Environmental Engineering Reference
In-Depth Information
Q
=
R
⋅
L
⋅
k
⋅
e
−
k
(
t
−
i
−
lag
)
(7)
LFG
,
t
,
i
i
0
lag = time to reach anaerobic conditions [year]
Software Application of First Order Decay Model: Landgem
U.S. EPA developed LandGEM (Landfill Gas Emissions Model), which is a software for
quantifying LFG emissions, based on the application of Scholl Canyon model in the form of
equation (6) (EPA, 2005).
The required inputs for estimating the amount of generated LFG are: design capacity of
the landfill; amount of waste in place or the annual acceptance rate; the LFG generation rate
constant k and LFG generation potential L
0
; the number of years of waste acceptance. Default
values for k and L
0
can be used or site-specific values can be introduced. The software can be
operated under the Windows environment. Graphs and reports of estimated gas emissions can
be produced.
Modified First Order Model
A modified version of the first order decay model assumes that LFG generation is
initially low and then rises to a maximum before declining exponentially. The equation of this
model is represented by Equation 8 (Van Zanten and Scheepers, 1995):
k
+
s
(8)
−
s
(
t
−
i
−
lag
)
−
k
(
t
−
i
−
lag
)
Q
=
R
⋅
L
(
−
e
)
k
⋅
e
LFG
,
t
,
i
i
o
s
where
s = rise phase LFG generation rate constant [1/year]
4.
T
HE
E
STIMATION OF
K
AND
L
0
IN THE
M
ODELS
The tricky parameters for the first order models are the gas generation rate constant (k)
and the waste potential LFG generation capacity (L
0
).
The potential for LFG generation capacity, usually expressed as the volume of gas per
mass of waste, can be estimated based on theoretical prediction, laboratory experiments or
actual gas production data. At present, there is no method for determining gas potential that is
without fault (Reinhart and Faour, 2005).
Experimental procedure to evaluate the gas potential has been developed (biochemical
methane potential - ASTM Method E1196-92), which determines the methane yield of an
organic material during its anaerobic decomposition by a mixed microbial flora in a defined
medium. Such a procedure has been modified for solid waste (Owens and Chynoweth, 1992),
so biochemical methane potential values are available for various waste fractions. Hence on
