A system dynamics model integrating urine diversion and resource recovery for sustainable wastewater management

Abstract

Wastewater treatment plants (WWTPs) in tourism-driven and climate-sensitive coastal regions experience pronounced seasonal hydraulic variability that challenge conventional performance assessment frameworks. The objective of this study is to apply system dynamics modeling to guide strategic decision-making in the adoption of urine diversion (UD) systems for increased nutrient recovery. Specifically, the study evaluates the environmental performance and strategic implications of integrating UD into centralized wastewater management under conditions of seasonal population variability and hydraulic stress. Using the case of Gotland, Sweden, and the Visby wastewater treatment plant, a 5-year simulation was conducted to represent tourism-driven population fluctuations. Environmental performance was assessed through nitrogen and phosphorus emissions, marine eutrophication potential (MEP), water footprint (WF), carbon footprint (CF), and avoided freshwater abstraction to reflect freshwater scarcity conditions. Six scenarios were analyzed, including three conventional treatment configurations under baseline and hydraulic stress conditions and three scenarios with progressively increased UD adoption. Simulation results revealed recurrent summer peaks in nitrogen (0.030kgm−3) and phosphorus (0.0018kgm−3) discharges under conventional configurations (S1) despite compliance with annual average thresholds. Progressive implementation of UD significantly reduced peak nutrient emissions across environmental indicators. Capture and treatment of urine enabled nutrient recovery which could be used as a locally available fertilizer that can off-set dependency on imported mineral fertilizers. Additionally, avoided water abstraction with higher levels of UD highlighted freshwater conservation benefits in water-limited contexts. Integrating urine diversion as a decentralized nutrient recovery strategy can enhance system resilience, reduce environmental impacts, and support circular sanitation objectives within centralized wastewater management systems.