Isotopic analysis of N sub(2)O produced in a conventional wastewater treatment system operated under different aeration conditions

• Published in: Rapid communications in mass spectrometry 2014-09, Vol.28 (17), p.1883-1892
• Main Authors: Tumendelger, Azzaya, Toyoda, Sakae, Yoshida, Naohiro
• Format: Article
• Language: English
• Subjects: Aeration; Aeration tanks; Bacteria; Nitrification; Nitrous oxides; Reduction; Sampling; Wastewater treatment
• ISSN: 0951-4198; 1097-0231
• DOI: 10.1002/rcm.6973

RATIONALE Dissolved oxygen (DO) concentration is a key parameter of nitrous oxide (N sub(2)O), a greenhouse gas, emitted from wastewater treatment systems. No study of stable isotopes has described N sub(2)O production during conventional activated sludge (CAS) treatment under different DO concentrations. METHODS Concentrations and isotope ratios, including intramolecular site preference of super(15)N in NNO (SP), of N sub(2)O were measured using gas chromatography/isotope ratio mass spectrometry (GC/IRMS) for samples from seven points in a wastewater treatment plant (WWTP) operated with three aeration conditions. The [delta] super(15)N values of NH sub(4) super(+) and the [delta] super(15)N and [delta] super(18)O values of NO sub(3) super(-) were measured using IRMS. RESULTS Aeration tank water was supersaturated with N sub(2)O. The highest value, 3700nmolkg super(-1), was observed at the aeration tank end and in settled sludge under the lowest aeration condition. About 0.03% of the influent NH sub(4) super(+) was emitted as gaseous N sub(2)O at the lowest aeration condition. The conversion rate was 0.14% under the highest aeration condition. The SP values were significantly higher at the middle and end of the aeration tanks under the highest aeration condition, but were nearly zero or slightly negative under lower aeration conditions. CONCLUSIONS Under the highest aeration condition, NH sub(2)OH oxidation (nitrification) was the main contributor to N sub(2)O production at about 90% and 57%, respectively, at the aeration tank middle and end. At other sampling points, 55-63% of the N sub(2)O was produced by bacterial NO sub(2) super(-) reduction (nitrifier-denitrification) with a lower nitrification contribution. For all sampling points in the lower aeration experiments, NO sub(2) super(-) reduction was a major N sub(2)O production pathway. Copyright copyright 2014 John Wiley & Sons, Ltd.