Environmental Engineering Reference
In-Depth Information
Table 15. Number, size and overall investment cost of the reciprocating engines and
energy production for each considered case in the operating and post-closure phases
Landfill with leachate
recirculation
Conventional landfill with
vertical collection system
Considered configurations
4 x 625 kW engines +
1 x 143 kW engines
3 x 625 kW engines +
3 x 143 kW engines
Investment cost [€]
2.246.740
2.469.720
Produced electric energy [GWh]
131
105
Table 16 summarises operation costs, grouping together the costs that last for the same
number of years. Operation cost have been assumed equal for the two different plants
considered.
Table 16. Summary of the operation costs
Operation costs
[year]
[€/year]
Personnel, covering soils
8
380.000
Leachate disposal, electricity, water, etc
9
630.000
Mechanical machines, fuels and lubricating oil, machine
maintenance
10
275.000
Leachate disposal, environmental and topographic analysis,
general maintenance, assurance
49
460.000
Vigilance
58
25.000
From an energy point of view, it is possible to calculate an overall energy conversion
efficiency, dividing the amount of generated electric energy (Table 15) by the energy content
of the LFG generated in the landfill life time (assuming an average low heating value of
16.000 kJ/Nm
3
).
From an environmental point of view, it is possible to calculate the specific GHE
production for the different considered cases. Contributions to GHE during operation and
post-closure phases come from collected LFG combustion and from uncollected LFG directly
emitted to the atmosphere; while after the end of the post-closure phase the residual LFG is
all emitted to the atmosphere contributing as well to GHE. These contributions have been
calculated for the two cases (landfill with leachate recirculation and conventional landfill).
Further, considering that the amount of electric energy produced by the engines fed with
LFG, is no more produced by conventional energy system, this term can be considered as an
avoided effect of GHE emissions and then subtracted from the overall balance. Being the
specific emission of about 0,551 kg of equivalent CO
2
/kWh for electric energy production
(with reference to the Italian situation (ENEL, 1999) the overall avoided effect can be
calculated.
Table 17 shows the results in terms of specific disposal cost for disposing one ton of
MSW, in the two cases of landfill with leachate recirculation and conventional landfill.
From the economical point of view, it appears that applying the leachate recirculation,
even if a slightly higher investment cost for the collection/recirculation system is required, a
lower specific disposal cost can be reached in comparison to a conventional landfill. The
lower cost is mainly due to the shorter time during which the LFG production exhausts with a
