Effect of Iron on Conversion of Acetic Acid to Methane During Methanogenic Fermentations

Abstract

Addition of iron (as a solution of reagent grade FeCl 2 , up to 20 mmol/1) to a methanogenic culture utilizing acetic acid markedly increased conversion of acetic acid to methane. The optimum soluble iron concentration was between 0.2 and 2 mM, with higher concentrations becoming slightly less stimulating. Most of the iron added precipitated within days after addition (mostly as ferrous carbonate or phosphate). Conversion of acetic acid to methane in liquid from municipal sewage digesters and from laboratory food processing waste digesters was also increased markedly by addition of iron. Results indicate that optimization of the conversion of acetic acid to methane in methanogenic fermentations requires soluble iron levels many times higher than those often required for maximum growth and activity in microbial cultures.