Effect of ferrous ion availability on growth of a corroding sulfate-reducing bacterium

Environmental conditions controlling growth and metabolic activity of the sulfate-reducing bacterium (SRB), Desulfovibrio gabonensis DSM 10636 which had been previously isolated from a corroded oil pipe, was investigated in a homogenous culture. The culture was conducted continuously in order to get steady-state conditions for growth. Several factors, such as stirring conditions, and the flow rate of N 2 injection into headspace of the culture, were found to influence growth performances. The maximum growth rate was markedly influenced by Fe 2+ concentration in the medium. Surprisingly, removal of Fe 2+ and replacement by a mild steel coupon allowed the strain to grow at pH 6.0 but not at pH 7.4. A proposed biocorrosion mechanism by which the excretion of acidic products can promote Fe 2+ availability for SRBs is put forward. Lowering the pH, metabolic products, such as acetic acid, increases the level of corrosive sulfides ( H 2 S, HS −) . The latter, in turn, promote the attack of metallic iron which produces Fe 2+. In such a way, acidic conditions ensure Fe 2+ for SBR growth and can account for the persistency of corrosion.