Effective N2O emission control during the nitritation/denitritation treatment of ammonia rich wastewater

Nitritation/denitritation (Nit/DNit) is widely applied as a cost-effective nitrogen reduction strategy for ammonia rich wastewater treatment compared to conventional nitrification/denitrification processes. However, Nit/DNit processes have often been reported to lead to high nitrous oxide (N2O) emission. Here, N2O emissions were effectively suppressed in a single stage Nit/DNit sequencing batch reactor (SBR) treating ammonia rich digester sludge thickening lagoon supernatant at room temperature (20 degrees C). The impacts of alternating frequencies of aerobic/anoxic phases on reactor performance and N2O emissions were investigated. With the same hydraulic retention time (HRT), N2O production from 2 subcycles of aerobic/anoxic phases was 9.73% of the removed total inorganic nitrogen (TIN), whereas 14 subcycles of aerobic/anoxic phases reduced the N2O production to 1.53% of the removed TIN. Aerobic phases accounted for > 83% of the total N2O emission, whereas anoxic phases accounted for < 17% of the total N2O emission throughout the operation. Aerobic N2O emissions correlated positively with the nitrite accumulated, and anoxic N2O emissions correlated negatively with the nosZ/(nirK+nirS) gene ratio. Changes in the phase alternation frequency did not negatively impact the TIN removal efficiency, which was maintained at 98% throughout the reactor operation. Mechanisms associated with N2O emission suppression were also discussed in the present study.