Environmental Engineering Reference
In-Depth Information
more concentrated energy recovery using a lower number of engines (lower investment), but
also to the possibility of higher landfill volume recovery due to the accelerated
biodegradation process with a consequent higher amount of disposed waste that corresponds
to a higher amount of LFG production.
Table 17. Specific disposal cost for MSW, overall energy
conversion efficiency and specific CO
2
emission
Landfill with
leachate
recirculation
Conventional landfill
with vertical
collection system
Disposed MSW [t]
817.390
792.518
Total cost [€]
32.980.512
37.679.930
Specific disposal cost [€/t
MSW
]
40,35
46,28
Overall energy efficiency and environmental impact
Overall energy conversion efficiency [%]
25
20
GHE [kg
CO2
/t
MSW
] without avoided effects
528
644
GHE [kg
CO2
/t
MSW
] with avoided effects
439
571
From the results concerned with overall energy conversion efficiency, a higher value was
obtained for the landfill with leachate recirculation with respect to the conventional landfill.
Concerning GHE production the landfill with leachate recirculation allows the reduction
of specific CO
2
equivalent emitted per each ton of landfilled waste, thanks to the less LFG
emitted directly to the atmosphere after the post-closure phase (without any collection and
combustion). When considering avoided effects, since in the landfill with leachate
recirculation case a higher energy recovery is possible, a further decrease in CO
2
equivalent
specific emission is registered.
C
ONCLUSION
Different landfill gas production mathematical models have been analysed, implemented
and compared among themselves and with data collected from existing landfills, selecting one
of them for application to some study cases.
The use of landfill gas production models is definitely useful in order to properly design
landfill gas collection and energy recovery systems since it supplies an estimation of landfill
gas amount during the landfill operation and post-closure phases. The accuracy of the landfill
gas production estimation depends in part on the complexity of the model and mainly on the
accuracy and specificity of the input data.
The selected model has been used to predict the landfill gas production of a case-study
landfill in order to properly size the energy recovery system, with the aim of obtaining the
maximum profits from selling the produced electric energy. The obtained configuration for
energy recovery was evaluated also from an energetic and environmental point of view,
estimating the overall contribution to Greenhouse Effect from escaped landfill gas, collected
and combusted landfill gas and recovered electric energy avoided emissions. Energy recovery
offers the possibility of decreasing the contribution to Greenhouse Effect, with respect to
