Distribution of sulfate-reducing bacteria in a hot water supply system and the origin of hydrogen sulfide in water

Causes for the occurrence of hydrogen sulfide in hot tap water in a small town with an open hot water supply system were analyzed. The system is fed with artesian water containing up to 150 mg/l sulfate and has a water temperature in its pipes ranging from 40 to 120 degrees C. The artesian water, water in the storage reservoir, water in pipelines, and corrosion deposits on the internal surface of the return water main were all found to be populated by thermophilic sulfate-reducing bacteria oxidizing organic compounds and hydrogen. X-ray phase analysis revealed the presence of iron minerals (Fe2+ and Fe3+) and elemental sulfur in the deposits and the absence of sulfur-containing compounds. The complex of processes occurring in corrosion deposits is considered: microbial formation of hydrogen sulfide and its involvement in abiotic reactions with iron oxides resulting in the formation of elemental sulfur. The conclusion is made that the occurrence of secondary hydrogen sulfide in hot tap water observed after an abrupt rise in water temperature to 100-120 degrees C during pipe repair is caused by hydrolytic decomposition of S-0.