INVESTIGATING SYNERGIES BETWEEN QUATERNARY TREATMENT AND HYDROGEN PRODUCTION FOR ENERGY-NEUTRAL MUNICIPAL WASTEWATER TREATMENT PLANTS : A techno-economic and energy performance assessment

Sammanfattning

Municipal wastewater treatment plants (WWTPs) in the European Union are facing dual challenges which are required to meet stricter regulations under the revised EU Wastewater Treatment Directive (EU WWTPD 2024/3019) by implementing quaternary treatment for removing micropollutants with energy neutrality goals by the end of 2045. The increasing oxygen demand and reducing energy targets creates an opportunity for water electrolysis integration as a potential solution to address these challenges. A techno-economic assessment (TEA) of alkaline water electrolyser integration at Mälar energi WWTP in Västerås, Sweden is performed. Three scenarios are evaluated based on electrolyser sizing based on oxygen demand for ozonation, oxygen demand for biological treatment and combined oxygen demand for ozonation and biological treatment each evaluated across three hydrogen utilization pathways: direct market sale (Pathway-A) methanation for biogas upgrading (Pathway B) and on-site fuel cell electricity generation (Pathway C). For each scenario, system performance, capital and operational expenditure, levelized cost of hydrogen, Net present value and payback period along with sensitivity analysis of key parameters were assessed. A supplementary incremental analysis was conducted to isolate electrolyser economics from regulatory ozonation baseline costs, validating that electrolyser alone gives positive incremental returns under pathway A and B across all scenarios. Further an integrated balance of energy including heat recovery was also developed to assess the contributions to WWTP neutrality. The results demonstrated that electrolysis integration creates meaningful synergies with WWTP treatment and energy recovery objectives, however, the economic variability depends on scale and utilization pathways. Sensitivity analysis confirmed that the electricity price and biomethane market price are dominant determinants of economic feasibility with access to low-cost renewable electricity under Power Purchase Agreement conditions is identified as a prerequisite for green hydrogen production at WWTP scale. The findings give a quantitative basis for investment, decision making and policy development focusing the integration of wastewater treatment compliance, energy neutrality and green hydrogen production objectives.