In an embodiment, the present invention provides a method for the biological cleaning of wastewater in an activated-sludge plant including at least one activated-sludge tank, the method including: contacting, in the plant, the wastewater with activated sludge in the activated-sludge tank so as to clean the wastewater; and after the cleaning of the wastewater, separating, in the plant, the suspended activated sludge from the cleaned wastewater by sedimentation in a secondary clarification tank downstream of the activated-sludge tank or in the activated-sludge tank. The activated sludge suspended in the wastewater is admixed with growth bodies in the activated-sludge tank in order to contact the growth bodies with the microorganisms present in the activated sludge and to bring about formation of a biofilm of microorganisms on the growth bodies.