Degradation of Azo Dyes by White-Rot Fungi - Microbial Degradation of Synthetic Dyes in Wastewaters - page 310

Fig. 1 Chemical structures of
different monoazo, diazo,
triazo and poliazo dyes

rst pollutant to be recognised in the wastewater and even the
presence of a concentration as low as 1 mg l − 1 is highly visible. An average
concentration of 300 mg l − 1 of dyes has been reported in ef

Colour is the

uents from textile-
manufacturing processes (Tony et al. 2009 ). A river polluted by the discharge of
dye-containing wastewater can be seen in Fig. 2 .
In addition, dyes have diverse negative effects on the environment, such as
inhibition of aquatic photosynthesis, depletion of dissolved oxygen and toxicity to

ora, fauna and humans. Furthermore, the reduction of azo bonds forms amines
which are highly toxic and carcinogenic in nature (Puvaneswari et al. 2006 ).
Therefore, the removal of azo dyes from wastewater before being discharged into the
environment is a matter of serious concern. Hence, environmental regulations in
most of the countries make their removal mandatory before discharging wastewater
into water bodies. However, the current existing chemical and physical methods to
remove synthetic dyes from ef

otation, Fenton oxidation,
reduction (Na 2 S 2 O 4 ), ion exchange, chlorination/ozonation and incineration, are
rather costly, time-consuming, mostly ineffective and sometimes generate hazardous
sub-products (Grassi et al. 2011 ). Although azo dyes are not degraded by bacteria
under aerobic conditions (Hu 1998 ), Kulla ( 1981 ) has reported the ability of
Pseudomonas strains to degrade certain azo dyes under aerobic conditions. As dyes
were not mineralised, novel strategies are needed to remove azo dyes from waste-
water. In this regard, white-rot fungi have been a subject of intensive research in the
last few years, as they have known to be the most ef

uents, e.g. adsorption,

cient micro-organisms in