Case study of H₂S release and transport in a trunk sewer with drops

Field work was performed to investigate the release of hydrogen sulphide (H₂S) and its transport in the sewer trunk with drops in the Bonnie Doon area in Edmonton, Alberta, Canada, in order to develop a proper odor control strategy. The liquid sulfide concentration in the upstream trunk was low (less than 1.0 mg/L), and no H₂S gas was detected in the head space under this low concentration. However, high H₂S gas concentration was detected in the middle reach of the trunk due to the stripping effect of the three drops (2.7 m, 5.2 m and 2.0 m) along the trunk. The released H₂S at drops was then transported in the sewer system and emitted at various locations and caused odor concerns. These drops played an important role in H₂S release, and the overall H₂S mass transfer coefficient at drops was much higher than that in normal gravity sewers. The overall oxygen and H₂S mass transfer coefficient (K_La) was estimated to be around 200 h^-1 and 300 h^-1 at the first two drops, respectively. Field sampling of biofilm indicates that Desulfomicrobium was identified as the sulfate-reducing bacteria (SRB) responsible for sulfide generation in sewer wall biofilm and Thiobacillus was the only predominant member in manhole wall biofilm contributing to sewer manhole corrosion.