Nitrous oxide emissions in sewer systems

Nitrous oxide emissions from urban wastewater were measured in a combined sewer in Bayreuth, Germany. The dosed-chamber method was used to evaluate N(2)O emissions Nitrous oxide was analysed by gas chromatography with electron capture detector. Longitudinal and daily variations of N(2)O fluxes were determined. N20 emissions ranged from 0.11...3.8 mg m(-2) h(-1) depending on the lever of wastewater in the sewer. Data indicate that N(2)O 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, N(2)O release was in a range of 42...429 ng N(2)O 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 N(2)O than wastewater samples It is assumed that high concentrations of NaCl inhibit further microbial reduction of N(2)O to N(2). Based on the field data, a first estimate for N(2)O emission from sewers is 3.5 g N(2)O per year and person.