Page 79 - Materials Chemistry, Second Edition

The Application of Life Cycle Assessment on Agricultural 65

Fig. 13 Estimated ranges of fossil (gasoline and diesel) energy balances and selected bioethanol
types (based on Worldwatch Institute 2006; Rajagopal and Zilberman 2007; FAO 2008; Earley
and McKeown 2009)

contributes to reducing dependence on fossil fuels. Albeit to widely varying
degrees, all bioethanol types are making a positive contribution in this regard. It is
worth to mention that the favorable fossil energy balance of sugarcane-based
ethanol depends not only on feedstock productivity but also on the fact that it is
processed using biomass residues from the sugarcane (bagasse) as energy input
(FAO 2008). Table 3 displays in detail the energy balance breaking down to its
secondary components for sugarcane bioethanol.
The range of estimated fossil fuel balances for cellulosic feedstocks is even
wider, reflecting the uncertainty regarding this technology and the diversity of
potential feedstocks and production systems. Similarly, the net effect of biofuels
on GHG emissions may differ widely. Nevertheless, as stated by Farrell et al.
(2006), energy ratios are sensitive to specification and assumptions and thus can
produce uninterpretable values.

5.2.1 Feedstocks

The actual potential to produce cellulosic ethanol as mentioned above is multi-
faceted. Because large-scale production, transport, processing, and conversion of
cellulosic materials have not been attempted to any real degree anywhere in the
world a number of sustainability issues related to energy inputs and environmental
quality need to be examined in conjunction with production, harvest, and