The project introduces a new systemic approach which might make a substantive contribution to the “energy turnaround” in sewage treatment. The approach incorporates a fuel cell which uses micro-organisms as biocatalysts in order to generate electrical energy from the (partial) biodegradation of organic constituents of sewage. Figure 1 illustrates the functional principle.
Fig. 1: Functional principle of a bio-electrochemical fuel cell
Based on the direct generation of power by bio-electrochemical fuel cells and the reduction in energy consumption for aeration, municipal sewage plants can in principle be turned into renewable energy sources. This does still require some considerable development work however. Furthermore, some basic questions need to be clarified with regard to efficiency and the possibilities for technical integration at sewage treatment plants.
The overall objective is to develop, investigate and evaluate a bio-electrochemical fuel cell at pilot scale. Other objectives are (a) to prove that net electricity production is possible and (b) to determine the extent to which such a system can be integrated into a treatment plant, and what effects it might have on plant operations. A further objective is to investigate the degradation of selected micro-pollutants, because in future sewage treatment is likely to be closely linked to micro-pollutant elimination. Complementary investigations relate to the development and evaluation of bio-electrochemical electrolysis for hydrogen production as a possible alternative to electricity production.
Areas of focus
(1) Development of electrodes, stacks and complete bio-fuel cell systems.
The work is aimed at optimising the construction, materials and shape of the electrodes and of the diaphragm as well as the fundamental arrangement and links of cell pairs.
(2) Optimisation of electrode materials and construction; component and stack design.
Further improvements to the shape, material and construction of electrodes, electrode stacks and components are being targeted, incorporating possibilities for cost-effective production and assembly. Questions relating to the nature, material and form of the sealing and insulation between the electrodes also need to be answered. A further objective is to establish a standard for reproducible product quality of electrodes and components. Material, electrochemical and biochemical analysis methods will be developed, or where existing adapted, in order to assess the quality of electrodes and components produced and improve it as necessary.
(3) Optimisation of plant efficiency with simultaneous recovery of electricity/hydrogen.
This work seeks to improve the efficiency of the fuel cell in terms of CSB degradation relative to electricity/hydrogen recovery. Questions relating to effects on nutrient elimination will also be investigated. Systematic investigations will be conducted in order to determine the various influencing factors (such as waste water composition, material, flow conditions, biofilm structure, etc.) and to optimise operating conditions and material properties such that as much as possible electricity or hydrogen per degraded CSB unit is recovered and the plant's operations are not disturbed. Other important aspects are scale-up questions from small to larger components as well as the serial and parallel configuration of cell pairs.
(4) Investigations into the degradation of micro-pollutants and the formation of degradation products.
A comparison with conventional verification methods for biological elimination techniques and a mass balance using radio-tracer analytical methods will verify the degradation of micro-pollutants for a targeted selection of pharmaceutical agents and other micro-pollutants. The selection represents both substances considered to date as bio-degradable as well as those that are not. The issue of transformation product creation will be investigated by appropriate internal and external analysis methods.
(5) Assessment of application potential.
The development, construction, installation and operation of a pilot system at a municipal sewage treatment plant will establish a data base for practice-oriented assessment of application potential from a technical waste water treatment, commercial, operational and environmental viewpoint. Application potential will be estimated for waste water treatment plants of (German) size classes 1 to 5.
(6) Communication of the new technology and dissemination of results.
Alongside the standard communication channels, such as the project website, newsletters, films, presentations, exhibitions, etc., additional workshops organised by DWA and DECHEMA are planned as well as an experimental display exhibit.
The development of the bio-electrochemical fuel cell demands interdisciplinary collaboration between the project partners whereby all partners are involved in all work packages. Figure 2 shows the structure and interlinking of the work packages.
Fig. 2: Structure and interlinking of work packages in BioBZ