Effect of pH on Anaerobic Mild Steel Corrosion by Methanogenic Bacteria

Methanogens can use H(2) produced by cathodic depolarization-mediated oxidation of elemental iron to produce methane. Thermodynamic consideration of the cathodic depolarization mechanism predicts more oxidation of Fe at lower pH. Methanogenic responses to pH by Methanococcus deltae, Methanococcus thermolithotrophicus, and Methanosarcina barkeri were examined. When grown on H(2)-CO(2), these bacteria had pH optima from 6.2 to 7.0, but when all H(2) was supplied from Fe, methanogenic pH optima were lower, 5.4 to 6.5. Corrosion was monitored with and without cultures and at various pHs; more corrosion occurred when cultures were present, biologically induced corrosion was greatest at the pH optima for methanogenesis from Fe, and corrosion without cultures increased with a drop in pH.