Energy and sustainability of operation of a wastewater treatment plant

The study summarises the energy consumption data obtained from the Slovak wastewater treatment plants. Overall, 51 large WWTPs using mesophilic anaerobic sludge digestion and biogas utilisation (the total capacity of 2.5 mil. p.e.) and 17 small rural WWTPs (the total capacity 15 000 p.e.) were compared in many technological and energy parameters. The average energy consumption in large WWTPs in Slovakia is 0.485 kWh/m3 and 0.915 kWh/m3 in small rural plants. The average energy demand related to BOD5 load represents the value of 2.27 kWh/kg BOD5, in Slovak plants. The specific energy production is relatively low - in average 1.2 kWh _el /m3 of produced biogas and 0.1 kWh _el /m 3 of treated wastewater, respectively. The average energy autarky in Slovak plants is 25.2%. Some plants have high energy autarky (>65%), despite no external biowastes being dosed to these during operation.