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a <br /> 720 CHAPTER 11; Intermittent and Recirculating Packed-Bed Filters <br /> TABLE 11-6 <br /> Design criteria for intermittent sand filters <br /> U.S.customary units Si ung <br /> Design factor . Unit Range Typical..,, Unit Range Typical <br /> Filter Medium <br /> Material Durable washed sand <br /> Effective size mm 0.25-0.75 0.35 mm 0.25-0.75 0.35 <br /> Depth in 18-36 24 mm 450-900 600 <br /> Uniformity coefficient <4 3.5 <4 3.5 <br /> Underdrain <br /> Type Slotted or perforated drain pipe <br /> Size in 3-4 4 mm 75-100 100 <br /> Slope % 0-0.1 0 % 0-0,1 0 <br /> Pressure distribution <br /> Pipe size in 1-2 1.5 mm 25-50 38 <br /> Orifice size in ' '- ' mm 3-6 3 <br /> B`4 8 <br /> Head on orifice ft 3-0 5 m 1-2 1.6 <br /> Lateral spacing ft 1.0-4 2 m 0.5-1.2 0.6 <br /> Orifice spacing ft 1.0-4 2 m 0.5-1.2 0.6 <br /> Design parameters <br /> Hydraulic loading* gal/ft2•d 1-1.5 1.25 Um2.d 40-00 50 <br /> Organic loading Ib1W-d 0.0005-0.002 . <0.001 kg BOD/m2-d 0.0025-0.01 <0-005 <br /> Dosing <br /> Frequency times/d 12-48 18 min -times/d 12-48 18 min <br /> Volume/orifice gal/orif•dose 0.15-0.30 0.25 Uorif-dose 0.6-1-1 0.9. <br /> Dosing tank volume flow/d 0.5-1.5 1.0 flow/d 0.5-1-5 1.0 <br /> *Based on peak flow- <br /> TABLE 11-7 <br /> Designation and size of opening <br /> of U.S. sieve sizes <br /> Sieve size Size of opening <br /> or number in mm <br /> e in 0-375' 9.51' <br /> a in 0.250' 6.35* <br /> 4 0.187 4.76 <br /> 6 0.132 3.36 <br /> 8 0.0937 2.38 <br /> 10 0.0787' 2.00' <br /> 12 0.0661 1.68 <br /> 16 0-0469 1.19 <br /> 18 0.0394' 1.00' <br /> 20 0.0331 0-841 <br /> 30 0.0234 0.595 <br /> 40 0.0165 0.420 <br /> 50 0.0117 . 0.297 <br /> 70 0.0083 0.210 <br /> 100 0.0059 . .0.149 <br /> *Size does not follow the ratio(2)0-5- <br />