Recovery method for excrement and organic acid， and production method for recycled pulp fibers

The purpose of the present disclosure is to provide a recovery method that makes it possible to individually recover excrement and an organic acid from a deactivating aqueous solution that includes the excrement and the organic acid. This recovery method has the following features. A method for recovering excrement and an organic acid from a deactivating aqueous solution that is for use on a highly water-absorbent polymer and includes the excrement and the organic acid， the method being characterized by including: a precipitation step (S1) in which a metal salt or a base is added to the deactivating aqueous solution to precipitate a water-insoluble salt of the organic acid; a mixture collecting step (S2) in which a mixture of the water-insoluble salt of the organic acid and solid excrement that originates from the excrement is collected from the deactivating aqueous solution; an organic acid generation step (S3) in which water and an acid that can generate the free organic acid and a water-insoluble salt are added to the mixture to form an aqueous solution that includes the organic acid， the water-insoluble salt， and the solid excrement; and an organic acid aqueous solution acquisition step (S4) in which the water-insoluble salt and the solid excrement are removed from the aqueous solution to obtain an organic acid aqueous solution that includes the organic acid.