Environmental Engineering Reference
In-Depth Information
LandGEM is considered a screening tool - the better the input data, the better the
estimates. The Input parameters in the model are described below in more details:
Methane generation potential (L
0
)
The methane generation potential is the total amount of methane that a unit mass of
refuse will produce given enough time. It depends upon the composition of the waste. Values
of L
o
can vary widely and are difficult to estimate for a particular landfill. As per IPCC
(1996), the values of L
o
may range from less than 100 to over 200m
3
/Mg.
Methane generation rate (k)
The k value is indicative of the fraction of the waste which undergoes decomposition in
the given year to produce methane. The k value for the given mass is actually related to its
half life time period of decay:
ln
2
(2)
k
=
t
1
/
2
Where, half life is the time taken by the degradable organic carbon in the waste to decay
to half of its initial mass.
This value is affected by a number of factors including the waste composition, climatic
conditions at the site, characteristics of the disposal site, waste disposal practices etc.
The most rapid rates (
k
= 0.2) are associated with high moisture conditions and rapidly
degradable material such as food waste. The slower decay rates (
k
= 0.02) are associated with
dry site conditions and slowly degradable waste such as wood or paper. IPCC (2006) has
provided default k values as dry and wet values for various types of waste depending upon the
climatic conditions.
There are two options to use the value of
k
for estimation of gas potential:
Bulk waste
option
in which single value of
k
is chosen for the entire waste and
Waste composition option
in which
k
value for each component of waste stream is considered for calculations.
LandGEM has bulk waste option for
k
.
C. IPCC-First Order Decay (FOD) Model
1. Model description
The Intergovernmental Panel on Climate Change (IPCC) methodology for estimation of
CH
4
emissions from the landfills is based on FOD method. This method assumes that the
degradable organic carbon (DOC) in the waste decays slowly throughout a few decades,
during which CH
4
and CO
2
are formed. If conditions are constant, the rate of CH
4
formation
depends solely on the amount of carbon remaining in the waste. Therefore, the CH
4
emissions
from the waste deposited in a landfill are highest in the first few years after closure and then
gradually start reducing.
The FOD model developed by IPCC (2006) has been widely adapted for calculation of
methane emissions from the landfills. Same model has been used by United Nations
Framework Convention on Climate Change (UNFCCC) in its “Tool to determine methane
