MUNICIPAL SOLID WASTE MANAGEMENT AND DISPOSAL - Environmentally Conscious Materials Handling - page 148

optimal truck routes and collection methods (Bhat 1996, Kulcar 1996, Movas-
saghi 1993, Teixeira et al 2004) as well as examining the insertion of certain
processing facilities (such as transfer stations, power plants, etc.) between the
waste source location and the final disposal destination, or in a general term the
assignment of city zones to specific processing facilities or disposal sites for solid
waste removal (Hsieh and Ho 1993, Chang and Wei 1999).
Optimization techniques can also be used in the planning of recycling drop-off
stations and collection networks. Improving the cost-effectiveness of curbside
collection schemes can be achieved by methods such as the distribution of recy-
cling containers designed to store plastic, metal, glass, and paper. In 2006, more
than 8,600 curbside recyclables collection programs were reported in the United
States. The extent of residential curbside recycling programs varies tremendously
by geographic region, with the most extensive curbside collection occurring in
the Northeast (84 percent) and least in the South (30 percent). Overall, 46 percent
of the population in the United States was served by curbside recyclables collec-
tion programs in 2006. Recycled materials are also collected by drop-off centers,
buy-back centers, and through deposit systems. According to U.S. EPA (2005),
ten states have container deposit systems: Connecticut, Delaware, Hawaii, Iowa,
Maine, Massachusetts, Michigan, New York, Oregon, and Vermont. In these
programs, the consumer pays a deposit on beverage containers at the point of
purchase, which is redeemed on return of the empty containers. California has
a similar system where containers can be redeemed, but the consumer pays no
deposit.

6 MATERIALS RECOVERY FACILITIES (MRF)

There are generally two types of materials recovery facilities (MRF). One type
that receives mixed solid waste (regular solid waste with recyclables mixed
together) is called the dirty MRF . The other type that only receives separated
recyclables is called the clean MRF . A typical dirty MRF consists of a large tip-
ping floor with a material processing area and a storage area for different waste
streams. All waste collected from the curbside is delivered to the tipping floor by
the collection truck. The waste brought to the facility is therefore a combination
of MSW garbage and recyclables. Easily separated recyclables such as cardboard
are removed on the tipping floor before entering the processing center. Material
is conveyed into a hopper from the tipping floor via bucket loader. There are
a series of screens that separate out the smaller garbage from the recyclables.
Recovery of recyclables can either be sorted automatically or manually. Manual
sorting usually results in higher-quality materials with less downtime, but can be
expensive because of the labor cost. Automated sorting is more effective for high
throughput. Automated sorting equipment may include magnetic belts or drums
for ferrous metal removal, eddy current separators for aluminum removal, and
classifiers for separating light and heavy materials. Generally, a mix of manual