title: Nitrous oxide emissions from wastewater treatment and water reclamation plants in southern California.
abstract: Nitrous oxide (N₂O) is a long-lived and potent greenhouse gas produced during microbial nitrification and denitrification. In developed countries, centralized water reclamation plants often use these processes for N removal before effluent is used for irrigation or discharged to surface water, thus making this treatment a potentially large source of N₂O in urban areas. In the arid but densely populated southwestern United States, water reclamation for irrigation is an important alternative to long-distance water importation. We measured N₂O concentrations and fluxes from several wastewater treatment processes in urban southern California. We found that N removal during water reclamation may lead to in situ N₂O emission rates that are three or more times greater than traditional treatment processes (C oxidation only). In the water reclamation plants tested, N₂O production was a greater percentage of total N removed (1.2%) than traditional treatment processes (C oxidation only) (0.4%). We also measured stable isotope ratios (δN and δO) of emitted N₂O and found distinct δN signatures of N₂O from denitrification (0.0 ± 4.0 ‰) and nitrification reactors (-24.5 ± 2.2 ‰), respectively. These isotope data confirm that both nitrification and denitrification contribute to N₂O emissions within the same treatment plant. Our estimates indicate that N₂O emissions from biological N removal for water reclamation may be several orders of magnitude greater than N₂O emissions from agricultural activities in highly urbanized southern California. Our results suggest that wastewater treatment that includes biological nitrogen removal can significantly increase urban N₂O emissions.
authors.affiliation: Dep. of Geology, Univ. of Cincinnati, OH 45221, USA. amy.towsend-small@uc.edu
authors.forename: Amy
authors.initials: A
authors.lastname: Townsend-Small
authors.forename: Diane E
authors.initials: DE
authors.lastname: Pataki
authors.forename: Linda Y
authors.initials: LY
authors.lastname: Tseng
authors.forename: Cheng-Yao
authors.initials: CY
authors.lastname: Tsai
authors.forename: Diego
authors.initials: D
authors.lastname: Rosso
mesh_terms: D002140:California; D052918:Environmental Restoration and Remediation / Q000379:methods*; D009609:Nitrous Oxide / Q000032:analysis*; D014873:Water Pollutants / Q000032:analysis*
chemical_list: D014873:Water Pollutants; D009609:Nitrous Oxide