1. Well to Gate (WtG) that includes algae biomass production,
collection, pretreatment, and biofuels synthesis;
2. Well to Tank (WtT) or Well to Pump that includes algae
biomass production, collection, pretreatment, biofuels synthesis, and transferring the synthesized biofuels to a fuel distribution station; and
3. Well to Wheel (WtW) that includes algae production, collection, pretreatment, biofuels synthesis, transferring the synthesized biofuels to a fuel distribution station, and use in an engine
or other power generation equipment.
It should be noted that the choice of system boundary substantially relies on the aim of the LCA analysis. The system boundary is
virtual control surface between the process and the rest of the
technosphere by taking into account unit process datasets as well
as product and waste streams. This means that all product and waste
streams that enter (e.g., algae, material, and energy to biofuel
production step) or leave (e.g., biofuel, by-product, and emissions
from biofuel production step) the process should be appeared in its
inventory. Moreover, all the elementary streams leaving the process
to the ecosphere directly or entering from there directly or in
another word, all the streams crossing the system boundary should
be taken into consideration [29]. The system boundary should be
schematically represented revealing the included and excluded parts
and life-cycle stages of the process (Fig. 3). This schematic should
be redrawn if the goal and scope of study need to be revised during
the project. It is suggested to provide a technical flow diagram for
the foreground system showing the main algal fuels production
steps. The flow chart should be refined later when carrying out
the data collection. It is noteworthy that the selected operations are
deliberately foreseen to be eliminated from the process boundary in
case of partly terminated systems. Therefore, the relevant product
in algal fuels and/or waste streams should also be removed from
the final inventory after aggregation, i.e., from the process boundary in the given dataset.
4.3 Defining Cut-Off
The quantitative cut-off criteria which have been targeted should
be defined, except for the cases where these have been identified in
the goal definition previously [29]. This primary aim should be
remarkably revised later if the study is aimed at comparing different
processes. The cut-off criteria should also be slightly revised later if
the intended integrity cannot be achieved because of the unavailability of databases or lack of resources. It is noteworthy that the
second can mean in rare conditions where the overall goal of the
study cannot be attained and that it requires revisions.
It should be noted that in algal fuel production systems, a 5%
cut-off can be considered for impact categories to be included
according to the ILCD handbook [31]. However, as elaborated
Life Cycle Analysis
129
collection, pretreatment, and biofuels synthesis;
2. Well to Tank (WtT) or Well to Pump that includes algae
biomass production, collection, pretreatment, biofuels synthesis, and transferring the synthesized biofuels to a fuel distribution station; and
3. Well to Wheel (WtW) that includes algae production, collection, pretreatment, biofuels synthesis, transferring the synthesized biofuels to a fuel distribution station, and use in an engine
or other power generation equipment.
It should be noted that the choice of system boundary substantially relies on the aim of the LCA analysis. The system boundary is
virtual control surface between the process and the rest of the
technosphere by taking into account unit process datasets as well
as product and waste streams. This means that all product and waste
streams that enter (e.g., algae, material, and energy to biofuel
production step) or leave (e.g., biofuel, by-product, and emissions
from biofuel production step) the process should be appeared in its
inventory. Moreover, all the elementary streams leaving the process
to the ecosphere directly or entering from there directly or in
another word, all the streams crossing the system boundary should
be taken into consideration [29]. The system boundary should be
schematically represented revealing the included and excluded parts
and life-cycle stages of the process (Fig. 3). This schematic should
be redrawn if the goal and scope of study need to be revised during
the project. It is suggested to provide a technical flow diagram for
the foreground system showing the main algal fuels production
steps. The flow chart should be refined later when carrying out
the data collection. It is noteworthy that the selected operations are
deliberately foreseen to be eliminated from the process boundary in
case of partly terminated systems. Therefore, the relevant product
in algal fuels and/or waste streams should also be removed from
the final inventory after aggregation, i.e., from the process boundary in the given dataset.
4.3 Defining Cut-Off
The quantitative cut-off criteria which have been targeted should
be defined, except for the cases where these have been identified in
the goal definition previously [29]. This primary aim should be
remarkably revised later if the study is aimed at comparing different
processes. The cut-off criteria should also be slightly revised later if
the intended integrity cannot be achieved because of the unavailability of databases or lack of resources. It is noteworthy that the
second can mean in rare conditions where the overall goal of the
study cannot be attained and that it requires revisions.
It should be noted that in algal fuel production systems, a 5%
cut-off can be considered for impact categories to be included
according to the ILCD handbook [31]. However, as elaborated
Life Cycle Analysis
129