NEW SYSTEMS FOR THE DIGESTION OF SOLID-WASTES

Two new systems for the digestion of solid wastes at thermophilic temperatures were developped and are currently being investigated at our research institute. The first system (ANCOM) was designed to process straw-rich cattle manure with a natural dry matter content of 18% to 22%. First results demonstrated a good specific gas production of 1.2 m3 biogas per m3 digester volume and day (54% methane) corresponding to a gas yield of 400 l per kg VS. A second digester system was developed to treat fruit, garden and vegetable (FGV-) waste. Because FGV-waste tends to float, a stirred tank reactor was designed in cooperation with an engineering firm. The reactor includes a distinguished new stirring system taking up strong shear forces and a hydraulic feeding system which guarantees that even during recirculation of the material, the hygenized digested substrate leaving the digester is not brought in contact with the fresh incoming material. First results measured at an HRT of 40 days demonstrated a specific gas production of 2.7 m3 per m3 fermenter and day.