Fuente: WIPO "organic farming" The invention relates to a bioreactor (1, 2, 3) and the use thereof for converting organic residual and/or waste materials into an organic nutrient solution having a proportion of at least 10% of plant-available mineralised nitrogen in relation to the total nitrogen content of the nutrient solution, comprising a reaction vessel (5), wherein the reaction vessel (5) has a supply line (6) via which a suspension (4) can be introduced into the reaction vessel (5), and wherein the reaction vessel (5) has a discharge line (7) via which the suspension (4) can be discharged out of the reaction vessel (5), as well as comprising an aeration device (8) for aerating the suspension (4) and/or a carrier element (10) arranged inside the reaction vessel (5), wherein the carrier element (10) has at least one inner and one outer attachment surface (11) on which ammonifying and/or nitrifying bacteria can attach in the form of a biofilm (12).