A spiral wound membrane module comprises a spiral wound membrane element
including a separation membrane having high back pressure strength. In
filtration running, raw water introduced from a raw water inlet of a
pressure vessel is subjected to dead end filtration, and permeate is taken
out from a permeate outlet. In washing, wash water containing a chemical
having a contaminant separating function is introduced from an end of a
water collection pipe through the permeate outlet for performing back wash
reverse filtration with a back pressure of 0.05 to 0.3 MPa. The filtration
running is temporarily stopped for maintaining the pressure vessel in a
state sealed with the raw water and the permeate for a prescribed time.
Thus, contaminants adhering to the membrane surface of the spiral wound
membrane element are separated. A treatment system is formed by connecting
units comprising spiral wound membrane modules in parallel with each
other. In the treatment system, one of the units is subjected to
filtration running when another one of the units is washed. In washing,
back wash reverse filtration and chemical soaking are performed.
