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Unfortunately, we realized that both the "Series of Orifices" and "PVC Cap as Orifice" designs do not generate enough head loss to dose with small amounts. Also, in order for the the "Spiral Tubing" design to successfully work, a extra tubing length of around 3.5 meters is needed; this is not feasible considering our desire to have a small overall filtration unit. Therefore, we needed to look into other viable options for the design of the alum doser (which will be a model for the required chlorine doser as well).
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Final Design Schematic (as of currently)
Because there were many problems with the alum/chlorine doser designs, a "batch" dosing system was used instead of a continuous system. In this system, the user will manually add alum into the holding tank and chlorine into the distribution tank, while stirring the mixtures together. Influent water dosed with alum from the holding tank flows into the filter column and is filtered through the depth of foam in the column. The height of the foam in the column will be ten inches; this was chosen empirically based on previous experimental results from Summer 2010, which indicated that a ten inch height would result in the least effluent turbidity. Heights greater than 10 inches generally performed about the same, providing diminishing returns. The diameter of the column will be four inches to give the operator easy access to the contents inside for the purposes of cleaning and maintenance. After the water is filtered through the column, it enters a flow accumulator designed to maintain constant flow through the unit. A float valve can be utilized to monitor the level of water in the flow accumulator and, thus, control flow through the system (see picture above). If we decide to forgo these parts, the unit may be cheaper to construct, and the variable flow would then be determined by the height difference from the water surface in the foam column to the highest location of the exit tubing through which filtered water travels to the distribution tank (see picture below). From the flow accumulator, the water flows into the distribution tank where it is manually dosed with chlorine to deactivate any residual pathogens. The water is then ready for distribution.
