Synergistic denitrification and phosphorus removal performance of a biofilm‐microflocculation system and its microbial community variations: A pilot‐scale study for a wastewater treatment plant

Aims For upgrading and reconstructing a municipal wastewater treatment plant, a biofilm-microflocculation filter system was designed and established towards synergistic improvement of denitrification and phosphorus removal from the secondary effluent. Methods and Results The establishment of the biofilm-microflocculation filter system underwent several processes, including sludge inoculation, biofilm formation and polyaluminum chloride (PAC) addition as flocculating agent. Microbial community analysis indicated that the dominant denitrification bacteria of the biofilm filter were in the phylum Proteobacteria and the genera Hydrogenophaga and Dechloromonas. On the basis of the initiation of filter system under optimal parameters such as C/N ratio of 5.3, hydraulic retention time of 1.06 h and PAC of 5 mg L-1, approximately 75% COD, 80% TN and 75% TP could be effectively removed to satisfy discharge standards. Comparing the variations of microbial community structure at the genus level during the operating period of the filter system, it was found that the relative abundance of denitrification bacteria merely shifted from 53.14% to 48.76%, demonstrating that the effect of PAC addition on the main micro-organisms is marginal. Conclusions From the above results, it can be verified that the established biofilm-microflocculation filter system has practical and reliable performance for simultaneous biological denitrification and phosphorus removal. Significance and Impact of the Study This study provides a reference method for improving the advanced treatment of wastewater plant secondary effluent.