Effects of Drop Structures and Pump Station on Sewer Air Pressure and Hydrogen Sulfide: Field Investigation

Abstract

Understanding hydrogen sulfide (H2S) emission into sewer air space and the rate of ventilation to the atmosphere is important in preventing/mitigating odor and corrosion problems in sewer systems. This study presents the results of a field monitoring program on the air pressure and H2S levels in a 3-km-long sanitary sewer system in Edmonton, Alberta, Canada, which has drop structures in the upstream section and a pump station in the downstream section. Nineteen manholes were monitored, including six drop structures. A positive correlation was found between the sewage flow rate and the observed diurnal patterns of air pressure and H2S concentration. Drop structures were found to have caused significant pressurization in the downstream sewer air space. More than 1 km of the trunk sewer upstream of the pump station was submerged due to the pump station operation. This reduces flow velocity, increases sewage retention time, and potentially enhances the generation of H2S. A unique pressure pattern was found at several locations upstream of the pump station, which was closely related to the sewage level variation in the wet-well as a result of pump operations. The results reveal the ventilation condition in the study sewer system and will be useful for developing sewer odor mitigation measures.