A Novel model for sewer ventilation

1. A Novel model for sewer ventilation Emil Dietz Fuglsang Department of civil engineering Aalborg university, denmark

2. Motivation – whyareweinterested in sewer ventilation? Broken covers leed to discharge of air Corrosion of concrete and metal

3. Methodology - how to useCO2 as a natural tracer Wastewater is always super saturated with CO2 For example at pH 7.5 water in equilibrium with atmospheric CO2: • 0.2 mMCO2 -equivalents in the wastewater BUT: • Biological processes in wastewater produce 0.5-1mM CO2 –eq. per hour • Furthermore, potable water is often CO2 -super saturated  Wastewater is always super saturated with CO2

4. Sewer ventilation • CO2 is continuously released from the water to the sewer gas and diluted by the sewer ventilation Alternating water levels can furthermore cause in- and outflow of sewer gas Balancing production and release allows determination of ventilation

5. Methodology – in the field CO2 + pH • Length profile • Inspected the sewer for openings to the atmosphere

6. Methods – computer simulations • Full dynamic transient hydraulic model • Upper boundary conditions: intermittent operated pump station • Resulting in rapid water level changes in the pipe… • WATS sewer process model • Full dynamic simulation of chemical and biological transformations • Quasi stationary friction-drag gas flow model

7. Results two hours in the upstream and downstream point Measured Simulated

8. Length profile of CO2 • Large effect of pump starts at the top of the system • Continuing release further downstream

9. Conclusions Combining CO2 as a natural tracer and an in-sewer process model it is possible to predict levels and dynamics of ventilation in an intercepting sewer

10. Questions?