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A stacked rapid sand filtration unit is preferable to a conventional rapid sand filtration unit as it requires less water to back wash since the filters are stacked, and use the same water for all filter layers to back wash. In addition, a stacked filtration system requires less planned area to achieve the same level of filtration.
Figure 1: Vertically Stacked Filtration Unit Design
For more information, please see the explanation of stacked rapid sand filtration theory and unit design.
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Filtration Unit Design
It is necessary to design a filtration unit that can be built at our existing water treatment plants, and be incorporated into future plant designs. This includes a hydraulic analysis to calculate the critical elevations for how the filter fits in with the sedimentation tank effluent weir and the distribution tank. This analysis must be done using the approach for the design tool with correctly named variables, and with the standard inputs of flow rate and then automated design of the filter system. This automated design must include full hydraulic design of all of the piping required.
Figure 1: Vertically Stacked Filtration Unit Design
Plane Assumption Test
In our initial design, we assumed that as long as the spacing between the filtration tubes in each layer is small in comparison to the depth of a layer of sand, then the flow of water out of the tubes will converge and form a plane of filtration. For our purposes, we assumed that a ratio of 1 to 10 of tube spacing versus filter depth was small enough. Laboratory experiments should be conducted to find the depth which will still allow the tubes to be modeled as a plane. The number of inlet and outlet tubes per plane can also be varied to see if our modeling of the layer of tubes as planes of filtration is accurate. We can decrease the space between the tubes to find the necessary ratio between the sand layer depth and the necessary spacing between the tubes that will allow us to model the layer of tubes as a plane.
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