Anaerobic Metabolism of Biodiesel and Its Impact on Metal Corrosion

Abstract

Biodiesels have gained widespread acceptance because they are domestically produced carbon-neutral fuels that ultimately decrease greenhouse gas emissions and reduce dependence on fossil imports. While they are chemically and physically stable fuels, their susceptibility to biological degradation in the absence of oxygen is underexplored. We incubated five anaerobic inocula with biodiesel. The microorganisms originated from fresh and marine environments with differing histories of exposure to hydrocarbons, biodiesel, and oxygen. All inocula were able to biodegrade biodiesel within 1 month. Biodiesel metabolism accelerated the rate of both sulfate reduction and methanogenesis above biodiesel-unamended controls. Metabolite profiling indicated that the methyl esters of biodiesel were readily hydrolyzed to the corresponding suite of fatty acids, and the latter were also metabolized. Electrochemical/corrosion experiments showed that the anaerobic microbial metabolism of biodiesel in coastal seawater samples accelerated the rate of pitting corrosion in carbon steel. The susceptibility of biodiesel to anaerobic biodegradation and its propensity to stimulate biocorrosion suggest caution when integrating this alternate fuel with the existing infrastructure.