Characterization and mitigation of nitrous oxide (N2O) emissions from partial and full-nitrification BNR processes based on post-anoxic aeration control

摘要

It has been reported that a directional change from anoxic to aerobic conditions is a common trigger for nitrous oxide (N2O) production by ammonia oxidizing bacteria (AOB). By extension, during anoxic-aerobic cycling, post-anoxic dissolved oxygen (DO) concentrations might likely play a role in the magnitude of N2O emissions observed. The overall goal of this study was to determine the impact of three select post-anoxic DO concentrations (0.8, 2.0, and 3.0mg O-2/L) on N2O emissions from partial-nitrification (PN) and full-nitrification (FN) reactors subjected to anoxic-aerobic cycling and, ultimately, to explore the development of strategies to minimize N2O emissions from PN and FN based biological nitrogen removal (BNR) processes. Statistically similar N2O emissions were observed during anoxia for both PN (0.62 +/- 0.21% N load) and FN (0.61 +/- 0.070% N load) processes. In contrast, N2O emissions were statistically lower for PN (0.86 +/- 0.25% N load) than for FN (4.6 +/- 2.8% N load), during the post-anoxic aerobic phase, when compared together for all three post-anoxic DO concentrations. Further, for PN, the highest N2O emissions were observed at the highest post-anoxic DO concentration of 3.0mg O-2/L (1.2%N load), likely due to the highest corresponding AOB specific growth rate. In contrast, for FN, the highest N2O emissions were at the lowest post-anoxic DO concentration of 0.8mg O-2/L (8.5%N load). The higher emissions from FN process at low DO concentrations were associated with a lag in nitrite oxidizing bacteria activity upon recovery to aerobic conditions. This lag phase contributed to transient nitrite accumulation, and in turn correlated positively to the observed N2O emissions. Based on our findings, a gradual ramp up in post-anoxic DO concentrations can minimize N2O emissions during PN-based BNR, whereas a completely different strategy, entailing a rapid increase in post-anoxic DO concentrations can minimize emissions during FN-based BNR operations. Biotechnol. Bioeng. 2015;112: 2241-2247. (c) 2015 Wiley Periodicals, Inc.