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710 CHAPTER 11: Intermittent and Recirculating Packed-Bed Filters <br /> 3.5 <br /> o Total coliform bacteria <br /> 3.0 • Indigenous coliphage <br /> 2.5 <br /> z� <br /> z _ <br /> 0 2.0 <br /> 1 <br /> >0 1.5 <br /> E <br /> 0 <br /> J 1.0 I <br /> t <br /> 0.5 <br /> 0.0 <br /> 0.00 0.05 0.10 0.15 0.20 <br /> Hydraulic loading rate,m/d <br /> Note: Dosing frequency=24 doses/d <br /> Error bars indicate 95%confidence intervals. h.ry <br /> Arrow indicates non detectable amounts of coliphage in at least orifi sarnpi"e,- <br /> resulting in unknown upper bound. <br /> FIGURE 11-7 <br /> Impact of dosing rate on the removal of male-specific coliphage in.intermittent <br /> sand filters (Emerick et al., 1997). <br /> et al., 1997b). In the study reported on in Fig. 11-7, indigenous coliphage found in <br /> wastewater were used to study the removal of viruses'.,B the concentration of <br /> indigenous coliphage was on the order of 103/100 mL, it is,not known what total <br /> removals may have been possible.Although not studied, it appears that the develop- <br /> ment of a dense uniform bacterial film may be the result of a more uniform supply of <br /> nutrients to the upper region of the filter through the application of multiple doses. It <br /> is interesting to note that Buswell, in his book The Chemistry of Water and Sewage` <br /> Treatment, published in 1928,recognized and discussed at length the:importance of <br /> intermittent dosing on the performance of filters (Buswell, 1928). <br /> Multipass filters. in multipass filters, the process variables that affect the re- <br /> moval performance for BOD,TSS, oil and grease, and turbidity are the same as de- <br /> scribed above for single-pass filters.The recirculated volume is'of great significance <br /> because it serves to dilute the effluent from the,septic tank, such that the organic <br /> matter applied in each dose,and absorbed in the bacterial film, can be"processed <br /> more easily by the bacteria between doses. Because the depth of the water layer as it <br /> flows through the filter is greater than that in an intermittent sand filter,it is possible <br /> for small colloidal-sized particles,including bacteria and viruses,to pass through the <br /> filter without being absorbed. The organic matter in the influent is distributed`to a <br /> greater depth within the filter because of the added liquid volume. The added liquid <br /> also serves to flush out of the filter partially decomposed organic materials,bacterial <br />