Analysis of Specific Energy Consumption of Wastewater Treatment Plants in the North of Portugal

Wastewater treatment plants (WWTPs) are becoming more energy intensive due to a growing urban population, an increment in the contaminant load to be treated, and a stringent regulatory and environmental protection standard for effluent quality and water reuse. As the energy demand in the water sector will continue to grow in the forthcoming decades, benchmark the energy performance of WWTPs is essential to improve their energy efficiency. Typically, the specific energy consumption of WWTPs is expressed through two common key performance indicators (KPIs): energy consumption per cubic meter of treated wastewater (kWh/m³) and per unit of chemical oxygen demand removed (kWh/kg COD rem). The first KPI (kWh/m³) is the most applied due to its reliability and accuracy as the volume of wastewater is measured continuously whereas, for example, COD concentrations are determined discontinuously. In this paper, these KPIs are used to compare the specific energy consumption of fifteen WWTPs located in the north of Portugal; these values are also compared against similar facilities and types of treatment found in literature. Despite the use of specific energy consumption indicators allows a simplified, yet quick, assessment of energy performance of WWTPs, the results show that is possible to identify some worse performances. In addition, results show that the joint utilization of several KPIs allows more complete and reliable conclusions.