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A vertically stacked filtration system meets many of the AguaClara Project constraints. Both normal filtration and back wash operations are gravity driven and require no electricity. In additon, it is an open system. The required construction materials(PVC pipes, sand, concrete, brick, and rebar) are relatively cheap and abundant available in Honduras. Most importantly, stacked rapid sand filtration is proven to consistently lower the effluent NTU standard to below 1 NTU.
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 a much smaller footprint to achieve the same level of filtration.
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