[Biodiversity of Thiocyanate-degrading Bacteria in Activated Sludge from Coking Wastewater]

Thiocyanate (SCN^-) is one of the main sources of COD in coking wastewater, and SCN^- removal efficiency of the aerobic unit impacts the requirement of discharging standard. Microbial population in the activated sludge plays an important role in SCN^- removal of coking wastewater treatment. However, the community structure has rarely been reported. Using SCN^- as the sole carbon and energy source, the removal of 100 mg·L^-1,300 mg·L^-1 and 600 mg·L^-1 SCN^- by activated sludge was studied and 454 sequencing technology was applied to investigate the biodiversity of SCN^--degrading bacteria. The results showed that 100-600 mg·L^-1 SCN^- could be effectively removed by acclimated activated sludge, the higher SCN^- concentration, the higher removal efficiency, but the lower bacterial community diversity indices. The bacterial communities in initial and acclimated sludge samples were mainly composed of Proteobacteria, Bacteroidetes, Chlorobi, Planctomycetes, Acidobacteria, Nitrospira, Firmicutes and Unclassified bacteria. Bacteroidetes and Proteobacteria were dominant phyla in the sludge. Thiobacillus was responsible for SCN^- biodegradation in coking wastewater, and its abundance in three sludge samples was 3.07%, 8.63% and 0.27%, respectively. When the concentration of SCN^- was less than 300 mg·L^-1, Thiobacillus was the main degrading bacteria. While at 600 mg·L^-1 SCN^-, low-abundance degrading bacteria might have synergistic degradation effect. These results have important significance for revealing SCN^- removal mechanism in the coking wastewater treatment.