| 摘要 |
PURPOSE:To dispense with a pressurizing pump for backwashing and to prevent contamination by microorganisms by executing backwashing by transmitting the pressure of permeate generated by at least one filter medium element to the permeate sides of other filter medium elements interposing pipings for permeate connected to said other filter medium elements. CONSTITUTION:When residue of filtration deposits on the surface of a membrane of a semipermeable module 3-3' after continued filtration for a certain period of time and a backwashing stage is to be commenced, a valve 2' is closed while keeping a valve 2 opened, and a degree of opening of a valve 6-6 is adjusted. The semipermeable membrane module 3 is allowed to continue normal operation and the permeate is decreased to 1/2 in quantity, but it is transported to a use point. No liquid pressure exerts to the feed liquid side of the semipermeable membrane module 3' but the liquid pressure from the semipermeable membrane 3 exerts on the permeate side of the semipermeable membrane module 3'; thus, backwashing effect occurs. Then, by reversing the conditions of the semipermeable membrance module 3 to the semipermeable membrane module 3', the semipermeable module 3 is backwashed.
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