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What Planning Challenges Face Utility Owners?
Eighteen low-density media were examined in an attempt to find media that were capable of effectuating a
90% mean single-pass solids removal efficiency (SPRE) for particles in the 5-m to 10-m range. Each of the
media was placed into a clean test column. Test water, containing approximately 100 mg/L of Arizona test dust,
was introduced into the columns and SPRE was calculated for each of four fluxrates including 81 L m-2 min-1
(2 gal ft-2 min-1), 204 L m-2 min-1 (5 gal ft-2 min-1), 407 L m3 m-2 min-1 (10 gal ft-2 min-1) and 611 L m-2
min-1 (15 gal ft-2 min-1). The two beads with the highest SPREs, Beads 11 and 17, had median particle
diameters equal to 1,200 m and 475 m, respectively, and had coefficients of uniformity (Uc) equal to 2.55
and 1.43, respectively. It was found that each of these media could attain 90% removal of particles in the
target range for the 82 L m-2 min-1 (2 gal ft-2 min-1) fluxrate. However, when the fluxrate was increased to
204 L m-2 min-1 (5 gal ft-2 min-1) only Bead 17 was capable of attaining 90% removal while Bead 11 was found
to reach 86%. While both beads exhibited a decrease in removal efficiency as a function of increasing
fluxrate, the SPRE for Bead 17 never fell below 80% for any test fluxrate while that of Bead 11 fell below
70% for the highest fluxrate. The high SPRE for Bead 17 indicates that bead filters are viable alternatives
to sand filtration in applications that require high single-pass removal efficiencies.
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