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.

Automated summary

This study effectively suppressed N2O emissions in the treatment of ammonia rich wastewater by altering the frequency of aerobic/anoxic phases. Increasing the number of aerobic phases resulted in a significant reduction of N2O emissions. Aerobic phases contributed more to the total N2O emissions compared to anoxic phases. Furthermore, N2O emissions were positively correlated with nitrite accumulation and negatively correlated with the nosZ/(nirK+nirS) gene ratio.