Decolorization of dye wastewater

Abstract

The textile industries use enormous amount of water and chemicals for the wet processing of textiles and also use various types of dyes to impart attractive colors of commercial importance to the fabrics. The textile effluents are currently treated in the industries by physicochemical methods such as coagulation and adsorption. This study presents the degradation of a model dye (Congo red) by combined method involving sonolysis and biodegradation. The dye was initially pretreated with sonolysis and then treated biologically using Bacillus subtilis isolated from tannery effluent contaminated environment. Sonochemical degradation of Congo red was carried out in a tank type sonochemical reactor. The effect of initial pH (3 9) and initial dye concentration (100 500 mg/l) on % decolorization was investigated. The results showed that the amount of dye removed increased with an increase in initial concentration up to 400 mg/l and further increase in concentration decreased the dye removal. The results also showed that the low pH levels offered higher % decolorization. Microbial decolorization of dye was carried out using Bacillus subtilis free cells. The influence of initial concentration (20 1000 mg/l), pH (3 8) and temperature (31 410C) on % decolorization was studied. Improved microbial decolorization was carried out using mutated microorganisms obtained from random mutagenesis of Bacillus subtilis. In the present study, UV and chemical mutagenesis (using EtBr) were followed. Best two mutants were isolated based on their decolorization efficiencies and isolated mutants were further subcultured in the media containing Congo red. SBR experiments were carried out with four different modes for the treatment of textile wastewater. The COD removal profile obtained in SBR treatment showed that mode 4 was effective compared to other three modes. In mode 4, pretreatment, fill, react (aerobic), settle time periods of 1, 1, 20 and 1 h, were maintained.