Microscopic Evaluation of Concrete Samples from Manholes Exposed on Hydrogen Sulphide

The field test of the sewer system in a rural area was made. The results from two different pressure-gravity systems localized in two settlements were compared. The investigated sewer system operates in serial connection; the sewage from one settlement is pumped to the expansion well in the next one. In both systems, the high concentration of hydrogen sulfide, exceeding 200 ppm, and visible concrete wells corrosion effects were recorded. The samples of corroded concrete from the internal walls of the chosen wells were collected. The results of an electron microscope with the EDS attachment (Energy dispersive X-ray Spectroscopy) analysis showed a significant sulfur content in a concrete surface layer from 11.2% to 64.2% for the first system and from 7.53% to 42.9% for the second one. The exposure of concrete to high concentrations of hydrogen sulfide and relatively high content of sulfur on the surface of concrete might be a reason for hydrogen sulfide corrosion of concrete in the investigated systems.