Measurement of direct greenhouse gas emissions from wastewater treatment basins

Climate neutrality in the water and wastewater business can only be fulfilled if emissions of methane and nitrous oxide are low. We need good methods to identify and quantify these emissions and this project will work with establishing a methodology to measure and identify hot-spots for these emissions.

Municipal wastewater treatment leads to direct emissions of methane and nitrous oxide, two strong greenhouse gases. Climate neutrality in the water and wastewater business can only be fulfilled if these emissions are low. However, we need good methods to identify and quantify these emissions.Biological nitrogen removal at municipal wastewater treatment plants (WWTPs) is an important source of emissions of nitrous oxide. The emissions varies between WWTPs and depends on different operational parameters.

Unintentional emissions of methane can occur direct from anaerobic digesters (operational disturbances), during biogas storage and usage and during sludge thickening. It is also common with methane emissions at the inlet of the WWTP and in the aerated grit removal due to methane formation in the sewer system. Significant emissions occurs also during aeration of sludge liquor from the dewatering of anerobically digested sludge.

Direct emissions of nitrous oxide and methane usually contributes to 40-70% of the total climate direct impact of the WWTPs.
Carbon dioxide emissions occurs during degradation of organic matter. Traditionally, these emissions have been accounted to be 100% biogenic. However, it has been observed that 4-14% of the influent organics has fossile origin and should be accounted into the carbon footprint. Addition of fossile based external carbon source, for e.g. denitrification, increases the climate impact as well.

VA SYD is now making an effort to establish a methodology to measure emissions of carbon dioxide, methane and nitrous oxide. Also, hot-spots for these emissions will be identified and quantified, and mitigation strategies should be suggested.

The project aims are to

  • Establish methodologies for measurements of methane and nitrous oxide emissions from wastewater treatment basins.
  • Identify hot-spots of emissions of methane, nitrous oxide and fossile carbon dioxide.
  • Suggest continued measurement campaigns with the focus on implementing mitigation strategies.