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• tested. Due to system hydraulics and chemical selection, sustained operation of the <br />microfiltration unit (i.e., greater than 7 hours) was not possible. Subsequent bench-scale tests <br />identified that precipitation was taking place within the pores of the ceramic filter which made <br />backpulsing ineffective, resulting in an increased pressure drop across the membrane causing the <br />microfiltration unit to clog. Further investigation at the bench-scale level determined that <br />increasing the residence time upstream of the microfiltration membrane would solve the <br />hydraulic problem. It was also determined during the bench-scale studies that the precipitation <br />reagent was substituting one anion for another, which resulted in higher than acceptable <br />concentrations of such substances as chloride and fluoride. As a result of the combined treatment <br />effectiveness issues, microfiltration was not identified as a viable approach for meeting the <br />objectives of water treatment. Therefore, microfiltration was not further considered. <br />4.4.3.2 Nanofiltration Bench-Scale and Pilot Testing <br />Bench-scale studies for nanofiltration were completed in December 1998, and afield-scale pilot <br />test was performed in late January 1999. The pilot test entailed pumping from well BF-2 at a <br />rate of approximately 5 gpm for a test period of approximately 7 days. Nanofiltration was <br />performed using several different membrane sizes. Post-filtration precipitation tasting was also <br />performed on the reject stream. <br />A series of tests were conducted using different membrane sets to determine the water quality at <br />recovery rates of 50 percent, 62.5 percent, and 75 percent. The recovery rate identifies the <br />percentage of the total influent that passes through the membrane. One set of membranes <br />consistently achieved the objectives of water treatment. Testing at 50 percent and 62.5 percent <br />recovery was successful. However, at 75 percent, there was evidence of membrane fouling and <br />75 percent recovery exceeded the maximum recovery point. Data for the test runs aze presented <br />in Table 4-1. The successful pilot testing of nanofiltration has resulted in this option being <br />retained for consideration. The complete pilot test report is found in Appendix C. <br /> <br />Batt(e Mountain Resources. /nc. <br />p:1/001671reporrslmarchrpArrl6wvmnglmarch.Aoc 49 Mnrch 12, /999 <br />