PURPOSE: To obtain titled reducing agent of high performance, non-toxic to both human and livestock, by first oxidizing an aquatic humus to a point of specific range of pH value while dehydrating, followed by bringing to a specific water content to terminate the oxidation to fix the pH value to any desired one within the above range.

CONSTITUTION: An aquatic humus (a colloidal substance produced in the aquatic environment, by the biodegradation and anaerobic fermentation of a deposit consisting of dead aquatic plants) is oxidized to a point of pH ranging from 2.0W4.5 while dehydrating under the water content ranging from 80 to 40% (for example, by a dehydration through spontaneous evaporation followed by air oxidation, or using a hot air stream) to bring the water content to 40% or lower to effect termination of the oxidation, resulting in fixing the pH value to any desired one within a range 4.5W2.0, thus obtaining the objective reducing agent.

USE: For recyling liverstock manure as fertilizer by removing its odor by the reducing action. Also, for recycling abandoned fishes as livestock feed by suppressing the odor and putrefaction.