A modeling framework for comparative evaluation of municipal sludge treatment technologies: case studies of Japanese wastewater treatment plants

Abstract Effective implementation of municipal sludge treatment technologies requires systematic evaluation across environmental, economic, and technical dimensions under site-specific constraints. This study develops a modeling framework to compare alternative sludge treatment technology combinations at municipal wastewater treatment plants (WWTPs). A total of 197 technology scenarios were generated by integrating bibliometric analysis with recent review studies, covering anaerobic digestion, thermal treatment, stabilization, and phosphorus recovery options. The model quantifies life-cycle-based greenhouse gas (GHG) emissions and costs, together with mass-based phosphorus recovery, and is applied to three Japanese WWTPs representing different plant scales. Sensitivity analysis indicates that sludge moisture content is the dominant driver of both treatment cost and GHG emissions, while electricity price and flocculant use show linear but secondary effects on cost. Scenario analysis reveals that introducing anaerobic digestion can increase GHG emissions in small-scale WWTPs due to additional energy demand, whereas it substantially enhances magnesium ammonium phosphate (MAP) recovery when combined with hydrothermal treatment. Incineration-based power generation is found to be infeasible without additional heat input when anaerobic digestion is implemented. By enabling consistent comparison of a large number of technology scenarios using limited plant-level data, the proposed modeling framework supports site-specific decision-making for sludge management and resource recovery. The results highlight the importance of scale, moisture control, and technology compatibility in designing low-carbon and resource-efficient sludge treatment systems.