basis of available techno-economic studies and current technologies, that microalgal
biofuel production is 4–5 times more expensive than current fossil fuels; and
actions to reduce that cost involve: (1) productivities of at least 30 g/m
2 /day and
minimum lipid content of 30%, (2) lowering the capital cost, discarding the use of
photobioreactors and centrifuges, reducing costs of dewatering, and finally identifying opportunities for lower-cost carbon and nutrient sources.
In addition to economic evaluation, biofuels from microalgae must also meet
favorable life cycle goals on energy return, and carbon and water footprint to
provide quantitative improvements to current fuels.
However, there is no common conclusion on sustainability of microalgae biofuels (Gnansounou and Raman 2017; Quinn and Davis 2015). The significant
variance in the studies could be due to diverse choices regarding technical (microalgae species, production units, downstream processing, and technology for
energy production, coproducts) and methodological alternatives (functional units,
boundaries, coproduct allocation methods) (Collet et al. 2015; Thomassen et al.
2017). But there is a general agreement that producing only biodiesel from algae is
not favorable and, in order to reduce the overall cost, the following have been
suggested: (i) process integration (CO 2 capture, wastewater treatment, and biofuel
production); (ii) optimization of photobioreactor design and conditions to improve
biofuel yield; and (iii) extraction of valuable products from algal biomass (biorefinery concept). Therefore, a multiproduct strategy in a biorefinery is indicated as
the future trend. Nevertheless, the absence of facilities for microalgae biofuels
production at industrial scale with accurate/reliable information entails theoretical
assumptions or extrapolation of laboratory information to make predictions,
whereas the design problem is mathematically formulated to describe the production systems and its performance. Recent theoretical studies about economic aspects
or LCA in a multiprocessing-downstream processing-multiproduct strategy have
been published (Gutiérrez-Arriaga et al. 2014; Martinez-Hernandez et al. 2013;
Menetrez 2012; Posada et al. 2016). Also, multiobjective optimization approaches
to trade off different criteria simultaneously have been performed (Andiappan et al.
2014; Brunet et al. 2015; Rizwan et al. 2015; Santibañez-Aguilar et al. 2014) by
applying mixed integer nonlinear programming (MINLP) models or Monte Carlo
simulations to maximize incomes or production yields, determine economic viability, and minimize the environmental impact to find the optimal processing
pathway for the production of biodiesel from microalgal biomass and treating
wastes. Although computational tools are developed, no scenario has reached 0.48
USD/L necessary to compete with the fossil alternative.
In general, most LCA studies concluded that bioenergy from algae has lower
greenhouse gas (GHG) emissions than fossil fuels and that energetically viable
process must use raceway ponds, process wet biomass (avoid drying), minimize
energy required for cell disruption, and minimize solvent use (de Boer and Bahri
2015).
126
P.-L. Gorry et al.
biofuel production is 4–5 times more expensive than current fossil fuels; and
actions to reduce that cost involve: (1) productivities of at least 30 g/m
2 /day and
minimum lipid content of 30%, (2) lowering the capital cost, discarding the use of
photobioreactors and centrifuges, reducing costs of dewatering, and finally identifying opportunities for lower-cost carbon and nutrient sources.
In addition to economic evaluation, biofuels from microalgae must also meet
favorable life cycle goals on energy return, and carbon and water footprint to
provide quantitative improvements to current fuels.
However, there is no common conclusion on sustainability of microalgae biofuels (Gnansounou and Raman 2017; Quinn and Davis 2015). The significant
variance in the studies could be due to diverse choices regarding technical (microalgae species, production units, downstream processing, and technology for
energy production, coproducts) and methodological alternatives (functional units,
boundaries, coproduct allocation methods) (Collet et al. 2015; Thomassen et al.
2017). But there is a general agreement that producing only biodiesel from algae is
not favorable and, in order to reduce the overall cost, the following have been
suggested: (i) process integration (CO 2 capture, wastewater treatment, and biofuel
production); (ii) optimization of photobioreactor design and conditions to improve
biofuel yield; and (iii) extraction of valuable products from algal biomass (biorefinery concept). Therefore, a multiproduct strategy in a biorefinery is indicated as
the future trend. Nevertheless, the absence of facilities for microalgae biofuels
production at industrial scale with accurate/reliable information entails theoretical
assumptions or extrapolation of laboratory information to make predictions,
whereas the design problem is mathematically formulated to describe the production systems and its performance. Recent theoretical studies about economic aspects
or LCA in a multiprocessing-downstream processing-multiproduct strategy have
been published (Gutiérrez-Arriaga et al. 2014; Martinez-Hernandez et al. 2013;
Menetrez 2012; Posada et al. 2016). Also, multiobjective optimization approaches
to trade off different criteria simultaneously have been performed (Andiappan et al.
2014; Brunet et al. 2015; Rizwan et al. 2015; Santibañez-Aguilar et al. 2014) by
applying mixed integer nonlinear programming (MINLP) models or Monte Carlo
simulations to maximize incomes or production yields, determine economic viability, and minimize the environmental impact to find the optimal processing
pathway for the production of biodiesel from microalgal biomass and treating
wastes. Although computational tools are developed, no scenario has reached 0.48
USD/L necessary to compete with the fossil alternative.
In general, most LCA studies concluded that bioenergy from algae has lower
greenhouse gas (GHG) emissions than fossil fuels and that energetically viable
process must use raceway ponds, process wet biomass (avoid drying), minimize
energy required for cell disruption, and minimize solvent use (de Boer and Bahri
2015).
126
P.-L. Gorry et al.