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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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