Anaerobic digester

An anaerobic digester system for recovery of a usable grade of methane gas from organic waste material slurry, comprising:

• an upwardly open containment vessel for containment of organic waste material slurry;
• a first cover made of gas permeable material conducive to bacterial colonization for installation on the surface of a body of organic waste material slurry in the containment vessel;
• a gas collection system installed on the top of the first cover when the first cover is installed on the surface of a body of organic waste material;
• a second cover made of gas impermeable material installed over the first cover and over the gas collection system forming a gas collection space with the first cover;
• the first and second covers having edges that are closed together in order to inhibit the escape of gas from between them;
• blower means connected to the gas collection system to move gas out of gas collection space to a remote location for storage or use.

A method of recovering a usable grade of methane gas from a body of organic waste material in slurry form, comprising:

• covering the surface of the slurry with a first cover of gas permeable material conducive to bacterial colonization;
• installing a gas collection duct having a plurality of gas collection apertures on the first cover;
• installing a second cover of gas impermeable material over the first cover and the gas collection duct with edges of the second cover closed to edges of the first cover to form a gas collection space between the first and second covers;
• drawing off through the gas collection duct gas which enters the gas collection space from the slurry through the first cover.