MANAGING PLASTIC WASTE - Plastics and Environmental Sustainability - page 405

collected depending on its design. Global landfills in 2007 were estimated
to release about 20% of the total (or 30-35 Tg) of CH 4 annually (Matthews
and Themelis, 2007). In the United States, landfills contribute about 17.5%
(84.1 MMT of CO 2 equivalents) of anthropogenic methane emissions.
Recovered LFG (primarily CH 4 ) can be burnt directly to generate liquid
fuel (that can be used in waste collection fleet), or used in natural gas
plants to produce electricity. At best, only 60-90% of the gas is typically
recovered and burnt to produce electricity. Burning LFG produces CO 2
which is a less potent GHG compared to the CH 4 . Landfill gas to energy
(LFGE) projects were particularly popular in the 1990s. In co-generation
projects, LFG is used to generate both electricity using turbines and heat.
Usingwaste-derived energynotonlyconserves fossilfuelsbutalsoavoidthe
externalities associated with using an equivalent amount of the fossil fuel.
According to the USEPA, presently there are about 620 operational LFG
projects in the United States.
There is no justification for landfilling waste plastics; plastics do not break
down anaerobically to any significant extent in landfills. Except for the
minimal fraction of biodegradable plastics, they do not contribute to LFG
generation. With no solar UV radiation available to initiate degradation,
plastics survive for very long periods of time in the landfill essentially
remaining in storage. But, the risk of additives in the plastics disposed of
in landfills breaking down and polluting groundwater has been pointed out
(Oehlmann et al., 2009; Teuten et al., 2009).
9.2.6 Plastics Waste Incineration
WTE plants burn MSW and convert some of the heat (in steam turbines)
into useful energy. 5 In the United States, about 30 MMT of MSW is
processed in about 80, mainly mass-burn, WTE facilities. The main
advantage of incineration is that it does not require presorting the waste.
Thus it is better suited for dealing with mixed waste streams such as
automotive shredder residue. While some noncombustibles are recovered
from the waste stream prior to incineration, the process generally results
in fly ash as well as bottom ash. Metals, especially iron, is recovered from
the bottom ash and recycled. Plants provide electricity as well as income
in the way of tipping fees and via the sale of recycled metals. Operating
on MSW (that include plastics), a WTE plant can be expected to yield at
least 600 kWh/ton of MSW and can potentially provide cogenerated heat