Microbial Degradation of Basic Dyes in Wastewaters - Microbial Degradation of Synthetic Dyes in Wastewaters - page 100

b

Fig. 2 Proposed N-demethylation pathway for decolorization of Brilliant green by Aspergillus sp.
strain CB-TKL-1 (Kumar et al. 2012 ). The different degradation intermediates of Brilliant green
(1, m/z = 385.1) identied by LC-ESI-MS were DAPPMCDME (2, m/z = 372.5) N-(diethylamino)
phenyl) (phenyl) methylene) cyclohexadienylidine) N-methylethanaminium; DAPPMCDE (3, m/
z = 356) N-(diethylamino) phenyl) (phenyl) methylene) cyclohexadienylidene) ethanaminium;
DEAPPMCDM, (4, m/z = 342) N-(diethylamino) phenyl) (phenyl) methylene) cyclohexadienylid-
ene) methanaminium; EMAPPMCDM (5, m/z = 328) N-(ethyl(methyl)amino)phenyl)(phenyl)
methylene) cyclohexadienylidine) methanaminium; EAPPMCDM (6, m/z = 314) N-((ethylamino)
phenyl) (phenyl)methylene) cyclohexadienylidine) methanaminium; MAPPMCDM (7, m/z = 300)
N-(methylamino) phenyl) (phenyl) methylene) cyclohexadienylidine) methanaminium; MAPPCD
(8, m/z = 286) (methylamino) phenyl) (phenyl) methylene) cyclohexadieniminium; APPMCD (9, m/
z = 275) (aminophenyl) (phenyl) methylene) cyclohexadieniminium; EMAPPMCD (10, m/z = 314)
(ethyl(methyl)amino) phenyl) (phenyl) methylene) cyclohexadieniminium; EAPPMCD (11, m/
z = 300) (ethylamino) phenyl) (phenyl) methylene) cyclohexadieniminium; DMAPPMCDM (12, m/
z = 314) N-(dimethylamino) phenyl (phenyl) methylene) cyclohexadienylidine methanaminium and
MAPPMCD (13, m/z = 286) (methylamino)phenyl) (phenyl) methylene) cyclohexadieniminium

exposed to higher concentrations, evolve mechanisms and pathways for degrading
them. This happens through expression of genes encoding for enzymes responsible
for degradation. Alternatively, the identi

cation, isolation, and transfer of genes
encoding for degradative enzymes can greatly help in designing microbes with
enhanced degradation capabilities. Thus, acclimatization and genetic engineering
both can be helpful in designing superbugs with enhanced degrading ability.
Another aspect, that needs to be explored, is the use of thermotolerant or ther-
mophilic microorganisms in decolorization systems. This would be of advantage as
many textile and other dye efuents are produced at relatively high temperatures
(50

C), even after a cooling or heat-exchange step. The availability of such
thermotolerant microbes for decolorization may consequently reduce the treatment
cost signi

- 60 °

cantly. The enzymatic approach has also attracted much interest in the
recent years for the bioremediation or decolorization of various dyes present in
wastewater or industrial ef uent. The enzymatic treatment has its own inherent

problems, such as the feedback inactivation of enzyme by its own product/products
and recalcitrant nature of the dyestuffs. The addition of some suitable redox
mediators can help oxidoreductive enzymes in enhancing the decolorization ability
of recalcitrant dyes. However, immobilized enzymes have been proven to be
superior to free enzymes and can be used successfully in the reactors for continuous
remediation of synthetic dyes from wastewater. Treatment of recalcitrant dyes by
using enzyme-redox mediator system will be helpful for targeting a number of dyes
with diversi

ed structures. The viability of developing commercial scale treatment
processes lies in using oxidoreductive enzymes. A two reactors system approach
can be useful for the decolorization/degradation of dyes wherein the rst reactor has

an immobilized enzyme, while the second reactor contains an adsorbent. The
immobilized enzyme would catalyze and breakdown the dye resulting in activated
by-products which would bind to the adsorbent in the second reactor and

nally
pollutant free water is released. Indeed to develop such a system which becomes
commercially viable necessitates the identi

cation of a cheaper biocatalyst and