MUNICIPAL SOLID WASTE MANAGEMENT AND DISPOSAL - Environmentally Conscious Materials Handling - page 152

154 Municipal Solid Waste Management and Disposal

such as landfill; (2) it causes air pollution problem; and (3) the disposal of ash
that may contain toxic metals. As with landfill, the siting of the facilities can be
another problem.
Most of the municipal solid waste incineration currently practiced in this coun-
try incorporates recovery of an energy product (generally steam or electricity)
at a waste-to-energy facility (WTE). The resulting energy reduces the amount
needed from other sources, and the sale of the energy helps to offset the cost
of operating the facility. Because of the success of the recycling program, it
is important to predict and characterize the MSW feed to the WTE to provide
enough waste and energy content of the waste for the generation of hot water or
steam for heating and the generation of electricity.
The total amount of U.S. MSW incineration with energy recovery has
decreased because of the success in recycling and reuse programs and the
objections of communities surrounding the WTE facilities. In 2006, the design
capacity of U.S. WTEs was 92,860 tons per day. There were 86 WTE facilities
in 2006, down from 102 in 2000 and 112 in 1997. The distribution in 2006 is
40 (46,573 tpd) in the Northeast, 24 (31,131 tpd) in the South, 16 (10,912 tpd)
in the Midwest, and 6 (4,280 tpd) in the West.

9 LANDFILLS

As mentioned before, landfills are a necessary disposal component in a MSW
management system. A landfill is a specially engineered site for disposing of
solid waste on land, constructed so that it will reduce hazard to public health and
safety. The most important process in a landfill is the anaerobic decomposition
of the organic portion of the MSW disposed in the landfill although aerobic
decomposition occurs briefly in the beginning stage of landfilling when the air
is available. The major products of the anaerobic decomposition are leachate
and gases, including carbon dioxide (CO 2 ) and methane (CH 4 ). The leachate,
a liquid containing high concentrations of organic compounds, can cause water
contamination if not properly controlled. Both of these gases are greenhouse
gases that cause global warming, although CH 4 is much more potent than CO 2 .
With a high energy content, CH 4 can be collected for energy production. If it
is not harvested, it must be flared to reduce the environmental impact. Because
the anaerobic decomposition process is relatively slow with limited moisture in
the landfill designed under RCRA Subtitle D, leachate recirculation and landfill
bioreactor have been developed to accelerate the organic decomposition rate in a
landfill (Townsend et al. 1996, Mehta et al. 2002, Haydar and Khire 2006a 2006b,
U.S. EPA 2006) and thus shorten the duration of the postclosure monitoring and
management requirements.
The primary features of a landfill include an impermeable lower layer to
block the movement of leachate into groundwater, a leachate collection system,
a gravel layer permitting the control of methane, and a daily covering of waste