Concerns with Resource Recovery
Plastic film has
provided farming with many benefits, but film also contributes significantly to
the growing municipal solid waste stream. Low density polyethylene (LDPE) is
the most commonly used film in the agricultural industry because of LDPE’s
inertness, flexibility, and moisture barrier properties. However, there are
several concerns and obstacles that must be addressed.
The most obvious is
the presence of a nearby waste-to- energy incinerator that will accept the
farmer’s used plastics. If there are no available facilities, it may not be
financially or physically possible to incinerate the used plastics. The cost of
building a facility is high— as much as 400 million dollars to build a large
incineration plant. Depending on the facility’s permit to operate, it may not
be approved to accept agricultural wastes, which are usually classified as
residual wastes—used materials that come from industrial, mining, or
agricultural operations. Also, without a strong and stable market to accept the
energy that is produced, processing the waste material may be economically
inefficient.
Contaminated LDPE
film presents some problems for incineration facilities. Baled or large clumps
of LDPE film creates hot spots that damage the incinerator’s boiler or grate.
LDPE film contains such a high heat value per pound that the trash must move
slowly through the process to balance the heat content and the amount of trash
processed. The film must be unbaled and fed evenly into the combustion chambers
to prevent these hot spots. This means slowing down the incineration process
which also means slowing down the amount of trash that can be processed. Since
many facilities do require a tipping fee, less trash means less profit. This
often makes the facility reluctant to accept the large quantities of LDPE film
that the agricultural community often generates.
Pesticide residue
presents a unique problem for incinerating LDPE film. The effects of the
quantity and types of pesticides in the incineration process has yet to be
determined. It is very likely that the high temperatures and complete
combustion would render any pesticide contamination harmless. Properly
rinsed containers are municipal solid wastes, not hazardous wastes. Unfortunately,
public misconceptions still perceive even properly rinsed containers as
hazardous wastes, and facilities need special permits to accept hazardous
wastes.
Another concern
about incinerating plastics is the toxins, such as acid gas and dioxin/furan,
in the emissions. Many plastics contain additives that have heavy metals such
as lead and cadmium, which might increase the toxicity of the incinerator
ashes. The metal content could cause the ashes to be classified as hazardous
wastes, making disposal of the ashes more difficult.
In 1989, the U.S.
Conference of Mayors formed an international panel of experts to discuss the
health and safety of waste-to-energy facilities. The panel concluded that a
properly equipped, operated, and maintained energy recovery facility can
operate within existing regulatory standards for human health and safety. The
Clean Air Act of 1991 provided additional security by tightening emission
standards.
Before the
waste-to-energy facility is permitted to landfill ashes, they are required to
have controls on the pollutants in the air and in the ashes. The effect of
certain metals in emissions and ashes has not been determined. Currently,
incinerator ashes are not categorized as hazardous wastes and can usually be
safely disposed of in properly equipped landfills. Research is underway to find
alternate uses for incineration ashes, which could further reduce the volume of
the waste.
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