NOVELTY - The anaerobic digester apparatus comprises: a container (102) including one of a circular vertical wall and planar walls; and an integrated cover and mixer system (110). The cover comprises: a material (116) configured to extend over and cover the surface of the wastewater in the container; and floats coupled to the cover. The container is configured to contain wastewater and waste material. The floats are configured to position the cover on the surface of the wastewater in the container. The cover is coupled to one wall of the container.    USE - The anaerobic digester apparatus is useful for treating wastewater from agricultural or industrial processes, where the waste is micro-organisms, biomass such as vegetation, biological waste such as manure, sludge, industrial waste or byproducts, and slurries of any such material.    ADVANTAGE - The economic anaerobic digester apparatus has high durability, requires little or no maintenance to be provided by user throughout its operating lifetime, can be maintained without draining the contents of the tank, and does not interrupt the treatment process during maintenance, repair or replacement of components of the apparatus.    DETAILED DESCRIPTION - The anaerobic digester apparatus comprises: a container (102) including one of a circular vertical wall and planar walls; and an integrated cover and mixer system (110). The cover comprises: a material (116) configured to extend over and cover the surface of the wastewater in the container; and floats coupled to the cover. The container is configured to contain wastewater and waste material. The floats are configured to position the cover on the surface of the wastewater in the container. The cover is coupled to one wall of the container. The floats are arranged between a portion of the cover and the wastewater surface. The mixer system comprises: a mixer float (132) coupled to the cover; and a mixer motor (140) coupled to the mixer float. The mixer motor is coupled to a shaft extending through the float and into the cylindrical tube into the wastewater. The shaft is coupled to an impeller configured to provide a down draft mixing motion of the wastewater and waste material. The integrated cover and mixer system is effectively integrated and coupled to the container to facilitate anaerobic digestion of the waste material in the container and collect biogas produced in the container. The planar walls are configured in one of a vertical orientation and a sloped orientation. The anaerobic digester apparatus further comprises: a flotation device coupled to the cover and mixer float; a mixer integration ring defining a shelf with the mixer integration ring coupled to the cover and configured to support the mixer float on the shelf; a pressure seal mounted on the shelf and disposed below the mixer float; a cylindrical tube coupled to the mixer float and extending below the mixer float; a tether post coupled to the container wall with one end of a first tether line coupled to the tether post and another end coupled to the mixer float; and an additional mixer system coupled to and integrated with the cover a spaced distance from the other mixer system. The flotation device is configured to circumvent/surround the perimeter of the mixer float. The floatation device is one of a foam log and discrete floats coupled together. The cylindrical tube is set at the center of the mixer float and present in fluid communication with the wastewater. A gas effluent pipe is disposed below the cover in a space defined by the cover and one wall of the container above the wastewater surface, and defines holes configured to receive any gas emitted in the container. A sump bucket is defined in the cover, and is positioned between the mixer float and the container wall. The floats are further arranged about the mixer float in a configuration of one of radial-orientation extending from the mixer float and parallel to each other between the mixer float and container wall. Each float is set in a pocket defined in the cover. An additional tether post is coupled to the container wall that is diametrically opposite to the other tether post with one end of a second tether line coupled to the tether post and the mixer float. The first and second tether lines are configured to position the mixer system at a predetermined location on the surface of the wastewater in the container. The predetermined location is the center of the surface of the wastewater in the container.    DESCRIPTION OF DRAWING(S) - The diagram shows a side view of an integrated cover and mixer system coupled to a wall of a container of an anaerobic digester apparatus.    Container (102)    Integrated cover and mixer system (110)    Material (116)    Mixer float (132)    Mixer motor. (140)