PURPOSE: To prevent the sticking of a microorganisms slime to a membrane and to stably maintain the permeation performance of the membrane by decreasing the hardness component of a feed water to less than a specified level and treating the feed water with a synthetic high polymer system composite membrane module under the presence of a dissolved oxidizing agent.
CONSTITUTION: In the case of treating the feed water containing abundantly the hardness component, a liq. feed pump 5 is driven to pass the feed water in a feed water tank through a water softener 3, and the hardness component such as calcium or magnecium is decreased down to ≤10ppm, and once, the feed water is stored in an intermediate tank 4. Then, the storage liq. in the intermediate tank 4 is fed to the synthetic high polymer system composite membrane module 2 consisting of the laminated body of the active skin layer having selective separating function and a porous supporting membrane by a liq. feed pump 6 while injecting the oxidizing agent such as sodium hypochlorite or hydrogen peroxide soln. from an oxidizing agent injector 7, and the feed water is filtrated by a cross-flow system, and a permeated water is taken out by a take out pipe 23 while returning the part of an nonpermeated feed water to the intermediate tank 4 by a return pipe 81.
KAWADA ICHIRO
YOSHIOKA NORIAKI
KAMIYAMA YOSHIYASU
