Biodigestion (also called anaerobic digestion or AD) operates in the absence of oxygen usually in a sealed, contained area. Bacteria decompose the organic matter, producing a biogas (methane and carbon dioxide) that can be captured to produce energy. After left over liquid (leachate) is removed, it can be processed into a fertilizer. The finished solid matter (digestate) is a productive soil enhancer. It can also be added to a compost system as a starter or to further minimize pathogens by putting the matter through a second process.