assumption are the studies of Lardon et al. (2009) and Clarens et al. (2011). The
assumptions outlined here are contestable. One might argue from an industrial
ecology perspective that nutrients derived from wastewater should have an energy
value >0, as they are apparently useful for microalgal biodiesel production.
Furthermore, when the substitution of conventional wastewater treatment is within
the system boundaries, there would appear to be no good case for keeping
wastewater treatment of effluents from microalgal biodiesel production, which
should at least serve the recycling of nutrients (Laurens et al. 2017), outside the
system boundaries (Stephenson et al. 2010; contrast, e.g., Mu et al. 2014). The
same would appear to hold for treatment of wastewater (e.g., sterilization) to
minimize infection risk for microalgal cultivation.
Furthermore, it should be noted that so far the autotrophic algal productivity of
triglycerides in wastewater has been found to be low, that the supply of wastewater
is unlikely to allow for producing large amounts of algal triglycerides, and that
by-product usage may be problematical due to the presence of hazardous substances
and pathogens (Rawat et al. 2016; Luangpipat and Chisti 2017).
4 Combination of Microalgal Biodiesel Production
with Co-located Power Plants Fueled by Carbonaceous
Substances and Cement Plants
Combinations of cultivating microalgae with co-located power plants (e.g., Colotta
et al. 2016b) can be conducive to good energy balances if ‘wastes’ of power plants
(flue gas, ‘waste’ heat) can be used as inputs in microalgal biodiesel production at
an assumed zero energy value, apart from energy input needed for the transport of
‘wastes’ (e.g., Brentner et al. 2011; Clarens et al. 2011; Xu et al. 2011; Yuan et al.
2015). A similar assumption may be made for the use of CO 2 from co-located
cement plants that generate CO 2 from calcium carbonate (Colotta et al. 2016b). The
assumption that inputs of such ‘wastes’ may be energetically valued at zero energy
input is contestable. From an industrial ecology perspective, one might argue that
‘wastes’ should have an energy value >0, as they are apparently useful for
microalgal biodiesel production. On the other hand, one may argue from a cost
perspective in favor of an energy credit (negative energy input) for using ‘waste’
CO 2 in microalgae cultivation as the use of flue gas may lower external costs.
It may furthermore be noted that algae can only capture a modest fraction of the
flue gas emitted by power plants (Benemann 2013). The co-location with power and
cement plants will severely limit the geographical scope for algal cultivation. And
future power production may well shift away from burning carbonaceous fuels.
8 Biofuels from Microalgae: Biodiesel
175
assumptions outlined here are contestable. One might argue from an industrial
ecology perspective that nutrients derived from wastewater should have an energy
value >0, as they are apparently useful for microalgal biodiesel production.
Furthermore, when the substitution of conventional wastewater treatment is within
the system boundaries, there would appear to be no good case for keeping
wastewater treatment of effluents from microalgal biodiesel production, which
should at least serve the recycling of nutrients (Laurens et al. 2017), outside the
system boundaries (Stephenson et al. 2010; contrast, e.g., Mu et al. 2014). The
same would appear to hold for treatment of wastewater (e.g., sterilization) to
minimize infection risk for microalgal cultivation.
Furthermore, it should be noted that so far the autotrophic algal productivity of
triglycerides in wastewater has been found to be low, that the supply of wastewater
is unlikely to allow for producing large amounts of algal triglycerides, and that
by-product usage may be problematical due to the presence of hazardous substances
and pathogens (Rawat et al. 2016; Luangpipat and Chisti 2017).
4 Combination of Microalgal Biodiesel Production
with Co-located Power Plants Fueled by Carbonaceous
Substances and Cement Plants
Combinations of cultivating microalgae with co-located power plants (e.g., Colotta
et al. 2016b) can be conducive to good energy balances if ‘wastes’ of power plants
(flue gas, ‘waste’ heat) can be used as inputs in microalgal biodiesel production at
an assumed zero energy value, apart from energy input needed for the transport of
‘wastes’ (e.g., Brentner et al. 2011; Clarens et al. 2011; Xu et al. 2011; Yuan et al.
2015). A similar assumption may be made for the use of CO 2 from co-located
cement plants that generate CO 2 from calcium carbonate (Colotta et al. 2016b). The
assumption that inputs of such ‘wastes’ may be energetically valued at zero energy
input is contestable. From an industrial ecology perspective, one might argue that
‘wastes’ should have an energy value >0, as they are apparently useful for
microalgal biodiesel production. On the other hand, one may argue from a cost
perspective in favor of an energy credit (negative energy input) for using ‘waste’
CO 2 in microalgae cultivation as the use of flue gas may lower external costs.
It may furthermore be noted that algae can only capture a modest fraction of the
flue gas emitted by power plants (Benemann 2013). The co-location with power and
cement plants will severely limit the geographical scope for algal cultivation. And
future power production may well shift away from burning carbonaceous fuels.
8 Biofuels from Microalgae: Biodiesel
175