microalgal meal (one of the potential outputs of biodiesel production) has been
considered a substitute for soybean meal (Maranduba et al. 2016). The equivalence
of algal meal and soybean meal has however not been proven. Choices regarding
the valuation of inputs, system boundaries, and allocation to outputs should be
explicitly stated. It would moreover be preferable to include in assessments a
sensitivity analysis indicating the impact of different choices on estimated energy
balances (‘scenario uncertainty’; Huijbregts et al. 2003).
There are two basic options for cultivating autotrophic algae: in open ponds and
in closed bioreactors. These options can be used singly, but hybrid systems
involving both bioreactors and open ponds have also been proposed (Khoo et al.
2011; Adesanya et al. 2014; Huntley et al. 2015). Published comparative life cycle
studies suggest that biodiesel from microalgae cultivated in open ponds tends to
have a better energy balance than biodiesel from microalgae cultivated in bioreactors (e.g., Stephenson et al. 2010; Clarens et al. 2011; Slade and Bauen 2013;
Hallenbeck et al. 2016; Monari et al. 2016; Togarcheti et al. 2017). Moreover, costs
of microalgal biodiesel from bioreactors are likely to be higher than the costs of
microalgal biodiesel from open ponds (e.g., Dutta et al. 2016; Hallenbeck et al.
2016). For these reasons in the next sections, the focus will be on open pond-based
cultivation systems for microalgae.
Table 1 Peer-reviewed life cycle assessments of energy balances associated with biodiesel
derived from microalgae grown in open ponds
Authors
Estimated cradle–to-gate energy balance
Lardon et al. (2009)
< 2
Batan et al. (2010)
*1
Brentner et al. (2011)
< 1
Clarens et al. (2011)
<4.1
Khoo et al. (2011)
< 1
Razon and Tan (2011)
< 1
Shirvani et al. (2011)
< 1
Xu et al. (2011)
< 3
Sills et al. (2012)
< 3
Frank et al. (2012)
< 2
Quinn et al. (2014)
< 2
Mu et al. (2014)
< 2
Adhikari and Pelegrino (2015)
< 1
Orfield et al. (2015)
< 2
Yuan et al. (2015)
< 2
Dutta et al. (2016)
< 2
Crowdhury and Francetti (2017)
< 3
Naraharisetti et al. (2017)
< 2
8 Biofuels from Microalgae: Biodiesel
173
considered a substitute for soybean meal (Maranduba et al. 2016). The equivalence
of algal meal and soybean meal has however not been proven. Choices regarding
the valuation of inputs, system boundaries, and allocation to outputs should be
explicitly stated. It would moreover be preferable to include in assessments a
sensitivity analysis indicating the impact of different choices on estimated energy
balances (‘scenario uncertainty’; Huijbregts et al. 2003).
There are two basic options for cultivating autotrophic algae: in open ponds and
in closed bioreactors. These options can be used singly, but hybrid systems
involving both bioreactors and open ponds have also been proposed (Khoo et al.
2011; Adesanya et al. 2014; Huntley et al. 2015). Published comparative life cycle
studies suggest that biodiesel from microalgae cultivated in open ponds tends to
have a better energy balance than biodiesel from microalgae cultivated in bioreactors (e.g., Stephenson et al. 2010; Clarens et al. 2011; Slade and Bauen 2013;
Hallenbeck et al. 2016; Monari et al. 2016; Togarcheti et al. 2017). Moreover, costs
of microalgal biodiesel from bioreactors are likely to be higher than the costs of
microalgal biodiesel from open ponds (e.g., Dutta et al. 2016; Hallenbeck et al.
2016). For these reasons in the next sections, the focus will be on open pond-based
cultivation systems for microalgae.
Table 1 Peer-reviewed life cycle assessments of energy balances associated with biodiesel
derived from microalgae grown in open ponds
Authors
Estimated cradle–to-gate energy balance
Lardon et al. (2009)
< 2
Batan et al. (2010)
*1
Brentner et al. (2011)
< 1
Clarens et al. (2011)
<4.1
Khoo et al. (2011)
< 1
Razon and Tan (2011)
< 1
Shirvani et al. (2011)
< 1
Xu et al. (2011)
< 3
Sills et al. (2012)
< 3
Frank et al. (2012)
< 2
Quinn et al. (2014)
< 2
Mu et al. (2014)
< 2
Adhikari and Pelegrino (2015)
< 1
Orfield et al. (2015)
< 2
Yuan et al. (2015)
< 2
Dutta et al. (2016)
< 2
Crowdhury and Francetti (2017)
< 3
Naraharisetti et al. (2017)
< 2
8 Biofuels from Microalgae: Biodiesel
173