NOVELTY - The liner (24) abuts the side walls (22) and bottom (23) of pit formed in ground to form a lined pit. The compostable material (30) including 40-75% of solids is located in lined pit. A cover (25) located on top of compostable material cooperates with the liner to form a sealed in-situ anaerobic composter. A gas management system extracts a gaseous anaerobic decomposition product from compostable material. A pipe injects an aqueous stream into compostable material, and a pipe removes aqueous materials collected on bottom of lined pit.    USE - In-situ anaerobic composter located at food manufacturing facility, for composting food waste. Can also be used in composting yard waste, manure, sludge, wood, pallets, brush, food waste, cellulosic materials like cardboard and construction waste.    ADVANTAGE - The parasitic heating load is decreased by placing the compostable material in-situ and by indirect heating or warming of the fermenting mass. The cover is attached and sealed, and hence the anaerobic fermentation condition is attained quickly. The digestate produced after fermentation of compostable material is used for various horticultural applications. The high quality methane can be produced by anaerobic fermentation. The in-situ design allows for fire suppression by complete aqueous filling of the reactor if needed.    DETAILED DESCRIPTION - The liner in the pit is selected from high density polyethylene (HDPE) liner, PCV liner and linear low density polyethylene (LLDPE) liner. The bottom of the lined pit is equipped with a layer of permeable material like wood chips, yard waste and geotextile and located above the liner. The top surface of compostable material is located above the surrounding ground in which the pit is located, and covered with a geomembrane material. The composter is partially surrounded by a berm at the point where the lined pit and the soil surface meet. An anchor trench is positioned around at the perimeter of the pit and filled with soil plug. The perimeter of liner and the perimeter of cover are located in the anchor trench. The piping associated with gas extraction system, leachate circulation system, and vacuum extraction system enters the composter at a piping offset or at a piping vault and passes through a plate of anchor trench. The gas extraction piping is attached to the lined walls of the pit or underside of the cover tarp and covered by geotextile material. INDEPENDENT CLAIMS are included for the following:    (1) composter complex is equipped with several in-situ anaerobic composter cells (10) located in a landfill such that each of anaerobic composter cells shares at one unit operation selected from the group consisting of bio-filter, leachate recirculation system and gas management system; and    (2) method for anaerobically fermenting compostable materials involves injecting leachate into the compostable material and seeding the compostable material with anaerobic microorganisms before placing the prepared compostable material in the cell or after placing the prepared compostable material in the cell. The vacuum is applied intermittently or continuously to the prepared compostable material in the pit. The air is blown into the prepared compostable material until the cell fermentation off gas is essentially oxygen free. The digestate is allowed to mature for 1 day, about four weeks or more. The new batch of compostable material is placed in the emptied cells to repeat the fermenting process. The prepared compostable material is the mixture of digestate and shredded compostable material in the ratio of 10:1 or 1:10.    DESCRIPTION OF DRAWING(S) - The drawing shows a sectional view of the in-situ anaerobic composter cell.    Anaerobic composter cell (10)    Pit side wall (22)    Pit bottom (23)    Liner (24)    Cover (25)