Partners and International Organizations
(English)
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B, CH, D, E, F, FIN, H, I, S, UK
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Abstract
(English)
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In this project the physico-chemical processes were studied, which take place at a steel surface (substratum) colonized by bacteria (biofilms). The action of bacteria on metals is normally destructive and is referred to as biocorrosion. Biocorrosion is a considerable problem in water bearing industrial Systems and has been demonstrated for several types of bacteria and under the most different conditions. The aim of this project was to investigate, whether there are conditions for which corrosion rates are not increased, but are reduced by bacterial activity. Foˆr this purpose mild steel coupons were incubated in cultures of three different aerobic bacteria and afterwards exposed to a corrosive aqueous medium. It was found that incubation of the steel coupons with growing, biofilm-forming bacteria, which had direct access to the steel surface, in a mineral medium containing more than 2 mM phosphate, significantly reduced corrosion occurring in the corrosive medium. It was shown that under these incubation conditions, a biologically induced surface reaction took place, by which vivianite was formed, an almost insoluble iron(ll)-phosphate. This layer of vivianite was found to be the reason for the observed reduction of the corrosion rate. The surface reaction was always accompanied by an increase in the iron concentration in the medium, but after some days, upon the build-up of the vivianite layer, the iron release stopped. The reported results were obtained for growing cells of the biofIm-forming bacterial species tested (Rhodococcus C125, Pseudomonas putida mt2) and for the carbon sources used (benzoate, ethanol, acetate). However, a non-biofilm forming microbial species (Streptomyces pilosus DSM 40714), resting cells or cells that had been separated from the steel surface by a membrane, were not able to form vivianite and to reduce the corrosion rate.
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