2012|13 Annual Report Fraunhofer IGB

112 Wastewater treatment plants as energy consumers Wastewater treatment plants make up on average 20 percent of the energy consumption of the municipalities. Thus they belong among the big energy consumers [1]. For this rea- son, in 2008, the water and wastewater administration union “Zweckverband” Bad Dürrenberg together with engineering consultants Ingenieurbüro Stockleben were looking for oppor- tunities to reduce the energy consumption of the wastewater treatment plant ABA Bad Dürrenberg (conversion for about 26,000 population equivalents). It was decided to convert the simultaneous aerobic sludge stabilization with high energy consumption for aeration into an anaerobic sludge stabiliza- tion plant that creates energy in the form of fermentation gas. Conversion of the treatment plant from aerobic to anaerobic sludge stabilization In order to achieve this task efﬁcient technology was required with which the conversion could be implemented at the low- est possible cost. This was when the Fraunhofer IGB and its high-load digester came into play. In 2010 and 2011 prelimi- nary studies concerning the digestion capacity of the raw sludge from Bad Dürrenberg were carried out. Planning docu- ments were created together with the customer and submit- ted to the authorities. In addition, tender documents were prepared. Eisenmann Anlagenbau won the public tender. In close cooperation and agreement with the individual parties the conventional high-load digestion system was enhanced by means of a new reactor type and implemented for the ﬁrst time in Bad Dürrenberg. Construction work started in March 2012 upon completion of the necessary preliminary work on pipelines and foundations, and the installation of primary treatment plant at the ABA. On June 14, 2012 the high-load digestion plant was ofﬁcially dedicated. Enhancement of high-load digestion In contrast to conventional sludge digestion in municipal treat- ment plants that, according to bulletin “Merkblatt ATV-DVWK M 368”, are designed to operate in the mesophilic range (around 37°C) and with a hydraulic residence time (HRT) of at least 18 days, high-load digestion plants are operated under considerably higher organic volume load and a HRT of only 7 days. High-load digestion is based on the two-stage Schwart- ing-Uhde-process that was developed and patented in 1979 by the then company Schwarting and the Fraunhofer IGB. The ﬁrst high-load digestion plant for municipal sewage sludge was commissioned as early as 1994 at the treatment plant Mittleres Glemstal (Leonberg). Further installations followed in Eching, Heidelberg, Tauberbischofsheim, Wutöschingen, Ils- feld, and the latest in Bad Dürrenberg. Original high-load digestion was characterized by the so- called phase mixing system in which the sludge is mixed in the reactor several times an hour by means of a strong impulse pump and integrated perforated plates. This system works well and requires relatively little energy input. Its disadvantage is that the effort in terms of the equipment required is rather high and that deposits can form between the individual plates in the course of several years as an inspection after about 10 years of operation showed. A similarly efﬁcient and low-ener- gy mixing action can also be achieved by means of a gas lift ENHANCED HIGH-LOAD DIGESTION IN BAD DÜRRENBERG REDUCES COSTS Dr.-Ing. Werner Sternad ENERGY 1 2 3

2012|13 Annual Report Fraunhofer IGB

Pages