Biological metal corrosion in saline systems by sulfur-reducing and iron-oxidizing bacteria

This study investigated whether any possible bio-corrosion of pumps could occur when operating underground pumping stations in coastal regions. Groundwater in the stations was found to contain Leptothrix sp. (iron-oxidizing bacteria, IOB) and Desulfovibrio sp. (sulfur-reducing bacteria, SRB). Four different metal specimens were exposed to saline water media, where Leptothrix sp. or Desulfovibrio sp. were inoculated solely or together. The result showed that IOB not only provoke the corrosion of galvanized and stainless steels but also accelerate (by 5-10 times) the formation of zinc/iron precipitates. The SRB specifically mediated the corrosion of zinc steel to a greater extent than the IOB. In a single medium, STS 304, galvanized steel, iron and zinc steel resisted corrosion in that order. However, in the mixed culture, the metals were corroded by a factor of 2-7 more than in the single medium. On disinfection, a higher NaOCl concentration surprisingly caused increased chemical corrosion, and UV light scattering due to corrosion precipitates enhanced microbial corrosion. Consequently, the metals showed more biochemical corrosion than the control, especially in a mixed culture. In particular, the level of STS 304 corrosion was significantly higher in the presence of microbes than the control.