Numerical Study on Air Movement in Sewer Systems

  • Author / Creator
    Qian, Yu
  • Uncontrolled air movement in sewer systems can lead to odor issues (i.e. H2S releasing), geysers, flooding, manhole cover blowup and public safety and health concerns, etc. However, the movement of the air flow in sewer systems has not been understood well, especially on the fundamentals of the transportation of air in sanitary systems and the mechanisms of geyser events and its mitigation methods in storm systems. This research is conducted in order to address the sewer odor issues and geyser events in sanitary and storm sewer system. This research is to focus on developing numerical models to predict the pressure distribution and potential odor hotspot in sanitary systems, and to investigate and assess potential geyser mitigation methods in storm sewer systems. A literature review was comprehensively conducted on the air movement in sewer systems. The knowledge gaps between the current understandings on this topic and practical applications were identified. The gaps are: 1, the drag coefficient between the wastewater and air in sewer pipes were missing; 2, the models and its application on air movement in sewer networks and 3, the generation and mitigation of geysers in storm sewer systems. Experimental and numerical models were then built to study the air movement in a single sewer pipe. In the numerical model, a drag coefficient was proposed to predict the air flow driven by the combined effect of the water drag and the pressure gradient. Both the results show that the existence of a hydraulic jump would substantially increase the air intake if the downstream of the hydraulic jump was open channel flow. The proposed model has been applied to a prototype sewer network in Edmonton, Alberta, Canada. A conceptual mathematical model was proposed to estimate the pressure distribution as well as the air flow rate in the prototype sewer pipe network. For the geyser events in storm sewer systems, a numerical model was built to study the mechanisms of geyser formation and to assess the potential geyser mitigation methods. The results show that the releasing of the entrapped air pocket can trigger geysers based on different initial flow conditions. All proposed geyser mitigation methods mitigate geyser events in terms of the amount of water flowing out of the manhole. For the implementation of orifice plates on top of the riser, a water-hammer like pressure was observed acting on the orifice plate and its peak pressure can reach up to 7.5 times of the pressure in the pipe. An analytical model by rigid column theory was also built to predict the movement of water slug, the pressure variation, and the water-hammer like pressure when the orifice plate was installed at the top of the riser. The power law relationship between the water-hammer like pressure and the relevant parameters were studied and analyzed. This thesis extends the knowledge in three aspects: (1) the air movement in a single sewer pipe with high water flow velocity, and with the existence of a hydraulic jump; (2) the air movement in sewer networks with dropshafts and a pump station; and (3) the mechanism, and ways of mitigating geyser event in a storm sewer system.

  • Subjects / Keywords
  • Graduation date
    Fall 2018
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
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