SR0033424_ENG DESIGNED PLAN - Laserfiche WebLink

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11-4 MULTIPASS (RECIRCULATING) PACKED-BED FILTERS 747 Flow splitter basin sized initially to accommodate Phase 4 Phase 1 Phase 2 Influent from septic tanks or from I collection system Phase 3 Phase 4 FIGURE 11-24 Diagram of modular filter design (adapted from Bali and Denn, 1997). -a -Modular design. Where the filter system is to be expanded to treat increased a future flows,a modular design is used.In a typical arrangement,additional filter units would be added in stages. The necessary pumps would be added in an-existing flow recirculation basin (see Fig. 11-24), designed to accommodate anticipated future flows. 'T i i Cold climate design considerations. Buried distribution systems.are nec- essary in cold climates to avoid freezing. It is suggested that a 1.0-ft (0.3-m) layer of 25-mm stone be used to cover the distribution piping. It is also recommended that. the septic tank and recirculating tanks be insulated and that a coarse medium be used (dta = 2 to 2.5 mm,maximum size 5 mm, and UC c 2)(Loudon et al., 1984, 1989). f I Construction Considerations 1 Construction considerations for recirculating filters are similar to those for TSF. Gra- i dation and lack of fines in the.medium as well as durability specifications for the r filter material are important. A typical recirculating fine gravel filter is shown un- der construction in Fig. 11-25. As noted previously, prefabricated RPBFs have been developed. The use of prefabricated units reduces construction errors in the field assembly of these units. j I I Operation and Maintenance j Recirculating filters can be operated'without surface clogging if the solids loading i .rate arid-medium size are in balance. Using the design criteria in Table 11-14 will result in operating systems that require'minimal operation and maintenance. The counters and meters discussed in the previous section also apply to recirculating filters. I