NOVELTY - The method comprises reacting an organic feedstock in a reactor. The organic feedstock is part of a reaction mixture that includes a first oxidizing acid and nitric acid. The weight ratio of solids in the organic feedstock to the total of the first oxidizing acid and the nitric acid is 0.5. The organic feedstock includes a sewage material (102). The reaction mixture, excluding solids, includes less than 5 wt.% of the first oxidizing acid and the nitric acid. The method further comprises maintaining the reaction mixture at temperature of less than 210 degrees C.    USE - The method is useful for: treating a waste such as food waste and organic waste from household, commercial, institutional, and industrial wastes; and converting the treated waste into fertilizer and/or biofuel, where the waste is sewage sludge, dewatered sewage, municipal sludge cake, lagoon sludge, animal manure, potato skins, farm waste and slaughterhouse runoff.    ADVANTAGE - The improved method is capable of effectively treating the waste and converting the treated waste into fertilizer and/or biofuel in an economic manner with desired conversion rate and less energy consumption and without emitting noxious gases.    DETAILED DESCRIPTION - The method comprises reacting an organic feedstock in a reactor. The organic feedstock is part of a reaction mixture that includes a first oxidizing acid and nitric acid. The weight ratio of solids in the organic feedstock to the total of the first oxidizing acid and the nitric acid is 0.5. The organic feedstock includes a sewage material (102). The reaction mixture, excluding solids, includes less than 5 wt.% of the first oxidizing acid and the nitric acid. The method further comprises: maintaining the reaction mixture at temperature of less than 210 degrees C; maintaining a pressure in the reactor of 1035 kPa; supplying oxygen gas to the reactor; and separating heavy metals from a liquid fraction. The step of reacting the organic feedstock in the reactor forms an effluent including the liquid fraction. The step of separating the heavy metals from the liquid fraction includes separating 80 wt % of the arsenic and/or mercury from the liquid fraction. The weight ratio of the solids in the organic feedstock to the nitric acid is 1.    DESCRIPTION OF DRAWING(S) - The diagram shows a block diagram of a feedstock processing system.    Sewage material (102)    Preprocessing system (206)    Mixing vessel (208)    Feeding device (216)    Valve. (218)