Effect of pH on Anaerobic Mild Steel Corrosion by Methanogenic Bacteria

Abstract

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 0 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 0 , 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 0 , and corrosion without cultures increased with a drop in pH.