Environmental Engineering Reference
In-Depth Information
uents from textile and dyeing industries are generally colored and contain
high concentrations of dissolved solids, total solids, BOD/COD, salts and variation
in pH and temperature. Such ef
The ef
uents also have the presence of heavy metals, such
as Cr, Zn, Cu and Al due to presence metal-based complexed dyes. Available
reports have indicated that direct and indirect toxic effects of the dyes and dyes
containing waste can cause tumours, cancers and allergies in humans. Besides they
inhibit the growth of bacteria, protozoan, algae, plants and different animals
including human beings. Improper discharge of textile dyes ef
uent in aqueous
ecosystems also leads to reduction in sunlight penetration, photosynthetic activity,
dissolved oxygen concentration and water quality. Thus, untreated dye containing
wastewater causes severe environmental and health problems worldwide (Saratale
et al. 2011 ; Solis et al. 2012 ).
Now-a-days, government
legislation is becoming more stringent
in most
developed countries, regarding the removal of dyes from industrial ef
uents. So, it
has become mandatory to treat dye containing wastewater before discharging to
sewage treatment plant or environment. Government has set limits for some
parameters for quality of water to discharge in sewage treatment plant and envi-
ronment. A number of biological and physico-chemical methods have been
developed for the ef
cient removal of industrial azo dyes (Solis et al. 2012 ).
has become a key microbial tool to deal with different pollutants,
is a key research area in the eld of environmental science. Biological methods are
environmentally friendly, produce less sludge than physico-chemical systems, and
are also relatively inexpensive, as the running cost is very low. A number of
bacteria, fungi, yeasts, algae and actinomycetes have been capable of decolorizing a
range of azo dyes (Saratale et al. 2011 ).
Particularly, bacteria are the most frequently applied microorganisms for deg-
radation of azo dyes, as they are generally fast to multiply rapidly under aerobic,
anaerobic, facultative conditions as well as in extreme environmental conditions,
like high salinity and wide variations in both pH and temperature (Solis et al. 2012 ).
In this chapter, biodegradation of azo dyes by bacteria has been discussed in details
with reference to mechanism of degradation, factors affecting and detoxi
Bioremediation
cation.
2 Decolorization and Degradation of Azo Dyes by Bacteria
Biological processes provide an alternative to existing technologies for dye con-
taining wastewater treatment, because of their cost-effectiveness and eco-friendliness.
Moreover, bacteria mediated process is faster than to fungal systems with regard
todecolorization and mineralization of azo dyes. Extensive studies have been carried
out to determine the role of the diverse groups of bacteria in the decolorization of azo
dyes under conventional anaerobic, facultative anaerobic and aerobic conditions.
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