title: Heterotrophic denitrification plays an important role in N₂O production from nitritation reactors treating anaerobic sludge digestion liquor.
abstract: Nitrous oxide (N2O) emissions from nitritation reactors receiving real anaerobic sludge digestion liquor have been reported to be substantially higher than those from reactors receiving synthetic digestion liquor. This study aims to identify the causes for the difference, and to develop strategies to reduce N2O emissions from reactors treating real digestion liquor. Two sequencing batch reactors (SBRs) performing nitritation, fed with real (SBR-R) and synthetic (SBR-S) digestion liquors, respectively, were employed. The N2O emission factors for SBR-R and SBR-S were determined to be 3.12% and 0.80% of the NH4(+)-N oxidized, respectively. Heterotrophic denitrification supported by the organic carbon present in the real digestion liquor was found to be the key contributor to the higher N2O emission from SBR-R. Heterotrophic nitrite reduction likely stopped at N2O (rather than N2), with a hypothesised cause being free nitrous acid inhibition. This implies that all nitrite reduced by heterotrophic bacteria was converted to and emitted as N2O. Increasing dissolved oxygen (DO) concentration from 0.5 to 1.0 mg/L, or above, decreased aerobic N2O production from 2.0% to 0.5% in SBR-R, whereas aerobic N2O production in SBR-S remained almost unchanged (at approximately 0.5%). We hypothesised that DO at 1 mg/L or above suppressed heterotrophic nitrite reduction thus reduced aerobic heterotrophic N2O production. We recommend that DO in a nitritation system receiving anaerobic sludge digestion liquor should be maintained at approximately 1 mg/L to minimise N2O emission.
authors: Advanced Water Management Centre (AWMC), The University of Queensland, QLD 4072, Australia.
authors: Qilin
authors: Q
authors: Wang
authors: Advanced Water Management Centre (AWMC), The University of Queensland, QLD 4072, Australia.
authors: Guangming
authors: G
authors: Jiang
authors: Advanced Water Management Centre (AWMC), The University of Queensland, QLD 4072, Australia; School of Chemical Engineering, The University of Queensland, QLD 4072, Australia.
authors: Liu
authors: L
authors: Ye
authors: Advanced Water Management Centre (AWMC), The University of Queensland, QLD 4072, Australia; Catalan Institute for Water Research (ICRA), Technological Park of the University of Girona, 17003, Spain.
authors: Maite
authors: M
authors: Pijuan
authors: Advanced Water Management Centre (AWMC), The University of Queensland, QLD 4072, Australia. Electronic address: zhiguo@awmc.uq.edu.au.
authors: Zhiguo
authors: Z
authors: Yuan
mesh_terms: D000332:Aerobiosis; D000393:Air Pollutants / Q000032:analysis; D064751:Ammonium Compounds / Q000032:analysis; D000693:Anaerobiosis; D061249:Batch Cell Culture Techniques / Q000295:instrumentation; D019149:Bioreactors / Q000382:microbiology*; D058440:Denitrification; D052836:Heterotrophic Processes; D006863:Hydrogen-Ion Concentration; D009566:Nitrates / Q000032:analysis; D009573:Nitrites / Q000032:analysis; D009609:Nitrous Oxide / Q000378:metabolism*; D010100:Oxygen / Q000032:analysis; D012722:Sewage / Q000382:microbiology*; D014865:Waste Disposal, Fluid; D062065:Wastewater / Q000737:chemistry; D018508:Water Purification / Q000295:instrumentation*
chemical_list: D000393:Air Pollutants; D064751:Ammonium Compounds; D009566:Nitrates; D009573:Nitrites; D009609:Nitrous Oxide; D010100:Oxygen; D012722:Sewage; D062065:Wastewater
keywords: Anaerobic digestion liquor; Dissolved oxygen; Free nitrous acid; Heterotrophic denitrification; Nitritation; Nitrous oxide