A 3-year study of steel pilings in German marine harbours with and without corrosion was performed to quantify the relevant corrosion causing bacteria (SRB and thiobacilli) in the biofouling layers on the pilings at, above, and below the low-water. These organisms occurred at the low-water level jointly, although spacially separated in the layers (closed sulfur cycle=sulfuretum), and caused the accelerated corrosion once the layer became sufficiently thick in the course of its ageing. At low tide the layer was thoroughly aerated, whereas at high tide partially anaerobic zones, especially near to the metal must have occurred. Consequently, this type of corrosion needs years to develop. The experimental data clearly indicate that the increased amount of corrosion products (mainly iron) at strongly corroded areas is correlated with enhanced contents of sulfur and sulfate, high cell counts, and (microbial and chemical) activities. Additionally, iron sulfide and pyrite are detectable at the low-water level. These sulfur compounds as well as elemental sulfur are known to be highly corrosive.
Keywords" SRB, SOB, thiobacilli, sulfur, sulfate, biofilm, biofouling, MIC, ALWC