Large municipal or
industrial landfills produce gas that can be tapped to generate electricity.
Microorganisms that live in organic materials such as food wastes, paper
or yard clippings cause these materials to decompose. This produces landfill
gas, typically comprised of roughly 60 percent methane and 40 percent
carbon dioxide (or "CO2").
The US Environmental
Protection Agency (EPA) requires all large landfills to install collection
systems at landfill sites to minimize the release of methane, a major
contributor to global climate change. Though not a renewable resource,
landfill gas will be in great supply absent major innovations in solid
waste management systems and could supply up to 1 percent of the nation's
Landfill gas is collected
from landfills by drilling "wells" into the landfills, and collecting
the gases through pipes. Once the landfill gas is processed, it can be
combined with natural gas to fuel conventional combustion turbines or
used to fuel small combustion or combined cycle turbines. Landfill gas
may also be used in fuel cell technologies, which use chemical reactions
to create electricity, and are much more efficient than combustion turbines.
What are the environmental
impacts of landfill gas begin with issues surrounding landfills themselves
- land use impacts and surface and groundwater issues. Does reliance on
landfills discourage more environmentally preferred waste management substitutes,
such as waste reduction, reuse and recycling?
Since the landfill, typically, is sited for other municipal
purposes, many of the negative issues associated with landfills themselves
are not incorporated in the analysis of landfill gas as a power source.
Use of the gas produced
by landfills may reduce the harmful environmental impacts that would otherwise
result from landfill operations. Landfill
gas electricity generation offers major air quality benefits where landfills
already exist or where the decision to build the landfill has already
Landfill gas power plants reduce methane emissions, a global
climate change agent with 23 times the negative impact of CO2.
gas power plant burns a waste - methane --- that would otherwise be released
into the atmosphere or burned off in a flaring process. Methane is a highly
potent agent of global climate change, having about 23 times the negative
impact on a pound-by-pound basis as CO2. Landfill gas combustion produces
some CO2, but the impact of these emissions on global climate change is
offset many times over by the methane emission reductions.
While new EPA regulations
require gathering and flaring of methane from large landfill operations,
small landfills, which fall outside the federal agency's jurisdiction,
may amount to as much as 40 percent of the methane generated by landfills
Landfill gas generators
produce nitrogen oxides emissions that vary widely from one site to another,
depending on the type of generator and the extent to which steps have
been taken to minimize such emissions. Combustion of landfill gas can
also result in the release of organic compounds and trace amounts of toxic
materials, including mercury and dioxins, although such releases are at
levels lower than if the landfill gas is flared.
There are few water
impacts associated with landfill gas power plants. Unlike other power
plants that rely upon water for cooling, landfill gas power plants are
usually very small, and therefore pollution discharges into local lakes
or streams are typically quite small.
EPA Fact Sheet: "Powering Microturbines with Landfill Gas" http://www.epa.gov/lmop/res/pdf/pwrng_mcrtrbns.pdf
EPA "LFG Energy Projects: Current Projects and Candidate Landfills" http://www.epa.gov/lmop/proj/index.htm