VALUATION OF THE ENVIRONMENTAL AND ECONOMIC ADVANTAGES DERIVING FROM THE ENERGETIC RECOVERY OF THE BIOGAS PRODUCED IN THE 1ST CATEGORY LANDFILL OF POIATICA (CARPINETI, RE) USING THE LCA (LIFE CYCLE ASSESSMENT) METHOD.
Taddei I.*, Neri P.**, Bergonzoni M.***, Spadoni G.****, Zago F.*****
* Student at the Engineering Faculty of the University of Modena and Reggio
Emilia, Italy
** ENEA (Bologna - Italy)
*** AGAC S.p.A.- Management of Energy and Environment Services (Reggio Emilia-
Italy)
**** DICMA, University of Bologna (Italy)
***** Jenbacher (Verona - Italy)
This study has been developed within a collaboration among AGAC S.p.A., The
University of Modena and Reggio Emilia, the University of Bologna and Enea. The
energetic recovery of biogas produced in landfills of urban solid and similar
waste is a very effective technical solution because it's economical and allows
the improvement of the most important environmental factors.
This energetic resource in nowadays more and more valued at national level also
with economic incentives such as the "Green Certificates". However
accurate technical data and reliable simulations are necessary to support the
advantage of an investment for the realization of an engine that allows an
energetic recovery.
AGAC S.p.A. has developed a specific planning and managerial experience thanks
to several years of activities related to the integrated management of the urban
solid and similar waste in the province of Reggio Emilia. AGAC S.p.A. worked out
a plan of energetic recovery at the 1st category landfill of Poiatica (Carpineti,
RE): it mainly consists in the installation of an engine that uses the biogas as
fuel and that makes a 700 kW generator work. Within few years (probably in 2008)
a second system of the same type but with a lower power (500 kW) will be
installed to support the first one according to the increasingly production of
biogas.
The study first considers the quantity of biogas that the landfill produces: it
was estimated with the EPA mathematical models and then compared with real data
that were collected by a monitoring and control system; in this way it was
possible to estimate the production of electric energy in the next years.
The landfill of Poiatica has been working since July 1995 with a total
authorized capacity of 520.000 m³; recently an extension of 473.000 m³ has
been approved and is now under realization.
In the landfill there are 40 wells located on the pile of waste: they suck the
biogas produced by the anaerobic fermentation of the waste. About the 50 % of
the wells are realized during the phase of contribution of the waste; the
remaining ones are instead drilled after the final covering of the exhausted
lots.
Combining the estimated production of biogas and the efficiency of the suction
system it was possible to summarize graphically the results as can be seen in
fig.1.
Considering, in a precautionary way, a 35-40 % methane content, the estimated
flow of biogas allows to make two engines work, each coupled with a generator;
supposing a total efficiency of 35 %, the generable electric power is
illustrated in the following tab.2.
The first engine connected to a generator almost completely replaces the torch
in which, previously, all the biogas was burnt with considerable environmental
and economic advantages since the first period of operation.
The study consists in the comparison between two different LCA regarding the
end-of-life cycle of the undifferentiated urban solid waste that are disposed in
the landfill of Poiatica. The first LCA considers the initial situation when all
the biogas was burnt in the torch. The second one analyses the case in which the
most of the biogas is used as fuel for the engine coupled with the generator in
order to produce electric energy while only a residual part of it is carried to
the torch.
The aim of this comparison is to prove the environmental and economic advantage
of the energetic recovery. One ton of waste was chosen as Functional Unit; its
composition represents the typical one of the waste of the landfill of Poiatica;
the study considers 30 years of permanence of the waste in the landfill. The
system boundaries are on the one hand the garbage collection whereas on the
other hand the combustion of the biogas in the torch (in the first LCA) and in
the engine (in the second LCA).
The method Eco-Indicator 99 was chosen for the characterization and the
estimation of the environmental damage and of the cost of the studied life cycle;
in particular it was modified in order to consider also the water consumption.
The SimaPro 5.0 code was then used for the LCA calculation. The amount of biogas
produced by a ton of waste in a period of 25-30 years was calculated using the
LandGEM code on the basis of the characteristics of the landfill and of the
waste given by AGAC S.p.A..
Referring to an other landfill controlled by AGAC S.p.A. ( Rio Riazzone,
Castellarano, RE) a correlation was estimated between the quantity of biogas
that is not sucked and the smell intensity; the application of this relation to
the data of smell intensity collected in several points of the landfill of
Poiatica allowed to have a more accurate idea of the efficiency of the suction
system.
In the second LCA the complete life cycle of the engine and of the components
connected to it was analysed using the data given by Jenbacher, the firm that
makes them.
Fig. 1.- Produzione/captazione biogas nella discarica di Poiatica di Carpineti
Tabella 2- Producibilità massima di energia elettrica dalla discarica