Environmental Engineering Reference
In-Depth Information
Nitrogen sources are also important for microbial decolouration. The metabolism
of organic nitrogen sources is considered essential for the regeneration of NADH
(Saratale et al.
2009
). However, several fungal species suppress their ligninolytic
activity in the presence of high concentrations of nitrogen (25
60 mM) (Kaushik
-
and Malik
2009
).
3.3 pH
Kaushik and Malik (
2009
) stated that the optimal decolouration pH for most fungi
was in the acidic range as fungal ligninolytic enzymes have maximal activity at acid
pH. In addition, fungi grow normally at a pH value ranging from 4 to 5 (Fu and
Viraraghavan
2001
). However, low pH values are not always suitable for the
treatment of dye-containing ef
uents. Hence, fungal strains capable of dye decol-
ouration at wide pH ranges are more suitable for industrial applications.
3.4 Temperature
Different micro-organisms have different optimum growth temperatures. Thus, most
fungi grow at 25
C (Fu and Viraraghavan
2001
). Also, several studies have
indicated that micro-organisms could degrade synthetic dyes best in the temperature
range of 25
35
°
-
37
°
C (Ali
2010
).
-
3.5 Effect of Initial Dye Concentration on Microbial
Decolouration
The microbial decolouration of dyes decreases with increasing dye concentration.
The results of some studies showed that with increasing initial dye concentration,
the decolouration decreased considerably. This could be attributed to the toxicity of
the dyes to the growing microbial cells at higher dye concentrations (Ali
2010
).
3.6 Salts
Wastewater from textile processing and dyestuff manufacture industries contains
substantial amounts of salts in addition to azo dyes (Khalid et al.
2008
). Thus,
microbial species capable of tolerating high salt concentrations will be suitable for
treating such wastewater. However, there are very few papers which report the
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