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HAWAII COUNTY MECHANICAL - BIOLOGICAL TREATMENT FACILITY CONCEPTUAL DESIGN <br />• Manual inspection and removal of contaminants from the mid and large sized fractions at <br />the finger screen. <br />• Magnetic removal of ferrous metals from all three fractions. <br />• Shredding of the large fraction. <br />• Recombination and mixing of three fractions using a continuous -flow pug -mill mixer. <br />Rather than a single processing system at each facility that handles all materials delivered, the <br />processing systems would be constructed with parallel lines (two at East Hawaii and three at <br />West Hawai i), each sized for a throughput of 40,000 to 45,000 tons per year. This provides <br />internal redundancy within each facility in the event of a breakdown. It also allows all five of <br />the processing lines to use the same type and size of equipment, providing a second layer of <br />redundancy between the two facilities and reducing the overall inventory of spare parts that is <br />required. <br />The splitting of processing systems into smaller parallel lines also allows for operation of a <br />single processing line when waste deliveries are lower than peak values, and for one line to be <br />run on an evening or weekend shift to reprocess materials if needed. <br />A schematic layout of the pre - processing system is provided in Exhibit 6. <br />Composting Technology Selection <br />Selection of a composting technology is a site - specific exercise. Each technology has advantages <br />and disadvantages which make it more or less appropriate for a particular situation. A <br />summary of general advantages and disadvantages of the more common composting <br />technologies is provided in Exhibit 7. <br />Utilizing a combination of technologies in series is becoming more common at composting <br />facilities in North America. This approach allows for technologies with a higher level of odor <br />and nuisance control (but higher cost) to be used at the start of the process, and lower cost <br />technologies to be used in the latter stages where nuisance risks are lower. <br />The various technologies summarized in Exhibit 7 were considered in terms of their <br />appropriateness for use as a primary or secondary processing method, or as a means of curing <br />compost at the two MMSW facilities. The results of the screening level evaluation of <br />technologies are summarized in Exhibit 8. <br />19 <br />