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C) <br /> 748 CHAPTER 11: Intermittent and Recirculating Packed-Bed Filters <br /> E <br /> t _ <br /> (e) (b) <br /> FIGURE 11-25 <br /> Views of large recirculating packed-bed filter under construction. (a) exposed underdrain <br /> system being prepared for sand placement and (b) sand being placed using a conveyor <br /> system fed from a sand stock pile. <br /> EXAMPLE 11-6. DESIGN OF RECIRCULATING GRAVEL. FILTER FOR A SINGLE DWELLING. Size <br /> and lay out a recirculating gravel filter and distribution system for an individual three- <br /> bedroom residence in a nonsewered area. Check the organic loading.rate. Determine <br /> the total volume of flow per dose. Calculate the orifice flowrate and the total flowrate. <br /> Determine the on and off cycle times.The recirculation tank is sized to provide a storage <br /> capacity of 2.5 times the average flow. Assume the following conditions apply. <br /> 1. Average occupancy = 3.0 persons/d <br /> 2. Average wastewater flow = 50 gal/capita•d <br /> 3. Assumed peaking factor = 2.5 (see Table 4-20) <br /> 4, Size of septic tank = 1500 gal <br /> 5. Effluent BOD from septic tank = 130 mg/L <br /> 6. Effluent TSS from septic tank = 30 nI <br /> 7. Hydraulic application rate 5.0 gal/ft2-d(204 l.,lm2-d)based on influent peak flow <br /> 8. Size of recirculation tank = 800 gal <br /> 9. Size of effluent pump basin = 400 gal <br /> 10. Filter dose rate per day = 48 times/d minimum <br /> 11. Distribution system orifice size = s in(3 mm) <br /> 12. Orifice discharge head = 5 ft minimum(1.5 m) <br /> 13. Recirculation ratio = 4:1 <br /> Solution <br /> 1. Determine the size of the filter. <br /> a. Determine the average flow and peak flowrate: <br /> Q. = (3.0)persons x 50 gal/capita•d = 150 gal/d <br /> Qp-.k = 150 gaud x 2.5 (see Table 4-20) = 375 gaud <br /> b. Determine the required area of the sand filter: <br /> Area = (375 gaVd)/(5.0 gallft2•d) = 75 ft2 <br /> c. Use a filter 8 ft x 10 ft. Check area(8 x 10) = 80 ft2.OK. <br />