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

Causes for the occurrence of hydrogen sulfide in hot tap water in a small t own with an open hot water supply system were analyzed. The system is fed w ith artesian water containing up to 150 mg/l sulfate and has a water temper ature in its pipes ranging from 40 to 120 degrees C. The artesian water, wa ter in the storage reservoir, water in pipelines, and corrosion deposits on the internal surface of the return water main were all found to be populat ed by thermophilic sulfate-reducing bacteria oxidizing organic compounds an d hydrogen. X-ray phase analysis revealed the presence of iron minerals (Fe 2+ and Fe3+) and elemental sulfur in the deposits and the absence of sulfur -containing compounds. The complex of processes occurring in corrosion depo sits is considered: microbial formation of hydrogen sulfide and its involve ment in abiotic reactions with iron oxides resulting in the formation of el emental sulfur. The conclusion is made that the occurrence of secondary hyd rogen sulfide in hot tap water observed after an abrupt rise in water tempe rature to 100-120 degrees C during pipe repair is caused by hydrolytic deco mposition of S-0.