Sedimentation Tank Design (Summer 2007)
Closed Top Design
Figure 1. Closed top sedimentation tank, as implemented in Summer 2007
This sedimentation tank was designed and built in Summer 2007 by Sara Schwetschenau and the Civil and Environmental Engineering Machine Shop, and has a closed top design.
Since the water entered the sedimentation tank on one side in this design, there was the problem of differences in the lengths of flow required to travel through each of the lamella, and thus differences in the amount of head loss experienced through each path. This would cause the flow rate through the various lamella to be different - specifically, the flow through the lamella closest to the flocculator would be the fastest. To attempt to avoid this problem in the design of this plant, a very large head loss was introduced at the top of the lamella in the sedimentation tank in the form of very small orifices; However, even with this design adjustment, there is still a visible difference in the flow of water through the first and last lamella of the sedimentation tank. This design also made it very difficult to clean out the sedimentation tank between uses.
Since this design featured a closed top sedimentation tank, a weir, shown below, was used to adjust the water level in the flocculator. Rotating the weir to adjust the height of the part open to the atmosphere allowed us to change the pressure head inside the sedimentation tank, and thus changed the water level of the flocculator.
