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Hi Bruce
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I am glad to hear
that you are doing this evaluation. We came across this issue when we were doing
our food recovery study for our county solid waste program. We were concerned
that the removal of the food from the landfill would negatively impact the
revenue from the sale of electricity ($400,000 a year) that we get from our
methane recovery system at our landfill, but after doing some research and
talking to some landfill gas engineers and our solid waste manager, our
conclusion was that the food decomposed so quickly that the methane recovery
system wasn't capturing much of this gas anyway. The way that our gas recovery
system is constructed is that the extraction wells are only slotted near the
lower part of the well to prevent drawing oxygen into the landfill and the
recovery system. This means that most of the gas generated in the upper layers
probably does not get captured. It also, of course, means that most of this gas
will escape into the atmosphere, contributing to global climate
change.
The data that we
found on rates of decomposition of material in a landfill vary greatly. At
a February 1988 solid waste conference here at the University of
Wisconsin-Madison, Professor Bob Ham gave the following for the expected
half-life for the decomposition of various materials in a
landfill:
Rapidly decomposable (food, garden debris): 1/2 year to 1.5
years
Moderatedly decomposable (paper, wood)
5 years to 25
There is a reference
to work by Pacey & Altmann, but no specific reference is
provided.
In contrast to these
data, a December 2000 report from Norway (Miljøkostnader ved avfallsbehandling
(Environmental Costs from Solid Waste Management), by the organization ECON for
the Norwegian Environmental Protection Department) reported the following
half-life for various materials (page 74):
Wet
organic 2.8 years
Paper
8.4 years
Wood
10.5 years
Textiles
10.5 years
Plastic
50 years
The source is given
as a 1996 report by the Norwegian Pollution Control Authority (SFT).
Unfortunately, one of the reports in the bibliography with this date has the
same data, but no reference source.
The December 2000
report from Norway goes a step further and assigns an enconomic cost to the
environmental impacts of landfills in Norway. Neglecting any potential long term
failure of a liner or cover, they conclude that there is a $17 a ton
environmental impact, of which about $13.50 a ton is from the emissions of
methane.
As we did our food
recovery study, we also talked to some university researchers and others on the
national level about the fate of methane from food and nobody seemed to have
investigated this issue or was aware of any published articles. However, they
agreed that the scenario we described on rapid decomposition and the majority of
the gas going to the atmosphere was logical.
I hope that this
helps and that you will share what you find with others. This seems to be an
issue overlooked by state and federal regulators and by others in the landfill
industry.
John
Reindl
Dane County,
WI
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