NOVELTY - An up-flow anaerobic sludge digester comprises a digester main body (16) having a reaction zone (2), a flow lowering zone (6), a settling zone (8), and a gas-liquid separation zone (5). Inner part of the main body is provided with a guide plate (3), a riser pipe (4), and a flow lowering pipe (7). Lower part of the digester main body is provided with the reaction zone, upper part of which is provided with a filler (14) and bottom of which is provided with a biogas aerator (15) connected with a biogas pump (13).    USE - An up-flow anaerobic sludge digester.    ADVANTAGE - By means of density difference of the biogas in and out of the riser pipe, there is a fluid circulation formed between the reaction zone and the settling zone to greatly improve the condition for mass transfer. The reaction zone is provided with filler so as to increase the concentration of the anaerobic microorganism in the reactor to guarantee a high efficiency of the sludge digester. The sludge and the liquid are discharged separately so as to be conducive to connect the subsequent processes and keep the concentration of anaerobic microorganism in the digester. The digester is advanced in increasing the degradability of the organic matters in the sludge and converting it into biogas. Hydraulic retention time is short and the energy consumption is drastically reduced.    DETAILED DESCRIPTION - An up-flow anaerobic sludge digester comprises a digester main body (16), a sludge inlet pipe (1), a sludge outlet pipe (12), and a biogas pipe (10) placed at the top of the digester. Lower part of the digester main body is provided with a reaction zone (2), upper part of which is provided with a filler (14) and bottom of which is provided with a biogas aerator (15) connected with a biogas pump (13). Mid upper part of the digester main body is provided with a flow lowering zone (6) and a settling zone (8). Upper part of the settling zone is provided with a supernatant pipe (9), while upper part of the digester main body is provided with a gas-liquid separation zone (5). The reaction zone is connected with the flow lowering zone through a riser pipe (4). Most of the space between the settling zone and the flow lowering zone is divided by a partition board, and the bottoms between them are connected by a guide plate (3). The bottom of the flow lowering zone is connected with a flow lowering pipe (7), the lower part of which is connected with the bottom of the reaction zone. The up-flow anaerobic sludge digester is a tower reactor. The outside of the digester main body is provided with a biogas tank that is connected with the biogas pump through a pipeline.    DESCRIPTION OF DRAWING(S) - The drawing is a schematic diagram illustrating the up-flow anaerobic sludge digester.    Sludge inlet pipe (1)    Reaction zone (2)    Guide plate (3)    Riser pipe (4)    Gas-liquid separation zone (5)    Flow lowering zone (6)    Flow lowering pipe (7)    Settling zone (8)    Supernatant pipe (9)    Biogas pipe (10)    Sludge outlet pipe (12)    Biogas pump (13)    Filler (14)    Biogas aerator (15)    Digester main body (16)