Environmental Engineering Reference
In-Depth Information
Applying the stoichiometric balance to the reaction above it is possible to obtain the
stoichiometric coefficients w, x, y, z and k as a function of a, b, c, d, e:
4
a
−
b
−
2
c
+
3
d
+
2
e
⎛
⎞
C
H
O
N
S
+
⋅
H
O
→
⎝
⎠
a
b
c
d
e
2
4
4
a
+
b
−
2
c
−
3
d
−
2
e
4
a
−
b
+
2
c
+
3
d
+
2
e
⎛
⎞
⎛
⎞
→
⋅
CH
+
⋅
CO
+
dNH
+
eH
S
⎝
⎠
⎝
⎠
4
2
3
2
8
8
(11)
Hence, total number of dry kilomoles of LFG will be:
4
a
+
b
−
2
c
−
3
d
−
2
e
4
a
−
b
+
2
c
+
3
d
+
2
e
kmol
LFG
=
x
+
y
+
z
+
k
=
+
+
d
+
e
=
a
+
d
+
e
[
kmol
,
dry
8
8
(12)
In order to consider the presence of water vapour in the LFG it has been assumed that the
gas is saturated with water vapour. From the total number of kilomoles it is then possible to
calculate the potential gas generation capacity (L
0
):
(13)
3
3
Nm
kmol
Nm
L
[
]
=
LFG
[
]
⋅
22
,
414
[
]
t
t
kmol
0
mol
Actually, the different components of waste undergo biodegradation according to
different degradation rates. The different behaviours have been considered distinguishing the
materials in rapidly, moderately and slowly biodegradable, according to (EMCON, 1980).
After a literature review (Nutting, 2001) (US-EPA, 1995) (IGES, 2000) (Metcalf and Eddy
(1991) (Baldwin et al., 1998) (Hartz et al., 1982) (Warith and Sharma, 1998) (Lifshits and
Galueva, 1997) (McBean et al., 2005) (Christensen et al., 1996), different values for LFG
generation rate constant have been assumed for each class of materials with different
biodegradation velocity, as reported in Table 3.
Also the potential LFG generation capacities (L0) for each class of material with different
biodegradation velocity were calculated separately (calculated values are reported in Table 3)
in order to apply the models - when this is allowed by the model itself - in order to proceed
with separate calculations and adding up the three contributions of LFG production.
From Equation 11 it is, also, possible to calculate LFG composition, which, in this case,
results: CH4 48,23%; CO2 47,95%; NH3 3,39%; H2S 0,42 %. The composition is assumed
not to change during the time.
5.
A
PPLICATION OF THE
M
ODELS TO A
S
TUDY
C
ASE
The above described models - with the exception of LandGEM - have been implemented
using a calculation worksheet. In reference to Scholl Canyon model, LandGEM and modified
first order model the input data consisted in: amount of waste landfilled yearly; potential LFG
