Role of redox properties of biofilms in corrosion processes

Dissolution of iron in the presence of inorganic and organic sulfides was investigated as a chemical model for sulfide induced microbiologically influenced corrosion processes. Sulfur species used in the model were based on the surface analysis of the biofilm and the cell wall composition of the sulfate-reducing bacteria. Oxide layer decomposition by the sulfide species in buffer solution is explained with the formation of surface complexes, promoting the reductive dissolution of iron oxide. The mixed-sulfide species in actual biofilms result in a transformation of the surface layer by the assembly of mixed-ligand complexes. This type of film modification enhances the reactivity of the corrosion product layer where accelerated redox reaction can occur, as an analogous reaction to the biochemical role of iron–sulfur clusters containing redox proteins. The possible functional role of corrosion products in the metabolic processes of hydrogen utilizing sulfate-reducing bacteria can be also considered.