Data-Driven Identification of Constraints and Enabling Pathways for Energy-Positive Wastewater Treatment

The wastewater sector accounts for ∼1% of global electricity use, and demand will rise as countries expand treatment to meet Sustainable Development Goal 6. Transitioning wastewater treatment plants (WWTPs) from energy consumers to net producers is therefore crucial, yet the system-level feasibility of energy-positive operation remains unclear. Using a national inventory of 2961 WWTPs, we remove operational bias through Stochastic Frontier Analysis (existing in 70% of plants) and develop an efficiency-adjusted energy baseline. Energy balance modeling shows that, under conventional scenarios, energy-positive treatment is achievable only for high-strength wastewater (COD 334-426 mg/L, COD/TN ratio 8.5-11.9), excluding most global facilities. However, when evaluating two carbon-redirection pathways that integrate enhanced primary treatment with mainstream Anammox, we find such pathways can reduce entry thresholds to COD 153-198 mg/L and COD/TN 4.9-5.7, enabling low-strength systems to approach energy positivity. Medium-scale facilities are found to be the most favorable candidates. This characteristic-driven framework motivates future research and pilot demonstrations aimed at expanding the frontiers of energy-positive wastewater treatment.