Page 147 - Materials Chemistry, Second Edition

134 S. H. Gheewala

3 System Boundaries

For biofuels, the system boundaries usually cover cultivation of the feedstock
(including agrochemical production and application), processing of the feedstock
for conversion to the biofuel, use of the biofuel, and transportation in all the
intermediate stages (Fig. 1) (Gheewala 2011). In recent years, the system
boundaries of biofuels have been expanded to include the pre-cultivation stage
which is land use change. This particular stage has significant implications on the
emissions of GHGs and on biodiversity, especially when forests and other high
conservation value lands are converted to agriculture for cultivation of biofuel
feedstocks (Danielson et al. 2008; Fargione et al. 2008).

4 Data Sources

For conducting environmental sustainability assessment, data are required at every
stage of the life cycle outlined in Fig. 1. If land use change from a natural system
to an agricultural one has taken place in the recent past (say, less than 20 years
ago), then data on the type of land that existed need to be known and, if possible,
the carbon stock in the soil as well as above and below ground biomass. In the
absence of very detailed data, default values from the Intergovernmental Panel on
Climate Change methodology could also be used (IPCC 2006).
At the cultivation stage, detailed data need to be collected on the use of
agrochemicals (herbicides, pesticides, and fertilizers), their rates, and frequency of
application throughout the cultivation period. Labor requirements, if necessary,
also need to be assessed. Use of irrigation water and agricultural machinery
(particularly fuel use) needs to be recorded as also the yield of the main product
and by-products. These data are usually from primary sources at the farm level
though in the case of national studies, national statistics from agricultural orga-
nizations may also provide useful information.

Fig. 1 Generic system
boundaries of biofuels Land use change
Biofuel feedstock cultivation
Energy
Transport of biomass to
conversion facilities
Transformation of biomass
Materials
to biofuels
Distribution of biofuels Emissions to air, water and soil
to gas stations
Use of biofuel in vehicles