Development and application of mixed cultures capable for decolorating and mineralizing azo dyes with an anaerobic-aerobic circle method

An anoxic-aerobic circle method was proposed to develop mixed cultures which could decolorate and mineralize azo dyes efficiently. With accumulation and acclimation processes, mixed cultures which completely degraded azo dyes in the medium containing 5 g/L yeast extract at pH 6-7 under anoxic-aerobic circumstance were obtained. Azoreductase, NADH-DCIP reductase, laccase, tyrodinase and lignin peroxidase were involved in the degradation reaction. The acclimated mixed cultures could decolorate a variety of water soluble dyes and completely mineralize aromatic amines without trichlorobenzo[d]thiazole structure. High-throughput 16S rDNA sequencing analysis revealed that members belonging to Aridibacter, Comamonas, Gemmatimonas and Nannocystis were enriched in anoxic environment which may be responsible for decoloration. The abundance of Brevundimonas, Petrimonas and Chryseobacterium genera increased under aerobic circumstance implying their important roles in mineralization stage. Process performances of the mixed cultures were studied using a 30 L SBR equipped with a stirrer and a covering. SBR was operated under anoxic-aerobic condition via hydraulic retention time shortened strategy and the azo dye removal rates could surpassed 90% with an initial concentration of 60 mg/L in 24 h. It is suggest that the mixed cultures demonstrate great adaptability to various types of azo dyes and can be used in biological treatment of azo dye wastewater.