Strategic framework for sustainable centralisation of wastewater treatment plants: integrating economic and environmental analysis

Across Europe, water utilities face increasing challenges, from aging infrastructure to limited operational capacity. Centralisation strategies, redirecting flows from smaller to larger facilities, might offer opportunities to improve performance and capacity. This study presents decision-support tools to evaluate the economic and environmental impacts of centralisation plans, using a real-world case involving five Wastewater Treatment Plants (WWTPs) (Døjsøvej, Skovby, Ry, Hørning, and Gl. Rye) in Skanderborg, Denmark. The framework combines techno-economic analysis (TEA) and life cycle assessment (LCA) to evaluate both the construction and operational phases. TEA estimates the net present value (NPV) over 40 years, considering five cost categories: capital expenditure (CAPEX), operational expenditure (OPEX), maintenance, staffing, and renovation. LCA helps identify critical environmental trade-offs, focusing on impacts to human health (HH), ecosystem degradation (EQ), and resource depletion (RD). Monte Carlo simulations propagate parameter uncertainty in both TEA and LCA to evaluate decision robustness. Results show centralisation is 18 % more profitable than decentralisation, NPVs of –$98 M versus –$119 M for the decentralised option. This difference is mainly driven by lower maintenance, OPEX, and staffing costs. Environmentally, centralisation showed substantially higher impacts: the construction phase damages were ∼ 75 % higher due to energy-intensive pipeline works. During operations, centralised systems also showed higher impacts, with freshwater eutrophication accounting for 65 % of ecosystem quality impacts in the centralisation scenario due to higher emissions to water. Uncertainty analysis confirmed the robustness of the TEA and LCA results. The proposed framework supports informed decision-making in utility planning and can be applied to other utilities facing similar challenges.