Bacterial Degradation of Textile Dyes - Microbial Degradation of Synthetic Dyes in Wastewaters - page 245

process was developed in the late 1970s (Lettinga et al. 1980 ). Initially the reactor
was designed to treat concentrated industrial wastewater and its application was
later extended to sewage treatment also. In the UASB reactor, wastewater

ows
upward through an anaerobic sludge bed, consisting of semi-immobilized microbial
communities. The critical elements of the UASB reactor design are the in uent

distribution system, the gas-solid separator, and the ef uent withdrawal system. The

UASB process, the most popular among anaerobic treatment processes, relies on
the establishment of a dense sludge bed or digestion zone at the bottom of the
reactor, where the anaerobic degradation of the wastewater organics occurs and
biogas is produced (Chinwetkitvanich et al. 2000 ).
Conventional activated sludge treatment of industrial wastes is an effective and
highly economical system for the degradation of dyes and other organic pollutants
from the wastewater. A lot of work has been done on the assessment of activated
sludge system for the degradation of industrial ef

uents. The activated sludge
treatment is the process in which the organic matter from wastewater is utilized as
an energy source for the survival and multiplication of microorganisms in an aer-
obic environment. The microbes convert carbon into cell mass and oxidize the dyes

nally to carbon dioxide and water. In addition, a limited number of microorgan-
isms may exist in the activated sludge which get energy by oxidizing ammonia to
nitrate, a process known as nitri cation (Adav et al. 2009 ).

Aerobic sludge granulation is a biotechnological process used in biological
wastewater treatment and treating chemical industrial in

uent (Adav et al. 2008 ).
Now-a-days microbial granules play a major role in biological wastewater treatment
due to several advantages over the conventional sludge ocks which include a

denser and stronger aggregate structure, better settleability and ensured solid-
ef

uent separation, higher biomass concentration and greater ability to withstand
high organic loading, etc. (Lin et al. 2005 ; Adav et al. 2009 ).
The continuous aeration and feeding lead to an increase in bacterial cell mass
and granulation was initiated at around 20 days and reached to mature granules in
60 days of reactor operation (Fig. 1 a). High hydraulic selection pressure will retain
denser, heavier, compact and smooth granules with improved metabolic activity
(Chen et al. 2007 ). The SEM images of granules during the granulation process in
the reactor depict average size of granules in the range of 5 8 mm (Fig. 1 b).

Biodegradation can be coupled with other degradation methods like, physical or
chemical treatments. A few investigations have shown that azo dyes can be com-
pletely decolorized and some intermediates, such as aromatic amines with side
groups (

-

- SO 3 , - OH, - COOH, - Cl) containing metabolites were quantitatively

detected (O Neill et al. 1999 ). Actinomycetes were also tested for decolorization

and degradation of textile dyes, as they produce peroxidases and also catalyses
hydroxylation, oxidation, and dealkylation during various xenobiotic biotransfor-
mation (Goszczynski et al. 1994 ). McMullan et al. ( 2001 ) have reviewed the
underlying mechanisms by which diverse categories of microorganisms from
bacterial and fungal domains degrade dyestuffs. In nature, the biodegradation of
pollutants (including textile dyes) was ef

'

ciently performed by a group of micro-
organisms in synergism. Hence, microbial consortium could be highly ef cient than