Estimation of Greenhouse Gas Emissions from a 2 MGD Full Scale WastewaterTreatment Plant

Estimation of the greenhouse gas (GHG) emissions from wastewater treatment plants is important for the selection of a specific treatment process, for determining its long-term sustainability, and for developing suitable strategies for reducing the GHG emissions. Although several methods are available for estimation of CH4 and N2O emissions from the waste constituent loading, accurate estimation of GHG emissions requires selection of suitable calculation approaches to determine appropriate emission factors relevant to the specific treatment process and the actual waste constituent loadings. Therefore, in this work, the basic steps involved and the various calculation approaches that could be used for the estimation of GHG emissions from wastewater treatment plants are presented with a case study of an existing 2 MGD full-scale wastewater treatment plant. Spreadsheets were set up as estimation tools, using routine operational data to estimate GHG emissions. Based on the design data, the total greenhouse gas emissions from the 2 MGD wastewater treatment plant was estimated as 2,243 Mg CO2e/yr, or 6.88 lb CO2e / 1000 gallons of wastewater processed. The results revealed that the offsite indirect GHG emissions from the use of electricity were about eight times larger than the direct GHG emissions from the process, indicating the potential for reducing offsite indirect GHG emissions at the wastewater treatment plant through process optimization or plant upgrades to cut down on electricity consumption.