In addition to being economically viable, biofuels from microalgae must also meet life cycle targets to provide quantitative improvements to current fuels. The key elements typically considered in life cycle assessment of biofuels include:

• Energy—Usually the net energy ratio (NER), that is, does it require more energy to produce the fuel than is available in the fuel.

• Greenhouse gas—Are the net greenhouse gas emissions lower than fossil fuels or current biofuels.

• Water use—How many litres of water are consumed to produce a litre of biofuel.

The key motivation for asking these questions is whether or not the proposed process is sustainable. A range of LCA is reviewed in de Boer et al. (2012) with a focus on energy consumption. These are provided in Table 17.5.

The motivation for analysing energy is that the energetic viability is very closely linked with the economic viability. That is, it is almost impossible to have a process which is economically viable when the process uses more energy than it produces. The review of the LCA studies shown in Table 17.5 leads to the following conclusions:

• IF PBR’s are used, then cultivation is typically the major energy user

• If raceway ponds are used, the major energy user is either dewatering, cell disruption or solvent extraction.

These conclusions suggest that an energetically viable process must use raceway ponds, process wet biomass (avoid drying), minimise energy required for cell disruption and minimise solvent recovery. Evaluation of different approaches by de Boer et al. (2012) indicated that hydrothermal liquefaction and wet processing methods with limited cell disruption were energetically feasible. This aligns with the processing focuses of the American laboratories as they process wet (fermen­tation and hydrothermal liquefaction) and do not use cell disruption.

As a final note, it is important to continually evaluate the key life cycle criteria (greenhouse gas emissions, net energy ratio and specific water consumption) in addition to the techno-economic analysis. This is simply because the lowest costs solution is not always the most sustainable.

Paper	Growth	Dewatering	Extraction	Conversion	Major energy consumption components
Batan et al. (2010)	PBR	Centrifugation	Solvent	Transesterification	PBR and solvent extraction
Brentner et al. (2011)	Flat plate PBR	Flocculation (Floe.)	Supercritical methanol transesterification of wet biomass	PBR
Lardon et al. (2009)	ORP	Floe., rotary press and drying	Solvent	Transesterification	Lipid extraction (90 % of energy dry, 70 % wet)
Razon and Tan (2011)	Flat plate PBR + ORP	Gravity and microfiltration	Bead mill and decanter	Transesterification	PBR and Bead mill
ORP	Floe., thickener and drying (belt dryer)	Solvent	Transesterification	Drying
Sander and Murthy (2010)	PBR + ORP	Filter press or centrifuge and drying	Solvent extraction	Transesterification	Dewatering and drying
Xu et al. (2011)	ORP	Floe., centrifuge, mechanical dehydration	Cell disruption, drying solvent	Transesterification	Dewatering and drying
Solvent (Bligh and dyer)	Flydro treating	Solvent extraction
Stephenson et al. (2010)	PBR	Floe.	Flomogenisation and solvent extraction	Transesterification	Cultivation in PBR
ORP	Floe, and centrifugation	Flomogenisation and solvent extraction	Transesterification	Cultivation

Table 17.5 Major energy consumption components in life cycle analysis studies (de Boer et al. 2012)

362 K. de Boer and P. A.

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17.3 Conclusion

This work provides a review of the economic and energy attributes of microalgae biofuels. The clear outcome of this analysis is that the economics of microalgae biofuels need to improve substantially before they can compete with current fuels. In addition to this, the challenges faced in reaching the metrics are productivity and capital cost and there are other barriers, including:

• The instability of algae monocultures and exposure to pests and viruses.

• The limited number of sites with access to the optimum climate, available land, low-cost CO2 source and abundant water.

• Competition from other options including biofuels from terrestrial crops, electric cars and unconventional fossil fuels.

Despite these substantial challenges, there is a very strong chance that micro­algae will become a source of liquid fuels into the future; however, this will be at a time when oil prices are higher, further development has driven costs down to suitable levels and there is strong markets for co-products. That is, microalgae biofuels are likely to form part of a solution to liquid transport fuels rather than being the ultimate solution.

K. Muylaert (H) • A. Beuckels • O. Depraetere • D. Vandamme Laboratory of Aquatic Biology, KU Leuven Kulak—University of Leuven,

Etienne Sabbelaan 53, BE8500 Kortrijk, Belgium e-mail: Koenraad. muylaert@kuleuven-kulak. be

I. Foubert

Research Unit Food and Lipids, Department of Molecular and Microbial Systems Kulak, KU Leuven Kulak, Etienne Sabbelaan 53, 8500 Kortrijk, Belgium

[2] Foubert

Leuven Food Science and Nutrition Research Centre (LFoRCe), KU Leuven, Kasteelpark Arenberg 20, 3001 Heverlee, Belgium

G. Markou

Department of Natural Resources Management and Agricultural Engineering, Agricultural University of Athens, Iera Odos 75, 11855 Athens, Greece

© Springer International Publishing Switzerland 2015

N. R. Moheimani et al. (eds.), Biomass and Biofuels from Microalgae,

Biofuel and Biorefinery Technologies 2, DOI 10.1007/978-3-319-16640-7_5

K. Muylaert (H) • D. Vandamme

Laboratory of Aquatic Biology, KU Leuven Kulak—University of Leuven,

Etienne Sabbelaan 53, 8500 Kortrijk, Belgium e-mail: Koenraad. muylaert@kuleuven-kulak. be

I. Foubert

Research Unit Food and Lipids, Department of Molecular and Microbial Systems Kulak, KU Leuven Kulak, Etienne Sabbelaan 53, 8500 Kortrijk, Belgium

[4] Foubert

Leuven Food Science and Nutrition Research Centre (LFoRCe), KU Leuven,

Kasteelpark Arenberg 20, 3001 Heverlee, Belgium

P. V. Brady

Sandia National Laboratories, Geoscience Research and Applications Group,

P. O. Box 5800, Albuquerque, NM 87185, USA © Springer International Publishing Switzerland 2015

N. R. Moheimani et al. (eds.), Biomass and Biofuels from Microalgae,

Biofuel and Biorefinery Technologies 2, DOI 10.1007/978-3-319-16640-7_12

[5]The information is summarised in DOE (2014); however, process economics data are drawn from Davis et al. (2014) for the ALU process and Jones et al. (2014) for the AHLT process. Harvest and dewatering numbers were taken from further work conducted on the original harmonisation report (ANL et al. 2012).