Incidence of microbial corrosion of metallic tubes in sanitary facilities

Galvanized steel tubes are used in sanitary water distribution systems for their corrosion resistance. In the last decades, corrosion rates found in these sanitary facilities have exceeded the expected values, shortening their lifetime. Following some assessments, the hypothesis of microbial corrosion has been put forward. This corrosion may be attributed to sulphate-reducing bacteria (SRB), which reduce sulphates contained in water, turning them into sulphides and acidifying the environment.
This work aimed to define the role of SRB as aggravating factor in the usual corrosion mechanisms. The principal purpose was to characterize the electrochemical influences of the biofilm present on metallic substrates (carbon steel, pure zinc and pure copper) by studying the evolution of chemical and electrochemical parameters with time.
Three various culture media were used: a sterile one (as reference) and two media respectively inoculated by a SRB commercial strain and by a strain coming from a sanitary pilot plant where SRB were detected.
The evolution of the thickness of the galvanized layers and of the corrosion products were followed. The water chemical composition was also quantified by ICP-AES and ionic chromatography.