CH4 and CO2 emissions rate of Iranian municipal wastewater treatment plants using IPCC and USEPA approaches

Background: Wastewater treatment plants are important sources of emissions of greenhouse gases (GHSs) such as carbon dioxide and methane in the atmosphere. Also, energy consumption in the wastewater treatment process causes indirect carbon dioxide emissions. Methods: One hundred thirty-three operating wastewater treatment plants in Iran treat municipal wastewater. The carbon dioxide and methane emissions from the wastewater treatment plants for the year 2022 were estimated by establishing a calculation model according to the methods recommended by the Intergovernmental Panel on Climate Change for National Greenhouse Gas Inventories (2006) and United States Environmental Protection Agency (USEPA) guidelines. Results: Based on the Intergovernmental Panel on Climate Change guideline, the total methane emission was 158.63 tons. Based on the USEPA guideline, the total emissions of methane and carbon dioxide were 47.61 and 351.47 tons, respectively. This amount is 3.2% of all the methane and carbon dioxide emissions of Iran. Isfahan and Tehran provinces have the highest emissions rates of methane at 31.85 and 22.91 tons, respectively. While South Khorasan and Kerman provinces have the lowest methane emissions rates of 0.46 and 0.67 tons, respectively. Conclusion: The results will provide a scientific basis and effective strategies for policymakers to reduce the methane and carbon dioxide emissions from the wastewater treatment plants of Iran.