A NOVEL MODEL FOR SEWER VENTILATION
EMIL DIETZ FUGLSANG
DEPARTMENT OF CIVIL ENGINEERING
AALBORG UNIVERSITY, DENMARK
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:
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𝐶𝑂𝐷 + 𝑂2 → 𝐶𝑂2
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
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
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Length profile
CO2 + pH
Inspected the sewer for openings to the atmosphere
Methods – computer simulations
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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
Results two hours in the upstream and downstream point
Measured
Simulated
Length profile of CO2
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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
QUESTIONS?