Nitrogen removal performance and microbial community of a novel combined electrochemical biofilter for treating a mixture of raw sewage and secondary effluent

A nitrogen removal biofilter coupled with electrode plates was established to treat a mixture of raw sewage and secondary effluent. The nitrogen removal characteristics and microbial community of the combined electrochemical biofilter (CEBF) and quartz sand biofilter (QSBF) were investigated. The results showed that when the influent concentrations of NH4+-N, NO3--N, and COD were 10, 8, and 60 mg/L, respectively, the average NH4+-N removal rate in CEBF (5.03 mg/(L center dot d)) was higher than that in QSBF (4.28 mg/(L center dot d)). The carbon source had a greater impact on denitrification performance than the electrochemical system when the influent C/N ratio was 4.28. When the influent C/N ratio was 3.67, specific anammox rates of CEBF and QSBF increased to 2.67 mg/(g center dot h) and 2.87 mg/(g center dot h), respectively. Furthermore, the successful construction of the electrochemical system was confirmed by the enrichment of electrochemically active bacteria on the anode plate, including Geobacter (33.73 %) and Desulfuromonas (10.44 %). The relative abundance of denitrifying bacteria (DNB) on the carriers' biofilm was lower in CEBF compared to QSBF. Anammox bacteria (AnAOB) Candidatus_Kuenenia in CEBF (0.06 %) was higher than that in QSBF (0.02 %). This study provided a reference for the application of electrochemical biofilter in nitrogen removal of WWTPs under low C/N.