Abstract: The invention provides for a sealed mix tank having two chambers: one chamber mixes waste material and water to form a slurry and collect gas, particularly ammonia gas, during the digestive process; and, a second chamber stores water used for mixing. A classifier separates anaerobically non-digestible material from the slurry by directing the slurry through a basin to settle heavy particles and to push scum-forming particles onto a strainer. A sealed digest tank allows for sparging of the slurry with gas and for collecting the bio-gas generated during the digestive process. A sealed sludge tank receives digested slurry from the digest tank, sparges the sludge with gas, and collects the resultant bio-gas. A sealed scrub tank contains a scrubbing liquid which first absorbs ammonia gas generated during the digestive process and subsequently absorbs carbon dioxide and hydrogen sulfide from bio-gas collected from the tanks during the process.