Filter runs

Durchlauf, m. sieve, colander running thru, flow, passage Med.) diarrhea, durchla en, v.i. filter run thru, flow thru. — — v.t. run thru, pass thru, traverse. — durchlaufend, p.a. continuous. Durchlkufermineral, n. mineral occurring in all zones. 

The cross-sectional area can be calculated by dividing the design flow rate by a quantity that is equal to the number of filter runs per day times the net water production per run per cross-sectional area ... 

The water production per filter run Vf is based on a relation proposed by Letter-man (1980) that assumes minimal surface cake formation by the time filtration is stopped because of head loss ... 

Many dual-media designs have been used. However, the media sizes have been kept relatively constant — that is, 1.0-mm coal and 0.43-mm sand with the depths of each material varied. As can be noted from Fig. 2, much of the fine sand has been removed, and the filter is much coarser. Headloss characteristics have been improved, and longer filter runs should be expected. 

Filter runs will vary with influent load and filter rate. Generally, however, the filters are designed to operate in the range of IS to 30 hours so that backwash water percentages are usually 2 percent or less. This minimizes disposal problems of the backwash water. Automatic operation of the filters is also suggested to reduce operator attention requirements. Backwash is generally initiated on filter hcadloss or on time. 

If the respective average sizes of the anthracite and sand layers are 1.6 mm and 0.5 mm, what is the length of the filter run to a terminal head loss of 3 m at a filtration rate of 200 h vs min Assume the clean water head loss is 0.793 m. Note Terminal head loss is the loss when the filter is about to be cleaned. 

Solution Because 200 L/m min is between 160 and 240 L/m min, only the data for these two flows will be analyzed. The length of the filter run for the 200 lW min flow will be interpolated between the lengths of filter run of the 160... 

Filter runs typically range from 2 to 4 d. The rate of the body feed and the diatomite media size are critical in determining the filter run length. Shorter filter runs will minimize... 

Vacuum diatomaceous earth filters are a variation of this technology that offer the advantages of visibility during backwashing and of not requiring pressure vessels. Their primary disadvantage is that they run an increased risk of the release of gases in the filter cake that shorten filter runs. 

The essential method to obtain sterile air, whether packed-bed or cartridge filters are used, is to reduce the humidity of the air after compression so that the filter material always remains dry. The unsterilized compressed air must never reach 100% relative humidity. Larger plants install instrumentation with alarms set at about 85% relative humidity. Careful selection of the cartridge design or the design of packed-bed filters will result in units that can operate in excess of three years without replacement of filter media. If a fiber material is used in a packed-bed type filter, the finer the fiber diameter the shallower the bed depth needs to be for efficient filtration. Other filter media are less common and tend to have special problems and/or shorter life. The bed depth of filters is only 10 to 18 inches for fibers of less than 10 microns. These filters run clean for 2 weeks or longer before being resterilized. 

The Standard Plant. The results presented in Figure 9 for the standard treatment plant indicate that effective removal (85% ) of suspended solids is produced by the flocculation-sedimentation process. Filter run length, as indicated by the time it takes to reach a head loss of 250 cm, is 28 hr. Filter ripening is rapid, and essentially complete removal of suspended solids is accomplished by the Alter throughout the run. The settling eflBciency, head loss development, and filtrate quality predicted by the model are consistent with typical water treatment plant performance. 

A comparison of Figures 9, 11, and 12 reveals that the performance of the water treatment plant is affected by the solids concentration in the raw water in complicated and unexpected ways. Influent water with the poorest water quality produces long filter runs and the best filter effluent quality. The standard influent produces good filtered water quality but the shortest filter runs. Influent water with the best quality... 

Plant performance in the absence of flocculation by fluid shear (G == 0 sec ) is examined in Figure 18. Some particle growth occurs by Brownian diffusion in the flocculator and by differential settling and Brownian diffusion in the settling tank. Removal efficiency by sedimentation is smaller than in the standard case (74% compared with 85% ), and filter runs are reduced from 28 to 16 hr. Filtrate quality is good throughout the run. 

A polyaeryImiSe filter aid will be added to the clarified water aa it antara the filtera to improve the quality of the treated water. The NFR filtera are quite similar to the standard Hanford filters used to produce cobling water for the slngle pasa reactors. The filter media consists of six Inches of sand topped by 24 inches of anthracite. The sand and anthracite are sised to provide a high quality of filtered water with reason ably long filter runs between filter backwash cycles. 

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