Bioelectrochemical systems (BESs) are considered to be a new device capable of converting the chemical energy of organic waste into electricity or hydrogen/chemical products, which have been applied in many fields including the biological recovery of heavy metal, reduction of nitrate and dechlorination of halogenated hydrocarbons. Recently, a fresh viewpoint that carbon dioxide can be fixed and transformed to produce multicarbon organic chemicals and fuels in BESs was put forward, which has attracted more interest of the scientists in this area.
Prof. Li Daping's team from Key Laboratory of Environmental and Applied Microbiology, Chengdu Institute of Biology, Chinese Academy of Sciences, has been engaged in the study of the BESs for carbon dioxide fixation for two years. Recently, they found carbon dioxide could be reduced to methane and acetic acid via direct and/or indirect extracellular electron transfer when methanogenesis and acetogenic bacteria were used as electroactive microorganisms attached on the cathode with carbon dioxide as the solar carbon source in BESs.
However, the metabolic pathway and end products were highly dependent on the cathodic potential, but only methane and hydrogen were produced when the cathodic potential was set in the range from -850 to -950 mV (vs. Ag/AgCl). Also, with the potential more negative than -950 mV, methane, hydrogen and acetic acid were simultaneously produced, and more methane (129.32 mL d-1) and more acetic acid (94.73 mg d-1) were obtained with a relatively large cathode surface area of 49 cm-2 at the cathodic potential of -1150 mV.
This research has suggested that mixed culture has the ability to accept electrons directly from the electrode or hydrogen to convert carbon dioxide to organic compounds, which can reduce carbon dioxide emissions and gain value-added substances simultaneously.
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