Polieletrolito Natural [5] LEEER

8/19/2019 Polieletrolito Natural [5] LEEER

1/15

Review

A review on chemical coagulation/occulation technologies for removal of colourfrom textile wastewaters

Akshaya Kumar Verma, Rajesh Roshan Dash, Puspendu Bhunia*

Department of Civil Engineering, School of Infrastructure, Indian Institute of Technology Bhubaneswar, Orissa 751 013, India

a r t i c l e i n f o

Article history:

Received 13 April 2011

Received in revised form

26 August 2011

Accepted 15 September 2011

Available online 5 October 2011

Keywords:

Dye

Decolourisation

Coagulation

Flocculation

Textile wastewater

a b s t r a c t

Textile industry is one of the most chemically intensive industries on the earth and the major polluter of

potable water. It generates huge quantities of complex chemical substances as a part of unused materials

including dyes in the form of wastewater during various stages of textile processing. The direct discharge

of this wastewater into environment affects its ecological status by causing various undesirable changes.

As environmental protection becomes a global concern, industries are nding novel solutions for

developing technologies that can diminish the environmental damage. However, colour removal from

textile wastewater by means of cheaper and environmental friendly technologies is still a major chal-

lenge. In this manuscript, several options of decolourisation of textile wastewater by chemical means

have been reviewed. Based on the present review, some novel pre-hydrolysed coagulants such as Pol-

yaluminium chloride (PACl), Polyaluminium ferric chloride (PAFCl), Polyferrous sulphate (PFS) and Pol-

yferric chloride (PFCl) have been found to be more effective and suggested for decolourisation of the

textile wastewater. Moreover, use of natural coagulants for textile wastewater treatment has also been

emphasised and encouraged as the viable alternative because of their eco-friendly nature.

2011 Elsevier Ltd. All rights reserved.

1. Introduction

Textile industries are one of the biggest users of water and

complex chemicals during textile processing at various processing

stages. The unused materials from the processes are discharged as

wastewater that is high in colour, biochemical oxygen demand

(BOD), chemical oxygen demand (COD), pH, temperature, turbidity

and toxic chemicals. The direct discharge of this wastewater into

the water bodies like lakes, rivers etc. pollutes the water and affects

the ora and fauna. Ef uent from textile industries contains

different types of dyes, which because of high molecular weight

and complex structures, shows very low biodegradability (Hsu and

Chiang, 1997; Pala and Tokat, 2002; Kim et al., 2004; Gao et al.,

2007). Also, the direct discharge of this industrial ef uent intosewage networks produces disturbances in biological treatment

processes. These ef uents produce high concentrations of inorganic

salts,acids andbases in biological reactorsleading to the increase of

treatment costs (Gholami et al., 2001; Babu et al., 2007). Moreover,

traditionally produced fabric industries generate residuals of

chemicals that evaporate into the air that we breathe or are

absorbed through our skin. Some of the chemicals such as heavy

metals either in free form in ef uents or adsorbed in the suspended

solids are either carcinogenic (Tamburlini et al., 2002; Bayramoglu

and Arica, 2007) or may cause harm to children even before birth,

while others may trigger allergic reactions in some people.

Industrial emissions and the waste ef uents generated from the

factories are associated with heavy disease burden (WHO, 2000,

2002) and this could be one of the reasons for short life expec-

tancy of 64 years in India compared to developed countries such as Japan, where life expectancy is 83 years (UNICEF, 2008). Although

the industrial sector only accounts for 3% of the annual water

withdrawals in India, its contribution to water pollution, particu-

larly in urban areas, is considerable. Wastewater generation from

this sector has been estimated as 55 106 m3 per day, of which

68.5 103 m3 are dumped directly into local rivers and streams

without prior treatment (MOWR, 2000). The developing countries

contribute the largest amount of textile wastewater. For an

example, developing countries of South Asia contributed around

35% textile wastewater out of total industrial wastewater generated

by South Asian countries in 2001 (World Bank, 2005). Out of seven

Abbreviations: BOD, biochemical oxygen demand; COD, chemical oxygen

demand; TDS, total dissolved solid; AOX , absorbable organic halides; SS, suspended

solid; TSS, total suspended solid; DS, dissolved solid; NTU, nephelometric turbidity

unit; DO, dissolved oxygen; UV, ultraviolet; nm, nanometer; AOP, advanced

oxidation process; PACl, polyaluminium chloride; PFCl, polyferric chloride; PFS,

polyferric sulphate; PAFCl, polyaluminium ferric chloride.

* Corresponding author. Tel.: þ91 674 2300 714; fax: þ91 674 2301 983.

E-mail addresses: [email protected] (A.K. Verma), [email protected]

(R.R. Dash), [email protected] (P. Bhunia).

Contents lists available at SciVerse ScienceDirect

Journal of Environmental Management

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c om / l o c a t e / j e n v m a n

0301-4797/$ e see front matter 2011 Elsevier Ltd. All rights reserved.

doi:10.1016/j.jenvman.2011.09.012

Journal of Environmental Management 93 (2012) 154e168

mailto:[email protected]:[email protected]:[email protected]://www.sciencedirect.com/science/journal/03014797http://www.elsevier.com/locate/jenvmanhttp://dx.doi.org/10.1016/j.jenvman.2011.09.012http://dx.doi.org/10.1016/j.jenvman.2011.09.012http://dx.doi.org/10.1016/j.jenvman.2011.09.012http://dx.doi.org/10.1016/j.jenvman.2011.09.012http://dx.doi.org/10.1016/j.jenvman.2011.09.012http://dx.doi.org/10.1016/j.jenvman.2011.09.012http://www.elsevier.com/locate/jenvmanhttp://www.sciencedirect.com/science/journal/03014797mailto:[email protected]:[email protected]:[email protected]


2/15

core countries of South Asia (Bangladesh, Bhutan, India, Maldives,

Nepal, Pakistan, and Sri Lanka), India is the major manufacturer of

textiles which constitute 83 composite mills and 2241 semi

composite processing units (COINDS, 2000). Hence, it can be said

that India may be the major contributor of textile wastewater in

South Asia. The textile industries in India are mainly located in

Mumbai, Surat, Ahmedabad, Coimbatore, Ludhiyana and Kanpur.

1.1. Characteristic and composition of textile wastewater

On the basis of waste and wastewater (or ef uent) generation,

the textile mills can be classied into two main groups namely dry

processing mills and wet processing mills (ISPCH, 1995). In the dry

processing mills, mainly solid waste is generated due to the rejects

of cotton. In the other group, desizing, scouring, bleaching, mer-

cerising, dyeing, printing, and nishing are the main processing

stages. The wastewater generated by textile industry includes

cleaning wastewater, process wastewater, noncontact cooling

wastewater, and storm water. The amount of water used varies

widely in this industry, depending on the specic processes oper-

ated at the mill, the equipment used, and the prevailing philosophy

of water use. The components of major pollutants involved at

various stages during wet processing of cotton-based textile

industry are shown in Fig. 1. On account of the involved complexity

of different processes at different stages, textile wastewater typi-

cally contains a complex mixture of chemicals. Apart from this,

large numbers of associated hazards have also been reported by the

various chemicals used in different stages of textile processing (Lee

et al., 2006; Jadhav et al., 2007; Shi et al., 2007; Anouzla et al.,

2009).

Wet processing operations (including preparation, dyeing, and

nishing) generate the majority of textile wastewater having very

high COD, BOD, TDS and very deep colour as shown in the Table 1.

Large numbers of chemical constituents such as alkali, acids,

bleaching chemicals, enzymes, starch, dyes, resins, solvents, waxes,

oils etc. are used in the various steps during textile processing andnally comes out in the ef uent after its consumption. Desizing, or

the process of removing size chemicals from textiles, is one of the

industry’s largest sources of wastewater pollutants (Bisschops and

Spanjers, 2003; Dos Santos et al., 2007). In this process, large

amount of size chemicals used in weaving processes are discarded.

Dyeing operation generates a large portion of the industry ’s total

wastewater. The primary source of wastewater in dyeing operations

is spent dye bath and wash water. Such wastewater typically

contains by-products, residual dyes, and auxiliary chemicals.

Additional pollutants include cleaning solvents, such as oxalic acid

(USPEA, 1997). Of the 700,000 tons of dyes produced annually

worldwide (Papic et al., 2004; Lee et al., 2006; Riera-Torres et al.,

2010), about 10e15 percent of the dyes are disposed off in ef uent

from dyeing operations (Snowden-Swan, 1995; Husain, 2006; Haiet al., 2007; Gupta and Suhas, 2009).

Dyes in wastewater may be chemically bound to fabric bers

(ATMI, 1997). Dyeing and rinsing processes for disperse dyeing

generate about 91e129 m3 of wastewater per ton of product

Constituents Process Wastewater characteristics

High pH, TDS

Oily fats, BOD (30% of

total), high pH, temp. (70-

80 C), dark colour

BOD (34-50% of total), high

COD, temp. (70-80 C)

Low alkalinity, low BOD, high

toxicity

Sizing

Desizing

Scouring

Bleaching

High BOD, high pH

suspended solidsMercerisation

High toxicity, BOD (6% oftotal), high dissolved solids,

high pH,

Dyeing

Finishing

High toxicity, high COD, high

BOD, high dissolved solids,

high pH, strong colour

Printing

Yarn waste, unused

starch-based sizes

Enzymes, starch,

waxes, ammonia

Disinfectants and

insecticides

residues, NaOH,

surfactants, soaps,

H2O2, AOX,

NaOCl, organics

NaOH

Colour, metals,

sulphide, salts,

acidity/alkalinity,

formaldehyde

Urea, solvents,

colour, metals

Chlorinated

compounds, resins,

spent solvents,

softeners, waxes,

acetate

High BOD, medium COD

Fig. 1. The component of major pollutants involved at various stages of a textile manufacturing industry (SEAM Project, 1999; Yusuff and Sonibare, 2004; Joseph, 2007; Paul, 2008;

Charoenlarp and Choyphan, 2009).

A.K. Verma et al. / Journal of Environmental Management 93 (2012) 154e168 155


3/15

(Snowden-Swan, 1995). Similar processes for reactive and directdyeing generate even more wastewater, about 113e151 m3 per ton

of product (Snowden-Swan,1995; Karcher et al., 2002; Riera-Torres

et al., 2010). This can be attributed by the fact that disperse dyes

show higher percentage of xation to the ber as compared to acid

and reactive dyes. Finishing processes typically generate waste-

water containing natural and synthetic polymers and a range of

other potentially toxic substances (Snowden-Swan, 1995). Textile

industries typically generate 200e350 m3 of wastewater per ton of nished product (Ranganathan et al., 2007; Gozálvez-Zafrilla et al.,

2008) resulting in an average pollution of 100 kg COD per ton of

fabric ( Jekel, 1997).

Raw textile wastewatercan be characterised by measurement of

BOD, COD, colour, suspended solids (SS), dissolved solids (DS) and

heavy metals etc. Typical characteristics of textile industry waste-water generally include a wide range of pH, COD, dissolved solids

and strong colour (El-Gohary and Tawk, 2009; Lau and Ismail,

2009; Ciabatti et al., 2010; Debik et al., 2010; Phalakornkule et al.,

2010), which may be comparable to moderate municipal waste-

water (Rott and Minke, 1999). However, the main challenge is to

eliminate the colour of wastewater, which is due to the remaining

dyes. The major characteristics of real textile wastewater have been

described in the Table 1. It has been observed from the Table 1, that

the textile wastewaters exhibit wide range of pH from 2 to 14, COD

from 50 mg/L to approximately 18,000 mg/L, TDS from 50 mg/L to

over 6000 mg/L and very strong colour. This wide variation in the

characteristics of textile wastewater is due to complexity of mate-

rials used in the textile industry during the processing of textiles.

1.2. Effects of textile wastewater

Textile wastewaters generated from different stages of textile

processing contains huge amount of pollutants that are very

harmful to the environment if released without proper treatment.

Harmful direct and indirect effects of textile wastewater have been

summarized in Fig. 2. The release of textile wastewater to the

environment causes aesthetic problems as the changed colour of

the water bodies such as lakes and rivers, after releasing of

wastewater from the industry, cannot be tolerated by the local

people. Also, the accumulation of colour hinders sunlight pene-

tration, disturbs the ecosystem of receiving water (Georgiou et al.,

2003; Merzouk et al., 2010). Ground water systems are also get

affected by these pollutants due to leaching through the soil

(Namasivayam and Sumithra,2005; Khaledet al., 2009). Apart fromthis, several dyes and their decomposition derivatives have proved

toxic to aquatic life (aquatic plants, microorganisms, sh and

mammals) (Georgiou et al., 2002; Kim et al., 2004; Ustun et al.,

2007). Additionally, fairly intensive studies has inferred that such

coloured allergens may undergo chemical and biological assimila-

tions, cause eutrophication, consume dissolved oxygen, prevent re-

oxygenation in receiving streams and have a tendency to sequester

metal ions accelerating genotoxicity and microtoxicity (Walshet al.,

1980; Foo and Hameed, 2010). In a wider sense, sporadic and

excessive exposure to coloured ef uents is susceptible to a broad

spectrum of immune suppression, respiratory, circulatory, central

nervous and neurobehavioral disorders presage as allergy, auto-

immune diseases, multiple myeloma, leukemia, vomiting, hyper-

ventilation, insomnia, profuse diarrhea, salivation, cyanosis, jaundice, quadriplegia, tissue necrosis, eye (or skin) infections,

irritation to even lung edema (Anliker, 1986; Foo and Hameed,

2010).

1.3. Present practices for treatment of textile wastewater

The available literature shows a large number of well estab-

lished conventional decolourisation methods involving physico-

chemical, chemical and biological processes, as well as some of

new emerging techniques like sonochemical or advanced oxidation

processes. However, there is no single economically and technically

viable method to solve this problem and usually two or three

methods have to be combined in order to achieve adequate level of

colour removal (Kang and Chen, 1997; Robinson et al., 2001).Researches on chemical coagulation/occulation, is observed as

one of the most practised technology. Regardless of the generation

of considerable amount of sludge, it is still used in developed and in

developing countries. Because the mechanism of coagulant applied

to decolourise wastewater is still not absolutely clear, colour

removal by coagulation is found in some cases very effective, in

some cases however, has been failed completely.

Hence, the objectives of this review are the analysis of various

chemical technologies developed for decolourisation of textile

wastewater, giving more stress upon chemical coagulation/occu-

lation technology, short description and critical appraisal of

decolourisation methods, comparison of their relative advantages

and disadvantages and propose for the effective and cheaper

alternatives.

Table 1

Major characteristics of real textile wastewater studied by various researchers.

pH COD (mg/L) BOD5 (mg/L) TSS (mg/L) TDS (mg/L) Colour Turbidity (NTU) References

8.8e9.4 595 131 379 110 276 76 e e e El-Gohary and Tawk, 2009

11.2 2276 660a e 47.9 e e Golob et al., 2005

5e10 1100e4600 110e180 e 50 1450e1475(ADMI) e Dos Santos et al., 2007

6.5e8.5 550e1000 e 100e400 e 7.50e25.50b 15e200 Ciabatti et al., 2010

2.7 7000 e 440 930 2140 Al-Malack et al., 1999

13.56 2968 e e e

3586 (C.U) 120 Joo et al., 200712e14 1500e2000 e e e Dark blue e Gozalvez-Zafrilla et al., 2008

10 1150 170 150 e 1.24436nm e Selcuk, 2005

9 750 160 e e e e Schrank et al., 2007

2e10 50e5000 200e300 50e500 e >300 (C. U) e Lau and Ismail, 2009

8.32e9.50 278e736 137 85e354 1715e6106 e e Phalakornkule et al., 2010

8.7 0.2 17900 100 5500 100 23900 50 1200 50 e e Rodrıguez et al., 2008

9.30 3900 e e e e 240 Paschoal et al., 2009

7.8 810 50.4 188 15.2 64 8.5 e 0.15669nm e Haroun and Idris, 2009

13 1 2300 400 e 300 100 e e e Debik et al., 2010

6.95 3422 1112 e e 5700 Bayramoglu et al., 2004

7.86 340 210 300 e >200 (Pt-Co) 130 Merzouk, 2010

7.5 0.3 131 18 e 75 13 1885 80 e e Ustun et al., 2007

a BOD7 and ef uent is from reactive dye bath.b Integral of the absorbance curve in the whole visible range (400e800 nm), ADMI : American dye manufacturer institute, C.U: Colour Unit.

A.K. Verma et al. / Journal of Environmental Management 93 (2012) 154e168156


4/15

2. Chemical composition and structure of colour causing dyes

in textile processing

A dye is used to impart colour to a material, of which it becomes

an integral part. An aromatic ringassociatedwith a side chain usually

required for resonance and thus to impart colour. Characterisation of

dyes is based on their chemical structure and application. They are

composed of the atoms responsible for the dye colour called chro-mophores as well as an electron withdrawing or donating substit-

uent that causes or intensies the colour of chromophores, called

auxochrome (Christie, 2001). Usual chromophores are eC]Ce(ethenyl), eC]O (carbonyl), eC]Ne (imino), eCH]S (thio-

carbonyl), eN]Ne (azo), eN]O (nitroso), eNO2 (nitro) and usual

auxochromes are eNH2 (amino), eCOOH (carboxylic), eSO3H (sul-

phonyl) and eOH (hydroxyl) (Van der Zee, 2002). The intensity of

colour depends upon the number of such groups. Compounds of

benzene containing chromophore radicals are called chromogens.

Such compounds, though coloured, are not dyes, since they do not

have the af nity or the ability to unite with tissue. To be a dye,

a compound must containnot only the chromophore groups,but also

the additional group(s) calledAuxochrome(s).These auxiliary groups

areresponsible for imparting the property of electrolyticdissociation

i.e.,the separation of the dye molecule into itscomponents or atoms

andto form saltswitheitheracidor alkali. They can alsobelong tothe

classesof reactive, acid, basic, direct,mordant, disperse,pigment, vat,

anionic, sulphur and disperse dye (Welham, 2000). Anthraquinone

dyes possesswide range of colours in the whole visiblespectrum and

constitute the second most important class of textile dyes after azo

dyes, which are used to give blue, green and violet colours ( Christie,

2001; Fontenot et al., 2003). The characteristics of different dyes thatare used widely in the textile industry have been summarised in

Table 2. It has been observed from the Table 2 that reactive dyes are

widely used to colour the cotton which contribute as half of the

worldwide textile-ber market. The reactive dyes that are used for

cotton, show poorest rate of xation due to which textile ef uent

possesses strong colour. The chemical structure of different azo dye,

vatdye andanthraquinonedye molecules comprisingof auxochrome

and chromophore has been illustrated in Fig. 3.

3. Physico-chemical methods for removal of colour from

textile wastewaters

Plenty of Physico-chemical methods in the form of pretreat-

ment, post treatment or main treatment have been investigated by

Fig. 2. Schematic representation of the effect of textile wastewater into the environment.



5/15

various researchers throughout the World. A brief discussion on

these methods along with a comprehensive discussion particularly,

on the chemical coagulation and occulation technology for colour

removal has been presented in this section.

One of the most commonly known methods is the ltration

technology. Filtration methods such as ultraltration, nano-

ltration and reverse osmosis have been used for water reuse and

the chemical recovery (Marcucci et al., 2001; Fersi and Dhahbi,

2008). In the textile industry, these ltration methods can be

used for both ltering and recycling of not only pigment rich

wastewaters, but also mercerising and bleaching wastewaters. The

specic temperature and chemical composition of the wastewaters

determines the type and porosity of the lter to be applied. Further,

the utilisation of membrane technology for dye removal fromtextile wastewater is very effective as reported by various

researchers (Ledakowicz et al., 2001; Ahmad et al., 2002). However,

the main drawbacks of membrane technology are the high cost,

frequent membrane fouling, requirement of different pretreat-

ments depending upon the type of inuent wastewaters, and

production of concentrated dyebath which further needs proper

treatment before its safe disposal to the environment (Robinson

et al., 2001; Akbari et al., 2006). For membrane ltration, proper

pretreatment units for removing SS of the wastewaters are almost

mandatory to increase the life time of the membranes. These make

the process more expensive and thereby limit the application of

this expensive technology for wastewater treatment.

Another most popular method is adsorption technology. Adsorp-

tion methodfor colour removal is based on the af nity of various dyesforadsorbents. It isinuenced by physicaland chemicalfactorssuchas

dyeeadsorbent interactions, surface area of adsorbent, particle size,

temperature, pH and contact time (Anjaneyulu et al., 2005; Patel and

Vashi, 2010). Themain criteria forselection of adsorbents are based on

the characteristics like high af nity, capacity of target compound and

possibility of adsorbent regeneration (Karcher et al., 2002). Activated

carbonis most commonly used adsorbentand canbe very effective for

many dyes (Walker and Weatherly, 1997; Pala and Tokat, 2002).

However, ef ciency is directly dependent upon the type of carbon

material used and wastewater characteristics (Robinson et al., 2001).

The limitations of this technology are the eco-friendly disposal of

spent adsorbents, excessive maintenance costs, and pretreatment of

wastewater to reduce the SS under acceptable range before it is fed

into the adsorption column. Because of these reasons,

eld scale

application of adsorption technology is limited not only for colour

removal of textile wastewaters but also for other water and waste-

water treatment.

Chemical methods mainly involve use of oxidising agents such

as ozone (O3), hydrogen peroxide (H2O2) and permanganate

(MnO4) to change the chemical composition of compound or group

of compounds, e.g. dyes (Metcalf and Eddy, 2003). Among these

oxidants, ozone is widely used because of its high reactivity with

dyes and good removal ef ciencies (Alaton et al., 2002). However, it

is also been reported that ozone is not ef cient in decolourising

nonsoluble disperse and vat dyes which react slowly and take

longer reaction time (Marmagne and Coste, 1996; Rajeswari, 2000).

The decoulorisation ef ciency also depends upon the pH. As the pH

decreases, ozonation of hydrolysed dyes (Reactive Yellow 84)decreases (Rein, 2001; Konsowa, 2003). It has also been reported

that the O3/UV as the more effective method for decolourising of

dyes compared to oxidation by UV or ozonation alone. However,

Perkowski and Kos, (2003) have reported no signicant differences

between ozonation and O3/UV in terms of colour removal. This may

be due to the fact that production of hydroxyl radical (HO) during

photodecomposition of ozone may improve the degradation of

organics. However, most of the UV light gets absorbed by the dyes

and hence very small amount of hydroxyl free radical can be

produced to decompose the dyes. Therefore, approximately same

colour removal ef ciencies using O3 and O3/UV could be expected.

In H2O2/UV process, HO radicals are formed when water con-

taining H2O2 is exposed to UV light, normally in the range of

200e

280 nm (Metcalf and Eddy, 2003). The H2O2 photolysis occursas per the reaction shown in Equation (1).

H2O2 þ UV ðl ¼ 200 280 nmÞ/HO$ þ HO$ (1)

This process is most widely used in Advanced Oxidation Process

(AOP) technology for the decomposition of chromophores present

in the dyes (Ferroro, 2000; Kurbus et al., 2002) and consequently

relies complete decolourisation. Fenton reaction is also an example

of AOP in which hydrogen peroxide is added in an acid solution (pH

2e3) containing Fe2þ ions (Equation (2)).

Fe2þ þH2O2/Fe3þ þ HO$ þ HO (2)

As compare to ozonation, this method is relatively cheap and

also presents high COD reduction and decolourisation ef

ciencies

Table 2

Characterisation of different class of dyes mainly used in textile industry and its method of application ( Easton, 1995; Akbari et al., 2002; Hees et al., 2002; Lau and Ismail,

2009).

Class Characteristics Substrate (bre) Dye-bre interaction Method of application

Acid Anionic, water soluble Nylon, wool, silk Electrostatic, Hydrogen bonding Applied from neutral to acidic dy ebaths

Basic Cationic, water soluble Modied n yl on, polyester Electrostatic attra ction App li ed from ac idi c d yebaths

Direct Anionic, water soluble Cot ton, rayo n, leather, nylon Inte rmolecular forces Applied from neutral or slightly

alkaline baths containing

additional electrolytesDisperse Very low water solubility Polyester, poly-amide, acetate,

plastic, acrylic

Hydrophobic- Solid state

mechanism

Fine aqueous dispersions often

applied by high temperature

pressure or lower temperature

carrier methods

Reactive Anionic, water soluble Cotton, nylon, silk, wool Covalent bonding Reactive site on dye reacts with

functional group on bre to bind

dye covalently under inuence of

heat and pH(alkaline)

Sulfur Colloidal, insoluble Cotton, rayon Covalent bonding Aromatic substrate vatted with s

odium sulde and re-oxidised to

insoluble sulfur-containing

products on bre

Vat Colloidal, insoluble Cotton, rayon Impregnation and oxidation Water insoluble dyes solubilised

by reducing with sodium hydrosulte,

then exhausted on bre and re-oxidised



6/15

(Van der Zee, 2002). The main drawback is high sludge generation

due to the occulation of reagents and dye molecules (Robinson

et al., 2001; Azbar et al., 2004). Most of the AOP for textile waste-

waters are highlyexpensive and its effectiveness varieswidely with

the type of constituents present in the textile wastewaters. Also,

from the several reports it is observed that the in some cases, at

certain conditions, these technologies give very attractive results,

however, in some other cases, their application has been reported

not worthy considering the cost and complexity involved in these

technologies.

Chemical coagulation and occulation in wastewater treatment

involves the addition of chemicals to alter the physical state of

dissolved and suspended solids and facilitate their removal bysedimentation. In some cases the alteration is slight, and removal is

affected by entrapment within a voluminous coagulate consisting

mostly the coagulant itself. Another result of chemical addition is

a net increase in the dissolved constituents in the wastewater.

Coagulation is used for removal of the waste materials in sus-

pended or colloidal form that do not settle out on standing or may

settle by taking a very long time. In water treatment, coagulation as

pretreatment is regarded as the most successful pretreatment

(Huang et al., 2009; Leiknes, 2009).

Coagulation of dye-containing wastewater has been used for

many years as main treatment or pretreatment due to its low

capital cost (Anjaneyulu et al., 2005; Golob et al., 2005). However,

the major limitation of this process is the generation of sludge and

ineffective decolourisation of some soluble dyes (Anjaneyulu

et al., 2005; Hai et al., 2007). Further, the sludge production can

be minimised if only a small volume of highly coloured ef uent

treated directly after the dyeing bath (Golob et al., 2005). The

reasons could be the non-availability of other chemical additives

except hydrolysing and xing agents in the ef uent coming from

dyeing bath. The chemical additives that are normally present in

the textile wastewaters provide hindrance to the colour removal.

If interfering chemical additives are absent in the textile waste-

water except colour causing dyes, then less coagulant dosage

might be required which in turns will reduce the sludge

production.

On account of this, coagulation of water soluble dyes is

challenging due to their high solubility. Further, due to devel-opment of synthesis technology, large number of innovative

dyes with complex structures have been synthesised and still in

process of synthesis, which provides dif culties for the selection

of appropriate coagulant (Yu et al., 2002). In general colour

removal decreases with increase in dye concentration and dye

solubility (Bouyakoub et al., 2009; Zahrim et al., 2010). There-

fore, re-evaluation of optimum conditions for coagulation of

different types of dyes is necessary. Moreover, the effectiveness

of the coagulation can be improved by appropriate selection of

coagulant, occulant aids, optimization of process parameters

such as pH, dosage of coagulant/occulant aids, mixing time,

settling time, etc. The relative advantages and disadvantages of

different physico-chemical methods have been summarised

in Table 3.

Fig. 3. Structure of various azo dyes showing chromophore and auxochrome (Van der Zee, 2002; Yang and McGarrahan, 2005; Dos Santos et al., 2007; Riera-Torres et al., 2010),

Anthraquinone dye (Kim et al., 2004) and vat dye (Silvia et al., 2007).



7/15

Operating cost and time required for the desired degree of

treatment may be the major criteria for the selection of suitable

method. It can be observed from the Table 3 that each and every

method is associated with some type of limitations such as oza-

nationgivesgood colour removal butnot signicant COD reduction,

also the expensive method. Good colour removal and COD reduc-

tion can be achieved by using Fentons reagent but comparatively

longer treatment time and handling of iron contaminated sludge is

the major problem. Oxidation using H2O2-UV is not very effective

since colour and COD reduction is not very signicant, moreover itis not applicable to all types of dyes, produces large number of by-

products and also suffers from UV light penetration limitation.

Sonolysis gives good colour removal by the destruction of chemical

bond present in the dye structure with the help of free radical

production, however it requires enormous amount of dissolve

oxygen and involves high electricity cost. Good removal of wide

variety of dyes can be achieved by adsorption but regeneration is

expensive and it also necessitates costly disposal. Removal of all

types of dyes may be achieved by selecting appropriate membrane

but production of concentrated sludge and high cost of the

membrane are again major limitations. Easy regeneration and

ef cient recovery of dyes may be possible in the ion exchange

method but cost of regeneration is high and the method is not

applicable to all types of dyes since, ion exchange resins are dyespecic.

Apart from these, various researchers have also proposed the

enzymatic degradation of synthetic dyes. In this direction Bhunia

et al. (2001) investigated the application of novel enzymes horse-

radish peroxidase for decomposition and precipitation of azo dyes.

The degradation rate was dependent on the pH of the wastewater.

In another study, Bumpus et al. (1991) revealed that the enzyme

from white rot fungus degraded Crystal Violet via N-demethylation

in a considerable amount. Hence, after standardisation and facili-

tation of accurate dosage, effective dye degradation performance

can be achieved. Simplicity in application and rapid modication

according to the character of dye to be removed makes it attractive

choice for decolourisation of textile wastewater. However, the

major limitation may be the denaturation of enzyme due the effect

of temperature since wastewater coming out from the textile

industry is generally having high temperature.

Both soluble and insoluble dyes can be effectively removed by

electro-coagulation process but high cost of electricity and gener-

ation of secondary pollutants from chlorinated organics, heavy

metals are the major limitations. Complete decolourisation may not

be achieved by the treatment with the help of irradiation for all

types of dyes. Though, there is no sludge production in this tech-

nology, but high cost of electricity may be the limitation. Cost

effectiveness of biological treatment process makes it attractivewhich can ef ciently remove most of the dyes used in the textile

industry because dyes generally possess high level of adsorption on

to the activated sludge. However, longer duration of treatment,

toxicity of dyes and its low biodegradability are the major limita-

tions. Excellent colour removal may be achieved by coagulation-

occulation which can remove most of the dyes used in the

textile industry. Though the sludge production is the major limi-

tation in this process, cost effectiveness of the treatment as

compared to other methods makes it one of the attractive options

for treatment of textile wastewaters.

Addition of some chemicals (polyelectrolyte) enhances coagu-

lation by promoting the growth of large, rapid settling of ocs.

Polyelectrolytes are high-molecular-weight polymers, which

contain absorbable groups and when small dosages of poly-electrolyte (1 mg/L to 5 mg/L) are added in conjunction with

coagulant, these are also referred as coagulant aids. The poly-

electrolyte is substantially unaffected by pH variations and serve as

a coagulant itself by reducing the effective charge on colloids. It

produces a large amount of ions in water and shows properties of

both polymers and electrolytes. The most practical benet of

polyelectrolyte is the formation of massive ocs. These massive

ocs speed up the oc settling velocity, reduce the expense of

decolourisation and also decrease the settled sludge volume

(Bidhendi et al., 2007).

Since Coagulation occulation is cost effective technology and

gives excellent colour removal for wide variety of dyes, it becomes

promising technology for decolourisation of textile wastewater.

Sludge production can also be minimised by optimising process

Table 3

Advantages and limitations of various methods of dye removal from textile ef uents.

Physical/chemical

methods

Method description Advantages Disadvantages References

Ozonation Oxidation using ozone gas Application in gaseous state,

no alteration of volume

Short half-life (20 min),

High cost

Hao et al., 2000; Ince and Tezcanli, 2001;

Robinson et al., 2001; Gogate and Pandi., 2004

Fenton reagents Oxidation using H2O2-Fe(II) Effective decolourisation

of both soluble and

insoluble dyes

Sludge generation and

its handling

Hao et al., 2000; Arslan and Balcioglu, 2001;

Meric et al., 2004

Photochemical Oxidation using mainly H2O2-UV No sludge production Formation of by-products Konstantinou and Albanis, 2004; Hai et al., 2007

Sonolysis Destruction of chemical bond by

producing free radical

using ultrasound

No Extra sludge production Requires a lot of dissolved

oxygen, High cost

Adewuyi, 2001; Arslan-Alaton, 2003

Adsor ption D ye removal b ased

on solid support

Excellent removal of

wide variety of dyes

Regeneration dif culties,

costly disposal of adsorbent

Hao et al., 2000; Fu and Viraraghavan, 2001;

Hai et al., 2007

Membrane ltration Physical separation Removal of all types of dye Production of concentrated

sludge, High cost

Marcucci et al., 2001;

Barredo-Damas et al., 2006

Ion exchange Ion exchange resin Easy regeneration Not effective for all dyes Slokar and Marechal, 1998;

Robinson et al., 2001; Hai et al., 2007

Electro-coagulation Treatment based on

anode and cathode

Good removal of dye High cost, less electrode

reliability

Chen et al., 2005; Merzouk et al., 2010;

Phalakornkule et al., 2010

Irra dia ti on T reatment ba sed on i

onizing radiation

Effective oxidation at lab scale Not effective for all dyes,

High cost

Robinson et al., 2001; Hai et al., 2007

Biological Process Treatment based on

microbiological degradation

Environmental friendly Slow Process, need of adequate

nutrients, narrow operating

temperature range

Lin and Peng, 1996; Sandhya and

Swaminathan, 2006; Togo et al., 2008

Chemical coagulation

and occulation

Addition of coagulants

and occulants

Economically feasible,

excellent colour removal

Sludge production Hao et al., 2000; Fu and Viraraghavan,

2001; Aboulhassan et al., 2006;

Gao et al., 2007; Ciabatti et al., 2010



8/15

parameters and suitable selection of coagulant and occulant. Due

to scarcity of landll sites, the disposal of sludge becomes more

problematic and expensive. Therefore, recycle of sludge becomes

the only viable option. In this regard, the use of sludge as a building

material (Balasubramanian et al., 2006), a soil conditioner (Pearson

et al., 2004; Rosa et al., 2007; Islam et al., 2009) o r a s a f u e l (Van der

Bruggen et al., 2005) has been studied by several researchers.

Coagulation by means of biopolymers is very effective method

for treatment of industrial wastewater. Chitosan as a bioocculant

can be successfully applied for the removal of both particulate and

dissolved substances (Renault et al., 2009). The main reasons for

the success of this biopolymer in wastewater treatment using

coagulation/occulation are, chitosan has the advantage of being

a non-toxic material, non corrosive and safe to handle (non

hazardous product, not irritating for skin and eyes) (Bolto and

Gregory, 2007; Bratby, 2007). Moreover, chitosan is also ef cient

in cold water and at much lower concentration than metal salts.

The lower concentration of polymers reduces the volume of sludge

production compared to sludge obtained with alum. In addition, as

biopolymers are biodegradable, hence, the sludge can be ef ciently

degraded by microorganisms. Various studies have been reported

that the sludge produced from the treatment of milk processing

plant wastewater (Chi and Cheng, 2006) and kaolinite suspensions(Divakaran and Pillai, 2001) was non-toxic and could be used to

stimulate growth in plants.

4. Chemical coagulation technologies

Chemical coagulation is a complex phenomenon involving

various inter-related parameters, hence it is very critical to dene

that how well coagulant will function under given conditions. On

the basis of effectiveness to decolourise the textile wastewater,

chemical coagulants can be categorised in the three parts as

described in the following Fig. 4.

It has been reported that pre-hydrolysed metallic salts are often

found to be more effective than the hydrolysing metallic salts such

as aluminium sulphate (alum), ferric chloride and ferric sulphatethose are readily soluble in water ( Jiang and Graham, 1998). Pre-

hydrolysed coagulants such as Polyaluminium chloride (PACl),

Polyaluminium ferric chloride (PAFCl), Polyferrous sulphate (PFS)

and Polyferric chloride (PFCl) seem to give better colour removal

even at low temperature and may also produce lower volume of

sludge. In this connection, Gregory and Rossi (2001) have studied

the effectiveness of various pre-hydrolysing coagulants for the

treatment of wastewater, and reported that PACl products give

more rapid occulation and strong ocs than that of alum at

equivalent dosage. This can be attributed by the fact that these

coagulants are pre-neutralised, have smaller effect on the pH of

water and so reduce the need of pH correction. Most of the dyes

used in textile industries are of negatively charged and hence

cationic polymer is preferred over anionic and nonionic polymers

due to the better dye removal performance. However, the mecha-

nisms of these products are not well established yet. Further, to

conduct and evaluate the work, it is necessary to consider only the

most critical controlling parameters. Various authors have sug-

gested the most important parameters to be consider in coagula-

tion are pH and concentration of applied metal ions (coagulant)

such as alum (El-Gohary and Tawk, 2009), FeCl3 (Kim et al., 2003;

Bidhendi et al., 2007), MgCl2 (Tan et al., 2000; Semerjian and

Ayoub, 2003; Gao et al., 2007), polyaluminium chloride (PACl)

(Sanghi and Bhattacharya, 2005; Choo et al., 2007), lime (Mishra

et al., 2002; Georgiou et al., 2003) and ferrous sulphate and

organic polymeric coagulants (Mishra et al., 2002; Bidhendi et al.,

2007).

Apart from these, mixing speed and time (Gurses et al., 2003),

temperature and retention time (Ong et al., 2005; Naimabadi et al.,

2009) also inuence the colour removal ef ciency. Hence, the

optimisation of these factors may signicantly increase the processef ciency. Different coagulants affect different degrees of destabi-

lisation. The higher the valence of the counter ion, the more is its

destabilising effect and the less is the dose needed for coagulation.

If pH is below the isoelectric point of metal hydroxide while

precipitation of colloids by different coagulants supported by

suitable polymer, then the positively charged polymers will prevail

and adsorption of these positively polymers can destabilise nega-

tively charged colloids by charge neutralisation. Above the

isoelectric point, anionic polymers will predominate where particle

destabilization may take place through adsorption and bridge

formation. At high dose of metal ions (coagulant), a suf cient

degree of oversaturation occurs to produce a rapid precipitation of

a large quantity of metal hydroxide, enmeshing the colloidal

particles which are termed as sweep oc (Peavy et al., 1985). Forexample, when Fe(III) salts are used as coagulants, monomeric and

polymeric ferric species are formed, the formation of which is

highly pH dependent (Abo-Farha, 2010). Some of the reported

chemical coagulation technology and their performance have been

summarised in Table 4.

The studies made by various researchers as described in the

Table 4 show that the natural pH of ferric chloride solution is acidic.

However, the effective colour removal can be achieved when the

• Aminomethyl polyacrylamide

• Polyalkylene

• Polyamine

• Polyethylenimine

• Polydiallyldimethyl ammonium

chloride (poly-DADMAC)

• Polyaluminium

• Polyferric

• Polyferrous sulphate (PFS)

•

(PAFCl)

•

• Ferric chloride

• Ferric sulphate

• Magnesium chloride

• Alum

Hydrolysing

metallic salts

Pre- hydrolysing

metallic saltsSynthetic cationic

polymers

Chemical coagulants

Polyaluminium

ferric chloride

chloride (PACl)

chloride (PFCl)

Polyaluminium

sulphate (PAS)

Fig. 4. Categorisation of chemical coagulants according to their effectiveness.



9/15

pH is maintained near to neutral, but it again depends upon the

type of dyes to be removed (Kim et al., 2004; Guendy, 2010;

Moghaddam et al., 2010). Hence, the addition of base to maintain

the pH becomes prime requirement. Lime or NaOH can be used for

this purpose. However, addition of lime may produce extra sludge.

Whereas, addition of polyelectrolyte as a coagulant aid generally

improves the performance of coagulant. It can be seen from the

Table 4 that optimum pH for alum is near to neutral and hence

higher colour removal ef ciency can be obtained at this pH.

Moreover, addition of polyelectrolyte generally improves the colour

removal performance. However, generation of large amount of

sludge associated with this process makes it unattractive.

PACl products are aluminium-based coagulants. They are similar

to alum, with several important differences:

- Partially pre-neutralised (Higher basicity than alum)

- Contains Cl instead of SO42

- Contains up to three times the aluminium content

- Rapid aggregation velocity, bigger and heavier ocs

Moreover, PACl shows better colour removal ef ciency in

a wider pH range of 7e10. The optimum pH for FeSO4 is alkaline in

the range 7e9 and gives higher colour removal at this pH range.Various researchers have also revealed that the addition of poly-

electrolyte generally increases turbidity and volume of settled

sludge. This undesired effect may be eliminated if the used

concentration of polyelectrolyte is less than 2 mg/L (Bidhendi et al.,

2007).

The optimum pH for magnesium chloride varies between 9 and

12 (Gao et al., 2007; El-Gohary and Tawk, 2009). It gives very good

colour removal performance if used with lime. However, it gener-

ates large amount of sludge which may cause sludge disposal

problem and also involves extra cost. Alum and magnesium chlo-

ride, because of large amount of sludge generation and production

of basic ef uent after treatment, may not be considered as the good

coagulants. Though, both the ferric chloride and alum give roughly

high ef ciency, at low concentration, colour removal ef ciency is

reported less for ferric chloride (Kim et al., 2004; Golob et al., 2005;

Bidhendi et al., 2007). However, signicant improvement in the

colour removal has been reported if ferric chloride used with small

amount of cationic polymer (Suksaroj et al., 2005). Very limited

information is available based on the coagulant studies using PFS.

PFS makes it attractive coagulant because it is practically soluble in

water, and forms large amount of polynucleic complex ions like

(Fe2(OH)3)3þ, (Fe2(OH)2)

2þ, (Fe8(OH)20)4þ, which are prone to

render occulation. It is advantageous as regards the following

points:

- Fast settling of ocs

- Broad pH compatibility

- Low iron contamination

- High heavy metal removal rate

- Easy dehydration of sludge etc.

The principle mechanism for coagulation is similar to the PACl

i.e. adsorption and charge neutralisation. At high turbidity, the

coagulation may follow Sweep coagulation (Peavy et al., 1985).Gao et al. (2001) have investigated the application of PAFCl for

the decolourisation of petrochemical wastewater and reported that

PAFCl gives better turbidity removal in 7.0e8.4 pH range and good

colour removal for suspension dyes over the other selected coag-

ulant such as PFS and PACl. In addition to the performance of better

coagulation ef ciency for colour removal, it also reects the ability

to quick formation of the ocs. The ability of quick formation of the

ocs and superior colour removal ef ciency may be due to the

reason that PAFCl combines the coagulatory advantages of both

aluminium and iron salts and hence able to form ocs rapidly with

more bulky and rapid sedimentation. This novel coagulant is not

Table 4

Effectiveness of different chemical coagulants studied by different researchers for colour removal of textile wastewater.

Name of coagulant Optimised

dose (mg/L)

Coagulant aids (if any ) Type o f dyes

present

Optimum

pH

% Colour

removal

Reference

Steel industry wastewater Disperse 4.25 99 Anouzla et al., 2009

Potassium ferrate 100 Polyamine based polymer 6.5e8.5 95 Ciabatti et al., 2010

Polyaluminium Chloride (PACl) 10 7.2 99.9 Choo et al., 2007

Poly-epichlorohydrin-diamine 20 7 95 Kang et al., 2007

Alum 200 Polyacrylamide

based polymer (Cytec)

5.3 78.9 El-Gohary and Tawk, 2009

Alum 5000 Copper sulphate as catalyst 4 74 Kumar et al., 2008

Alum 20 Commercial cationic

occulant (Coloc-RDeCiba)

Reactive

and acid

Near to

neutral

98 Golob et al., 2005

Alum 7 104 5.7e6.5a 74 Patel and Vashi, 2010

Ferrous Sulphate 200 Polyelectrolyte Sulfur 9.4 90 Bidhendi et al., 2007

Ferric chloride 400 Sulfur 8.3 100 Bidhendi et al., 2007

Ferric chloride 293 Reactive and

disperse

6 71 Kim et al., 2004

Ferric chloride 56 Cationic polymer 4 92 Suksaroj et al., 2005

Magnesium chloride 400 Polyelectrolyte (Koaret PA 3230) Reactive 11 85 Tan et al., 2000

Magnesium chloride 120 Lime 11 100 El-Gohary and Tawk, 2009

Magnesium chloride 800 Hydrated lime Reactive and

disperse

12 98 Gao et al., 2007

P oly aluminium chloride (P ACl) 0.1 P oly acrylamide-seed gum React ive ,

acid and direct

8.5 80 Sanghi et al., 2006

Polyaluminium chloride (PACl) 800 Anionic polyacrlamide,

Exeroc 204

7.5 75 Tun et al., 2007

Ferrous sulphate 400 Lime and Cationic polymer Reactive 12.5 90 Georgiou et al., 2003

Ferrous sulphate 1000 Anionic

polyelectrolyte (Henkel23500)

9.5 60 Selcuk, 2005

Ferrous sulphate 7 104 5.7e6.5a 85 Patel and Vashi, 2010

Ferric sulphate 7 104 5.7e6.5a 58 Patel and Vashi, 2010

a

Experiments were carried out at original pH of raw wastewater.



10/15

widely studied for textile wastewater treatment hence very limited

information is available. The principle mechanism of PAFCl is

charge neutralisation and bridging (Chen et al., 2010). Recently,

Ciabatti et al. (2010) have studied the use of potassium ferrate in

combination of polyamine based polymer for treatment of dyeing

ef uents and found excellent colour removal as well as COD

reduction. Since ferrate (VI) ion is a strong oxidant in entire the pH

range, hence after reduction to Fe(III) ion or ferric hydroxide during

oxidation process, it possesses the ability to act as coagulant. Hence

potassium ferrate represents a unique dual function (Oxidant and

coagulant) chemical reagent that can be an effective alternative to

current approaches for water and wastewater treatment.

5. Coagulation with the help of natural coagulants

Chemical coagulation with the help of above discussed coag-

ulants may be the method of choice for decolourisation of textile

wastewater before being fed to the biological treatment, if

necessary. However, it has also some drawbacks as the ef ciency

of the treatment strongly depends on pH. Moreover, the coagu-

lation process is not always ef cient enough because at different

environmental conditions such as at extreme pH and at very low

or very high temperature, it may produce very sensitive, fragile

ocs, which result in poor sedimentation. These ocs may rupture

under any type of physical forces. To improve the ef ciency of

coagulation process, number of high molecular weight

compounds such as polymers from synthetic or natural originmay be recommended. These polymers can function as coagulant

itself or in the form of coagulant aids/bioocculants, depending

upon the wastewater and polymer characteristics. These polymers

are normally macro-molecular structure with variety of functional

groups which can either work as coagulants by destabilising the

charged stable particles mainly through the process of adsorption

and neutralisation or can work as coagulant aids by attaching the

destabilised particles with the functional groups by interparticle

bridging. Here organic polymeric compounds are advantageous

over inorganic materials, which posses several novel characteris-

tics such as their ability to produce large, dense, compact ocs

that are stronger and have good settling characteristics (Renault

et al., 2009). In contrast to some traditionally used coagulant

such as alum, organic polymers are bene

cial because of the

lower coagulant dosage requirement, ef ciency at low tempera-

ture and produce small volume of sludge whereas inorganic

polymers and chemical coagulants generally involve higher cost,

less biodegradability and toxicity. For example, acrylamide is very

much toxic and gives severe neurotoxic effects (Bratby, 2007).

Toxicity effect due to cationic polymers to the plants has been

established long back (Gao et al., 2001). In this connection, Bolto

and Gregory (2007) also reported that anionic and nonionic

polymers are generally less toxic as compared to cationic poly-

mers especially to aquatic organisms. The major advantage of

natural polymer is its non-toxicity to the environment and

biodegradability. Therefore, the ef uent after natural polymer

treatment can be treated by biological means, if required. Thisef uent will not pose any harm to the biological organisms, as is

offered, if it is treated by means of synthetic coagulants. Not only

this, the sludge generated by the natural polymers can further be

treated biologically or can be disposed off safely as soil condi-

tioners because of their non-toxicity. Hence, there is an urgent

need to establish the use of natural low cost polymers for textile

wastewater treatment.

In the view of this, many researchers have studied the effec-

tiveness of various natural coagulants ( Joshi and Nanoti, 1999)

extracted from plants or animals (Christman, 1967) for the treat-

ment of textile wastewater. These natural coagulants may also

prove their effectiveness if used as coagulant aids along with the

chemical coagulants. Most of the natural coagulants fall under the

category of polysaccharides, hence also termed as polymericcoagulants. On the basis of the origin of production, natural coag-

ulant can be divided in to three categories as shown in Fig. 5. Unlike

synthetic coagulants, natural coagulants generally exhibit two

types of mechanism namely i) adsorption and charge neutralisa-

tion, and ii) adsorption and interparticle bridging. As their molec-

ular weight is high and contain long chained structure, therefore

offers a large number of available adsorption sites. Adsorption and

charge neutralisation refers to the sorption of two oppositely

charged ions, while interparticle bridging occurs when poly-

saccharide chain of coagulant sorbs the particulates (Miller et al.,

2008). The existence of adsorption and interparticle bridging

between dye molecules and polysaccharides is due to the interac-

tion of p- electron system of dyes and OH group of poly-

saccharides (Fig. 6), which was

rst suggested by Yoshida et al.

Micro-organism basedAnimal basedPlant based

Natural coagulants

• Guar gum

• Gum Arabic

• Seed extract from

Strychnos potatorum,

Moringa Oilifeira etc.

• Cactus latifaria extract

• Potato starch

• Chitosan • Xanthan gum

Fig. 5. Categorisation of natural coagulants with their examples.



11/15

(1964) and then reviewed by Blackburn and Burkinshaw (2002)

and Yin (2010).

5.1. Plant based polymers as coagulants

Various plant extracted polymers such as starch, guar gam, gum

arabic, nirmali seeds, tannin, Moringa oleifera and cactus etc. are

generally well known as coagulants within the scientic commu-

nity. These polymers have large number of industrial application as

these are polysaccharides and possess various commercial appli-

cations such as in paper industry, as food additives etc. By virtue of

the effectiveness of natural polymer as coagulant, Sanghi et al.

(2006) have investigated the use of Ipomeoa dasysperma seedgum and guar gum as coagulant aids along with PACl and found 86%

and 87% removal of acid dye at the PACl dosage of 1 mg/L and

I. dasysperma seed gum and guar gum dosage of 5 mg/L each, at

optimum pH of 9.5. Signicant removals of the order 73% and 80%

were also been reported for direct dye at the same dosage of

coagulant and coagulant aid and at the same pH of 9.5.

Adinol et al. (1994) have reported that polysaccharide extrac-

ted from Strychnos potatorum (Nirmali) seeds can effectively reduce

upto 80% turbidity of kaolin solution. M. oleifera, known as drum-

stick tree is widely found throughout India, Asia, some parts of

Africa and America. The tree’s bark, root, fruit, owers, leaves seeds

and gum are also used as medicines. The seed of these trees is also

used as coagulant and/or occulants in the water and wastewater

treatment. Beltrán-Heredia et al. (2009) have investigated the useof M. oleifera seed extract for the removal of anthraquinone dye and

reported 95% dye removal at the coagulant dose of 100 mg/L and at

pH 7. Further, Lea (2010) has investigated the effectiveness of M.

oleifera seed extract for the treatment of turbid water and found

99.5% turbidity removal at the dosage of 400 mg/L. Typically,

increased dosage of seed extract does not enhance the dye removal

after maximum adsorption is reached. It might be due to the fact

that no more new sites for adsorption remain available at the

surface of seed extract. M. oleifera seeds are also considered as an

excellent biofuel source for making biodiesel.

Gum Arabic, also known as Gum Acacia is highly branched with

beta-Galactose backbone having high molecular weight of

250,000e750,000 Da, water and fat soluble polysaccharide. The

coagulation studies with this novel natural coagulant are yet to beestablished. Although the mechanism of coagulation with natural

coagulants has not been extensively investigated but the presence

of hydroxyl groups along the polysaccharide chain provides a large

number of available adsorption sites that might lead to the inter-

particle bridging between polysaccharide and dye molecule as

shown in Fig. 7.

Paulino et al. (2006) studied the removal of methylene blue with

the help of hydrogel formed by modied Gum Arabic, polyacrylate

and polyacrylamide and reported that 98% of dye removal can be

achieved at pH 8 with maximum adsorption capacity of 48 mg of

the dye per gram of hydrogel. However, use of gum arabic and guar

gum for colour removal due to the widely used dyes in the textile

industries are yet to be established. In connection with application

of natural coagulants, various researchers (Kumar, 2000; No and

Meyers, 2000; Kurita, 2006; Renault et al., 2009) have studied the

effectiveness of animal extracted polymer as coagulants for

industrial wastewater treatment.

5.2. Animal based polymers as coagulants

Chitosan is a linear copolymer of D-glucosamine (deacetylated

unit) and N-acetyl-D-glucosamine (acetylated unit) produced by

the deacetylation of chitin, a natural polymer of major importance

(Roberts, 1992; Kurita, 2006). The degree of deacetylation can be

determined by NMR spectroscopy. Chitin is the structural element

in the exoskeleton of crustaceans (crabs, shrimps etc.) and in the

endoskeleton of other invertebrate.

Chitosan possesses several intrinsic properties such as non-

toxicity, its biodegradability and its outstanding chelation

behavior that make it an effective coagulant and/or occulant for

removal of contaminant in the dissolved state. Various studies for

treatment of industrial wastewater using chitosan have been

carried out during late 70’s by Bough and coworkers (Bough, 1975,

1976; Bough et al., 1978). They have investigated the effectivenessof chitosan for coagulation and recovery of suspended solids (SS) in

processing of waste from variety of food processing industries and

found that this novel coagulant is very much effective for ef cient

reduction of COD as well as removal of SS and turbidity. Numerous

works claim that chitosan involved in a dual mechanism including

coagulation by charge neutralisation and occulation by bridging

mechanism (No and Meyers, 2000; Guibal and Roussy, 2007). The

possible interactions between dye molecules and chitosan have

been shown in Fig. 8. Zhang et al. (1995) have used carboxymethyl

chitosan for printing and dyeing wastewater treatment. The

experimental results showed that, carboxymethyl chitosan in

wastewater decolourisation and COD reduction, are superior over

other commonly used polymer occulants. Szygula et al. (2009)

reported approximately 99% colour removal from the simulatedtextile wastewater containing Acid Blue 92 at an optimum chitosan

dosage of 100 mg/L maintaining optimum pH of 9. In continuation

of this, Mahmoodi et al. (2011) investigated the effectiveness of

chitosan for removal of Acid Green 25 and Direct Red 23 and re-

ported approximately 75% and 95% dye removal respectively in

10 min at optimum pH 2 maintaining the stirring speed of 200 rpm.

5.3. Microorganism based polymer as coagulant

Xanthan gum is a polysaccharide, derived from the bacterial

coat of Xanthomonas campestris, used as food additive and rheology

modier (Davidson, 1980). It is produced by the fermentation of

glucose by the X. campestris bacterium. After fermentation, the

polysaccharide is separated from the growth medium with the help

Fig. 6. Schematic representation of intermolecular interaction between p- electron

from dye molecule and hydroxyl group of polysaccharide (Yoshida et al., 1964).

Fig. 7. Schematic representation of the interaction of dye molecule with (a) Guar Gum

and (b) Gum Arabic.



12/15

of solvent separation technique, dried and ground into a ne

powder (Cohan, 2010). The use of xanthan gum for the treatment of

textile wastewater is not been reported in the literature yet. Due to

complex structure and higher molecular weight of xanthan gum

(250,000e750,000 Da), as compared to guar gum (about

220,000e250,000 Da), it may also be considered as one of the

promising coagulant and/or coagulant aids for the treatment of

textile wastewater. Hence, extensive study is required to be con-

ducted to establish the various facts about effectiveness of xanthan

gum for the treatment of textile wastewater. The possible mecha-

nism of coagulation by interparticle bridging as observed for guar

gum can also be observed for xanthan gum (Fig. 9).

It can be summarised from the above discussions that plant

extracted coagulant may be encouraged over animal extracted

coagulant for the treatment of textile wastewater due to the factthat non plant sources possess limited potential for the mass

production as compared to the plant sources. Extra involvement of

cost in the processing of microorganism based coagulant may not

be an attractive option. Application of plant based coagulants will

become more attractive if the coagulants producing plants are

indigenous.

The main advantage of coagulation and occulation is decol-

ourisation of the waste stream due to the removal of dye molecules

from the dyebath ef uents, 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/

occulation processes is the production of sludge. However, the

sludge amount could be minimised if only a low volume of the

highly coloured dyebath could be eliminated by chemical treat-

ment directly after the dyeing process (Golob et al., 2005).

6. Future scope of research

Very limited work has been carried out on the decolourisation of

textile wastewater containing multiple dyes of different classes

along with the various chemical additives which are used during

textile processing. Also the effectiveness of most of the pre-

hydrolysed coagulants for decolourisation of textile wastewater

containing multiple dyes is yet to be established. Considering the

industries dependencies on the cost effective chemical coagulation

and occulation technologies for their coloured wastewater treat-

ment, it is required to conduct more and more future research to

come up with best coagulants or combinations of coagulants along

with coagulant aids which can produce very promising results even

at a wider variations of pH and other interfering agents of the

textile wastewaters. Investigation of the effectiveness of more

number of natural coagulants is also need to be assessed. This

assessment may be carried out using natural polymers as coagulant

aids as well as coagulant itself. Effectiveness of natural coagulants

also required to be carried out against simulated as well as raw

textile wastewater.

7. Conclusion

All decolourisation methods described in this review have some

advantages as well as some drawbacks, and their selection will

mostly governed by the textile wastewater characteristics like class

and concentration of dyes, pH, organic contents, heavy metals, etc.

Among different physical, chemical, biological, and advanced

Fig. 8. Schematic representation of the formation of chitosan from chitin polysaccharide and its interaction with dye molecules.

Fig. 9. Schematic representation of possible interaction between xanthan gum and dye

molecule.



13/15

chemical oxidation technologies, chemical coagulation and oc-

culation is still a cost-comparative alternative for the treatment of

industrial textile wastewaters and is widely practiced by the small

to large scale industries. Among chemical coagulation and occu-

lation technologies, comparatively, pre-hydrolysed coagulants such

as PACl, PFCl, PFS and PAFCl may be considered as the better

coagulants because of their superior colour removal even at small

dosage and affectivity at wider pH range of wastewater. Ferrous

sulfate may also be considered as a better coagulant over other

hydrolysing metallic salts. Additionally, due to some novel prop-

erties of natural coagulants such as non-toxic, biodegradability,

environment friendly, ability to encapsulate etc., these may also be

considered as the promising coagulants as well as coagulant aids

for textile wastewater treatment specially at rst stage, which will

not hinder the biological treatment (if required) because the

residual coagulant may act as nutrient for the microorganisms.

However, till date the applicability of these natural coagulants for

the textile wastewater is very limited. More and more studies

required to evaluate their application for colour removal of textile

wastewaters particularly, their behaviour at high pH of textile

wastewaters.

Acknowledgement

The authors wish to thank all the reviewers for their valuable

suggestions for improving the quality of the manuscript and

Department of Civil Engineering, School of Infrastructure, Indian

Institute of Technology Bhubaneswar, India, for providing facilities

for carrying out research work in the related area.

References

Abo-Farha, S.A., 2010. Comparative study of oxidation of some azo dyes by differentadvanced oxidation processes: fenton, fenton-like, photo-fenton and photo-Fenton-Like. Journal of American Science 6 (10), 128e142.

Aboulhassan, M.A., Souabi, S., Yaacoubi, A., Baudu, M., 2006. Improvement of paint

ef uents coagulation using natural and synthetic coagulant aids. Journal of Hazardous Materials B138, 40e45.

Adewuyi, Y.G., 2001. Sonochemistry: environmental science and engineeringapplications. Industrial & Engineering Chemistry Research 40, 4681 e4715.

Adinol, M., Corsaro, M.M., Lanzetta, R., Parrilli, M., Folkard, G., Grant, W.,Sutherland, J., 1994. Composition of the coagulant polysaccharide fraction fromStrychnos potatorum seeds. Carbohydrate Research 263, 103 e110.

Ahmad, A.L., Harris, W.A., SyaieOoi, B.S., 2002. Removal of dye from wastewater of textile industry using membrane technology. Universiti Teknologi Malaysia

Jurnal Teknologi 36 (F), 31e44.Akbari, A., Desclaux, S., Rouch, J.C., Aptel, P., Remigy, J.C., 2006. New UV-

photografted nanoltration membranes for the treatment of colored textiledye ef uents. Journal of Membrane Science 286, 342e350.

Akbari, A., Remigy, J.C., Aptel, P., 2002. Treatment of textile dye ef uent usinga polyamide-based nanoltration membrane. Chemical Engineering Protocols41, 601e609.

Al-Malack, M.H., Abuzaid, N.S., El-Mubarak, A.H., 1999. Coagulation of polymericwastewater discharged by a chemical factory. Water Research 33, 521 e529.

Alaton, I.A., Balcioglu, I.A., Bahnemann, D.W., 2002. Advanced oxidation of a reactive

dye bath ef uent: comparison of O3, H2O2/UV-C and TiO2/UV-A processes.Water Research 36, 1143e1154.

Anjaneyulu, Y., Chary, N.S., Raj, D.S.S., 2005. Decolourization of industrial ef uents-available methods and emerging technologies-a review. Reviews in Environ-mental Science and Biotechnology 4, 245e273.

Anliker, R.,1986. In: Richardson, M. (Ed.), Toxic hazard assessment of chemicals. TheRoyal Society of Chemistry, London.

Anouzla, A., Abrouki, Y., Souabi, S., Sa, M., Rhbal, H., 2009. Colour and COD removalof disperse dye solution by a novel coagulant: application of statistical designfor the optimization and regression analysis. Journal of Hazardous Materials166 (2e3), 1302e1306.

Arslan, I., Balcioglu, A., 2001. Degradation of Remazol Black B dye and its simulateddyebath wastewater by advancedoxidation processes in heterogenous andhomogeneous media. Coloration Technology 117, 38 e42.

Arslan-Alaton, I., 2003. A review of the effects of dye-assisting chemicals onadvanced oxidation of reactive dyes in wastewater. Coloration Technology 119,345e353.

ATMI, 1997. American Textiles Manufacturers Institute, Comments on draft of this

document.

Azbar, N., Yonar, T., Kestioglu, K., 2004. Comparison of various advanced oxidationprocesses and chemical treatment methods for COD and colour removal froma polyester and acetate ber dying ef uent. Chemosphere 55, 35e43.

Babu, B.R., Parande, A.K., Raghu, S., Kumar, T.P., 2007. Cotton textile processing:waste generation and ef uent treatment. Textile technology. The Journal of Cotton Science 11, 141e153.

Balasubramanian, J., Sabumon, P.C., Lazar, J.U., Ilangovan, R., 2006. Reuse of textileef uent treatment plant sludge in building materials. Waste Management 26,22e28.

Barredo-Damas, S., Alcaina-Miranda, M.I., Iborra-Clar, M.I., Bes-Pià, A.,

Mendoza, J.A., Iborra-Clar, A., 2006. Study of the UF process as pretreatment of NF membranas for textile wastewater reuse. Desalination 200, 745 e747.

Bayramoglu, G., Arica, M.Y., 2007. Biosorption of benzidine based textile dyes DirectBlue 1 and Direct Red 128 using native and heat-treated biomass of Trametesversicolor . Journal of Hazardous Materials 143 (1e2), 135e143.

Bayramoglu, M., Kobya, M., Can, O.T., Sozbir, M., 2004. Operating cost analysis of electrocoagulation of textile dye wastewater. Separation and PuricationTechnology 37, 117e125.

Beltrán-Heredia, J., Sánchez-Martín, J., Delgado-Regalado, A., Jurado-Bustos, C.,2009. Removal of Alizarin Violet 3R (anthraquinonic dye) from aqueous solu-tions by natural coagulants. Journal of Hazardous Materials 170, 43 e50.

Bhunia, A., Durani, S., Wangikar, P.P., 2001. Horseradish peroxidase catalyseddegradation of industrially important dyes. Biotechnology and Bioengineering72, 562e567.

Bidhendi, GR.N., Torabian, A., Ehsani, H., Razmkhah, N., 2007. Evaluation of indus-trial dyeing wastewater treatment with coagulants and polyelectrolyte asa coagulant aid. Iranian Journal of Environmental Health, Science and Engi-neering 4, 29e36.

Bisschops, I.A.E., Spanjers, H., 2003. Literature review on textile wastewater char-acterisation. Environmental Technology 24, 1399 e1411.

Blackburn, R.S., Burkinshaw, S.M., 2002. A greener approach to cotton dyeing, Part2: application of 1:2 metal complex acid dyes. Green Chemistry 4, 261 e265.

Bolto, B., Gregory, J., 2007. Organic polyelectrolytes in water treatment. WaterResearch 41, 2301e2324.

Bough, W.A., 1975. Coagulation with Chitosan-an aid to recovery of by productsfrom egg breaking wastes. Poultry Science 54, 1904 e1912.

Bough, W.A., 1976. Chitosan-a polymer from seafood wastes for use in treatment of food processing wastes and activated sludge. Process Biochemistry 11, 13 e16.

Bough, W.A., Salter, W.L., Wu, A.C.M., Perkins, B.E., 1978. Inuence of manufacturingvariables on the characteristics and effectiveness of chitosan products.Biotechnology and Bioengineering 20, 1931e1943.

Bouyakoub, A.Z., Kacha, S., Lartiges, B.S., Bellebia, S., Derriche, Z., 2009. Treatment of reactive dye solutions by physicochemical combined process. Desalination andWater Treatment 12 (1e3), 202e209.

Bratby, J., 2007. Coagulation and Flocculation in Water and Wastewater Treatment,second ed.. IWA Publishing.

Bumpus, J.A., Mileski, G., Brock, B., Ashbaugh, W., Aust, S.D., 1991. Biological

oxidations of organic compounds by enzymes from a white rot fungus. Inno-vative Hazardous Waste Treatment Technologies 3, 47 e54.Charoenlarp, K., Choyphan, W., 2009. Reuse of dye wastewater through colour

removal with electrocoagulation process. Asian Journal on Energy and Envi-ronment 10 (4), 250e260.

Chen, X., Shen, Z., Zhu, X., Fan, Y., Wang, W., 2005. Advanced treatment of textilewastewater for reuse using electrochemical oxidation and membrane ltration.Water South Africa 31, 127e132.

Chen, T., Gao, B., Yue, Q., 2010. Effect of dosing method and pH on color removalperformance and oc aggregation of polyferricchloride-polyaminedual-coagulant in synthetic dyeing wastewater treatment. Colloids and Surface A:Physicochemical and Engineering Aspects 355, 121 e129.

Chi, F.H., Cheng, W.P., 2006. Use of chitosan as coagulant to treatwastewater frommilk processing plant. Journal of Polymers and the Environment 14, 411 e417.

Choo, K.H., Choi, S.J., Hwang, E.D., 2007. Effect of coagulant types on textilewastewater reclamation in a combined coagulation/ultraltration system.Desalination 202, 262e270.

Christie, R., 2001. Colour Chemistry. The Royal Society of Chemistry, Cambridge,United Kingdom.

Christman, R.F., 1967. Report for Kypro Co. Bellvina, Washington.Ciabatti, I., Tognotti, F., Lombardi, L., 2010. Treatment and reuse of dyeing ef uents

by potassium ferrate. Desalination 250, 222e228.Cohan, Wendy, 2010. Could xanthan gum Sensitivity be Complicating your Celiac

disease Recovery?. www.celiac.com.COINDS, 2000. Comprehensive Industry Documents Series on Textile Industry.

Central Pollution Control Board, India. 59.Davidson, L.R., 1980. Handbook of Water Soluble Gums and Resins. McGraw Hill,

NewYork.Debik, E., Kaykioglu, G., Coban, A., Koyuncu, I., 2010. Reuse of anaerobically and

aerobically pre-treated textile wastewater by UF and NF membranes. Desali-nation 256, 174e180.

Divakaran, R., Pillai, V.N.S., 2001. Flocculation of kaolinite suspensions in water bychitosan. Water Research 35, 3904 e3908.

Dos Santos, A.B., Cervantes, F.J., Van Lier, J.B., 2007. Review paper on current tech-nologies for decolourisation of textile wastewaters: perspectives for anaerobicbiotechnology. Bioresource Technology 98, 2369e2385.

Easton, J.R., 1995. The dye maker’s view. In: Cooper, P. (Ed.), Colour in DyehouseEf uent. Society of Dyehouse and Colour, Bradford, England, pp. 9e21.


http://www.celiac.com/http://www.celiac.com/http://www.celiac.com/


14/15

El-Gohary, F., Tawk, A., 2009. Decolourisation and COD reduction of disperse andreactive dyes wastewater using chemical-coagulation followed by sequentialbatch reactor (SBR) process. Desalination 249, 1159e1164.

Ferroro, F., 2000. Oxidative degradation of dyes and surfactant in the Fenton andphoto-Fenton treatment of dye house ef uents. Coloration Technology 116(5e6), 148e153.

Fersi, C., Dhahbi, M., 2008. Treatment of textile plant ef uent by ultraltration and/or nanoltration for water reuse. Desalination 222, 263e271.

Fontenot, E.J., Lee, Y.H., Matthews, R.D., Zhu, G., Pavlostathis, S.G., 2003. Reductivedecolorisation of a textile reactive dyebath under methanogenic conditions.

Applied Biochemistry and Biotechnology 109, 207e225.Foo, K.Y., Hameed, B.H., 2010. Decontamination of textile wastewater via TiO2/

activated carbon composite materials. Advances in Colloid and Interface Science159, 130e143.

Fu, Y., Viraraghavan, T., 2001. Fungal Decolorization of dye wastewaters: a review.Bioresource Technology 79, 251e262.

Gao, B., Yue, Q., Miao, J., 2001. Evaluation of polyaluminium ferric chloride (PAFC) asa composite coagulant for water and wastewater treatment. Water Science andTechnology 47 (1), 127e132.

Gao, B.Y., Yue, Q.Y., Wang, Y., Zhou, W.Z., 2007. Color removal from dye-containingwastewater by magnesium chloride. Journal of Environmental Management 82,167e172.

Georgiou, D., Melidis, P., Aivasidis, A., Gimouhopoulos, K., 2002. Degradation of azo-reactive dyes by ultraviolet radiation in the presence of hydrogen peroxide.Dyes and Pigments 52, 69e78.

Georgiou, D., Aivazidis, A., Hatiras, J., Gimouhopoulos, K., 2003. Treatment of cottontextile wastewater using lime and ferrous sulfate. Water Research 37,2248e2250.

Gholami, M., Nasseri, S., Fard, M.R.A., Mesdaghinia, A., Vaezi, F., Mahvi, A.,Naddaf , K., 2001. Dye removal from ef uents of textile industries by ISO9888method and membrane technology. Iranian Journal of Public Health 30, 73 e80.

Gogate, P.R., Pandi, A.B., 2004. A review of imperative technologies for wastewatertreatment: hybrid methods. Advances in Environmental Research 8, 553 e597.

Golob, V., Vinder, A., Simonic, M., 2005. Ef ciency of coagulation/occulationmethod for treatment of dye bath ef uents. Dyes and Pigments 67, 93 e97.

Gozálvez-Zafrilla, J.M., Sanz-Escribano, D., Lora-García, J., León Hidalgo, M.C., 2008.Nanoltration of secondary ef uent for wastewater reuse in the textileindustry. Desalination 222, 272e279.

Gregory, J., Rossi, L., 2001. Dynamic testing of water treatment coagulants. WaterScience and Technology, Water Supply 1 (4), 65 e72.

Guendy, H.R., 2010. Treatment and reuse of wastewater in the textile industry bymeans of coagulation and adsorption techniques. Journal of Applied SciencesResearch 6 (8), 964e972.

Guibal, E., Roussy, J., 2007. Coagulation and occulation of dye containing solutionsusing a biopolymer (chitosan). Reactive and Functional Polymers 67, 33 e42.

Gupta, V.K., Suhas, 2009. Application of low-cost adsorbents for dye removal-a review. Journal of Environmental Management 90, 2313e2342.

Gurses, A., Yolcin, M., Dogar, D., 2003. Removal of remazol red RB by using Al (III) ascoagulant- occulant; effect of some variables on settling velocity. Water, Airand Soil Pollution 146 (1e4), 297e318.

Hai, F.I., Yamamoto, K., Fukushi, K., 2007. Hybrid treatment systems for dyewastewater. Critical Reviews in Environmental Science and Technology 37,315e377.

Hao, O.J., Kim, H., Chiang, P.C., 2000. Decolorisation of wastewater. Critical Reviewsin Environmental Science and Technology 30, 449 e505.

Haroun, M., Idris, A., 2009. Treatment of textile wastewater with an anaerobicuidized bed reactor. Desalination 237, 357 e366.

Hees, U., Freche, M., Kluge, M., Provost, J., Weiser, J., 2002. Developments in textileink jet printing with pigment inks. In: Image Science and Technology NIP 18Digital Printing Conference, San Diego, pp. 242 e245.

Hsu, T.C., Chiang, C.S., 1997. Activated sludge treatment of dispersed dyefactory wastewater. Journal of Environmental Science and Health 32,1921e1932.

Huang, H., Schwab, K., Jacangelo, J.G., 2009. Pretreatment for low pressuremembranes in water treatment: a review. Environmental Science and Tech-nology 43, 3011e3019.

Husain, Q., 2006. Potential applications of the oxidoreductive enzymes in thedecolorization and detoxication of textile and other synthetic dyes frompolluted water: a review. Critical Reviews in Biotechnology 26, 201 e221.

Ince, N.H., Tezcanli, G., 2001. Reactive dyestuff degradation by combined sonolysisand ozanation. Dyes and Pigments 49, 145e153.

Islam, M.M., Halim, M.A., Islam, M.S., Islam, M.S., Biswas, C.K., 2009. Analysis theplant nutrients and organic matter in textile sludge in Gazipur, Bangladesh.

Journal of Environmental Science and Technology 2 (1), 63e67.ISPCH, 1995. Industrial Safety and Pollution Control Handbook. 2nd reprint, second

ed. A joint publication of National Safety Council and Associate (Data)Publishers Pvt. Ltd., Hyderabad, pp. 451 e466.

Jadhav, J.P., Parshetti, G.K., Kalme, S .D., Govindwar, S.P., 2007. Decolourization of azodye methyl red by Saccharomyces cerevisiae MTCC 463. Chemosphere 68,394e400.

Jekel, M., 1997. Wastewater Treatment in the Textile Industry. In: Treatment of Wastewaters from Textile Processing. TU Berlin. Schriftenreihe BiologischeAbwasserreiigung des Sfb 193, Berlin, pp. 15e24.

Jiang, J.Q., Graham, N.J.D., 1998. Pre-polymerised inorganic coagulants and phos-phorus removal by coagulation-a review. Water SA 24, 237e244.

Joo, D.J., Shin, W.S., Choi, J.H., Choi, S.J., Kim, M.C., Han, M.H., Ha, T.W., Kim, Y.H.,2007. Decolorization of reactive dyes using inorganic coagulants and syntheticpolymer. Dyes and Pigments 73, 59e64.

Joseph, E.I., 2007. Wastewater treatment in the textile industry. Pakistan Textile Journal, 60 e66.

Joshi, V.A., Nanoti, M.V., 1999. Laboratory studies on Tarota as coagulant aid in watertreatment. Indian Journal of Environmental Protection 19 (6), 451 e455.

Kang, S.F., Chen, M.C., 1997. Coagulation of textile secondary ef uents w