Abstract
Corrosion of mild steel under completely anaerobic conditions in the presence of a mixed population biofilm, including sulfate-reducing bacteria (SRB), has been studied in a continuous flow system. The open channel flow reactor was continuously fed with low concentration substrate at different dilution rates which influenced biofilm accumulation. No direct correlation was observed between corrosion and SRB activity in the absence of ferrous ion. Furthermore, corrosion of mild steel in the SRB environment was mainly determined by the nature of the metal and environmental conditions such as dissolved iron. When formation of iron sulfide film on mild steel was prevented before the biofilm accumulated, the metal surface retained its scratch lines after a 21-day experiment (SRB at 2.6 × 109/cm2) . However, when iron sulfide film was formed before the accumulation of biofilm,, visible localized corrosion appeared after 14 days and increased up to 21 days. Intergranular and pitting attack were found in the localized corrosion area. Inclusions (A1, Mn, and Fe) and grain boundary triple points were found in the localized corrosion area. At high iron concentration (about 60 mg/L in the bulk water), all biogenic sulfide was precipitated and corrosion rate significantly increased. Intergranular attack was found over the entire metal surface.
