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In this study, we calibrated the BioWin model to assess the energy consumption, greenhouse gas emissions, and volumetric nitrification rate in the treatment of high-ammonia-containing, source-separated urine within a decentralised wastewater treatment plant (WWTP) setting. Initially, we validated the model using lab-scale urine membrane bioreactor (MBR) treatment processes. Subsequently, the upscaled BioWin model was employed to evaluate the performance of a full-scale urine treatment system. Simulation results for urine treatment by MBR process, optimized at a dissolved oxygen set point of 3 mg/L, revealed an energy consumption of 3 kWh/kg N, greenhouse gas emissions of 25.6 kg CO2e/m3, and a volumetric nitrification rate of 310 mg N/L/d. Remarkably, this constitutes only 25–30 % of the total energy expended in the industrial-scale synthesis of a virgin fertiliser using the Haber-Bosch process. Our findings indicate that the collective energy demand of a urine diverted WWTP and a separate urine MBR for fertiliser recovery is comparable to that of a conventional MBR WWTP without nutrient recovery. Importantly, urine diversion reduces greenhouse gas emissions and the overall footprint of the WWTP compared to conventional ones. Moreover, nutrient recovery through urine source separation and treatment contributes significantly to nutrient recovery and circular economies.