Decolorization and Mineralization of Azo Dye-Acid Orange 7 by Salt-tolerant Mixed Cultures Developed with Anaerobic and Aerobic Circle Method

Salt-tolerant mixed cultures proficient in complete decolorization and mineralization of azo dye - Acid Orange 7 (AO7) were developed through anaerobic and aerobic circle method. The salt-tolerant culture performed well in the medium containing no carbon source and 5 g/L yeast extract and could degrade 60 mg/L of AO7 within 48 h efficiently under static and shaking condition. The suitable pH range for the mixed cultures was 6-7. Decolorization and mineralization efficiency was found to be unchanged under salt concentration of 20 g/L NaCl. Microbial community composition based on 16S rDNA gene analysis showed that the dominated genera involved in the mixed cultures were Lactococcus, Acinetobacter and Bacteroides. With UV-Vis analysis, it is speculated that AO7 was degraded to sulfanilic acid and 1-amino-naphtol first. The two chemical intermediates were further mineralized to low-molecular-weight organic acids with the broken aromatic rings. The developed mixed cultures might be a promising alternative for treatment of saline azo dye wastewater.