Corrosion of Mild Steel in Cultures of Ferric Iron Reducing Bacterium Isolated from Crude Oil I. Polarization Characteristics

The polarization characteristics of mild steel were studied under microaerobic conditions in four media, including a synthetic medium and the produced water from an oil field. In all the media, anodic depolarization was always observed when a ferric iron reducing bacterium (Pseudomonas sp.) was present. In produced water, both anodic and cathodic depolarization of the mild steel could occur, although transiently. Addition of sodium lactate as a substrate to boost the total available energy in the produced water caused the anodic depolarization to be sustained while cathodic depolarization was not abolished. Anodic depolarization was accompanied by the bacterial reduction of ferric to ferrous compounds. In the absence of the ferric iron reducing bacterium, both the anode and the cathode were polarized. A mechanism for the bacteria induced anodic depolarization is suggested.