Page 247 - Biofuels for a More Sustainable Future

222 Biofuels for a More Sustainable Future

The eco-profiles of the raw materials, materials and energy sources, the
transport and end-of-life processes are referred to environmental databases
(Frischknecht et al., 2007).

2.3 Life cycle impact assessment and interpretation
The energy impact (CED) for the functional unit (1MJ of exergy) is
4.91E 02MJ,ofwhichabout96%isnonrenewableenergy(4.71E 02MJ).
The production step is responsible of about 76% of CED (3.73E 02-
MJ), while the operation and end of life give a contribution to the total
impact of about 20% (9.82E 03MJ) and 4% (1.94E 03MJ), respectively.
Focusing on the production step, the steel used in the manufacturing of
the digester is responsible for about 51% of the energy impact, while about
28% of the impact is attributable to the use of steel in the cogeneration plant.
Table 7.3 presents the environmental impact of the functional unit. The
contribution of each life cycle step to the total impacts is illustrated in Fig. 7.2.
The results highlighted that the operation step gives a contribution of
about 66% to the impact on HT c and higher than 90% to almost all the
examined impacts categories.
The end-of-life step causes about 87.7% of the impact on E FW , mainly
due to the copper treatment, and contributes for less than 5% to the other
impacts. The production step is responsible of the main impacts on IR
(about 88%), OD (about 50%), and RD (about 96%).

Table 7.3 Environmental impacts of 1MJ of exergy
Impact category Unit of measure Quantity
AP Mole of H+ eq 4.20E 04
CTUe 3.31E 01
E FW
FE kg P eq 1.70E 05
CTUh 5.84E 10
HT c
CTUh 1.16E 08
HT nc
IR kg U235 eq 1.45E 01
GWP kg CO 2eq 9.56E 02
ME kg N eq 9.03E 06
TE Mole of N eq 1.51E 03
OD kg CFC 11eq 1.36E 10
PM kgPM2.5 eq 1.16E 05
POF kg NMVOC 1.10E 04
RD kg Sb eq 7.03E 08
TFC UBP 6.03E 02