Effects of nanoscale zero valent iron (nZVI) concentration on the biochemical conversion of gaseous carbon dioxide (CO2) into methane (CH4)

This study presents the effects of nanoscale zero valent iron (nZVI) concentration on the biomethanation of gaseous CO2. During anaerobic batch experiment with 9 times injection of CO2, the CO2 concentration in the headspace rapidly decreased by dissolution. Then, when nZVI was added at 6.25 and 12.5 g/L, the dissolved CO2 was biochemically transformed into CH4 at a maximum production rate of 2.38 and 3.93 μmol/hr, respectively. Biomethanation at these two nZVI concentrations continued until the end of experiment. In spite of more H2 evolution by nZVI at 25 g/L, biomethanation did not occur, due to the significant inhibition of methanogenesis by nZVI. As the nZVI concentration increased, relative abundance of the hydrogenotrophic methanogens, especially Methanobacteriales, increased. However, at 25 g/L of nZVI concentration, acetic acid was accumulated and the relative abundance of Clostridium became predominant, indicating that homoacetogenesis was superior over methanogenesis.