Operating a wastewater system at full capacity? Evaluating options from centralized to decentralized using spatial multicriteria analysis

Abstract

Urban development pressures, aging infrastructure, and growing environmental constraints are forcing many municipalities to reconsider conventional wastewater management strategies. In Quebec, Canada, as in many regions, centralized systems are approaching capacity limits, while decentralized and hybrid configurations remain underused, despite their potential to provide more context-sensitive solutions. Previous multi-criteria decision-analysis (MCDA) studies have either focused on non-spatial technology selection or applied spatial MCDA mainly to green stormwater management infrastructure, leaving a gap for a spatially explicit, participatory comparison of wastewater system configurations across scales. This study develops a spatial MCDA decision-support framework based on value-focused thinking that integrates stakeholder-defined objectives into a planning support system to compare centralized, decentralized, and hybrid wastewater systems. The approach is structured around two system-specific objective hierarchies that jointly represent implementation opportunities and territorial needs and operationalizes these objectives using spatial indicators and value functions. Applied to a medium-sized municipality in southern Quebec, the results show that suitability patterns are strongly determined by urban form, environmental vulnerability, and infrastructure constraints, and that no single system type is optimal across the territory. Hybrid configurations, particularly those combining infiltration and surface discharge, consistently achieve the highest suitability across both opportunity- and need-based perspectives, whereas purely centralized solutions show limited alignment with spatially distributed needs. One-at-a-time extreme-weight sensitivity analysis further demonstrates the influence of stakeholder preferences on spatial prioritization, highlighting the framework's contribution to transparency. Although case-specific, the proposed participatory spatial MCDA approach provides a transferable decision-support framework for strategic wastewater planning in municipalities facing similar capacity and sustainability challenges.