Wastewater treatment plant of the future: energy storage in interaction with technical infrastructure between the poles of energy generation and consumption
Generally, municipal wastewater treatment requires a considerable input of energy. However, at the same time, wastewater contains energy in the form of heat and chemically bound energy, both utilizable within the wastewater treatment process. In municipal wastewater treatment plants, energy consumption and generation are usually subject to separately optimized processes and are separated in space and time, as well.
By crosslinking energy consumption and generation the subsystem “wastewater treatment plant” can become an efficient energy storage. Furthermore, by interacting with technical infrastructure facilities, e.g. power providing companies or large-scale energy consuming resp. generating enterprises (industry, waste incineration plants, etc.) new potentials of efficient energy utilization and generation can be identified.
Fig. 1: Wastewater treatment plant as energy consumer, producer and storage
Due to its potential regarding energy storage and generation, sewage sludge treatment is an important component of this system. In the frame of the joint project, the system of sewage sludge treatment is to be further developed, targeting at an intelligent and flexible energy concept, in which the different forms of energy, i.e. electricity, heat, cooling energy, chemically bound energy (sewage sludge, gas) and work are to be brought together. In this context, energy and mass balancing are highly relevant, i.e. regarding the expansion of the system’s boundaries by including the chemically bound energy of sewage sludge resp. co-substrate.
The objective is to develop a manual-based planning tool as well as tools for real-life application, whilst considering technical, ecological, economic and social aspects for operating future wastewater treatment plants in interaction with infrastructure facilities. Target is the identification of the sewage sludge treatment plant as energy systems provider, with the focus on sewage sludge digestion as energy consumer, storage and producer, and providing maximum flexibility of energy flows.
Results from the investigations to be carried out in the scopes “system”, “technology”, “ecology” and “economy and society” using the example of the city of science Darmstadt, are brought together via the planning tool that also enables the evaluation from different perspectives. The planning tool forms the transfer for application by mapping key figures and decision trees.
The interdisciplinary handling of the project facilitates a holistic view, represented by the project partners from local authorities, industry and science. By initially featuring the city of Darmstadt as example in the investigations, high application relevance will be ensured. With approx. 145,000 inhabitants, Darmstadt is the southern regional center of the metropolitan area Rhein-Main, serving as example for many cities. The planning tool to be developed will thereby safeguard the transfer of research results. To successfully apply this application tool, assessments and, in particular, key figures from the individual working objectives will be integrated, and expert workshops are organized to directly involve potential users.
The joint project includes five major fields of activity:
System analysis: Identification and visualization of the dynamic energy flows of the wastewater treatment plant in interaction with technical infrastructure; further development of the wastewater treatment plant to become an energy systems provider in the multi-sectoral interplay of energy flows (electricity, heat, cooling energy as well as potential storage media such as sewage sludge, substrates, biogas).
Technology: Development of a sewage sludge treatment process as functional module of a flexible energy system, i.e. for energy consumption, storage and production
Optimization of the digestion process to ensure flexible energy utilization (heat storage, batch feeding, biogas production/utilization, etc.); development on / enhancement of operational and dimensioning approaches (utilization of co-substrates); development on / enhancement of the application of new digestion processes (high-load digestion)
Development of process combinations for the utilization of persistent substances by using “surplus” energy (heat sink) or regenerative energy (solar energy) via thermal pressure hydrolysis
Development of an overall system of thermal sewage sludge treatment (incineration) in consideration of new process technologies (pyrolysis, gasification); the objective is to implement a sustainable sewage sludge treatment process whilst ensuring high operational safety and safe disposal, i.e. optimization with regard to energetic (application of suitable co-generation processes for electricity and heat) as well as material recovery (phosphorus recovery)
Ecological assessment of the measures for energy optimization with regard to environmental impact resp. wastewater and sewage sludge treatment.
Analysis of the driving and limiting forces of the investigated process variants, multi-sectoral organization, integration of decision makers, multi-criteria evaluation, into which – based on a business-based approach - further economic, ecological and social costs and benefits are incorporated.
Transfer: Development of a planning tool for the incorporation of the wastewater treatment plant into an energy network system. The objective is the transfer of the research data, collected and assessed exemplarily for the city of Darmstadt, as base for a planning tool. This way, an application tool is formed via the identified key figures, including the possibilities for down- as well as up-scaling. Realization is based on a combination of manual and application tool.
Fig. 2: Illustration of the nexuses within the joint project including the planning tool (guideline and application tool)