The Braunschweig wastewater treatment plant (WWTP) is located in Lower Saxonia in Germany. It is a large-size WWTP with nutrient removal and reuse of treated wastewater and sludge for agriculture purposes. Due to decreasing production of biogas from the landfill and the very dynamic and seasonal variation of the energy demand and production of the WWTP, the intention of the project partners operating in the case study is to increase the energy autonomy of the WWTP through innovative energy management strategies.
- Pilot testing of thermoelectric generators (TEG) at one Combined Heat and Power (CHP) unit for utilisation of excess heat for electricity production
- Target: +5% electricity yield from biogas valorization, with a payback time less than 5 years
- Comparison of TEG and SRC in cost-benefit assessment
- Optimisation of dynamic heat management with storage systems
- Target: recovery of min. 20% of excess heat and avoiding external fuel demand in winter
- Optimizing the operation of the plant against energy markets and energy consumption, production and storage
- Target: + 10% energy revenues for WWTP compared with constant / regular energy management strategies.
In WWTPs producing electricity from biogas, a high quantity of potential energy is lost in the form of excess heat that cannot be recovered locally because of existing processes or inappropriate equipment. In the future, following the concepts of enhanced biogas production tested in POWERSTEP, a significant amount of heat is expected to be produced on 24/7 basis, and heat management will be essential to improve the overall efficiency of WWTPs.
One option will be to convert this heat into a useable form of electricity. Conventionally, thermal conversion motors like Organic Ranking Cycle (ORC) engines or Steam Ranking Cycle (SRC) engines are used. Thermoelectric generation (TEG) is a new technology based on the capacity of some materials to produce electricity from a heat gradient. Another way to make use of seasonal heat excess is to find economical ways to store and recover low grade heat. The partners will review available heat storage technologies and assess their economical viability under the conditions of Braunschweig WWTP.
In addition, they will perform the evaluation of options for dynamic energy management on WWTP based upon data of Braunschweig WWTP, including technologies tested in POWERSTEP (i.e. biological biogas upgrade). The intention is to make large WWTPs with digestors a flexible energy player in the energy market
In the future, WWTP will be one of the elements of decentralized energy management in the cities
Christoph Siemers, Veolia