2. Focus on the chief sustainability-oriented concerns about
biofuels. Those include climate change, energy efficiency, and
land occupation issues [26].
Global Warming Potential (GWP): could be used as an indicator showing the contribution of biofuels to climate change. GWP is
computed through equivalent carbon dioxide emissions per energy
unit (g CO 2 eq/MJ) [40].
– Consider LCA GWP100 as the impact category for climate
change [41].
– It should be noted that since different gases are removed from
the atmosphere (through chemical and biogenic processes) at
different rates, therefore, their short-term impacts could be
quite different [31]. For instance, methane has a GWP of
28 CO 2eq over 100 years, but 84 CO 2eq over 20 years
[37]. This could be explained by the lifetime of methane in the
atmosphere, i.e., 12.4 years [42].
– It should be emphasized that the GWP20 should not be
regarded more important than the GWP100 as this could result
in decisions leading to a warmer temperature trajectory [43]. In
light if the reasons mentioned, both the GWP100 and GWP20
should be included as impact categories for algal fuels.
– To obtain the latest knowledge on climate change impacts, use
the GWP100 and GWP20 values reported by the latest IPCC
report, i.e., AR5 instead of the values reported by ReCiPe
Characterisation Report [31].
– For GaBi, generate a validated AR5-based LCA impact category
database.
Energy Ratio Output/Input (ER): By using this indicator, it
would be possible to quantify the total fossil-oriented energy inputs
required to produce 1 MJ of biofuels from algae [26].
– Calculate the energetic efficiency indicator, also called net
energy ratio (NER). This is in fact a ratio of the energy content
(MJ) of a specific amount of biofuel to the input energy required
(total or fossil) to produce the same amount of biofuel
(MJ) [44].
– Calculates Energy Return On Investment (EROI). This could
be obtained through the ratio of the output energy of a system
over the total fossil energy input [45].
– It should be noted that if NER is higher than 1.0, this indicates
that the biofuel life cycle creates more energy than it consumes
[26]. In another word, higher NER values represent more
favorable (i.e., more renewable) biofuel. On the other hand,
taking EROI into account, a minimum EROI value of 3.0
would be essential for a given biofuel to be sustainable [46].
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Homa Hosseinzadeh-Bandbafha et al.
biofuels. Those include climate change, energy efficiency, and
land occupation issues [26].
Global Warming Potential (GWP): could be used as an indicator showing the contribution of biofuels to climate change. GWP is
computed through equivalent carbon dioxide emissions per energy
unit (g CO 2 eq/MJ) [40].
– Consider LCA GWP100 as the impact category for climate
change [41].
– It should be noted that since different gases are removed from
the atmosphere (through chemical and biogenic processes) at
different rates, therefore, their short-term impacts could be
quite different [31]. For instance, methane has a GWP of
28 CO 2eq over 100 years, but 84 CO 2eq over 20 years
[37]. This could be explained by the lifetime of methane in the
atmosphere, i.e., 12.4 years [42].
– It should be emphasized that the GWP20 should not be
regarded more important than the GWP100 as this could result
in decisions leading to a warmer temperature trajectory [43]. In
light if the reasons mentioned, both the GWP100 and GWP20
should be included as impact categories for algal fuels.
– To obtain the latest knowledge on climate change impacts, use
the GWP100 and GWP20 values reported by the latest IPCC
report, i.e., AR5 instead of the values reported by ReCiPe
Characterisation Report [31].
– For GaBi, generate a validated AR5-based LCA impact category
database.
Energy Ratio Output/Input (ER): By using this indicator, it
would be possible to quantify the total fossil-oriented energy inputs
required to produce 1 MJ of biofuels from algae [26].
– Calculate the energetic efficiency indicator, also called net
energy ratio (NER). This is in fact a ratio of the energy content
(MJ) of a specific amount of biofuel to the input energy required
(total or fossil) to produce the same amount of biofuel
(MJ) [44].
– Calculates Energy Return On Investment (EROI). This could
be obtained through the ratio of the output energy of a system
over the total fossil energy input [45].
– It should be noted that if NER is higher than 1.0, this indicates
that the biofuel life cycle creates more energy than it consumes
[26]. In another word, higher NER values represent more
favorable (i.e., more renewable) biofuel. On the other hand,
taking EROI into account, a minimum EROI value of 3.0
would be essential for a given biofuel to be sustainable [46].
136
Homa Hosseinzadeh-Bandbafha et al.