Bacterial Methanogenesis and Growth from CO2 with Elemental Iron as the Sole Source of Electrons

Previous studies of anaerobic biocorrosion have suggested that microbial sulfur and phosphorus products as well as cathodic hydrogen consumption may accelerate anaerobic metal oxidation. Methanogenic bacteria, which normally use molecular hydrogen (H2) and carbon dioxide (CO2) to produce methane (CH4) and which are major inhabitants of most anaerobic ecosystems, use either pure elemental iron (Fe0) or iron in mild steel as a source of electrons in the reduction of CO2 to CH4. These bacteria use Fe0 oxidation for energy generation and growth. The mechanism of Fe0 oxidation is cathodic depolarization, in which electrons from Fe0 and H+ from water produce H2, which is then released for use by the methanogens; thermodynamic calculations show that significant Fe0 oxidation will not occur in the absence of H2 consumption by the methanogens. The data suggest that methanogens can be significant contributors to the corrosion of iron-containing materials in anaerobic environments.