Bacterial Degradation of Textile Dyes - Microbial Degradation of Synthetic Dyes in Wastewaters - page 243

The reaction time is an important factor in the anaerobic removal of azo dyes. A
decrease in the hydraulic retention time of the anaerobic stage was found to result in
lower color removal ef

ciency and anaerobic azo dye reduction is also slow
reaction (An et al. 1996 ). The biomass concentration also plays an important role in
the anaerobic removal of azo dyes. Decrease in biomass and retention time of a
sequencing batch reactor results in lower color removal ef o et al.

2000 ). The percent recovery of aromatic amines ranged between <1 % to almost
100 %. A wide range in percent recovery may partly be explained by the dif

ciency (Louren ç

culties
encountered in analyzing these often chemically unstable compounds. Partial or
complete removal of many aromatic amines can be suspected from the decrease or
disappearance of the sometimes unidenti ed peaks in HPLC chromatograms

(O o et al. 2000 ) as well as from the decrease in UV

absorbance. Moreover, a large decrease in toxicity to aerobic bacterial activity was
measured between the ef

' Neill et al. 1999 ; Louren ç

Neill et al. 1999 ).
In summary, combined anaerobic-aerobic biological treatment holds to be a
promising method to remove azo dyes from wastewater. However, there are two
possible bottlenecks: (i) anaerobic azo dye reduction is a time-consuming process
as re

uents of anaerobic and aerobic stage (O '

ected by the requirement of long reaction time and (ii) the fate of aromatic
amines during aerobic treatment is not conclusively elucidated.

2.2 Fungal Biodegradation

Lignin-degrading fungi, white-rot fungi, can degrade a wide range of aromatics. In
earlier reports,

ciently by wood-rotting fungi (e.g.
Phanerochaete chrysosporium, Trametes sp.). Eventually, they were also found to
be responsible for the degradation of lignin (David et al. 1994 ). In the fungal
degradation, there are a few reports of adsorption of dyes on the fungal cells which
forms sludge which requires further treatment. In this scenario, the fungal treatment
of dye containing ef

the dyes were degraded ef

cult also (Erden el al.
2011 ). This property is mainly due to the relatively non-speci

uents is usually time consuming and dif

c activity of fungal
lignolytic enzymes, such as lignin peroxidase, manganese peroxidase and laccase.
The reactions catalyzed by these extracellular enzymes are oxidation reactions, e.g.
lignin peroxidase catalyses the oxidation of non-phenolic aromatics, whereas
manganese peroxidase and laccase catalyze the oxidation of phenolic compounds
(McMullan et al. 2001 ).
The degradation of dyes by white-rot fungi was rst reported as early as in 1983

(Glenn and Gold 1983 ). Since then, it has been the subject of many research
projects. Virtually all dyes from chemically distinct groups are prone to fungal
oxidation, but there has been a wide difference among fungal species with respect to
their catalyzing power and dye selectivity. Fungal degradation of aromatic struc-
tures is a secondary metabolic event which starts when nutrients (C, N and S)
become limiting factors (Kirk and Farrell 1987 ). Therefore, the enzymes are opti-
mally expressed under the starving conditions. However, supplementation of