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 CO 2 as a natural tracer Wastewater is always super saturated with CO 2 For example at pH 7.5 water in equilibrium with atmospheric CO 2 : 0.2 mM CO 2 -equivalents in the wastewater BUT: Biological processes in wastewater produce 0.5-1mM CO 2 –eq. per hour Furthermore, potable water is often CO 2 -super saturated  Wastewater is always super saturated with CO 2

Sewer ventilation  CO 2 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 CO 2 + 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

Results two hours in the upstream and downstream point MeasuredSimulated

Length profile of CO 2 Large effect of pump starts at the top of the system Continuing release further downstream

Conclusions Combining CO 2 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?