NOVELTY - Highly accelerated fermentation of biodegradable material is carried out in only 4-5 days. Large pellets of preconditioned from human, animal and/or plant residues from agriculture and industry, are placed irregularly in boxes in a gas-tight chamber for mesophilic and thermophilic anaerobic generation of biogas containing 70-80% methane, with addition of enzymes. Methane, steam and water vapor are injected into the system. The apparatus also has a vacuum and gas recirculation ventilators, heat exchanger, dewatering system and fittings for controlling the volume, product and fermentation process.    USE -   The biogas is used as an alternative to primary energy, e.g. natural gas and light oil, to operate a diesel engine for generating electrical and thermal energy. The process can be used for this purpose in sewage works. The fermented pellets are useful in agriculture for addition to soil and as fuel akin to lignite. Pellets made from waste from distilleries and breweries or by co-fermentation of fresh grass and straw can be used as animal feed. It is also possible to use the biogas as fuel for a steam generator and use the steam as such or for driving a turbine, and the pellets in a low temperature boiler. The biogas diesel can be used for all stationary or mobile diesel engines (all claimed).    ADVANTAGE -   Gas generation can be intensified to increase the methane content to 70-80%, so that the gas need not be purified before use in a biogas diesel engine. Additional ignition with natural gas or light oil is unnecessary, the engine power is increased and wear reduced. The process gives large, dry, hardened pellets, which can be stored and transported without problems, as they are biologically stable, have little odor and have only 50% of their original mass, which makes them economical. When the fermented pellets are used in agriculture, the microorganisms do not cause nitrification or odor pollution. If the process is used in sewage works, sifted solids can be fermented, with no need for complete clarification, which reduces the clarification time and makes it possible to use smaller plant. No carbon dioxide is formed in co-fermentation of fresh grass and straw to biogas and animal feed (all claimed).