A method of processing ammonia-containing liquids in a multi-stage evaporator system, wherein each stage of the evaporator system, referred to as evaporator stage hereinafter, consists of an evaporator vessel, a vacuum device producing negative pressure in said vessel, and a heat exchanger, and wherein - an ammonium salt solution obtained from the condensate of at least one of the heat exchangers (II.2) of the subsequent evaporator stages by the addition of an inorganic acid is introduced, via an inlet (I.6), into the evaporator vessel (I.1) of the first evaporator stage which is operatively connected to a heating device, - in the evaporator vessel (II.1) of at least one second evaporator stage which holds the ammonia-containing liquid, the latter is heated, by means of the condensation heat of the heat exchanger (I.2) of the respective upstream evaporator stage, to a lower temperature level, yet at a higher vacuum degree, than in the respective upstream evaporator vessel (I.1), - beginning at the second evaporator stage, the condensate produced is collected in a condensate container (II.3) and is mixed with an inorganic acid for setting a pH value to be inferior to 7 in order to prepare a buffer solution, and - the concentrate accumulating at the bottom of the at least two evaporator vessels (I.1, II.1) is removed for further treatment of for disposal, characterised in that - the ammonia-containing liquid is introduced into the evaporator vessels (II.1, III.1) of at least two evaporator stages (II, III) arranged in series downstream of the first evaporator stage, - the buffer solution obtained from the condensate of the heat exchangers (II.2, III.2) of said downstream evaporator stages (II, III) and mixed with said inorganic acid is subjected to reverse osmosis, resulting in the creation of an ammonia-free permeate and an ammonium salt as a concentrate in equal parts by mass, and - the concentrate obtained from said reverse osmosis is supplied to the evaporator vessel (I.1) of the first evaporator stage. - an ammonium salt solution obtained from the condensate of at least one of the heat exchangers (II.2) of the subsequent evaporator stages by the addition of an inorganic acid is introduced, via an inlet (I.6), into the evaporator vessel (I.1) of the first evaporator stage which is operatively connected to a heating device, - in the evaporator vessel (II.1) of at least one second evaporator stage which holds the ammonia-containing liquid, the latter is heated, by means of the condensation heat of the heat exchanger (I.2) of the respective upstream evaporator stage, to a lower temperature level, yet at a higher vacuum degree, than in the respective upstream evaporator vessel (I.1), - beginning at the second evaporator stage, the condensate produced is collected in a condensate container (II.3) and is mixed with an inorganic acid for setting a pH value to be inferior to 7 in order to prepare a buffer solution, and - the concentrate accumulating at the bottom of the at least two evaporator vessels (I.1, II.1) is removed for further treatment of for disposal, - the ammonia-containing liquid is introduced into the evaporator vessels (II.1, III.1) of at least two evaporator stages (II, III) arranged in series downstream of the first evaporator stage, - the buffer solution obtained from the condensate of the heat exchangers (II.2, III.2) of said downstream evaporator stages (II, III) and mixed with said inorganic acid is subjected to reverse osmosis, resulting in the creation of an ammonia-free permeate and an ammonium salt as a concentrate in equal parts by mass, and - the concentrate obtained from said reverse osmosis is supplied to the evaporator vessel (I.1) of the first evaporator stage.