Role of redox properties of biofilms in corrosion processes

Dissolution of iron in the presence of inorganic and organic sulfides was i nvestigated as a chemical model for sulfide induced microbiologically influ enced corrosion processes. Sulfur species used in the model were based on t he surface analysis of the biofilm and the cell wall composition of the sul fate-reducing bacteria. Oxide layer decomposition by the sulfide species in buffer solution is explained with the formation of surface complexes, prom oting the reductive dissolution of iron oxide. The mixed-sulfide species in actual biofilms result in a transformation of the surface layer by the ass embly of mixed-ligand complexes. This type of film modification enhances th e reactivity of the corrosion product layer where accelerated redox reactio n can occur, as an analogous reaction to the biochemical role of iron-sulfu r clusters containing redox proteins. The possible functional role of corro sion products in the metabolic processes of hydrogen utilizing sulfate-redu cing bacteria can be also considered. (C) 2001 Elsevier Science Ltd. All ri ghts reserved.