Influence of culture age and environmental conditions on the decolorization and biodegradation of Reactive Orange 13 by Bacillus sp. SBT8

Abstract

The release of azo dyes from industrial effluents is a serious environmental concern because of their colors and unfavorable impact on water quality. One method for combating their release is biological degradation. In this study, the potential of a newly isolated Bacillus sp. SBT8 strain for the decolorization and degradation of Reactive Orange 13 (RO13) was investigated. Conditions favorable for decolorization including temperature (25-42 degrees C), pH (5.0-10.0), culture age (0-24 h), and dye concentration (25-200 mg/L) were determined. Adding RO13 during the mid-exponential phase (8 h following inoculation) accelerated the rate of decolorization. Efficient decolorization was observed in broad pH (6.0-10.0) and temperature (25-35 degrees C) ranges with the optima at pH 7.0 and 33 degrees C, respectively. A complete decolorization was observed at pH 7.0, 35 degrees C, and 25 mg/L dye concentration in 48 h. Increased dye concentrations (over 100 mg/L) had inhibitory effects on the degradation of dye as measured after 48 h: 25, 50, and 100 mg/L dye concentrations were decolorized by 100, 83.58 +/- 3.07, and 42.68 +/- 3.02%, respectively. Decolorization and biodegradation were confirmed by UV-VIS spectroscopy, FTIR, and LC-MS. The analysis with FTIR affirmed the cleavage of the azo bond and the formation of novel products. The metabolites were determined by LC-MS analyses and a possible biodegradation pathway was proposed. Phytotoxicity was tested on Lens culinaris and the non-toxic nature of the metabolites was revealed. This study provides insights into the potentiality of Bacillus sp. SBT8 isolate on the decolorization and biodegradation of azo dyes.