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N of methane, about 50 percent. To capture this biogas the process must be in a closed vessel. When anaerobic digestion is applied to the organic fraction of MSW, the primary purpose of the facility shifts from landfill diversion to biogas production. There are many anaerobic digestion plants both in use today and historically that have been installed to produce and utilize biogas as well as manage a waste. However, most of these facilities utilize sewage sludge, animal manures and other homogenous wastes as feedstock. Very few utilize MSW as a feedstock. It has long been common practice in Europe to use anaerobic digestion at waste water treatment plants to treat sewage sludge. It has been less common over the same period to use anaerobic digestion to treat industrial effluents and agricultural sludges, although there are a number of examples dating back to the 1950s. In the last ten years or so in Europe, because of the introduction of a requirement that the separated organic fraction of MSW be treated before landfill disposal, anaerobic digestion has been adopted for this purpose. Anaerobic digestion has long been popular in India where a large number of small and simple plants are in use processing farm wastes. Currently, a number of vendors are offering farm -based systems in both Europe and the United States. The process of producing biogas from MSW by anaerobic digestion has similar steps to the production of liquid biofuel discussed above. The process includes: 1. A "pretreatment" phase to make the organic material more available for digestion by size reduction and to remove recyclable materials and contaminates; 2. Digestion of the organic material in a closed vessel by microorganisms; 3. Treatment of the biogas to remove water, compress the gas, and other processes depending on the end use; and 4. Curing of the solid residue from the digestion to produce a compost product which may be marketable. The longest established anaerobic treatment processes include: • Anaerobic suspended growth, • Upflow and down -flow anaerobic attached growth, • Fluidized -bed attached growth, • Upflow anaerobic sludge blanket (uasb), • Covered anaerobic lagoons, • Membrane separation anaerobic processes, and • Dry process anaerobic digestion of MSW. The above emerge in process designs, when developed and offered by the technology providers, which are either optimized to: 1. Efficiently remove material (mostly organic) from liquid streams to permit discharge of a treated effluent to a specified water quality standard, and biogas production may be just incidental; or 2. To provide treatment of a waste material, including MSW, to make it suitable for diversion away from landfill, with biogas generation optimized for revenue creation, and potential sales of fibrous and liquid fertilizer by- products. GBB/C08027 -01 B -18 August 15, 2008