Page 47 - Materials Chemistry, Second Edition

Key Issues in Conducting Life Cycle Assessment 33

within Europe (Potting et al. 1998). For eutrophication, the uncertainty associated
with field emissions contributes more than the uncertainty associated with emis-
sions from the other system components (Basset-Mens et al. 2006).
Inherent differences associated with variability in soil types and complex
interactions with local climates must be considered in order to obtain a more
representative value in relation to location-dependent aspects. Other types of
influencing variability are different soil management and vegetation types. Simi-
larly, dryer climates will rely increasingly on irrigation placing pressure on
groundwater supplies. In this regard, the impacts of biofuels on water are highly
regional (Sheehan 2009). This issue is of concern for LCA methods in general as
well as a challenge specific to biofuel development.

5 Future Trends

Most of the assumptions and data used in LCA studies of existing bioenergy
systems are related to conditions and practices in Europe and North America, but
more studies are now becoming available for other regions such as Brazil, China,
and Southeast Asia (Cherubini and Strømman 2011). First-generation biofuel
options based on sugar or starch feedstock are currently available commercially,
but lignocellulosic biofuels are expected to be deployed over the year 2020 (IPCC
2011). In this regard, LCA studies of prospective bioenergy options are more
uncertain than LCA studies on current bioenergy feedstocks. The way that
uncertainties and parameter sensitivities are handled is an important aspect to be
developed. Another important aspect to be resolved in the LCA of bio-based
renewable energy systems is the proper way to define system boundaries, partic-
ularly in relation to direct and indirect effects of land use and land-use change.
Further, consensus on the treatment of biogenic carbon should also be prioritized.

6 Conclusion

Bio-based renewable energy sources are presently the largest global contributor to
renewable energy as alternative sources of heat, electricity, and biofuel. From the
perspective of LCA, they pose more methodological challenges than other
renewable energy systems. One of the main reasons is that biomass feedstocks are
produced through agricultural systems that are a notorious case to LCA. Agri-
cultural land use has been indicated as the major contributor of GHG emissions in
the bioenergy life cycle chain. However, this is not conclusive since quantification
methods in terms of functional unit, system boundary, the treatment of biogenic
carbon and multi-functional processes, and regionalized impact assessment are not
agreed upon. In addition, the inherent variability in the agricultural data and
immature production technology increase the uncertainty of the result of LCA