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 N2O, a potent greenhouse gas, accumulate. Little research has focused on reducing N2O emissions. Intermittent aeration (IA) suppresses NO3− accumulation, but its effectiveness in N2O reduction remains unclear. Therefore, we investigated the relationship between N2O emission and decreasing NO3− under different aeration conditions using swine wastewater in a 1-m3 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 N2O 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 N2O emissions. The mitigation of greenhouse gas emissions from wastewater treatment plants is expected to contribute to the realization of a sustainable society.