The document discusses textile wastewater and its treatment. Textile wastewater is one of the main sources of water pollution worldwide due to dyes and other chemicals used in the textile production process. Dyes can be detected in water at low concentrations and absorb light, inhibiting aquatic plant growth. Textile wastewater is difficult to treat due to fluctuations in pH, organic content, color, and other parameters depending on the chemicals used. Major pollutants come from dyeing and finishing steps. Anaerobic treatment is commonly used but produces aromatic amine byproducts, so sequential anaerobic-aerobic treatment is often employed for complete degradation.

2. TEXTILE WASTEWATER
With the increased demand for textile products, there
is increase in the textile industry and its wastewater
proportionally, making it one of the main sources of severe
pollution problems worldwide. In particular, the release of
colored effluents into the environment is undesirable, not
only because of their color but also because of the breakdown
products. The release of colored wastewater in the ecosystem
is a remarkable source of esthetic pollution, eutrophication,
and perturbations in aquatic life.
Dyes can absorb light with wavelength in visible
region (350–700 nm); they are colored and are detectable
even in the concentration of 1 mg/l. Furthermore, the
absorption of light due to textile dyes creates problem to
photosynthetic aquatic plants and algae.

3. Processes Used in Fabric Production
1. Sizing and Desizing The sizing process is the process where the
yarn is wrapped for easy working in weaving, knitting, and the
tufting process. Sizing is carried out by the application of the
chemicals like polyvinyl alcohol (PVA), carboxymethyl cellulose
(CMC), and polycyclic acids. PVA and CMC are resistant to
biological degradation, but starch is easily biodegradable. As such,
there is little or no waste from this stage of textile processing
2. Scouring In this process, cotton wax and other non cellulosic
components of cotton are removed by hot alkali, detergent, or soap
solution like glycerol ethers and scouring solvents. The pH of the
wastewater is highly alkaline ranging from 10 to 11.
3. Bleaching Mostly sodium hypochlorite, sodium silicate, hydrogen
peroxide, and organic stabilizers like enzymes are used as
bleaching agents. High levels of chlorides or peroxide might cause
inhibition problem, and this contributes to little or no residual
waste with high pH-containing wastewater.

4. 5. Dyeing Dyes Depending on the dyeing process, many
chemicals like metals, salts, surfactants, organic processing
assistants, sulfide, and formaldehyde may be added to
improve dye adsorption onto the fibers, which are the major
pollutants in the wastewater.
6. Finishing Finishing is the final process of the fabric
preparation, which is done to get some desired properties of
the fabric. Cotton fabrics are given temporary starch
finishing. In this, various fabrics are used, and small amount
of which can enter into wastes.
4. Mercerizing It improves luster of the fabric and dye uptake.
For mercerizing, the fabric is padded through 25 % caustic
soda wash. This increases the pH of the wastewater.

5. TOXICITY
Textille Wastewater Components and Treatment Difficulties
Wastewater from textile industries constitutes a threat
to the environment in a large part of the world. The
characteristics of wastewater generated by composite,
processing, and woolen industries are given in Table 1. There
are extreme fluctuations in different parameters such as
chemical oxygen demand (COD), BOD, pH, color, and salinity
with textile processing. The wastewater composition will
depend on the different organic-based compounds, chemicals,
and dyes used in the industrial dry- and wet-processing steps.
The main pollutants of textile wastewater originates
from the dyeing and finishing steps that involve dying of the
man-made or natural fibers to the desired permanent color
and processing of those fibers into final commercial products.

7. PROBLEM POLLUTANTS
Major Pollutants in Textille Wastewater and it’s Impact of Textille Chemicals in
Biological Treatment

8. BIODEGRADATION
1. Organic load Scouring and desizing effluents are a major
contribution to the organic load in textile effluents.
Traditional sizes such as starches and their derivatives are
readily biodegradable under aerobic and anaerobic
conditions. However, bulking of activated sludge occurs
frequently if a large proportion of the wastewater consists of
desizing wastewater. Anaerobic treatment produces little
sludge when compared with aerobic treatment.
2. Color Reduction of the chromophore can be achieved
under reducing conditions prevailing in anaerobic
bioreactor. The amines produced by the reduction of the azo
dyes are colorless, but they are very resistant to further
degradation under anaerobic conditions. Under aerobic
conditions, the mineralization of these amines can be
accomplished. Complete treatment can thus be obtained by a
sequenced anaerobic–aerobic treatment.

9. 3. Toxicity The anaerobic microbial community that maintains the
reducing conditions for the decolorization of the textile dyes is
known to be sensitive to toxic shocks and is one of the reasons for the
retardation in color removal.
4. Co-substrates Glucose, raw municipal wastewater, and yeast
extract, among others, have been reported as examples of an essential
co-substrate needed to obtain good color removal.
5. Redox potential The redox potential has been reported to be below
−450 and −500 mV for azo dye reduction to occur.
6. Nutrients Additives containing nitrogen and phosphorus (e.g.,
urea, ammonium acetate, ammonium sulfate, and ammonium
phosphate) are the main sources of nutrients in the textile effluent.
Textile effluents were found to be major inhibitors of the nitrifying
bacteria in aerobic treatment systems, thus hampering nitrogen
removal. Importance should be given in the COD/N ratio in
considering anaerobic treatment of textile effluents. Effort should be
put into the reduction of the amounts of dye bath additives applied
and the selection of nitrogen- and phosphorus-free alternative
auxiliaries in the production process so as to minimize the need for
nutrient removal in wastewater treatment.

10. TREATMENT
Anaerobic Treatment of Textile Wastewater
Under anaerobic conditions, dyes are readily cleaved via a four electron
at cleavagegenerating aromatic amines, which is a stable
biotransformation product of metabolism. Dye decolorization under
methanogenic condition requires an organic carbon/energy source.
Simple substrates like glucose, starch, acetate, ethanol, whey, and tapioca
have been used as dye-decolorizing substrate.
Decolorization under Anoxic Condition
Although many of these microorganisms were able to grow aerobically,
decolorization was achieved only under anoxic condition.
Decolorization of azo dyes under anoxic conditions also required co-
substrates such as yeast extract, peptone, or carbohydrates
Sequential Degradation
It has been repeatedly suggested that aromatic amines formed during
anaerobic cleavage of the azo dyes could be further degraded in an
aerobic treatment. The feasibility of this strategy was first demonstrated
for sulfonated azo dyes Mordant Yellow. After aeration, the amines
formed were completely mineralized by the microorganisms.