NOVELTY - An anaerobic digester comprises an intermediate blanket made of flexible PVC in any color acquired by calendering process, and also outspreads through a whole perimeter of set for corrective or preventive maintenance. The intermediate blanket is squarely proportional to an extension of a descending wall height and also outspreads through the whole perimeter of the set.    USE - For biogas captation.    ADVANTAGE - The anaerobic ensures anaerobiosis of the bacteria environment.    DETAILED DESCRIPTION - An anaerobic biodigester comprises plastic blankets, and any color of flexible PVC or other equivalent material, acquired through calendering process or not which make up the set's two main parts, where the first one is a base blanket (1) that makes up a reservoir or lake for the collection of organic matter, while the second one is a cover blanket like a dome (2) that works as an actual chamber to gather the generated gas, so that the gas may be collected and employed as energy for different appliances. The base blanket is outspread covering totally a big cove (3), molding itself against the bottom and side walls, so that it can form a reservoir or lake (4) for collection of organic matter to be processed, and also outspreads, beyond the peripheral limits of the cove, where it is confined by a anchoring groove (5) with a trapezoidal profile, defined by a first inclined descending side, a bottom part and a last inclined ascending side, where it ends or where the border of the base blanket that forms the lake is positioned, and, in the inside of the referred anchoring groove, preferably on its descending side, both blankets present overlapping stretches, where linked by preferably chemical bonds and, after anchoring groove is filled with an appropriate material, e.g. anchoring earth, hail or an ersatz to finish the ways of the biodigester's body which includes other numberless parts that are not intrinsic parts of the system, mostly piping for the intake of material to be processed, piping for gas output, structural pieces or reinforcement pieces. On the stretch where both blankets overlap, there are mechanisms included for corrective or preventive maintenance, e.g. intermediate blanket made of flexible PVC in any color acquired by calendering process, and also outspreads through the whole perimeter of the set. The intermediate blanket is squarely proportional to the extension of the height of the descending wall and also outspreads through the whole perimeter of the set, where the height of intermediate blanket is proportional to the extension of the height of the descending wall. The inferior border of the intermediate blanket is linked to the base blanket by a preferably chemical bond that precedes the first hermetic bond to keep an appropriate distance between them. An access is formed so that the cover blanket may be subject to a section, either partial or along its whole perimeter, separating itself from the base blanket for total replacement or repair. The new cover blanket is bond to the complementary blanket by a chemical bond.    DESCRIPTION OF DRAWING(S) - The figure is an exploded perspective view of the biodigester's body.    A base blanket (1)    Dome (2)    Cove (3)    Lake (4)    Groove (5)