Page 75 - Materials Chemistry, Second Edition

The Application of Life Cycle Assessment on Agricultural 61

impacts of biofuel life cycle with respect to ‘‘base case’’ such as fossil fuel-based life
cycle (Sreejith et al. 2013). Additionally, nearly all LCA studies on the role of
biofuels in mitigating global warming and boosting energy security have concluded
that ‘‘second-generation’’ (or ‘‘advanced’’) biofuels which rely on non-food feed-
stocks and offer improved energy and GHG profiles are necessary to make wider use
of biofuels feasible worldwide (Earley and McKeown 2009).

5.1 LCA of Biogas Production from Lignocellulosic
and Non-Food Feedstocks

Production of biogas is an integrated process in which many stages and combi-
nations are involved. The overall biogas production can be divided into three
distinguished phases, namely the input phase (i.e., production/collection of the
feedstock, transportation, and storage), the biogas plant/processing phase (i.e., pre-
treatment, anaerobic digestion per se, gas treatment, and digestate treatment), and
the output phase (i.e., production of various goods and value-added products as in
biorefineries).

5.1.1 System Boundaries

The employment of LCA in biogas production necessitates the expansion of the
typical agriculture LCA boundaries (Fig. 12a) to include transport and process
energy flows and related environmental burdens (Fig. 12b) for biomethane pro-
duction and transportation of digestate, an anaerobic residue, back to the field.

5.1.2 Goal and Scope

The goal of an LCA study shall unambiguously state the intended application to
the intended audience of the study whereas the scope should be adequately defined
so as to ensure compatibility with the goal (Singh et al 2010).

5.1.3 Functional unit
In all bioenergy assessment systems, the choice of an appropriate FU, as the basis
for comparisons, is of major importance (Ekvall and Finnveden 2001). In practice,
the FU consists of a qualitatively defined function or property (e.g., environmental
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impact) and quantified unit (e.g., 1 m or 1 MJ of fuel). There is significant
diversity in relation to the FU used in LCA, particularly in the case of biofuels.
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Korres et al. (2010) defined the FU as m biomethane year . In addition, according