Utilisation of azo and triphenylmethane dyes as sole source of carbon, energy and nitrogen by Bacillus sp.

Abstract

Bacillus sp isolated from soil contaminated with untreated textile mill effluent utilized an azo dye (methyl orange) and a triphenylmethane dye (malachite green) as sole source of carbon, energy and nitrogen. Highest percentage decolourisation (primary biodegradation) of 61.44% for malachite green and 75.85% for methyl orange was obtained in cultures without nitrate (sodium nitrate). In cultures with added nitrate (sodium nitrate) degradation decreased with increasing nitrate concentration. Data obtained at nitrate concentration of 0.20gL-1 were 57.20% for malachite green and 52.46% for methyl orange. At nitrate concentration of 1.0gL-1percentage decolourisation was 20.50% (malachite green) and 30.45% (methyl orange). The azo-nitrogen and phenyl-nitrogen of the dye substrates provided the nitrogen requirement of the organism in cultures without nitrogen. Decolourisation of dyes is a reduction process which requires redox equivalents (electron donors) that transfer electrons to the chromophoric group dyes. Nitrate (NO 3 -) has higher oxidation character compared to the chromophoric group dyes. The result obtained was attributed to competition between (NO3-) and the chromophoric group for the redox equivalents, which results in preferential reduction of (NO3-) relative to the chromphoric group. Decolourisation was accompanied by increase in total viable count. Ring opening of the aromatic moiety of the dyes and demethylation of malachite green produced the carbon and energy source for the organism. The results show the potential of a bioprocess under nitrate-starvation condition for the treatment of dye wastewater.



Keywords: Bacillus sp, primary biodegradation, methyl orange, malachite green

AJAZEB Vol. 7 2005: pp. 87-94