Microbiological Corrosion: Hydrogen Permeation and Sulfate-Reducing Bacteria

This study was undertaken to evaluate cathodic depolarization as the action mechanism triggered by sulfate-reducing bacteria (SRB) in microbiologically induced corrosion (MIC), using an inert substrate such as a 1-mm thick Pd foil with and without cathodic polarization, a H⁰ permeation conventional Devanathan-type cell, and the bacteria Desulfovibrio desulfuricans subsp. desulfuricans ATCC 7757. The permeation tests were run using a deaerated sterile culture medium inoculated or not with 10% D. desulfuricans at 10⁸ cell/mL. Serial dilution was used to evaluate the bacterial growth, and scanning electron microscopy (SEM) was used to analyze the characteristics of the biofilm and products formed on the Pd foil. Results indicated bacterial growth on the order of 4 × 10¹⁰ CFU/mL at 24 h in both polarization and nonpolarization tests, and hydrogen permeation tests without cathodic polarization determined that there were no conditions for the reduction of the H⁺ generated by hydrogen sulfide (H₂S) dissociation. These results show that these bacteria develop similarly, whether or not they are on a polarized surface as a source of H⁰, generating H₂S as a product of sulfate-dissimilating activity. Furthermore, hydrogen permeation tests with cathodic polarization determined an increase in the permeation current, which was associated with the maximum enzymatic activity phase of the bacteria. This good SRB development with cathodic polarization could be an indication that cathodic protection does not control MIC problems.