Aerobic and Anaerobic Transformations of Sulfide in a Sewer System – Field Study and Model Simulations

The formation and fate of sulfide in a force main and a downstream-located gravity sewer were investigated in an extensive field study. Sulfide formation during approximately 4 hours of anaerobic transport in the force main was significant. The following gravity sewer was aerobic and a fast reduction of the sulfide concentration was observed due to sulfide oxidation and emission of hydrogen sulfide gas to the sewer atmosphere. During 14 minutes of transport in the gravity sewer, the sulfide concentration decreased on average 30%. Despite the continuous emission of hydrogen sulfide, the concentration in the atmosphere of the gravity sewer was generally below 3% of the concentration in equilibrium with the sulfide concentration in the wastewater. This observation demonstrated that removal of hydrogen sulfide gas by adsorption onto the sewer walls exposed to the sewer atmosphere was fast compared with emission from the wastewater. An application of a conceptual sewer process model for simulating the formation and fate of sulfide in wastewater collection systems was demonstrated. The model was able to reproduce the average conditions in the investigated intercepting sewer satisfactory, but could not account for the observed variability. Overall, the model predicted that approximately 90% of the decrease of the sulfide concentration in the gravity sewer was due to sulfide oxidation and that only a small fraction entered the sewer atmosphere, causing odor and corrosion. Even so, the model predicted concrete corrosion rates of up to 1.2 mm per year in the gravity sewer section.