Development of long-term stable partial nitrification and subsequent anammox process

The partial nitrification reactor was successfully started up and operated stably for more than 250 days with a maximum nitrite production rate of 1.12 kg-N m−3 day−1. The important factors for successful partial nitrification were high ammonium loading rate (>1.0 kg-N m−3 day−1) and relatively high pH (ca. 8.0), giving high free ammonia concentrations (>10 mg NH3-N L−1). In addition, the air flow rate must be controlled at the ratio of air flow rate to ammonium loading rate below 0.1 ( m air 3 day - 1 ) /(kg-N m−3 day−1). After the establishment of stable partial nitrification, the effluent NO 2 - -N / NH 4 + -N ratio and effluent NO 3 - -N concentration were 1.20 ± 0.33 and 1.2 ± 1.0 mg-N L−1, respectively, which was then fed into an granular-sludge anammox reactor. Consistent nitrogen removal was achieved for more than 250 days with a maximum nitrogen removal rate of 15.0 kg-TN m−3 day−1.