Microbial decolorization of Reactive Black 5 dye by Bacillus albus DD1 isolated from textile water effluent: kinetic, thermodynamics & decolorization mechanism

Reactive Black 5 is one of the most widely used dye in textile and other industries. It is one of the significantly toxic azo dye which poses a serious threat to the environment when discharged into water bodies. A bacterial strain having potential to decolourise and degrade RB5 was isolated from textile effluent, and further identified and characterized. On the basis of morphological, biochemical, and 16s rRNA sequence analysis, the isolate was identified as Bacillus albus DD1. It showed 98% removal of RB5 from aqueous medium within 38 h under optimum parameters, pH 7, temperature 40 °C, in the presence of 1% yeast extract as a co-substrate, and 25% inoculum size at the initial dye concentration of 50 mg/l. Kinetic study revealed the decolorization reaction is a first order non- spontaneous reaction. The rate constant and reaction rate for RB5 decolourization in presence of the isolate was 0.0523 s(−1) and 2.6 × 10(−3) mol/m(3) sec, respectively. Values for ΔH and ΔS of the decolourization reaction, determined by thermodynamic analysis, were estimated to be +20.80 kJ/mol and ΔS = −0.1 kJ/mol K, respectively. LC-MS analysis revealed that decolorization was due to degradation of RB5 by cleavage of azo-bond by the bacterium, with the formation of s 3,6,8-trihyroxynapthalene and phthalic acid as degradation products. Therefore, the bacterium Bacillus albus DD1 has potential for application in biological treatment of dye contaminated industrial waste water.