Emissions of NO, TVOC, CO2, and aerosols from a pilot-scale wastewater treatment plant with intermittent aeration

Atmospheric emissions from a pilot wastewater treatment plant performing aerobic and anoxic processes were investigated. The experiment was performed by sealing the whole aeration tank with an airtight cover of polyethylene in order to obtain a defined flow rate of the off-gas. By measuring concentrations in the known flux of the off-gas emission rates were determined. Due to the dimensions of the pilot plant and the air and water flows these emission rates represent upper limits. The emission rates were put into relation to CO2 to obtain normalized data that can be used for emission inventories. Normalized emission rates (g component×g−1 CO2) were 8.9×10−3 for TVOC, 6.6×10−6 for non-methane hydrocarbons C2–C7 (NMHC), 2.1×10−5 for NO and 3.0×10−6 for particulate organic carbon (POC). Emission rates per capita equivalent per year accounted at the most for 244 g C TVOC, 0.18 g C NMHC, 0.58 g NO and 0.08 g C POC on a basis of 27,400 g CO2 per capita. The non-aeration periods also contributed to the production of NO and TVOC emissions of approximately one-third of the total emissions. From this, we conclude that the implementation of denitrification stages in European wastewater treatment plants according to the EU-directive 91/271/EEC will increase trace gas emissions in Europe. However, according to our estimates, emissions of trace gases and aerosols from wastewater treatment compared to anthropogenic sources will still remain very low.