NOVELTY - The anaerobic digestion system comprises: a tank (3) having front and rear walls and containing a liquid (4); a unit for heating the liquid contained in the tank; and anaerobic digesters (1) mounted within the tank and immersed in the liquid. Each digester comprises: a waterproof container having a front open end and a rear open end; covers removably attached to the container at the front and rear open ends to provide gas-tight and liquid-tight seals at the open ends; and ports for the loading and unloading of digesting fluids and evacuation of the biogas generated inside the digesters.    USE - The anaerobic digestion system is useful for biogas production from organic materials using digesting fluids (claimed), where the organic materials comprise agricultural biomass, animal manure, waste water, sludge and organic solid waste.    ADVANTAGE - The anaerobic digestion system simply and economically produces the biogas from the organic materials in a convenient manner, and can be economically manufactured.    DETAILED DESCRIPTION - The anaerobic digestion system comprises: a tank (3) having front and rear walls and containing a liquid (4); a unit for heating the liquid contained in the tank; and anaerobic digesters (1) mounted within the tank and immersed in the liquid. Each digester comprises: a waterproof container having a cross-sectional shape, a long axis, a short axis, a front open end and a rear open end, where the open ends at each end of the long axis and the container long axis are oriented in horizontal position within the tank, and the front and rear open ends extend through and are sealed to holes in the front and rear walls of the tank; covers removably attached to the container at the front and rear open ends to provide gas-tight and liquid-tight seals at the open ends; and ports for the loading and unloading of digesting fluids and evacuation of the biogas generated inside the digesters. The digesters are re-loaded with organic material by loading bales of the organic material into the front open end by pushing already digested organic material out the rear open end. The cross-sectional shape is circular, and the bales of the organic material are roto-bales. The digestion system further comprises: a hook located at the front open end and oriented such that the bales slide over the hook and the hook engages the bales to prevent their movement out the front open end as the bales of the organic material are loaded into the front open end; a loading machine for loading bulk solid material into the digesters; belts supporting the digesters and having two ends attached to pulleys, which are capable of rotation such that the belts transfer the rotary motion to the digesters causing the digesters to rotate about their long axis when the pulleys rotate; a shaft on which the pulleys are mounted on the shaft having two ends; and a support for the shaft. The loading machine comprises: a hopper having a top, two ends, a cross-sectional shape and a size, where the cross-sectional shape same as the cross-sectional shape of the digester and the size are selected such that the hopper is fitted to mate with the front open end of the digester; a piston that is located within the hopper and comprises a cross-sectional shape and size, where the cross-sectional shape is same as the hopper, and the piston is movable between a first position and a second position; and doors attached to the top of the hopper. The doors on the hopper are opened, and the piston is located in the first position when the loading machine is mated to the digester. The hopper is loaded with the bulk solid material, the doors are closed, and the piston moved to a second position by forcing the bulk material into the front open end of the digester. The cross-sectional shape and size of the digester and the hopper are selected such that roto-bales snugly fit within the hopper and the digester. The anaerobic digesters are partially supported by buoyancy. The ends of the shaft are mounted in the support. The supports are motorized to raise and lower the two ends of the shaft independently such that the digester is tilted along its long axis when one end is raised and the other end is lowered. The pulleys and the supports are simultaneously activated by producing a simultaneous rotary motion and tilting motion of the digester. An INDEPENDENT CLAIM is included for a method for digesting material for the production of biogas.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic longitudinal sectional view of a cylindrical digester fixed in a structure of the tank and immersed in the heated liquid.    Anaerobic digesters (1)    Tank (3)    Liquid (4)    Tension rods (6)    Tooth. (19)