Thiobacillus neopolitanus implicated in the degradation of concrete tanks used for potable water storage

Following commissioning of a small water treatment plant, the pH of its finished water dropped by 0.5 units during the fourth year. Concrete surfaces of storage tanks were degrading and submerged steel surfaces became colonized with large rust-coloured nodules. Changes in chemical additions along with engineering changes did not improve the symptoms. Raw water was taken from a eutrophic lake and contained high levels of hydrogen sulphide. Microbiological analyses of various plant sites yielded the presence of Thiobacillus neopolitanus and apparent autotrophic Pseudomonas spp. After evaluating the results a number of modifications were recommended and the major one was that a low hydrogen sulphide containing source water should be used. To address this recommendation the water treatment plant now uses water from a moderately sized river resulting in lower in-plant acid production and a better finished water.