considered – microwave pyrolysis, direct combustion, hydrothermal liquefaction,
and lipid extraction – altogether creating 16 unique production pathways. Impacts
evaluated were fossil fuel use, GHG emissions, eutrophication, and water use.
Overall, the results showed that wastewater-based algal biofuels had lower environmental impacts than freshwater-based fuels, depending on the characteristics of the
wastewater and the conversion technologies. Although both did not generally
perform better than petroleum diesel, the centrate cultivation with wet lipid pathway
and the centrate cultivation with combustion pathway had lower impacts across all
impact categories compared to petroleum diesel. Yang et al. (2011) specifically
focused on the life cycle water and nutrients usage of biofuels from microalgae.
They estimated that in the case of algal biodiesel from freshwater, 3726 kg of water
is needed to produce 1 kg of biodiesel, if no water is recycled. Recycling water can
significantly reduce life cycle consumption of nitrogen, phosphorous, potassium,
magnesium, and sulfur. Furthermore, wastewater-based biofuels can reduce nitrogen
impacts by 94% and do not require potassium, magnesium, and sulfur (Yang
et al. 2011).
Most LCA studies on algal products have focused on quantifying the global
warming potential, net energy ratio (NER), and the energy return on investment
(EROI). There have been several LCA studies of microalgal biofuels (Adesanya
et al. 2014; Azadi et al. 2014; Batan et al. 2010; Brentner et al. 2011; Campbell et al.
2011; Collet et al. 2014; Frank et al. 2011, 2013; Grierson et al. 2013; Handler et al.
2014; Liu et al. 2013; Passell et al. 2013; Ponnusamy et al. 2014; Quinn et al. 2014;
Shirvani et al. 2011; Sills et al. 2013; Soh et al. 2014; Vasudevan et al. 2012; Woertz
et al. 2014). As with LCAs of emerging technologies and energy systems, there is a
large variability of results, mostly driven by differences in productivity rates and
technology pathways. Furthermore, methodological differences, such as system
boundaries, core LCA assumptions, coproduct allocation methods, energy mixes,
and inventory data, can all significantly contribute to the variability of LCA results.
The majority of these studies have focused on traditional lipid extraction systems,
while others considered utilized thermochemical conversion, secretion, or supercritical water bio-oil recovery technologies (Quinn and Davis 2015). A compilation of
these studies reported greenhouse gas emissions ranging from À95.7 to 534 g CO 2 -
eq/MJ, all with a well-to-pump (WTP) system boundary (Quinn and Davis 2015).
Studies surveying thermochemical conversion, specifically hydrothermal liquefaction (HTL), showed GHG emissions as low as À44 g CO 2 -eq/MJ and as high as 33 g
CO 2 -eq/MJ (Frank et al. 2013; Liu et al. 2013). The lowest result among all studies
was reported by Ponnusamy et al. (2014), which considered a supercritical water
technology for lipid recovery. Most LCAs of biofuels exclude infrastructure from
their system boundaries. However, both Adesanya et al. (2014) and Canter et al.
(2012) studied the integration of facility construction-related impacts, with the latter
focusing solely on infrastructure associated emissions. Results from these studies
showed that infrastructure can have significant impacts on GHG emissions
depending on yields.
296
J.-H. Hwang et al.
and lipid extraction – altogether creating 16 unique production pathways. Impacts
evaluated were fossil fuel use, GHG emissions, eutrophication, and water use.
Overall, the results showed that wastewater-based algal biofuels had lower environmental impacts than freshwater-based fuels, depending on the characteristics of the
wastewater and the conversion technologies. Although both did not generally
perform better than petroleum diesel, the centrate cultivation with wet lipid pathway
and the centrate cultivation with combustion pathway had lower impacts across all
impact categories compared to petroleum diesel. Yang et al. (2011) specifically
focused on the life cycle water and nutrients usage of biofuels from microalgae.
They estimated that in the case of algal biodiesel from freshwater, 3726 kg of water
is needed to produce 1 kg of biodiesel, if no water is recycled. Recycling water can
significantly reduce life cycle consumption of nitrogen, phosphorous, potassium,
magnesium, and sulfur. Furthermore, wastewater-based biofuels can reduce nitrogen
impacts by 94% and do not require potassium, magnesium, and sulfur (Yang
et al. 2011).
Most LCA studies on algal products have focused on quantifying the global
warming potential, net energy ratio (NER), and the energy return on investment
(EROI). There have been several LCA studies of microalgal biofuels (Adesanya
et al. 2014; Azadi et al. 2014; Batan et al. 2010; Brentner et al. 2011; Campbell et al.
2011; Collet et al. 2014; Frank et al. 2011, 2013; Grierson et al. 2013; Handler et al.
2014; Liu et al. 2013; Passell et al. 2013; Ponnusamy et al. 2014; Quinn et al. 2014;
Shirvani et al. 2011; Sills et al. 2013; Soh et al. 2014; Vasudevan et al. 2012; Woertz
et al. 2014). As with LCAs of emerging technologies and energy systems, there is a
large variability of results, mostly driven by differences in productivity rates and
technology pathways. Furthermore, methodological differences, such as system
boundaries, core LCA assumptions, coproduct allocation methods, energy mixes,
and inventory data, can all significantly contribute to the variability of LCA results.
The majority of these studies have focused on traditional lipid extraction systems,
while others considered utilized thermochemical conversion, secretion, or supercritical water bio-oil recovery technologies (Quinn and Davis 2015). A compilation of
these studies reported greenhouse gas emissions ranging from À95.7 to 534 g CO 2 -
eq/MJ, all with a well-to-pump (WTP) system boundary (Quinn and Davis 2015).
Studies surveying thermochemical conversion, specifically hydrothermal liquefaction (HTL), showed GHG emissions as low as À44 g CO 2 -eq/MJ and as high as 33 g
CO 2 -eq/MJ (Frank et al. 2013; Liu et al. 2013). The lowest result among all studies
was reported by Ponnusamy et al. (2014), which considered a supercritical water
technology for lipid recovery. Most LCAs of biofuels exclude infrastructure from
their system boundaries. However, both Adesanya et al. (2014) and Canter et al.
(2012) studied the integration of facility construction-related impacts, with the latter
focusing solely on infrastructure associated emissions. Results from these studies
showed that infrastructure can have significant impacts on GHG emissions
depending on yields.
296
J.-H. Hwang et al.