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During the first stage, we conducted a literature and online review of existing filtration technology and research. We determined the flow rate needed to sufficiently expand and clean the sand filter bed. This will help us determine how high the clear well needs to be above the filter, how large the flow pipes should be, and how much water should be in the clear well. Click here for the synopsis of our review of existing filtration technology and researchwork.

Using what we learned from our research, we developed a MATHCAD file, which generate design parameters for our filtration/backwash system when provided with plant flow rate and properties of the granular filter. Besides being the basics for the final design of the filtration and backwash system for an actual AguaClara plant, this program would also generate scaled down parameters for bench-scale or pilot plant-scale testing. Click here for the description of the MATHCAD file our MATHCAD File and description.

The accuracy of our MATHCAD generated design parameters depend on the accuracy of the empirical fluidization velocity equations that we used. We developed a bench-scale model of our filtration system and conducted an experiment measuring the expansion of a filter bed as backwash velocity is varied. We then compared the empirically calculated fluidization velocities with the actual fluidization velocities required. Click here for the Fluidization Velocity Experiment.

The accuracy of our model also required for the headloss occurring through an expanded bed to be more or less constant. According to our research, headloss should be constant once fluidization of the bed is achieved regardless of the degree of expansion. We simulated a variety of different bed expansion and observed headloss to be constant. Click here for the Expanded Bed Headloss Experiment.

Results and Discussion

Our experiments demonstrate that Okun and Schulz equation for headloss through a fluidized bed is a valid tool to use in our design. Once fluidization is achieved, headloss through an expanded bed is constant. For a 5 cm filter bed, headloss was around .7 cm regardless of the level of bed expansion. This is a positive discovery because a constant value for expanded bed headloss means that we can calculate all the headloss in our backwash system and design the height difference between the clear well and the filter bed appropriately.

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