| 摘要 |
PROBLEM TO BE SOLVED: To provide pretreating device capable of preventing deterioration of water quality of secondary filtered water fed to a reverse osmosis membrane treating device, even in an operation of the device for long hours, as a sealed piping type (a non-open piping type) pretreating device for pretreating raw water fed to the reverse osmosis membrane treating device. SOLUTION: This pretreating device is provided with a flocculant addition device 7, a filter device 8 (a primary filter means), a protection filter 9 (a secondary filter means), a pH adjusting agent addition device 11, a sterilizer addition device 13, a water intake pump 14, a high pressure pump 15, a backward washing device 60, and a germicide addition device 64, and the bite. The backward washing device 60 stores mixed liquid of primary filtered water and a germicide added solution in a backward washing water tank 61, and also adds the germicide added solution via a piping 73 to the mixed liquid taken out from the backward washing water tank 61 with backward washing liquid feed means 63 to be mixed, then feeds it to the filter device 8 to backward wash the filter device 8.
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