Increasing nitrogen and organic matter removal from swine manure digestate by including pre-denitrification and recirculation in single-stage partial nitritation/anammox

Abstract

A novel two-stage process comprising pre-denitrification and single-stage partial nitritation/anammox was developed to treat swine manure digestate with a constant nitrogen loading rate of 1.0 gN/L/d. As the influent NH4+-N concentration increased from 500 to 1500 mg/L, a nitrogen removal efficiency of 88 %–96 % and 5-day biochemical oxygen demand removal efficiency of 93 %–97 % were achieved. Owing to the high influent chemical oxygen demand (COD)/nitrates and nitrites (NOX) ratio of 8.2–9.2 and high COD utilization of denitrifying bacteria (DB), the NO2−-N and NO3−-N removal efficiencies in the denitrification reactor reached 96 %–99 % and 97 %–99 %, respectively. The contribution of anammox bacteria to nitrogen removal was 70.9 %–84.3 %, whereas that of DB was 11.7 %–18.3 %. The contributions of DB and ordinary heterotrophic organisms to COD removal were 19.5 %–49.3 % and 17.9 %–39 %, respectively. This study will help guide the anammox process in swine wastewater treatment.