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A NOVEL MODEL FOR SEWER VENTILATION
E M I L D I E T Z F U G L S A N G
D E PA R T M E N T O F C I V I L E N G I N E E R I N G
A A L B O R G U N I V E R S I T Y, D E N M A R K
Motivation – why are we interested in sewer ventilation?
Broken covers leed to discharge of air Corrosion of concrete and metal
Methodology - how to use CO2 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 mM CO2 -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
𝐶𝑂𝐷+𝑂2→𝐶𝑂2
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
Methodology – in the field
• Length profile CO2 + pH
Inspected the sewer for openings to the atmosphere
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
Length profile of CO2
• Large effect of pump starts at the top of the system
• Continuing release further downstream
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