Nitrous Oxide Emissions in Sewer Systems

Abstract

AbstractNitrous oxide emissions from urban wastewater were measured in a combined sewer in Bayreuth, Germany. The closed‐chamber method was used to evaluate N2O emissions. Nitrous oxide was analysed by gas chromatography with electron capture detector. Longitudinal and daily variations of N2O fluxes were determined. N2O emissions ranged from 0.11…3.8 mg m−2 h−1 depending on the level of wastewater in the sewer. Data indicate that N2O is mainly formed in the biofilm by nitrification and/or denitrification. In laboratory experiments, samples with wastewater and wastewater/biofilm mixture were incubated with and without NaCl. After two hours of incubation, N2O release was in a range of 42…429 ng N2O per millilitre wastewater or wastewater/biofilm. Incubated samples without NaCl addition showed no significant difference between wastewater and wastewater/biofilm mixture. If salt (NaCl) was added before incubation, samples with wastewater/biofilm mixture emitted 4.8 times more N2O than wastewater samples. It is assumed that high concentrations of NaCl inhibit further microbial reduction of N2O to N2.Based on the field data, a first estimate for N2O emission from sewers is 3.5 g N2O per year and person.