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Stacked Rapid Sand Filtration |
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Introduction
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a novel self-backwashing filter invented by the AguaClara team. Its unique stacked geometry allows it to use the same flow rate for the filtration and backwash cycles, without the expensive pumps or elevated tanks required to backwash conventional rapid sand filters. In addition, a stacked filtration system requires a much smaller footprint |
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than a conventional filter to treat a given flow rate. A vertically stacked filtration system meets many of the AguaClara Project constraints. Both normal filtration and |
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backwash 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 available in Honduras. Most importantly, stacked rapid sand filtration is proven to consistently lower the effluent to below |
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For more information, please see the explanation of stacked rapid sand filtration theory and unit design, Field Implementation and the General Filtration Page.
Keep up to date with Reflection Reports and Future Challenges for the Stacked Filtration Team!
Current Research
Bench Scale Model Design
To test the theory behind the stacked rapid sand filter, a bench scale model was designed and built. Using this model, a series of experiments will be conducted to test the filtering capacity of a stacked rapid sand filter.
Back Wash
The most important challenge to prove is the ability to clean the stacked rapid sand filter by the back wash method. In order to back wash the filter, we must prove that the individual filter layers can be fluidized in sequence, and thus result in a fully fluidized filter. Once fully fluidized, the filter can then be back washed, and require significantly less water than a comparable conventional single layer filter.
Performance Comparison
In order to learn if the flow distribution in the stacked rapid sand filter system is working reasonably well, it is necessary to conduct an experimental comparison to a conventional single layer filter of the same depth as a single layer of our stacked filter (20 cm).
Head Loss Measurement
The head loss across the filter over time is the governing factor that determines the effective filtration time. The build up of head loss ultimately determines how often the filtration unit will require back washing.
Future Research
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.
Performance Study
A number of parameters will need to be studied in order to find the optimal design conditions for a filtration unit. The variables to be studied experimentally include diameter of sand grains, depth of each filter layer, horizontal spacing between pipes, and filtration velocity. A robust study of all these variables will require a long period of time, and it is thus recommended that we proceed with the design and installation of a filtration unit with conservative design parameters. Once full-scale performance can be analyzed, we can proceed with an exhaustive performance study to further optimize the stacked rapid sand filtration unit design.
Past Research
Summer 2010 SRSF Research
Built initial bench scale model and initialized proof of concept.
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