Environmental Engineering Reference
In-Depth Information
1,40E+07
Conventional landfill
1,20E+07
Landfill with leachate recirculation
1,00E+07
8,00E+06
6,00E+06
4,00E+06
2,00E+06
0,00E+00
1
6
11
16
21
26
31
36
41
46
51
56
Year
Figure 13. Comparison of model results - LFG production - for landfill with leachate recirculation and
conventional landfill.
The accelerated biological degradation also strongly contributes to the volume reduction
of the landfilled waste. In order to evaluate the overall waste volume reduction it is necessary
to account for both the increasing density of the waste, due to the weight of the upper layers,
and the accelerated biodegradation. Assuming that waste density passes from 0,6 to 1 t/m
3
in
thirty years and then it keeps constant, both in a conventional landfill and landfill with
leachate recirculation, and combining this effect with the material loss in LFG, it is possible
to estimate the overall volume reduction in the two cases. It was calculated that at the end of
the seventh year (last year of operation) in both plants the volume reduction allows further
landfilling, but while in the conventional landfill the recovered volume can host about 55.000
t, in the landfill with leachate recirculation about 80.000 t of waste can still be placed. This
possibility of higher recovered volumes and higher capacity has been accounted in the
following considering as input to the landfill with leachate recirculation the higher amount of
waste.
In order to understand the benefits that can derive from leachate recirculation, the two
hypothetical plants have been compared from an economic, environmental and energetic
point of view.
From an economic point of view, the considered investment costs included: bottom
impermeabilisation cost, LFG and leachate collection system costs and capping (Table 13).
In the case of landfill with leachate recirculation a horizontal piping system for both LFG
collection and leachate recirculation has been assumed (with a LFG collection efficiency of
about 70%), while for the conventional landfill a vertical LFG collection system (with a LFG
collection efficiency of about 60%) and a separate conventional leachate draining system
were considered.
In order to properly calculate the annual instalment connected to the investments relative
to bottom impermebilisation, collection system, capping and flaring it is necessary to consider
