Evaluating the greenhouse gas emissions of a municipal wastewater treatment plant with sludge incineration

This study addresses the assessment of greenhouse gas emissions (GHG) produced by a large municipal wastewater treatment plant (WWTP), which includes the management of sludge by incineration. For the scope, a WWTP, processing mainly domestic wastewater with a treatment capacity of 358,448 PE (population equivalent), was considered. The assessment of GHG emissions considered both the plant in its current configuration, which involves the co-management of primary and secondary sludge, anaerobic digestion and disposal of mechanically dewatered sludge in landfills, and the plant in the configuration based on sludge incineration (which involves the fluidized bed technology) with energy recovery. The quantification of GHG emissions was carried out through the holistic approach implemented with ECAM 2.0 (Energy Performance and Carbon Emissions Assessment and Monitoring), a tool developed within the WaCClim project. The obtained results showed how the thermal scenario produces higher GHG emissions than the reference scenario and the largest GHG contribution was made by the additional fuel (methane) used for starting up and supporting the combustion process. It is therefore advisable to reduce the consumption of additional fuel. In this regard, it was estimated that by adopting an integrated thermal sludge treatment (drying + incineration), instead of conventional incineration, would result in a 98% GHG emissions reduction due to auxiliary fuels alone.