Denitrification processes and microbial communities in a sequencing batch reactor treating nanofiltration (NF) concentrate from coking wastewater

A biological denitrifying process was employed for the treatment of nanofiltration concentrate with high conductivity, which was generated from coking wastewater in a sequencing batch reactor (SBR). The results showed that the average removal efficiencies of COD, TN and nitrate were 47.6%, 61.1% and 94.6%, respectively. Different microbial communities were identified by sequencing the V1-V3 region of the 16S rRNA gene using the MiSeq platform, showing that the most abundant bacterial phylum in the SBR system was Proteobacteria , with the subclasses β-Proteobacteria and α-Proteobacteria being dominant. The key microorganisms responsible for denitrification belonged to the genera Thauera, Hyphomicrobium, Methyloversatilis, Hydrogenophaga , Ignavibacterium , Rubrivivax and Parvibaculum. Quantitative real-time PCR was used to assess the absolute abundance of microbial genera9s, using 16S rRNAs and denitrifying genes such as narG , nirS , nirK , nosZ , in both SBR start-up and stable operation. The abundances of narG , nirK and nosZ were lower during stable operation than those during the start-up period. The abundance of nirS at a level of 10 4 –10 5 copies/ng in DNA was much higher than that of nirK , thus being the dominant functional gene to proceed nitrite reduction.