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The benefits of CFD as applied to the design of new wastewater treatment plants (WWTP), or the expansion of existing ones, have been featured in a series of previous posts.  A recent project dealt with the analysis of a CSO (Combined Sewer Outflow), which is a sewer designed to collect rainwater runoff, domestic sewage, and industrial wastewater in the same pipe. Most of the time, combined sewer systems transport all of their wastewater to a sewage treatment plant, where it is treated and then discharged to a water body. For this project, a netting facility and extension was being designed and analysis was required to provide some reassurance that the energy dissipation through the netting structures would not cause an overflow condition in the adjoining basins.

A detailed 3D CAD model of the basins, channel and netting structure was provided by the client and a computational grid of several million cells was created from the 3D CAD files. Simulations were then conducted to determine the upstream liquid level for various flow conditions.  Based on these simulations, it was determined that the netting structures would be able to filter out the required products while not exceeding the allowable head loss in the overall system—thus providing reassurance that the client could proceed with the proposed design.

This is another example of how CFD simulations can be utilized at the design stage to provide accurate flow predictions through complex geometric structures in open channel flows for important water collection, conveyance and treatment systems.