Accelerate low water corrosion: the microbial sulphur cycle in microcosm

Accelerated low water corrosion is a form of marine steel corrosion caused by bacterial activity. It has a global spread and is potentially responsible for billions of pounds of damage. We have determined in detail both the chemistry of corrosion products and the associated microbiology at a UK site. The corrosion products form a layered structure with iron sulphides at the steel surface and iron oxides and sulphates in contact with water. The iron sulphides are formed by reaction of steel with hydrogen sulphide formed by sulphate reducing bacteria and are oxidised through a series of sulphur oxidation states by sulphide oxidising bacteria, forming acid at all stages and encompassing the whole of the bacterial sulphur cycle. The bacteria involved are endemic in anoxic bed sediment, and the process is a response to the presence of steel as an electron donor, and the generation of anoxic microenvironments within corrosion products.