of the cyclic contact drum and collecting the filtrate which has passed the filter and a drainer for draining a cake discharged from the contactor application_number US 61471706 A description the pulp to be used in the present invention may be preferably in the form of powder or chips the pulp powder may be available by pulverizing a pulp sheet and it is in the form of powder an average particle size of the pulp powder may be but not limited to usually 10 to 1 000 u03bcm although no limitation is imposed on the preparation method of the pulp powder a pulverizer such as knife and hammer mill can be used although no limitation is imposed on the preparation method of pulp chips the pulp chips may be produced by cutting a pulp sheet with an known cutting device such as a slitter cutter a continuous cutting device may be advantageous from the viewpoint of investment cost the plane surface area of the chip may be usually from 4 to 10 000 mm 2 especially preferably from 10 to 2 500 mm 2 it may be difficult to prepare the chip having the plane surface area smaller than 4 mm 2 the chip having the plane surface area greater than 10 000 mm 2 may pose difficulties in handling such as introducing into a rotary feeder type contactor transferring inside of the contactor and introducing into a drainer considering the pulp chip as a hexahedron the plane surface area of the chip is the largest surface area of six surface areas of the hexahedral chip a rotary feeder type contactor usually rotates in a housing comprising several blades.