Appendices to Integrated Resources & Solid Waste Management Plan - Dec 2009

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HAWAf COUNTY MECHANICAL - BIOLOGICAL TREATMENT FACILITY CONCEPTUAL DESIGN Removal of some components, or failure to remove others, may also affect the quality of the compost product produced by the MBT plant. For example, removing too much of the paper fraction may result in a moisture or carbon imbalance that can affect the biological breakdown processes. Failure to remove special wastes (e.g., household hazardous wastes, car batteries) may also negatively affect the chemical content of the finished product and make it unsuitable for certain applications. Mixed MSW often contains bulky items such as tires, fire extinguishers, propane tanks and cylinders, mattresses, carpet and furniture, or long "stringy" items such as rope, chains, or hoses. These items must be removed prior to or during pre - processing to prevent clogging or damage to equipment. Finally, processing of MSW feedstocks poses many health and safety concerns including exposure to dust and bioaerosols, and the risk of cuts and puncture wounds from sharp objects (which can lead to infection and /or diseases such as tetanus, hepatitis, and HIV). Typically, there is a higher reliance on mechanical sorting (versus manual sorting) at mixed MSW facilities when compared to traditional MRF's. Also, the HVAC systems at mixed MSW handling facilities generally require more complicated designs to maintain an acceptable working environment for staff in areas where manual sorting is implemented. Pre - processing equipment commonly used at mixed MSW facilities includes: • Bag- openers • Disc or finger screens for separation of materials based on size 5 • Slow speed shredders for size reduction • Air classifiers or suction devices for removal of film plastics • Over -head and /or head - pulley magnets on conveyor belts for ferrous metal removal • Eddy current separators for removal of larger non - ferrous items (e.g., soda cans) • Sorting conveyors with "picker stations" where targeted materials can be removed by hand MSW materials are typically handled and transferred between processing stages using a combination of wheel loaders, grapple cranes, and conveyor belts. Experience gained at other MBT plants in North America, in particular those at Edmonton (Alberta), Cobb County (Georgia) and Sumpter County (Florida), indicate that there are advantages to using simplified pre - processing lines that rely primarily on mechanical methods (and to a lesser extent on manual sorting). Based on this experience and the nature of the waste streams anticipated for Hawaii County, the following pre - processing system for the two MBT facilities has been developed. • Initial removal of bulky items, and loading of materials onto the processing line using a grapple crane. • Opening of plastic garbage bags with a rotary drum bag opener. • Use of two finger screens in series to separate materials into three size fractions (less than 4 inches, 4 to 12 inches, and greater than 12 inches). 5 Trommel screens can also be used for size separation, but have a tendency to become clogged if the moisture content of the MSW is high or if there is a high amount of textiles, ropes 18