Sustainability assessment of wastewater treatment systems in the Global South: A multi-scenario study of the Philippines

Untreated wastewater remains a major challenge in developing countries, as implementing treatment systems is complex and requires sustainable management for long-term impact. Existing sustainability assessments of wastewater treatment rely on predefined indicators, focus on urban contexts, and fail to capture municipal realities. This case study presents the development and application of a sustainability assessment matrix decision-support tool for municipal wastewater planning in the Philippines, using multi-criteria decision analysis and systematic literature review to identify relevant indicators. The Analytic Hierarchy Process was utilized to obtain priority weights from experts in academe, industry, and government sectors. Five wastewater treatment scenarios were evaluated. Results show that among the sustainability criteria, the environmental pillar had the highest weight (0.4985), followed by resilience (0.2535), social (0.1278), and economic (0.1203) pillars. The scenario incorporating CAS, BNR, and struvite recovery achieved the highest sustainability score (0.3048). Robustness of the ranking was supported through deterministic sensitivity analysis using equal-weighting comparison (Spearman's ρ = 0.90) and a perturbation approach, alongside a leave-one-expert-out analysis. Sludge quality was identified as the most critical indicator. The sustainability assessment matrix offers a practical, transferable decision-support tool for sustainable municipal wastewater planning in developing countries through local recalibration of indicators and stakeholder priorities.