2002-081-RES ACCEPT PROPOSAL OF FREESE & NICHOLS FOR PROFESSIONAL ENGINEERING SERVICES FOR PRODUCTION STUDY OF WATER TREATMENT OF COP

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or automatic effluent flow control valve. At the beginning of the filter run, the filter is clean and has little resistance. If the full driving force were applied across the filter, the flow rate would be very high. To maintain a constant flow rate or water level, some of the available driving force is dissipated by a effluent control valve. Variable declining rate filters operate with no individual control systems except for a flow limiting device (orifice plate). The TNRCC allows at the beginning of filter run a maxirn~ range for declining rate filters, the maximum filtration rate is 6.5 gpm/sf. The filter discharge piping is usually designed with an orifice or other permanently installed flow limiting device to ensure that the ma...wnurn filter rate can not be exceeded. In variable declining rate filters, each filter will accept the portion of the total flow permitted by the common water level above all the filters. The water level above the filters, or head, provides the driving force for the water through the filter media As filtration continues, the flow through dirtiest filter will decrease more rapidly than through the other filters, causing the flow to re-distribute itself automatically so that #1e cleaner filters pick up the capacity .lost by the, dirtier filte{s. The water level rises slightly and the re-distribution of flow to provide the additional head needed by cleaner filters to compensate for the decreased flow through. the dirtier filters. The cleanest filter accepts the greatest flow increase and the redistribution. TIlls method of operation causes a gradually declining rate toward the end of a filter" run. Rate changes throughout the day due to changes in total plant flow, both upward and downward, occur gradually and smoothly without any automatic control equipment. The .. declining rate filtration systems main advantage is the savings in valve and piping arrangements. It is a simpler system to operate and allows for greater operating flexibility. Figure 5 illustrates the variable declining rate filter structure. 6) Air assisted backwash capabilities provided at the filters. There are three traditionally used backwash methods: . water only backwash · water and surface or sub-surface wash media scour · water and air scour . Figure 5: Declining Rate Filter Structure ~. ~---------------------------------------------------------~ , " J I I . ~---------------------------------------------------------~ n'~-.e .,.rr 'llfrll1 ~ ~ ~ - -=- -=-== -..... . -. .