Inhibitory effect of clay mineral on methanogenesis by Methanosarcina mazei and Methanothermobacter thermautotrophicus

Abstract

With increased concentration of methane in the atmosphere and its impact on climate, effective mitigation of methane emission is of global importance. Recent studies have shown the inhibition of microbial methanogenesis upon addition of ferruginous clay minerals. To better elucidate the mechanism of the inhibitory effect of clay minerals on methanogenesis, laboratory experiments with Methanosarcina mazei and Methanothermobacter thermautotrophicus were performed in batch systems in which pristine kaolinite or iron-coated kaolinite were added as representative clay minerals. Soluble Al in solution and production of Fe(II) and methane gas were monitored over the course of the experiments. The mineralogical changes in the kaolinites were characterized with scanning electron microscopy. The results confirmed that both Ms. mazei and Mt. thermautotrophicus were capable of reducing ferric iron with H2/CO2 as methanogenic reactants. Both pristine and iron-coated kaolinites could act as effective inhibitors of methanogenesis. The overall methane production was similar with pristine kaolinite and iron-coated kaolinite, although at the beginning of the experiment less CH4 was observed in iron-coated kaolinite system. The inhibition of methanogenic activity observed in pristine kaolinite was primarily ascribed to the toxicity effect of aluminum. A more effective inhibition of methanogenesis in iron-coated kaolinite during the first several days could be explained by the combined effects of aluminum toxicity and diversion of electron flow from CO2 to Fe(III). Our results have important implications for mitigating methane emission in natural or anthropogenic settings.