NOVELTY - The carrier material as growth surface for the immobilization of biofilm containing microorganisms in wastewater for biological treatment of wastewater, comprises disk-, ring- or unsymmetrical calotte shaped hollow plastic bodies with a rough surface. The roughness of the surface is adjustable by elution of organic- and/or inorganic water-soluble materials, which are produced out of plastic matrix. The particle size of the water-soluble materials is 0.01-5 mm. The disk, ring or calotte have a ratio between surface and volume of 10.000-80.000 m2/m3.    USE - For the immobilization of biofilm containing microorganisms in wastewater for biological treatment of wastewater.    ADVANTAGE - The carrier material ensures the durability of the biofilm and has an efficiency to permit controllable aerobic- and anaerobic reactions in the biofilm.    DETAILED DESCRIPTION - The carrier material as growth surface for the immobilization of biofilm containing microorganisms in wastewater for biological treatment of wastewater, comprises disk-, ring- or unsymmetrical calotte shaped hollow plastic bodies with a rough surface. The roughness of the surface is adjustable by elution of organic- and/or inorganic water-soluble materials, which are produced out of plastic matrix. The particle size of the water-soluble materials is 0.01-5 mm. The disk, ring or calotte have a ratio between surface and volume of 10.000-80.000 m2/m3. The carrier parts of the material are round and have a thickness of 0.5-10 mm, a diameter of 20-100 mm, a length of 10-100 mm and a width of 10-100 mm. The diameter and the height of the calotte are 2 less than or equal toD less than or equal to15 cm and H less than or equal to D/2 respectively. The calotte shows an opening. The cavity of the hollow bodies is subdivided into niches like partial areas by lamella. An INDEPENDENT CLAIM is included for a procedure for the production of carrier material.    DESCRIPTION OF DRAWING(S) - The figure shows a carrier part:    External surface; (1)    Visibility; (2)    Shaped surfaces; (3)    Depression. (4)