Process for preparing nitric acid, in which a. ammonia is reacted with oxygen to give nitrogen oxides and steam in an ammonia combustion plant, b. the nitrogen oxides and the steam from step (a.) are cooled in a condenser to a temperature at which at least some of the reaction products condense, with the nitrogen oxides in part reacting with the condensed steam and oxygen to give an aqueous, nitric acid-containing solution and in part remaining in a nitrogen oxide-containing gas mixture, c. the nitric acid-containing solution from step (b.) is supplied from the condenser via a connection conduit to a first absorption tower, d. the nitrogen oxide-containing gas mixture from step (b.) is supplied to the first absorption tower, in which it is brought into contact with water or with an aqueous solution, wherein the nitrogen oxide-containing gas mixture reacts with water at least in part to form an aqueous, nitric acid-containing solution which, together with the nitric acid-containing solution from step (c.), accumulates at the base of the first absorption tower, e. nitric acid-containing solution from step (d.) is supplied via a conveying conduit to a bleaching column, wherein f. oxygen is introduced into at least one conduit (12, 14) that conducts nitric acid-containing solution and/or into a reactor (3, 4, 6) comprising nitric acid-containing solution (12, 14), characterized in that g. the oxygen is supplied in step (f.) to the nitric acid-containing solution in the conduit (12, 14) and/or in the reactor (3, 4, 6) at least partly in the form of oxygen-containing nanobubbles having a diameter of between 20 nm and 1 μm. a. ammonia is reacted with oxygen to give nitrogen oxides and steam in an ammonia combustion plant, b. the nitrogen oxides and the steam from step (a.) are cooled in a condenser to a temperature at which at least some of the reaction products condense, with the nitrogen oxides in part reacting with the condensed steam and oxygen to give an aqueous, nitric acid-containing solution and in part remaining in a nitrogen oxide-containing gas mixture, c. the nitric acid-containing solution from step (b.) is supplied from the condenser via a connection conduit to a first absorption tower, d. the nitrogen oxide-containing gas mixture from step (b.) is supplied to the first absorption tower, in which it is brought into contact with water or with an aqueous solution, wherein the nitrogen oxide-containing gas mixture reacts with water at least in part to form an aqueous, nitric acid-containing solution which, together with the nitric acid-containing solution from step (c.), accumulates at the base of the first absorption tower, e. nitric acid-containing solution from step (d.) is supplied via a conveying conduit to a bleaching column, wherein f. oxygen is introduced into at least one conduit (12, 14) that conducts nitric acid-containing solution and/or into a reactor (3, 4, 6) comprising nitric acid-containing solution (12, 14), characterized in that g. the oxygen is supplied in step (f.) to the nitric acid-containing solution in the conduit (12, 14) and/or in the reactor (3, 4, 6) at least partly in the form of oxygen-containing nanobubbles having a diameter of between 20 nm and 1 μm.