More than 2,700 curbside collection programs may be operating in the United States (Glenn and Riggle, 1991). Operating or planned MRFs exceeded 100 in 1991, and the number of such facilities is increasing rapidly (ICF Inc., 1991). The destination of the material collected by programs that are not operated in association with an MRF is unclear. Inadequate data are available on the amounts of materials actually collected, recovered, and sold or beneficially used; most sources report on the design capacity of MRFs.
The field of materials recovery is still relatively new, and systems for encouraging participation, collection, and processing continue to evolve. Better estimates of the amounts of material collected by curbside programs are needed. The validity of the frequent assertion that additional education can motivate greater participation has apparently not been tested, and no study has established the maximum sustainable levels of participation. Some sources have reported nationwide data on the effectiveness of dropoff programs, especially by comparison with curbside collection programs. Limited data are reported in Appendix E (see page E-20).
The effects of "bottle bill" legislation on amounts of materials set out in curbside programs remain unclear. One study has covered that issue, but confirmation of the results would be useful (White et al., 1990). In particular, no data are available on the effect of bottle bills on the total diversion of containers from MSW disposal (that is, the total number of containers set out at curbside or returned for payment at redemption centers). One study included a model to estimate potential effects; however, the results give no clear indication whether bottle bills have a consistently positive or negative effect (Ackerman and SchatEki, 1991).
The yield of reusable glass, metals, and paper that is picked up for separation is not well documented. For example, the breakage of glass during collection is substantial in some communities as a consequence of the trucks that are used. The broken, mixed color glass cannot be sold, and becomes process loss. One community reports that the reason for wetting all the paper it receives is "to prevent blowing." The extra water distorts the accounting of actual yields.
Little information is available on the effectiveness of mixed waste MRF programs. The few reported data suggest that such programs divert twice as much recyclable waste as curbside collection of separated materials. If so, research to encourage the mixed waste approach is needed.
If additional studies make it clear that certain materials are unlikely to find a market in certain regions, then alternative uses need to be found for those materials in those regions. For example, new economic uses for mixed paper and glass are clearly needed in some areas.
Reliable data on actual fuel use in collection and processing for materials recovery are not available for comparison with fuel use for standard MSW collection and disposal. Most MRF studies assume that the trucks used for transporting reusable materials have the same energy consumption as a packer truck, but differences between the two may be significant.
The estimates of energy used for processing are based on design documents. Estimates for operating MRFs of actual power use per ton processed would be more reliable.
All the detailed comparisons of energy use for recycling with energy use for production of virgin metals and glass are now 14-17 years old, and process improvements may have strongly affected the conclusions (Battelle 1975; Kusik and Kenahan, 1978). In addition, no energy balances were found for reuse of collected materials in applications other than remanufacture of the original product (e.g., glass used as a substitute for sand in glasphalt, or mixed plastic used as a substitute for wood composites to produce "plastic lumber").
Like data on energy use, emissions data for operating collection programs are sparse. Specific needs include:
Only anecdotal accounts of environmental releases from actual MRF operations have been reported. Good data are not yet available.
Studies of the environmental advantages of recycling individual materials (e.g., paper, metals, and glass) seem to be based on limited data and analysis, and they need to be updated. Many of the advantages claimed for recycling assumed high effluent levels for virgin manufacture that no longer reflect actual current practice.
Most recycling of waste and of materials that would otherwise become waste occurs outside the traditional MSW management system. Waste paper, postindustrial plastic, and scrap steel are widely collected and recycled in the secondary materials business. A systems study on secondary materials reclamation could show the effectiveness of various industry-commercial-community initiatives and their interactions with recycling efforts.
The present inability of the market to absorb all locally generated recovered materials shows that parts of the system are unable to keep up with supplies available. The supply of separated material is under the control of a waste management authority. Demand for the separated material is under the control of a large number of consumers. Obvious imbalances between supply and demand are reflected in the current prices for some separated materials. Research is needed to determine the effects of such imbalances on the ultimate benefits of curbside collection programs. For example, if depressed prices affect all scrap, curbside-collected material that enters the scrap cycle may simply displace other types of scrap, substituting large quantities of industrial waste for smaller quantities of municipal waste.
Reliable system studies will depend on the availability of cost data generated on a consistent basis, as outlined above.
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