General Introduction

Chapter − 1 General Introduction

1.1. Introduction

Water is an elixir of life. It covers about three quarters of the earth’s surface

area. About 95% of earth’s water is in the oceans, which is unfit for human

consumption and other uses because of its high salt content. Of the remaining 5%,

about 4% is locked in the polar ice caps. The remaining 1% constitutes all the fresh

water in the hydrological cycle including ground water reserves. Only 0.1% is

available as fresh water in rivers, lakes and streams, which is suitable for human

consumption [1, 2].

The merits of water are decreasing day by day due to pollution. Water is said

to be polluted, if its physical and chemical properties are altered due to the addition of

unwanted matter, which makes it unfit for its intended use, although natural

phenomena such as volcanoes, algae blooms, storms and earthquakes also cause

major changes in water quality and the ecological status of water [3, 4]. Water

pollution has many causes and characteristics. Increase in nutrient loading may lead to

eutrophication. Organic wastes such as sewage impose high oxygen demands on the

receiving water leading to oxygen depletion with potentially severe impacts on the

whole ecosystem. Industries discharge a variety of pollutants in their effluents

including heavy metals, resin pellets, organic toxins, oils, nutrients and solids [5-14].

Discharges can also have thermal effects, especially those from power stations and

these too reduce the available oxygen. Silt-bearing runoff from many activities

including construction sites, deforestation and agriculture can inhibit the penetration

of sunlight through the water column, restricting photosynthesis and causing

blanketing of the lake or river bed, in turn damaging ecological systems. [15]

Effects of Water Pollution

• Waterborne diseases like typhoid, amoebiasis, diardiasis, ascariasis,

hookworm, respiratory infections, hepatitis, encephalitis, gastroenteritis,

diarrhea, vomiting, and stomach aches

• Parkinson’s disease, multiple sclerosis, Alzheimer’s disease, heart disease and

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even death

• Cancer, including prostate cancer and non-Hodgkin’s lymphoma

• Hormonal problems that can disrupt reproductive and developmental

processes

• Damage to the nervous system

• Liver and kidney damage

• Damage to the DNA

• Damage of sea foods chain

• Damage to people may be caused by vegetable crops grown/washed with

polluted water

1.2. Water Quality Parameters

A number of parameters are considered to check the quality of water. Table

1.1 shows certain parameters with permissible limits as prescribed by Bureau of

Indian Standard for domestic water supplies.

Table 1.1. Indian standard specification for drinking water IS: 10500.

S. No. Parameter Desirable limit Permissible limit

1 Colour (Hazen Units) 5 50

2 Turbidity (NTU) 10 25

3 pH 6.5-8.5 9.2

4 Total hardness 300 600

5 Ca 75 200

6 Mg 30 100

7 Cu 0.05 1.5

8 Fe 0.3 1

9 Mn 0.1 0.5

10 Chlorides 250 1000

11 Sulphates 150 400

12 Nitrates 45 No relaxation

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13 Fluoride 0.6 to 1.2 Not less than 0.6 and

max limit 1.5

14 Phenols 0.001 0.002

15 Hg 0.001 No relaxation

16 Cd 0.01 No relaxation

17 Se 0.01 No relaxation

18 As 0.05 No relaxation

19 Cyanide 0.05 No relaxation

20 Pb 0.1 No relaxation

21 Anionic detergents 0.2 1

22 Cr(VI) 0.05 No relaxation

23 Polynuclear aromatic

hydrocarbon

-- --

24 Mineral oil 0.01 0.03

25 Residual free chlorine 0.2

26 Pesticide Absent --

27 Radioactive -- --

28 Alkalinity 200 600

29 Al 0.03 0.2

30 B 1 5

Unit; mg/l, otherwise mentioned

1.3. Classification of Water Pollutants

Water pollution can be classified as point source and non point source. Point

source of pollution occurs when harmful substances are emitted directly into water

body. A non point source delivers pollutants indirectly through environmental

changes. An example of this type of water pollution is when fertilizer from a field is

carried into a stream by rain, in the form of run off which in turn effects aquatic life.

Pollution arising from non point sources accounts for a majority of the contaminants

in streams and lakes. Water pollutants can be broadly classified into the following

four major categories:

• Organic pollutant

• Inorganic pollutant

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• Suspended solids and sediments

• Radioactive material

1.3.1. Organic Pollutant

Organic substances comprise a potentially large group of pollutants,

particularly in urban environments. Even at low levels, some of these organic

pollutants can be hazardous to human health, particularly if the exposure is long term.

Some organic pollutants also play an important role in the formation of photochemical

smog. Motor vehicle emissions are a major source of these pollutants together with

the petroleum and chemical industries, emissions from waste incinerators, service

stations, domestic solid fuel and gas combustion, cigarette smoke, spray painting, dry

cleaning and other solvent usage etc. The pathogenic microorganisms present in

polluted water causes water born diseases such as cholera, typhoid, dysentery, polio

and hepatitis in humans [16] . The pesticides, detergents, insecticides, dyes and other

industrial chemicals are toxic to plants, animals and humans, as these chemicals may

enter the hydrosphere either by spillage during transport and use or by intentional or

accidental release of wastes from their manufacturing establishments. Oil pollution

results in the reduction of light transmission through surface waters, thereby reducing

photosynthesis by marine plants. Further, it reduces the dissolved oxygen in water and

endangers water birds, coastal plants and animals. Thus, oil pollution leads to

unsightly and hazardous conditions, which are deleterious to marine life and sea food

[17].

1.3.2. Inorganic Pollutants

Inorganic pollutants comprise of mineral acids, inorganic salts, finely divided

metals or metal compounds, trace elements, cyanides, sulphates, nitrates,

organometallic compounds and complexes of metals with organics present in natural

waters. The metal-organic interactions involve natural organic species [18]. These

interactions are influenced by redox equilibria, acid-base reactions, colloid formation

and reaction involving microorganisms in water. Metal toxicity in aquatic ecosystems

is also influenced by these interactions. Various metals and metallic compounds

released from anthropogenic activities add up to their natural background levels in

water. Some of these trace metals play essential roles in biological processes, but at

higher concentrations, they may be toxic to biota [19].

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General Introduction

1.3.3. Suspended Solids and Sediments

Sediments are mostly contributed by soil erosion by natural processes,

agricultural development, strip mining and construction activities. Suspended solids in

water mainly comprise of silt, sand and minerals eroded from the land. Soil erosion by

water, wind and other natural forces are very significant for tropical countries like

India leading to qualitative and quantitative degradation of the soil in land area. Thus,

soil may get removed from agricultural land to the areas where it is not at all required,

such as water reservoirs [20-22]. Soil particles eroded by running water ultimately

find their way into water reservoirs and such a process is called ‘siltation’. Reservoirs

and dams are filled with soil particles and other solid materials, because of siltation.

This reduces the water storage capacity of the dams and reservoirs and thus shortens

their life. Apart from the filling up of the reservoirs and harbours, the suspended

solids present in water bodies may block the sunlight required for the photosynthesis

by the bottom vegetation. This may also smother shellfish, corals and other bottom

life forms. Deposition of solid in quiescent stretches of streams impairs the normal

aquatic life in the streams. Further, sludge blankets containing organic solids

decompose, leading to anaerobic conditions and formation of obnoxious gases. The

tremendous problem of soil erosion can be controlled by proper cultivation practices

and efficient soil and forest management techniques. The organic matter content in

the sediments is generally higher than that in soils. Sediments and suspended particles

exchange cations with the surrounding aquatic medium and act as repositories for

trace metals such as Cu, Co, Ni, Mn, Cr and Mo [23]. Suspended solids such as silt

and coal may injure the gills of the fish and cause asphyxiation.

1.3.4. Radioactive Materials

Radioactive pollution can be defined as the release of radioactive substances

or high energy particles into the water or earth as a result of human activity, either by

accident or by design. The sources of such waste are nuclear weapon testing or

detonation, the nuclear fuel cycle including mining, separation and production of

nuclear materials for use in nuclear power plants or nuclear bombs and accidental

release of radioactive material from nuclear power plants. The radioactive isotopes

found in water include Sr90, I131, Cs137, Cs141, Co60, Mn54, Fe55, Pu239, Ba140, K40 and

Ra226. These radioactive isotopes are toxic to life forms [24-27].

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General Introduction

1.4. Dyes

Since this thesis deals with the removal of dyes which falls under the category

of organic pollutant, the following section is devoted to the brief description of dyes.

A coloured substance can act as a dye only when it fulfills the following conditions:

• It must have suitable colour.

• It must be able to attach itself permanently to the fabric.

• The fixed dye must have fastness properties. Its colour should not fade in

light. It should be rasistant to the action of water, dilute acid, alkalies,

detergents and organic solvents used in dry cleaning.

Mauveine, was the first synthetic organic dye containing N-phenyl

phenosafranine, produced by William Henry Perkin in 1856. Thousands of synthetic

dyes have since been prepared. At present, almost all the dyes are synthetic and are

prepared from very few starting materials, such as benzene, phenol, aniline, etc. These

starting materials are obtained from coal tar and hence synthetic dyes are also known

as coal tar dyes [28].

According to Otto N. Witt (1876), the colour of the organic compounds is

associated with the presence of certain groups in the molecules called

“chromophores” and the colour is augmented by the presence of certain groups called

“auxochromes”.

Dye = Chromogen + Auxochrome

The important chromophores are nitroso, nitro, azo, azoxy, azomethine,

ethynyl, azo amine, carbonyl, o-quinonoid, p-quinonoid etc. Auxochromes are unable

to produce colour itself, but can deepen the colour produced by chromophore.

Auxochromes are certain acidic or basic groups eg. −COOH, −SO3H, −OH, −NH2,

−NHR, −NH2 etc.

1.4.1. Nomenclature and Classification of Dyes

The commercial names of dyes are frequently followed by letters, some of

which have special designation. For example, B stand for blue, BB or 2B stand for

more bluish and the numbers (2, 3, 4 etc.) indicate the intensity of shade. G stands for

yellow and occasionally for greenish. R stands for reddish. [29].

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General Introduction

Most of the commercial dyes are classified in terms of colour, structure or

method of application in the Colour Index (C.I.), which is edited every three months

since 1924 by the "Society of Dyers and Colourists" and the “American Association

of Textile Chemists and Colourists". The last edition of the Colour Index lists about

13000 different dyes. Each dye is assigned to a C.I. generic name determined by its

application and colour. Dyes may be classified in two ways

• According to the methods of application

• According to their chemical constitution

1.4.1.1. Classification According to Methods of Application

1.4.1.1.1. Direct or Substantive Dyes

These can be directly applied to the fiber. These dyes are two types.

(i) Acid Dyes

These are the sodium salts of the colour acids containing sulfonic and

phenolic groups. These are always used in an acidic solution. They dye silk and

wool (animal fiber) directly. For example- Maritus yellow, orange II, naphthol

yellow etc.

(ii) Basic Dyes

These are either hydrochloride or zinc chloride complexes of colour bases

which are directly used for silk or wool in basic medium. Azo dyes and triphenyl

methane dyes are the typical example of this class.

1.4.1.1.2. Mordent Dyes

These are unable to attach themselves to the fiber. Therefore, they require a

pretreatment of fiber with the certain substance called “mordent” like tannin or

tannic acid. The mordent gets itself attached to the fiber and then combines with the

dye to form an insoluble coloured complex. Alizarin, anthraquinone and azo dyes

belong to this class.

1.4.1.1.3. Vat Dyes

These dyes are insoluble in water, but their reduced form is soluble in an

alkali solution whereby leuco vat is obtained. The leuco compound is adsorbed on

fiber and upon exposure to the air, is oxidized to the dye which remains fixed to the

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General Introduction

cloth. Indigo and anthraquinone vat dyes are the good example of this class.

1.4.1.1.4. Ingrain Dyes

These are synthesized within the fiber and may be applied to both animal and

vegetable fibers by diazotization and coupling process. The colour obtained in this

type of dyeing are also called ice colour because diazotization and coupling process

are carried out at low temperature. Para red is an example of ingrain dyes.

1.4.1.1.5. Sulphur Dyes

These are similar to vat dyes and are sulphur containing complex, which are

insoluble in water, but soluble in cold alkaline solution of sodium sulphide. These

also form leuco complex. These dyes are dark in colour, inexpensive and have good

fastness propertis. Sulphur black is an example of this class and are used for dyeing

cotton.

1.4.1.1.6. Disperse Dyes

These dyes are used to dye acetate rayons, dacron, nylon and other synthetic

fiber. The fiber to be dyed is dipped in a dispersion of finely divided dye in a soap

solution in the presence of some solubilising agent such as phenol, cresol or benzoic

acid. The adsorption onto the fiber is carried out at high temperature and pressure.

Important example of this class is fast pink B and celliton fast blue.

1.4.1.1.7. Pigment Dyes

These dyes form insoluble compounds or lakes with salts of Ca, Cr, Ba, Al

or phosphomolybdic acid. These dye molecules contains −OH and −SO3H groups.

Due to their fastness to light, heat, acids and bases, they are valuable for paints,

printing ink, synthetic plastic, fibers, rubbers etc. Lithol red, pigment red and acid

red are the member of pigment dyes.

1.4.1.1.8. Solvent or Sprit Soluble Dyes

These are simple azo or triarylmethane bases or anthraquinone which are

used to colour oils, waxes, varnishes, lipsticks, dressings and gasoline.

1.4.1.1.9. Food Dyes

These are harmless and used in colouring food, candles, confectionaries and

cosmetics.

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1.4.1.2. Classification According to Their Chemical Constitution

This classification is useful for the chemists who are interested in the synthesis

and chemical constitution of dyes. Table 1.2 represents the classification of dyes

based on their chemical constitution.

Table 1.2. Classification of dyes based on their chemical constitution.

S. No. Class of Dyes Remark Example

1 Nitroso Nitro group as chromophores ,

phenolic as auxochrome in o-

postion

Fast green,

Napthol green Y

2 Nitro Nitro group as chromophore Martius yellow,

Napthol yellow S

3 Anthraquinone

Presence of chromophore

=C=O and =C=C arranged in

anthraquinone complex

Alizarin red S,

Alizarin blue

4 Triphenylmethane Quinonoid group as chromophore

and acidic –OH and basic −NH2,

−NHR, etc group as auxochrome

Malachite green,

Methyl violet

5 Diphenylmethane NH=C= group as chromophore,

also contains a diphenylmethane

nucleus

Auraine−O

6 Phthaleins Regarded as derivative of

triphenylmethane

Phenolphthalein

7 Xanthene =C=O or =C=N- as chromophore Eosin

8 Thiazole >C=O, S−C, etc as chromophore Premuline

9 Azo dye

(i) Acid azo

(ii) Basic azo

−N=N− as chromophore

Acidic group as –COOH, −SO3H,

−OH as auxochrome

Amino or substituted amino

group as auxochrome

Methyl orange

Aniline yellow

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General Introduction

1.4.2. Source of Dye Pollution and Hazardous Effects

Dyes are extensively used in textiles, paper, rubber, plastics, leather,

cosmetics, pharmaceuticals and food industries, resulting in a steadily growing

demand and production. Today there are more than 10,000 synthetic dyes available

commercially and more than 7×105 tonnes are produced annually [30, 31] . Synthetic

dyes usually have a complex aromatic molecular structure which possibly comes from

coal tar based hydrocarbons such as benzene, naphthalene, anthracene, toluene,

xylene, etc. [32]. From an environmental point of view, the disposal of synthetic dyes

is of great concern [33]. Dyes are known pollutants that not only affect aesthetic merit

but also reduce the sun light penetration and photosynthesis thereby increasing the

biological oxygen demand and causing lack of dissolved oxygen that sustains aquatic

life and some are considered toxic, even carcinogenic for human [34, 35]. The

harmful effects of the few important dyes are presented in Table 1.3.

Table 1.3 . Some important dyes and their hazardous effects.

Dye Hazardous Effects

Methylene blue Toxic to blood, reproductive system, liver, upper respiratory

tract, skin and eye contact (irritant), central nervous system

Rhodamine B

Causes respiratory tract irritation, eye and skin irritation,

digestive tract irritation, adverse reproductive and fetal effects in

animals, vomiting and diarrhea

Fast green Tumors of the liver, testes, or thyroid.

Fast ponceau

disazo dye

Mutagen and a potential carcinogen; highly toxic, skin and eye

irritant, must never be handled during pregnancy

Fast red salt B Potential carcinogen, irritant to eyes and the respiratory tract,

very toxic

Malachite green Accumulates in the tissues, liver, thyroid gland and bladder

Crystal violet Mutagen and mitotic poison

Eosin Carcinogenic, estrogenic and clastogenic properties

Congo red Mutagenic, hazardous in case of skin contact, eye irritant

Diamond black Thyroid cancers, mutagenic effects, DNA-damaging

Dye production and textile industries are the major source of colour pollution.

Easton, [36] estimated the degree of fixation for different dye/fibre combinations

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which is indicated in Table 1.4.

Table 1.4. Estimated degree of fixation for different dye/fiber combinations.

Dye class Fiber Degree of fixation (%) Lost to effluent (%)

Acid Polyamide 80-95 5-20

Basic Acrylic 95-100 0-5

Direct Cellulose 70-95 5-30

Disperse Polyester 90-100 0-10

Metal-complex Wool 90-98 2-10

Reactive Cellulose 50-90 10-50

Sulphur Cellulose 60-90 10-40

Vat Cellulose 80-95 5-20

Choy et al., [37] reported that 10–20% of dyes in the textile sector is lost in

residual liquors through incomplete exhaustion and washing operations. These

coloured effluents pollute surface water and ground water system. Due to the large

degree of organics present in these molecules, the effluents of textile and related

industry have to be treated carefully before discharge. This has resulted in a demand

for environment friendly technologies to remove the dyes from effluents.

1.5. Wastewater Treatment

Various treatment methods used in sewage and industrial wastewater

treatment are as follows

1.5.1. Preliminary Treatment

The aim of preliminary treatment is the removal of gross solids such as large

floating and suspended solid matter, grit, oil and grease if present in considerable

quantities. Large quantities of floating rubbish such as cans, cloth, wood and other

objects present in wastewater are usually removed under preliminary treatment.

1.5.2. Primary Treatment

Primary treatment involves the removal of gross solids, gritty materials and

excessive quantities of oil and grease, followed by the removal of the remaining

suspended solids as much as possible. This is aimed at reducing the strength of the

wastewater and also to facilitate secondary treatment.

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1.5.3. Secondary Treatment

Biological processes involve bacteria and other microorganisms to remove the

dissolved and colloidal organic matter present in wastewaters. These processes may

be aerobic or anaerobic. Secondary treatment reduces BOD, it also removes

appreciable amounts of oil and phenol. However, commissioning and maintenance of

secondary treatment systems is expensive.

1.5.4. Tertiary Treatment

It is the final treatment, meant for “polishing” the effluent from the secondary

treatment processes and to improve the quality further. The main objectives of tertiary

treatment are the removal of fine suspended solids, bacteria, dissolved inorganic

solids and final traces of organics. Schematic representation of wastewater treatment

is shown in Fig. 1.1 [38] .

Fig 1.1. Schematic representation of wastewater treatment [38].

Depending upon the required quality of the final effluent and the cost of

treatment that can be afforded in a given situation, the major methods for coloured

wastewater treatment can be divided into three classes:

• Biological treatment

• Chemical treatment

• Physical treatment

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1.6. Biological Treatments

Biological treatment processes are very useful and remove all types of

dissolved degradable substances. Biodegradation is the process by which organic

substances are broken down by other living organisms. Organic material can be

degraded aerobically with oxygen, or anaerobically, without oxygen. A term related to

biodegradation is biomineralisation, in which organic matter is converted into

minerals. White-rot fungi are able to degrade dyes using enzymes, such as lignin

peroxidases (LiP), manganese dependent peroxidases (MnP). Other enzymes used for

this purpose include H2O2-producing enzymes, such as, glucose-1-oxidase and

glucose-2-oxidase, along with lactase, and a phenoloxidase enzyme [39-41].

The ability of bacteria to decolorize the wastewater has been investigated by a

number of research groups under the anaerobic and aerobic condition. [42-45]. These

microbial systems have the drawback of requiring a fermentation process and are

therefore unable to cope with larger volumes of textile effluents. This process is time

taking, may require nutrients, very large aeration tanks, lagoons, land areas and many

toxic compounds are not removed.

Dead bacteria, yeast and fungi have also been used for the purpose of

decolorizing dye-containing effluents. Textile dyes vary greatly in their chemistry and

therefore their interactions with micro-organisms depend on the chemistry of a

particular dye and the specific chemistry of the microbial biomass [46]. The use of

biomass has its advantages, especially if the dye-containing effluent is very toxic.

Biomass adsorption is effective when conditions are not always favorable for the

growth and maintenance of the microbial population. Adsorption by biomass occurs

by ion exchange [47].

1.7. Chemical Treatment

1.7.1. Ozone Treatment

Ozone wastewater treatment is a thorough and effective oxidation process and

is a suitable disinfectant for the organic matter found in wastewater. Ozone is a very

good oxidizing agent due to its high instability (oxidation potential - 2.07) compared

to chlorine, another oxidizing agent (1.36) and H2O2 (1.78). The dosage applied to the

dye-containing effluent is dependent on the total colour and residual COD to be

removed with no residue or sludge formation [48]. After ozone treatment,

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General Introduction

chromophore groups in the dyes are generally organic compounds with conjugated

double bonds that can be broken down forming smaller molecules, resulting in

reduced colouration [49]. These smaller molecules may have increased carcinogenic

or toxic properties, and so ozonation may be used alongside a physical method to

prevent this. Decolouration occurs in a relatively short time.

Ozone for the treat wastewater has many benefits

• Kills bacteria effectively.

• Oxidizes substances such as iron and sulphur so that they can be filtered out of the

solution.

• There are no nasty odours or residues produced from the treatment.

• Ozone converts into oxygen quickly and leaves no trace once it has been used.

The disadvantages of using ozone as a treatment for wastewater are

• The treatment requires energy in the form of electricity, which is costly and

cannot work when the power is lost.

• The treatment cannot remove dissolved minerals and salts.

• Ozone treatment can sometimes produce by-products such as bromate that can

harm human health if not controlled.

• A major disadvantage of ozonation is its short half-life (20 min).

1.7.2. Photochemical Treatment

Photochemical treatment is degradation of a photodegradable molecule caused

by the absorption of photons, particularly those wavelengths found in sunlight, such

as infrared radiation, visible light and ultraviolet light. Various processes like

UV/H2O2, UV/Fenton’s reagent, UV/O3 etc are photochemical methods based on the

formation of free radicals due to UV irradiation. The UV-based methods in the

presence of a catalyst, e.g. a semiconductive material such as TiO2 and ZnO have also

shown to distinctly enhance colour removal [50, 51]. Thus, different combinations

such as ozone/TiO2, ozone/TiO2/H2O2 and TiO2/ H2O2 have been investigated, but

they are enormously influenced by the type of dye, dye concentration and pH [52].

Degradation is caused by the production of high concentrations of hydroxyl radicals.

The rate of dye removal is influenced by the intensity of the UV radiation, pH, dye

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structure and the dye bath composition [53]. There are some advantages of

photochemical treatment of dye-containing effluent i.e. no sludge is produced and

foul odours are greatly reduced. The main disadvantage of this method is production

of secondary pollutant.

1.7.3. Electrochemical Destruction

This is a relatively new technique, which was developed in the mid 1990s. It

has some significant advantages for use as an effective method for dye removal by

oxidation reactions using electricity [54]. There is little or no consumption of

chemicals and no sludge build up. The breakdown metabolites are generally not

hazardous leaving it safe for treated wastewaters to be released back into water ways.

It shows efficient and economical removal of dyes and a high efficiency for colour

removal and degradation of recalcitrant pollutants [55, 56]. Relatively high flow rates

cause a direct decrease in dye removal and the high cost of electricity is the main

disadvantage of this technology.

1.8. Physical Treatment

1.8.1. Coagulation/Flocculation

Coagulation/flocculation is a commonly used process in water and wastewater

treatment in which compounds such as ferric chloride or polymer are added to

wastewater in order to destabilize the colloidal materials which cause the small

particles to agglomerate into larger settleable flocs [57, 58]. The first step, coagulation

is the addition of a coagulant to the wastewater and mixing. This coagulant

destabilizes the colloidal particles that exist in the suspension, allowing particle

agglomeration. Flocculation is the physical process of bringing the destabilized

particles in contact to form larger flocs that can be more easily removed from the

solution. The main advantage of the conventional processes like coagulation and

flocculation is decolourization of the waste stream due to the removal of dye

molecules from the dye bath effluents and not due to a partial decomposition of dyes,

which can lead to an even more potentially harmful and toxic aromatic compound.

The major disadvantage of coagulation/flocculation processes is the production of

sludge [59, 60].

1.8.2. Filtration Method

Filtration methods such as ultrafiltration, nanofiltration and reverse osmosis

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General Introduction

have been used for water reuse and chemical recovery. These methods has the ability

to clarify, concentrate and most importantly, to separate dye continuously from

effluent [61, 62]. Membrane filtration has some special features unrivalled by other

methods i.e. they are resistance to, temperature, an adverse chemical environment and

microbial attack. The specific temperature and chemical composition of the

wastewater determine the type and porosity of the filter to be applied [63]. The main

drawbacks of membrane technology are the high investment costs, the potential

membrane fouling and the production of a concentrated dye bath which needs to be

treated [47]. The recovery of concentrates from membranes, e.g. recovery of the

sodium hydroxide used in the mercerizing step or sizing agents such as polyvinyl

alcohol (PVA), can attenuate the treatment costs [63]. Water reuse from dye bath

effluents has been successfully achieved by using reverse osmosis. However, a

coagulation and micro-filtration pre-treatment was necessary to avoid membrane

fouling [64]. A very good option would be to consider an anaerobic pre-treatment

followed by aerobic and membrane post-treatments, in order to recycle the water

1.8.3. Ion-Exchange

The use of ion exchangers for demineralization of water is well known. Ion

exchange has not been widely used for the treatment of dye-containing effluents,

mainly due to the opinion that ion exchangers cannot accommodate a wide range of

dyes [53, 65]. Wastewater is passed over the ion exchange resin until the available

exchange sites are saturated. Both cation and anion dyes can be removed from dye-

containing effluent this way. Advantages of this method include no loss of adsorbent

on regeneration, reclamation of solvent after use and the removal of soluble dyes.

Despite the simplicity of its operation, a major disadvantage is the high cost of ion-

exchanger, its regeneration process and its ineffectiveness for all kind of dyes

treatments [66].

1.8.4. Adsorption

Adsorption is one of the most efficient methods for the removal of colour,

odour, organic and inorganic pollutants from industrial effluents. Adsorption process

is considered better in water treatment because of the convenience, ease operation and

simplicity of design. Adsorption operations exploit the ability of certain solids

preferentially to concentrate specific substances from solution onto their surfaces.

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General Introduction

Conventional and Non-conventional adsorbents are used in this approach.

Activated carbon is the most widely used conventional adsorbent for this purpose

because of its extensive surface area, microporous structure, high adsorption capacity

and high degree of surface reactivity. However, its widespread use in wastewater

treatment is sometimes restricted due to its high cost and poor regeneration capacity

[67-69]. During the last decades, a lot of studies on dye adsorption by various non-

conventional adsorbents such as algae [70-74], fungi [75-78], industrial wastes [79-

83], clays [84-87], polymers [88-91], metal oxides [92-95], composites [96-99],

agricultural wastes [100-103] etc. have been undertaken in order to find out an

alternate to the costly conventional adsorbent. It has been found that various

adsorbents developed from different origins show little or poor sorption potential for

the removal of dyes as compared to commercial activated carbon. Therefore, the

search to develop efficient adsorbents is still going on.

Adsorption generally depends on the nature of adsorbate, adsorbent and

solution conditions. Structural properties of the adsorbate molecule or ion have an

influence on its adsorption. The solution conditions like pH, temperature, co-ions etc.

may alter the adsorption of adsorbate. The adsorption also depends on the adsorbent

characteristics such as size, shape, surface area, porosity, functional groups on the

surface, surface charge etc. Therefore characterization of the adsorbent is very

important to understand the mechanism of adsorption process. There are many

techniques which are generally used to characterize the adsorbent. Some of them are:

• The Brunauer-Emmett-Teller (BET) analysis – to determine the surface

area and pore structure of the adsorbent.

• Zeta potential and Zero point charge analysis – to determine the surface

charge on the adsorbent.

• Elemental analysis – to study the elemental composition such as C, N, H, O

etc of the adsorbent.

• Boehm titration analysis – to determine the concentration of oxygenated

surface groups on the adsorbent.

• Scanning electron microscopy (SEM) – to examine the surface morphology

of the adsorbent.

17

General Introduction

• Transmission electron microscopy (TEM) – to determine the shape and size

of the adsorbent.

• Fourier transform infrared spectroscopy (FTIR) analysis – to determine

the presence of functional groups on the adsorbent.

• X-ray diffraction (XRD) analysis – to determine the amorphous or

crystalline nature of the adsorbent.

• Thermal analysis – to determine the thermal stability of the adsorbent.

• Inductively coupled plasma-mass spectrometer (ICP-MS) - The analysis of

the impurities composition, namely, Al, Ca, Cu, Fe, Li, Mg, Mn, P, Ti, V, and

Zn in the adsorbent.

1.9. Theoretical Aspects of Adsorption

1.9.1. Adsorption

The term adsorption was first used by “Kayser” in 1881 and it refers strictly

to the existence of higher concentration of any particular component at the surface of

the liquid or solid phase than in the bulk. The adsorption may be of two types namely

physical and chemical. The physical adsorption occurs mainly due to weak forces like

ion-dipole, dipole-dipole, polarization or induced dipole, Van der Waals force etc.

The physical adsorption is reversible, temporary in character. It usually involves

lesser heat exchange. While chemical adsorption is due to formation of chemical

linkages between adsorbate and adsorbent. The chemical adsorption is non reversible

and is carried out at high temperature. It is characterized by a large heat change during

adsorption.

1.9.2. Mechanism of Adsorption

A solid surface in contact with a solution has the tendency to accumulate a

layer of solute molecules at the interface due to imbalance of surface forces. This

accumulation of molecules is a vectorial sum of the forces of the attraction and

repulsion between the solution and the adsorbent. Majorities of the solute ions or

molecules, accumulated at the interface are adsorbed onto the large surface area

within the pores of adsorbent and relatively a few are adsorbed on the out side surface

of the adsorbent. Adsorption from an aqueous solution is influenced largely by the

competition between the solute and solvent molecules for adsorption sites. The

18

General Introduction

tendency of a particular solute to get adsorbed is determined by the difference in the

adsorption potential between the solute and the solvent when the solute-solvent

affinity is large. The low adsorption capacity of polar adsorbents like zeolite for solute

in a polar solvent like water is an example of this phenomenon. In general, the lower

the affinity of adsorbent for the solvent, the higher will be adsorption capacity for

solutes. A polar (or non polar) adsorbent will preferentially adsorb the more polar (or

non polar) component of a non- polar (or polar) solute.

Many factors influence the rate of adsorption and extent to which a particular

solute can be adsorbed. The general effects of some more important factors like nature

of adsorbent and adsorbate, concentration, extent of agitation, pH, temperature,

contact time, etc., are summarized in Table 1.5.

Table 1.5. Effects of various operational parameters on adsorption.

Parametrs Effects

Agitation/relative velocity At low agitation film diffusion is rate controlling. At

high agitation pore diffusion is rate limiting.

Contact time Adsorption increases with increase in contact time

until equilibrium achieved.

Adsorbent characteristics Adsorption is a surface phenomenon. Adsorption rate

increases with decreasing particle size of adsorbent

and presence of surface charges.

Size and shape of adsorbate Adsorption usually decreases, as the size of the

molecules becomes large due to steric effect.

Concentration Rate of adsorption increases with increase in

concentration. Rate constant is directly proportional to

concentration.

pH Strong influence on adsorption due to change in ionic

concentrations of water and solutes.

Temperature Affects rate and capacity of adsorption.

1.9.3 Adsorption Isotherm

The relation of dye concentration in the bulk and the adsorbed amount at the

interface is a measure of the position of equilibrium in the adsorption process and can

generally be expressed by one or more of a series of isotherm models. The accuracy

19

General Introduction

of these isotherms to simulate experimental data varies and is greatly influenced by

the specific interactions between the adsorbate and adsorbent. The interpretation of

adsorption data through theoretical or empirical equations is essential for the

quantitative estimation of the adsorption capacity or amount of the adsorbent required

to remove the unit mass of pollutant from wastewater. Different isotherms that are

commonly used for the dyes adsorption process and the linear equations of the applied

models are

Langmuir model: (Ce/qe) = (Ce/qm) + (1/ qmb) (1)

Freundlich model: ln qe = ln KF + (1/n) ln Ce (2)

Temkin model: qe = B ln A + B ln Ce (3)

Dubinin-Radushkevich model: ln qe = ln qm – B1∑ 2 (4)

∑ = RT ln (1 + 1/Ce) (5)

E = 1 2.B1 (6)

where Ce is the equilibrium dye concentration in the solution (mg/l), b is the

Langmuir adsorption constant (l/mg) and qm is the theoretical maximum monolayer

adsorption capacity (mg/g). KF (mg/g) and n are Freundlich isotherm constants

indicating the capacity and intensity of the adsorption, respectively. A is equilibrium

binding constant (l/mg) and B is related to the heat of adsorption. B1 is the D–R

model constant (mol2 kJ−2) related to the mean free energy of adsorption per mole of

the adsorbate and ∑ is the polanyi potential. E is mean free energy of adsorption

(kJ/mol).

The Langmuir isotherm is generally more appropriate to a monolayer

adsorption where all binding sites are energetically equivalent and there is neither

interaction between adsorbed molecules nor the transmigration of adsorbate in the

plane of the surface [104,105]. Meanwhile, the Freundlich isotherm can be used for

non-ideal sorption that involves heterogeneous sorption [106,107].

Temkin isotherm [108] contains a factor explicitly taking into account of the

adsorbent–adsorbate interactions. By ignoring the extremely low and large value of

concentrations, the model assumes that heat of adsorption (as a function of

temperature) of all molecules in the layer would decrease linearly rather than

logarithmic with coverage [109]. As implied in the equation, its derivation is

20

General Introduction

characterized by a uniform distribution of binding energies (upto some maximum

binding energy [110].

Dubinin–Radushkevich isotherm [111] is generally applied to express the

adsorption mechanism with a Gaussian energy distribution onto a heterogeneous

surface [112]. The model has often successfully fitted well to high solute activities

and the intermediate range of concentrations data, but has unsatisfactory asymptotic

properties and does not predict the Henry’s law at low pressure [113]. The approach

was usually applied to distinguish the physical and chemical adsorption.

1.9.4. Adsorption Kinetics

The study of adsorption kinetics is important in wastewater treatment because

it provides valuable information on the reaction pathways and the mechanism of

sorption. In addition, predicting the solute uptake rate is of utmost importance in

designing an appropriate wastewater treatment plant because it can control the

residence time of solute at the solid-solution interface. Various kinetic models have

been proposed by different research groups where the adsorption has been treated as a

pseudo-first order [114], a pseudo-second order [115], Elovich [116] and intraparticle

diffusion [117]. The linear equations of kinetic model are

Pseudo-first order model: log (qe−qt) = log qe− (k1t/2.303) (7)

Pseudo-second order model: t/ qt = (1/ k2qe2) + (t/ qe) (8)

Elovich model: qt = (1/β) ln (αβ) + (1/β) ln t (9)

where qe and qt are the amount of adsorption at equilibrium and at time t in (mg/g). k1

(1/min) and k2 (min g/mg) are the rate constant for the pseudo-first and pseudo-

second order adsorption kinetics. α is the initial adsorption rate in (mg/g min) and β is

related to the extent of surface coverage and the activation energy for chemisorptions

in (g/mg).

Intra-particle diffusion model

The adsorption can be described by three consecutive steps:

• The transport of adsorbate from bulk solution to the outer surface of the

adsorbent by molecular diffusion, known as external or film diffusion.

• Internal diffusion, i.e. the transport of adsorbate from the particle surface into

21

General Introduction

interior sites.

• The adsorption of solute molecules from the active sites into the interior

surfaces of pores.

To determine rate limiting step (either film diffusion or intraparticle diffusion)

as well as the corresponding rate constants, Weber and Morris intra-particle diffusion

model is widely used.

qt = Kid t1/2 + C (10)

where, Kid is the intra-particle diffusion rate constant. The adsorption rates for intra-

particle diffusion (Kid) under different conditions were calculated from the slope of

the linear portion of the respective plot with units of mg/g min0.5.

1.9.5. Adsorption Thermodynamics

Thermodynamic parameters are evaluated to confirm the nature of the

adsorption process. The thermodynamic constants, free energy change, enthalpy

change and entropy change are calculated to evaluate the thermodynamic feasibility

and the spontaneous nature of the process. Thermodynamic parameters such as

standard free energy change (∆Gº), enthalpy change (∆Hº) and entropy change (∆Sº)

are calculated using the following equations:

Kc = Cac/ Ce (11)

where, Kc is the equilibrium constant. Cac and Ce are the equilibrium constants (mg/l)

of the dye on the adsorbent and in the solution respectively. ∆G0 was calculated from

the Gibb’s equation:

∆Gº = − RT ln Kc (12)

where, T is the temperature in Kelvin and R is gas constant (8.314 J/mol K). ΔHo and

ΔSo were obtained from the slope and intercept of Van’t Hoff plot of ln Kc versus 1/T.

ln Kc = (∆Sº/ R) − (∆Hº/ RT) (13)

On the basis of thermodynamic parameters following conclusion can be made

for the adsorption process. If:

22

General Introduction

ΔHo

ΔHo.

ΔGo

ΔGo

ΔSo

ΔSo

+ve

−ve

+ve

−ve

+ve

−ve

Endothermic process

Exothermic process

Non-spontaneous process

Spontaneous process

Increase in randomness at solid/solution interface

Decrease in randomness at solid/solution interface

1.9.6. Design of Large-Scale Batch Adsorption System

The experimental data and the models obtained for any adsorption study can

be used in designing a large scale batch system for dyes containing liquid. In order to

achieve a desirable removal of dyes on large scale for a given initial dye concentration

and a finite liquid volume, the amount of adsorbent to be used and the residence time

of the liquid in the batch need to be determined. For a given equilibrium

concentration, Ce, the amount of dye adsorbed onto the adsorbent at equilibrium, qe,

can be estimated from the Langmuir isotherm model. The required amount of

adsorbent, mD, to treat a volume of liquid, VD, can then be calculated as given below:

mD = (Ci-Ce) VD/ qe (14)

where Ci is the initial dye concentration in liquid. In practical, there would be a trade-

off between the maximized utilization of the adsorbent and the adsorption time since

the adsorption rate is very low when the equilibrium approaches. The adsorption

system would thus usually be designed at less than 100% saturation of the adsorbent,

such as 90–95% saturation [118,119].

The residence time (cycle time) of the liquid in the batch could then be

estimated using the pseudo-second order kinetics. The design amount of dye removal

qt, can be estimated as below

qt = (Ci−Ct)VD/mD (15)

where Ct is the specified (or design) dye concentration remaining in the liquid at the

end of the adsorption cycle.

23

General Introduction

1.10. Objectives

The overall objective of the thesis is preparation and characterization of

adsorbents for the removal of dyes from aqueous medium under wide range of

conditions. The specific objectives of the study are:

• To preparation and characterization of adsorbent.

• To determine the equilibrium time of dye adsorption.

• To determine the optimum concentration of the dye and solution pH at which

maximum adsorption occur.

• To study the effect of temperature and determine the values of the

thermodynamic parameters.

• To study the kinetics and diffusion rate of dye adsorption.

• To study the adsorption isotherm of dye adsorption.

1.11. Significance and Future Prospect of the Study

Adsorption is a fundamental process in the physicochemical treatment of

wastewaters, a treatment which can economically meet today's higher effluent

standards and water reuse requirements. This study is of general interest to

applications relating to solid/liquid interface and wastewater remediation. This study

shall give an idea about the mechanism of adsorption of different dyes on the

adsorbent surface, which also has the scope of enhancing the basic understanding of

the adsorption process under different conditions.

The effective design and application of the adsorption operation in

physicochemical treatment requires performance prediction, which in turn requires

thorough knowledge of the process itself and of the interplay of control and response

variables. Once the process is defined thermodynamically and kinetically and

conditions of specific operation are delineated, mathematical modeling techniques can

be employed for forward prediction of performance and adsorber design.

The findings from this research have many potential applications such as it can

be used to evaluate sorption performance and design the reactors for wastewater

purification at large scale. Furthermore, variations in the interaction force between

surfaces, due to sorption of charged species, can be used to develop sensors. Synthetic

24

General Introduction

organic/inorganic composites are potential materials for the wastewater purification.

Such kind of materials helps to generate nanosheet as well as nanofilter for the

purification of wastewater.

1.12. Organization of Thesis

The thesis has been organized in six chapters.

Chapter-1 is an introductory chapter which deals with water and dye pollution,

wastewater treatment technologies, various aspects of adsorption process and survey

of literature.

Chapter-2 explores the adsorption efficiency of bael shell carbon for the

removal of congo red dye. In this chapter efforts have been made to explain the

adsorption mechanism on the basis of different functional groups present on the

adsorbate and adsorbent surface.

Chapter-3 presents the adsorption of malachite green from aqueous solution

using treated ginger waste in batch and column process.

Chapter-4 deals with the kinetics and thermodynamics of brilliant green

adsorption onto carbon/ iron oxide nanocomposite.

In chapter-5, polyaniline/ iron oxide composite and amido black 10 have been

used as model adsorbent and adsorbate, respectively.

Chapter-6 describes the preparation and characterization of alumina reinforced

polystyrene for the removal of amaranth dye from aqueous solution.

1.13. Survey of Literature

Various kind of conventional and non-conventional adsorbents have been used

for the removal of dye. Recent literature survey on the adsorbent used for the removal

of dyes form aqueous solution and wastewater are summarized in Table 1.6.

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General Introduction

Table. 1.6. Survey of literature

Adsorbent Dyes Remark Reference

Unburned

carbon

Basic violet 3

Acid black 1

The adsorption of dye increased with

increasing temperature but decreased

with increasing particle size and

followed pseudo-second order kinetic

model.

[119]

Activated

carbons

Methylene blue

Crystal violet

Rhodamine B

The effect of acidic treatments of

activated carbons on dye adsorption was

investigated. For methylene blue, the

adsorption shows an order of AC > AC-

HCl > AC-HNO3 while for crystal

violet and rhodamine B, the adsorption

order is AC-HCl > AC > AC-HNO3.

[120]

Sawdust Methylene blue

Red basic 22

Sulphuric acid treatment increases the

sorption capacity of sawdust because of

opening of the lignocellulosic matrix’s

structure and the increasing of the BET

surface area and number of dye binding

sites.

[121]

Bentonite Reactive blue 19 The maximum monolayer adsorption

capacity of dodecyltrimethylammonium

modified bentonite was found to be

206.58 mg/ g.

[122]

Activated

palm ash

Acid green 25 The maximum adsorption capacities of

the activated palm ash for removal of

AG25 dye was determined with the

Langmuir equation and found to be

123.4, 156.3 and 181.8 mg/g at 30, 40,

and 50 °C, respectively.

[123]

Hectorite Reactive orange

122

Batch experiments were carried out for

the adsorption process in terms of effect

of pH, adsorbent dosage, contact time,

[124]

26

General Introduction

effect of salts and different dye

concentrations. Experimental results

show that acidic pH favours maximum

dye removal.

Aspergillus

fumigatus

beads

Reactive brilliant

red K-2BP

Reactive brilliant

blue KN-R by

Four materials sodium carboxymethyl-

cellulose, sodium alginate, polyvinyl

alcohol and chitosan were prepared as

supports for entrapping fungus

Aspergillus fumigatus. The adsorption

efficiencies of reactive brilliant red K-

2BP and reactive brilliant blue KN-R by

CTS immobilized beads were 89.1%

and 93.5% in 12 h respectively.

[125]

Sepiolite Reactive blue 221 The adsorption kinetics of CI reactive

blue 221, onto sepiolite was investigated

in aqueous solution in a batch system

with respect to stirring speed, contact

time, initial dye concentration, pH, and

temperature. The experimental data

fitted very well the pseudo-second order

kinetic model and also followed the

intra-particle diffusion model.

[126]

Jalshakti Methylene blue,

Safranine T,

Rhodamine B,

Crystal violet,

Malachite green,

Brilliant green,

Basic fuchsine

The adsorption of dyes reaches

equilibrium in 60–90 min and follows

the Langmuir and Freundlich isotherm

models. The particle diffusion study

showed that the initial boundary layer

diffusion was followed by intraparticle

diffusion model.

[127]

Carbon

nanotubes

Procion red MX-

5B

Langmuir isotherm and pseudo-second

order kinetic model fitted the

experimental results well.

[128]

Diatomace- Methylene blue The acid treated diatomite was used to [129]

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General Introduction

ous silica adsorb methylene blue from aqueous

solutions. The equilibrium data were

fitted to different adsorption isotherms

and the best fit was obtained using

Langmuir isotherm. The maximum

loading capacity was found 126.6 mg/g

at 30 0C and increases slightly as the

temperature increases.

Zeolite Reactive black 5

Reactive red 239

The adsorption capacity of Reactive Red

239 was found to be two times higher

than reactive blue 5 due to the

hydrophilicity of the dye molecules. The

calculated maximum adsorption

capacity increased with increasing initial

dye concentration, but there is no linear

relationship with pH and temperature.

[130]

Clay Methylene blue The removal of a basic dye, methylene

blue from aqueous solution on a natural

Moroccan clay mineral has been

investigated and maximum adsorption

capacity was found to be 135 mg/g.

[131]

Bituminous

coal

Methylene blue

Basic red

The adsorption mechanism was found to

follow pseudo-second order and

intraparticle-diffusion models, with

external mass transfer predominating in

the first 5 min of the experiment.

[132]

Activated

Carbon

Methylene blue

Acid blue 25

Acid red 151

Reactive red 23

Activated carbon derived from waste

wood pallets treated with phosphoric

acid was used for adsorption of dye. The

effect pH on the adsorption of different

classes of dyes signified the importance

of both electrostatic interaction and

chemical adsorption.

[133]

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General Introduction

Bentonite Methylene blue Batch adsorption tests for removal of

methylene blue dye from aqueous

solutions onto bentonite were

investigated using sulphuric acid and

microwave treated bentonite. The uptake

of dye by the microwave-treated

bentonite was the highest, followed by

the acid-treated and finally the untreated

bentonite.

[134]

Poly [N-vinyl

pyrrolidone/

2-methacryl-

oyloxye-thyl)

trimethyl-

ammonium

chloride]

Orange-II

Reactive orange-

13

Reactive orange-

14

Adsorption of dyes increases with

increase in solution concentration. The

binding ratio of the hydrogel/dye system

increases in the following order: OR-

II>RO-14>RO-13

[135]

Calix[4]arene

β-

cyclodextrin

Direct violet 51

Methyl orange

Titanium yellow

Oraing II

Physical adsorption, hydrogen bonding

and formation of an inclusion complex

were the main forces involved in the

sorption of dye onto adsorption surface.

[136]

Sawdust Disperse blue 56

Disperse red

The pH had a considerable influence on

adsorption and optimum pH for

adsorption of disperse dyes was found to

be in the range of 2–3. The data were

fitted well to pseudo-first order equation.

[137]

Chitosan/

organomont-

morillonite

Congo red A series of novel chitosan/organomont-

morillonite nanocomposites were

synthesized and used for the removal of

dye. The adsorption kinetics and

isotherms were in good agreement with

a pseudo-second order equation and the

Langmuir equation.

[138]

Wood fungus Congo red The biosorption equilibrium data obeyed [139]

29

General Introduction

the Langmuir and Temkin isotherms

well. Acidic pH was favorable for the

biosorption of the dye. Studies on the pH

effect and desorption show that

chemisorption seems to play a major

role in the biosorption process.

Peat Yellow CIBA

Dark blue CIBA

Navy CIBA WB

Red CIBA WB

The maximum adsorption capacities

were between 15 and 20 mg/ g. The

Langmuir extended model indicated that

there was competition for adsorption

sites and without interaction between

dyes.

[140]

Montmorillo-

nite

Eriochrome black

T

Orange II

Methyl orange

Thioflavin T

Methylene blue

Crystal violet

The adsorption property of montmorillo-

nite modified with a cetylpyridinium

chloride was investigated. In single-

solute sorption, the sorption affinity, as

represented by Freundlich sorption

coefficient and Langmuir sorption

capacity, was in the order of EBT > OR

>MO for anionic dyes and in the order

of TT > MB > CV for cationic dyes.

[141]

Chitin Black DN

Scarlet R

Brilliant orange

3R

The adsorption and desorption studies

were carried out at pH 3 and 11,

respectively. the highest efficiency of

desorption, nearly 100%, was obtained

for brilliant orange 3R and lower ones

for rcarlet R and black DN, at 89% and

90%, respectively.

[142]

Chitosan Acid green 25

Acid orange 10

Acid orange 12

Acid red 18

Acid red 73

The equilibrium data have been studied

using Langmuir, Freundlich and

Redlich-Peterson equations. The best

correlations were obtained using the

Langmuir isotherm suggesting the

[143]

30

General Introduction

mechanism involves one process step of

dyes complexing with the free amino

group.

Bentonite Quinalizarin The results showed the largest

adsorption capacity of the homoionic

bentonite; the saturation level was

reached, the high adsorption capacity

(79 meq/100 g), close to the cation

exchange capacity of the synthesized

bentonite (89 meq/100 g), indicates a

strong interaction between the dye

molecule and the adsorbent.

[144]

Sand Coomassie blue

Malachite green

Safranin orange

65-70% adsorption was reported under

the optimum sorption condition. The

adsorption kinetics followed the pseudo-

second order equation for all dyes.

[145]

Caulerpa

lentillifera

Astrazon blue

FGRL

Astrazon red

GTLN

Astrazon golden

yellow

The adsorption reached equilibrium

within the first hour and the kinetic data

fitted well with the pseudo-second order

kinetic model. Increasing salinity of the

system caused a decrease in adsorption

capacity possibly.

[146]

Luffa

cylindrica

fibers

Methylene blue The adsorption isotherms could be well

defined with Langmuir model instead of

Freundlich model. The thermodynamic

parameters of MB adsorption indicated

that the adsorption was exothermic and

spontaneous. The average MB

adsorption capacity was found out as 49

mg/g

[147]

Poly(N,N

dimethyl-

aminoethyl-

Apollofix red

Apollofix yellow

The adsorption capacity of

P(DMAEMA) hydrogel was found to

increase from 85 to 131 mg/g for AR

[148]

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General Introduction

methacrylate) dry gel and from 58 to 111 mg/g for AY

dry gel with decreasing pH of the dye

solutions.

Titanate

nanotubes

Basic green 5

Basic violet 10

Effects of the pore structure variation on

the basic dyes adsorption of TNT were

discussed. Moreover, the adsorption

mechanisms of basic dyes from aqueous

solution onto TNT were examined with

the aid of model analyses of the

adsorption equilibrium and kinetic data

of BG5 and BV10.

[149]

Alginate/

polyaspartate

hydrogels

Methylene blue,

Malachite green

Methyl orange

The ionic interaction between the dye

molecule and gel matrix appears to be

responsible for the efficient adsorption

of cationic dyes in this system. Type-S

adsorption isotherms were obtained,

which is characteristic of a weak solute–

solid interaction.

[150]

Polyaniline Orange G

Methylene blue

Rhodamine B

Alizarine cyanine

green

Coomassie

brilliant blue R-

250

Remazol brilliant

blue

Polyaniline emeraldine salt was

synthesized by chemical oxidation and

used for the adsorption of sulfonated

dyes from water. A mechanism was

proposed based on the chemical

interaction of PANI with the sulfonate

group of the dyes.

[151]

Activated

carbons

Acid blue 15 Activated carbons prepared from

sunflower seed hull have been used as

adsorbents for the removal of acid blue

15. The optimum conditions for AB-15

removal were found to be pH 3,

[152]

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General Introduction

adsorbent dosage 3 g/l and equilibrium

time 4 h at 30 0C.

Sludge Reactive red 2

Reactive red 141

The maximum monolayer adsorption

was found to be 53.48 mg/g and 78.74

mg/g, for RR2 and RR141, respectively.

The equilibrium adsorption capacity for

the dye RR2 increased with increase in

the packed column height from 15 to 30

cm in the proportion 1 : 1.7 with a fixed

flow rate of 12 ml/min, and for an

increase in the flow from 8 to 16 ml/

min.

[153]

Hydrogel-

clay nano-

composite

Safranine-T

Brilliant cresyl

blue

The equilibrium was established within

10 min and maximum adsorption was

found to be 484.2 and 494.2 mg/g for

the ST and BCB dyes, respectively.

[154]

Pleurotus

ostreatus

Methylene blue The adsorption isotherm of methylene

blue followed the Langmuir model and

the maximum adsorption capacity was

70 mg of dye per g of dry fungus at pH

11, 70 mg/l dye, and 0.1 g/l fungus

concentration, respectively. The

percentage of desorbed methylene blue

was 80% by 1M H2SO4.

[155]

Activated

carbon

Methylene blue Adsorption process was attained to the

equilibrium within 5 min. The adsorbed

amount MB dye on activated carbon

slightly changed with increasing pH,

and temperature, indicating an

endothermic process.

[156]

Carbon

nanotubes

Direct yellow 86

Direct red 224

The adsorption percentage of direct dyes

increased as CNTs dosage, NaCl

addition and temperature increased. The

[157]

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General Introduction

capacity of CNTs to adsorb DY86 and

DR224 was 56.2 and 61.3 mg/g.

Bottom ash

De-oiled

soya

Metanil yellow For both adsorbents, the adsorption

process has been found governing by

film diffusion, and saturation factors for

columns have been calculated as 99.15

and 99.38%, respectively.

[158]

Polyacrylam-

ide/nanoclay

Basic blue 12

Basic blue 9

Basic violet 1

The adsorption studies indicated that the

rates of dye uptake by the

nanocomposite hydrogels increased in

the following order: BB 9 > BB 12 >

BV 1. In the dye absorption studies, S-

type adsorption in the Giles

classification system was found for the

BB 12 and BV 1 dyes, whereas L-type

was observed for the BB 9 dye.

[159]

Perlite Congo red The dye adsorption equilibrium was

rapidly attained after 40 min of contact

time and followed pseduo-first order

kinetic.

[160]

Rice husk

ash

Methylene blue

Congo red

The maximum percentage removal of

MB was 99.939%, while 98.835%

removal was observed for CR. Batch

desorption studies revealed that 50%

acetone solution was optimum for CR,

while desorption of MB varied directly

with acetone concentration

[161]

Fly ash Acid blue 113

Tartrazine

Adsorption of dyes has been studied

from their single and binary solutions.

Modeled isotherm curves using isotherm

parameters of the Freundlich and

Dubinin- Radushkevich equations

adequately fit to equilibrium data.

[162]

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General Introduction

Equilibrium adsorption of AB in binary

solutions has been quite well predicted

by the extended Freundlich and the

Sheindorf-Rebuhn-Sheintuch models

Activated

carbon cloth

Basic blue 9

Basic red 2,

Acid blue 74

The pseudo-second order model for the

kinetics and the Freundlich isotherm

model for the equilibrium of the

adsorption were found to fit the

experimental data reasonably well.

[163]

Amberlite

IRA-900

Amberlite

IRA-910

Allura red

Sunset yellow

Adsorption decreased with increase in

solution pH and increased with increase

in temperature.

[164]

Euphorbia

macroclada

carbon

Acid yellow17

Acid orange 7

Thermally activated Euphorbia

macroclada carbon was used for the

removal of dyes by batch and

continuous packed bed adsorption

systems. The maximum adsorption

capacity of AY17 and AO7 onto

activated carbon was found to be 161.29

and 455 mg/g, respectively by Langmuir

isotherm at 55 ºC. Maximum desorption

was observed at pH 11 by NaOH.

[165]

Lemon peel Methyl orange

Congo red

The adsorption capacities of lemon peel

adsorbent for dyes were found 50.3 and

34.5 mg/g for MO and CR, respectively.

The adsorption data was well described

by the Langmuir model and pseudo-first

order kinetic model

[166]

MCM-41 Crystal violet The calcined and sulfated MCM-41 was

used for the removal of CV. Freundlich

and pseudo-second order rate models

ware appropriate model to explain the

[167]

35

General Introduction

adsorption isotherm and kinetics. The

thermodynamic studies suggested that

the adsorption is exothermic in nature.

Hydrilla

verticillata

Malachite green Response surface methodology was

used for designing. The optimum

conditions for maximum removal of

malachite green from an aqueous

solution of 75.52 mg/l were as follows:

adsorbent dose (11.14 g/L), pH (8.4),

temperature (48.4°C) and contact time

(194.5 min).

[168]

Organo-

attapulgite

Congo red The amount adsorbed of CR on the

organo-attapulgite increase with

increasing dye concentration,

temperature and by decreasing pH.

Kinetic and desorption studies both

suggest that chemisorption should be the

major mode of CR removal.

[169]

β-cyclo-

dextrin

Methylene blue β-cyclodextrin exhibited adsorption

capability toward methylene blue 105

mg/ g. carboxyl and ester groups were

mainly involved in the adsorption of

dye.

[170]

Activated

Carbon

Methylene blue The removal increased from 74.20 to

93.58% with decrease in concentration

of dye from 100 to 60 mg/l at 30 °C,

150 rpm, and pH 5.3. The removal

exhibited an increasing trend with

increasing temperature, exhibiting the

endothermic nature of adsorption.

[171]

Polyaniline Orange G

Methylene blue

Rhodamine B

P-toluenesulfonic acid (PTSA) and

camphorsulfonic acid (CSA) dopped

polyaniline was used for the removal of

[172]

36

General Introduction

Malachite green

Alizarine cyanine

green

Brilliant blue R

250

Remazol brilliant

blue R

dyes. The maximum dye

adsorption/removal by PANI clearly

depends on the nature of the dopant (the

order being CSA > PTSA > HCl.

Silica Acid orange 10

Acid orange 12

Monoamine modified silica particles

have been used for the removal of

dyes.The adsorption of AO 10 followed

pseudo-first order kinetics whereas AO

12 followed pseudo-second order.

Desorption of the loaded dyes was

carried out at pH 10 and found to be

10.4 and 91.6% for AO-12 and AO 10,

respectively.

[173]

Clinoptilolite Amido black 10B

Safranine T

Clinoptilolite has a limited adsorption

capacity for amido black 10B (0.0112

mg/g) and has a good adsorption

capacity for safranine T (0.05513 mg/g).

[174]

Magnetic/

cellulose/

activated

carbon

composite

Methyl orange

Methylene blue

The adsorbent was prepared by blending

Fe2O3 nanoparticles with cellulose and

activated carbon via an optimal

dropping technology The sorbent could

efficiently adsorb the organic dyes from

wastewater, and the used sorbents could

be recovered completely.

[175]

Activated

sepiolite

Remazol red B The optimum contact time and pH were

found to be 120 min., pH 2–3 and it was

found that the adsorption capacity of

acid activated sepiolite was higher than

that of thermal one.

[176]

Activated oil Reactive red 120 The Freundlich model and pseudo- [177]

37

General Introduction

palm ash second order kinetics agreed very well

with the experimental data. The

maximum monolayer adsorption was

found to be 376.41 mg/g at 50°C.

Trichoderma

harzianum

Rhodamine 6G

Erioglaucine

The maximum adsorption was found to

be at pH of 8 and 4 for the removal of

rhodamine 6G and erioglaucine

respectively. Adsorption of dyes onto

fungal biomass satisfied the Langmuir

and Freundlich adsorption isotherms.

[178]

Polyacrylami

de-bentonite

composite

Malachite green

Methylene blue

Crystal violet

Amine functionalized Polyacrylamide-

bentonite composite adsorbent behaved

like a cation exchanger and more than

99.0% removal of dyes was observed at

the pH range 5.0 to 8.0. Four adsorption

desorption cycles (using 0.1 M HNO3)

were performed without significant

decrease in adsorption capacity.

[179]

Stipa

tenacessima

L alfa fiber

Acid blue 25

Acid yellow 99

Reactive yellow

23

Acid blue 74

The sorption capacities were obtained as

follows: 541, 513, 395, and 223 mg/g,

respectively, for acid blue 25, acid

yellow 99, reactive yellow 23, and acid

blue 74. The percentage of desorbed dye

varied between 52% for acid blue 74,

70% for reactive yellow 23, 76% for

acid yellow 99 and 78% for acid blue

25.

[180]

zeolite Methylene blue The maximum adsorption capacities of

MB by the three zeolites calculated

using the Langmuir equation, ranged

from 23.70 to 50.51 mg/g. The

adsorption of MB by zeolite was

essentially due to electrostatic forces.

[181]

38

General Introduction

Regeneration of used zeolite was

achieved by thermal treatment.

Poly(MAA)-

starch

Safranine T,

Methylene blue,

Crystal violet

A series of poly(MAA)-cross linked

pregelled starch graft copolymer were

used for the removal of basic dyes.

Adsorption of dyes increased with

increase in starch grafting, contact time,

solution pH, agitation speed and

adsorbent dose.

[182]

Activated

carbon

Malachite green The kinetic sorption data fitted well to

the second-order kinetic model. It was

found that the Langmuir isotherm have

the high correlation coefficients

compared to the Freundlich

[183]

Fly ash Acid orange

Acid red BG

The adsorption equilibrium of ARBG

could reach in 1.5 h, faster than that of

AOII. The saturated adsorptive amount

of ARBG and AOII on the fly ash was

3.15 and 1.10 mg/g at 20 ºC.

[184]

Multiwalled

carbon

nanotubes

Carbon

nanofibers

Methylene blue

Orange II

The removals of OII and MB by

adsorption on MWCNT were maximum

at pH 3.0 and pH 7.0, respectively.

While for CNF, the optimum values of

pH were 9.0 and 5.0 for OII and MB,

respectively. Equilibrium data were well

described by the Langmuir isotherm.

[185]

Calcite Methylene blue

Safranine T

Competitive Adsorption of basic dyes

onto calcite in single and binary

component systems. Extended

Freundlich and Langmuir models fit to

MB–ST adsorption in binary solutions.

[186]

γ-Fe2O3 Acid red dye 27 The equilibrium was achieved in less than

4 minutes. The removal of AR27

[187]

39

General Introduction

decreased with the increase in solution

pH and temperature. The addition of

chloride and nitrate anions has no

remarkable influence on AR27 removal

efficiency. The adsorption process was

found to be spontaneous, exothermic and

physical in nature

Polymer/

bentonite

Disperse blue

SBL

Vat scarlet R

Reactive violet K-

3R

Acid dark blue

2G

The sorption property of

polyepicholorohy- drin-dimethylamine

and bentonite composite was investigated

for non-ionic dyes and anionic dyes. The

Langmuir model was the most suitable to

describe non-ionic dye adsorption, but for

anionic dyes the Freundlich model was

best.

[188]

Chitosan/zinc

oxide

Direct blue 78

Acid black 26

The equilibrium data of AB26 and DB78

adsorption followed with Langmuir and

Tempkin isotherms, respectively. In

addition, adsorption kinetics of both dyes

was found to conform to pseudo-second

order kinetics.

[189]

chitosan/

kaolin/

γ-Fe2O3

Methyl orange About 71.0 % of MO was adsorbed

within 180 min from 20 mg/l MO

solution at pH = 6.0 by 1.0 g/L adsorbent

dosage.

[190]

Bottom ash

De-oiled

soya

Crystal violet Pseudo-second order kinetics was found

to describe the adsorption of the dye.

Recovery of the dye was made by eluting

HCl solution through the exhausted

columns and almost 95% and 78% of the

dye was recovered from BA and DOS

columns, respectively.

[191]

Polyaniline Methylene blue The binding sites of the interactions [192]

40

General Introduction

nanotubes available in the NTs (amine and imine

nitrogens) and according to Langmuir

adsorption isotherm the majority of the

adsorption was due to one site (imine

nitrogens) which has a lone pair of

electrons that can increase interaction

with the cationic MB dye.

Activated

carbon cloth

Crystal violet

Basic blue 7

Basic blue 11

Both the rate and extent of adsorption and

electro sorption of dyes were found to

increase in the order of BB-7 < BB-11 <

CV. The main type of attractive at natural

pH was expected to be dispersion forces

between π-electrons of polycyclic

aromatic rings and of the ACC surface.

[193]

Sepiolite

Pansil

Methylene blue The Sips model agrees well with the

experimental data, and the pseudo-second

order kinetic model reproduces properly

the kinetic experimental data of the

system MB-sepiolite. The highest MB

adsorption was obtained at acid pH for

sepiolite and at basic pH for pansil.

[194]

Chitosan Remazol brilliant

blue RN

Basic blue

The adsorption behavior of two dyes of

different nature/class on several chitosan

derivatives was studied. The adsorbents

used were grafted with different

functional groups (carboxyl, amido,

sulfonate, N-vinylimidazole) to increase

their adsorption capacity and cross-linked

to improve their mechanical resistance.

The experimental equilibrium data were

successfully fitted to the Langmuir-

Freundlich isotherms.

[195]

MCM-41 Methylene blue The decrease in temperature or the [196]

41

General Introduction

increase in pH enhanced the adsorption of

dye onto MCM-41. The Freundlich and

Redlich-Peterson models expressed the

adsorption isotherm better than the

Langmuir model.

Turbinaria

conoides

Acid blue 9 The optimum conditions for maximum

removal of acid blue 9 from an aqueous

solution of 100 mg/l were found as

follows: temperature (33 ºC), adsorbent

dose (3 g/l), contact time (225 min),

adsorbent size (85 mesh) and agitation

speed (226 rpm).

[197]

Industry

waste

materials

Malachite green Pyrolysed industry waste materials: one

de-inking paper sludge (HP) and one

organic sludge from virgin pulp mill (RT)

were used as adsorbent for the removal of

MG. Maximum adsorption obtained by

Langmuir equation was higher for the

adsorbent from HP (982 mg/g) than RT

(435 mg/g).

[198]

Glycidyl

methacrylate-

g-poly

(ethylene

terephthalate)

fiber

Congo red The maximum adsorption capacity of the

reactive fiber for CR is 16.6 mg/g fiber.

The rates of adsorption were found to

conform to the pseudo-second order

kinetics with good correlation. It was

found that the adsorption isotherm of CR

fitted Freundlich model.

[199]

Mustard cake

Activated

carbon

Rhodamine-B The optimum contact time, pH and dose

was found to be 6 h, 2.3 and 5 g/L,

respectively. The on going adsorption

validates both the Langmuir and the

Freundlich adsorption isotherms.

[200]

Boron Acid red 183 The adsorption capacities of AR183 and [201]

42

General Introduction

industry

waste

Reactive blue 4 RB4 on waste in single dye solutions

were found to be 9.11 x 10−5 mol3/g and

7.33 x 10−5 mol3/g respectively. Because

of competitive adsorption, the adsorption

capacities in binary solutions were

reduced to 7.43 x 10−5 mol3/g and 6.37 3

x 10−5 mol3/g, respectively. In column

experiments, the adsorption of dyes from

single and binary solutions was fit well

by the Thomas model.

Graphite

oxide

Methylene blue

Malachite green

The amount of the dyes, methylene blue

and malachite green, adsorbed on the

graphite oxide was much higher than that

on graphite, and the adsorption capacity

based on the Langmuir isotherm is (351

and 248) mg/g, respectively, much higher

than activated carbon. The adsorption

mechanism was proposed as electrostatic

attraction.

[202]

Multiwalled

carbon

nanotube

Methylene blue

Methyl orange

In the absence of electrochemistry, the

MWNT filter completely removed all dye

from the influent solution until a near

monolayer of dye molecules adsorbed to

the MWNT filter surface.

[203]

Palm shell

powder

Chitosan

Reactive red 141

Reactive blue 21

pH 4 was suitable for the adsorption of

both reactive dyes onto chitosan and was

independent of pH in the ramge pH 2-9

using palm shell as the adsorbent. The

process of dye removal followed pseudo-

second order kinetics.

[204]

p-tert-butyl-

calix[8]arene

Reactive red 45

Reactive black 5

The sorption of selected azo dyes is

highly pH dependent and newly

immobilized material has potentially

[205]

43

General Introduction

more effective sorbent as compared to

pure silica as well as p-tert-butyl-

calix[8]arene. The optimized pH for the

effective removal of RB5 and RR45 dyes

was 9 and 3, respectively.

Magnetic/

triazine-

based

framework

Methyl orange A novel type of magnetic porous

carbonaceous polymeric material,

(covalent triazine-based framework), has

been synthesized by a facile microwave-

enhanced high-temperature ionothermal

method. The maximum adsorption

capacity of composites was found to be

291 mg/g at 0.889 mmol/g dye

concentration.

[206]

Chitosan

Direct red 23

Acid green 25

The isotherm data of direct red 23 and

acid green 25 in single and binary

systems followed Tempkin isotherm. In

addition adsorption kinetics of dyes was

studied in single and binary systems and

rate sorption was found to conform to

pseudo-second order kinetics

[207]

Magnetic

silica

Methylene blue

Acridine orange

The superparamagnetic mesoporous silica

microspheres was synthesized and

modified with anhydride functionalized

silane to graft carboxylic groups and

developed for removing basic dye. The

results showed that the as-prepared

adsorbent exhibits high adsorption

capacity, extremely rapid adsorption rate

and separation convenience for basic dye.

[208]

Carbon Acid blue 113

Reactive red 241

Two type of high surface area carbons

namely, a carbon xerogel and a templated

carbon was used a adsorbent for the

[209]

44

General Introduction

removal of dyes. Dispersive forces were

involved in the adsorption mechanism,

resulting from the interaction of the

delocalized π electrons in the carbon

basal planes, and the free electrons of the

aromatic rings and multiple bonds of the

dye molecules.

Bagasse Methylene blue The sorption performance of raw bagasse

(RB) and tartaric acid-modified bagasse

(TAMB) was investigated. Maximum

decolorization (78.16%) for RB was

achieved at 0.82 g of adsorbent dosage,

pH 9.4, 122 rpm of shaking speed, 44

min of contact time and 55°C. For

TAMB, maximum decolorization

(99.05%) was achieved at 0.78 g

adsorbent dosage, pH 9.4, shaking speed

of 120 rpm, 34 min contact time and

49°C.

[210]

Styrene–

divinyl-

benzene

copolymer

Anthranilic acid

p-aminobenzoic

acid

Bromaminic acid

Styrene–divinylbenzene copolymer

functionalized with a-hydroxyphosphonic

acid was used for the removal of three

dyes. The adsorption capacity and the

percentage of removal, increase with the

increasing of the initial dye

concentration.

[211]

Yeast sludge Reactive blue 49 The biosorption capacity was maximum

at initial pH 3 that the effect of

temperature on biosorption of reactive

blue 49 was only slight in relation to the

large biosorption capacity (25 º C, 361

mg/g) according as the biosorption

capacity decreased only 43 mg/g as the

[212]

45

General Introduction

temperature increased from 25 to 50 º C.

Activated

carbon

multiwalled

carbon

nanotubes

Methyl red The dye adsorption process followed

pseudo-second order model under

involvement of an intra-particle diffusion

mechanism. The adsorption process was

endothermic in nature.

[213]

Activated

carbon

Acid violet 17 Maximum colour removal was observed at

pH 2. The adsorption increased with the

increase in adsorbent dosage. As the

adsorption capacity increased with the

increase in temperature, the process was

concluded to be endothermic.

[214]

Hollow

chitosan

Methyl orange

Xylenol orange

The experiment shows that the adsorption

capacities of the two dye-hollow chitosan

microsphere systems are higher than those

stated in other literature using chitosan

particles. The difference in the degree of

adsorption may also be attributed to the size

and chemical structure of the dye molecule.

[215]

Na-alginate/

acrylamide

Basic violet 7 The maximum amount of dye adsorbed was

found to be 78.1.0 mg/g at pH 9.0. By

increasing ionic strength the adsorption of

the dye was decreased.

[216]

Activated

carbon

Malachite green The maximum removal of MG was

obtained at pH 6 as 99.86% for adsorbent

dose of 1 g/50 ml and 25 mg/l initial dye

concentration at room temperature.

[217]

Volcanic

ashes

Methylene blue Volcanic ashes (VAs) and Ti-modified

volcanic ashes (TVA) were investigated

adsorbents to remove methylene blue

(MB). TVA displayed higher and faster MB

adsorption than VA. MB adsorption data

described satisfactorily by the Langmuir

[218]

46

General Introduction

equation, whereas adsorption kinetic data

fit a pseudo-second order kinetics model.

Polyamido-

xime resins

Methyl violet Poly(acrylic acid–amidoxime) [P(AA–

AO)] and poly(maleic acid–amidoxime)

[P(MA–AO)] resins were used for the

removal of methyl violet. The equilibrium

data was described well by the Langmuir

isotherm model with maximum adsorption

capacities of 398.4 and 396.8 mg/g for

P(AA–AO) and P(MA–AO), respectively.

[219]

Waste beer

yeast

Methyl orange The adsorption capacities of Fe3+, Mg2+,

Ca2+ and Na+ modified biomass for methyl

orange were 90.8, 51.3, 23.0, and 20.6

mg/g, which were 30, 17, 8, and 7 times

that of the unmodified biomass,

respectively. Results showed that 96.9 and

80.0% of the methyl orange could be

desorbed from the Fe3+, and Mg2+, modified

biomass at pH 12.

[220]

47

General Introduction

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