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103 <br />Comprehensive Review of <br />Solid Waste Collection and Disposal Options <br />Exblbit 12 -8. Basic Autoclave Process <br />TH ERIr1AL <br />(autoclave) <br />Steam <br />Heat Odor <br />Trealn�nl <br />-- Reactor'�p CPktic+�at <br />MSW [Atatarlove} Prcie rg BY-pradLvs_ <br />- - -- • RDF for <br />pQxer P1art <br />Debris y Sail • £t MCA <br />Removal Pressure Anrendmeni <br />12.4.2 Biological <br />There are two types of biological processes being utilized for WC. These include the anaerobic <br />and aerobic process technologies. The following paragraphs briefly describe these technologies. <br />12.4.2.1 Anaerobic Process <br />Anaerobic digestion is the bacterial breakdown of organic materials in the absence of oxygen. <br />This biological process produces a gas, sometimes called biogas, principally composed of <br />methane and carbon dioxide. The anaerobic process is often used to treat organic wastes other <br />than nonsegregated MSW, and that is where it is used the most. This anaerobic process is used <br />to digest sewage sludge (i.e., biosolids — produced from treated sanitary sewage), yard <br />vegetation, agricultural wastes (both animal and plant) and some industrial waste sludge. The <br />number of plants processing these materials is currently hi the thousands worldwide. <br />The anaerobic digestion process occurs in three steps: <br />1. Decomposition of plant or animal matter by bacteria into molecules such as sugar. <br />2. Conversion of decomposed matter to organic acids. - <br />3. Organic acid conversion to methane gas. <br />Depending on the waste feedstock and the system design, biogas is typically 55 to 75% methane. <br />A basic anaerobic process is shown in Exhibit 12 -9. <br />v2.1 169 10%22,/12 <br />