Environmental Engineering Reference
In-Depth Information
So, parameters such as chemical oxygen demand (COD), biochemical oxygen
demand (BOD), total organic carbon (TOC) and ADMI values are measured to
analyse extent of mineralization and degradation of dye containing wastewater.
8 Pathway of Degradation
The pathway of azo dye degradation has been proposed on the basis of results of
GC-MS and enzyme systems involved. Here a degradation pathway of is shown in
Fig. 1 . Acid Black 210 is a very complex azo dye containing three azo groups in its
structure and has a molecular weight of 859.8. Decolorization of AB210 by a
bacterial consortium under microaerophilic condition was studied by Agrawal et al.
( 2014 ).
In initial degradation, azo reductase enzyme cleaved molecule symmetrically
and produced four intermediates viz. benzene 1, 2, 4-triamine, 4-amino phenyl-N-4
(aminophenyl) benzene sulfonamide, 4-nitroaniline and an unidenti
ed compound
with M.W. 364. Presence of laccase enzyme cleaved 4-amino phenyl-N-4 (ami-
nophenyl) benzene sulfonamide asymmetrically and formed aniline and 4-amino
benzene sulfonamide. Further, aniline and 4-amino benzene sulfonamide undergo
deamination and desulfonation to produce benzene as end product. On the other
hand nitro group was removed from 4-nitroaniline resulting in yield of aniline
which was further converted to produce benzene as
nal product by deamination. In
addition, benzene1,2,4-triamine undergoes deamination forming benzene. The
presence of an unidenti
ed product could not be detected from GCMS analysis due
to its very transient existence. The unidenti
ed compound probably undergoes
deamination and desulfonation to produce 1-napthol, which on dehydroxylation
yields naphthalene at the end. Similarly, enzymatic degradation pathway of azo
dyes, such as Reactive Orange 13, Reactive Red BLI, Direct Brown MR, Direct
Blue-6 and many others has been studied by many researchers in details (Kalme
et al. 2007 ; Kalyani et al. 2008a ; Ghodake et al. 2009 ; Shah et al. 2012 ).
9 Microbial Toxicity of Azo Dyes
Recently, adverse effects of hazardous chemicals present in industrial ef
uent on the
environment and health are becoming subject of scienti
c study. Many azo dyes in
puri
ed form are mutagenic or carcinogenic, except for some azo dyes with free
amino groups. Bacterial degradation of azo dyes under anaerobic condition pro-
duced aromatic amines, which are reported to be mutagens and carcinogens.
Therefore, it is necessary to evaluate the toxicity of azo dyes and also of its
metabolites resulted from bacterial degradation. Toxic effects of dyes especially of
azo dyes have been studied for several decades. Brown and DeVito ( 1993 ) have
postulated the mechanism of azo dye toxicity as mentioned below:
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