Page 77 - Materials Chemistry, Second Edition

The Application of Life Cycle Assessment on Agricultural 63

5.1.4 Reference System
A typical objective of LCA is to discover essential differences in potential envi-
ronmental impacts between two alternative systems fulfilling the same functions
(Lindfors et al. 1999). Therefore, the choice of the reference system to which the
bioenergy system is compared is critical because the estimated benefits of bio-
energy based on the replacement of the assumed energy system can differ sig-
nificantly depending on the chosen reference system. In the case of biofuels, diesel
production is used as reference system.

5.1.5 Life Cycle Inventory

The same process as it has been described in Korres (2013) should be followed.
Very briefly, the preparation of data collection and data collection spreadsheet
followed by data collection and data validation by which data are related to FU are
the major first steps of the LCI. According to Fava et al. (1994), the major LCA
inventory stages to be considered while collecting data for LCI development and
which are generally applicable to biogas production include activities such as raw
materials (feedstock) acquisition and energy consumption; manufacturing, pro-
cessing and formulation; distribution and transportation; use/re-use/maintenance;
recycling; and waste management.

5.1.6 Energy Consumed in AD Plant

The energy consumed in the AD plant for the production of biogas can be cal-
culated based on the Eq. (9).
ð9Þ
E AD ¼ E Direct þ E Indirect ¼ E H þ E Mc þ E MX þ E P þ E L
where E H energy (direct) required to heat the digester up to an operational tem-
perature; E Mc energy for feedstock pre-treatment (e.g., macerating); E MX electrical
energy for feedstock mixing during digestion process; E P electrical energy nec-
essary for water pumping or, as in the case of continuously stirred tank reactor, for
recirculation of liquid from one digester to the other; E L energy loss. A detailed
analysis and calculations of the net energy (and related emissions) in bioreactors
which involve the thermal and the electrical energy necessary to run the bioreactor
are reported in anonymous (2007); Smyth et al. (2009); Ruggeri et al. (2010), and
Korres et al. (2010). Very briefly, the outcome of a GHG LCA on grass biome-
thane (produced by anaerobic digestion and used as a transport fuel in place of
diesel) conducted by Korres et al. (2010) is presented in Table 2. The largest
contributors were emissions from the anaerobic digestion process followed by crop
production. Indirect emissions from the production of nitrogen and potassium
fertilizers were the major contributors to agricultural emissions, and, in the