Biocorrosion dans les eaux douces

Abstract

Biologically-induced corrosion frequently occurs in industrial water systems. Many microorganisms are involved in this process : sulphate reducing bacteria, sulfur oxidizing bacteria, iron oxidizing bacteria, common heterotrophic bacteria, fungi, algae. Biocorrosion occurs in several ways. A biofilm generally develops before corrosion and enhances it. The biofilm is made up by a large number of different micro-organisms enclosed in extra-cellular polymeric substances which binds new particles and cells from the stream. This creates a microenvironment favourable to sulfate reducing bacteria, keeps corrosive by-products in and prevents biocide from penetrating into the biofilm.Different technics are used for measurement of total microbial biomass in system water. Direct (immunology, autofluorescence) or indirect (culture) methods have been developed for the detection of sulphate reducing bacteria or their specific enzymes in circulating water but they do not indicate the number and the activity of these bacteria in the biofilm where they are more much numerous.Biofilm probes are appropriate for evaluation of biofilm extend and for testing biocide efficiency on the site. However, formation, composition and activity of these microbial communities remain quite unknown.Chemical treatment with both a corrosion inhibitor and a biocide can be efficient for prevention but inactive against established biofilms which protect sulphate reducing bacteria. Mechanical and thermal treatments are the most efficient in removing biofilm.Research trends toward selection of specific biocides against sulphate reducing bacteria and inhibition of biofilm formation by anti-adhesive products.