Environmental Engineering Reference
In-Depth Information
than they are to sulfide odors. The odor threshold for ammonia is between 28,000 and 50,000
ppb. Landfill gas has been reported to contain between 1,000,000 and 10,000,000 ppb of
ammonia, or 0.1% to 1% ammonia by volume. Concentrations in ambient air at or near the landfill
site are expected to be much lower.
NMOC.
Some
NMOC
, such as vinyl chloride and hydrocarbons, may also cause odors.
In general, however, NMOC are emitted at very low (trace) concentrations and are unlikely to
pose a severe odor problem.
Odor control technologies prevent odor-causing gases from leaving the landfill. Installing
a landfill cover will prevent odors from newly deposited waste or from gases produced during
bacterial decomposition. Covering a landfill daily with soil can help reduce odors from newly
deposited wastes. More extensive covers are installed at landfill closure to prevent moisture
from infiltrating the refuse and encouraging bacterial growth and decomposition. Vegetative
growth on the landfill cover also reduces odors. Flaring is another technique that can
eliminate landfill gas odors by thermally destroying the odor-causing gases. Venting landfill
gas through a filter is another technology used to reduce odors. Landfill gas is collected and
vented through a filter of bacterial slime. As long as oxygen is present, bacteria will
decompose landfill gas under aerobic conditions, producing carbon dioxide and water.
VI.
M
ODELING OF
M
ETHANE
G
AS
G
ENERATION
AND
E
MISSION FROM
L
ANDFILLS
A. General
Several models are available for estimating the LFG generation rate using site-specific
input parameters. These models vary widely, not only in the assumptions that they make, but
also in their complexity, and in the amount of data they require. The LandGEM model is one
of these models and was developed by the US Environmental Protection Agency to estimate
landfill gas emissions and to determine regulatory applicability to CAA requirements. There
are other LFG emission models in use by industry that also work very well. The
Intergovernmental Panel on Climate Change (IPCC) methodology for estimation of CH
4
emissions from the landfills is based on First-Order decay (FOD) method. Regardless of what
model is used, the accuracy of the inputs drives the results and given the level of uncertainty,
it makes estimating landfill emissions very difficult.
Estimates of the amount of landfill gas generated throughout the lifetime of the landfill
site are highly variable with estimates of between 39 to 500 m
3
/tonne (McBean et al 1995).
For the estimation of landfill gas throughout the lifetime of a site for the assessment of energy
recovery from landfill gas utilization, values of between 150 and 250m
3
/tonne are typically
used (Loening 2003). Annual rates of gas production have been estimated for a typical
municipal solid waste landfill at between 6 and 8m
3
/tonne/year but much higher rates of over
25m
3
/tonne/year have been recorded (Characterization of 100 UK landfill sites 1995). This
allows the potential amount of energy which could be generated from the site, knowing that
undiluted landfill gas can have a calorific value of between 15 and 21 MJ/m
3
, compared to the
calorific value of natural gas at about 37 MJ/m
3
(Waste Management Paper 27, 1994). The
