Bacterial Degradation of Textile Dyes - Microbial Degradation of Synthetic Dyes in Wastewaters - page 240

are found to be more ef cient and effective (Chang et al. 2001 ; Khehra et al. 2005 ).

In the biodegradation, the original dye structure is cleaved into fragments by the
microbial cells. Sometimes, bacterial degradation achieves complete mineralization,
i.e. conversion of dyes into CO 2 , biomass and inorganics (Kolekar et al. 2012 ).
Thus, textile industries have to develop an effective biological ef

uent treatment

method as an alternative to the conventional physico-chemical ef uent treatment

methods.

2.1.1 Decolorization Under Aerobic Conditions

Several bacterial strains, that can aerobically decolorize azo dyes, have been iso-
lated during the past few years. Many of these strains require organic carbon
sources, as they cannot utilize dye as the growth substrate (Stolz 2001 ). Pseudo-
monas aeruginosa decolorized a commercial tannery and textile dye, Navitan Fast
blue S5R, in the presence of glucose under aerobic conditions along with other azo
dyes (Nachiyar and Rajkumar 2003 ). In the degradation of dyes, these bacteria
cleave

bonds reductively and utilize amines as the source of carbon and
energy for their growth. Such organisms are very speci

- N=N -

c to their substrate. Other
bacterial strains with this trait are Xenophilus azovorans KF46 (previously known
as Pseudomonas sp. KF46) and Pigmentiphaga kullae K24 (previously known as
Pseudomonas sp. K24), which were grown aerobically on carboxy-orange I and
carboxy-orange II, respectively (Zimmermann et al. 1982 ). These organisms,
however, could not grow on structurally analogous sulfonated dyes, acid orange 20
and acid orange 7. Long adaptation of 4-aminobenzene sulfonate degrading Hy-
drogenophaga intermedia for growth on 4-carboxy-4

-sulfoazobenzene as the sole
organic carbon source led to the isolation of other strain which reduced the dye and
utilized the two amine metabolites formed (Blumel et al. 1998 ). Sphingomonas sp.
strain 1CX, an obligate aerobic bacterium, was able to grow on azo dye, acid orange
7, as sole source of carbon, energy and nitrogen (Coughlin et al. 1999 ). This strain
degraded only one of the component called amines (1-amino 2-naphthol) formed
during decolorization of acid orange 7 and 4-aminobenzene sulfonate degradation.

′

2.1.2 Decolorization Under Anaerobic Conditions

Methanogenesis of complex organic compounds requires the co-ordinated partici-
pation of many different groups of bacteria, including acidogenic, acetogenic and
methanogenic bacteria (Wuhrmann et al. 1980 ). Dye decolorization under these
conditions requires an organic carbon/energy source. Simple substrates, like glu-
cose, starch, acetate, ethanol and more complex ones, such as whey and tapioca,
have been used for dye decolorization under methanogenic conditions (Yoo et al.
2001 ; van der Zee and Villaverde 2005 ). Extensive studies have been carried out to
determine the role of the diverse groups of bacteria associated with the decolor-
ization of azo dyes under methanogenesis (Carliell et al. 1996 ). However, a few