| 摘要 |
PROBLEM TO BE SOLVED: To reduce clogging, to prevent the leakage of a granular filter medium, and to operate filtration stably for a long period by specifying the ratio between the average diameter of voids formed by the filter medium and that of voids of a filter bed which prevents the leakage of the filter medium. SOLUTION: A granular filter medium 19 which separates suspended substances in a bathtub water into solid and liquid is packed in a filtration means 16 which filters the bathtub water and the inside of the means 16, and the leakage of a filter medium 19 is prevented by a filter bed 20. In this process, when the average diameter of filtration voids formed by the medium 19 is represented byε, the average diameter of voids of the filter bed 20 is represented byε', and the ratioε/ε' is represented by R, R shall be 0.27<=R<=0.8. Since the medium 19 is constituted of sintered Al2 O3 as a main component, has fine internal structure, and is spherical in shape, strong particle strength is obtained, and an antibacterial layer containing heavy metal such as Ag, Cu, etc., is formed on the surface. When the diameter of the filtration voids and the diameter of the filter bed voids are set up in this way, since the change of a flow velocity and the generation of dead water are prevented, local clogging by suspended substances can be prevented.
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