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100 <br />Comprehensive Review of <br />Solid Waste Collection and Disposal Options <br />• Air emissions from burning the RDF product; <br />Concerns with contamination and quality of the resulting biological compost product; <br />and, <br />+ The need for additional infrastructure to utilize the generated power. <br />12.4 ALTERNATIVE WC TECHNOLOGIES <br />The alternative waste conversion technologies are numerous and can be grouped many ways, but <br />for this discussion, SCS has grouped technologies by three major processes that include: <br />+ Thermal <br />+ Biological <br />+ Bio-Chemical <br />Within these groups are many methods and technologies that have been developed to extract <br />different benefits from the processed waste stream including; <br />• Gases for power production; <br />Gases for feedstock for vehicular fuels; <br />• Basic chemicals for use as a raw feedstock; <br />• Compost/ soil amendments; and, <br />• Slag for use an alternative building material. <br />A brief description of the main technologies in each of the three groups is presented below with <br />discussion as to potential relevancy to the Town and region, benefits, estimated costs, and <br />potential advantages and disadvantages. <br />12.4.1 Thermal <br />The thermal technologies are based on taking the solid waste and processing it under moderate to <br />very high temperatures in a closed reactor vessel, sometimes under pressure and with or without <br />the introduction of air or steam. Depending on the particular process, traditional recyclables may <br />be removed at the front end of the process or during the process stages. The predominant <br />processes are pyrolysis - gasification and autoclaving. <br />12.4.1.1 Pyrolysis - Gasification <br />In a pyrolysis process air is excluded from the reactor vessel and results in the waste <br />decomposing into certain gases (methane, carbon dioxide, and carbon monoxide), liquids <br />(oils /tar), and solid materials (char). The proportions are determined by operating temperature, <br />pressure, oxygen content, and other conditions. Because there is little to no air or oxygen, the <br />waste does not combust as it breaks down (there are no flames). <br />When the amount of air in the process is less than that required to support combustion, but <br />greater than in a pyrolysis process, the process is termed gasification. This process is typically <br />v2.1 166 10/22 /12 <br />