Modeling of Heavy Nitrate Corrosion in Anaerobe Aquifer Injection Water Biofilm: A Case Study in a Flow Rig

Abstract

Heavy carbon steel corrosion developed during nitrate mitigation of a flow rig connected to a water injection pipeline flowing anaerobe saline aquifer water. Genera-specific QPCR primers quantified 74% of the microbial biofilm community, and further 87% of the community of the nonamended parallel rig. The nonamended biofilm hosted 6.3 × 10⁶ SRB cells/cm² and the S³⁵-sulfate-reduction rate was 1.1 μmol SO₄^2–/cm²/day, being congruent with the estimated SRB biomass formation and the sulfate areal flux. Nitrate amendment caused an 18-fold smaller SRB population, but up to 44 times higher sulfate reduction rates. This H₂S formation was insufficient to form the observed Fe₃S₄ layer. Additional H₂S was provided by microbial disproportionation of sulfur, also explaining the increased accessibility of sulfate. The reduced nitrate specie nitrite inhibited the dominating H₂-scavenging <i>Desulfovibrio</i> population, and sustained the formation of polysulfide and Fe₃S₄, herby also dissolved sulfur. This terminated the availability of acetate in the inner biofilm and caused cell starvation that initiated growth upon metallic electrons, probably by the sulfur-reducing <i>Desulfuromonas</i> population. On the basis of these observations we propose a model of heavy nitrate corrosion where three microbiological processes of nitrate reduction, disproportionation of sulfur, and metallic electron growth are nicely woven into each other