Page 33 - Materials Chemistry, Second Edition

Key Issues in Conducting Life Cycle Assessment 19

pointed out that most of the previous LCA studies provided only a limited analysis
to the life cycle of biofuel system. They failed to account for the indirect effects
(i.e., those taking place outside the biofuel value chain) by excluding emissions
from land-use change. As shown in Fig. 1, indirect effects may result from the
competition for land currently used for food, feed, or fiber to fuel production
(Hedegaard et al. 2008). Interaction between various influencing factors and dis-
placement mechanisms can occur in many forms. The main challenge now is how
to quantitatively measure the indirect impact of biofuel development on other
chains (food, feed, and fiber) that is modeled based on global economic interac-
tion. A CLCA was also used to address problems like the environmental conse-
quences of including the production of second-generation biofuels from biomass
residues compared to a current palm oil biodiesel production system in Malaysia
(Lim and Lee 2011) or to investigate the expected indirect effects of the devel-
opment of a grass biomethane industry in Ireland (Smyth and Murphy 2011).
Currently, there is no clear distinction between ALCA and CLCA in most
policy guidelines of a country or region, partly due to unresolved debate in framing
direct/indirect effects and allocation of co-products (Brander et al. 2009; van Dam
et al. 2010). This conclusion is based on at least three policy guidelines (UK’s
Renewable Transport Fuel Obligation (RTFO), EC’s Renewable Energy Directive
(RED), and US’s Renewable Fuel Standard (RFS)) that tend not to distingusih
ALCA and CLCA. For example, EC’s RED and UK’s RTFO include only direct
land-use change, while US’s RFS includes both direct land-use change and indirect
land-use change; EC’s RED is based on energy allocation, while UK’s RTFO and
US’s RFS prefer system expansion (van Dam et al. 2010). These conditions may
result in a combination of the two approaches within a single analysis and, con-
sequently, an unfair comparison of results derived from different methods (Brander
et al. 2009).

2.2 Functional Unit

A product system is defined based on a functional unit of a product, specified in
relation to the nature of a system, geographical, and time boundary. The main role
of a functional unit is to be used as a reference to quantitatively connect inputs and
outputs of a life cycle inventory (LCI). In this way, LCA results of the same
functional unit can be compared between one another provided that, among other
things, the system boundaries are similar and the scales are normalized. A proper
functional unit that positively reflects the reality is very important in LCA studies.
This is important since different choices of functional units from the same system
may result in different outcomes when compared to each other. A nice illustration
on the effect of different functional units on the results of biofuel LCAs is given by
van der Voet et al. (2010).
Theoretically, a functional unit in the form of one MJ would be more appro-
priate to compare the best use of biomass feedstock for bioenergy of different