Page 38 - Materials Chemistry, Second Edition

24 E. I. Wiloso and R. Heijungs

gasoline. In this regard, Liska and Perrin (2009) illustrated that livestock and
military security also had a significant impacts in the case of the US bioenergy
system. The inclusion of these indirect effects in the bioenergy system understudy
can change the direction of the final results. There is, however, much scientific
uncertainty in measuring these indirect emissions related to both bioenergy and
fossil oil systems, thus creating a problem on how to properly calculate them.

3.3 Biogenic Carbon

One of the important aspects in bioenergy systems is related to biogenic (short-
cycle) carbon. Although under debate, it has been recognized that bioenergy is not
carbon neutral since it requires a significant input of fossil fuels. In practice, many
studies exclude biogenic carbon from biofuel LCAs, rather than including it ini-
tially as an extraction and later as an emission. This convention is so widespread
that in the majority of biofuel LCA case studies, the aspect of biogenic carbon is
not even mentioned (van der Voet et al. 2010).
The neutrality of biogenic carbon is part of the natural carbon cycle over a
relatively short period of time, resulting in stable atmospheric carbon. As illus-
trated in scenario 1 of Fig. 3, this is the case when the emission of biogenic carbon
in the form of naturally decayed or burned biomass is compensated by the same
amount of photosynthetic carbon sequestered by naturally grown vegetation.
However, this cycle can no longer be ‘neutral’ if the input–output inventory is out
of balance. This occurs, for example, when large-scale bioenergy systems

Fig. 3 Biogenic carbon cycle versus ‘irreversible’ geologic carbon emission