Heterotrophic denitrification plays an important role in N2O production from nitritation reactors treating anaerobic sludge digestion liquor

• Published in: Water research (Oxford) 2014-10, Vol.62, p.202-210
• Main Authors: Wang, Qilin, Jiang, Guangming, Ye, Liu, Pijuan, Maite, Yuan, Zhiguo
• Format: Article
• Language: English
• Subjects: Aerobiosis; Air Pollutants - analysis; Ammonium Compounds - analysis; Anaerobic digestion liquor; Anaerobiosis; Applied sciences; Bacteria; Batch Cell Culture Techniques - instrumentation; Biological and medical sciences; Biological treatment of waters; Bioreactors - microbiology; Biotechnology; Climatology. Bioclimatology. Climate change; Denitrification; Digestion; Dissolved oxygen; Earth, ocean, space; Emission; Environment and pollution; Exact sciences and technology; External geophysics; Free nitrous acid; Fundamental and applied biological sciences. Psychology; General purification processes; Heterotrophic denitrification; Heterotrophic Processes; Hydrogen-Ion Concentration; Industrial applications and implications. Economical aspects; Meteorology; Nitrates - analysis; Nitritation; Nitrites; Nitrites - analysis; Nitrous oxide; Nitrous Oxide - metabolism; Nitrous oxides; Oxygen - analysis; Pollution; Reactors; Receiving; Sewage - microbiology; Sludge digestion; Waste Disposal, Fluid; Waste Water - chemistry; Wastewaters; Water Purification - instrumentation; Water treatment and pollution
• ISSN: 0043-1354; 1879-2448
• DOI: 10.1016/j.watres.2014.06.003

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. [Display omitted] •Heterotrophic denitrification plays a crucial role in N2O emission.•Heterotrophic nitrite reduction likely stopped at N2O rather than N2.•DO at 1 mg/L or above reduce aerobic heterotrophic N2O production.•DO should be about maintained at 1 mg/L to minimise N2O emission.