Comparison of wastewater treatment processes through a water-energy-carbon lens: insights from South Korean sewerage statistics and process-based modelling

This study evaluated water-energy-carbon performance of municipal wastewater treatment plants in South Korea by integrating the Korean Sewerage Statistics Yearbook (2018–2024) with process simulations. Greenhouse gas emissions were evaluated following the 2019 refinement of Intergovernmental Panel on Climate Change guidelines. The public data analysis showed that electricity-related emissions accounted for 44.9% of total greenhouse gas emissions, while direct emissions of nitrous oxide and methane from bioreactors accounted for 42.6%. Environmental performance of six processes was assessed using an integrated water–energy–carbon coupling index combining effluent quality, energy consumption, and carbon footprint. As a result, each process had weakness on following factors: energy consumption for anaerobic-oxic (AO), effluent quality for modified Ludzack-Ettinger, and greenhouse gas emission for AO, anaerobic-anoxic-oxic, and four-stage biological nutrient removal. Multi-linear models for estimating direct emissions with operational factors based on simulation results were built. Dissolved oxygen and sludge retention time had a negative relationship with direct emissions. Simulation results further indicated that higher effluent ammonia concentrations were associated with increased direct emissions. Simulation would be a powerful tool for finding weakness of process and guiding management on the integrated perspective.