Electrochemical Analysis of Long-term Corrosion and Reactions Caused by Sulfate-reducing Bacterial Isolates

Microbiologically influenced corrosion (MIC) accelerates metal infrastructure corrosion under anaerobic conditions. Sulfate-reducing bacteria (SRB) cause corrosion through Chemical-MIC (CMIC) and Electrical-MIC (EMIC). EMIC has been reported as a phenomenon that promotes cathodic reactions of corrosion by acquiring electrons from solid metals for microbial growth, inducing significant corrosion. However, information about the EMIC mechanism to assess EMIC risk and develop EMIC mitigation strategies is limited. In this study, the corrosion of carbon steel by two SRB strains, Desulfovibrio sp. strain SDB1 and Desulforhabdus sp. strain SDB2 were characterized and compared by electrochemical techniques and microscopic observation. Both isolates increased corrosion of carbon steel by 3.1 or 12.3 times than that in the abiotic control, respectively. Long term corrosion test revealed strain SDB2 has ability to continue corrosion for 1 year. Relative to the abiotic control, linear polarization resistance decreased in both isolates and a 4 and 50.5 folds increase in the corrosion current was noted with the strain SDB1 and strain SDB2, respectively. EIS analysis also showed low resistance of corrosion products formed on carbon steel by strain SDB1 and strain SDB2. Cyclic voltammetry measurements confirmed that electrons could be transferred between the isolates and carbon steel. SEM-EDS indicated semiconductive iron sulfides were included in corrosion products formed on carbon steel. These findings suggested that both SRB promote corrosion by forming different conductive corrosion crusts including biofilms that uptake electrons from corroding metal surfaces. Since the electrochemical profiles of both isolates were distinct from those of previously reported EMIC SRB, it is anticipated that future research will provide further insights into the mechanisms of EMIC.