Mitigating nitrous oxide emission by an ultra-fast bioprocess enabling the removal of high concentration N ₂ O

Nitrous oxide (N₂O) is known as a greenhouse gas as well as an ozone-depleting substance. Wastewater treatment process is one of the sources of N ₂ O emission, and the high concentrations of N₂O in off-gas were reported from an anaerobic ammonium oxidation process. This study developed a novel N₂O removal process using a down-flow hanging sponge reactor to remove high concentrations of N₂O. More than 96% removal efficiencies were achieved for up to 300 ppm N₂O with 3 min gas retention time (GRT), and more than 99% removal efficiency was obtained for 2,000 ppm N ₂ O with 18 min GRT. A maximum removal rate of 161 ± 26 mg-N/L-reactor/day was achieved, that was over 10 times faster than the pioneering process. Kinetic analysis indicated that the N₂O dissolution rate is a crucial factor in determining the N₂O removal rate in the reactor. Various N₂O reducers belonging to both clade I and II were detected in reactors, and Azonexus was thought to play a key role.