Assessing Eco‐Efficiency and the Cost of Carbon Abatement in Wastewater Treatment: Evidence From Spain

Abstract

Wastewater treatment plants (WWTPs) play a critical role in protecting public health and the environment but are also contributors to carbon emissions. Improving the eco-efficiency of WWTPs is essential for advancing sustainability in the sector. This study proposes a parametric approach using stochastic frontier analysis to evaluate the eco-efficiency of 108 WWTPs in Spain and estimate the marginal cost of reducing GHG emissions. The eco-efficiency index (EcoEI) integrates operational costs, pollutant removal efficiency, and indirect carbon emissions. Results show an average EcoEI of 0.638, suggesting that WWTPs could improve performance by approximately 36%. The estimated marginal abatement cost of carbon emissions ranges from €0.010 to €1.240 per kg CO2eq, with an average of €0.309/kg CO2eq. Significant differences in marginal costs were found across secondary treatment technologies, though not in eco-efficiency scores. These findings have important implications for utilities and regulators aiming to enhance sustainability and meet the targets set by EU Directive 2024/3019.