Environmental Engineering Reference
In-Depth Information
producing laccase (Eggert et al. 1996 ). Crude cultures of P. chrysosporium and
puri
ed LiP were able to degrade Methyl violet and six other triphenylmethane
dyes by sequential N-demethylation. Methyl violet (N,N,N
-hexamethyl
pararosaniline) on biodegradation showed only three degradation products, viz., N,
N,N
,N
,N
,N
-tri-methylpararosaniline when
cultured in a nutrient with nitrogen-limiting conditions (Bumpus and Brock 1988 ).
In case of Bacillus subtilis IFO 13719 (Yatome et al. 1991 ) and Nocardia corallina
IAM 12121 (Yatome et al. 1993 ), the major Methyl violet biodegradation products
were identi
,N
,N
-penta-, N,N,N
,N
-tetra-, and N,N
,N
-
dimethylaminophenol. Later, detailed investigations were performed on Methyl
violet (Kumar et al. 2011 ) and Brilliant green (Kumar et al. 2012 ) degradation using
Aspergillus sp. strain CB-TKL-1. This process followed a stepwise N-demethyla-
tion pattern and N-demethylated intermediates were observed before its
ed as 4,4-bis-dimethylamine benzophenone (Michler
'
s ketone) and
α
nal
mineralization. The proposed N-demethylation pathway for decolorization of
Methyl violet and Brilliant green by Aspergillus sp. strain CB-TKL-1 is shown in
Figs. 1 and 2 , respectively.
6 Microbial Toxicity of Dyes and Their Degradation
Products
Many treatments can be ef
cient in decolorization and degradation of dyes, how-
ever, it is prudent to evaluate whether there is formation of toxic products during
the treatment process. The efciency of a degradation process can be evaluated on
bioindicators, such as Artemia salina and Daphnia magna (Matthews 1995 ;de
Souza et al. 2007 ). The Ames mutagenicity test is evaluated against Salmonella
typhimurium strains (Azizan and Blevins 1995 ; Schneider et al. 2004 ). The com-
mon phytotoxicity tests includes seed germination and plant growth bioassays
(Kapanen and Itavaara 2001 ), as newly formed degradation products must be non-
toxic for use of treated wastewater for irrigation purpose.
7 Future Prospectives
Biodegradation of synthetic dyes using different fungi, bacteria, yeasts, and algae is
becoming a promising approach for the treatment of dye wastewaters. In order to
establish ef
cient biological decolorization and biodegradation systems, concerted
efforts are still required. The biodegradation abilities of microorganisms can be
enhanced by gradually exposing them to higher concentrations of dyestuffs. The
adaptation of a microbial community toward toxic or recalcitrant dyestuffs is
viewed as a useful approach in improving the rate of decolorization process. The
adaptation of microorganisms to higher concentrations of pollutants is called
acclimatization and leads to forced or directed evolution. Microorganisms, thus
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