 35, 46, 53, 69, 74, 82 Langmuir adsorption isotherm 47 Langmuir and Freundlich isotherm models 51 Langmuir and Freundlich isotherms 50, 71 Langmuir and linearized Freundlich model 75 Linear cellulose chains 56 Linear isotherm 77, 78, 81 Linearized Freundlich model 75 Liquid chlorine 25 Liquid-phase adsorption 75 Liquid-phase adsorption isotherms 49 Local waste water 11 Longitudinal direction 56 Long lived radionuclide concentrations 33 Low capacities 70, 71 Low concentration waste water 14 Low-cost adsorbents 87 Low-cost carbonaceous adsorbent 87 Low cost materials 38 Low-cost materials 35, 36 Low density materials 72, 73 Lower surface area 59 Low-priced adsorbents 72

M Macadamia nutshells 58 Major adsorption site 45 Major hazardous materials 6 Major physical constituents of effluents 4 Major solid waste products 66 Mango peel waste (MPW) 65 Manufactured processes 25 Manufacturing processes 11, 22, 23, 26 Manufacturing process waste 29 Mass emission flow 15 Mass emission rates 15, 16

Green Adsorbents 119

Mass transfer 78, 79 Mass transfer model 78 Mathematical problem 79, 80 Maximum adsorption capacities 43 MB adsorption 40, 70 Meat processing 12 Mechanical properties 43, 44 Membrane processes 35 Mercaptans 5 Mercury 6, 8, 9, 61, 62, 63 Mercury poisoning 9 Metal finishing industries 25, 26 Metal finishing process 15 Metal finishing sewage water 71 Metal ions 9, 44, 48, 60, 62, 73 Metal ions adsorption 72 Metal surface treatment processes 15 Methane 6 Methylene 61, 62 Methylene blue 36, 61, 65, 66, 69 Methylene blue (MB) 36, 37, 39, 61, 62, 63, 65, 66, 69, 70, 83 Methyl parathion (MP) 65, 75 Methylthionine chloride 62 Metric tons 63, 64, 89 Microfibril 56 Microorganisms 10, 26, 27 Milk processing carbohydrates 12 Mineral processing reactions 9 Mining effluents 9 Miscellaneous industrial wastes 68 Mixed diffusion-reaction model 81 Modified extended Langmuir isotherm 40 Monolayer adsorption 43 Monolayer adsorption capability 50 Montmorillonite 38 Mordant dyes 43 Multilayer adsorption 48 Multilayer adsorption derivation 52 Multilayer adsorption systems 51 Municipal effluents 4 Municipal solid waste 38, 55 Municipal wastes 55, 57, 66 Musa spp adsorbent 71

N Namasivayam 64, 65, 87 Natural sources 55, 56 Natural water bodies 32 Natural water systems 9 Natural zeolite 71 Nitrite ion 10 Nitrobenzene adsorption 87

120 Green Adsorbents

Non-compatible effluents 14 Non-compatible pollutants 13, 28, 30 Non-compatible pollutants interchange 13 Non-equilibrium adsorption model 80 Non-linear form 53

O Obtaining activated carbon 68 Operating adsorption 91 Orange dyes 37 Orange peels 41, 64, 65, 73, 83 Ordinary differential equations 81 Organic compounds 6, 13, 30, 39, 48, 60, 61, 90 Organic dyes 40 Organic materials 6, 55 Organic matter 4, 6, 10 Organic pollutants 10, 40, 63 Organic processing assistants 32

P Parallel adsorption mechanisms 41 Parametric dependency 81 Partial differential equations 81 Peak waste water flows 23 Peanut hulls 38, 58, 59, 64 Peanut husk charcoal 71 Pecan shells 58, 59, 72 Persistent temperature 46 Petroleum acid sludge 57 Phenols 3, 7, 61, 62, 63, 66, 67, 69, 74, 89 Phenols adsorption 73 Photosynthesis process 32 Physical activation 59 Physical meaning 78, 86, 87 Pilot installations 94 Pollutant concentration 14 Pollutant removal efficiency 29 Pollutant’s mass for removal 93 Polluted wastewater 92 Polyester fabrics 31 Polyester fibers 30, 31 Pore size distributions 39 Potato processing 12 POTW collection systems 21, 24, 29 POTW effluent and sludge 30 POTW system’s discharge 23 POTW treatment processes 27 Power generation processes 14 Pre-adsorption thermal regeneration cycle 42 Predominant dye adsorption mechanism 61 Pre-treated waste water 30 Pre-treatment system 14, 15 Pre-treatment waste water 30

George Z. Kyzas

Printed circuit board (PCBs) 6, 8, 11 Printing processes 30, 31 Produced activated carbons 41 Producing effluents 3 Producing pollutants 23 Production of dirty water in metropolitan areas 11 Pulp processing 7 Pumping station 22, 23 Pump station 23, 25 Pure oxygen 25 Purifying process 15 Pyridine adsorption 87

R Radioactive wastes 33, 34 Radioactive wastewaters 33 Radke-Prausnitz isotherm model 51 Ramifications 15, 16 Reactive dyes 39, 43, 44, 45, 83 Real effluent 96 Real industrial dyeing waste waters 38 Real textile process effluent 41 Recovery processes 23, 26 Recycling cost 90, 91 Recycling of adsorbents 89, 90 Redlich-Peterson isotherm models 50, 74 Reduced adsorption capacity 45 Reduction process 31 Refractory organics 10 Regeneration methods 42 Relative pressures 51, 52 Released waste water 18 Removal of Cd 63, 65 Removal process 38 Removing dyes 67 Removing Methylene blue 65 Removing pollutants 65 Removing toxic pollutants 65 Required adsorbent’s mass 93 Residential wastewater streams 17 Residual dyes 30, 31, 38 Residue effluents 9 Reversible adsorption 48 Rice hulls 57, 58, 63, 72 Rice husk (RH) 40, 41, 58, 63, 70, 72, 75 Rice husk ash 72 Rice husks 40, 41, 58, 63, 70, 75 Rice straw 58 Rubber processing 7

S Saturated activated carbons 41 Saturation adsorption capacity 45 Scrubbing processes 17

Subject Index

Secondary sewage treatment processes 10 Selected activated carbons 40 Sewage sludge 61, 62 Sewage water 71, 72 Short lived waste 33 Showed excellent adsorption capacities 62 Showed low adsorption potentials 72 Sludge processes 27 Slug loadings 24, 28, 29, 30 Sodium hydroxide 25, 31, 90 Solid phase 79, 80 Solid wastes 38, 68 Spherical adsorbent particle 79 Stagnant waste water 25 Steel industry 67, 72 Stringy materials 22 Strong effluent 16 Sulphuric acid 15, 24, 25, 90 Superb removal capacities for anionic dyes 42 Surface area 37, 39, 57, 58, 59, 60 Surface chemistry 40, 60 Surface diffusion 84 Surface diffusivities 79, 80 Surface properties 45, 46 Surface water 31 Suspended solids 12, 13, 31

T Tannery effluents 3, 89 Tapered bed adsorption 40 Technology transmission 97 Temkin 35, 47, 49 Temperature of effluent 5 Term waste water 3 Tertiary physical-chemical process 30 Tertiary processes 29 Textile bleaching 7 Textile dyeing waste water 31 Textile Dyeing Wastewater Risk 32 Textile industries 5, 7, 32 Textile industry standards for water pollutants 32 Textile waste waters 38 Theoretical model assumptions 50 Thermal regeneration 42 Total adsorbate amount 81 Total adsorbent particles 78 Total adsorption cost 91 Total operating costs 92 Total organic carbon (TOC) 6 Toth isotherm model 51 Toxic adsorbents chemicals 89 Toxic components 30 Toxic organics 29

Green Adsorbents 121

Toxins 65, 66 Trace elements 5, 9 Traditional steam activation process 39 Treated effluent 5, 6 Treated peels 73 Treatment network 19 Treatment of effluents 4, 13 Treatment plant 21, 26, 28 Treatment principles 15 Treatment processes 5, 15, 16, 27, 28, 33 Treatment system discharging 21 Treatment systems 13, 15, 20, 26, 29, 30 Trickling filter process 28 Trout stream 21 Typical concentration parameters 12

U Underground water 9, 10, 14 Unit adsorbent mass 76 Untreated industrial discharge 20

V Variation of temperature of effluent 5 Virgin adsorbents 89, 90 Volatile organic carbons (VOC) 6 Volatile solids 4

W Waste carbon slurry 67 Waste changes 18 Waste cotton 70 Waste materials 23, 41, 61 Waste products 23, 33, 66, 67, 68 Waste tires 39 Waste treatment sites 42 Waste water 3, 6, 11, 13, 14, 15, 19, 21, 22, 23, 24, 27, 29, 31, 32, 35, 38, 39, 43, 66, 67, 74, 90 Waste water characteristics 21 Waste water components 22 Waste water cycles 17 Waste water decolourization 39 Waste water discharge 21, 22 Waste water disposal 21 Waste water effluents 11 Waste water flow 27 Wastewater nonstop 18 Wastewater release 16, 17 Wastewaters 3, 4, 5, 7, 8, 10, 11, 12, 15, 16, 17, 18, 30, 35, 55, 60, 70, 92, 94, 95, 97 Waste water standards 31 Waste water stream 16 Wastewater streams 7

122 Green Adsorbents

Waste water treatment 35, 40 Water plants 55 Water Pollutants 32

George Z. Kyzas

Water treatment 31, 57, 64 Wollastonite adsorbent 85