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Renewables > Bioenergy

Capturing Electrical Current via Microbes to Produce Methane

Start Date: September 2011
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Investigators

Alfred Spormann, Departments of Chemical Engineering, and of Civil and Environmental Engineering, Stanford University; and Bruce Logan, Department of Civil and Environmental Engineering, Pennsylvania State University

Objective

The focus of this research is to gain a fundamental understanding of the biology and ecology of methane-producing (methanogenic) microbial cultures for use in a microbial electromethanogenesis cell (MEMC).  When fully implemented, the proposed MEMC will result in the cost-effective, carbon-neutral production of methane from atmospheric CO2 using electrons generated from renewable energy sources. The research will advance the science and the technology of the MEMC process and the ultimate commercialization of this technology.

Background

Methanogens are single-celled organisms that use electrons to convert carbon dioxide (CO2) into methane. Bruce Logan demonstrated that methane can be produced by a process called electromethanogenesis using a biocathode containing methanogens. The basic MEMC design is shown in Figure 1.  This scheme includes multiple and alternative scenarios for how such a system can operate.

Figure 1

Figure 1: Microbes in the cathode compartment convert electrons plus CO2 into methane. Hydrogen-consuming methanogens (1) are expected to be the dominant microorganism mediating primarily methanogenesis. Other microbes that may be present include acetate-producing bacteria (2), acetate-consuming methanogens (3) and methane-consuming microbes (4). The thickness of an arrow indicates the expected flux of matter between these processes. Methanogens cannot tolerate oxygen (O2). However, the anode compartment will be operated either electrolytically, releasing O2 that may leak through the proton exchange membrane and result in traces of O2 in the cathode, or as a fuel cell oxidizing organic matter. Methane-consuming bacteria at the cathode will use this O2 plus methane (CH4) to render the cathodic cell anaerobic.

Approach

A key goal of the project is to understand the long-term ecological and evolutionary fate of microbial electromethanogenesis processes.  Methanogenic and methane-consuming microbes can be found in a number of naturally occurring aerobic-anaerobic interfaces, often in a mutualistic ecological relationship.  The underlying hypothesis of this project is that aerobic methane-consuming bacteria play an important supporting and stabilizing role in a robust MEMC cathodic chamber.  This research will directly address this hypothesis by investigating the role of these bacteria in stabilizing defined methanogenic microbial communities at the cathode.  The main research tasks include the isolation of single strains or defined microbial communities capable of sustained cathodic methanogenesis, and to design and test advanced electrode systems (Figure 2).  Cathode surfaces will be chemically modified to increase the electrical conductivity and reduce contact resistances based on successful approaches with bacterial biofilms.   Materials that have higher surface areas and avoid the need for precious metal inorganic catalysts activity for oxygen evolution at the anode will be examined.

Figure 2

Figure 2: Side view of electrodes (left) showing a planar surface of electrodes and close-up of the electrode (right)

References

  • Cheng, S., et al., Direct biological conversion of electrical current into methane by electromethanogenesis. Environ Sci Technol, 2009. 43(10): p. 3953.
  • Logan, B.E., et al., Microbial electrolysis cells for high yield hydrogen gas production from organic matter. Environ Sci Technol, 2008. 42(23): p. 8630.
  • Nam, J.Y., et al., Variation of power generation at different buffer types and conductivities in single chamber microbial fuel cells. Biosens Bioelectron, 2010. 25(5): p. 1155.
  • Liu, H., et al., Power generation in fed-batch microbial fuel cells as a function of ionic strength, temperature, and reactor configuration. Environ Sci Technol, 2005. 39(14): p. 5488.