A method for sterilizing a solid substance including contacting a solid substance with a Fenton reaction catalyst, the Fenton reaction catalyst including a reaction product, wherein the reaction product includes divalent iron, wherein the reaction product is obtained by providing a feedstock for supplying a component having a reduction effect, the feedstock being selected from the group consisting of (i) coffee grounds after extraction of coffee and (ii) tea dregs, the feedstock being a dried product, and mixing the feedstock with an iron ion-supplying source containing divalent or trivalent iron, and then adding water, the source being at least one substance selected from the group consisting of iron (II) chloride, iron (III) chloride, iron (II) nitrate, iron (III) nitrate, iron (II) sulfate, iron (III) sulfate, iron (II) hydroxide, iron (III) hydroxide, iron (III) oxide a heme iron a product obtained by dissolving iron ore, metallic iron or iron (III) oxide-rich red soil with an acid and rust, and wherein in the mixing, the iron ion-supplying source is mixed so that elemental iron is contained in an amount of 0.1 to 10 parts by weight with respect to 100 parts by weight of the dried product of the feedstock.
