To provide a raw tap water purification method which can reduce the load of pollutants on membrane filtration, reduce the installation area of an apparatus and system and a construction cost, and reduce the volume of wastewater from the whole plant.

After adding an inorganic coagulant D to raw tap water A containing organic matter, rapid agitation and slow agitation are carried out to form coagulated flocs. The raw tap water is introduced a single treatment tank 3 where a pressure floatation part is formed in the upper space, and an immersed filtration membrane module 13 is installed in the lower space. In the treatment tank 3, the coagulated flocs are subjected to a pressure floatation in the upward direction, and at the same time the raw tap water is subjected to suction filtration through the immersed filtration membrane module 13 to obtain purified water B.

COPYRIGHT: (C)2008,JPO&INPIT