Economic and environmental performance of wastewater treatment plants: Potential reductions in greenhouse gases emissions

•We assessed the pure and mixed environmental performance of WWTPs assuming variable returns to scale.•DEA models including undesirable outputs allow quantifying potential reductions in greenhouse gases emissions.•All WWTPs exhibited PEPI values equal or higher than MEPI.•Economics of scale do not affect WWTPś mixed environmental performance.

Sanitation and wastewater treatment are essential for protecting human health and environmental sustainability. Treatment processes are not free of environmental impacts; consequently assessment of the environmental performance of wastewater treatment plants (WWTPs) has gained interest in recent years. Unlike other methods, a direct approach is followed to estimate environmental performance indicators (EPIs) using data envelopment analysis (DEA), i.e. an index of overall performance is directly obtained. The present study represents pioneering work to integrate environmental impacts in the assessment of the efficiency of WWTP estimating pure (PEPI) and mixed (MEPI) environmental performance indices for a sample of 60 Spanish WWTPs. Both direct and indirect greenhouse gas (GHG) emissions were considered as undesirable outputs. The best functioning WWTPs to be used as references were identified, and the potential for GHG reductions was quantified. A second-stage analysis was conducted to isolate factors affecting WWTP environmental performance. The results of this study are valuable for WWTP operators and policy makers, since the benchmark procedure allows support for environmental and managerial decision-making.