Textile Industry Wastewater: Environmental and Health Hazards and Treatment Approaches

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47
3Textile Industry
Wastewater
Environmental and Health
Hazards and Treatment
Approaches
Sujata Mani and Ram Naresh Bharagava
CONTENTS
3.1 Introduction ....................................................................................................48
3.2 Types and Classication of Dyes ....................................................................50
3.2.1 Classication Based on the Source of Materials ................................ 50
3.2.1.1 Natural Dyes ........................................................................ 51
3.2.1.2 Synthetic Dyes ..................................................................... 51
3.2.2 Classication Based on the Chemical Composition of the Dye ......... 52
3.2.3 Classication Based on the Nuclear Structure of Dyes ...................... 52
3.2.3.1 Cationic Dyes ....................................................................... 53
3.2.3.2 Anionic Dyes ....................................................................... 53
3.3 Sources of Dye Contamination in the Environment ....................................... 53
3.4 Environmental Pollution and Health Hazards From Dye Contamination ...... 54
3.5 Bioremediation Approaches for Dyes Contaminated Environments ............. 55
3.5.1 Physical Treatment Methods ...............................................................55
3.5.1.1 Adsorption............................................................................55
3.5.1.2 Ion Exchange ........................................................................ 55
3.5.1.3 Membrane Filtration ............................................................ 56
3.5.2 Chemical Treatment Methods ............................................................56
3.5.2.1 Chemical Precipitation .........................................................56
3.5.2.2 Coagulation and Flocculation .............................................. 56
3.5.2.3 Chemical Oxidation ............................................................. 57
3.5.2.4 Ozonation ............................................................................. 57
3.5.3 Biological Treatment Methods ............................................................57
3.5.3.1 Aerobic Process ...................................................................58
3.5.3.2 Anaerobic Process ............................................................... 59
3.6 Adoption of Best Practices .............................................................................62
3.6.1 Reducing and Recycling Water ...........................................................62
3.6.2 Awareness to Go Green ...................................................................... 62
3.6.3 Air Dyeing Technology ...................................................................... 62

48 Recent Advances in Environmental Management
3.1 INTRODUCTION
Growing environmental pollution resulting from rapid industrial development is one
of the challenges faced by the modern world. Overpopulation and environmental
pollution are two rate-limiting factors for industrialization. Many South Asian
countries, including India, are experiencing severe environmental problems due
to their rapid industrialization. This phenomenon is very common where water-
polluting industries such as dye manufacturing, textile dyeing, leather tanning,
paper and pulp processing, and sugar manufacturing thrive as clusters. The colored
efuent discharged by these industries leads to the serious pollution of surface water,
groundwater, and soil (Chowdhary etal. 2018, 2017; Chandra etal. 2008; Saxena
etal. 2017). Among the above mentioned industries, dye manufacturing industries
and textile industries are the largest source of dye-containing efuent for which the
discharge generates serious environmental threats (Mani and Bharagava 2016, 2017).
Generally, such industrial units are functioning in small or medium scales with high
employment generation and foreign exchange potential. But, the pollution control
mechanisms among these units are extremely weak.
The textile dyeing industry has been in existence for over 4000 years. The dyeing
of cloth and the fermentation of sugar to produce alcohol are the two specialized areas
that date back to antiquity. Fabrics dyed with indigo and madder have been found in
the tombs of predynastic Egypt. These and a few matters extracted from insects and
tropical woods formed the only sources of dyes until the middle of the last century. In
ancient times, dyes were obtained from natural sources and not everyone could possess
colored fabrics. The rst synthetic dye was made in 1856 by William E. Perkin, which
he named “mauveine.” He obtained this dye by oxidation of impure aniline (Sujata
and Bharagava 2016; Zainith etal. 2016). A few years later, the structures of natural
dyes, indigo and alizarin were determined, and these compounds were prepared by
synthesis. However, the majority of development in chemistry of synthetic dyes was
the discovery of diazotization and azo coupling. Since 1856, tens of thousands of dyes
have been synthesized. Well over one thousand dyes are commercially available now.
Dye is an integral to imparting color to materials. Textile industries consume a major
share of dyes in India. Further, the textile industry of India also contributes nearly
14% of the total industrial production of the country.
Synthetic dyes are used in many spheres of our everyday life, and their applications
are continuously growing in various industries such as textile, leather, cosmetics,
paper, paint, and food (Saxena and Bharagava 2017). Approximately 10,000 different
dyes and pigments are used industrially, and over 0.7 million tons of synthetic dyes are
produced annually (Zollinger 1987). Among various applications of synthetic dyes,
about 3 × 105 ton of different dyestuffs are used per year for textile dyeing operations,
thus making dye houses a major consumer of synthetic dyes and, consequently, the
3.7 Challenges and Future Prospects ....................................................................63
3.8 Conclusions ..................................................................................................... 63
Acknowledgments ....................................................................................................64
References ................................................................................................................ 64

49Textile Industry Wastewater
major cause of water pollution. Most of the textile industries do not treat their dark
color-containing efuent prior to discharging. It ends up in nearby water bodies,
rendering these water ecosystems to a ood of problems. The photosynthetic activity
of aquatic plants is distressed due to reduction of sunlight penetration because of the
formation of a thin lm of discharged dyes over the surface of the receiving water
body. Other complications involve the induction of toxicity to aquatic life due to the
presence of aromatics, heavy metals, and chloride (Bharagava and Mishra 2018; Gill
etal. 2002; Liu etal. 2004; Yadav etal. 2017). If the discharged efuent happens
on terrestrial land or agricultural lands or nds its way to land, it constrains the
process of seed germination (Bharagava etal. 2017a,b; Kalyani etal. 2008; Mishra
and Bharagava 2016).
In recent years, interest in environmental control of dyes has increased due to
their toxic and genotoxic effects on living organisms as these dyes contain known
carcinogens, such as benzidine and other aromatic compounds (Gautam et al.
2017). Currently, various chemical and physical treatment methods, including
adsorption, chemical precipitation and occulation, oxidation, electrolysis, reduction,
electrochemical treatment, and ion pair exchange are used to remove this dye from the
sewage. These methods are attractive because of their efciency, but are complicated
and expensive. As a viable alternative, biological processes have received increasing
attention due to their cost, effectiveness, ability to produce less sludge, and harmless
nature on the environment as these processes can convert or degrade the pollutants
into water, carbon dioxide, and various salts of inorganic nature.
A wide variety of microorganisms are able to degrade a wide range of dyes,
including bacteria (single and mixed culture), fungi, and algae; they can biologically
decolorize and even completely mineralize many dyes under certain conditions (pH,
temperature, nutrient components), and the medium condition can inuence this
process. Bacterial strains such as Pseudomonas putida, Agrobacterium radiobacter,
Bacillus sp., Sphingomonas paucimobilis, and Aeromonas hydrophila; fungi such as
Mycobacterium avium, Mycobacterium intracellular, Mycobacterium scrofulaceum,
Mycobacterium marinum, and Mycobacterium chelonae; yeast; and actinomycetes
have been reported to be effective for the decolorization of dye and thus can be
applied as a bioremediation tools. Besides the advantages, biological methods also
have certain limitations in their application and also suffer due to toxicity of dyestuff
(Daneshvar etal. 2007).
From bestowing colors to varied materials to curing medical glitches, dyes no doubt
have played and contributed their valuable aspects. Yet they are deemed biohazardous
and potent when found in places that possess a threat to our viability as humans and
to our ecosystems as a whole. Here we are in the twenty-rst century manipulating
microorganisms to x what we have synthesized into this world. Though, it is not a
recent trend to manipulate microbes to our utmost importance; we have been doing
it since ancient times: the Egyptians used yeast to make bread. Either making a loaf
of bread or cleaning tainted ecosystems from biohazardous dye like crystal violet,
microbes have found a way to x our problem. Hence, the enzymatic degradation of
various dyes by bacteria, fungi, yeast, and actinomycetes at various environmental
conditions has been duly emphasized.

50 Recent Advances in Environmental Management
3.2 TYPES AND CLASSIFICATION OF DYES
There are several ways for classication of dyes. Dye is a complex of unsaturated
aromatic compounds fullling characteristics like intense color, solubility,
substantiveness, and fastness. Each class of dye has a very unique chemistry, structure,
and particular way of bonding. Some dyes react chemically with the substrates to
form strong bonds in the process, while physical forces can hold others. Some of the
prominent ways of classication are given here.
3.2.1 ClassifiCatioN based oN the sourCe of Materials
A very common classication of the dyestuff is based on the source from which it
is made. Most dyes are organic molecules and are complex in nature. The synthesis
of organic dyes began with azulene synthesis; before that, colors were made from
pigments. As a result, dyes can be classied as natural dyes and synthetic dyes,
according to their sources of origin (Figure 3.1).
Dyes
From
insects
From
minerals
Water
soluble
Water in-
soluble
In-situ color
formation
Azoic
colors
Vat dyes
Direct dyes
Iron oxideCochineal
Plants
Buff Basic dyes Disperse
dyes
Sulphur
dyes
Acid dyes
Reactive dyes
Metal
complex dyes
Solubilised
vat dyes
Lac
Grass weeds
Leaves
Stem
Roots
Flowers
Seeds Tyrian
purple
From
vegetable
matter
Synthetic
dyes
Natural
dyes
FIGURE 3.1 Classication of dyes based on the source of materials.

51Textile Industry Wastewater
3.2.1.1 Natural Dyes
For thousands of years, coloring materials have been used and modied in cloth,
food, pottery, leather, and housing. Painting and dyeing are the two old ways of
coloring materials in which pigments obtained from colored rocks and minerals were
used in painting, and dyes obtained from animals and plants were used for dyeing.
Some of the most common dyes obtained from natural sources have been termed as
natural dyes. The color index used for classication and the naming system of dyes
is according to the pattern
Natural + base color + number
This classication is based on the dye’s source and color but doesn’t contain any
chemical information or information regarding mechanism by which staining occurs.
Natural dyes are usually negatively charged, that is, the colored part of the molecule
is frequently the anion, but positively charged natural dyes do occur, but very rarely.
Dyes that have been used since ancient times include Kermes (natural red 3), which is
also mentioned in the Bible book of Exodus, carmine (natural red 4), and lac (natural
red 25). These three dyes are all obtained from insects of the genus Coccus.
3.2.1.2 Synthetic Dyes
Man-made dyes derived from organic and inorganic compounds are commonly
known as synthetic dyes, which are generally prepared from petroleum byproducts
or earth minerals types of synthetic resources. “Mauveine” was the rst man-made
organic aniline dye, which was coincidently discovered as the result of failed attempt
of the synthesis of quinine by William Henry Perkin in 1856. Since then, thousands of
synthetic dyes, such as fuchsine, safranin, and indulines, have been prepared (Hunger
2003; Zollinger 2003). Synthetic dyes have been divided into many other classes:
Acid dyes: These dyes are anionic, water-soluble dyes, which are applied to silk,
nylon, wool, or modied acrylic bers through neutral to acid dye baths.
Dyes are attached to the bers by salt formation between the anionic groups
of the dyes and cationic groups of the bers. These dyes are usually not
considered for cellulosic bers. Most types of synthetic food colors generally
fall in this category of dyes.
Basic dyes: These types of dyes are cationic, water-soluble dyes that are mainly
applied on acrylic bers, but sometimes are used for wool and silk and are
also used in the coloration of paper. For uptake of these dyes by bers, acetic
acid is generally added to the dye baths.
Direct or substantive dyeing: These types of dyes are usually carried out in
either a neutral or slightly alkaline dye bath or at near-boiling point with
the adding up of either NaCl (sodium chloride), Na2SO4 (sodium sulfate),
or Na2CO3 (sodium carbonate). These dyes are generally used for dyeing
wool, paper, cotton, silk, and nylon and are also used as a pH indicators and
biological stains.
Mordant dyes: These types of dyes improves stability of dye in opposition to
water, light, and perspiration with the help of a sardonic. The selection of

52 Recent Advances in Environmental Management
mordant is very important since selecting different mordants can change the
nal color on fabrics. Since most of the natural dyes are mordant dyes, a large
amount of literature is available which describes the dyeing technologies,
but some are synthetic dyes also which are very helpful in providing black
and navy shades to wools. It is most important to keep in the view that most
of the mordant dyes fall in the category of heavy metals, which are very
hazardous to health, and thus extreme care should be taken during their
applications (Sujata and Bharagava 2016).
Vat dyes: Vat dyes are insoluble in water and thus, are incapable of dyeing
fabrics directly. The reduction in alkaline liquor produces a water-soluble
alkali metal salt of the dye, which has an afnity for the textile ber, whereas
successive oxidation helps in reforming the original insoluble dye. The color
of denim is due to indigo, which is an original vat dye.
Reactive dyes: This dye utilizes the chromophoric group of a substituent, which
is capable of directly reacting with the substrate of bers. Reactive dyes have
covalent bonds, which attract natural bers to them making them the most
permanent dyes, and they have become the best choice for dyeing cotton and
other cellulose bers at home. Most commonly used reactive dyes are known
as “Cold” reactive dyes such as Procion MX, Cibacron F, and Drimarene K
since these can be used and applied very easily at room temperature.
Disperse dyes: These dyes are water insoluble and were originally developed
for dyeing cellulose acetate. This dye is sold either as a paste or dry-sprayed
or as a powder which is prepared by grinding dyes in the presence of a
disperse agent. This very ne particle size of dye gives a large surface area
that aids dissolution to allow uptake by the ber. Disperse dyes are mainly
used for dyeing polyesters but can also be used for dyeing nylon, cellulose
triacetate, or acrylic bers (Sujata and Bharagava 2016).
Azoic dyeing: Azo dye is produced directly onto or within the ber by treating
bers with combined diazoic and coupling components in this technique.
This technique of dyeing bers is unique since the nal color is controlled
by the choice of diazoic and coupling components. But, this method is not
applied on dyeing cottons due to the toxic nature of the chemicals used.
Sulfur dyes: These dyes are used for dyeing cotton with dark colors. Dyeing is
effected by heating the fabric in solution of an organic compound, which
reacts with the sulde source to form dark colors that adhere to the fabrics.
3.2.2 ClassifiCatioN based oN the CheMiCal CoMPositioN of the dye
According to a system of chemical classication, dyes can be divided according to
the nature of their chromophore and to the industries applied as demonstrated in
Table 3.1.
3.2.3 ClassifiCatioN based oN the NuClear struCture of dyes
This type of classication of dyes is not very popular but dyes can be categorized as
cationic and anionic on this basis.

53Textile Industry Wastewater
3.2.3.1 Cationic Dyes
Cationic dyes were the rst synthetic dyes to be taken out from derivatives of coal
tar. These dyes are used in printing and for preparing leather, paper, straw, wool,
etc. Recently, these also have been used with some ready-made bers like acrylics.
Cationic or basic dyes were originally used for coloring wool, silk, linen, hemp, etc.
without the use of any mordant, but with mordant such as tannic acid, they were
used to color cotton and rayon. They can also be used on nylon and polyesters. An
example of cationic dyes is basic brown 1, which is readily protonated under the pH
2 to 5 conditions of dyeing.
3.2.3.2 Anionic Dyes
These dyes are highly water-soluble and applied to textiles at a very low pH. These
are suitable for coloring protein bers such as wool, silk, and nylon. Acid dyes are
complex in structure with large aromatic molecules, a sulfonyl group and an amino
group to enhance solubility. Acid dyes have three main groups: anthraquinone dye,
diazo dyes, and triarylmethanes dyes.
3.3 SOURCES OF DYE CONTAMINATION IN THE ENVIRONMENT
The textile industries are one of the major sources of dye pollution in the environment
worldwide. More than 1,000,000 synthetic dyes are generated worldwide with an
annual production of approximately 7 × 105 metric tons (Chen etal. 2003). These
dyes are widely used in textile, paper, pharmaceutical, food, and cosmetics industries
(Chandra and Bharagava 2013), but textile industries are the largest consumers of the
dyes (Franciscon etal. 2009). The World Bank estimates that approximately 20%
of global industrial water pollution comes from wastewater treatment and dyeing
of textiles. The textile industries are second to agriculture practices as the biggest
polluting agents for fresh water bodies globally. Dyeing, rinsing, and treating textiles
TABLE 3.1
Classification of Dyes Based on Chromophore Groups and Industrial
Applications
S.No. Chromophoric Group Industries
1. Acridine dyes, derivatives of acridine >C=N– and >C=C,
anthraquinone dyes, arylmethane dyes, diarylmethane dyes,
triarylmethane dyes, triphenylmethane dyes, azo dyes based on
–N=N– azo structure, cyanine dyes, nitro dyes, nitroso dyes, etc.
Textiles
2. Phthalocyanine dyes, derivatives of phthalocyanine >C=NPaper
3. Azin dyes, eurhodin dyes, safranin dyes, derivatives of safranin
dyes –C–N=C–, –C–N–C
Leather and textile
4. Quinone-imine dyes, derivatives of quinine Wool and paper
5. Xanthene dyes, derived from xanthene –O–C6H4–O Cotton, silk, and wool
6. Indophenol dyes and its derivatives >C=N– and >C=OColor photography
7. Oxazin dyes, derivatives –C–N=C, =C–O–C=Calico printing

54 Recent Advances in Environmental Management
all use large volumes of fresh water. Millions of gallons of wastewater discharged
from textile industries contain many harmful chemicals such as formaldehyde
(HCHO), chlorine, and toxic heavy metals such as lead and mercury. These chemicals
cause both environmental damage and human disease.
Textile industries also discharge with wastewater an array of hazardous organic and
inorganic compounds/substances such as aromatic amines (benzidine and toluidine),
heavy metals, ammonia, alkali salts, and toxic solids, as well as large amount of
pigments and chlorine, a known carcinogen, which causes serious environmental
and health problems (Kumari etal. 2016). The untreated dyes cause chemical and
biological changes in aquatic resources, which threaten sh and other aquatic species.
The presence of these compounds makes water unt for other purposes also. The
enormous amount of water required by textile production competes with the growing
daily water requirements of approximately a half billion people that live in drought-
prone regions of the world. By 2025, the number of inhabitants of drought-prone
areas is projected to increase to almost one-third of the world’s population. If global
consumption of fresh water continues to double every 20 years, the polluted waters
resulting from textile production will pose a greater threat to human lives (Mani and
Bharagava 2016).
3.4 ENVIRONMENTAL POLLUTION AND HEALTH
HAZARDS FROM DYE CONTAMINATION
Textile mills and industries discharge millions of gallons of colorful toxic hazardous
wastes containing organic chemicals into the environment. The presence of chemicals
such as sulfur, naphthol, vat dyes, acetic acid, soaps, nitrates, chromium compounds,
and heavy metals such as copper, lead, arsenic, cadmium, mercury, nickel, and cobalt
collectively makes the wastewater highly toxic with high temperature and pH, which
makes it extremely damaging. The colors and oil present in wastewater increases
its turbidity and give a bad appearance and foul smell to the water (Parshetti etal.
2011). This efuent when discharged to fresh water prevents sunlight penetration
necessary for the process of photosynthesis for aquatic ora and fauna (Bharagava
and Chandra 2010a,b, 2008; Chandra etal. 2011; 2012). It also interferes with the
oxygen transfer mechanism at the air-water interface, which is the most serious effect
of the textile wastewater and thus hinders the self-purication process of water. When
agricultural elds are watered with these efuents, the pores of the soil are clogged,
which results in the loss of soil productivity (Chandra etal. 2009). It also hardens the
soil texture and thus prevents root penetration (Chandra etal. 2009). The wastewater,
when own in drains, corrodes and varnishes the sewage pipes, whereas in rivers, it
affects the drinking water quality in hand pumps making the water unt for human
consumption.
Textile wastewater has become a signicant causative agent of environmental
degradation and human illness. The major concern in the treatment of textile
wastewater is the organic chemicals present as they may react with many disinfectants.
Chemicals evaporating from these efuents into the air are absorbed through our
skin, which shows up as allergic reactions and may also cause harm to children even
before their birth.

55Textile Industry Wastewater
3.5 BIOREMEDIATION APPROACHES FOR DYES
CONTAMINATED ENVIRONMENTS
Due to the existence of dyes and other chemicals, the extremely polluted textile
wastewater from cotton dyeing textile industries has high color intensity, high BOD,
COD, and total solids. The photosynthetic activity and development of aquatic
organisms are directly hindered by the presence of color in the wastewater, resulting
in the imbalance in the environment. The wastewater ooded in river water used for
drinking and other used processes by human beings should be colorless and free from
toxic compounds. Therefore, textile wastewater should go through many treatment
processes including physical, chemical, and biological methods before discharging
into any fresh water body, and some green approaches can also be incorporated.
3.5.1 PhysiCal treatMeNt Methods
The methods of removal of toxic compounds and substances present in textile
wastewater from ordinarily taking place by forces such as electrical attraction,
gravity, Van der Waal forces, or by physical barriers are known as physical treatment
methods. The chemical structure of the pollutant present in wastewater is not
hindered by these methods or techniques but only some changes in the physical state
or coagulation of some dispersed substances can take place. Some of these methods
have been discussed here.
3. 5.1.1 Adsorption
The most commonly equilibrium separation physico-chemical method used in the
potential treatment of wastewater is the adsorption method. For the removal of
pollutants, the adsorption technique has gained more favor recently due to its high
efciency compared with other methods. Activated carbon, silicon polymers, and
kaolin are the most commonly used adsorbents and have the capability of adsorbing
different dyes with high adsorption capacity (Jadhav and Srivastava 2013). This method
is based on two phases, where ions or molecules present in one phase (either gas or
liquid) tend to accumulate and concentrate on the surface of another phase (usually
solids). The process of physical adsorption takes place when a weak interspecies bond
exists between the adsorbate and adsorbent, but chemical adsorption occurs when
strong interspecies bonds exists due to exchange of electrons (Bizuneh 2012). This
treatment method is modernized by development of several new adsorbents such as
eggshells, sugarcane bagasse, hen feathers, almond peel, etc. (Ahmad and Mondal
2009; Chakraborty etal. 2012a,b,c,d; Chowdhary etal. 2013a,b,c).
3.5.1.2 Ion Exchange
Ions are replaced between two electrolytes or linking an electrolyte solution and
a complex in the ion exchange method. Generally, the ion-exchange technique
is applied as a technique of purication, separation, and decontamination of ion
and aqueous solution through some typical ion exchangers such as resins, zeolites,
montmorillonite, and clay and soil humus. The ion exchangers used are unable to
hold a wide range of dyes and therefore have not been widely used in the treatment

56 Recent Advances in Environmental Management
of textile wastewater efuents. Thus, they are only used in the removal of undesirable
cationic (basic dyes) or anionic (acid, direct, and reactive dyes) dyes from wastewater.
There are some amphoteric exchangers, which are able to exchange both cations and
anions simultaneously and are efciently used in mixed beds containing a mixture
of cation and anion exchange resins. Meanwhile, the advantage of the ion exchange
treatment method is the recovery of adsorbent, the retrieval of solvent after use, and
the effective removal of soluble dyes (Mani and Bharagava 2016).
3.5.1.3 Membrane Filtration
The membrane ltration method has emerged as a feasible alternative method used
for the removal of dyes from efuent effectively and has proven to be cost effective
and to consume less water (Koyuncu 2002). Thus, this method simultaneously
reduces the coloration and BOD or COD of wastewaters and has special features
like resistance to temperature and adverse chemical effects. The advantage of the
membrane ltration method is its quick processing with low requirements and its
drench can be reused; however its high cost, clogging possibility, and replacement
of membrane affects its applicability (Bizuneh 2012). Further, this method has been
divided into ultraltration, nanoltration, microltration, and reverse osmosis.
3.5.2 CheMiCal treatMeNt Methods
Chemicals play a very important role in the process of accelerating the disinfection of
wastewater and its treatment. These chemical processes including chemical reactions
are known as chemical unit processes, which are used alongside with physical and
biological processes. These include various processes such as chemical precipitation,
coagulation and occulation, chemical oxidation, and Fenton oxidation, which are
applied during wastewater treatment.
3.5.2.1 Chemical Precipitation
The most common method used for the treatment of textile efuent for removing
dissolved toxic metals is chemical precipitation. In this process, the dissolved metals
in wastewater are converted into solid particle forms by adding a precipitation
reagent, which triggers a chemical reaction causing dissolved metals to form solid
particles, which are further removed through a ltration method. The probability of
the method depends on the kind of metals present, their concentration, and the kind
of reagents used. In hydroxide precipitation, sodium or calcium hydroxides are used
as reagents to convert dissolved metals into solid particles, but it is very difcult to
create hydroxides since wastewater consists of mixed metals.
3.5.2.2 Coagulation and Flocculation
These processes are generally used for removing organic materials by partly
removing BOD, COD, TDS, and color from efuent (Aguilar et al. 2005). This
method basically depends on the law of addition of coagulants, which associates with
pollutants, forming coagulate or ock and later precipitate, which is removed either
by otation, settling, ltration, or other physical technology to form sludge, which is
further treated for reducing its toxicity (Golob and Ojstrsek 2005; Mishra and Bajpai

57Textile Industry Wastewater
2005). The high cost for treating sludge and disposal restrictions into the environment
are the major disadvantages of this process (Bizuneh 2012).
3.5.2.3 Chemical Oxidation
Chemical oxidation is totally a chemical operation based on strict chemical reactions.
Chemical treatment depends on the chemical interactions of the desired contaminants
to be removed and applied chemicals, which either separate it from wastewater or
destruct it or neutralize its harmful effects. Chemical treatment processes can also
be applied alone or with physical treatment methods (Ranganathan etal. 2007). In
textile wastewater, chemical operations either oxidize the pigments in the dyeing and
printing wastewater or bleach it. From various chemical oxidation processes, Fenton
oxidation and ozone oxidation are often used for the treatment of wastewater.
Oxidizing agents such as O3 and H2O2 are used in chemical oxidation methods,
which form strong non-selective hydroxyl radicals at high pH. These formed radicals
effectively break the conjugated double bonds of the chromophores group of dyes
as well as its functional groups (complex aromatic rings), which ultimately reduces
the color of the wastewaters. These oxidizing agents have a low degradation rate due
to less hydroxyl radical production as compared with advanced oxidation processes
(AOPs) (Asgher etal. 2009). The main advantage of using ozone in ozonation process
is its gaseous form, which can be used as is and thus does not raise the volume of
wastewater and neither produces sludges. Despite of this, the disadvantage of ozone
is the formation of toxic byproducts from biodegradable dyes in wastewater.
3.5.2.4 Ozonation
The most effective and fast treatment process, which decolorizes textile wastewater
and breaks double bonds of most of the dyes, is the ozonation process. It oxidizes a
considerable amount of COD and inhibits or destroys the foaming nature of residual
surfactants. It also increases the biodegradability of the wastewaters containing a
high fraction of non-biodegradable and toxic compounds of the efuents with a high
fraction of non-biodegradable and toxic compounds also increases by converting it
into effortlessly biodegradable intermediates. The major advantage of this process is
that it neither produces sludge nor increases the efuent volume. Sodium hypochlorite
has been widely used as an oxidizing agent that initiates and increases azo bond
cleavage, but the drawback of this agent is the release of carcinogenic amines and
other toxic molecules, thus restricting its use.
In this method, ozone is used as a strong and effective oxidizing agent because
of its high reactivity, which effectively degrades phenols, chlorinated hydrocarbons,
aromatic hydrocarbons, and pesticides (Lin and Lin 1993). The main negative aspect
of this process is ozone’s short half-life as it decomposes in 20 min, thus continuous
O3 supply is required, which is very expensive (Gogate and Pandit 2004; Gosavi and
Sharma 2014).
3.5.3 biologiCal treatMeNt Methods
Earlier, adsorption of dyes on the bacterial cells biomass was considered as the
technique of removal of color, which was similar to other physical mechanisms. But,

58 Recent Advances in Environmental Management
this method was not suitable for long-term treatment of color removal since, with time,
the adsorbed amount of dyes on the bacterial biomass could become saturated. This
association between the dye and the bacterial cells has become the rst step in the
reduction of azo dyes but this method is a destructive treatment technology. Initially,
two stages are involved in the degradation of azo dyes. The reductive cleavage of
the azo bond (–N=N–) of dyes are involved in the rst stage, which results in the
formation of colorless aromatic amines (potentially hazardous), which, in the second
stage, are degraded under aerobic conditions.
In anaerobic conditions, the azo dyes are reduced with the help of azo reductase
enzymes. This involves transfer of four electrons, which are carried through two
stages at azo linkage and at each stage; two electrons are transferred to azo dye as a
nal electron acceptor resulting in the decolorization of dye (Figure 3.2). Further, the
resulting metabolites are degraded aerobically or anaerobically (Chang etal. 2000,
2004). The azo bond reduction activity is usually inhibited in the presence of oxygen
since it may dominate the NADH utilization, thus hindering the electron transfer to
azo bonds from NADH (Chang etal. 2004).
3.5.3.1 Aerobic Process
The stabilization of textile wastes by decomposing them into harmless inorganic
solids is done by involving bacteria during treatment. Bacteria can be divided into
aerobic, anaerobic, and facultative bacteria on the source of the oxygen requirements
by these different bacteria. An aerobic treatment method puries the water by
decomposing the wastes and reducing the unpleasant odors with the help of aerobic
and facultative bacteria. The aerobic treatment process is performed by an activated
sludge process and biolms process.
Aerobic
Anaerobic
Azo dyes
Aromatic amines
NN
NN
4[H]
NH2
O2
NH2NH2
NH2
RR
R
R
R
R
Autoxidation
CO2 + H2O + NO3
–
R
+
R
FIGURE 3.2 Schematic representation of decolorization and mineralization of azo dyes
under aerobic-anaerobic conditions. (Adopted from Dafale, N. et al. 2010. Bioresource
Technology 101: 476 –484.)

59Textile Industry Wastewater
3.5.3.1.1 Activated Sludge Process
Activated sludge process (ASP) is the frequently used biological treatment process of
textile wastewater at efuent treatment plant/common efuent treatment plant (ETP/
CETP) in India. It is a kind of colony mainly comprising microorganisms, which have
strong decomposition and adsorption rates of organic compounds and thus are called
“activated sludge.” It is the most normally applied aerobic wastewater treatment method
that removes the dissolved organic solids and also removes the settleable and non-
settleable suspended solids. Microorganisms, especially bacteria, are used in the ASP
methods, which produce a high quality of wastewater by feeding on the organic pollutants
present in the wastewaters. It is an effective and higher removal efciency method, which
works on the principle of microorganisms that form a colony by growing and clumping
together, forming and settling down to the bottom of the tank forming an organic material
and suspended solids free of clear liquid. Oxidation ditch and sequencing batch reactor
(SBR) process are the most commonly used activated sludge methods.
3.5.3.1.2 Biofilm
A biolm is an efuent biological treatment process that involves microorganisms
attaching at the surface of the xed object, forming a lm and purifying the owing
wastewater just through the contact. Mainly, the biolm processes are biological
contact oxidation, rotating biological contractors and biological uidized bed.
3.5.3.2 Anaerobic Process
Three different types of mechanisms are described by researchers for the anaerobic
bio-reduction of azo dyes: a) direct enzymatic reduction, b) indirect/mediated
reduction, and c) chemical reduction (organic and inorganic compounds). A direct
and mediated/indirect enzymatic reaction is catalyzed by electron carriers or through
biologically regenerated enzyme cofactors. However, chemical reduction of azo
dye results from chemical reactions with biogenic reductants like suldes. These
azo dye reduction mechanisms are accelerated by the addition of redox-mediating
compounds, for example, anthraquinone-sulfonate and anthraquinone-disulfonate
(Cerventes 2002; Guo et al. 2006; Van der Zee and Villaverde 2005). The anaerobic
azo dye reduction mechanism by bacteria is shown in Figure 3.3.
3.5.3.2.1 Direct Enzymatic Dye Decolorization
Various reductive enzymes such as azo reductase, NADH-DCIP reductase and MG
reductase and oxidative enzymes such as lignin peroxidase and laccase facilitate the
ED ED
Azo dye
Direct enzymatic Indirect (mediated) biological Direct chemical
Azo dye Azo dye
Aromatic
amines
Aromatic
amines
Aromatic
amines
BB
EDox EDox
RMox H2S
‘S0’
RMred
FIGURE 3.3 Mechanisms of azo dye reduction by bacteria. (Adopted from Van der Zee, F.
etal. 2002. Advances in Environmental Science and Technology 37: 402–408.)

60 Recent Advances in Environmental Management
bacterial decolorization of dyes (Kalme etal. 2007; Kalyani etal. 2009; Parshetti
etal. 2006).
3.5.3.2.1.1 Reductive Enzymes
• Azo reductase: This is avoprotein located on either the intracellular or
extracellular site of the bacterial cell membrane. For the reduction of an azo
bond, the azo reductases require NADH, NADPH, or FADH as an electron
donor, but toxic amines are generated after reduction of an azo dye (Russ
etal. 2000) (Figure 3.4). The azo reductases substrate particularity depends
on the functional group present near the azo bond. Pseudomonas sp. KF46
has oxygen-sensitive orange II azo reductase, which shows high specicity
toward the carboxy group substituted sulfophenyl azo dyes (Zimmerman
etal. 1982). Earlier, several researchers have reported the induction of azo
reductase during azo dye decolorization under static conditions (Dawkar
etal. 2009; Dhanve etal. 2008).
• NADH-DCIP reductase: This belongs to the bacterial mixed-function
oxidase system and takes part in xenobiotic compounds detoxication.
These reductase enzymes reduce DCIP, which is blue in oxidized form and
colorless after reduction, using NADH as an electron donor.
• MG reductase: The noteworthy induction of non-specic reductase in the
biodegradation of malachite green dye is termed MG reductase. This enzyme
reduces malachite green dye into leuco-malachite green using NADH as an
electron donor (Parshetti etal. 2006).
Colored solution
containing dye
Colorless solution
containing amines
XX
NNH2
NH2
Chromophor
e
Redox
mediatorox
Redox
mediatorred
N
XX
Azoreductase
Cell
NADH NAD+
Carbon
complexes
Oxidation
products
Dehydrogenase
(enzyme liberating e–)
FIGURE 3.4 Mechanism for reduction of azo dyes by azo reductase. (Adopted from Keck,
A. etal. 1997. Applied Environmental Microbiology 63(9): 3684–90.)

61Textile Industry Wastewater
3.5.3.2.1.2 Oxidative Enzymes
• Lignin peroxidase (LiP): Lignin peroxidase enzyme belongs to the family
of oxidoreductases. LiP catalyzes oxidation in the side chains of lignin and
related compounds by one-electron abstraction to form reactive radicals
(Kersten etal. 1990; Tien and Kirk 1983). Several decolorized sulfonated
azo dyes were efciently decolorized by puried LiP from Brevibacillus
laterosporous MTCC 2298 and Acinetobacter calcoaceticus NCIM 2890
(Ghodake etal. 2009b; Gomare and Govindwar 2009).
• Laccase: These are Cu-containing enzymes, which catalyze oxidation
of electron-rich substrates. It catalyzes oxidation of substituted phenolic
and non-phenolic compounds in the presence of oxygen as an electron
donor (Sharma etal. 2007). Prokaryotic laccase rst was reported from
rhizospheric bacterium Azospirillum lipoferum and from melanogenic
marine bacterium Marinomonas mediterranea, producing two different
polyphenol oxidases (PPO) (Solano et al. 2004). Laccase-like activity
has also been reported in the CopA protein from Pseudomonas syringae
and Pedomicrobium sp. (Ridge etal. 2007). Azo dyes are decolorized by
laccase through a highly non-specic free-radical mechanism and thus
avoid toxic aromatic amines formation (Chivukula and Renganathan 1995).
The puried laccase from Pseudomonas desmolyticum NCIM 2112 showed
100% decolorization of direct blue 6, green HE4B and red HE7B dyes
(Kalme etal. 2009).
3.5.3.2.2 Indirect/Mediated Biological Dye Decolorization
Azo dyes are unable to cross the cell membrane because of their high molecular
weight, and thus their reduction mechanism is independent from the transport into
the cell membrane (Levine 1991). Many researchers have reported the role of redox
mediators using bacteria under anaerobic conditions in the reduction of azo bonds
(Keck etal. 1997; Dos Santos etal. 2007; Van der Zee etal. 2001). The reduction of
mordant yellow 10 dye using anaerobic granular sludge was signicantly enhanced
in a small amount of riboavin (Field and Brady 2003). The acid orange 7 azo dye
decolorization rate was increased by 1-amino-2-naphthol by mediating the transfer
of reducing equivalents (Mendez-Paz etal. 2005). The decolorization rate of many
azo dyes can also be increased by the addition of some synthetic electron carriers
(Van der Zee etal. 2002).
During the aerobic degradation of xenobiotic compounds, Keck etal. (1997)
reported the formation of anaerobic cleavage of azo dye by redox mediators. The
decolorization rate of amaranth dye was increased by 10–20 fold under anaerobic
conditions on addition of cell suspensions of Sphingomonas sp. strain BN6, which
was grown aerobically in the presence of 2-naphthyl sulfonate (NS). Additionally, the
cell suspensions grown in the absence of NS could also enhance the decolorization
rate anaerobically. The dye decolorization rate could also be enhanced through the
redox intermediates generated during aerobic degradation of aromatic compounds
(Keck etal. 1997). The azo dye decolorization rate could also be enhanced by the
addition of culture supernatant containing metabolites of a dye-decolorizing E. coli
NO3 (Chang etal. 2004).

62 Recent Advances in Environmental Management
3.5.3.2.3 Chemical Reduction
The decolorization of azo dyes can also take place by chemical reactions with inorganic
compounds such as sulde or ferrous ion, which, under anaerobic conditions, are
formed as end products of metabolic reactions. The extracellular decolorization of
azo dyes results by sulfate-reducing bacteria generating H2S under methanogenic
conditions (Diniz etal. 2002; Yoo etal. 2001). But, in the absence of sulfur compounds,
decolorization readily occurs in the presence of granular sludge, demonstrating the
importance of enzymatic mechanisms. The relative importance of chemical dye
reduction mechanisms in high-rate anaerobic bioreactors has been specied by the
analysis of decolorization kinetics in batch reactor and anaerobic sludge bed reactors
in the laboratory scale (Van der Zee etal. 2001). The oxidoreductase enzymes various
inducers and stabilizers such as indole, o-toluidine, veratrole, CaCO3, and vanillin
also enhance the azo dye decolorization rate (Dawkar etal. 2008).
3.6 ADOPTION OF BEST PRACTICES
3.6.1 reduCiNg aNd reCyCliNg Water
Before the nal disposal of wastewaters, it is very important to reduce the various
pollutants to avoid different hazards. If all forms of wastewater are reduced, then
industries can cut and save up to 20%–50% of their expenditure on water- and
efuent-treatment charges, which in turn can improve their prots. The next step is to
introduce appropriate water saving measures like reuse of water, which can be made
in the series of water tanks progressively used in the rinsing of the products. The rinse
water can be further reused elsewhere in the washing of oors, rinsing containers, etc.
3.6.2 aWareNess to go greeN
The techniques of processing and nishing fabrics must be changed so that luxurious
and sensuous fabrics can be produced in nontoxic, ethical, and sustainable modes.
The environmental friendly and appealing techniques should be made available
to the conventional manufacturers so that people can become conscious about the
implications in their textile choices. This can be better seen in the customers showing
consciousness in the purchase of ecofriendly cloths, drapes, or even carpets. But, this
new ecofriendly wave has thrown a major challenge to several apparel manufacturers
since the dyes used to color garments generate polluted water in the dyeing process
(Mahajan 2004). Some companies have taken action and stopped using dyes on certain
garments but again, not everyone could be happy with these only white clothing
items. Therefore, a x and permanent solution for this problem should be taken.
3.6.3 air dyeiNg teChNology
This technology seems to be a permanent method, which uses air instead of water
for dyeing the garments and ultimately allows companies to create vivid designs and
colors of garments without polluting the water and environment. As air is an ideal
transport medium, airow is the main key element in this technology (AET 2011).

63Textile Industry Wastewater
This replacement of dye liquor with air in jet-dyeing machines was a big step toward
reducing water and chemical consumptions. The air dyeing technology works on the
principle of using mass ow, which provides a major improvement in the fabric hank
lying, which prevents creasing (Figure 3.5).
3.7 CHALLENGES AND FUTURE PROSPECTS
The complex nature of the wastewater is the major problem in its treatment because
of the presence of the complex dye groups and other poorly or non-biodegradable
recalcitrant pollutants. Textile wastewater not only consists of recalcitrant molecules
but also toxic heavy metals with powerful inhibitory and antimicrobial activity. For
complete degradation and detoxication, the nature and toxicity of the recalcitrant
pollutants should be explained. Further, studies should also be conducted on the
toxicity of the decolorized wastewater.
3.8 CONCLUSIONS
Different textile and other industries uses azo dyes, and parts of the dye used for
coloring purposes are discharged into the environment in the form of wastewaters,
which causes serious human and ecological risks. The azo dye in its original form,
as well as their biotransformation products, causes toxic effects, principally DNA
damage. Azo dye consists of an important class of environmental mutagens and
hence develops genotoxic dyes. Therefore, an effective treatment method is required
for efuents and drinking waters to avoid their deleterious effects on humans and
aquatic organisms on their exposure.
Dye concentrate
production
Dye preparation
Solvent recycle
Water
Air-dye
placement
process
Synthetic textile
Power Natural gas
Air-dye
donor media
preparation
Colored synthetic
textile
(use and end of life
is out of scope)
Dye transfer
equibement
preparation Recycling
waste processing
Solvent production
Kraft paper
production
Chemical
production
FIGURE 3.5 Flowchart showing Air-Dyeing Technology. (Adopted from Dhanabalan, V.
etal. 2015. Air Dyeing Technology-A review. Textile Today.)

64 Recent Advances in Environmental Management
ACKNOWLEDGMENTS
The authors are highly grateful to the University Grants Commission (UGC),
NewDelhi, India, for providing the nancial support as RGNF Fellowship to Ms.
Sujata for this work.
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