Reducing carbon source consumption through a novel denitratation/anammox biofilter to remove nitrate from synthetic secondary effluent

This study presents a novel denitratation/anammox biofilter (DABF) for nitrate removal from secondary effluent, where denitratation (NO3–→NO2–) is coupled with anammox (NO2– +NH4+→N2) instead of denitritation (NO2–→N2). Total nitrogen (TN) was removed by 81.90% in this DABF when the average effluent TN concentration was 7.82 mg/L. Meanwhile, organic carbon source consumption and backwash sludge production in the DABF were reduced by 63% and 70%, respectively, compared to conventional denitrifying biofilter (DNBF). Nitrogen banlance analysis indicates that 93% of the nitrogen gas produced in DABF was via anammox. Batch tests confirmed that the DABF biofilm reduced nitrite using ammonium as the electron donor, and accumulated nitrite during denitratation, thus providing nitrite for the anammox bacteria. Moreover, high-throughput sequencing approach also revealed that the anammox bacteria Candidatus Brocadia dominated the community, which could also be responsible for the stable processes in DABF by interacting with the other denitrifying bacteria.