| Abstract: | The influence of extra-cellular polymeric substances in microbiologically influenced corrosion Unexpected pitting failures in copper potable water installations have occurred in some countries (Germany, Sweden, Scotland, South-West England, Saudi-Arabia) in the mid-eighties. These failures could not be expected in a single case based on the chemical composition of the potable water. Further typical manifestation characteristics of this microbiologically influenced corrosion have been i.) an uptake of dissolved and undissolved copper species in an obsolete, non regular fashion, ii.) black layers of copper(II)-oxide on the inner tube surface, accompanied by posniakite and malachite in the pitting areas, and, iii.) the detection of extracellular polymeric substances (EPS). These EPS consist partly of polysaccharides. They could either be produced by microorganisms within the potable water installation or be transported in a dissolved or undissolved state into the installation. Consequently, they sediment on the inner surfaces of the copper tubes. The physico-chemical properties of some kinds of EPS, especially their membrane properties and their cation selectivity, play a key role in this corrosion process. This is shown exemplarily performing diffusion potential measurements and contact corrosion experiments. |
