Opportunities to improve energy use in urban wastewater treatment: a European scale analysis

Wastewater treatment is an essential public service that has a major impact on energy use in the urban water cycle, thus receiving increasing attention in context of the Water-Energy Nexus. Understanding the current energy use for wastewater is an essential step to design reliable policies promoting a more efficient use of resources. This paper develops a pan European estimation of electricity use for the treatment of wastewater, based on a dataset of wastewater treatment plants(WWTPs) across the continent. Prediction of electricity use has been performed using a statistical model that accounts for economies of scale. Different scenarios of improvements of energy use efficiency have been investigated to understand the possible reductions in electricity consumption at the continental scale. The overall WWTP electricity use in Europe (only plants with no less than 2000 population equivalent (PE) have been considered)was estimated at 24 747 GWh yr−1 , about the 0.8% of the electricity consumption in the EU-28. Small plants(less than 50 000 PE)represent almost 90% of the total number of plants, but process only 31% of the PE and require 42% of electricity use. Plants from mid to very large size (more than 50 000 PE), being only 10% of the plants, process about 70% of the PE with 58% of the total electricity use. If all plants that use more than the current average were shifted to the average value, the saving would be slightly more than 5500 GWh yr−1 . With highly stringent targets of efficiency improvement, saving of about 13 500 GWh yr−1 could be expected. Further considerations on the emerging role of WWTPs as energy and material producer are finally discussed.