Producing biofuels from algae is still in a pre-commercial state of technology development. But algae-based biofuels are considered to be a promising upcoming alternative to fossil fuels as they could reduce GHG emissions when compared to fossil fuels, and because algal biofuels may have additional advantages over traditional biofuels such as higher per acre yields and less competition for arable land. The main obstacle to a wide spread use of algae-based biofuels are the high production costs. A number of research initiatives are working on improving the production processes and decreasing costs.
Algae include a diverse group of microorganisms and occur in a variety of natural habitats, including terrestrial habitats such as soil and aquatic habitats ranging from freshwater and brackish waters to marine and hyper-saline environments (US DOE, 2010). Biofuel from algae may be produced from microalgae, macroalgae, i.e. seaweed, or cyanobacteria. Cultivation of microalgae and cyanobacteria can be done through so-called photoautotrophic methods in open or closed ponds or through heterotrophic methods. Photoautotrophic refers to the fact that in these processes algae need light to grow and generate new biomass. In a heterotrophic process, algae are grown without light and feed on carbon sources, for example sugars, in order to create new biomass (US DOE, 2010).
Macroalgae, i.e. seaweed, require different cultivation methods. Macroalgae cultivation is normally done in open off-shore or coastal installations (US DOE, 2010)
There are a large number of potential pathways for generation of biofuels from algal biomass, some of which are similar to conversion processes used for traditional biofuels. It is possible to distinguish three types of pathways:
- Processing extracts from algae such as lipids or carbohydrates to generate fuel molecules. This is the most typical approach used today, and produces mostly biodiesel (US DOE, 2010). Most frequently, oil is extracted from the algae biomass, e.g. through an oil press, and then, through a transesterification process, biodiesel is generated from the algae oil.
- It is also possible to process the whole algal biomass into fuels (or biogas) using similar processes as applied for traditional biofuels such as pyrolysis or gasification.
- In addition, in heterotrophic fermentation processes, algae can also directly produce fuel molecules such as ethanol, hydrogen, methane, and alkanes (US DOE, 2010).
To grow optimally, microalgae need specific environmental conditions in terms of light, temperature ranges, CO2 concentrations, nutrient compositions and salinities. The required environmental conditions differ widely among algae species (Alabi et al., 2009). Very generally speaking, regions with a high number of hours of sunshine per year, few freezing days, high average temperatures and high availability of water have the most suitable climate for microalgae cultivation.
Today, the main barrier to the production of biofuels from algae is costs (see for example Alabi et al., 2009; Lundquistl et al., 2010).
Specifically for developing countries, additional considerations include (van Iersel et al., 2009):
- Producing algae for biofuels (excluding simple seaweed production) requires significant capital investments, which may be a significant barrier in countries with weak investment climate.
- Producing biofuels from algae is still in a pre-commerical state of technology development. Most production plants are therefore prototypes, and the development and engineering of such plants requires a high level of expertise. Similarly, R&D efforts for example with the aim to increase the productivity of algae production or to reduce production costs, also requires a high level of knowledge and experience.
- While operation and maintenance itself, as well as processing of algae biomass are not expected to require very specific knowledge, planning of economic viability and of plant productivity remains a challenge.
- Large-scale facilities are more economically competitive, but there is a higher likelihood of social and environmental impacts.
Biofuels from algae are in the R&D and demonstration stage of technology development. Activities supporting the development of algae-based biofuels have increased significantly over the past 3 to 5 years.
In October 2008, the UK based Carbon Trust launched for example a large program to support the development of algae biofuels, called the Algae Biofuels Challenge (Carbon Trust, 2009 & 2010). The program is planned in 2 stages, the first of which, from 2008 until 2011, will address fundamental R&D challenges, while the second one from 2012 to 2015 has the aim to demonstrate large-scale production of algae oil.
The US government, via the Department of Energy had funded the so-called Aquatic Species Program from 1978 to 1996 with the aim of illustrating the potential of algae as a feedstock for biodiesel (US DOE, 2010). The main focus of the program lay in producing biodiesel from high lipid-content algae which were grown in ponds, utilizing waste CO2 from coal fired power plants (NREL, 1998). 13 years later, the DOE revived its investment into research, development, and demonstration (RD&D) projects addressing the technical hurdles for commercializing algae-based biofuels (US DOE, 2010).
Researchs on biofuels from algae is also ongoing in some major developing countries such as China and India.
Producing biofuels from algae instead of traditional biofuel sources such as corn, sugar cane or palm oil may offer several benefits, including
- Algae may offer higher biomass yields per acre of cultivation than traditional biofuels.
- Algae cultivation may minimize or avoid competition for arable land used for conventional agriculture and food production.
- Algae may be grown using waste water, and saline water, which may reduce competition for limited freshwater supplies.
- Algae can recycle carbon, for example by using CO2 from stationary sources, such as power plants and other industrial emitters (US DOE, 2010).
In adition, producing biofuels from algae may have similar benefits as traditional biofuel production including increasing energy security and decreasing the dependence on imported fossil fuels.
The GHG impact of producing biofuels from algae is still contended. Generally, it is assumed that over the whole life-cycle of the fuel, biofuel from algae have a lower GHG impact than fossil fuels, and have an additional advantage of lower GHG emissions when compared to traditional biofuels produced from corn, sugar cane or palm oil.
However, some recent studies show less positive GHG balances for algal biofuel. Clarens et al. (2010), for example, compared open pond algae production with the production of bioenergy from corn, canola and switch grass in Virginia in the US and found GHG emissions to be highest for algae cultivation while the three other approaches were found to sequester GHG emissions. However, later comments in the same journal (Subhadra, 2010; Starbuck, 2011) criticize some of the assumptions made by Clarens et al. (2010), suggesting that their results are overly negative for algal biofuels.
Other studies do show a positive GHG balance for algae based biofuels. Luo et al. (2010), for example, find that the production of ethanol through cyanobacteria leads to reduction in carbon footprint of between 67% and 87% when compared to fossil fuel based gasoline.
Further research based on the latest production methods and on expected future technical and biological improvements is needed to gain clarity.
Production costs for biofuel from algae are not yet competitive with fossil fuels or with conventional biofuels. Most of the ongoing R&D efforts ultimately aim at reducing these costs.
In 2010, the Energy Biosciences Institute of the University of Berkeley, California has published an estimate of overall costs of production (including capital costs, operating expenses and potential credits for electricity production and wastewater treatment) of biofuel produced from microalgae assuming five different cases (Lundquistl et al., 2010). The examples differ in their plant size, primary process objective, i.e. either wastewater treatment with biofuels as byproducts or biofuel production with treated wastewater as a byproduct, and the process outputs, i.e. either oil plus biogas or biogas only. The study concludes that according to the analysis undertaken, when biofuel production is a byproduct of wastewater treatment, it is highly economically with production costs of US$ 28/barrel of oil. When biofuel production is the main process objective, however, production costs are still very high with between US$ 240/barrel or US$ 332/barrel depending on plant size.
The researcher at the University of Berkeley (Lundquistl et al., 2010) see the biggest potential for long-term production cost decreases in biological improvements, e.g. in at least doubling the algae’s productivity in terms of biomass and oil production. This may be achieved through strain selection and genetic modification. Additional costs reductions could come from cheap harvesting, reliable cultivation in outdoor ponds, engineering improvements in system components such as in reactor construction, harvesting, dewatering, and oil recovery.
Algae producing companies have announced much more aggressive price targets. While industry sources report current prices which are even higher than the ones suggested by the Energy Bioscience Institute at around $9-$30 per gallon ($378-$1260/barrel) (BiofuelsDigest, 2009), Aurora Biofuels, for example, has stated that the company targets full production cost of $1.30/gallon ($55/barrel) in the coming years (BiofuelsDigest, 2009b).
The research program initiated by the Carbon Trust (2010) aims at a five to ten-fold reduction in open pond algae production costs until a level where algae biofuels can be sold as a premium fuel blend in UK by 2020.
Alabi, A.O., M. Tampier, Bibeau, E. (2009). Microalgae technologies and processes for biofuels/bioenergy production in British Columbia: Current technology, suitability and barriers to implementation. Final report submitted to the British Columbia Innovation Council. Seed science, January, 2009. Available at http://www.bcic.ca/images/stories/publications/lifesciences/microalgae_report.pdf
BiofuelsDigest (2009). One billion gallons by 2014: algal fuel price, capacity projections. June 22, 2009. Available at http://www.biofuelsdigest.com/blog2/2009/06/22/biofuels-digest-algae-fuel-price-capacity-projections-for-2009-2014/
BiofuelsDigest (2009b). Aurora Biofuels: In Florida, the panther roars as a little-seen algae producer targets $1.30 algae fuel “at the gate”. March 12, 2009. Available at http://biofuelsdigest.com/blog2/2009/03/12/aurora-biofuels-in-florida-the-panther-roars-as-a-little-seen-algae-producer-targets-130-algae-fuel-at-the-gate/
Carbon Trust (2009). Algae – Fuelling the future. Biofuels case study CTS155. Available at http://www.carbontrust.co.uk/SiteCollectionDocuments/Various/Emerging%20technologies/Current%20Focus%20Areas/Algae/Fuelling%20the%20future%20case%20study.pdf
Carbon Trust (2010). Algae Biofuels Challenge. Available at http://www.carbontrust.co.uk/emerging-technologies/current-focus-areas/algae-biofuels-challenge/pages/algae-biofuels-challenge.aspx
Clarens, A., E.P. Resurreccion, M.A. White, L. M. Colosi (2010). Environmental Life Cycle Comparison of Algae to Other Bioenergy Feedstocks. In Environ. Sci. Technol., 2010, 44 (5), pp 1813–1819. Available at http://pubs.acs.org/doi/pdf/10.1021/es902838n
van Iersel, S. et al. (2009). Algae-based Biofuels: A Review of Challenges and Opportunities for Developing Countries. Ecofys, Global Bioenergy Partnership, FAO. Aailable at ftp://ftp.fao.org/docrep/fao/011/ak333e/ak333e00.pdf
Lundquistl, T.J., I.C. Woertz1, N.W.T. Quinn, J.R. Benemann (2010). A Realistic Technology and Engineering Assessment of Algae Biofuel Production. Energy Biosciences Institute, University of California, Berkeley. October 2010. Available at http://www.energybiosciencesinstitute.org/media/AlgaeReportFINAL.pdf
Luo, D., Z. Hu, D.G. Choi, V.M. Thomas, M.J. Realff, R.R. Chance (2010). Life cycle energy and greenhouse gas emissions for an ethanol production process based on blue-green algae. In Environ Sci Technol. 2010 Nov 15;44 (22) : 8670-7. Available at http://www.ncbi.nlm.nih.gov/pubmed/20968295
Subhadra, B.G. (2010). Comment on “Environmental Life Cycle Comparison of Algae to Other Bioenergy Feedstocks”. In Environ. Sci. Technol., 2010, 44 (9), pp 3641–3642. Available at http://pubs.acs.org/doi/full/10.1021/es100389s
Starbuck, C.M. (2011). Comment on “Environmental Life Cycle Comparison of Algae to Other Bioenergy Feedstocks”. In Environ. Sci. Technol. 2011, 45, 833. Available at http://pubs.acs.org/doi/pdf/10.1021/es103102s
US Department of Energy (DOE) (2010). National Algal Biofuels Technology Roadmap. U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Biomass Program. Available at www1.eere.energy.gov/biomass/pdfs/algal_biofuels_roadmap.pdf