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