Characterization of functional microbial communities involved in diazo dyes decolorization and mineralization stages

A new sequencing anaerobic-oxic-sedimentation (AOS) bioreactor was constructed to characterize the functional microbial communities involved in different diazo dye transformation stages. Two typical refractory diazo dyes, Congo red (CR) and Amino Black (AB), were treated in the two AOS bioreactors as model contaminants. Chemical oxygen demand (COD), dissolved oxygen (DO), pH and diazo dye intermediates in each compartment in the two bioreactors were distinct, leading to the difference in the corresponded microbial communities. High-throughput sequencing was applied to study the microbial community structure. Bacteroides, Parabacteroides, Chryseobacterium and Comamonas were dominant genera. Linear discriminant analysis (LDA) effect size (LEfSe) was employed to characterize significantly different genera involved in anaerobic and oxic zones. Multiple linear regression was employed to further evaluate the relationship between azo dye intermediates and bacterial community compositions, and the results were demonstrated in t-value biplots. Functional genera corresponding to azo bond reduction and aromatic amines mineralization were characterized and the mechanism of biotransformation of two diazo dyes to CO2 was proposed. These findings were beneficial for process optimization and efficiency improvement.