Benchmarking energy efficiency in wastewater treatment plants: A latent class analysis

Improving energy efficiency in wastewater treatment plants (WWTPs) is critical for reducing operational costs and greenhouse gas (GHG) emissions. This study evaluates the energy performance of 203 Spanish WWTPs using a latent class stochastic frontier analysis, a method that accounts endogenously for unobserved heterogeneity across facilities. This methodological approach provides policy-relevant insights by uncovering operational heterogeneity that conventional models overlook, enabling class-specific benchmarking and more targeted interventions aligned with the energy-neutrality objectives of Directive (EU) 2024/3019. The analysis identifies two distinct operation classesEstimated energy efficiency scores average 0.581 for Class 1 and 0.639 for Class 2, indicating potential energy savings of up to 41.9 % and 36.1 %, respectively, without compromising treatment quality. These savings translate into annual reductions of 16.9 GWh, €1.48 million in energy costs, and 4399 tCO 2 equivalent in GHG emissions. The results emphasize the importance of class-specific benchmarking and support the use of frontier-based indicators over traditional energy intensity metrics. This approach offers actionable insights for meeting the energy neutrality targets and highlights the need for tailored strategies in optimizing WWTP energy performance. • A latent class stochastic frontier analysis was applied to assess energy efficiency. • Two operational classes were identified, revealing unobserved heterogeneity. • Potential energy savings of up to 41.9 % were identified. • Results support class-specific benchmarking over pooled models.