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MathCad Results: Empirical vs. Simple Hydraulics (Conservative) Approach Image Removed

Figure 2: Agalteca Plant with Filter Designed from the Conservative Approach

1) Our design based on simple hydraulics will work. However, it is a very large filter (see exact dimensions in Figure 2) and will not be sustainable economically. The material cost for construction will be too high.
2) The design based on the empirical Weber equation is smaller and less expensive. However, the validity of the empirical equations is not yet certain, inspite of our Fluidization Velocity Experiment. Therefore more testing needs to be done in pilot scale models.
3) If the empirical equations are valid, then we can change parts of the design, by changing the sand parameters. For example, lower the dimensions of the clear well by lowering the backwash velocity by decreasing the d60 and specific weight of the media.

Figure 3: Small Change in D60 can fix the error at 30% Expansion by over 100%

4)An additional advantage to Clear Wells is that the distribution tank does not have to be below the filtration tank, and in fact, it could be the clear well as well.

Figure 4: Distribution Tank can be the Clear Well Tank

Experiment Results
We had mixed results with regards to Weber's equation for filter bed expansion. At low levels of filter bed expansion, the Weber equation accurately predicted the fluidization velocity required to achieve the targeted bed expansion. As the target bed expansion increased, so did the degree of error. At 9% expansion, the degree of error was at 14%. At 38% expansion, the degree of error was at 37%.

Figure 5: Error Between Calculated and Actual Expansions

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