To efficiently discharge a suspended substance or the like within a reverse osmosis membrane module by backwashing the reverse osmosis membrane module with a pressurized gas-liquid two-phase flow.
When the pressure loss of a reverse osmosis membrane module 5 becomes large, a raw water supply pump 3 is stopped and a raw water supply valve 2 and a pressure adjusting valve 9 are closed while a backwashing blow valve 11 is opened. A backwashing pump 12 is started in this state to perform the passage of backwashing water under a pressure of 3-4 kg/cm2G in a flow rate of 1-2 m3/h and a compressor 14 is started at the same time to intermittently open and close an air cutting-off valve 13 to intermittently supply air three times under a pressure of 6-7 kg/cm2G. Blow drain water becomes a transparent state only by the passage of backwashing water but waste water becomes turbid by suspended components by the intermittent charging of air and the adhesion matter of the reverse osmosis membrane module causing a rise in differential pressure can be discharged and removed.
NAGAI MASAHIKO
IWAHASHI HIDEO
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