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Extracting electrical current from organic compounds in wastewater

Final Report Summary - BIOANODE (Extracting electrical current from organic compounds in wastewater)

In microbial electrochemical systems, living microorganisms act as catalysts for electrochemical reactions. Certain microorganisms can oxidize organic compounds and produce electrical current by transferring electrons to an anode. Other microorganisms can harvest electrons from a cathode and produce valuable chemicals. During the past 10-15 years, researchers have shown many possible applications of microbial electrochemical systems. One example is the microbial fuel cell in which organic compounds present in e.g. wastewater can be converted into electrical energy. Other examples include microbial electrolysis cells, which use the energy content of wastewater organics to produce energy carriers such as hydrogen or methane, or valuable chemicals such as hydrogen peroxide. Other types of microbial electrochemical systems could also be used for metal recovery, detoxification, or as sensors.

In this project we have investigated how biological anodes can be used and controlled in various microbial electrochemical processes. One example is the use of biological anodes to support simultaneous hydrogen generation and ammonium recovery from sludge liquor at wastewater treatment plants. Currently, ammonium is removed from wastewater by conversion into innocuous nitrogen gas. However, the use of a bioelectrochemical system could potentially allow energy-efficient recovery of ammonium instead. We developed a reactor which recovered 79% of the ammonium present in real sludge liquor. Another example is the use of biological anodes to support the recovery of metals from leachate solutions. Municipal solid waste incineration ash and contaminated soil contains high concentrations of valuable metals such as copper and zinc. These can be leached out using acids. Microbial electrochemical reactors can be used to energy-efficiently recover the metals from the acid leachates. However, careful control and operation of the reactor is needed for the biological anodes to function. We have investigated how to control the reactor for the biological anode to work properly. New technologies for metal recovery is important, both because we have a lot of metal-contaminated materials that need treatment and because metals are essential raw materials in society. In addition to the control of biological anodes in the aforementioned systems, we have investigated preservation methods for biological electrodes. Researchers and engineers working with well-functioning biological may want to store the electrodes during inactive periods. We compared three storage methods: refrigeration, freezing, and dehydration. Using refrigeration, the electrodes were still bioelectrochemically active after five weeks of storage. However, storage led to more diverse microbial communities, and only 75% of the pre-storage current could be recovered during a 13-day reactivation period.

In the project we have also investigated biological cathodes capable of reducing carbon dioxide to acetate and methane. Such systems could be used to e.g. store electrical energy as chemical fuels. However, starting up biological cathodes is challenging. We have tested different strategies and electrode materials, and investigated the microbial communities that develop on the cathodes and the biochemical reactions they catalyze.

During the course of this project, the research fellow has been employed as associate professor at Chalmers University of Technology. The Marie Curie Career Integration Grant together with funding obtained from the Swedish Research Council has enabled him to build up a small research group in the field of microbial electrochemistry at Chalmers University of Technology consisting of himself and one PhD student. The PhD student has recently completed his licentiate thesis entitled “Acetate formation and oxidation on microbial electrodes”.

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