The cloth are released to wastewater streams and

The textile industry
being one of the very important and developing industries in Pakistan. It is
the source of large amounts of colored and toxic wastewaters; because of its
need to large volumes of water is used in different production steps. After
dying process, dyes which could not be fixed onto the cloth are released to
wastewater streams and cause high color intensity. It is indicated in
literature that about the half of reactive dyes, 8 to 20% of dispersed dyes and
1% of pigments remain unfixed in the solution and are sent to the treatment
processes (Hassan et al., 2006; Pirgal?o?lu,2008).

Wastewater from textile industry is generally
characterized by high levels of chemicals, biological oxygen demand (BOD),
total suspended solids and color. Disposal of textile wastewater is an
environmental concern since the associated color is noticeable to the public,
and some azo dyes may have carcinogenic and/or teratogenic effects on public
health 1. Color, depending on its origin, it is not only a problem of
aesthetics but also of toxicity and reduced biodegradability 2-4. Color is
also the primary problem for water reuse and material recovery in dyeing
operations 5. Therefore, it is necessary to find an effective method of
wastewater treatment capable of removing color and toxic organic compounds from
textile effluents. These less or non-biodegradable compounds, called
xenobiotics, cannot be completely removed by biological treatment and
wastewater contaminated with these substances must be treated by physical and
chemical means.

Because the chemical structures of dyes are rather
complicated, biological treatment methods are not efficient for their
degradation. These methods do not result in dye degradation. They merely
provide the physical removal of the dye material from the effluent, which still
creates a waste disposal problem; that is a large amount of sludge or solid
waste generated resulting in high operational costs for sludge treatment and
disposal 6.

Hence, the use of conventional oxidants has been
the standard chemical method for years, for the treatment of dye wastewater,
however, these procedures are not always feasible owing to thermodynamic and
kinetic limitations of the common reagents to attack refractory compounds. To
remedy this situation, advanced oxidation processes or techniques (AOPs, AOTs),
which generate powerful hydroxyl radicals (HO., Eº= 2.8 V vs. normal
hydrogen electrode), have been proposed for color removal and degradation of
dyes 7-10. Particularly, these techniques have been found to be suitable for
azo-type dyes, which are the mostly used textile colorants 11-14.


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