MICROBIOLOGICALLY INFLUENCED CORROSION OF COPPER IN POTABLE WATER INSTALLATIONS - A EUROPEAN PROJECT REVIEW

Copper tubes are considered as material of choice for most domestic an d institutional plumbing requirements. However, to a few instances pro blems have arisen which were shown to involve microbiological activity . The BRITE/EURAM Project ''New Types of Corrosion Impairing the Relia bility of Copper in Potable Water Caused by Microorganisms'' (Contract -No. BREU-CT 91-0452) was launched to examine the interactions between microorganisms and their secreted products and a copper tube surface involving a cross-disciplinary consortium. A review of this project is reported in this contribution. Based upon chemical analysis of biofil ms from failed copper tubes, it was possible to develop model biopolym ers of defined composition and well characterised surface adsorption p roperties to establish suitable electrochemical test procedures. Cultu re biopolymers showing similar chemical compositions could be produced from a range of copper-pitting-associated bacteria. It was possible t o demonstrate cation selective behaviour by layers of these relevant m odel and culture biopolymers. Two linked copper electrodes, one bare a nd the other coated with a cation selective biopolymer, were shown to establish a corrosion element. The covered areas acted as the cathode whilst the bare areas were anodic. This was also seen in single metal samples with disrupted polymer coatings giving ''bare'' patches. In an odic areas the corrosion follows a chloride induced mechanism leading to repassivation of the surface. This could also be demonstrated in th e original potable water taken from an institutional building affected by Microbially Influenced Corrosion (MIG). Sulphate ions inhibit this expected passivation process. The basic corrosion process appears to follow the chloride model, but this can become overshadowed by the eff ects of additional anions such as sulphate and bicarbonate.