| 摘要 |
PROBLEM TO BE SOLVED: To provide a filter apparatus hard to generate clogging and capable of obtaining the planar uniformity of sufficient flow rate distribution at a time of backwashing. SOLUTION: In a filter apparatus wherein unfiltered raw water is added to the filter medium bed arranged on a support bed from above and passed through the filter medium bed and the support bed to obtain filtered clean water under the support bed, as the support bed, a perforated plate obtained by heating and welding a large number of spherical synthetic resin particles while keeping them almost spherical is used. The diameter of the synythetic resin particles is set to about 4 mm and the average void size of the perforated plate is set to about 1,000μm and the void ratio thereof is set to about 33%.
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