PURPOSE: To easily recover and remove algae and green powder at a low cost by using a ceramic perforated body having a three-dimensional network structure as a filter medium, adsorbing large fibers on the surface of this filter medium and sticking small-diameter materials in porous labyrinth, then burning these materials.

CONSTITUTION: The ceramic perforated body 1 which has the three-dimensional network skeleton structure or the three-dimensional network porous structure, such a nonwoven fabric-like structure irregularly intersected with fibers and is formed with holes 3 by three-dimensional entanglement of skeleton 2 is used as the filter medium. The large fibers 4 are adsorbed on the surface and accumulate thereon if water 8 contg. the algae and green powder is passed through the ceramic perforated body 1. A degradation in filtration capacity is then resulted. The ceramic perforated body is removed outside the line and the large fibers 4 on the surface are peeled 5 at this time. On the other hand, the small-diameter materials stick to the inside of the ceramic perforated body 1 and, therefore, the deposits are burned and dried by heating 6 the perforated body 1 or applying hot air thereto and thereafter, the residues are removed by suction 7.