Page 34 - Materials Chemistry, Second Edition

20 E. I. Wiloso and R. Heijungs

forms (heat, electricity, biofuel). However, in practice, the functional units vary
among studies. Based on current reviews, typical functional units commonly used
in LCAs of biofuel systems are volume or mass of input biomass feedstock,
volume or mass of biofuel, caloric value of biofuel, driving distance of a car, and
agricultural land area (van der Voet et al. 2010; Cherubini and Strømman 2011;
Wiloso et al. 2012). These choices of functional units are driven by the main
questions or goals of the LCA study. For example, to compare the benefit of
gasoline and biofuel systems as transportation fuels will lead to a functional unit in
terms of 1 km driving distance. Land area required to produce biomass feedstock is
an extremely important parameter since bioenergy can compete against food, feed,
or fiber under land availability constraints. However, there are only a few bio-
energy LCAs based on this parameter. One of them is the study by Lim and Lee
(2011) that used a one-year use of one-hectare palm oil plantation as a functional
unit to produce both biodiesel and bioethanol.

3 Inventory Analysis

An LCI of a product or process quantifies economic and environmental inputs and
outputs around the system boundary. It is constructed as a flow model of a tech-
nical system according to the system boundary decided in the goal and scope
definition. The model is basically a mass and energy balance over a system, but
only environmentally relevant flows are considered. Activities of the LCI also
include data collection of all activities in the system and calculation of the envi-
ronmental loads in relation to the functional unit (Baumann and Tillman 2004).
There are five key aspects specific to bioenergy systems that need further elabo-
ration, i.e., system boundary, land use, biogenic carbon, multi-functional pro-
cesses, and data variability.

3.1 System Boundary

In LCA of bioenergy studies, the choice of system boundary is often arbitrary.
With the basic cradle-to-grave principle of LCA, everything should be included;
however, in practice, many processes are left out for different reasons. System
boundaries define what are to be included and what are not. In general, capital
goods and wastes as an input feedstock are cut off from the system. This implies
that the emissions by the production of capital goods and wastes are not taken into
account.
As previously indicated in Sect. 2.1, one of the main issues related to CLCA is
the identification of the processes to be included in the analyzed system, which
implies the way in which boundaries are defined. In the case of biofuels, for
example, the system boundary is expanded to include emissions and resources