Energy efficiency in Spanish wastewater treatment plants: A non-radial DEA approach

► Non radial Data Envelopment Analysis methodology to obtain an efficiency indicator for each of the variables in the process. ► Operating energy efficiency of WWTPs as the starting point for any energy-saving initiative. ► Assessment of energy efficiency as a measure to reduce the carbon footprint of the WWTPs. ► The role of internal and external factors in WWTP energy efficiency. ► Potential savings of CO2 emissions and economic costs as a result of efficiency improvements.