Pilot-scale Evaluation of an Anaerobic/Anoxic/Oxic Process for Nitrogen Removal from Sewage Using Metagenomic Sequencing

A modified pilot plant with two sequencing batch reactors on the strength of utilizing the inner carbon supply and adding suspended carriers was operated for 280 d to analyze nitrogen removal performance and microorganism community. Despite a low chemical oxygen demand (COD)/total nitrogen (TN) ratio of 3.5, the TN in the effluent decreased from 37.2 to 10.4 mg N/L. High-throughput sequencing indicated significant differences in the abundance of the phylum Actinobacteria (p<0.0001), Firmicutes (p<0.0001), Bacteroidetes (p<0.001), Uroviricota (p<0.0001) and Planctomycetes (p<0.0001) between the anoxic-carrier biofilms and flocculent sludge. Quantitative PCR revealed that denitrification and anammox genes were additional abundant in the anoxic-carrier biofilms than flocculent sludge (narG: p<0.0001; nirS: p<0.01; narH: p<0.01; norB: p<0.0001; hzsB: p<0.01; hdh: p<0.01). Thus, enrichment with denitrification and anammox bacteria might improve nitrogen removal; this was supported by KEGG pathway annotation. Collectively, this study suggests that anoxic-carrier biofilms might enhance nitrogen removal through partial denitrification and anammox process in CWWTPs.