The energy and environmental performance of the bio fuel production
chain, including raw bio gas upgrading, fuel production, storage,
distribution, fueling and final conversion in bus engines was included
in the study. The study was based on the LCA methodology described
in ISO standards 14040 and 14044 [25,26], however some important deviations
from the standards were made; the assessment was limited to
only two impact categories and only energy allocation was included.
This is similar to the methodology described in the sustainability criteria
for biofuels in the EU [23]. Further the study had an attributional modelling
approach, i.e. accounts for the immediate physical flows in a life
cycle. This can be compared to consequential LCA-modelling, which examines
the environmental consequences of change in a life cycle, often
with a market-oriented approach [27]