TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Method: The duckweed or algae is produced as fast-growing aquatic plants in the culturing device. The biogas booster is mixed to the biomass of aquatic plants before or with introduction in the fermentation chamber of the biogas plant. The thick phase is pyrolyzed or is treated in other carbonization step. The thin phase is ventilated and/or a precipitating agent is provided before introduction into the aquatic culturing device with air-oxygen. A culture of legumes and/or Azolla is initially supplied for the metabolization of the resulting air-nitrogen, and is passed on to the other aquatic culturing device. The filling of the biogas plant is carried out via automatic filler, which mixes the mixed biogas auxiliary substance in the defined reproducible amount ratio to the present fermentation mash. Preferred Components: The culturing device is provided with closed or closable film housing, where a high concentration of carbon dioxide is introduced in the film housing. The film housing is provided with a constant curvature with respect to the vertical cross-section, and bottom is connected or provided with collecting trays for collecting the condensed evaporation water. The amount of the mixture of aquatic plants and biogas booster in fermentation mash of the biogas plant is 2-90% wet mass of fermentation mash of the thick phase introduced in the fermentation chamber. The biogas plant is arranged in or directly next to the culturing device for aquatic plants, and the heat cycles are connected together such that the culturing device is heated at least partially by the waste heat of the biogas plant. The mixing device is a controlled mixing device, and a defined reproducible mixing ratio is obtained on the basis of the introduced starting materials. The culturing device for the aquatic plants in a bottom area is made of a base assembled from system stones. A floor system of culture water troughs are placed on the base. The culturing device comprises a bottom side base tray embedded in or with the base, where the base tray provides water supply for the culture water. EXAMPLE - No suitable example given.