Numerical Simulations on Dropshafts with Air Circulation Pipes in Drainage Networks

Dropshafts are widely employed in urban drainage systems to convey wastewater from higher to lower elevations. To mitigate odor and corrosion issues, air circulation pipes have been installed in certain drainage networks, such as those in Edmonton, Canada. This study used validated numerical models to assess the performance of these pipes under varying inlet flow conditions. At a low inlet velocity (0.2 m/s), the pipes reduced downstream manhole air velocities by up to 43%, demonstrating significant effectiveness. However, at higher velocities (1.0 m/s), the reduction became less pronounced and even negative at specific locations. A similar trend was observed at the system level, where the air mass inflow reduction rate decreased from 38% to −17% with increasing inlet velocity. These findings highlight a velocity-dependent interaction between sewage flow and ventilation behavior, offering practical insights for the design and optimization of air circulation systems in urban drainage networks.