The reduction of energy consumption in industrial wastewater treatment plants (IWTPs) is an important issue because of global warming, fossil-fuel scarcity, and high energy cost. This paper studied the energy-efficiency index (EEI) of IWTPs across Iran and discussed the impact of different factors on it. Data-envelopment analysis (DEA) was used, in which an efficiency score of was allocated for every IWTP. Maximum potential saving, in terms of energy consumption and of emissions, was measured. It was found that of IWTPs had poor energy efficiency, with EEIs lower than , and only of IWTPs achieved an EEI of higher than Each effective variable on the EEI of IWTPs, such as treatment plant age and size, COD removal, process type, pumping station, and aeration method, had their own effect on EEI, energy consumption, and emission. According to the results, the improvement of the EEI of IWTPs will result in savings in energy cost, and about t less will be emitted into the atmosphere annually. Therefore, upgrading the EEI of all IWTPs in the world can significantly reduce both energy costs and emission. The results contribute to energy management in IWTPs.
