Bacterial community dynamics during treatment of anthraquinone dye in a hydrolytic reactor, an aerobic biofilm reactor, and a combined hydrolytic-aerobic reactor system

Synthetic dyes are extensively used in industrial processes but do not degrade easily in the environment. Microbial decomposition is a cost-effective alternative to chemical and physical degradation processes. In the present study, we studied the potential effects of using an aerobic biofilm reactor, a hydrolytic reactor, and a combined aerobic-hydrolytic reactor system for treating the anthraquinone dye Reactive Blue 19 (RB19). Compared with the aerobic and hydrolytic reactors, the combined aerobic-hydrolytic reactor system achieved the highest removal efficiency regarding color and chemical oxygen demand, at 95.6% and 83.7%, respectively. Microbial communities in the reactors were analyzed with denaturing gradient gel electrophoresis based on bacterial 16S rRNA genes. A statistical analysis of the denaturing gradient gel electrophoresis profiles demonstrated that the structure of the RB19-degrading consortium changed between the different reactors. All band sequences recovered were assigned to two phyla, Proteobacteria and Firmicutes. A clone corresponding to a Shewanella strain was assumed to be responsible for the RB19 decomposition. A Thauera-like microorganism that was active in the combined reactor system was suggested to be a key bacterium responsible for intermediates. Results of this study provide a basis for further research on the degradation of anthraquinone dyes.