Environmental performance of a full-scale wastewater treatment plant with advanced process control: A multi-year life cycle assessment using dual functional units

Wastewater treatment plants (WWTPs) are crucial for sustainable development, yet stricter discharge limits often require more energy and chemicals, increasing their environmental burdens. This study evaluates and compares, through life cycle assessment (LCA), the environmental performance of a full-scale municipal WWTP before and after adopting advanced process controls (APCs). Unlike most published studies relying solely on volumetric functional units (FUs) and aggregated results, this work addresses the gap by presenting a multi-year analysis with full operational data, reporting impacts per process stage, and applying both FU1 (treatment of 1 m 3 of wastewater) and FU2 (removal of 1 kg of total nitrogen, TN) to better capture treatment efficiency. Key plant upgrades include APC modules for nutrient removal (2016, 2019), and sludge line optimization and the integration of biogas valorization and photovoltaic panels (2022). Results show that electricity use remained the main contributor across most categories. When normalized to FU1, 2016 exhibited the lowest impacts due to lower influent pollution and energy use. However, FU2-based results reveal that in 2022, despite more polluted influent and higher electricity per m 3 (0.243 vs. 0.201 kWh/m 3 in 2016), the plant achieved 30 % less electricity per kg TN removed outperforming earlier years in 13 out of 16 categories. Sensitivity analysis confirmed that increasing renewable electricity further decreases climate change, toxicity, and resource use burdens. These findings highlight the importance of FU selection and process-level reporting in WWTP LCAs, showing that APC tools with renewables improve eco-efficiency while ensuring compliance with stricter effluent discharge limits. • A multi-year LCA was conducted on a full-scale municipal WWTP (2016–2022). • Two functional units were applied: m 3 of wastewater and kg of nitrogen removed. • Advanced process control tools improved nutrient removal and energy efficiency. • Electricity use was the main contributor to environmental impacts across categories. • FU2 enabled fairer comparison by considering influent load and efficiency.