Hi Bruce
~
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
We are engaged in a broad LCA-type assessment
of domestic food waste management options for local city councils. A
key issue seems to be whether landfill gas recovery systems actually capture
any of the methane from decomposition of food waste or if the food waste
decomposes too quickly for the methane to be captured. My research has
uncovered several mentions of reports on the issue but no definitive
references. Any ideas?
Many thanks
Bruce Middleton
Resource Consultant
Waste Not
PO Box
331410
Takapuna North Shore City
New Zealand
Phone: 64 9 486
3635