Species of Sulphur Bacteria Associated with the Corrosion of Concrete

IT has already been shown1 that in the highly acidic end-products of corrosion of concrete sewers exposed to atmospheres containing hydrogen sulphide, there are present large numbers of a sulphuric acidforming species of sulphur bacterium provisionally named Thiobacillus concretivorus. Further, it has been shown2 that the typical corrosion process is a case of bacterial corrosion; it cannot proceed under sterile conditions and can only be carried to the acid stage through the activity of this organism. It is typical of this form of corrosion that the pH of the products falls continuously as the corrosion process becomes established. As the organism cannot exist at a higher pH than 6.5, its activity could not explain the initial stage of the process in which the pH of the fresh concrete surface (11–12) falls to 6.5 or less. It was then suggested that this preliminary drop in pH could be brought about either by purely chemical reactions or by the activity of further species of bacteria.