co-products, is excluded from the whole system and as a result,
just the main product is considered.
(a) It should be noted that since various approaches may
result in considerably different outcomes, the allocation
method used should suit the study under investigation. In
case of algal biofuels however, there exist multiple storable
and non-storable co-products and therefore, no empirically justified best allocation method has been highlighted
in the published literature [31].
(b) Null allocation approach does not suit algal fuels and must
be avoided [26]. In better words, this method does not
encompass the actual contribution of these fuels.
(c) Energy content or mass allocation method is advantageous over the economic allocation method because the
former is based on data that do not vary over time, while
the latter is opposite. In better words, when marketmediated effects are taken into account in LCA studies,
uncertainty is considerably elevated [26].
(d) In spite of the above, the economic allocation approach is
more favorable than the energy content or mass allocation
one in systems where large quantities of co-products of
low economic values are produced [32]. In fact, in such
systems, the results obtained using the economic allocation approach would be more rational.
(e) Based on ISO recommendation, system expansion, displacement, or substitution method is often preferred over
content or mass allocation and economic allocation methods [22]. This is ascribed to the fact that this method
avoids allocation and moreover no division of the unit
process would be needed [33]. It should also be mentioned that this method also suffers from a number of
limitations, especially when no reliable LCI data are available for the co-products or if several potential replacements are possible [34].
6 Life-Cycle Impact Assessment
LCIA in algal fuels production/use includes mandatory and
optional steps. These steps are presented and discussed as follows:
6.1 Classification
and Characterization
To carry out impact assessment at midpoint and/or endpoint level,
the first step involved, called “Classification,” would be to assign
the elementary flows to one or more related impact categories
[22]. In the subsequent step, called “Characterization,” the inventory result for each elementary flow is usually linearly multiplied by
the relevant impact factor from the applied LCIA methods [35].
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Homa Hosseinzadeh-Bandbafha et al.
just the main product is considered.
(a) It should be noted that since various approaches may
result in considerably different outcomes, the allocation
method used should suit the study under investigation. In
case of algal biofuels however, there exist multiple storable
and non-storable co-products and therefore, no empirically justified best allocation method has been highlighted
in the published literature [31].
(b) Null allocation approach does not suit algal fuels and must
be avoided [26]. In better words, this method does not
encompass the actual contribution of these fuels.
(c) Energy content or mass allocation method is advantageous over the economic allocation method because the
former is based on data that do not vary over time, while
the latter is opposite. In better words, when marketmediated effects are taken into account in LCA studies,
uncertainty is considerably elevated [26].
(d) In spite of the above, the economic allocation approach is
more favorable than the energy content or mass allocation
one in systems where large quantities of co-products of
low economic values are produced [32]. In fact, in such
systems, the results obtained using the economic allocation approach would be more rational.
(e) Based on ISO recommendation, system expansion, displacement, or substitution method is often preferred over
content or mass allocation and economic allocation methods [22]. This is ascribed to the fact that this method
avoids allocation and moreover no division of the unit
process would be needed [33]. It should also be mentioned that this method also suffers from a number of
limitations, especially when no reliable LCI data are available for the co-products or if several potential replacements are possible [34].
6 Life-Cycle Impact Assessment
LCIA in algal fuels production/use includes mandatory and
optional steps. These steps are presented and discussed as follows:
6.1 Classification
and Characterization
To carry out impact assessment at midpoint and/or endpoint level,
the first step involved, called “Classification,” would be to assign
the elementary flows to one or more related impact categories
[22]. In the subsequent step, called “Characterization,” the inventory result for each elementary flow is usually linearly multiplied by
the relevant impact factor from the applied LCIA methods [35].
134
Homa Hosseinzadeh-Bandbafha et al.