Investigation of isolation and immobilization of a microbial consortium for decoloring of azo dye 4BS

Eight high-effective decolorization strains were isolated by enrichment using Direct Fast Scarlet 4BS as sole source of carbon and energy. The optimal microbial consortium consisting of fungus 8-4* and bacterium 1-10 was selected by optimizing combination decolorization experiments with these eight freely suspended strains, whose decolorization activity was higher than individual strains due to synergistic reaction with each other. The optimal microbial consortium was also immobilized using polyvinyl alcohol (PVA) as the carrier. This paper optimized the immobilization and operational conditions, investigated the effect of the environmental factors (temperature, pH and dissolved oxygen (DO)) and initial dye concentration on the rate of decolorization by immobilized microbial consortium. The results showed that the optimal decolorization activity was observed in pH range (5–8), temperature range (25–40°C) under shaking culture of high DO level. Decolorization with the optimal microbial consortium gave a relatively high maximum decolorization activity (ca. 81.25 mg l−1 h−1), which occurred at a dye concentration of 1000 mg l−1, suggesting the applicability of the strains in remediation of wastewater containing high azo dye concentrations. The immobilized beads could be reused for more than 30 cycles, without losing any degradation capacity. The changes of UV-visible spectra and the change curve of COD of 4BS solution before and after decolorization cultivation and the proliferation and distribution of microbial consortium in gel beads were also microscopically observed, which could be used for conferring the decolorization mechanisms of dye 4BS.