Assessing wastewater treatment configurations for performance and greenhouse gas emissions: a simulation-based study for a plant in Ecuador

Wastewater treatment plants (WWTPs) lie at the water–climate nexus, emitting greenhouse gases (GHGs)—particularly methane and nitrous oxide—often unaccounted for in Global South regulations. Using high-quality influent data (2017–2020) from an Ecuadorian plant, we simulated four common configurations in STOAT: conventional activated sludge (CAS), anaerobic–anoxic–aerobic (A²/O), trickling filter (TF), and sequencing batch reactor (SBR). All met local effluent standards, but their climate footprints differed significantly. The SBR had the lowest emissions (12,160 t CO₂-eq/year)—28% less than A²/O—due to superior nitrogen removal that minimized N₂O, despite higher energy demand. A²/O emitted the most (16,961 t CO₂-eq/year), revealing a critical design–performance gap. In hydroelectric-dominant grids, where indirect CO₂ is low, nitrogen management—not energy use—becomes the primary lever for decarbonization. Our results show that regulatory compliance alone does not ensure climate sustainability. We provide a replicable, data-driven framework to guide low-carbon, climate-resilient WWTP planning in data-scarce regions.