| 摘要 |
PROBLEM TO BE SOLVED: To reduce the turbidity of filtered water right after cleaning. SOLUTION: This backward washing process is divided into two stages and is performed. In the first backward washing stage which is performed at first, the backward washing is performed at a backward washing rate S1 which is equal to or close to a usual backward washing flow rate which is ordinarily applied in order to obtain a sufficient backward washing effect for a predetermined time t1. After the lapse of the prescribed time t1, the backward washing rate is lessened and the transfer to the second backward washing stage is performed. The second backward washing stage consists of a first step which is performed at a second backward washing rate S2 smaller than the first flow rate S1 for a second predetermined time t2 and a second step which is performed at a third flow rate S3 smaller than the second flow rate S2 for a third predetermined time t3. After the completion of the second backward washing stage, the backward washing is completed by making the flow rate zero.
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