Biological method for decolourisation of an azo dye: clean technology to reduce pollution load in dye waste water

Abstract

A bacterium isolated and identified as Bacillus cereus from tannery effluent was employed for decolourisation of an azo dye. This strain rapidly decolourises the Acid Black dye sample that belongs to azo category. The optimum activity of B. cereus was found at pH 7.3, temperature 37° C, and duration of 4 days. The decolourisation rate was found out to be 80 and 96% for the agitated and static conditions. UV-vis spectra analysis showed that the peaks which appeared in the visible region of the treated dye disappeared, indicating complete decolourisation of dye. The FT-IR analysis for the B. cereus treated sample showed the transformation of azo linkage into N₂ or NH₃ or incorporated into complete biomass. The presence of aromatic amine in the decolourised sample indicated the presence of azoreductase activity. The mass spectra analysis showed the conversion of the azo dye into new intermediate metabolites such as p-nitroaniline, 2,8 diamino, 3,6 dithio 1-napthanol, and 2,8 diamino-1-napthalol with mol. wt. of 139, 240, and 174, respectively. COD and TOC values of the B. cereus treated sample showed reduction of 85 and 87%, respectively at 120 h duration.