Microbe-Mediated Degradation of Synthetic Dyes in Wastewater - Microbial Degradation of Synthetic Dyes in Wastewaters - page 225

Violet, Direct Brown and Direct Green (Wafaa et al. 2010 ). Oscillatoria curviceps
is able to use Acid Black 1 as a nitrogen source in an oligotrophic environment
(Priya et al. 2011 ). Nitrogen sources are also important for microbial decolorization.
The use of yeast extract by some of the microorganisms enhances dye removal, as
observed in the consortium of Paenibacillus polymyxa, Micrococcus luteus and
Micrococcus sp. during Reactive Violet 5R decoloration and Aspergillus avus

during True Blue dye decoloration (Ponraj et al. 2011 ). The addition of peptone,
beef extract, or rice husk and rice straw extracts as nitrogen sources in the synthetic
media, results in maximal decoloration of Brilliant Blue G by a consortium of G.
geotrichum and Bacillus sp. (Jadhav et al. 2008 ). The decoloration of a mixture of
reactive azo dyes by A. fumigatus and the decoloration of a mixture of Reactive
Black RC, Reactive Yellow HF2-GL, Reactive Blue BGFN, Reactive Black B-150
and Reactive Red A-6BF by A. fumigates improved using ammonium sulphate and
ammonium chloride as nitrogen sources (Saratale et al. 2010 ).

3.3 In uence of Salinity, Dye Concentration, pH,

Temperature and Oxygen in the Decoloration Process

The operation conditions affect the ef ciency of microorganisms to decolorate azo

dyes, such as the presence of salts, concentration of the dyes, pH, temperature and
oxygen. However, there are examples of halotolerant microorganisms that are able
to decolorate azo dyes in the presence of salts (Meng et al. 2012 ). Bacillus sp.
decolorates Navy blue 2GL in 48 h, but this process takes 18 h in presence of
CaCl 2 , as extracellular LiP and intracellular Lac activities are induced with CaCl 2
(Dawkar et al. 2009 ). Exiguobacterium acetylicum, Exiguobacterium indicum and
Staphylococcus gallinarum are able to decolorate Reactive Black 5 even in cultures
containing 60,000 ppm NaCl (Chen et al. 2011 ). The dye concentration also affects
microbial azo dye decoloration. For example, Lysinibacillus sp. effectively decol-
orates 100 % of Metanil Yellow at 200 ppm, but was only able to decolorate 62 %
of Metanil Yellow at 1,000 ppm (Anjaneya et al. 2011 ). Sphingomonas paucimo-
bilis decolorated completely Methyl Red at 750 ppm, whereas only 38 % of a
1000 ppm dye solution was decolorated by this microbe (Ayed et al. 2011 ). The
time required for complete decoloration of Reactive Blue 172Reactive Blue 172 at
50, 100, 150 and 200 ppm with Proteus mirabilis was 8, 12, 18 and 26 h,
respectively (Saratale et al. 2011b ). Bioaccumulation percentage is reduced with
increasing dye concentration, and the speci c growth rate of yeast is also decreased.

For example, C. tropicalis adsorbed 100 % of Direct Red 28 at 10 ppm, 70 % at
30 ppm and only 60 % at a concentration of 50 ppm (Charumathi and Nilanjana
2010 ). Adsorption and enzymatic activity are dependent on the pH. As the extent of
decoloration is in

uenced by the pH of the media, pH also affects the color of the
solution and the solubility of the dye. Candida tropicalis adsorbs 45 % of Basic
Violet 3 at pH 3, 85 % at pH 4 and 33 % at pH 9 (Das et al. 2010 ). Micrococcus sp.
decolorates 65 % of 300 ppm of Orange MR at pH 4, 80 % at pH 6, and 40 % at pH