Use of Air Circulation Pipes in Deep Dropshafts for Reducing Air Induction into Sanitary Sewers

Abstract

AbstractFalling water in dropshafts can induce large amounts of air into the airspace of sewers, and the subsequent release of the pressurized air can cause sewer odor concerns. The construction of a vertical airshaft that is connected to a dropshaft via pipes is expected to circulate the air and reduce air induction into sewers. In this study, two deep dropshafts with drop heights of 24 and 11 m were retrofitted sequentially with air circulation pipes in a sanitary sewer system. Air pressure inside the sewer line and air flow rates inside the air circulation pipes were monitored in 2006–2011. The results show that the retrofits reduced the manhole air pressure by about 10–47%. Air pressures in the manholes and the dropshafts, as well as air flow rates in the air circulation pipes, were noticed to have diurnal patterns, which appeared to relate to wastewater discharge and air pipe elevation. Overall, the ratios of air flow rate to water flow rate were found to be 160±78 and 144±113 for the two dropshafts,...