• Energy Research

AbstractIn future, an additional potential of control reserve as well as storage capacities will be necessary to compensate fluctuating energy generators such as wind and solar power plants. The core objective of the joint research project “arrivee” is the integration of widely available wastewater treatment plants (WWTP) with anaerobic sludge digestion into an optimized control reserve and storage concept. Therefore the excellent technical conditions of those plants such as combined heat and power (CHP) units as well as gas storage units will be used. By means of analyzing energy consumption and production processes of existing WWTPs the potential to provide ancillary services for energy grids is investigated. Using a mathematical model of an existing WWTPs the effects of external interventions for the supply of ancillary services under different conditions are tested. Therefore, different processes will be analyzed in detail. The integration of WWTPs into a virtual power plant (VPP) is mandatory because a single plant can’t provide enough capacity to participate on energy markets. The initial results present a theoretical potential of control reserve of WWTPs in Germany focusing on a CHP/gas unit of a magnitude of 300 MWel. This results show a substantial potential of WWTPs to provide ancillary services, by reshaping the existing infrastructure in a sustainable, ecological and economic way. This may contribute significantly to a stable operation of energy grids and to further integration of renewable energy sources in the frame of energy system transition.

To achieve the Paris climate protection goals there is an urgent need for action in the energy sector. Innovative concepts in the fields of short-term flexibility, long-term energy storage and energy conversion are required to defossilize all sectors by 2040. Water management is already involved in this field with biogas production and power generation and partly with using flexibility options. However, further steps are possible. Additionally, from a water management perspective, the elimination of organic micropollutants (OMP) is increasingly important. In this feasibility study a concept is presented, reacting to energy surplus and deficits from the energy grid and thus providing the needed long-term storage in combination with the elimination of OMP in municipal wastewater treatment plants (WWTPs). The concept is based on the operation of an electrolyzer, driven by local power production on the plant (photovoltaic (PV), combined heat and power plant (CHP)-units) as well as renewable energy from the grid (to offer system service: automatic frequency restoration reserve (aFRR)), to produce hydrogen and oxygen. Hydrogen is fed into the local gas grid and oxygen used for micropollutant removal via upgrading it to ozone. The feasibility of such a concept was examined for the WWTP in Mainz (Germany). It has been shown that despite partially unfavorable boundary conditions concerning renewable surplus energy in the grid, implementing electrolysis operated with regenerative energy in combination with micropollutant removal using ozonation and activated carbon filter is a reasonable and sustainable option for both, the climate and water protection.

The development of a power system based on high shares of renewable energy sources puts high demands on power grids and the remaining controllable power generation plants, load management and the storage of energy. To reach climate protection goals and a significant reduction of CO2, surplus energies from fluctuating renewables have to be used to defossilize not only the power production sector but the mobility, heat and industry sectors as well, which is called sector coupling. In this article, the role of wastewater treatment plants by means of sector coupling is pictured, discussed and evaluated. The results show significant synergies—for example, using electrical surplus energy to produce hydrogen and oxygen with an electrolyzer to use them for long-term storage and enhancing purification processes on the wastewater treatment plant (WWTP). Furthermore, biofuels and storable methane gas can be produced or integrate the WWTP into a local heating network. An interconnection in many fields of different research sectors are given and show that a practical utilization is possible and reasonable for WWTPs to contribute with sustainable energy concepts to defossilization.