Three of the four approaches for separation of reusable materials from MSW begin with collection of the waste. Source-separated materials can be collected in several ways. One common approach is to collect the separated materials in a truck with compartments designed to segregate the various types; a second truck stops at the same locations to pick up the remaining MSW. In another variation, called blue bag, the generator of the waste can bundle all the "recyclable material" together in one (blue) plastic bag and set it out with the rest of the MSW. One packer truck is used to collect both the blue bag and the remaining MSW, and the blue bag is sent to a facility for further separation of the contents.
After reusable materials are collected, they can be taken to an MRF for processing to make them suitable for recycling and remanufacture into useful products. The processing facilities can be loosely categorized as low-technology or high-technology. About one-half of all operating and planned MRFs are "high-technology" facilities (Berenyi and Gould, 1990).
A low-technology MRF is a facility that relies mainly on manual labor to separate the collected material into individual components. These facilities usually consist of a series of belt conveyors from which materials are removed by hand. Mechanical separation is often limited to magnetic separation of ferrous metal and volume reduction equipment such as a baler, a glass crusher, and an aluminum can flattener/blower.
A high-technology MRF supplements manual labor with screens, magnetic separators, air classifiers, shredders and balers, and sometimes with eddy current separators (Savage and Diaz, 1990). Figure 7.1 shows a high-technology MRF. The separated products from a facility of this type could include corrugated boxboard, ferrous metals, aluminum, plastic film, high-density polyethylene (HDPE) and polyethylene terephthalate (PET) containers, and sometimes product components such as household and automobile batteries (see Appendix E).
HIGH-TECH MRF PROCESS PLAN (JOHNSTON, RHODE ISLAND)
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Either low-technology or high-technology approaches can be used for "mixed-waste processing," a not yet common approach that eliminates the need for source separation. The recyclable materials are separated at a mixed-waste MRF, and the remainder of the waste is sent for disposal (Apotheker, 1991). More detailed technology descriptions for these facilities are presented in Appendix E. Figure 7.2 presents a flowsheet of a mixed waste MRF.
Typical MRFs associated with curbside collection programs process a collected feed stream that consists of 50-70% newspaper, 20-50% glass, 1-10% aluminum and ferrous metals, 0-2% plastic, and 0-20% cardboard (Berenyi and Gould, 1990). That feed is quite different in composition from typical raw MSW. Despite the separation, as the collected material is processed, some materials are classified as not recyclable and are rejected. Quantities of rejects vary, but 10% is a common estimate (Berenyi and Gould, 1990). For this study, the marketable products of an MRF are assumed to be 60% newspaper, 30% glass, 4.5% cardboard, 2.5% aluminum, 2.5% ferrous metals, and 0.5% plastic; those estimates are the means of the ranges of values found for operating facilities (Berenyi and Gould, 1990).
FLOOR PLAN FOR PROPOSED MIXED WASTE MRF
(GASTON COUNTY, NORTH CAROLINA)
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