1 Increasing the Energy Efficiency of Sewage Plants – Experiences of Energy Analyses carried out in Germany Gerd Kolisch*, Thomas Osthoff*, Inka Hobus*, Joachim Hansen** *WiW mbH, Untere Lichtenplatzer Straße 100, D-42289 Wuppertal, kol@wupperverband.de **tectraa, Paul Erlich Straße 13/251, D-67633 Kaiserslautern Abstract The power consumption of municipal and industrial sewage plants has increased over the last decade because of enhanced requirements on nutrient removal. In addition, the cost for external power provision has significantly increased in the last years. The portion of the energy cost today is about 5 to 10 % of the annual cost of wastewater treatment. However, compared with the operational cost of wastewater treatment a much higher portion must be related to power consumption. With the tool of an energy analysis the energy consumption related to wastewater treatment can be efficiently optimized. Energy analyses carried out by the authors on sewage plants in Germany show that an increased energy efficiency of sewage treatment can be achieved. Keywords Energy analysis, process optimization, sewage treatment INTRODUCTION During the last years, the energy consumption of wastewater treatment has got more and more into the focus of operators of sewage plants. The power consumption of sewage plants in Germany is estimated to more than 4 TWh el per year. It is significantly higher than the consumption of all school buildings or the road lighting (Schröder und Schrenk, 2008). The energy requirement of the single sewage plant varies in dependence of the serving size, the technical concept of wastewater treatment, the kind of sludge treatment and the specific location factors. In relation to the average load of a sewage plant, specific power consumption values between 30 and 60 kWh el /(PE*a) for the whole plant and between 15 and 40 kWh el /(PE*a) for the biological stage are stated. At small sewage plants serving about 1,000 to 5,000 PE significantly higher consumption values of up to 150 kWh/(PE*a) may occur. However, at unaerated sewage ponds values even lower 10 kWh el /(PE*a) can be achieved. Compared to the power consumption of a representative household with four persons, which is about 3,500 to 4,500 kWh el per year, the population related specific power consumption of sewage treatment is low. It corresponds to the consumption of an electric bulb with a power of 60 W and a power-on time of about 650 hours per year. However, the sewage plant is usually the largest and central municipal power consumer. Therefore, it is of high importance for measures to reduce the power uptake and the related CO 2 emissions. The total reduction that can be achieved by an optimization of the power consumption for sewage treatment in Germany is estimated to be about 1.25 TWh el /a (Schröder und Schrenk, 2009). Assuming a price of about 12 Ct/kWh el , this corresponds to a cost saving of about 150 m. € per year in total. However, in the single case the energy related investment and the operational costs have to be compared with the cost savings yield by the optimized power consumption.