Microbial communities in biological denitrification system using methanol as carbon source for treatment of reverse osmosis concentrate from coking wastewater

A biological denitrifying process using methanol as a carbon source was employed for the treatment of reverse osmosis concentrate (ROC) from coking wastewater in a sequencing batch reactor (SBR). The results showed that the average removal efficiencies of chemical oxygen demand (COD), total organic carbon, total nitrogen and nitrate were 81.4%, 83.7%, 90.6% and 92.9%, respectively. Different microbial communities were identified on the MiSeq platform, showing that the most abundant bacterial phyla were Proteobacteria and Bacteroidetes, the sum of which, in this study, accounted for almost over 92%. The key genera responsible for denitrification were Hyphomicrobium, Thauera and Methyloversatilis. Quantitative real-time polymerase chain reaction was used to quantify the absolute abundances of microbial genera by using 16S rRNAs and denitrifying genes, such as narG, nirS and nirK, during both start-up and stable operations in the SBR. nirS was much more abundant than nirK, thus became the main functional gene to execute nitrite reduction. The high removal efficiency of COD and nitrate suggests that a biological denitrifying process using SBR is an effective technique for treating ROC from coking wastewater.