Page 148 - Biofuels for a More Sustainable Future

134 Biofuels for a More Sustainable Future

It is also of note that some of the social indicators in Table 5.3 do not span
the entire life cycle of the system under assessment either because they are
only applicable to one stage or because data are lacking. In some cases it is
possible to estimate whole life cycle impacts using an “input-output”
approach. This involves using national statistics or corporate data on, for
instance, employment levels and injury rates in various sectors and dividing
those figures by the annual output of those sectors to estimate the number of
employees or injuries per unit of product. The same can be done for each
sector or subsector in the life cycle to arrive at a final estimate per functional
unit. The difficulty of such an approach is that it is time consuming and
requires sufficient resolution in the sectoral statistics to avoid producing
inaccurate estimates. Examples of such approaches are found in Stamford
and Azapagic (2012) and Atilgan and Azapagic (2016).
The generation of extensive databases for use in social LCA is gaining
momentum. Often such efforts are based on input-output approaches as
outlined before, including recent resources such as the Social Hotspots Data-
base (SHDB, 2018).

2.4 Allocation of impacts
Industrial processes—and particularly those that involve biological
systems—are often multioutput systems with various coproducts. These
include, for instance, crops which yield edible and nonedible components,
or animal systems such as cattle that yield meat, hide, milk, and fertilizer
(manure). Therefore in the bioenergy sector there is a particular need to allo-
cate impacts between the fuel/energy output and the system’s coproducts.
Allocation has been explored widely in LCA and often proves contro-
versial. According to ISO 14040/14044, allocation should be avoided where
possible by either subdividing the system under study or by system expansion.
The latter is often seen to be the preferable option and, in its simplest form,
involves crediting the system with the avoided burdens incurred by the
coproducts. This is sometimes referred to as the “substitution” or
“avoided burden” approach.
For instance, an anaerobic digester produces biomethane as its primary
coproduct and a nitrogen-rich digestate as a secondary coproduct which
can be used as a fertilizer. Under system expansion, we might determine
the environmental impacts of producing an equivalent amount of chemical
fertilizer and subtract those impacts from the overall system. Such an
approach can be applied in LCSA by subtracting the economic and social
impacts of the fertilizer as well as the environmental impacts.