PURPOSE: To make it possible to perform filtration at a high rate and to reuse it when used as a filter medium by forming a porous granules with a mixture of magnesium oxide and powdering org. waste material.

CONSTITUTION: Magnesium, a powdering org. waste material, (e.g. a plastic waste material) and a granulating agent (e.g. bentonite) are mixed, granulated and fired to make it porous. As the result, it is used as a filter medium for removing inclusions, oils etc., in a liq. to make it possible to perform filtration at a high rate and to use it again.