9

CHAPTER 2

LITERATURE REVIEW

This Chapter will provide the detailed information and discussion

about the types of dyes and their harmful effects on environment and human

health. Furthermore the current technologies available for dye removal were

discussed with their advantages and disadvantages. Commercial adsorbents

and non conventional adsorbents in adsorption processes were described as

well.

2.1 GENERAL INFORMATION

Human are dependent upon ecosystem services such as air, water

and food for survival. Statistical figures reveal that more than 70 percent of

the surface of the Earth is covered with water. However, a large proportion of

this water is not suitable for human consumption. Water pollution is due to

the increase in population, growth of industries, urbanization, lack of

environmental awareness, use of chemical fertilizers instead of organic

manures and untreated effluent discharge from industries and municipalities.

Developing nations are likely to be affected more severely by the shortage of

water as well as water pollution, where already almost 80 percent of health

illness is directly or indirectly related with water quality.

Many industries are providing employment, increasing local

income and earning foreign exchange for the development of country.

However, these industries discharge their waste into the ecosystems without

10

treatment which adversely affecting livelihood and day to day life. The

industrial wastewater may have undesirable color, odour, taste, organic

matter, harmful chemicals, toxic metals, total dissolved solids, acids, alkalis,

virus, bacteria, worms and industrial waste products.

In India, the textile industries have great economic significance by

virtue of its contribution to overall industrial output and employment

generation when compared to other industries such as leather, paper, pulp and

food industries. But most of them lack effluent treatment plants. Instead, they

directly discharge untreated colored and toxic effluent into the nearby canals,

rivers, lakes, and streams. The discharge of industrial wastewater cause

serious environmental problems due to their chemical structure gives them a

persistent and recalcitrant nature.

The textile wastewater contains non-biodegradable organic and

inorganic materials such as dyes, metals, phosphates, aerosols, high COD and

BOD concentration, surfactants and phenols. Due to usage of dyes and

chemicals, effluents are dark in color, which increase the turbidity of the

water body. This affects the photosynthesis process and affects the habitat

(Joseph Egli 2007). Nowadays, the dyes mainly consists aromatic and

heterocyclic compounds, with color imparting groups and polar groups. The

structure is more complicated and stable, resulting in greater difficulty to

degrade the printing and dyeing wastewater (Ding et al 2010).

2.2 THE SOURCE OF COLOR IN DYES

Dye is an organic compound that imparts colour to substances such

as leather, plastic materials, food, hair, wax and textile fibre (Zollinger et al

1991) Dyes have been derived from natural plants in the ancient times.

Nowadays, almost all the dyes, even the naturally occurring dyes are

synthesized chemically. Dyes contain two groups; the chromophore and

11

auxochromes. The colour of the dye is provided by the presence of

chromophore groups. They are groups of atoms, which controls the color of

the dye and are usually the electron withdrawing groups. The most important

chromophores are –N=N–,–C=C–, –C=N–, –C=O–, –NO2, –NO groups.

The auxochrome is an electro donating sunstituent that can intensify the

colour of the chromophore and provides solubility and adherence of the dye

to the fibre. The most important auxochromes are –NH2, –NR2, –NHR, –

COOH, –SO3H, –OH and –OCH3 groups (Dos Santos 2005). Together, the

dye molecule is often described as chromogen (Wallace 2001).

2.3 CLASSIFICATION OF DYES

Dyes can be broadly classified in two ways either based on the

chemical composition (chemical classification) or application (colouristic

classification) (Rys and Zollinger 1972; Trotman 1990). Chemical

classification is probably the most appropriate classification and offers

advantages over colouristic classification. Both classifications are used by the

Colour index (1971) which lists all dyes and pigments used commercially for

large colouration purposes such as dyeing of textile fibres, pigment

colouration of plastics, paints, printing inks and the colouration of liquids

(solvents). Based on the usage or method of application, the dyes are

classified as given below (Agarwal 2006):

2.3.1 Acid Dyes

These are water soluble anionic dyes with different groups

substituted with acidic functional groups such as nitro-, carboxyl- and

sulphonic acid for the dye to become soluble. They dye animal fibres such as

silk, wool but not unmordanted vegetable fibres such as cotton and linen.

They are always used in an acidic solution. Some of the examples for acid

12

dyes are picric acid, martius yellow and orange II etc. Acid dyes are not

substantive to cellulosic fibres (Agarwal 2006).

2.3.2 Basic Dyes

These dyes are cationic dyes and water–soluble. They are applied

on paper, polyacrylonitrile, modified nylons, and modified polyesters. In

addition, they are used to apply with silk, wool, and tannin–mordant cotton

when brightness shade was more necessary than fastness to light and washing.

Mostly, the chemical classes are diazahemicyanine, triarylmethane, cyanine,

hemicyanine, thiazine, oxazine and acridine (Agarwal 2006).

2.3.3 Direct Dyes

These are water–soluble anionic dyes when dyed from aqueous

solution in the presence of electrolytes, which are substantive to have high

affinity for cellulose fibers. They are applied on cotton, cellulose, paper,

leather, and nylon. Most of the dyes in this class are polyazo compounds,

along with some stilbenes, phthalocyanines and oxazines (Agarwal 2006).

2.3.4 Mordant Dyes

These dyes have mordent dyeing property by good quality of the

presence certain groupings in the dye molecule which are capable to hold

metal residuals by formation of covalent and coordinate bonds involving a

chelate compound. The salts of aluminium, chromium, copper, cobalt, nickel,

iron, and tin are used as mordant that their metallic salts (Agarwal 2006).

2.3.5 Vat Dyes

These are insoluble in water that can apply mainly to cellulose fiber

by converting them to their leuco compounds by reduction and solubilization

13

with sodium hydrosulphite and sodium hydroxide solution that is called as

vatting process. The main chemical classes of vat dyes are anthraquinone and

indigoid.

2.3.6 Reactive Dyes

These dyes form a covalent chemical bond with fiber is ether or

ester linkage under suitable conditions. The major chemical classes of

reactive dyes are azo that including metallized azo, triphendioxazine,

phthalocyanine, formazan and anthraquinone. These chemical classes are

used for dyeing and printing of cotton, wool, etc (Agarwal 2006).

2.3.7 Disperse Dye

These are substantially water–insoluble nonionic dyes for

application to hydrophobic fibers from microfine aqueous dispersion. They

are used predominantly on polyester, polyamide, polyacrylonitrile,

polypropylene fibers and a lesser on nylon, cellulose acetate, and acrylic

fibers. Chemical classes of dyes mainly belong to azo and anthraquinonoid

(Agarwal 2006).

2.3.8 Sulfur Dyes

They are insoluble in water and are applied to cotton in the form of

sodium salts by the reduction with sodium sulphide as reducing agent under

alkaline conditions (Agarwal 2006).

2.4 TECHNOLOGIES AVAILABLE FOR DYE REMOVAL

The literature so far reviewed has shown a large number of

conventional dye removal methods involving physico chemical, chemical and

biological processes and some emerging techniques. Many of the

14

conventional methods used for the treating dyes wastewater have not been

widely applied on large scale industries due to high cost and sludge disposal

problems. At the present time, no single process capable of adequate

treatment, mainly due to the complex nature of the effluents (Crini 2006).

2.4.1 Biological Methods

Biological treatment is often the most economical alternative when

compared microbial biocatalysts to remove dyes in textile effluents offers

potential advantages over conventional processes due to minimal impact on

the environment and cost effectiveness (Hiroyuki et al 2002). These processes

do not require rigorous monitoring and complete mineralization with non

toxic end products .This process may be single phase aerobic or anaerobic or

a combination of the two (Stolz 2001). In these processes, bacteria, fungi and

algae are the microorganism groups that have been most widely studied for

their ability to treat dye wastewater. Fungi can be classified into two kinds as

living cells to biosorb and biodegrade dyes and dead cells (fungal biomass) to

adsorb dyes (Fu and Viraraghavan 2001). The major mechanism is

biodegradation for living cells because they can produce the lignin modifying

enzyme, laccase ,manganes peroxidase and lignin peroxidase to mineralize

synthetic lignin or dyes. For dead cells, the mechanism is biosorption which

involves physico – chemical interactions, such as adsorption, deposition and

ion exchange (wesenberg et al 2003).

2.4.1.1 Aerobic biodegradation

a ) Fungi

Most of the dyes such as Direct blue 1, Direct Yellow 12 and

Direct Red 28 have been removed by the well known White Rot fungi

(Phanaerochaete Chrysosporium) in aerobic conditions (Kaushik and Sharma

2011). The high capability of these fungi for biodegradation of dyes from

15

wastewater is due to the presence of the enzyme, lignin peroxidase. However,

Wong and Jain (1999) reported that the practical application of these fungi is

not possible for the degradation of dyes. This is due to the fact that the growth

of lignin peroxidase is inhibited by the presence of carbon and nitrogen (Perie

and Gold 1991).

Wong and Jain (1999) proposed the use of Trametes versicolor for

the removal of dyes from the textile effluents. Laccase is the enzyme

responsible for the degaradation of dyes and can be generated even in the

presence of carbon and nitrogen. Laccase does not require any secondary

metabolites to catalyse the oxidation. It was shown that T.versicolor

DSM11269 can decolorize the dyes Alizarin Red S and Direct Blue 71

without addition of any redox mediators (Theerachat et al 2012)

b) Bacteria

Several bacterial strains such as Aeromonas hydrophilia (Jiang and

Bishop 1994), Pseudomonas (Kulla et al 1983) and Pseudomonas luteola

(Hu 1994) have been successfully employed for the biodegradation of dyes. It

has been affirmed that most of the strains require additional carbon and

energy sources for the formation of micro anaerobic zones within an aerobic

system (Zissi et al 1997). It is also expected that these anaerobic zones might

have facilitated the anaerobic reduction of azo dyes (Costerton et al 1994).

The ability of a Kurthia sp. to decolorize Magenta, Crystal Violet, Malachite

Green, Pararosaniline and Brilliant Green has also been reported (Sani and

Banerjee 1999).

2.4.1.2 Anaerobic biodegradation

The anaerobic biodegradation of azo dyes was studied by many

researchers (Carliell et al 1998, Banat et al 1996). The exact mechanism of

16

anaerobic biodegradation is still not known. It has been suggested that the

biodegradation of azo dyes occurs by oxidation-reduction mechanism

(Carliell et al 1998). The major restriction of anaerobic azo dye reduction is

that the aromatic amines formed from reductive cleavage cannot be further

minimized (Rafii et al 1990, Chung et al 1992, Van der Zee 2002).Their

accumulation is a serious cause of concern since they are presumed

carcinogenic (e.g. naphthylamine or benzene derivatives) (Chung et al 1992).

A combined anaerobic and aerobic process is preferred for the complete

degradation of dyes. The intermediate products generated in the anaerobic

process can be degraded in the aerobic process (Forgacs et al 2004, Rai et al

2005).

2.4.1.3 Living / dead microbial biomass

Modak and Natarajan (1995) suggested that the dead bacteria, fungi

and yeast (microbial biomass) can be used for the removal of dyes when the

dyes are very toxic. But this process also have disadvantages as it requires

some degree of involvement of physical, chemical or physico- chemical

processes as pretreatment. The cost of operation is increased to cool the

textile effluents (Banat et al 1996). It was shown that Reactive Orange

107 dye was removed by the live and heat treated biomass of Alternaria

raphani, a fungus isolated from the dye industry effluent canals in the textile

industry of Tirupur, Tamilnadu (Ramalakshmi et al 2011).

2.4.2 Chemical Methods

Chemical methods include coagulation/ flocculation, electro kinetic

coagulation, oxidation and photo catalysis. In most chemical methods,

chemical reactions occur for the separation of contaminants from water or

neutralization of the harmful compounds present in the contaminants. In these

methods, oxidizing agents such as ozone, hydrogen peroxide and

17

permanganate are needed for the removal of dyes. But these oxidizing agents

produce harmful disinfection by-products.

2.4.2.1 Oxidation

Chemical oxidation is the traditional technique for the removal of

odour, colour and impurities from wastewater. Oxidising agents such as

ozone, chlorine, hypochloride and hydrogen peroxide attack the

chromophores which impart colour (Letterman 1999).

a) Ozone

Ozonation is the effective method for the removal of dyes from

textile effluents because it is very fast, no sludge or any toxic by products

obtained. It is carried out in two ways, either by direct application or indirect

application. In direct method, the molecular ozone is applied. In ozonation,

the ozone gas breaks the conjugate double bonds which are responsible for

the colour of the dyes (Srinivasan et al 2009). The effective decolorisation

requires the continuous supply of ozone which involves high costs (Xu and

lebrun 1999).

b) Sodium hypochlorite

The use of hypochlorite is avoided because of the presence of

chlorine. Chlorine gas in wastewater treatment is restricted nowadays as it

produces harmful by products such as trihalomethanes and haloacetic acid,

which are mutagenic and carcinogenic and pose a threat to human and aquatic

life (Ratnayaka et al 2009). Sodium hypochlorite reacts with dye molecules,

resulting in the formation of aromatic amines which are toxic and

carcinogenic (Banat et al 1996).

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c) Fenton’s Reagent

Hydrogen peroxide which is known as Fenton’s reagent and whose

decomposition gives water and radicals in presence of catalyst is now widely

used in wastewater treatment for its ecofriendly nature (Rearick et al 1997).

Direct Blue 160, Acid Blue 40 and Reactive Red 120 have been successfully

removed by H2O2 (Forgacs et al 2004).The main drawbacks of the method are

the significant addition of acid and alkali to reach the required pH, the

necessity to abate the residual iron concentration, too high for discharge in

final effluent, and the related high sludge production (Sheng et al 1997).

2.4.2.2 Photo catalysis

This method results in formation of carbon dioxide and water as a

result of decomposition of dye molecule using UV –light along with

hydrogen peroxide. During the course of reaction there is production of

hydroxyl free radicals as result of action of UV light on Hydrogen peroxide

which in turn causes oxidation of organic substrates under consideration. This

method is mainly used for the removal of organic contaminants. The rate of

photo degradation increases in the presence of photo catalysts such as TiO2,

ZnO, ZrO2, CdO , Fe2O3 and WO3. Liakou et al (1997) examined the photo

degradation of Acid Blue40, Direct Blue 87, Direct Blue 160 and Reactive

Red 120 The main advantage of photo catalysis is non toxicity, no foul smell

and no sludge formation. The drawback of this process is the use of expensive

catalysts and the poor efficiency for the treatment of industrial wastewaters.

No much research has been done on the end use of photo catalysts or reuse or

disposal methods (Kabra et al 2004).

2.4.2.3 Coagulation/ flocculation

Coagulation is the popular conventional physical method employed

for the treatment of wastewater. Coagulants such as alum and iron salts are

19

added to wastewater to increase the tendency of the smaller particles to

aggregate (Martinez – Hutile and Brillas 2009). The natural coagulants

extracted from plants such as guar gum and galactomannans proved to be

workable alternatives for conventional coagulants as they are biodegradable,

safe to human health and cost effective (Sanghi et al 2006). The cationic dyes

do not coagulate at all and the floc formed is generally of poor quality and

low settling ability (Raghavacharya 1997). The coagulation requires

additional processes such as sedimentation, flocculation and filtration

(Letterman 1999). But disposal of sludge is the major problem in this process.

2.4.3 Physical Methods

A conventional treatment process is not a single process; it

composed of many processes, with the output of one process becoming the

input of the next process. The first stage will usually be made up of physical

processes. The common physical methods are shown as followed.

2.4.3.1 Membrane separation processes

The membrane separation process such as reverse osmosis, ultra

filtration, nanofiltration and microfiltration is often used for treatment of

dyeing wastewater mainly based on membrane pressure. Membrane

separation process is a new separation technology, with high separation

efficiency, low energy consumption, easy operation, and no pollution and so

on. It uses the membrane to filter and separate dye stuffs and impurities from

wastewater. However, this technology is still not large-scale promoted

because it has the limitation of requiring special equipment, and having high

investment and the membrane fouling and so on (Ranganathan et al 2007).

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2.4.3.2 Adsorption

The dye removal from wastewater by adsorption techniques has

become popular day by day. It refers the accumulation of a substance at the

interface between two phases such as solid and liquid and solid and gas. The

substance that adsorbs on the surface is called adsorbate. The substance on

which it adsorbs is called adsorbent. Adsorption can either be physical or

chemical in nature, and frequently involves both (Cheremisinoff and Morresi

1978). Adsorption capacity depends on the physical and chemical

characteristics of both the adsorbent and adsorbate, concentration of the

adsorbate in liquid solution, experimental conditions such as temperature and

solution pH, and the amount of time the adsorbate is in contact with the

adsorbent (residence time).

2.5 COMMERCIAL ADSORBENTS

A number of materials have been investigated as adsorbents in

wastewater treatment. Some of the important ones include silica gel, activated

alumina, zeolites and activated carbon, etc.

2.5.1 Silica Gel

Silica gel is a non-toxic, inert and efficient support and is generated

by decreasing the pH value of the alkali silicate solution to less than ten.

Reactive sites of silica gel exist in large numbers, and therefore, the number

of immobilized organic molecules is high, which results in good sorption

capacity for metal ions (Rangsayatorn et al 2004). Various researchers

investigated the adsorption of basic dyes on silica, although the adsorption

capacities were high but the drawback was that silica is expensive adsorbent

(Gupta and Suhas 2009).

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2.5.2 Zeolites

Natural zeolites are abundant low cost resources, which are

crystalline hydrated aluminosilicates with a framework structure containing

pores occupied by water, alkali and alkaline earth cations. Han (2010)

recently used natural zeolite for the removal of Malachite Green from

aqueous solution in batch mode and reused it with the help of microwave

irradiation. Spent zeolite was treated by microwave irradiation for 10 min at

160 W, it was found that yield of regeneration was 85.8 percent and

adsorption capacity was 25.14 ± 0.59 mg/g at 308 K.

2.5.3 Activated Alumina

The activated alumina comprises a series of nonequilibrium forms

of partially hydroxylated alumina oxide, Al2O3. Activated alumina is a filter

media made by treating aluminium ore so that it becomes porous and highly

adsorptive. The main disadvantage of activated alumina is that the adsorption

efficiency is highest only at low pH and contaminants like arsenites must be

preoxidized to arsenates before adsorption. In addition, the use of other

treatment methods would be necessary to reduce levels of other contaminants

of health concern (Johnson et al 2005).

2.5.4 Activated Carbon

Activated carbon has undoubtedly been the most popular and

widely used adsorbent in treatment of wastewater throughout the world.

Wood products and low-grade coal have some original porosity and are easier

to activate than dense materials such as anthracite (Sun et al 1997). Therefore,

researchers are looking for low cost adsorbents for water pollution control,

where cost factors play a major role. Low cost adsorbents can be prepared

from a wide variety of raw materials which are abundant and cheap, having

22

high organic content and low inorganic content and these can be easily

activated. The preparation of low cost adsorbents from waste materials has

several advantages, mainly of economic and environmental nature.

2.6 LOW COST ADSORBENTS

Materials which are locally and abundantly available such as

agricultural wastes and industrial by-products can be utilized as low cost

adsorbents. Conversion of these materials into adsorbents for wastewater

treatment would help to reduce the cost of waste disposal and provide an

alternative to commercial activated carbon (Kurniawan et al 2006).

2.6.1 Agricultural Wastes

Agricultural waste materials are viable option for wastewater

treatment due due to ecofriendly and economic nature, unique chemical

composition, availability in abundance and renewable in nature. It is highly

anticipated that this work would abate the environmental nuisance if these

waste materials are used for removal of different contaminants from industrial

wastewater.

a) Adsorbents from rice and wheat wastes

Rice is one of the major crops grown throughout the world and

most important staple food for the human population. Rice husk, rice hull,

rice bran and rice husk are the by-products of rice industry which have been

used to prepare low cost adsorbents for removal of heavy metals and dyes

from wastewater. Rice husk has been used as an effective adsorbent for the

removal of dyes such as Reactive Orange16, Reactive Yellow 2 and Reactive

Blue 2 (Low and Lee 1997), Direct Blue 67 (Safa and bhatti 2011), Direct

Red 23 (Abdel wahab et al 2005) Malachite Green (Gong et al 2006) and

23

Acid yellow 36 (Malik 2003) from wastewater. Wheat is another important

staple food which produces some by-products such as wheat bran, wheat husk

etc. The adsorption of dyes, Reactive Blue 19, Reactive Red 195 and Reactive

Yellow 145 by wheat bran was examined by Fatma et al (2007).

b) Fruit stones and Nut Shells of agricultural by products

Many researchers have investigated Shells of various agricultural

products as adsorbent for the toxic pollutants from wastewater. Hard shell of

apricot stones was selected from agricultural solid wastes to prepare effective

and low cost adsorbents for gold separation from gold plating wastewater

(Soleimani and Kaghachi 2008).

More studies have been carried out on the feasibility of using

agricultural adsorbents such as, kapok fruit shell carbon and cashew nut shell

carbon (Kannan and Murugavel 2008), Sunflower seed shell (Suteu et al

2011), tamarind fruit shell (Vasu 2008), kapok hull (Shahabudeen 2011),

Cocoa Shell (Theivarasu et al 2011), Almond shell (Aygun et al 2003),

Groundnut shell (Malik et al 2007) and Hazel nut carbon (Yavuz and Aydin

2006) and Walnut Charcoal (Sumanjit et al 2008) for the removal of dyes

from wastewater.

c) Seeds of agricultural products

Fruit seeds have not received serious consideration as sorbents.

However, there are considerably high amounts of waste arising from human

consumption or food-processing plants. Seeds of many fruits have also been

investigated as the inexpensive adsorbents for the removal of dyes from

wastewater. The feasibility of papaya seeds for the removal of Methylene

Blue has been investigated (Hameed 2009).

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d) Stalks of agricultural wastes

Sun flower stalks as adsorbents were used for the removal of two

basic dyes (Methylene Blue and Basic Red 9) and two direct dyes (Congo

Red and Direct Blue 71) from aqueous solutions by Sun and Xu (1997).

Banana stalk has been effectively used as an adsorbent for the removal of

basic dye, Methylene Blue from aqueous solutions (Hameed et al 2008a,b).

Recently, cotton stalk has been explored as a bioadsorbent for the removal of

Methylene Blue from aqueous solutions in batch mode system (Ertas et al

2010).

e) Saw dust

Saw dust is the most abundantly available agro waste which has

been used for the removal of dyes in wastewater treatment. Neem sawdust

(Azadirachta indica) was used as an adsorbent for the removal of Malachite

Green dye from an aqueous solution (Khattri and Singh 2009). Saw dust ,

polymerized sawdust and sawdust carbon were employed for the removal of

Malachite Green, Acid Orange 7, Direct Blue 6 and Disperse Blue 26 (Jadhav

and Vanjara 2004). Ansari and Raofie (2006) dealt with a new application of

polyaniline synthesized chemically, coated on and used as an effective

adsorbent for removal of mercuric ion or other heavy metals from aqueous

solution.

f) Coconut waste

Coconut palms are grown in more than 80 countries of the world

with a total production of 49 billion nuts (Bhatnagar and Sillanpaa 2010).

Coconut waste such as coir pith, coconut bunch waste, coconut husk, male

flowers and coconut tree etc have been widely explored as adsorbents for the

various pollutants from wastewater. Adsorption of Disperse Red 343

25

(DR 343) and Direct Blue 86 (DB 86) from aqueous solution by coconut coir

activated carbon and Commercial activated carbon were examined (Khan and

Chaudhuri 2011). The adsorption studies of Rhodamine-B and Acid Violet by

coir pith carbon was carried out by varying the parameters such as agitation

time, dye concentration, adsorbent dose and pH. The adsorption was reported

to obey both Langmuir and Freundlich isotherm (Namashivayam et al 2001).

g) Peels of different agricultural waste

Peel, also known as skin, is the outer protective layer of fruit or

vegetable, currently gaining attention as adsorbent in wastewater treatment.

Peels of different fruits such as, orange, banana, jack fruit, mango, pine apple

and cassava etc have been used as inexpensive adsorbents for the dye removal

from wastewater. The effectiveness of orange peel in adsorbing Acid Violet

17 (Sivaraj et al 2001), Direct Blue 86 (Nemr et al 2009), Congo Red,

Procion Orange and Rhodamine B (Namasivayam et al 1997) was studied as

a function of agitation time, adsorbent dosage, initial dye concentration and

pH. Lemon peel was examined as an adsorbent for the removal of Malachite

Green (Kumar 2007).

h) Miscellaneous adsorbent

Different miscellaneous agricultural wastes such as sugarcane dust

for the removal of basic dyes (Ho et al 2005), bagasse, dry cow dung, pea

shells, used tea leaves, wheat straw for adsorption of acid dyes (Sumanjit et al

2007), Pandanus carbon for Malachite Green, Congo Red, Rhodamine – B

(Hema and Arivoli 2007) and Nirgudi plant powder for acid dyes (Ubale et al

2010) have also been investigated as low cost adsorbents besides the various

agricultural by products mentioned above.

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2.6.2 Industrial and Municipal Wastes

Widespread industrial activities generate huge amount of solid

waste materials as by-products. The industrial waste material is available

almost free of cost and causes disposal problem. If the solid wastes could be

used as low cost adsorbents, the volume of waste materials cab ne partly

reduced as well as the pollution of wastewater can be reduced at reasonable

cost. Thus, a number of industrial wastes with or without treatment have been

investigated as adsorbents for the removal of pollutants from wastewaters.

Some of them are discussed below.

a) Fly Ash

Fly ash is the major solid waste byproduct of thermal power plants

based on coal burning. Bhatnagar and Minocha (2006) reported that, fly ash

is not a very good adsorbent due to its low adsorption efficiency as compared

to activated carbon. Fly ash was utilized as a potential low-cost adsorbent for

the removal of Methylene Blue, Malachite Green and Rhodamine B from

synthetic textile wastewater. The removal of Methylene Blue, Malachite

Green and Rhodamine B varied from 0.228 to 0.814, 0.219 to 0.644 and

0.184 to 0.618 mg/g respectively when the initial dye concentration was

raised from 5 to 20 mg/L (Khan et al 2009).

b) Steel industry waste

The steel industry produces a number of wastes in large quantities

such as blast furnace slag, dust and sludge which have been investigated as

adsorbents. The utilization of treated basic oxygen furnace slag was

successfully carried out to remove three synthetic textile dyes such as

Reactive Blue 19, Reactive Black 5 and Reactive Red 120 from aqueous

27

solutions by Xue et al (2009). The maximum RB5, RB19 and RR120 uptake

capacities (500mg/L dye concentration) were 76, 60 and 55mg/g at pH 2.

c) Aluminium industry waste (red mud)

Red mud, a solid waste product of aluminium industry produced

during bauxite processing, was explored as adsorbent for wastewater

treatment (Lopez et al 1998). Fly ash and red mud have been employed as

adsorbents for the removal of Methylene Blue dye from aqueous solutions by

Wang et al (2005). Namasivayam and Arasi (1997) investigated the

adsorption potential of red mud for Congo Red dye removal from aqueous

solution with a removal capacity of 4. 05 mg/g.

d) Fertilizer industry waste

A number of low cost adsorbents from steel and fertilizer industries

wastes have been prepared and investigated for the removal of anionic dyes

such as Ethyl Orange, Metanil Yellow and Acid Blue 113 from aqueous

solutions. The results indicate that inorganic wastes, i.e. blast furnace dust,

sludge and slag from steel plants are not suitable for the removal of organic

materials, whereas a carbonaceous adsorbent prepared from carbon slurry of

fertilizer industry was found to adsorb 198, 211 and 219 mg/g of Ethyl

Orange, Metanil Yellow and Acid Blue 113, respectively (Jain et al 2003).

2.6.3 Natural Materials

a) Natural Clays

Natural Clay minerals such as Kaolinite , bentonite, sepiolite,

diatomite and Fuller’s earth have been utilized for dye removal. The sorption

capacity of basic dye on clay is higher than the acidic dyes because of the

ionic charges on the dyes and character of the clay. Due to high surface area,

28

bentonite is a good adsorbent for basic dye removal (Espantaleon et al 2003).

The adsorption to kaolinite was about 20 times greater than to alumina (Harris

et al 2001).

b) Siliceous Minerals

The natural siliceous minerals such as silica beads, alunite, perlite,

zeolite and dolomite are abundantly available which can be utilized as low

cost adsorbents in wastewater treatment. Phan et al (2000) showed that

modified silica beads have a better potential for the removal of acid dyes

compared to unmodified silica beads. Calcined alunite showed the adsorption

capacity of 212.8 mg/g of Acid Blue where as the commercial activated

carbon showed the adsorption capacity of 57.47 mg/g (Ozacar and Sengil

2002, 2003).

2.6.4 Biosorbents

a) Chitin and Chitosan

Chitin and Chitosans are biopolymers which can be commercially

extracted from crab, krill and crayfish. They can remove the dyes from

wastewaters even at low concentration. Wong et al (2004) and Wu et al

(2000) investigated the removal of acid dyes and reactive dyes on Chitosan.

However, the bead type chitosan gives higher capacity for dye than the flake

type. The adsorption capacity for Reactive Red 222 by chitosan flake was

293 mg/g and by chitosan beads was 1103 mg/g. This can be due to the fact

that beads possessed a greater surface area than the flakes. Chitosan based

biosorbents have also demonstrated for the removal of direct dyes.

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b) Peat

Peat is a porous and complex solid material with organic matter in

various stages of decomposition. Peat can effectively remove dyes from

solution due to its polar character. The removal performance of peat was

comparable with activated carbon for basic and acid dyes, where as the

performance was much better for disperse dyes. The maximum adsorption

capacities for Basic Violet 14, Basic Green 4 were 400 and 350 mg/g on

treated peat respectively (Sun and yang 2003).

c) Biomass

Biosorption is a promising potential alternative to conventional

processes for dye removal (Robinson et al 2001). A wide variety of

microorganism such as algae, yeasts, bacteria and fungi are capable of

decolorizing a wide range of dyes with high efficiency (Nigam et al 1996).

Fungi can be classified into two kinds ; living cells and dead cells. Fu and

Viraraghavan (2002) demonstrated that dead fungal biomass Aspergillus

niger is a promising biosorbent for dye removal. The performance of yeasts as

a low cost adsorbent has been demonstrated by Aksu et al (2003).

2.7 PROBLEM STATEMENT

Water treatment process selection is a complex task involving the

consideration of many factors which include, available space for the

construction of treatment facilities, reliability of process equipment, waste

disposal constraints, desired finished water quality and capital and operating

costs. Most of the technologies discussed above, have some drawbacks such

as high cost, disposal problem and not feasible at large scale. Among those

technologies, adsorption process is considered better because of convenience,

ease of operation and simplicity of design. Furthermore, this process can

30

remove different type of pollutants and thus it has a wider applicability in

wastewater treatment. Over the years, considerable amount of researches

have been done on the development of effective, low cost, and easily

available alternative adsorbents. However, none of the material studied so far

can fulfill all the requirements effectively. Therefore low cost and effective

adsorbents were prepared from the sawdust of Thevetia Peruviana and

applied in the removal of different types of dyes from aqueous solutions in

the present study.

2.8 AIM AND OBJECTIVES

The main aim of the present work is to study the adsorption of four

different dyes namely, Acid violet 49 (AV49), Basic Green 4 (BG4), Reactive

Orange 4 (RO4 ) and Direct Blue 71 (DB71) using three adsorbents Activated

Carbon (TPAC), Polyaniline Conducting Polymer (PAC) and Polypyrrole

Conducting Polymer (PPC) prepared from Thevetia Peruviana wood.

The Specific Objectives are as follows:

1. To prepare variety of activated carbon from Thevetia

Peruviana wood using different physical and chemical

activation methods. Among the activated carbon, one superior

carbon was selected for the adsorption studies based on their

physico chemical characteristics and SEM studies

2. To synthesize two conducting polymers namely Polyaniline

Conducting Polymer (PAC) and Polypyrrole conducting

Polymer (PPC) on the surface of the saw dust of Thevetia

Peruviana wood.

3. The selected activated carbon and conducting polymers were

used for the removal of Acid violet 49 (AV49), Basic Green 4

31

(BG4), Reactive Orange 4 (RO4) and Direct Blue 71 (DB71)

from its aqueous solutions in batch mode adsorption.

4. Various kinetics and Isotherm parameters were studied to

analyze the feasibility of the activated carbon and conducting

polymers for the removal dyes from wastewater.

5. Comparison between the adsorbents for their adsorption

capacity of the given dyes was also studied.

6. Application of these adsorbents for the treatment of the

various dyeing industrial effluents was also demonstrated to

identify the cheap and efficient low cost method for

industries.

7. The operating cost of wastewater treatment using these

adsorbents was compared with the commercial activated

carbon.