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J. Bio. & Env. Sci.
2015
501 | Mostafa
RESEARCH PAPER OPEN ACCESS
Waste water treatment in textile Industries - the concept and
current removal technologies
Mohammad Mostafa
Institute of National Analytical Research and Service (INARS), BCSIR, Dhaka- 1205, Bangladesh
Article published on July 30, 2015
Key words: Textile process effluents, Standard of textile effluents, Current removal technologies.
Abstract
The textile industry is one of the most promising industrial sectors that provide huge unskilled employment in
the developing countries in Asia, particularly China, India and Bangladesh. Since textile industry is a very diverse
sector in terms of raw materials, processes, products and equipment and has a very complicated industrial chain.
The textile finishing covers the bleaching, dyeing, printing and stiffening of textile products in the various
processing stages (fibre, yarn, fabric, knits, finished items). These units are being used in various chemicals and
large amounts of water during the production processes and also generate a substantial quantity of effluents,
which can cause various environmental problems, if disposed of without proper treatment. So the
characterization of textile process effluents is very important to develop strategies for wastewater treatment and
reuse. The paper describes the characteristic and composition of textile wastewater, some national standard of
the textile effluents and reviews the currently available primary, secondary, tertiary and advanced pollutants
removal technologies used in the textile industries.
*Corresponding Author: Mohammad Mostafa drmostafabcsir@yahoo.com
Journal of Biodiversity and Environmental Sciences (JBES)
ISSN: 2220-6663 (Print) 2222-3045 (Online)
Vol. 7, No. 1, p. 501-525, 2015
http://www.innspub.net
J. Bio. & Env. Sci.
2015
502 | Mostafa
Introduction
The word textile comes from the Latin word ‘texere’
which means to weave. Textiles can be woven by both
hand and machines. The textile industries are
classified on the basis of the types of textile fiber they
use. The raw materials for textiles are natural and
synthetic fibres (Elliott et al., 1954). The textile raw
materials can be classified into three main categories:
cellulose fibres (cotton, rayon, linen etc), protein
fibres (wool, silk etc) and synthetic fibres (polyester,
nylon, acrylic etc). Cellulose fibers are obtained from
plant sources such as cotton, rayon, linen, ramie,
hemp and lyocell (Bledzki and Gassan, 1999). Protein
fibers are obtained from animals and include wool,
angora, mohair, cashmere and silk. Artificially
synthesized fibres include polyester, nylon, spandex,
acetate, acrylic, ingeo and polypropylene. However,
the most of the textiles are produced from cotton
liners, petrochemicals and wood pulp. China is the
biggest exporter of almost all the textiles followed by
European Union, India, USA and Korea as shown in
Table 1 (Ghaly et al., 2014). The production process
of textiles industry involves three or four fragmented
group of establishment that can be yarn formation,
fabric formation, wet processing and textile
fabrication. A flow diagram for various steps involved
in processing textile in a cotton mill shown in figure 1.
Various manufacturing processes are carried out for
different types of textiles. The major exporters of
clothing are shown in Table 2 (Ghaly et al., 2014). The
production process of textiles can be broadly divided
into two categories: the spinning process (the dry
process) and the wet process (involves the usage of
dyes). Production of cotton textiles involves the
separation of cotton fibres from the cotton seeds
which are then spun into cotton yarns (Sette et al.,
1996). These yarns are weaved successfully into
cloths. The cloths then undergo various wet processes
including singeing and scouring. This process uses a
large amount of water. Dyeing is one of the most
important steps in the wet process which involves
changing the colour of the textile spun using dyes.
Finishing is the final step in manufacturing and uses
chemicals like HS-ULTRAPHIL, ECODESIZEPS- 10
and Amino silicone fluid to treat the cloths for
obtaining a better quality (Wang et al., 2002) So the
different manufacturing steps, such as desizing,
mercerization, bleaching, neutralization, dyeing,
printing and finishing, in Textile industry consumes
huge amount of dyes and chemicals as well as large
amount of water and also produces large volumes of
textile wastewater effluents. The textile effluents
contains different type of dyes, organic acid and salts,
inorganic acid and salts, bleaching agent, trace
metals in variable concentration. These un- treated
industrial effluents not only deteriorate surface water
quality, ground water, soil and vegetation, but also
cause many diseases like haemorrhage, ulceration of
skin, nausea, severe irritation of skin and dermatitis
(Nese et al., 2007).
The characterization of the textile effluents is also
needed to assess the pollution level for the protection
of environment and natural resources. Such analysis
report is important for the textile industries for
selecting proper technologies to prevent
environmental pollution. As the textile wastewater is
harmful to the environment and people, some
environmental protection agencies worldwide have
imposed rules entrusted with the protection of human
health and guarding the environment from pollution
caused by the textile industry. These agencies
imposed certain limits on the disposal of effluents
into the environment. Some of the regulations
imposed by several countries. However, due to the
difference in the raw materials, products, dyes,
technology and equipment, the standards of the
wastewater emission have too much items. It is
developed by the national environmental protection
department according to the local conditions and
environmental protection requirements which is not
fixed. It varies according to the situation in different
regions. Therefore, the purpose of this investigation is
to characterize the effluents of the textile industries
and review the current available technologies in
textile industry.
J. Bio. & Env. Sci.
2015
503 | Mostafa
Materials and methods
Characterization and Composition of textile
wastewater
The different manufacturing steps in Textile industry,
such as desizing, mercerization, bleaching,
neutralization, dyeing, printing and finishing have
been discharging the following
Colour.
A major contribution to colour in textile wastewater is
usually the dyeing and the washing operation after
dyeing which as much as 50% of the dye might be
released into the effluents (Joshi et al., 2004). Textile
dyes are mainly cationic, anionic and non-ionic dyes.
The chromophores in anionic and non-ionic dyes are
mostly azo group or anthraquinone types. The
reactive cleavage of azo linkage is responsible for the
formation of toxic amines in the effluents. Presence
of colour in the waste water is one of the main
problems in textile industry. Anthraquinone based
dyes are most resistance to degradation due to their
fused aromatic structure and therefore remain
coloured for long time in the textile wastewater.
These colours are easily visible to human eyes even at
very low concentration. Hence, colour from textile
wastes carries significant aesthetic importance. Most
of the dyes are stable and has no effect of light or
oxidizing agents.
TDS and TSS
Total dissolved solids (TDS) is a measure of the
combined content of all inorganic and organic
substances contained in a liquid in molecular, ionized
or micro-granular (colloidal sol) suspended form.
TDS is used as an indication of aesthetic
characteristics of drinking water and as an aggregate
indicator of the presence of a broad array of chemical
contaminants. TSS is solid materials, including
organic and inorganic, that are suspended in the
water. TDS are difficult to be treated with
conventional treatment systems. Disposal of high
TDS bearing effluents can lead to increase in TDS of
ground water and surface water. TSS in effluent may
also be harmful to vegetation and restrict its use for
agricultural purpose.
Toxic Metals
Waste water of textiles is not free from metal
contents. There are mainly two sources of metals.
Firstly, the metals may come as impurity with the
chemicals used during processing such as caustic
soda, sodium carbonate and salts. Secondly, the
source of metal could be dye stuffs like metalised
mordent dyes.
The metal complex dyes are mostly based on
chromium. A number of metals including cadmium,
chromium, copper, iron, lead, mercury, nickel and
zinc. Many metals, which are usually only available
naturally in trace quantities in the environment, can
be toxic to humans, plants, fish and other aquatic life.
Sulphur and Sulphide
Textile dyeing uses large quantities of sodium
sulphate and some other sulphur containing
chemicals. Textile wastewaters will therefore contain
various sulphur compounds and once in the
environment sulphate is easily converted to sulphide
when oxygen has been removed by the BOD of the
effluents
Oil and Grease
This includes all oils, fats and waxes, such as kerosene
and lubricating oils. Oil and grease causes unpleasant
films on open water bodies and negatively affect
aquatic life. They can also interfere with biological
treatment processes and cause maintenance problems
as they coat the surfaces of components of ETPs.
Residual Chlorine
The use of chlorine compounds in textile processing,
residual chlorine is found in the waste stream. The
waste water (if disposed without treatment) depletes
dissolved oxygen in the receiving water body and as
such aquatic life gets affected. Residual chlorine may
also react with other compounds in the waste water
stream to form toxic substances.
J. Bio. & Env. Sci.
2015
504 | Mostafa
pH
pH is a measure of the concentration of hydrogen ions
in the wastewater and gives an indication of how acid
or alkaline the wastewater is. This parameter is
important because aquatic life such as most fish can
only survive in a narrow pH range between roughly
pH 6-9.
BOD and COD
Biochemical oxygen demand ( BOD) is defined as the
amount of dissolved oxygen needed by aerobic
biological organisms in a body of water to break down
organic material present in a given water sample at
certain temperature (20oC) over a specific time period
(5-day). BOD can be used as a gauge of the
effectiveness of wastewater treatment plants. COD is
a measure of the oxygen equivalent of the organic
material chemically oxidised in the reaction and is
determined by adding dichromate in an acid solution
of the wastewater.
So the textile wastewater effluent contains high
amounts of agents causing damage to the
environment and human health including suspended
and dissolved solids, biological oxygen demand
(BOD), chemical oxygen demand (COD), chemicals,
odour and colour. Most of the BOD/COD ratios are
found to be around 1:4, indicating the presence of
non-biodegradable Substances (Arya and Kohli,
2009). Typical characteristics of textile effluent are
shown in Table 3.
National Standard for textile effluents
The characteristics of textile effluents vary and
depend on the type of textile manufactured and the
chemicals used. The textile effluents contain trace
metals like Cr, As, Cu and Zn, which are capable of
harming the environment (Eswaramoorthi et al.,
2008). Dyes in water give out a bad colour and can
cause diseases like haemorrhage, ulceration of skin,
nausea, severe irritation of skin and dermatitis (Nese
et al., 2007). They can block the penetration of
sunlight from water surface preventing
photosynthesis. Dyes also increase the biochemical
oxygen demand of the receiving water and in turn
reduce the reoxygenation process and hence hamper
the growth of photoautotrophic organisms (Nese et
al., 2007). The suspended solid concentrations in the
effluents play an important role in affecting the
environment as they combine with oily scum and
interfere with oxygen transfer mechanism in the air-
water interface (Laxman, 2009). Inorganic
substances in the textile effluents make the water
unsuitable for use due to the presence of excess
concentration of soluble salts. These substances even
in a lower quantity are found to be toxic to aquatic life
(Tholoana, 2007). Some of the inorganic chemicals
like hydrochloric acid, sodium hypochlorite, sodium
hydroxide, sodium sulphide and reactive dyes are
poisonous to marine life (Blomqvist, 1996; Tholoana,
2007). The organic components are found to undergo
chemical and biological changes that result in the
removal of oxygen from water (Tholoana, 2007).
Human exposure to textile dyes have resulted in lung
and skin irritations, headaches, congenital
malformations and nausea (Lima et al., 2007; Mathur
et al., 2005).) detected benzidine, a known
carcinogen in a textile effluent which contained
disperse orange 37, disperse blue 373 and disperse
violet 93 dyes. Mathur et al. (2005) tested a total of
seven dyes (cremazoles blue S1, cremazoles brown
GR, cremazoles orange 3R, direct bordeaux, direct
royal blue, direct congo red and direct violet) using
AMES tests and witnessed the presence of mutagenic
agents. It was noted that direct violet was the only dye
with a mutagenicity ratio less than 2:0. They observed
that the cremazoles dyes were so toxic to
microorganisms. Morikawa et al. (1997), reported
evidence of kidney, liver and urinary bladder cancers
on workers after prolonged exposure to textile dyes. It
was found that dermatitis, asthma, nasal problems
and rhinitis were acquired by workers after prolonged
exposure to reactive dyes (Nilsson et al., 1993).
There are strict requirements for the discharge of the
waste water as the wastewater is harmful to the
environment and the human being by the textile
J. Bio. & Env. Sci.
2015
505 | Mostafa
industry. However, the raw materials, dyes and
chemicals, products, technology and equipment used
in textile industries are different; the standards of the
discharged wastewater are also different. Generally it
is developed by the national environmental protection
department according to the local conditions and
environmental protection requirements which is not
fixed. The disposal limits are found to differ from
country to country. Some of the regulations imposed
by several countries are presented in Table-4.
Textile effluent treatment processes
Many pollutant removal technological processes have
been developed in the past decades to treat the textile
wastewater. The treatment processes is being chosen
on the basis of composition, characteristics and
concentration of material present in the effluents.
These processes are pre-treatment or preliminary,
primary or physicochemical, secondary, tertiary
treatment or combined treatment processes
depending on type, sequence and method of removal
of the harmful and unacceptable constituents. Most
commonly used processes are being discussed below:
Pre-treatment processes or preliminary treatment
Prior to textile Dyeing, the fabric must be clean &
clear of all impurities. It should be free from dust
particles and coloring materials. In order to obtain a
white pure fabric, the fabric undergoes a series of
cleaning steps covered in Pretreatment. The process
of fabric treatment prior to dyeing or printing in order
to achieve a clean fabric is known as pretreatment.
The basic aim of the pretreatment is to prepare the
fabric for dyeing and printing which gives the best
result in respect to economy and quality. It is
assumed that 70% dyeing & printing faults are
coming from the pretreatment. Natural fibers and
synthetic fibers contain primary impurities that are
contained naturally, and secondary impurities that
are added during spinning, knitting and weaving
processes.
The most conventional treatment processes in textile
wastewater treatment is the removal of suspended
solids, excessive quantities of oil and grease and gritty
materials (Eswaramoorthi et al., 2008). The coarse
suspended materials such as yarns, lint, pieces of
fabrics, fibres and rags is being removed from the
effluent by using bar and fine screens (Das, 2000).
The screened effluent then undergoes settling for the
removal of the suspended particles. The floating
particles are removed by mechanical scraping
systems. Neutralization is done to reduce the acidic
contents of the effluents. Sulphuric acid and boiler
flue gas are the most commonly used chemicals to
alter the pH. A pH value of 5-9 is considered ideal for
the treatment process (Babu et al., 2007; Das, 2000;
Eswaramoorthi et al., 2008). The common primary
treatment processes are shown as follows.
Equalization
Effluent treatment plants are usually designed to treat
wastewater that has a more or less constant flow and
a quality that only fluctuates within a narrow margin.
The equalization tank overcomes this by collecting
and storing the waste, allowing it to mix and become
a regular quality before it pumped to the treatment
units at a constant rate.
Floatation
The floatation produces a large number of micro-
bubbles in order to form the three-phase substances
of water, gas, and solid. Dissolved air under pressure
may be added to cause the formation of tiny bubbles
which will attach to particles. Under the effect of
interfacial tension, buoyancy of bubble rising,
hydrostatic pressure and variety of other forces, the
microbubble adheres to the tiny fibers. Due to its low
density, the mixtures float to the surface so that the
oil particles are separated from the water. So, this
method can effectively remove the fibers in
wastewater.
Coagulation flocculation sedimentation
Coagulation flocculation sedimentation is a physical
process which involves slow mixing of the effluent
with paddles bringing the small particles together to
form heavier particles that can be settled and
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removed as sludge (Heukelekian.,1941; Tripathy et
al., 2006). Active on suspended matter, colloidal type
of very small size, their electrical charge give
repulsion and prevent their aggregation. Adding in
water electrolytic products such as aluminum
sulphate, ferric sulphate, ferric chloride, giving
hydrolysable metallic ions or organic hydrolysable
polymers (polyelectrolyte) can eliminate the surface
electrical charges of the colloids. This effect is named
coagulation. Normally the colloids bring negative
charges so the coagulants are usually inorganic or
organic cationic coagulants (with positive charge in
water). The metallic hydroxides and the organic
polymers, besides giving the coagulation, can help the
particle aggregation into flocks, thereby increasing
the sedimentation. The combined action of
coagulation, flocculation and settling is named
clariflocculation. Settling needs stillness and flow
velocity, so these three processes need different
reactions tanks. This processes use mechanical
separation among heterogeneous matters, while the
dissolved matter is not well removed
(clariflocculation can eliminate a part of it by
absorption into the flocks). The dissolved matter can
be better removed by biological or by other physical
chemical processes (Sheng et al., 1997). But
additional chemical load on the effluent (which
normally increases salt concentration) increases the
sludge production and leads to the uncompleted dye
removal.
Adsorption
The adsorption process is used to removes colour and
other soluble organic pollutants from effluent. The
process also removes toxic chemicals such as
pesticides, phenols, cyanides and organic dyes that
cannot be treated by conventional treatment
methods. Dissolved organics are adsorbed on surface
as waste water containing these is made to pass
through adsorbent. Most commonly used adsorbent
for treatment is activated carbon (Sultana et al.,
2013). It is manufactured from carbonaceous material
such as wood, coal, petroleum products etc. A char is
made by burning the material in the absence of air.
The char is then oxidized at higher temperatures to
create a porous solid mass which has large surface
area per unit mass. The pores need to be large enough
for soluble organic compounds to diffuse in order to
reach the abundant surface area.
The activated carbon once it is saturated needs
replacement or regeneration. Regeneration can be
done chemically or thermally. The chemical
regeneration can be done in within the column itself
either with acid or other oxidizing chemicals. This
normally effects partial recovery of activity and
necessitate frequent recharging of carbon. For
thermal regeneration, the exhausted carbon is
transported preferable in water slurry to regeneration
unit where it is dewatered and fed to furnace and
heated in a controlled conditions. This process
volatilize and oxidize the impurities held in carbon.
The hot reactivated carbon is then quenched with
water and moved back to the site. This results in
almost complete restoration of its adsorption. There
are some other materials such as activated clay, silica,
flyash, etc are also known to be promising adsorbents.
Secondary Treatment
The Secondary treatment process (Figure 2) is mainly
carried out to reduce the BOD, phenol and oil
contents in the wastewater and to control its colour.
This can be biologically done with the help of
microorganisms under aerobic or anaerobic
conditions. Aerobic Bacteria use organic matter as a
source of energy and nutrients. They oxidize dissolved
organic matter to CO2 and water and degrade
nitrogenous organic matter into ammonia. Aerated
lagoons, trickling filter and activated sludge systems
are among the aerobic system used in the secondary
treatment. Anaerobic treatment is mainly used to
stabilize the generated sludge (Das, 2000).
Aerated lagoons are one of the commonly used
biological treatment processes. This consists of a large
holding tank lined with rubber or polythene and the
effluent from the primary treatment is aerated for
about 2-6 days and the formed sludge is removed.
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The BOD removal efficiency is up to 99% and the
phosphorous removal is 15-25% (Das, 2000). The
nitrification of ammonia is also found to occur in
aerated lagoons. Additional TSS removal can be
achieved by the presence of algae in the lagoon (EPA,
2002). The major disadvantage of this technique is
the large amount of space it occupies and the risk of
bacterial contamination in the lagoons (Das, 2000;
Lafond, 2008).
Trickling filters are another common method of
secondary treatment that mostly operates under
aerobic conditions. The effluent for the primary
treatment is trickled or sprayed over the filter. The
filter usually consists of a rectangular or circular bed
of coal, gravel, Poly Vinyl Chloride (PVC), broken
stones or synthetic resins (Etter et al., 2011). A
gelatinous film, made up of microorganisms, is
formed on the surface of the filter medium. These
organisms help in the oxidation of organic matter in
the effluent to carbon dioxide and water (NODPR,
1995). Trickling filters do not require a huge space,
hence making them advantageous compared to
aerated lagoons. However, their disadvantage is the
high capital cost and odour emission (Etter et al.,
2011).
Aerobic activated sludge processes are commonly
used. It involves a regular aeration of the effluent
inside a tank allowing the aerobic bacteria to
metabolize the soluble and suspended organic
matters. A part of the organic matter is oxidized into
CO2 and the rest are synthesized into new microbial
cells (NESC, 2003). The effluent and the sludge
generated from this process are separated using
sedimentation; some of the sludge is returned to the
tank as a source of microbes. A BOD removal
efficiency of 90-95% can be achieved from this
process, but is time consuming (Yasui et al., 1996).
Sludge’s formed as a result of primary and secondary
treatment processes pose a major disposal problem.
They cause environmental problems when released
untreated as they consist of microbes and organic
substances (Wright, 2013). Treatment of sludge is
carried out both, aerobically and anaerobically by
bacteria. Aerobic treatment involves the presence of
air and aerobic bacteria which convert the sludge into
carbon dioxide biomass and water. Anaerobic
treatment involves the absence of air and the
presence of anaerobic bacteria, which degrade the
sludge into biomass, methane and carbon dioxide
(Mittal, 2011).
Tertiary Treatment or Advance methods treatment
Textile effluents may require tertiary or advance
treatment methods to remove particular contaminant
or to prepare the treated effluent for reuse. There are
several technologies used in tertiary treatments
including electrodialysis, reverse osmosis and ion
exchange. Electrolytic precipitation of textile effluents
is the process of passing electric current through the
textile effluent using electrodes.
As a result of electro chemical reactions, the dissolved
metal ions combine with finely dispersed particles in
the solution, forming heavier metal ions that
precipitate and can be removed later (Wright, 2013).
One of the disadvantages is that a high contact time is
required between the cathode and the effluent (Das,
2000).
Membrane separation process
Membrane separation process is the method that uses
the membrane’s microspores to filter and makes use
of membrane’s selective permeability to separate
certain substances in wastewater. Currently, the
membrane separation process is often used for
treatment of dyeing wastewater mainly based on
membrane pressure, such as reverse osmosis,
ultrafiltration, nanofiltration and microfiltration.
Membrane separation process is a new separation
technology, with high separation efficiency, low
energy consumption, easy operation, no pollution and
so on. However, this technology is still not large-scale
promoted because it has the limitation of requiring
special equipment, and having high investment and
the membrane fouling and so on (Ranganathan et
al.,2007).
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Reverse osmosis
Reverse osmosis is a well-known technique which
makes use of membranes that have the ability to
remove total dissolved solid contents along with ions
and larger species from the effluents. A high efficiency
of >90% has been reported (Babu et al., 2007).
Cotton dyeing processes use electrolytes such as NaCl
in high concentrations. These high concentrations of
salts can be treated using reverse osmosis membrane
(Kannan et al., 2006).
Reverse osmosis can be used as end-of-pipe
treatment and recycling system for effluent. After
primary, secondary and/or tertiary treatment, further
purification by removal of organics and dissolved
salts is possible by use of reverse osmosis. RO
membranes are susceptible to fouling due to organics,
colloids and microorganism. Scale causing
constituents like hardness, carbonate, Silica, heavy
metals, oil etc has to be removed from the feed.
Reverse osmosis membranes have a retention rate of
90% or more for most types of ionic compounds and
produce a high quality of permeate (Ghayeni et al.,
1998).
Reverse osmosis membranes are available in different
configurations. In spiral wound system, membrane
and supporting material are placed in alternate
layers, rolled into a cylindrical shape and inhoused in
tube of suitable martial. The support material is
porous and serves as transport medium for permeate.
Tubular systems are available in which the membrane
and its support are wound to fit inside a containment
tube. Permeate is withdrawn from the support
medium, while reject passes through the core of the
membrane. Hollow fiber membranes are extremely
small tubes. These fibres can be suspended in the
fluid without the use of support medium. The feed
water is usually on outside of fibre, while the
permeate is withdrawn through the centre. The disc
module is relatively new in the reverse osmosis
application. Unlike conventional membrane modules
such as spiral wound, the design of disc module
facilitates an open feed flow path over membrane
element. The membrane is housed in hydraulic disc
which works as membrane spacers.
Nanofiltration
Nanofiltration has been applied for the treatment of
colored effluents from the textile industry. A
combination of adsorption and nanofiltration can be
adopted for the treatment of textile dye effluents. The
adsorption step precedes nanofiltration, because this
sequence decreases concentration polarization during
the filtration process, which increases the process
output (Chakraborty et al., 2003). Nanofiltration
membranes retain low molecular weight organic
compounds, divalent ions, large monovalent ions,
hydrolyzed reactive dyes, and dyeing auxiliaries. The
treatment of dyeing wastewater by nanofiltration
represents one of the rare applications possible for
the treatment of solutions with highly concentrated
and complex solutions (Freger et al., 2000; Kelly and
Kelly, 1995; Knauf et al., 1998; Peuchot, 1997;
Rossignol et al., 2000).
A major problem is the accumulation of dissolved
solids, which makes discharging the treated effluents
into water streams impossible. Various research
groups have tried to develop economically feasible
technologies for effective treatment of dye effluents
(Karim et al., 2006).
Ultrafiltration
This process is similar to reverse osmosis. The
difference between reverse osmosis and ultrafiltration
is primarily the retention properties of the
membranes. Reverse osmosis membranes retain all
solutes including salts, while ultrafiltration
membranes retain only macro molecules and
suspended solids. Thus salts, solvents and low
molecular weight organic solutes pass through
ultrafiltration membrane with the permeate water.
Since salts are not retained by the membrane, the
osmotic pressure differences across ultrafiltration
membrane are negligible. Flux rates through the
membranes are fairly high, and hence lower pressures
can be used. Ultrafiltration can only be used as a pre-
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treatment for reverse osmosis or in combination with
a biological reactor (Babu et al., 2007).
Microfiltration
Microfiltration is suitable for treating dye baths
containing pigment dyes (Al-Malack and Anderson.,
1997), as well as for subsequent rinsing baths. The
chemicals used in dye bath, which are not filtered by
microfiltration, will remain in the bath.
Microfiltration can also be used as a pretreatment for
nanofiltration or reverse osmosis (Ghayeni et al.,
1998).
Electrodialysis
Electrodialysis is a membrane process in which ions
are transported through ion permeable membranes
from one solution to another under the influence of
an electrical potential gradient. It has the ability to
separate dissolved salts. The electricity used in
electrodialysis influences the ions to get transported
through a semi permeable membrane by passing an
electrical potential across water (WTS, 2012). The
membranes used are charge specific and anion-
selective which allows negatively charged particles to
pass through and traps positively charged particles
and vice versa. Placing numerous membranes
throughout the system hinders the flow of effluent
and the effluent would reach a point at which the ions
are trapped or settled down and the remaining ions
are neutral in charge (Jurenka, 2010). Membrane
fouling (the process where solutes or other particles
get attached to the membrane or into the membrane
pore) has to be prevented by removing suspended
solids, colloids and turbidity prior to electrodialysis
(Marcucci et al., 2002).
Ion exchange process
Ion exchange process is normally used for the
removal of inorganic salts and some specific organic
anionic components such as phenol. All salts are
composed of a positive ion of a base and a negative
ion of an acid. Ion exchange materials are capable of
exchanging soluble anions and cations with
electrolyte solutions (Neumann et al., 2009; WWS,
2013). For example, a cation exchanger in the sodium
form when contacted with a solution of calcium
chloride will scavenge the calcium ions from the
solution and replace them with sodium ions. This
provides a convenient method for removing the
hardness from water or effluent. Ion exchange resins
are available in several types starting from natural
zeolite to synthetics which may be phenolic, sulphonic
styrenes and other complex compounds. The divalent
ions such as calcium and magnesium in general have
high affinity for the ion exchange resins and as such
can be removed with high efficiencies. In the ion
exchange process the impurities from the effluent
streams is transformed into another one of relatively
more concentrated with increased quantity of
impurities because of the addition of regeneration
chemicals. The process cannot be used for removal of
non-ionic compounds
Biological wastewater treatment method
The biological process removes dissolved matter in a
way similar to the self-depuration but in a further and
more efficient way than clariflocculation. The removal
efficiency depends upon the ratio between organic
load and the bio mass present in the oxidation tank,
its temperature, and oxygen concentration. The bio
mass concentration can increase, by aeration the
suspension effect but it is important not to reach a
mixing energy that can destroy the flocks, because it
can inhibit the following settling. Normally, the
biomass concentration ranges between 2500-4500
mg/l, oxygen about 2 mg/l. With aeration time till 24
hours the oxygen demand can be reduced till 99%.
According to the different oxygen demand, biological
treatment methods can be divided into aerobic and
anaerobic treatment. Because of high efficiency and
wide application of the aerobic biological treatment, it
naturally becomes the mainstream of biological
treatment.
Aerobic biological treatment
According to the oxygen requirements of the different
bacteria, the bacteria can be divided into aerobic
bacteria, anaerobic bacteria and facultative bacteria.
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Aerobic biological treatment can purify the water with
the help of aerobic bacteria and facultative bacteria in
the aerobic environment. Aerobic biological
treatment can be divided into two major categories:
activated sludge process and biofilm process.
Anaerobic biological treatment
Anaerobic biological treatment process is a method
that make use of the anaerobic bacteria decompose
organic matter in anaerobic conditions. This method
was first used for sludge digestion. In recent years it
was gradually used in high concentration and low
concentration organic wastewater treatment. In
textile industry, there are many types of high
concentration organic wastewater, such as wool
washing sewage, textile printing and dyeing
wastewater etc., which the organic matter content of
it is as high as 1000 mg/L or more, the anaerobic
wastewater treatment process can achieve good
results. The anaerobicaerobic treatment process is
usually adopted in actual project that is using
anaerobic treatment to treat high concentration
wastewater, and using aerobic treatment to treat low
concentration wastewater. Currently, the hydrolysis
acidification process is the main anaerobic treatment
process, which can increases the biodegradability of
the sewage to facilitate the following biological
treatment process.
The hydrolysis acidification process is the first two
stages of the anaerobic treatment. Through making
use of the anaerobic bacteria and facultative bacteria,
the macromolecule, heterocyclic organic matter and
other difficult biodegradable organic matter would be
decomposed into small molecular organic matter,
thereby enhancing the biodegradability of the
wastewater and destructing the colored groups of dye
molecules to remove part of the color in wastewater.
More importantly, due to the molecular structure of
the organic matter and colored material or the
chromophore has been changed by the anaerobic
bacteria, it’s easy to decompose and decolor under the
aerobic conditions, which improve the decolorization
effect of the sewage. Operating data shows that the
pH value of the effluent from hydrolysis tank usually
decrease 1.5 units. The organic acid which is produced
in hydrolysis can effectively neutralize some of the
alkalinity in wastewater, which can make the pH
value of sewage drop to about 8 to provide a good
neutral environment for following aerobic treatment.
Currently, the anaerobic digestion process is a
essential measure in the biological treatment of textile
dyeing wastewater. In addition, there are many other
processes used in textile dyeing wastewater treatment
currently, such as upflow anaerobic sludge bed
(UASB), upflow anaerobic fluidized bed (UABF),
anaerobic baffled reactor (ABR) and anaerobic
biological filter and so on.
Biochemical and physicochemical combination
processes
In recent years a large number of difficult
biodegradable organic matter such as PVA slurry,
surface active agents and new additives enter into the
dyeing wastewater, which result in the high
concentration of the organic matter, complex and
changeable composition and the obvious reduction of
the biodegradability. The CODCr removal rate of the
simple aerobic activated sludge process which was
used to treat the textile dyeing wastewater has
decreased from 70% to 50%, and the effluent cannot
meet the discharge standards. More seriously, quite a
number of sewage treatment facilities can’t normally
operate even stop running. Therefore, the
biochemical and physicochemical combination
processes has been gradually developed and its
application is increasingly widespread (Sheng-Jie et
al., 2008). The types of the combination process are
various, and the main adoptions currently are as
following:
Hydrolytic acidification-contact oxidation-air
floatation process
This combination process is a typical treatment
process of the textile dyeing wastewater, which is
widely used (Fig. 10). The wastewater firstly flows
through the bar screen, in order to remove a part of
the larger fibers and particles, and then flows into the
J. Bio. & Env. Sci.
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regulating tank. After well-distributed through a
certain amount of time, the sewage flows into the
hydrolysis acidification tank to carry out the
anaerobic hydrolysis reaction. The reaction
mechanism is making use of the anaerobic hydrolysis
and acidification reaction of the anaerobic
fermentation to degrade the insoluble organic matter
into the soluble organic matter by controlling the
hydraulic retention time. At the same time, through
cooperating with the acid bacteria, the
macromolecules and difficult biodegradable organic
matter would be turned into biodegradable small
molecules, which provide a good condition for the
subsequent biological treatment. Next, the sewage
enters into the biological contact oxidation tank. After
the biochemical treatment, the wastewater directly
enters into the flotation tank for flotation treatment,
which is adopted the pressurized full dissolved air
flotation process. The polymer flocculants added in
flotation tank react with the hazardous substances,
which can condense the hazardous substances into
tiny particles. Meanwhile, sufficient air is dissolved in
the wastewater. And then the pressure suddenly is
released to produce uniformly fine bubbles, which
would adhere to the small particles. The density of the
formation is less than 1kg/m3, which can make the
formation float and achieve the separation of the solid
and liquid.
The anaerobic hydrolysis acidification tank equipped
with semi-soft padding and the biological contact
oxidation tank equipped with the new SNP-based
filler. The following physicochemical treatment uses
the dosing flotation tank, which has four
characteristics. Firstly, the deciduous biofilm and
suspended solids removal rate can reach 80% to 90%.
Secondly, the color removal rate can reach 95%.
Thirdly, the hydraulic retention time in the flotation
tank is short, which is only about 30 min, while the
precipitation tank is about 1.15 h to 2 h, so the volume
and area of the flotation tank is small. Finally, the
sludge moisture content is low, only about 97% to
98%, which can be directly dewatered. But the
flotation treatment need an additional air
compressor, pressure dissolved gas cylinders, pumps
and other auxiliary system. The operation and
management is also relatively complicated. After the
treatment of this process, the CODCr removal rate can
be up to 95% or more. The actual effluent quality is
about: pH=6~9, color<100times, SS<100mg/L,
BOD5<50mg/L, CODCr<150mg/L (Honglian Li,
2006).
Anaerobic-aerobic-biological carbon contacts
The treatment process is a mature and widely used
process in wastewater treatment in recent years (Fig.
11). The anaerobic treatment here is not the
traditional anaerobic nitrification, but the hydrolysis
and acidification. The purpose is aiming at degrading
some poorly biodegradable polymer materials and
insoluble material in textile dyeing wastewater to
small molecules and soluble substances by hydrolysis
and acidification, meanwhile, improving the
biodegradability and BOD5/CODCr value of the
wastewater in order to create a good condition for the
subsequent aerobic biological treatment. At the same
time, all sludge generated in the aerobic biological
treatment return into the anaerobic biological stage
through the sedimentation tank. Because of the
sludge in the anaerobic biochemical stage has
sufficient hydraulic retention time (8h~10h) to carry
out anaerobic digest thoroughly; the whole system
would not discharge sludge that is the sludge achieves
its own balance. Anaerobic tank and aerobic tank are
both installed media, which is a biofilm process.
Biological carbon tank is filled with activated carbon
and provided oxygen, which has the characteristics
both of suspended growth method and fixation
growth method. The function of pulse water is mixing
in the anaerobic tank. The hydraulic retention time of
various parts is about: Regulating tank: 8h~12h;
anaerobic biochemical tank: 8h~10h Aerobic
biochemical tank: 6 ~8h; biological carbon tank:
1h~2h Pulse generator interval: 5min~10min.
According to the textile dyeing wastewater standard
(CODCr ≤1000 mg/L), the effluent can achieve the
national emission standards, which can be reused
through further advanced treatment. For the five
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years operation project, the results show that the
operation is normal, the treatment effect is steady,
there is no efflux of sludge and the sludge was not
found excessive growth in the anaerobic biochemical
tank.
Coagulation-ABR-oxidation ditch process
The treatment has been adopted widely in the textile
dyeing wastewater treatment plants (Fig. 6). The
characteristics of the textile dyeing plant effluent are
the variation in water, the higher of the alkaline, color
and organic matter concentration , and the difficulty
of the degradation (BOD5/CODCr value is about 0.25).
The workshop wastewater enter into the regulating
tank by pipe network to balance the quantity and
quality, after wiping off the large debris by the bar
screen before the regulating tank. The adjusted
wastewater flow into the coagulation reaction tank, at
the same time, the FeSO4 solution was added into it to
carry out chemical reaction. Finally, the effluent flows
into the primary sedimentation tank for spate
separation, meanwhile enhancing the BOD5/CODCr
ratio. The effluent of primary sedimentation tank
flows into the anaerobic baffled reactor (ABR) by
gravity. After the anaerobic hydrolysis reaction, it
enters into the integrated oxidation ditch for aerobic
treatment, and then goes into the secondary
sedimentation tank for spate separation. The upper
liquid was discharged after meeting the standards,
but the settled sludge was returned to the return
sludge tank, most of which was returned to ABR
anaerobic tank by pump. The remaining sludge was
pumped to the sludge thickening tank for
concentration.
UASB-aerobic-physicochemical treatment process
For the high pH value dyeing wastewater treatment
systems should adjust the pH value to the range from
6 to 9 before entering the treatment system. The
"UASB-aerobic-physicochemical method" treatment
process is shown in Fig. 7.
At present, the treatment process has been applied in
a number of textile dyeing factories which sewage
component is complex. Before the sewage enters into
the regulating tank, the suspended particles in which
must be removed by bar screen, at the same time, an
appropriate amount of acid was added to adjust the
pH value of the sewage. Then adjusting the water
quantity and quality to make it uniformed. After pre-
treatment, the textile dyeing wastewater carries out
anaerobic reaction firstly in UASB reactor to improve
the biodegradability of wastewater and the
decolourization rate, and then flows into the aerobic
tank. In the aerobic tank, the organic matter in
sewage is removed. Finally, in order to ensure the
effective removal of the suspended particles particular
the activated sludge, some flocculants was added in
the sedimentation tank to improve its effect. Through
this sewage treatment process, the removal rate of
pollutants is shown in table 5 (Zhang, 2007).
Cutting edge advanced oxidation processes (AOP)
AOP uses a powerful and effective combination of
ozone, UV and hydrogen peroxide to decompose
unwanted chemical and organic compounds, TOC,
COD and BOD. Unlike physical and biological
treatment methods, AOP doesn’t produce additional
by-products and sludge, eliminating the need for
further handling. Furthermore, physical and
biological treatment methods fall short of meeting the
new environmental standards. AOP is a proven, more
efficient and effective means of treating waste streams
that meets and exceeds industry requirements.
AOP systems can be adapted to suit specific
applications and are fully automated, reducing capital
and operating costs. These processes are ideal for:
• Reclaim, recycle and reuse of process and waste
water
• Waste water treatment
• Gas effluent treatment
• Treatment for ultra-pure water
Advanced Oxidation Processes (AOPs)
AOPs were defined by Glaze and et al. (1987) as near
ambient temperature and pressure water treatment
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processes which involve the generation of highly
reactive radicals (specially hydroxyl radicals) in
sufficient quantity to effect water purification. These
treatment processes are considered as very promising
methods for the remediation of contaminated ground,
surface, and wastewaters containing non-
biodegradable organic pollutants. Hydroxyl radicals
are extraordinarily reactive species that attack most of
the organic molecules. The advanced oxidation
processes (AOPs) are: UV/O3 process, UV/H2O2,
O3/H2O2, Fe3+/ UV-vis process, UV/TiO2
(Heterogeneous photocatalysis), H2O2 / Fe2+ (known
as Fenton’s reagent).
Among various AOPs, the Fenton reagent (H2O2/
Fe2+) is one of the most effective methods of organic
pollutant oxidation. The Fenton reagent has been
found to be effective in treating various industrial
wastewater components including aromatic amines, a
wide variety of dyes as well as many other substances,
e.g. pesticides and surfactants (Rodríguez, 2003).
Therefore, the Fenton reagent has been applied to
treat a variety of wastes such as those associated with
the textile and chemical industries.
The advantage of the Fenton reagent is that no energy
input is necessary to activate hydrogen peroxide
(Rodríguez, 2003). Therefore, this method offers a
cost-effective source of hydroxyl radicals, using easy-
to-handle reagents. However, disadvantages in using
the Fenton reagent include the production of a
substantial amount of Fe(OH)3 precipitate and
additional water pollution caused by the
homogeneous catalyst that added as an iron salt,
cannot be retained in the process (Rodríguez, 2003).
To solve these problems, the application of alternative
iron sources as catalysts in oxidizing organic
contaminants has been studied extensively. A number
of researchers have investigated the application of
iron oxides such as hematite, ferrihydrite,
semicrystalline iron oxide and crystalline goethite
(Rodríguez, 2003). They generally have observed a
greatly accelerated decomposition of hydrogen
peroxide but variable amounts of contaminant were
lost.
The Fenton reaction was discovered by H.J.Fenton in
1894 (Fenton, 1894). Forty years later the Haber-
Weiss. (1934) mechanism was postulated, which
revealed that the effective oxidative agent in the
Fenton reaction was the hydroxyl radical.
The Fenton reaction can be outlined as follows:
Mn++H2O2_M(n+1)++HO - + HO• (1)
where M is a transition metal as Fe or Cu.
The HO• radical mentioned above, once in solution
attacks almost every organic compound. The metal
regeneration can follow different paths. For Fe2+, the
most accepted scheme is described in the following
equations (Sychev and Isak, 1995)
Fe3++H2O2_Fe3++HO + HO• (2)
Fe3++H2O2_Fe2++ HO2• + H+ (3)
Fe2++HO•_Fe3++HO•- (4)
HO•+H2O2_HO•+H2O (5)
Fe3++HO•_Fe2++H++ O2 (6)
Fe3++O2•-_Fe2++O2 (7)
Fe2++HO2•_Fe3++HO2•- (8)
Fenton reaction rates are strongly increased by
irradiation with UV/visible light (Ruppert et al.,
1993).
Photochemical oxidation
Photochemical oxidation has many advantages of the
mild reaction conditions (ambient temperature and
pressure), powerful oxidation ability and fast speed,
etc. It can be divided into four kinds, which are light
decomposition, photoactivate oxidation, optical
excitation oxidation and photocatalysis oxidation.
Among them, the photocatalysis oxidation has been
more researched and applied currently.
This technology can effectively destroy a lot of organic
pollutants whose structure is stable and difficult to
biologically degrade. Compared with the physical
treatment in traditional wastewater treatment
process, the most obvious advantages of this
technology are significant energy efficiency,
completely pollutants degradation and so on. Almost
all of the organic matter can be completely oxidized to
CO2, H2O and other simple inorganic substances
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under the light catalyst. However, towards high
concentration wastewater, the effect of the
photocatalysis oxidation process is not ideal. The
research about photocatalysis oxidation degradation
of dye mainly focused on the study of photocatalyst.
Electrochemical oxidation
The mechanism of the electrochemical process
treating dyeing wastewater is making use of
electrolytic oxidation, electrolytic reduction,
electrocoagulation or electrolytic floating destruct the
structure or the existence state to make it bleached. It
has the advantages of small devices, small area
covering, operation and management easily, higher
CODCr removal rate and good bleaching effect, but the
precipitation and the consumption of electrode
material is great, and the operating cost is high. The
traditional electrochemical methods can be divided
into power flocculation, electrical float, electro-
oxidation, micro-electrolysis and the electrolysis
method. With the development of electrochemical
technologies and the appearing of a variety of high
efficiency reactor, the cost of treatment will decrease
largely. Electro-catalytic advanced oxidation process
(AEOP) is a new advanced oxidation technology
developed recently. Because of its high efficiency, easy
operation, and environmental friendliness, it has
attracted the attention of researchers. Under normal
temperature and pressure, it can produce hydroxyl
radicals directly or indirectly through the reactions in
the catalytic activity electrode, thus the degradation of
the difficultly biodegradable pollutants is effective. It
is one of the main directions in future research.
Ultrasonic technology
Using ultrasonic technology can degrade chemical
pollutants, especially the refractory organic pollutants
in water. It combines the characteristics of advanced
oxidation technology, incineration, supercritical
water oxidation and other wastewater treatment
technologies. Besides the degradation conditions are
mild, degradation speed is fast and application
widely; it can also use individually or combined with
other water treatment technologies. The principle of
this method is that the sewage enters into the air
vibration chamber after being added the selected
flocculants in regulating tank. Under the intense
oscillations in nominal oscillation frequency, a part of
organic matter in wastewater is changed into small
organic molecule by destructing its chemical bonds.
The flocculants flocculation rapidly companied with
the color, CODCr and the aniline concentration was
fall under the accelerating thermal motion of water
molecules, which play the role of reducing organic
matter concentration in wastewater. At present, the
ultrasonic technology in the research of water
treatment has achieved great achievements, but most
of them are still confined to laboratory research level.
High energy physical process
High energy physical process is a new wastewater
treatment technology. When the high energy particle
beam bombard aqueous solution, the water molecules
would come up with excitation and ionization,
produce ions, excited molecules, secondary electrons.
Those products would interact with each other before
spreading to the surrounding medium. It would
produce highly reactive HO. radicals and H atoms,
which would react with organic matter to degrade it.
The advantages of using high-energy physics process
treat dyeing wastewater are the small size of the
equipment, high removal rate and simple operation.
However, the device used to generate high energy
particle is expensive, technically demanding is high,
energy consumption is big, and the energy efficiency
is low and so on. Therefore, it needs a lot of research
work before put into actual project.
Results and discussion
Textiles and Garments is one of the oldest and largest
industries in the world. The textile industries have
great economic significance by virtue of its
contribution to overall industrial output and
employment generation in so many countries. The
textile industry utilizes various dyes, chemicals and
large amount of water during the production process.
The waste water produced during this process
contains large amount of dyes and chemicals
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containing trace metals such as Cr, As, Cu and Zn
which are capable of harming the environment and
human health. The textile waste water causes
haemorrhage, ulceration of skin, nausea, skin
irritation and dermatitis. The chemicals present in
the water block the sunlight and increase the
biological oxygen demand thereby inhibiting
photosynthesis and reoxygenation process.
Table 1. Major Exporters of Textiles.
Country
Value ($ Billion)
Share (%)
China
94.4
32.1
European Union 27
76.6
26.1
India
15.0
5.1
United States of America
13.8
4.7
Korea Republic
12.4
4.2
Turkey
10.8
3.7
Pakistan
9.1
3.1
Indonesia
4.8
1.6
Vietnam
3.8
1.3
Bangladesh
1.5
0.5
Rest of the World
51.7
17.5
Total
294
99.9
Table 2. Major Exporters of Cloths.
Country
Value ($ Billion)
Share (%)
China
153.8
35.6
European Union 27
116.4
27.1
Bangladesh
19.9
4.6
India
14.4
3.3
Turkey
13.9
3.2
Vietnam
13.2
3.1
Indonesia
8.0
1.8
United States of America
5.2
1.2
Pakistan
4.6
1.1
Korea Republic
1.8
0.4
Rest of the World
79.8
18.5
Total
431
99.9
Table 3. Characteristics of typical untreated textile wastewater.
Parameter
Range
pH
6-10
Temperature (C)
35-45
Total d solids (mg/L)
8,000-12,000
BOD (mg/L)
80-6,000
COD (mg/L
150-12,000
Total suspended solids (mg/L
15-8,000
Total dissolved solids (mg/L)
2,900-3,100
Chlorine (mg/L)
1,000-6,000
Free chlorine (mg/L)
<10
Sodium (mg/L)
70%
Trace metals (mg/L
Fe
<10
Zn
<10
Cu
<10
AS
<10
Ni
<10
B
<10
F
<10
Mn
<10
V
<10
Hg
<10
PO4
<10
Co
<10
Oil and Grease (mg/L)
10-30
TNK (mg/L
10-30
NO3-N (mg/L
<15
Free Ammonia (mg/L
<10
Sulphate (mg/L
600-1000
Silica (mg/L
<15
Total Kjeldahl Nitrogen (mg/L
70-80
Color (Pt-Co)
50-2,500
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Table 4. Some Textile waste water pollution regulations imposed by several countries.
Parameter
CCME
China
BIS
Hong Kong
FEPA
MEX
THA
PHI
INDO
BD
SL
pH
6.5-8.5
6-9
5.5-9
6-10
6-9
6-8.5
5-9
6-9
6-9
6.5-9
6-8.5
Temperature (C)
30
-
50
43
40
-
-
40
-
40-45
40
Color (Pt-Co)
100
80
None
1 (Lovibond)
1 (Lovibond)
-
-
100-200
-
-
30
TDS (mg/L)
2000
-
2100
-
2000
-
2000-5000
1200
-
2100
2100
TSS (mg/L)
40
150
100
800
30
-
30-150
90
60
100
500
Sulphide (g/L)
200
1000
2000
1000
200
-
-
-
-
1000
2000
Free Chlorine (g/L)
1000
-
1000
-
1000
-
-
1000
-
-
-
COD (mg/L)
80
200
250
2000
80
125
120-400
200-300
250
200
600
BOD (mg/L
50
60
30
800
50
30
20-60
30-200
85
150
200
Oil and Grease (mg/L)
-
-
10
20
10
-
300
5-15
5
10
30
Dissolved Oxygen (g/L)
6000
-
-
4000
-
-
-
1000-2000
-
4500-8000
-
Nitrate (g/L)
13000
-
10000
-
20000
10000
-
-
-
10000
45000
Ammonia (g/L)
0.1
-
-
500
0.2
-
-
-
-
5000
60
Phosphate (g/L)
4000
1000
5000
5000
5000
-
-
-
2000
-
2000
Calcium (g/L)
-
-
-
-
20000
-
-
20000
-
-
24000
Magnesium (g/L)
20000
-
-
-
20000
-
-
-
-
-
15000
Chromium (g/L)
1
-
100
100
100
50
500
50-500
500
2000
50
Aluminium (g/L)
5
-
-
-
1000
5000
-
-
-
-
-
Copper (g/L)
1000
2000
3000
1000
1000
1000
1000
1000
2000
500
3000
Manganese (g/L)
5
2000
2000
1000
5.0
200
5000
1000-5000
-
5000
500
Iron (g/L)
300
-
3000
500
20000
1000
-
1000-20000
5000
2000
1000
Zinc (g/L)
30
5000
5000
1500
10000
10000
-
5000-10000
5000
5000
10000
Mercury (g/L)
0.026
-
0.01
1
0.05
-
5
5
-
10
1
Note: CCME-Canadian Council of Ministers of the Environment, BIS-Bureau of Indian Standards, FEPA-Federal
Environmental Protection Agency (USA), Mex-Mexico, Tha-Thailand, Phi-Philipines, Indo-Indonesia, Bd-
Bangladesh SL-Srilanka
Table 5. The removal of the processing units.
Items
Raw Water
(regulating tank)
Biochemical treatment system
Physiochemical treatment system
Effluent
Removal rate
Effluent
Removal rate
pH
8-12
7-8
6-9
CODcr (mg/L)
1000-2000
100-200
90
100
50
BOD5 (mg/L
300-600
15-30
95
30
Color (times)
100-600
60
80
40
35
In the recent year, many consumers in the developed
countries are demanding biodegradable and
ecologically friendly textiles. Some countries have
already strictly applied their ecological standards for
water pollution in textile industries throughout
processing from raw material selection to the final
products. The main challenge for the textile industries
today is to modify production methods, so they are
more ecologically friendly by using safer dyes and
chemicals and by reducing cost of effluent treatment.
Waste minimization is of great importance in
decreasing pollutions load and production costs.
Traditionally the effluent water discharged from the
textile industries undergoes various physio-chemical
processes such as flocculation, coagulation and
ozonation followed by biological treatments for the
removal of nitrogen, organics, phosphorous and
metal. The whole treatment process involves three
steps: primary treatment, secondary treatment and
tertiary treatment. The primary treatment involves
removal of suspended solids, most of the oil and
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grease and gritty materials. The secondary treatment
is carried out using microorganisms under aerobic or
anaerobic conditions and involves the reduction of
BOD, phenol and remaining oil in the water and
control of color.
Fig. 1. A flow diagram for various steps involved in processing textile in a cotton mills.
Fig. 2. Components of conventional physico-chemical treatment.
Fig. 3. Components of conventional physico-chemical treatment.
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The tertiary treatment involves the use of
electrodialysis, reverse osmosis and ion exchange to
remove the final contaminants in the wastewater. The
major disadvantages of using the biological process
are that the presence of toxic metals in the effluent
prevents efficient growth of microorganisms and the
process requires a long retention time.
Fig. 4. Secondary treatment Processes.
Fig. 5. Secondary treatment Processes.
Fig. 6. Secondary treatment Processes.
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The advanced oxidation processes is gaining attention
in the recent days due to the ability to treat almost all
the solid components in the textile effluents. The
photo-oxidation of the effluents is carried out using
H2O2, combination of H2O2 and UV and Combination
of TiO2 and UV.
Fig. 7. A typical Electrodialysis (ED) flow diagram.
Fig. 8. A Flow diagram of Ion Exchanger.
Fig. 9. Secondary treatment Processes.
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Advanced oxidation process generates low waste and
uses hydroxyl radicals (OH●) as their main oxidative
power. The hydroxyl radicals (OH●) are produced by
chemical, electrical, mechanical or radiation energy
and therefore advanced oxidation processes are
classified under chemical, photochemical, catalytic,
photocatalytic, mechanical and electrical processes.
Fig. 10. Hydrolytic acidification-contact oxidation-air floatation process flow diagram.
Fig. 11. Anaerobic-aerobic-biological carbon contacts process flow diagram.
Fig. 12. Coagulation-ABR-oxidation ditch process flow diagram.
J. Bio. & Env. Sci.
2015
521 | Mostafa
The effluents treated with advanced oxidation
process were found to reduce 70-80% COD when
compared to 30-45% reduction in biological
treatment.
Fig. 13. UASB-aerobic-physicochemical treatment process flow diagram.
Fig. 14. Advanced Oxidation Processes (AOPs) flow diagram.
Conclusion
Proper selection and application of individual or
combination the advance treatment methods in
textile industry can effectively make recovery of water
from the wastewater for their reuse in production
processes. The advance methods can also be applied
to meet stringent environmental or regulatory
requirements by the reusing the water and chemicals.
On the other hand, clean production is also an
important research, which can shift the focus from
end of the treatment to the prevention of pollution
and conduct more in-depth research on the printing
and dyeing production technology and process
management. Moreover, the strategic,
comprehensive, preventive measures and advanced
production technology can be used to improve the
material and energy utilization. Also, we can reduce
and eliminate the generation and emissions of wastes
as well as the production of excessive use of resources
and the risks to humans and the environment.
Prevention and treatment of dyeing wastewater
pollution are complementary. We can both use
preventive measures as well as a variety of methods to
control the wastes and make use of treated water.
This will not only reduce water consumption, but also
effectively reduce the pollution of the printing and
dyeing wastewater and achieve sustainable
development of society.
Acknowledgement
The author is thankful to Mr. Manual Alberto
Sanchez, Jefe Sseccion Ingenieria Forense, National
J. Bio. & Env. Sci.
2015
522 | Mostafa
Police of Peru, Peru for assisting the review works.
The author is also grateful to the Technical Secretariat
of Organization of the Prohibition of Chemical
Weapons (OPCW), The Hague, Netherlands for
financial assistance to formulate the manuscript
during the Associate Programme 2014.
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