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Textile industry is one of the largest water-consuming industries in the world, and its wastewater contains many pollutants such as dyes, degradable organics, detergents, stabilizing agents, desizers, inorganic salts, and heavy metals. In Pakistan, most of the textile industries discharge untreated wastewater into water bodies without any treatment, which percolates into the groundwater posing a threat to the health and socioeconomic life of the people. Pretreatment, dyeing, printing, and finishing are the main steps in dyeing and printing process of textile industries. A large amount of wastewater is being generated by all these processes, which contains many pollutants like reactive dyes, chemicals, high chemical oxygen demand (COD), biological oxygen demand (BOD), and organic compounds. Research has been conducted since long to treat textile wastewater in an economical and efficient way. There are many processes for removal of polluted compounds from water that include physicochemical, biological, combined treatment processes, and other technologies. All over the world, ecological standards are gaining importance in every step of textile unit. Due to the strict implementation of environmental standards, it is important to adopt an eco-friendly model of textile industry that overcomes all flaws from its start to end product. The main challenge is to develop a design that can be considered as cost-effective and to substitute chemicals that are less harmful or can be easily treated. On the basis of wastewater characteristics and literature review, appropriate scheme of treatment processes was proposed.
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Textile Wastewater Treatment Options:
A Critical Review
Khadija Siddique, Muhammad Rizwan, Munazzam Jawad Shahid,
Shafaqat Ali, Rehan Ahmad, and Hina Rizvi
Abstract Textile industry is one of the largest water-consuming industries in the
world, and its wastewater contains many pollutants such as dyes, degradable
organics, detergents, stabilizing agents, desizers, inorganic salts, and heavy metals.
In Pakistan, most of the textile industries discharge untreated wastewater into water
bodies without any treatment, which percolates into the groundwater posing a threat
to the health and socioeconomic life of the people. Pretreatment, dyeing, printing, and
finishing are the main steps in dyeing and printing process of textile industries.
A large amount of wastewater is being generated by all these processes, which
contains many pollutants like reactive dyes, chemicals, high chemical oxygen
demand (COD), biological oxygen demand (BOD), and organic compounds.
Research has been conducted since long to treat textile wastewater in an economical
and efficient way. There are many processes for removal of polluted compounds from
water that include physicochemical, biological, combined treatment processes, and
other technologies. All over the world, ecological standards are gaining importance
in every step of textile unit. Due to the strict implementation of environmental
standards, it is important to adopt an eco-friendly model of textile industry that
overcomes all flaws from its start to end product. The main challenge is to develop
a design that can be considered as cost-effective and to substitute chemicals that are
less harmful or can be easily treated. On the basis of wastewater characteristics and
literature review, appropriate scheme of treatment processes was proposed.
Keywords Textile wastewater • Treatment • Toxicity • Chemicals • Pollution
Textile Industry Wastewater: Challenges
The increasing population in Pakistan is requiring economic growth so the indus-
trial progress has been stirred up to meet the demands of growing population.
On the other hand, the regulatory measures are being neglected from the very
K. Siddique • M. Rizwan • M.J. Shahid • S. Ali (*) • R. Ahmad • H. Rizvi
Department of Environmental Sciences and Engineering, Government College University,
Allama Iqbal Road, Faisalabad 38000, Pakistan
e-mail: shafaqataligill@yahoo.com
©Springer International Publishing AG 2017
N.A. Anjum et al. (eds.), Enhancing Cleanup of Environmental Pollutants,
DOI 10.1007/978-3-319-55423-5_6
183
first, and the situation is getting worse as the implementation policy for control
measures is being neglected (Husain and Hussain 2012). The textile sector is playing
an important role in Pakistans economy as it is providing employment to 38% of
people; along with, it is an important source of foreign exchange. Out of the total
export, 65% of country export is provided by the textile sector alone (Bauer 2001). In
all over the country, many industries are working and strengthening the economy by
their production; out of this total production, textile industry accounts for 46%.
Some of the industrial products are also exported to foreign countries; textile
products are also exported and provide 9% of gross national product (GNP) (Sudipta
et al. 2005). Keeping in view, all these facts, we can say that textile industry is the
backbone of Pakistan economy. The textile sector is based on 670 industries that are
working in all over the country. Out of this 670, 300 are situated in Karachi alone,
and the remaining 370 are working in different areas of Punjab (Ara 1998).
It has been published in the yearbook of China that 390 million tons of sewage
water is producing each year in China. Out of these 390 million tons, 51% is
produced by industrial sector, and this rate is increased by 1% each year (Ho and
McKay 2003). According to a rough estimate, the textile sector has a major
contribution toward 51% of the sewage wastewater as 70 billion tons per year of
wastewater is coming out of dyeing industries alone. This wastewater has heavy
pollution load, and it is ridiculous to discharge this water without any prior
treatment. As compared to agricultural use, the industrial use of water is very little.
The heavy pollution load in wastewater makes water resources unfit for other uses.
In water-scarce countries like Pakistan, the reuse of water is a constant demand
because an extensive amount of water is needed for agricultural activities. There-
fore, water management is a challenge for us as freshwater resources are decreasing
rapidly and water is getting polluted with industrial activities (Anindya et al. 2005).
Textile industry is one of the biggest industries in the world, and a large amount
of water is consumed in its processing. Different stages of textile industry are
named as singeing, desizing, scouring, bleaching, mercerizing, dyeing, printing,
and finishing. All textile industries use these processes according to their require-
ment (El-Gohary and Tawfik 2009). The environmental problems created by textile
industry wastewater are due to increased oxygen demand, high color, and large
amount of suspended solids. Wastewater of textile unit contains many pollutants,
like inorganic compounds, dye waste, color residues, catalytic chemicals, and
cleaning solvents (USEPA 1997). It has been studied that in all over the world,
overall production of dyes is 700,000 tons each year (Riera-Torres et al. 2010).
There are different combinations of dyes that are being used to color different
stuffs. Some of these dyes are degraded naturally, but some need special treatment,
as they cant be degraded naturally. There are different types of dyes that are
chemically different from each other. These dyes include azo dyes, xanthene
dyes, nitro dyes, phthalocyanine dyes, etc. (Gupta and Suhas 2009). Dyes can be
further classified as acid dyes, basic dyes, and reactive dyes. The combination of
different dyes used to achieve different shades makes the treatment process more
difficult as each dye has different chemical natures (Andre et al. 2005). It is
believed that all over the world, more than one million tons of dyes are
184 K. Siddique et al.
manufactured each year and out of this, 0.28 million tons are discharged into
wastewater (Robert and Sanjeev 2005). Textile industry wastewater especially
from dyeing and printing industries needs proper treatment before its discharge in
water bodies as major contribution of the largest amount of textile wastewater is
from the developing countries. In textile processing industry, wastewater contains
many pollutants and needs to be treated as they can cause serious health impacts to
aquatic life as well as human beings (Lau and Ismail 2009). Therefore, it is an
utmost need to treat textile wastewater so that problems related to pollution caused
by it can be avoided.
Pretreatment, dyeing, printing, and finishing are the main steps in dyeing and
printing process of textile industries. A large amount of wastewater is being generated
by all these processes, which contains many pollutants like reactive dyes, chemicals,
high chemical oxygen demand (COD), biological oxygen demand (BOD), and
organic compounds (El-Gohary and Tawfik 2009). Research has been conducted
since long to treat textile wastewater in an economical and efficient way. There are
many processes for removal of polluted compounds from water that include physi-
cochemical, biological, and combined treatment processes and other technologies
(Phan et al. 2000). There are many sulfide compounds used in textile industry that are
environmental concerns because of their hazardous nature. So, a combination of
biological and chemical methods is being reviewed for sulfur treatment (Nguyen and
Juang 2013). All over the world, ecological standards are gaining importance in every
step of textile unit. Due to the strict implementation of environmental standards, it is
important to adopt an eco-friendly model of textile industry that overcomes all flaws
from its start to end product (Robinson et al. 1997).
The main challenge is to develop a design that can be considered as cost-
effective and to substitute chemicals that are less harmful or can be easily treated.
Recycling can be a preferred option in this regard as it can solve two problems. First
of all, recycling means less generation of waste. Secondly, it is economically
beneficial to develop techniques to use recycled products. Control techniques can
be divided into three types: (1) an efficient design using less polluting agents and
minimizing waste generation; (2) after generation of waste, an effective treatment
option for this wastewater; and (3) finding suitable steps where recycled products
can be applied (Sule and Bardhan 1999). Dyeing and finishing processes in textile
industry are major threats as they are using large quantities of chemicals and dyeing
agents that cannot be treated easily (Mustafa and Delia 2006). Organic nature of
these chemicals makes the problem serious as they have complex structure. Heavy
metals are another concern.
Main Steps in Textile Processing Industry
The main processes of a textile industry include singeing, desizing, scouring
bleaching, mercerizing, dyeing, printing, finishing, and marketing. Textile waste-
water includes (a) suspended solids, (b) mineral oils, (c) nonrecyclable or low
Textile Wastewater Treatment Options: A Critical Review 185
recyclable surfactants, (d) wet-finishing process that produces phenols (e.g., dye-
ing), (e) halogenated organics produced in bleaching that is using solvents, and
(f) textile effluents that are usually hot and highly colored and may have heavy
metals (e.g., chromium, copper, zinc).
Treatment Options
Textile wastewater handling is a blend of different methods. The principal phase
comprises typically of physical steps. Physicochemical methods have been exten-
sively used in textile treatment plants, which give good removal efficiency of
suspended materials, but it is not as much effective to remove COD. Various textile
wastewater approaches are given below.
Physical Methods of Decoloration
Equalization and Homogenization
Textile dyeing wastewater usually needs pre-handling to ensure uniform flow of
water for steady operation. Generally, the flexible container is fixed to handle the
wastewater. Meanwhile, to avoid the cotton fur and the slurry settle in depth, air is
used in the container for mixing. Eight hours of retention time is usually required.
Floatation
Floatation is a triple-phase combination of water, gas, and solid. In this process, air
under pressure is introduced that combines with particles in the form of bubbles.
This mixture settled down due to its lower density, and the heavy material separated
out due to higher density. It can successfully eliminate the fibers from textile
wastewater.
Adsorption
Some organic dyes are not easily biodegradable because of their structure. They
have long chain of carbon, which causes a limitation, and they are resistant to
degrade in normal biotic conditions. Treatment of such organic dyes is important,
and it demands best knowledge of abiotic conditions to degrade such compounds.
Adsorption is the greatest applied technique in wastewater management that can
mix the wastewater and the spongy material powder or granules, such as carbon and
clay, or allows the wastewater to pass through the sieve bed made up of granular
186 K. Siddique et al.
matter. Through this technique, contaminants in the wastewater are adsorbed on the
surface of the spongy material or sieve.
Adsorption is said to be a feasible abiotic condition to treat such organic waste. It
is important to have an idea about the conditions affecting adsorption capabilities of
such compounds, which may depend on water hardness, time of treatment, and
many other factors. Sludge of adsorption process is an important component so it is
necessary to develop better understanding about the treatment process and sludge
quality (Ozcan et al. 2004). It has been suggested that there should be 3 g per liter of
sludge, and minimum time of reaction should be 24 h and 6 days for maximum. The
maximum time limit is rarely needed because most of the dyes require 1-day
treatment only. Hardness of water should be 80 mg per liter, which gives best
removal. The removal efficiency of dyes from this process is considered to be 1 g
per liter to 30 mg per liter. The concept of activated sludge treatment gives
tremendous improvement in treatment process. There are various materials used
as adsorbents in sludge treatment such as charcoals, activated carbons, clays, soils,
and coagulants (Silva et al. 2004). Some information about molecule size and
charge on dye, its pH, and salt complex is important because adsorption process
is not that simple but its a combination of adsorption and ion exchange process.
Although there is a vast variety of adsorbent available in the market, not all are
appropriate for commercial use. Price, ease to handle the adsorbent, and binding
capacity are parameters which should be kept in mind while applying them in
treatment processes for commercial use. Lignocellulose is one of the effective
adsorbents, which is used on a large scale because it is not costly and effective
against acid dyes (Pignon et al. 2000). Adsorption is a time-consuming process, and
sludge produced by this process may not be easy to handle which is the main
drawback of this process.
Low-Cost Adsorbents
The nonconventional low-cost adsorbent should have some specific properties in
order to be used as dye adsorption. Those properties can be (a) efficient to remove
an extensive variety of dyes, (b) high rate of adsorption and capacity, (c) high
ability to tolerate extensive range of wastewater parameters, and (d) highly selec-
tive for different concentrations.
Natural Materials
Clays
Natural clay minerals have grabbed the attention of mankind since the civilization
time. Clay materials are famous as adsorbents due to their low cost, ease of
availability in most of the world continents, high potential for ion exchange, and
Textile Wastewater Treatment Options: A Critical Review 187
sorption properties. The clay materials have a layered structure and mostly favor-
able as host materials. The classification of clay materials is based on the differ-
ences in the layered structures such as mica (illite), smectites (saponite,
montmorillonite), serpentine, pyrophyllite (talc), kaolinite, vermiculite, and sepio-
lite (Shichi and Takagi 2000). The natural clay shows adsorption capabilities due to
a net negative charge on the mineral structure. The negative charge of clay minerals
attracts the positive-charged species, and so adsorption takes place. The sorption
properties depend on the high porosity and high surface area (Alkan et al. 2004).
Montmorillonite clay possesses the largest surface area and highest capacity for
cation exchange. The current market price of montmorillonite clay is about US$
0.04–0.12/kg and is considered as 20 times cheaper than the activated carbon
(Babel and Kurniawan 2003). The clay minerals such as kaolinite, bentonite,
diatomite, and Fullers earth are now becoming popular to be used in recent years
due to their unique adsorption capacity for organic and inorganic molecules.
Different scholars have extensively studied the interactions between the dyes and
clay particles reported in articles (Alkan et al. 2005,2004; Gu¨rses et al. 2004;
Wang et al. 2004; Al-Bastaki and Banat 2004; Ozcan et al. 2004; Ozdemir et al.
2004; Al-Ghouti et al. 2003; Atun et al. 2003).
Siliceous Materials
Natural siliceous sorbents such as glasses, alunite, silica beads, perlite, and
dolomite are becoming popular to be used for wastewater due to their abun-
dance, low price, and availability. The most prominent in inorganic materials are
the silica beads (Crini and Morcellet 2002;Woolardetal.2002;Harrisetal.
2001;Phanetal.2000), having silanol groups on the hydrophilic surface
responsible for the chemical reactivity. Their porous texture, mechanical stabil-
ity, and high surface area are the key factors, which make them suitable as
sorbents in decontamination applications. The presence of acidic silanol on the
siliceous material surface causes an irreversible and strong nonspecific adsorp-
tion. So the negative features of sorbents should be eliminated. The interaction
of siliceous materials with dyes can be promoted by modifying the silica surface
using silane-coupling agents having amino functional group (Krysztafkiewicz
et al. 2002). Another important sorbent from siliceous materials is alunite (Dill
2001). Alunite mineral comes from the jarosite group and consists of approxi-
mately 50% SiO
2
. The characteristics of alunite are discussed in the review by
Dill in 2001. The untreated alunite does not show good adsorbent properties
(Ozacar and Sengil 2003). In order to use alunite as good adsorbent for removing
colors, a suitable process is done to obtain alunite-type layered structure (Ozacar
and Sengil 2002).
188 K. Siddique et al.
Zeolites
Zeolites are the highly porous aluminosilicates having different cavity structures.
Zeolites are extensively used as substitute materials in particular areas such as
sorptive applications. Zeolites are useful in removing the trace amounts of pollut-
ants, e.g., phenols and heavy metal ions due to their cage-like structures appropriate
for ion exchange. A lot of the literature is available on sorbent behavior of the
neutral zeolites (Ozdemir et al. 2004; Armagan et al. 2004; Meshko et al. 2001).
The zeolite efficiency to remove dyes may not be better than clay materials, but the
easy access, availability and low cost make them suitable for many applications
(Calzaferri et al. 2000).
Biosorbents
Chitin and Chitosan
The emerging biosorption method uses biopolymers such as chitin and chitosan for
sorption of dyes. Chitin and chitosan are renewable, abundant, and biodegradable
resources. Several studies on chitin and chitosan revealed that chitosan-based
biosorbents are competent materials and have tremendously high attraction for
many categories of dye years (Chiou and Li 2002,2002; Chao et al. 2004; Chiou
et al. 2004). They are versatile materials and can be used as sorbents in different
forms, from flake types to bead types, gels, or fibers (Wu et al. 2000,2001a,b).
Wong et al. (2004) demonstrated the chitosan performance to remove acid dyes as
an adsorbent in detail. According to his research, the adsorption capacities of
chitosan for acid red 18, acid red 73, acid orange 10, and acid orange 12 were
693.2, 728.2, 922.9, and 973.3 mg/g, respectively.
Peat
Peat possesses porosity and is a complex soil material having organic matter in
several stages of decomposition. The classification of peat is based on nature of
parent materials. Peats are identified into four groups such as moss peat, woody
peat, herbaceous peat, and sedimentary peat. The peat is plentiful, inexpensive, and
available as biosorbent for a variety of pollutants. The polar property of peat makes
them suitable for removal of dyes from solution (Allen et al. 2004; Ho and McKay
2003). The raw peat has some limitations such as low mechanic strength; poor
chemical stability, to leach fulvic acid; a high affinity for water; and a tendency to
shrink or/and swell (Sun and Yang 2003).
Textile Wastewater Treatment Options: A Critical Review 189
Biomass
Bioadsorption and/or decolorization of dye wastewater by white-rot fungi, (dead or
living) biomass, and other microbial cultures was the subject of much research as
reviewed in several recent papers (McMullan et al. 2001; Robinson et al. 2001;
Stolz 2001; Pearce et al. 2003; Aksu 2005). In fungal decolorization, fungi can be
categorized into two classes based on their life state: living cells to biosorb and
biodegrade dyes and dead cells to adsorb dye (Fu and Viraraghavan 2001a). The
recent studies have focused on the removal of dyes with strains of Aspergillus niger
(Fu and Viraraghavan 2002a,b) and Rhizopus arrhizus (Aksu and Tezer 2000). Fu
and Viraraghavan (2001b,2002a,b) confirmed that Aspergillus niger as biosorbent
shows remarkable properties for dye removal.
Miscellaneous Sorbents
Starch has been studied as low-cost sorbent (Delval et al. 2001,2002,2003) and
cyclodextrins (Crini and Morcellet 2002; Crini et al. 2002a,b; Crini 2003). Starch
belongs to carbohydrate class and is present as an energy storage material in living
plants. It has also been demonstrated that cross-linked cyclodextrin gels can be used
for efficient extraction of dyes. The sorption properties are enhanced due to
existence of CD molecules in the polymer network (Crini and Morcellet 2002;
Crini et al. 2002a,b; Crini 2003).
Chemical Methods
Oxidative Process
Oxidative procedures are characterized as an extensively applied chemical tech-
nique for the handling of textile discharge, where decolorization is the purpose. The
key chemical is hydrogen peroxide (H
2
O
2
) that forms hydroxyl radicals, which are
strong oxidizing agents and are capable to decolorize a variety of dyes (Entezari and
Pe´trier 2004). Oxidation process is being used from so long, and it is found to be an
easy to handle process that has been extensively used on commercial basis. Hydro-
gen peroxide is highly stable, and there are various methods of its activation, which
are named accordingly.
Fenton Treatment
It is a very useful technique for wastewater treatment. It has its own specification
which is found to be very effective to treat COD and gives the best removal against
190 K. Siddique et al.
many dyes. In the first technique, hydroxyl radical is produced from H
2
O
2
during
Fenton reaction, where hydrogen peroxide is added to an acidic mixture (pH ¼2–3)
having Fe
2+
ions. The reaction is exothermic and must be performed at temperature
greater than ambient (Hassan and Hawkyard 2002). Besides many advantages, this
process also has a limitation. Sludge produced by this process contains many
impurities, and it requires proper land disposal that is not easy to handle. Fenton
sludge recycling is a proposed technique to get rid of harmful impacts that makes it
easy to handle this sludge (Joseph et al. 2000). Mechanical handling of this sludge is
a possible option. The sludge contains phosphate that can be removed, that makes
this sludge less harmful, and it may be treated through biotic processes.
Ozonation
Ozone is being used for the wastewater treatment since 1970. It is highly instable
which makes it a strong oxidizer. When compared to chlorine having oxidizing
potential of 1.36, it was found to be a better oxidizing agent with an oxidizing
potential of 2.07 (Koch et al. 2002). It was mainly used against drinking water,
and the main purpose was to make it clean, but its other properties against toxic
compounds of wastewater make it a favorable option in textile wastewater treat-
ment. It was found to be effective against many aromatic hydrocarbons, phenols,
pesticides, etc. It is a very active and rapid decolorization handling method.
Ozonation can tackle with the double bonds in dyes, and COD can be lowered
by this method. Many of the nonbiodegradable products can be easily
decomposed. 18.5 and 9.1 mg/l concentrations of ozone are enough to remove
50 and 60% COD after 60 and 90 min, respectively (Selcuk 2005). In this process,
the usual application is the use of sodium hypochlorite that has the ability to break
azo bond. The shortcoming of this process is that it releases amine compounds and
these can cause cancer. It also has a limitation that it is readily decomposed in
water having a life span of just 20 min. This is the main drawback of this
treatment, and the time may get shortened enough when the wastewater having
dyes is projected toward this treatment (El-Din and Smith (2002)). Other factors
may influence its stability in water such as pH, temperature, etc. Ozone stability is
highly affected by the presence of alkaline salts. It may get reduced when alkaline
water is treated against it, while natural salts have a positive impact and enhance
its stability (Arslan 2001). Temperature has a negative impact on ozone solubility.
With increasing temperature, it becomes less soluble in water (Ma and Graham
2000).
Several options are keeping concern regarding the reduction in the parameter
like COD, BOD, and TOC. Ince and Tezcanli (2001) stated that ozone treatment
doesnt reflect any changes in COD. Ikehata (1975) conveyed a decrease in COD
and BOD standards, while Koch et al. (2002) found that the use of ozone treatment
will increase in the value of two parameters. Practices with TOC decline are
constant, viz., treatment with ozone does not effect it. Meanwhile, addition in
oxygen in soluble composites with ozone is not successful at an initial stage.
Textile Wastewater Treatment Options: A Critical Review 191
Carriere et al. (1991) advocate ozone treatment as a tertiary treatment, succeeding
as an activated sludge process. The ratio of other substances present in dye
wastewater is lesser than the present in the pure solution (up to 20% of dye leftover
in the water after ozone treatment). At the very first step, eradication of foaming and
reducing agents increases color removal efficiency by ozone treatment (Andreozzi
et al. 2001a).
H
2
O
2
UV Radiation
All the above-stated complications (sludge evolution and renewal increase the
intensity of polluted wastewater caused by ozonation) can be stated away by
oxygen addition with hydrogen peroxide, initiated with UV light. The single
element used in the treatment is H
2
O
2
, and due to its final breakdown into oxygen,
it is not problematic. Peroxide is activated by UV light. Aspects persuading H
2
O
2
/
UV processes are concentration of hydrogen peroxide, the strength of UV radiation,
pH, dye composition, and dyebath structure. Overall, discoloration is utmost suc-
cessful at pH ¼7, at greater UV irradiant concentrations (1600 W rather than
800 W), with an ideal concentration of H
2
O
2
, which varies for diverse dye sessions,
and through a dyebath that does not cover oxidizing agents having an oxidizing
capacity advanced than that of peroxide (Andreozzi et al. 2001a). According to
Andreozzi et al. (2001b), the easiest decomposable dyes are acid dyes, and with an
accumulative number of azo groups, the discoloration efficiency declines. Arslan
et al. (2000) reported prolonged decoloration required by the yellow and green
dyes, while on the other hand, quick decoloration is showed by the direct, metal-
complex, and disperse dyes. In the collection of blue dyes eliminated, only blue
dyes were not vat decolorized, yet their composition alters with the procedure in
such a way that they can be simply filtrated. The filtrate is colorless. For pigments,
H
2
O
2
/UV method is not appropriate, since they form a filmlike covering which is
tough to eliminate.
Hydrogen Peroxide
The efficiency of method relies on the peroxidase usage, its strength, pH, and the
temperature of the medium. Fukushima and Tatsumi (2001) studied the discolor-
ation of acid dye by three kinds of peroxidases [horseradish (HRP), soybean (SPO),
and Arthromyces ramosus (ARP)] as peroxide activator. By calculating the absor-
bance capacity, they found that the persistency was the highest via ARP. The
discoloration rate augmented with higher peroxidase accumulation and temperature
of medium and was the highest at pH 9.5.
192 K. Siddique et al.
NaOCl
Cl compounds are useful in the chemical oxidation of colored wastewaters. Elec-
trophilic breakdown occurs at the amino group by Clþpledgees and speeds up the
consequent azo bond cleavage. Namboodri et al. (1994) reported the adequate
discoloration of acid and direct dyes. Treatment of reactive dyes prerequisite longer
times, while solutions of metal-complex dyes persisted partially colored (Manu and
Chaudhari 2003). Disband dyes do not decolorize with NaOCl. Decoloration rate
rises with increase in chlorine intensity and declining pH of medium. According to
Omura (1994), dyes encompassing amino or exchanged amino groups on the
naphthalene ring, i.e., dyes derivative from aminonaphthol- and naphthylamine-
sulfonic acids, are the greatest subject for chlorine decoloration. One feature which
has come to the front in current years, and which is related to chlorine-centered
decoloration practices, is that, for atmosphere causes, the upcoming use of
chemicals comprising chlorine should be controlled. Since 5 and 60% of
European chemical manufacture openly or ultimately rest on chlorine, the influence
of such a prohibition could be huge, mainly for organic colorant production.
However, it must be illustrated that even though about 40% of worldwide used
pigments comprise chlorine, this corresponds to less than 0.02% of the total
chlorine production (Clarke and Steinle 1995).
Ion Exchange
Its a treatment process that has been used to treat wastewater excluding
dye-containing wastewater. The main reason of avoidance was a misconception,
and it was thought that this method is not effective against dye-containing waste-
water and its effectiveness slows down further when wastewater is loaded with
other additives in consort with dyes. This flaw was removed with an excellent work
of Baouab et al. (2001) who proved in his experiment that sulfur-containing dyes
and those with acidic nature could better be treated with a combination of anion
exchange column that is packed in series and a nonpolar resin. This was a great
turning point in treatment of textile wastewater because it added another positive
option against dye treatment and it could be further explored within time. The ion
exchange resins needed to be regenerated after one-time removal, and this task was
completed with the help of organic solvents. The organic solvents are not that much
cheap, and their use increased the operational cost that was the major drawback of
ion exchange method.
The research on the highlighted above method provided wise choices and the use
of quaternized cellulose. The sulfonate group of dye makes an association with the
amine group of resin through columbic forces, or other bonding forces may be
developed between them such as van der Waals forces or hydrogen bonding
(Glover 1993). The efficiency of a resin to remove dye from wastewater can be
judged through these bonding. If there is a strong bonding present between dye and
Textile Wastewater Treatment Options: A Critical Review 193
resin, there will be effective removal of dye. There are many theories about the
effectiveness of this method. According to Laszlo (1994), chloride concentration
has a negative impact of dye removal efficiency. With the increased concentration
of chlorine, there will be less bonding between dye and resin, while sulfate and
carbonate have a null impact on this bonding so their concentration does not affect
the dye removal efficiency. In the same way, with the addition of sodium hydroxide,
the binding process completely gets stopped. This can be positively used in
treatment process, and using sodium hydroxide can regenerate the resin. The
main reason of this poor bonding is that, when pH is increased, the proton may
be removed from quaternary amine and makes conjugate base which may increase
the hydroxyl group that may result in a repulsion force between dye and resin.
Coagulation and Sedimentation
This technique is one of the most used techniques in the past. In this process, some
of the chemicals are added in the water that assists the charged particles to make
some compound that can be coagulated in water. Usually, the colloids carry
negative charges so the coagulants are normally inorganic or organic cationic
coagulants (with positive charge in water). Some of the organic polymers cause
coagulation to an extent that these coagulants combine to give groups and form
sediments that is easy to extract (Ciardelli and Ranieri 2001). The most commonly
used chemicals are FeCI
3
,AI
2
(SO
4
)
3
, FeSO
4
, and lime (Verma et al. 2012).
Electrocoagulation
In this technique, effluents are treated in a chamber in which metal electrodesare used
to treat wastewater. Electrode plates are suspended in effluent solution, and it can
remove metal oxide at a specific pH. Metal oxides are coagulated and can be easily
removed from the solution. This method is effective and has been reviewed in many
articles (Khandegar and Saroha 2013). This technique uses direct current source
between metal electrodes immersed in the effluent, which causes the dissolution of
electrode plates into the effluent. The metal ions, at an appropriate pH, can form wide
range of coagulated species and metal hydroxides that destabilize and aggregate
particles or precipitate and adsorb the dissolved contaminants. Therefore, the objec-
tive of the present manuscript is to review the potential of electrocoagulation for the
treatment of industrial effluents, mainly removal of dyes from textile effluent.
Reverse Osmosis
Reverse osmosis membranes have a holding degree of 90% or greater for most
kinds of ionic complexes. Decolorization and removal of chemical auxiliaries in
dyehouse wastewater can be done in a single step by reverse osmosis. Reverse
194 K. Siddique et al.
osmosis causes the elimination of all mineral salts, hydrolyzed responsive dyes, and
chemical auxiliaries. This process needs a very high energy since a very high
pressure is required herein (Babu et al. 2007).
Nanofiltration
Nanofiltration has been used for the management of color discharges from the
textile industry. Nanofiltration membranes hold low molecular weight organic
complexes, divalent ions, big monovalent ions, hydrolyzed responsive dyes, and
dyeing auxiliaries (Ellouze et al. 2012). In most available studies regarding
dyehouse discharges, the amount of mineral salts does not surpass 20 g/L, and the
amount of dyestuff does not surpass 1.5 g/L (Babu et al. 2007).
Biological Treatment
As compared to physiochemical and photochemical methods, biological methods
can be categorized as cost-effective substitutes of textile wastewater treatment. All
the other methods are costly and have major drawbacks when applied to textile
industry. All the possibilities of biological methods have been studied, and they are
being applied in textile industries using different microorganisms (Sarayu and
Sandhya 2012). It has been studied that a single strain of bacteria or fungi is
effective to remove a dye, but it cannot be applied to remove another dye. There-
fore, this method cant be adopted at commercial scale (Mendez-Paz et al. 2005).
Recently, a natural colonized algae and duckweed plants were found to be very
effective to treat textile wastewater in a pond experiment (Sekomo et al. 2014).
Biological methods can be categorized as aerobic and anaerobic processes, and they
give the best results when applied to remove organic pollutants from textile
wastewater (Frank et al. 2001). In field applications, aerobic methods did not give
the best results in color removal. Many of the dyes, especially azo dyes, are found to
be resistant in aerobic application (Mustafa and Delia 2006). Urban anaerobic
sludge blanket reactor has been introduced in textile wastewater treatment, and it
gives the best results in treatment of xenobiotic compounds. It has the ability to
handle very resistant compounds also (Jantsch et al. 2002).
Aerobic Biodegradation
There is a natural process in the aquatic ecosystem named as aerobic biodegrada-
tion that is necessary to treat the wastewater of rivers and streams and makes them
clean from pollution loads. The biodegradability of many compounds can be judged
by many parameters such as chemical oxygen demand (COD), biological oxygen
demand (BOD), dissolved oxygen (DO), and the evaluation of carbon dioxide
Textile Wastewater Treatment Options: A Critical Review 195
(Dos Santos et al. 2003). The main factor of the whole procedure is the assessment
of the chemicals that can be easily biodegraded. There are OECD 301 guidelines
available that must be adopted, and by using this method, there should be 70% DOC
removal (OECD 1993).
If the compound is assessed as biodegradable and conditions are favorable, there
is a possibility that the compound will be biodegraded in wastewater plant same
like it can be degraded in natural environment (Cruz and Buitron 2000). Strotmann
et al. (1995) made a research and developed COz/DOC scheme for effective
removal of DOC. In this design, the compound was mineralized and DOC was
eliminated. There were remarkable results of this procedure, and when it was
compared with Zahn-Wellens test, it provided better information of biodegradabil-
ity of compounds. On the basis of these results, the behavior of many compounds
can be explored in natural environment and in wastewater treatment plants as well.
Anaerobic Biodegradation
Anaerobic degradation is degradation when there is an absence of oxygen or very
low oxygen present in the medium. This kind of degradation usually occurs in lower
sediments in natural aqueous environment because that is poor oxygen medium.
Some kind of sewage waste is also degraded by this procedure. So it can be
predicted that a compound having low solubility in water and can be adsorbed on
solids can be subjected to anaerobic degradation. Anaerobic bacteria or microor-
ganisms achieve this task. This is a complete sequence step process in which
bacteria that act in acidic medium act on organics such as carbohydrates and fats.
These organics may be converted in alcohols and other simple compounds with the
action of acidic bacteria. These products then stimulate the acetogenic bacteria,
which further convert them in carbon dioxide and molecular hydrogen. Then, after
reduction of these products, methane is generated, and methanogen bacteria per-
form this task. Biogas is an important parameter in anaerobic treatment that gives
an assessment about the rate of experiment. There are many researches available
which can explore the aerobic and anaerobic treatment, but a comparative study of
both procedures is missing. There was an effort to assess the volume of biogas, but
there are no set standards to make predictions on the basis of this research (Cruz and
Buitron 2000; Dos Santos et al. 2004).
Complexometric Methods (Refining with Cucurbituril)
Its a tough choice to use the effective method to treat wastewater because each
process has its own merits and demerits. When we used activated carbon treatment,
this can be effective against organic dye removal, but the other impurities cantbe
handled by using this process in the same way; each process has its own limitation.
It was not until 1905, when there was a little noise about an organic compound
196 K. Siddique et al.
introduced with the name of cucurbituril. But a remarkable research was not
conducted on this compound. Freeman et al. (1981) explored its chemical proper-
ties. Cucurbituril is a polymer that is made up of glycoluril and formaldehyde.
Studies have revealed that the complex has fairly good sorption capability for
various types of textile dyes. Cucurbituril is recognized to make a complex with
aromatic dyes, and it is reflected that this method is effective for the absorbance of
reactive dyes (Robinson et al. 2001). Cucurbituril was not found to be soluble in
aqueous medium, and its macrocyclic property made it more appropriate against
dye treatment. It makes insoluble complexes that can be easily removed from
wastewater. Later, Buschmann et al. (1996) did an extensive research on this
compound.This was an effective method and can be used in solid state as well.
The removal efficiency of cucurbituril was checked against many dyes such as acid,
base, reactive, and direct dyes, and it provided excellent results against all of them.
The rate of removal depends on many factors such as there may be high solubility of
the complex formed, or there may be poor bonding between dye and cucurbituril.
One of the plus points of this method is that it can never be disturbed by the
presence of organic compounds in wastewater.
Comparison of Different Treatment Methods
There are different methods and technologies that are being applied to treat the
textile wastewater. Different methods provide different efficiencies to remove color
and organic waste. For example, advanced oxidation process is found to be most
effective and gives the best result in color removal. Fentons reagents (H
2
O
2
and Fe
2+
)
and ozonation are the termed as advanced oxidation technologies that can be
applied to textile wastewater to achieve the best results, but they have some
limitations as well. They are costly, and a large amount of waste in the form of
sludge is produced by these methods. The sludge produced by this method is
difficult to manage (Marco and Jose 2007). Some of the physical methods such as
coagulation flocculation are also found to be effective, but lime, alum, and poly-
electrolytes used in this process cause an enormous amount of sludge that is
difficult to manage and treat, as it cant be disposed easily. Therefore, this method
cant be applied alone in textile wastewater treatment. Adsorption process is an
expensive process as it uses activated carbon that is very costly. Other adsorbents
used in adsorption of dyes have high cost, and the textile industry cant adopt this
method due to high operational cost. Reverse osmosis technique in textile waste-
water treatment is found to be very useful, but its operational cost is also very
high, as it requires very high pressure, and a large amount of energy is consumed
in this process. The budget of textile industries adopting membrane filtration
techniques can be disturbed as nanofiltration and ultrafiltration processes require
high energy, and sludge produced by this process is not easy to handle (Allegre
et al. 2006). Another method uses ultraviolet light, and oxidation compounds such
as H
2
O
2
are also being used to treat textile waste, but different catalysts used in
Textile Wastewater Treatment Options: A Critical Review 197
this process produce by-products that are very harmful (Muruganandham and
Swaminathan 2004). There are some methods having high color removal effi-
ciencies. Electrochemical oxidation is one of them as it has the ability to remove
color, and by-products produced by this method are nontoxic and easy to handle.
But it has its own limitation as its operational cost is also very high and it can
disturb the budget of textile industry (Mohan et al. 2007).
Generally, a combination of two or more advanced oxidation processes such as
UV/ozone, UV/H
2
O
2
, ultrasound/ozone, sonophotochemical/sonophotocatalytic oxi-
dation, etc. leads to an enhanced generation of the hydroxyl radicals, which eventu-
ally results in higher oxidation rates. The efficacy of the process and the extent of
synergism depend not only on the enhancement in the number of free radicals but also
on the alteration of the reactor conditions or configuration leading to a better contact
of the generated free radicals with the pollutant molecules and also better utilization
of the oxidants and catalytic activity (Gogate and Pandit 2000a).
Combining ozone and hydrogen peroxide with ultrasound leads to a better
utilization of both the oxidant, hence higher degradation rates due to the dissocia-
tion of ozone and hydrogen peroxide under the action of ultrasound. The mass
transfer resistance, which is a major limiting factor for the application of ozone or
hydrogen peroxide alone, is also eliminated due to the enhanced turbulence gener-
ated by ultrasound. The operating frequency is a crucial factor in deciding the
synergism and should not be increased beyond 500 kHz (Gogate and Pandit 2000b).
The problems of high-frequency operation and existence of optima beyond which
the rates of degradation decrease have been discussed in detail in the earlier work
(Gogate et al. 2002). Ozone/hydrogen peroxide hybrid technique gives better
results as compared to the use of ozone or hydrogen peroxide especially for the
treatment of pollutants, refractory toward ozone, e.g., organophosphoric acid
tri-esters. As the synergism is strongly dependent on the efficient use of hydroxyl
radicals, concentration of radical scavenging agents plays a crucial role in deciding
the overall efficacy of the process (Gogate and Pandit 2004).
In the case of sonophotochemical/sonophotocatalytic reactors, it is important to
have simultaneous irradiation of ultrasound and UV light rather than sequential
operation. Addition of hydrogen peroxide or ozone to this hybrid system until an
optimum value as an additional source of the free radicals also increases the extent of
destruction (Fung et al. 2001) The major factor controlling the overall efficiency of
destruction is, however, the stability of the photocatalyst under the effect of ultra-
sound, and efforts are required in terms of new designs, which will protect the catalyst
but at the same time will give enhanced effects (Fung et al. 2001). Photo-Fenton
processes offer additional advantages in terms of possibility in the use of sunlight
instead of UV light with a minor decrease in the rate of degradation, which is a very
important factor for the scale-up and commercial use as the costs of treatments will be
substantially lower for the sunlight irradiation.
All the processes discussed above have their own merits and demerits. Indeed,
the selection of the process that gives the best outcome with less polluting
by-products and low cost is a difficult task (Rajkumar and Kim 2006) (Table 1).
198 K. Siddique et al.
Table 1 Representative studies on the applications of combined treatment systems on textile
effluent
Treatment
processes First stage Second stage Outcome References
Physical/
membrane
treatment
Coagulation Ultrafiltration Achieved substantial colloidal
particle removal (>97%) of
turbidity removal) regardless
of type and dosage of coagu-
lants used, but degree of mem-
brane fouling was highly
dependent on type of coagu-
lants used. Study has proven
that inorganic coagulants were
more efficient to reduce fouling
compared to polymeric
coagulants
Choo et al.
(2007)
Membrane
treatment
Ultrafiltration Nanofiltration Authors claimed that UF was
an appropriate pretreatment of
an NR/RO process for textile
wastewater reuse. To deal with
the wastewater with high vari-
ability values of COD and
conductivity, they observed
that flux decline was significant
at the lowest cross flow veloc-
ity studied due to the solid
deposition onto the membrane
surface
Barredo-
Damas
et al.
(2006)
Physical/
membrane
treatment
Coagulation/
flocculation
Nanofiltration Study reported that the quality
of permeate after coagulation/
flocculation did not match the
requirement of reuse on the
site. However, this method
could act as pretreatment of NF
to limit membrane fouling. By
using this integrated approach,
high-quality permeate could be
obtained
Suksaroj
et al.
(2005)
(continued)
Textile Wastewater Treatment Options: A Critical Review 199
A combination of physical, chemical, and biological method can be cost-
effective and efficient treatment option for textile wastewater treatment. In a recent
study, a combination of Fenton and anaerobic oxidation (F þSBR) reactor was
found to be very effective in removing E. coli and toxic organic compounds (Blanco
et al. 2012). A best strategy toward the textile industry pollution reduction is
adoption of cleaner production technologies.
Table 1 (continued)
Treatment
processes First stage Second stage Outcome References
Chemical/
membrane
treatment
(2005)
Electrochemical
oxidation
Membrane
filtration
Study indicated the feasibility
of combined processes for
treatment of textile wastewater.
Membrane prior to electro-
chemical oxidation process
showed promising results in
terms of COD, turbidity, and
color removal (RCOD ¼89.2%,
Rturbidity ¼98.3%,
Rcolor ¼91.1%) compared to
electrochemical oxidation prior
to membrane process
(RCOD ¼86.2%,
Rturbidity ¼95.1%,
Rcolor ¼85.2%). This is due to
lower color concentration
remaining in wastewater after
the electrochemical oxidation
process
Chen et al.
(2005)
Chemical/
biological
treatment
(2003)
Ozonation Aerobic The use of ozonation as
pretreatment was able to
increase the bioavailability of
the dye before it was treated
with the aerobic process. To
achieve higher color (99.8%)
and DOC (85%) removal,
higher doses of ozone were
required. This would make it
less economically favorable
Libra and
Sosath
(2003)
Physical/
membrane
treatment
Sand filtration
and membrane
filtration
Nanofiltration Sand filtration and MF in a
pilot plant were fundamental in
reduction of suspended solids
(100%) and turbidity (78%).
To completely remove COD,
conductivity, and color, NF
was responsible for removal
Marcucci
et al.
(2002)
200 K. Siddique et al.
There are three strategies that can be implemented in textile industry designs.
These strategies are briefly summarized hereunder.
Less Polluting Raw Material
Selection of less polluting raw material is a prescreening process, and by adopting
this strategy, textile companies can reduce waste generation from the very first step
such as, instead of azo dyes, use vat dyes when possible, and reuse dye and wash
wastewater for preceding process (Tsai and Chou 2004).
Substituted Products
The less polluting and easily degradable chemicals can substitute highly polluted
chemicals that cannot be easily degraded. In the same way, textile companies can
select the treatment designs that cause less pollution like substitution of chemical
treatment with the mechanical one (Fitzpatrick et al. 2010).
Process Modification
Industries should adopt the process that is cost-effective, is energy efficient, and
according to local conditions provides the best degradation. Usually a hybrid model
can be used to achieve the best removal (Van der Bruggen et al. 2004). The
objective of this study was to provide the best treatment options according to
Pakistan situation. The combination of two processes enhances the ability to
degrade the pollutants. The best design should have unique characteristics such as
(a) the capacity to provide high biodegradation and maximum removal rate that
cannot be achieved by the single process, (b) retention time which does not exceed
the time of single process, and (c) its cost-effectiveness.
Conclusions and Perspectives
It must be said that the advanced oxidation processes or even the hybrid methods
may not be useful in degrading large quantum of the effluent with economic
efficiency and hence it is advisable to use these methods for reducing the toxicity
of the pollutant stream to a certain level beyond which biological oxidation can take
care of the complete mineralization of the biodegradable products. An optimized
pretreatment stage (in terms of the oxidant dose and the reduction in the toxicity
Textile Wastewater Treatment Options: A Critical Review 201
level) will substantially decrease the total treatment time and hence the size of the
reactor using the combination technique. It is recommended that the added oxi-
dants, e.g., hydrogen peroxides, are completely utilized in the pretreatment stage
alone, as its continued presence may hamper the activity of the microorganisms. It
is also important to analyze the constituents of the effluent stream after the
pretreatment stage as it may happen that some of the intermediates formed as a
result of the oxidation are biorefractory or more toxic than the parent compound.
It is also important to develop realistic and generalized kinetic and yet mecha-
nistic models for predicting the rates of the degradation process as a function of
different operating parameters. The developed kinetic model should consider the
effect of all the constituents of effluent stream even if the concentrations are in
traces, e.g., radical scavengers and also the different reactions taking place in the
chain of radical reactions. In Pakistan, most of the textile industries discharge
untreated wastewater into water bodies without any treatment, which percolates
into the groundwater posing a threat to the health and socioeconomic life of the
people. Characterization of wastewater is necessary to determine the type and
scheme of treatment required. This chapter proposes the treatment options to
control textile wastewater pollution. It is clear that textile wastewater can be treated
through different processes including Fenton treatment, ozonation, adsorption,
nanofilteration, aerobic biological treatment, and anaerobic treatment such as
upflow anaerobic sludge blanket reactor, etc. After comparing the advantages and
disadvantages of these processes, the best strategy is to use aerobic and anaerobic
biological treatment in combination for textile industry wastewater treatment
(Manu and Sanjeev 2003). Moreover, instead of focusing on end-of-pipe treatment,
the adoption of cleaner production technologies is necessary to reduce pollution at
source. This can be done through selection of less polluting alternate raw materials,
reuse of wash water, and conservation of water, chemicals, and energy by following
cleaner production practices in textile industries.
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Textile Wastewater Treatment Options: A Critical Review 207
... The water from the last rinse in a batch dyeing procedure is particularly clean and may be utilized for washing or setting up the future dye baths straight away. With minimal initial expenses, this reuse method has the potential to save 10-30% of water (Siddique et al. 2017). In this work, we have investigated the influence of ultrasound on the pretreatment process and dyeing of 100% cotton knit fabric with reactive dye at lower temperature than conventional processes. ...
... The variations in shades are measured by color differences, which is given by the CIE color lab equation. Color difference is measured as function of lightness, red-greenness scale, yellow blueness scale, saturation, and hue angle, which are expressed by L*, a*, b*, c*, and h°, respectively, and are calculated from: ΔE = √ ΔL * 2 +Δa * 2 +Δb * 2 , where L* is the lighter/darker, a* is the redder/greener tone, b* is the yellower/bluer tone, c* is the saturation, and h° is the hue angle of the fabric (Hannan et al. 2019;Sharma 2018). Color difference is the cumulative difference of all functions and is determined using the above formula. ...
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... The textile industry releases a large amount of wastewater through various unit operations like scouring, bleaching, dyeing, and printing that are seen during textile making. Of the 1 million tons of toxic dye and ink effluents generated, about 0.3 million tons are discharged without proper treatment [9]. Printing and dye wastewater (PDW) is the aqueous effluent released by factories that operate the dyeing and finishing of wool and silk, among other things. ...
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... Most scientific researches seek efficient and inexpensive treatments capable of degrading dye, mitigating effluents toxicity and presenting advantageous cost/benefit for textile industries in order to make the textile sector totally sustainable (Khadija et al., 2017). The methods of ion exchange, industrial enzymes and electrocoagulation with the metallic iron anode as a catalyst are efficient and low cost, but have other disadvantages. ...
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Removal of C.I. Acid Blue 29 from an aqueous solution by biosorption on dead Aspergillus niger fungus was investigated. Pretreatment with sulfuric acid was most effective with a biosorption capacity of 13.82 mg/g biomass compared with 6.63 mg/g of living biomass. Batch pH, kinetic, and isotherm studies were conducted to evaluate the biosorption capacity of the most effective pretreated biomass. The pH of the dye solution strongly affected the biosorption capacity. The effective pH was 4 and the corresponding biosorption capacity was 18.15 mg/g biomass. The kinetic studies showed that equilibrium was reached in 24 hours, and Lagergren first-order and Ho, et al. pseudo second-order rate equations were able to provide a realistic description of biosorption kinetics. Isotherm studies indicated that biosorption followed the Langmuir, Freundlich, and BET isotherms models.
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The phenomenon of spun yarn failure is strongly dependent on the yarn structure namely, the configuration, alignment and packing of the constituent fibers in the yarn cross-section. The structure of yarn is solely determined by the methods of consolidating the fibers into yarns. In the present study, ring, rotor, air-jet and open-end friction spun yarns were produced from identical fibers and their structural parameters; namely, mean fiber extent, spinning-in-coefficient, helix angle of the fibers, percentage of different hooks and their extents, number of fibers in yarn cross-section and yarn diameter were measured. These yarns were subjected to uniaxial loading on the tensile testers with a large range of gauge lengths (0 to 500 mm) and strain rates (5 to 400 m/min). The results showed that the strength of yarns largely depends on the structure of the yarns, gauge lengths and strain rates. A combined effect of fiber extent in the yarn and gauge length influences the yarn strength. At high strain rates the yarn failure is dominated by the breakage of fibers rather than the slippage of fibers. Furthermore, the analysis of the region of yarn failure provides more direct evidences of the influence of yarn structure and testing parameters on the strength of different spun yarns.