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<br />In the design of the plant is the ability to bypass the clarifier unit and send the coagulated
<br />water directly to filtration. To date, this option has not been exercised by the plant operators,
<br />Refer to Figure 3, which shows a 12" bypass line, This practice is probably acceptable,
<br />During normal operations at historical peak flow of about 1043 g,p.m, (the output of Pump
<br />No, I), hydraulic detention time (HDT) in the 98,000 gallon clarifier is about 94 minutes,
<br />Only a portion of this time can be attributed to the flocculation process, Refer to Table 4,
<br />Surface overflow rate (SOR) is 1.08 gal/min ft2, about 50 percent higher than maximum
<br />recommended rates, The excessive overflow rate indicates that particles are not able to
<br />adequately settle out. An unknown percentage of solids escapes the clarifier at high flow
<br />rates and is carried over to the filters, Observations during the plant visit indicated that the
<br />circular, perforated launder for capturing clarifier effluent may be operating inefficiently due
<br />to floc build-up inside the piping,
<br />As an example of an approach to process improvements, consider the data in Table 4, Assume
<br />a flocculation time of 20 minutes at a design flow rate of 1,5 MGD (1043 g,p,m,),
<br />Flocculation would require about 21 percent of the existing volume in the center of the
<br />clarifier. With tube settling units installed in the remaining space, with a rated SOR not to
<br />exceed 2,0 g,p,m.!ft2, the 1.5 MGD flow rate could be accommodated, Changes would be
<br />needed in the baffling and launder systems,
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<br />In summary, the clarifier is not adequate in its current configuration to properly flocculate
<br />turbidity and settle out floc particles during periods of high flow, Thus, these particles pass to
<br />the filters, To fully understand the clarifier, the clarifier needs further assessment to
<br />determine its optimal operating characteristics and identify the possibilities for improving
<br />performance,
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<br />Filtration
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<br />The WTP has two standard, mixed-media gravity filter units, Each has a surface area
<br />of 10 ft, x 18 ft" or 180 s,f, The filters have the subsystems required for proper operation;
<br />these are a surface wash system, a backwash to waste system, and a control system, The
<br />filters were rebuilt in the 1981-1982 expansion, which included new granular media, additional
<br />piping, and controls, However, under current state criteria the existing filter system cannot
<br />filter-to-waste as required,
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