Bacterial Degradation of Textile Dyes - Microbial Degradation of Synthetic Dyes in Wastewaters - page 244

energy substrates and nutrients are necessary for the propagation of cultures. Other
important factors for the cultivation of white-rot fungi and expression of lignolytic
activity are the availability of enzyme co-factors and the pH of the environment.
Although stable operation of continuous fungal bioreactors for the treatment of
synthetic dye solutions has been achieved (Mielgo et al. 2001 ), but application of
white-rot fungi for the removal of dyes from textile wastewater faces many prob-
lems. As the wastewater is not natural, the enzyme production in white-rot fungi
may be unreliable and the biomass growth and retention in bioreactors may be a
matter of serious concern (Stolz 2001 ). Treatment of large volumes of wastewater
may be very dif

cult, as extraction and concentration of dyes are necessary factors
prior for the fungal treatment (Nigam et al. 2000 ). Furthermore, the low optimum
pH for lignin peroxidase (4.5 cation of the usually

highly alkaline textile wastewater which causes inhibition of other useful micro-
organisms, like bacteria. Moreover, other wastewater constituents, especially aro-
matics, may also interfere with fungal dye degradation (Stolz 2001 ).

5.0) requires extensive acidi

-

2.3 Algal Biodegradation

Degradation of azo dyes by algae has been reported only in few studies. The
degradation pathway is thought to involve reductive cleavage of the azo linkage,
followed by further degradation (mineralization) of aromatic amines formed.
Hence, algae have been demonstrated to degrade several aromatic amines, even
sulfonated azo dyes. In open wastewater treatment systems, especially in (shallow)
stabilization ponds, algae may, therefore, contribute to the removal of azo dyes and
aromatic amines from the wastewater. However, algal biodegradation of dyes has
some limitations: one of very common problem is the adsorption. It was reported
that Chlorella vulgaris could absorb Supranol Red 3BW (35.62 mg dye g − 1 bio-
mass), Lanaset Red 2GA (44.98 mg dye g − 1 biomass), Leva x Navy Blue EBNA

(43.17 mg dye g − 1 biomass), but the degradation from algal biomass is not com-
petitive if we compare it with the bacterial degradation (Lim et al. 2010 ). Oscill-
atoria curviceps can alone degrade Acid Black (100 ppm) up to 84 % in 8 days
(Priya et al. 2011 ). The ef

uenced by the structure
of the dye, species of algae and physical parameters, like pH, temperature, etc.
(Sol

ciency of adsorption is highly in

í s et al. 2012 ).

2.4 Bioreactor for Effective Decolorization of Textile Dyes

Many bioreactors for the degradation of textile dyes have been developed by many
researchers and a fair amount of research was conducted to assess their viability for
biodegradation study. Different types of bioreactors were developed, such as up

ow
anaerobic sludge blanket reactor (UASB), activated sludge reactors, etc. The UASB