To provide a waste treatment method capable of constructing an ideal comprehensive plant where waste including decanter drainage in a potato starch production process can be effectively utilized as by-products without performing heat treatment.

Decanter drainage is subjected to isoelectric point treatment and centrifugal separation with acid utilized as a silage conditioner, thus solid contents such as protein are precipitately separated, and they are recovered, and are mixed with the potato pulp of strained less (waste) as by-products in a potato starch production process, so as to produce feed having a high protein content for a dairy cattle. In this production, a plant where drying treatment by fuel consumption or the like are not used at all is constructed, and is applied to silage making in which the existent small-sized facilities are made the most of as they are, and the insufficiency in drainage treatment capacity and an environmental problem derived from the waste of resources are solved.

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