4.2.1 Details of
Functional Unit (FU) and
Reference Flow
The study FU(s) and/or reference flow(s) should be quantitatively
and qualitatively determined. This information should be revised
later if necessary typically when they do not favorably represent the
objective of the study. It is worth noting that there is no agreement
regarding the choice of FUs in the published literature, making
comparative assessment much more difficult. Four different classes
of FUS can be identified in LCA analyses of algal fuel production
systems [26]:
– Input-based unit: This FU is determined on the basis of a unit of
input biomass like energy and mass. Such basis is preferred on
which the purpose of study is to comparatively assess various
resources consumption patterns for algal biomass production,
e.g., one ton of algal biomass or one MJ of energy from algal
biomass.
– Output-based unit: This FU is determined on the basis of a unit
of output like useful energy generated or kilometer of transportation. Such basis is preferred when the goal of study is to
evaluate the provision of a given service, e.g., one MJ of energy
from algae fuel.
– Agricultural land-based unit: This FU exhibits the agricultural
land area being cultivated to yield a given amount of algal
biomass feedstock, e.g., one ha algal cultivation.
– Year-based unit: This FU reports the final results on the basis of
annual average. Such basis is preferred for projects in which
multiple final products are expected since there is no need to
allocation.
It is noteworthy that the interpretation of final results is profoundly influenced by the choice of the FU. Therefore, it is advisable to show the results using several FUs to increase the
comparability of the system under investigation with those
reported in the literature.
4.2.2 Defining System
Boundary
A primary system boundary should be defined and a series of
potentially excluded life-cycle stages, activity types, processes, and
elementary flows should be provided, if any. This initial setting
should be substantially revised later, if necessary [27]. This is
extremely vital since it permits comparatively assessment of LCA
studies of various competing systems. According to Jose and Archanaa [28], a system boundary or control surface should be defined
in order to determine what unit processes/operations should be
considered in an LCA like algae cultivation, harvesting, dehydration and handling, and biofuels production by different methods.
Notably, no individual process will be identified at this stage as that
would be the first step of the LCI stage carried out later.
Algal fuels such as bioethanol, biodiesel, biomass, and oil can
be investigated through three different approaches [26]:
128
Homa Hosseinzadeh-Bandbafha et al.
Functional Unit (FU) and
Reference Flow
The study FU(s) and/or reference flow(s) should be quantitatively
and qualitatively determined. This information should be revised
later if necessary typically when they do not favorably represent the
objective of the study. It is worth noting that there is no agreement
regarding the choice of FUs in the published literature, making
comparative assessment much more difficult. Four different classes
of FUS can be identified in LCA analyses of algal fuel production
systems [26]:
– Input-based unit: This FU is determined on the basis of a unit of
input biomass like energy and mass. Such basis is preferred on
which the purpose of study is to comparatively assess various
resources consumption patterns for algal biomass production,
e.g., one ton of algal biomass or one MJ of energy from algal
biomass.
– Output-based unit: This FU is determined on the basis of a unit
of output like useful energy generated or kilometer of transportation. Such basis is preferred when the goal of study is to
evaluate the provision of a given service, e.g., one MJ of energy
from algae fuel.
– Agricultural land-based unit: This FU exhibits the agricultural
land area being cultivated to yield a given amount of algal
biomass feedstock, e.g., one ha algal cultivation.
– Year-based unit: This FU reports the final results on the basis of
annual average. Such basis is preferred for projects in which
multiple final products are expected since there is no need to
allocation.
It is noteworthy that the interpretation of final results is profoundly influenced by the choice of the FU. Therefore, it is advisable to show the results using several FUs to increase the
comparability of the system under investigation with those
reported in the literature.
4.2.2 Defining System
Boundary
A primary system boundary should be defined and a series of
potentially excluded life-cycle stages, activity types, processes, and
elementary flows should be provided, if any. This initial setting
should be substantially revised later, if necessary [27]. This is
extremely vital since it permits comparatively assessment of LCA
studies of various competing systems. According to Jose and Archanaa [28], a system boundary or control surface should be defined
in order to determine what unit processes/operations should be
considered in an LCA like algae cultivation, harvesting, dehydration and handling, and biofuels production by different methods.
Notably, no individual process will be identified at this stage as that
would be the first step of the LCI stage carried out later.
Algal fuels such as bioethanol, biodiesel, biomass, and oil can
be investigated through three different approaches [26]:
128
Homa Hosseinzadeh-Bandbafha et al.