Wastewater treatment plants as energy storage systems for power grids
The amount of energy provided by renewable sources, e. g. wind and solar power, is constantly increasing. Availability of renewable energy is subject to fluctuations. To balance this fluctuations energy storage systems are required, e. g. pumped-storage reservoirs. Wastewater treatment plants can also be used as energy storage systems.
Objective of this project is to develop an energy storage system operating in wastewater treatment plants. This system consists of an energy source and an energy consuming part. Energy source is a biofuel cell operating with waste water. For removal of micropollutants energy is consumed by a new electrochemical process. Dependent on the demand of the power grid either the biofuel cell or the electrochemical process is activated.
Results of this project will be beneficial not only for power companies but also for wastewater treatment plants. Biofuel cells can reduce the amount of sludge and a new process for degradation of micropollutants will be provided.
Fig. 1: Scheme of the two-stage process for elimination of micropollutants
Key aspects of the working plan
The project consists of two main work packages: development of a biofuel cell and of an electrochemical system to degrade micropollutants.
Wastewater is a steady resource of energy. In contrast to solar and wind energy it is independent of weather and rhythm of day and night. In a biofuel cell waste water ingredients are decomposed by bacteria and electrical energy is gained. A side effect is the diminishment of sludge. At the second electrode oxygen is reduced.
The degradation of micropollutants is challenging for waste water plants. Established technologies fail in many cases. In the environment a growing number of pharmaceuticals, corrosion inhibitors, pesticides and further micropollutants are detectable. In this project degradation of micropollutants will be accomplished by a two-step process. In the first step micropollutants are accumulated by adsorption on activated carbon. In the second step the activated carbon is regenerated and micropollutants are electrochemically degraded by applying a voltage. This process was developed by DECHEMA-Forschungsinstitut and DVGW-Technologiezentrum Wasser. Both steps need energy for pumping the waste water. In the second step additional energy for electrochemical degradation is consumed. The characterization of the environmental compatibility of the electrochemically formed products also is part of this project.
Fig. 2: Pilot plant for electrochemical water treatment (disinfection of process water)
The time line is divided into two parts. The first part is focused on laboratory experiments: optimization of the performance of the biofuel cell by variation of materials, construction and microbiology. Simultaneously the system for degradation of micropollutants has to be further optimized and the operating parameters determined. Municipal and industrial wastewater will be used for these studies.
In the following part demonstrators of a biofuel cell and of a micropollutant degradation system will be tested in a wastewater treatment plant nearby Braunschweig. A calculation of profitability completes the working plan.