Abstract
The single-stage nitrogen removal by anammox and partial nitritation (SNAP) process was evaluated for tolerances to fluctuations in pH (5.6 to 8.9), temperature (15 to 35 ℃), and dissolved oxygen (DO) concentration (2 to 5 mg/l) using large-scale (80－l) reactors. The nitrogen removal rate (NRR) increased with increases in DO concentrations up to 5 mg/l, indicating oxygen supply enhanced the specific activity of the ammonia-oxidizing bacteria (AOB) without inhibiting the anammox activity. Additionally, the NRR was stable at pH levels of 6.1 to 8.6; however, the NRR decreased at pH 5.6 with the occurrence of NH4+－N accumulation due to a decrease in AOB activity, but was then quickly restored after adjusting the reactor pH to 7.5. Furthermore, the NRR decreased at pH levels over 8.9, as evidenced by increases in effluent NH4+－N and NO2－－N concentrations; in this case, though, a long time was required to recover from this deleterious effect of pH on the core anammox activity. Finally, a high NRR could be maintained over a temperature range of 15 to 35 ℃, indicating the feasibility of the SNAP process over a substantial range of environmental conditions.
