Complete nitrogen removal from low-strength wastewater via double nitrite shunt coupling anammox and endogenous nitrate respiration: Functional metabolism and electron transport

Autotrophic nitrogen removal processes based on anammox are facing huge challenges of high effluent quality in wastewater treatment. In this study, a novel hybrid system of anammox coupled with heterotrophic endogenous metabolisms was developed in a single-stage bioreactor to treat real domestic wastewater. Complete nitrogen removal was achieved at a low carbon to nitrogen (C/N) ratio of 2.8 and more than 95.2% nitrogen removal was maintained under an extremely low C/N ratio of 1.9. The nitrite shunt supplied by dual partial pathways (partial nitritation and endogenous partial denitratation) guaranteed the anammox activity with a high contribution to nitrogen removal above 60%. While endogenous denitrification (ED) and denitrifying phosphorus removal (DPR) both participated in nitrate respiration, contributing more than 28% and 9% to nitrogen removal, respectively. The coexistence and enrichment of anammox bacteria (Ca. Brocadia, 0.9%), glycogen accumulating organisms (Ca. Competibacter, 6.4%) and phosphorus accumulating organisms (Dechloromonas, 3.9% and Ca. Accumulibacter, 0.7%) contributed to the co-metabolism of carbon, nitrogen and phosphorus. The functional genes encoding the above metabolism were highly correlated with the dominant strains, indicating that the multiple pathways of carbon and nitrogen metabolism supported the continuous supply of electrons required for nitrogen removal. This study puts forward a novel complete nitrogen removal process by successfully coupling autotrophic and endogenous heterotrophic metabolism.