Involvement of Organic Acid During Corrosion of Iron Coupon by Desulfovibrio desulfuricans

Microbiologically influenced corrosion (MIC) is an electrochemical process where the participation of microorganisms initiates, facilitates, or accelerates the corrosion reaction. Sulfate-reducing bacteria (SRB) reduce sulfate to sulfide and are known to be the most destructive microorganisms in anaerobic MIC. Accordingly, the current study attempted to elucidate the mechanisms involved and the relative importance of the corrosive products in SRB-induced corrosion. The measured rate of anaerobic corrosion of iron coupons by Desulfovibrio desulfuricans was $89.9{\;}\mu\textrm{g}{\;}\textrm{m}^{-2}{\;}d^{-1}$. Direct contact between the cells and the iron coupon did not seem to be necessary for corrosion to occur, since the corrosion rate was similar ($100.8{\;}\mu\textrm{g}{\;}\textrm{m}^{-2}{\;}d^{-1}$) when the coupon was enclosed in a dialysis bag. The participation of sulfide in the corrosion process was only marginal, as the specific corrosion rate was 2.5 times higher in a sulfate-free pyruvate medium than in an $H_2S-producing$ lactate medium. Acetate (18.8-22.1 mM), the end-product of pyruvate and lactate metabolism, was identified in the culture medium and thus presumed to play a major role in the corrosion process involving Desulfovibrio desulfuricans.