9. Estimation of Greenhouse Gas Emissions from Wastewater Treatment in Ulaanbaatar and a Potential Approach for Emission Reductions

Mongolia’s population is concentrated in Ulaanbaatar, making the capital city a densely occupied urban area. Pollution, such as the contamination of soil, water, air quality, and solid waste, is caused by population concentration and overload of social and public services. It negatively impacts the comfort of the living environment and has become a limiting factor of human development. The biggest issue surrounding the current wastewater treatment is greenhouse gas (GHG) emissions during the treatment process. In Ulaanbaatar, citizens mostly dispose of wastewater in two ways: through a central sewage system or direct disposal into the soil; the latter causes severe soil and groundwater pollution problems. In this study, the authors applied the IPCC’s GHG inventory methodology to estimate the total emission of GHGs from six municipal districts (138 subdistricts) in Ulaanbaatar city. These districts comprised households connected to the central wastewater treatment plant (WWTPs) and those that directly dispose of waste in the land. Subsequently, GHG emissions from the wastewater treatment process were predicted based on the development plan of Ulaanbaatar city. The result showed that 107.2 Gg CO₂e GHGs were emitted from the WWTP, a 70% increase compared to 2005 (44.1 Gg CO₂e). Ger districts accounted for 24% of the total GHG emissions, while residential areas (residential, private houses) accounted for 76%. According to the prediction, GHG emissions will increase by 32% per square meter by 2030 if the total population of Ulaanbaatar City moved to the residential areas without upgrading the central WWTP. However, GHG emissions are projected to decline by 52% in 2030. Even residents in Ger district moved into the residential area, while the central WWTP upgraded as well as the industrial wastewater pretreated at the Khargia WWTP. A total area of 18111.0 ha can be allotted for the development of vegetation cover in the city, which would absorb 3266.7 Gg CO₂e of GHGs per year. The amount of water needed (12.6 thousand m³/day) to grow and maintain the vegetation cover could be supplied by the treated gray water from the central WWTP.