Agenda - 09-02-2008 - 7a - Laserfiche WebLink

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1.3.3 Anaerobic Digestion As applied to the processing of MSW, anaerobic digestion is a wet treatment process where waste is first pre -sorted and then fed into water tanks. Using agitators, pumps, conveyors and other materials handling equipment, MSW is wetted and dissolved. Metals, glass and other constituents of MSW that have no affinity for water are eventually discharged from the system into dedicated containers for recycling, further processing or final disposal. The paper, garbage, soluble components, etc., generate "black water" which has a relatively high organic content. This stream is taken to a series of digesters where the time it sits in the chamber, the residence time, will be sufficient to generate an off -gas. The process is shown in the schematic in Figure B -13. Figure B -13. Process Flow for Anaerobic Digestion Systems? This gas is rich in methane and other organics and can be burned as a fuel for heating or for electric power generation. The solid residual from the digestion process is similar to compost and can be used as a soil amendment. The process also separates out recyclable materials such as glass and metals. There are many such facilities processing sewage sludge, manure and other homogeneous wastes. ArrowBio of Haifa, Israel, is an example of a vendor that is offering to construct anaerobic digestion facilities to process MSW in the United States. They have responded to procurements in Los Angeles and New York. They operate a 300 TPD full -scale MSW demonstration process line in Tel Aviv, illustrated in Figure B -14.17 The system operates without high temperatures or pressure. In theory, it is extremely simple, relying on non - specialized mechanical equipment (pumps, screens, macerators, tanks, conveyors, etc.) for operation. Digestion occurs through the presence of natural microorganisms in MSW, so charging with specialty or unique bacteria is not necessary. It has a high resistance to upsets because of the scale of its operation, i.e., 300 tons of MSW entering the system per day, and any poisons that might threaten the digestion process (as has been experienced with sewage treatment plant digesters) are likely to be of such small fraction that it will have no significant effect on digester cultures. The system is equipment and labor intensive. Although redundancy is normally built into the system, with multiple process lines and duplication of critical pumps, 17 Source: ArrowBio, Haifa, Israel. GBB/C08027 -01 B -20 August 15, 2008