Assessment and Design Optimization of Retrofitting Dropshaft with Air Circulation Pipes for Downstream Depressurization

摘要

Plunging flow dropshafts in urban drainage systems have been reported to cause downstream air pressurization and subsequent sewer odor issues. Retrofitting dropshafts with air circulation pipes has been attempted to reduce sewer odour complaints in Edmonton, Alberta, Canada. In the current work, laboratory model study, field monitoring, and model prediction were conducted to assess the effectiveness of this retrofit and explore its design optimization. This retrofitting was found to be effective in reducing air entrainment of the dropshaft and depressurizing the downstream sewers. However, the study showed that horizontal air circulation pipes at various elevations contributed differently in reducing the air entrainment. Based on the air flow model, increasing the size of the horizontal pipes had a more significant effect on reducing the downstream air pressure compared to increasing the number of the pipes. It was found that the retrofitting can be optimized by removing the bottom horizontal air circulation pipes while increasing the pipe size.