Mitigation of Nitrous Oxide Emissions from Wastewater Treatment Using Intermittent Aeration in a Pilot-Scale Tank

Wastewater treatment plants employ continuous aeration (CA) methods, during which nitrogen compounds including N 2 O, a potent greenhouse gas, accumulate. Little research has focused on reducing N 2 O emissions. Intermittent aeration (IA) suppresses NO 3 − accumulation, but its effectiveness in N 2 O reduction remains unclear. Therefore, we investigated the relationship between N 2 O emission and decreasing NO 3 − under different aeration conditions using swine wastewater in a 1-m 3 aeration tank. Three test conditions were employed: CA, IA-1 (3 h aeration and 1 h of non-aeration), and IA-2 (ON/OFF aeration repeated every 2 h). IA suppressed N 2 O emissions compared to CA, achieving decreases of 42% under IA-1 and 64% under IA-2. Microbial community analysis revealed a tendency for higher relative abundances of Nitrosomonas (ammonia-oxidizing bacteria), Nitrospira (nitrite-oxidizing bacteria), Zoogloea , Hydrogenophaga , and Dokdonella (among denitrifying bacteria) in activated sludge samples. This pilot-scale study demonstrated that changing the aeration conditions from continuous to intermittent in wastewater treatment plants may effectively reduce N 2 O emissions. The mitigation of greenhouse gas emissions from wastewater treatment plants is expected to contribute to the realization of a sustainable society.