A review on emission and mitigation of N2O in biological wastewater treatment

Abstract

Nitrous oxide (N2O) is a potent greenhouse gas as well as an ozone-depleting substance. N2O is emitted during the biological nitrogen removal process in wastewater treatment systems (WTSs), and has significant environmental impacts. In this study, N2O emission in WTSs was comprehensively reviewed to better understand the effects of key parameters on N2O emission and obtain useful guidelines for N2O mitigation strategies in WTSs. Three biological pathways leading to N2O emission are hydroxylamine oxidation, nitrifier denitrification, and heterotrohic denitrification. Measurements at lab-, pilot- and full-scale WTSs have shown large variations in N2O emission (0−95% of N-loaded) during wastewater treatment. In the full-scale WTSs (0−14.6% N2O of N-loaded), the average and median values were 1.95% and 0.2% of N-loaded, respectively. Dissolved oxygen, nitrite concentrations, and chemical oxygen demand (COD)/N ratio are the most important parameters leading to N2O emission. A variety of operational strategies have been suggested to minimize N2O emission from WTSs. A new N2O mitigation strategy involving the introduction of microorganisms with high N2O reductase activity or oxygenic denitrification ability has been proposed as an alternative canonical denitrification. © 2018, The Korean Society for Microbiology and Biotechnology.