The measurement of nitrous oxide emissions from sewage systems in Belgium

Abstract

To quantify the nitrous oxide emissions from waste water, an experimental measurement campaign has been set up; waste water was sampled at the collector tubes entering sewage treatment plants and at the settling tanks in these plants. The gas phase developing in the static head space of the water samples was analysed; gas chromatography by means of electron capture detection was the analytical tool by which the nitrous oxide concentration in batch samples of gas was determined. The methodological analysis was based on the concentration/time curves obtained.

The formation of nitrous oxide from the waste water matrices is the result of the microbiological denitrification of the organic substrate present; this could be deduced from the response of the nitrous oxide signal to the addition of NaNO₃, NH₄NO₃ and (NH₄)₂SO₄ to the samples. Application of the Lineweaver-Burk kinetic equation for enzyme-catalysed reactions on our results, combined with the yearly mean nitrate concentration and the seasonal mean waste water temperature, enabled us to deduce emission coefficients for the two types of waste water sampled: raw waste water: (4.3 ± 1.0)µg N₂O/gss, settled waste water: (800 ± 180)µg N₂O/gss, where “gss” stands for “gram suspended solids”, a water quality parameter continuously monitored in Belgium.