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| Fig. 1: A raceway pond used in the production of microalgae. (Source: Wikimedia Commons) |
The term "biofuel" refers to fuels produced from biorenewable and combustible feedstocks. As the world population continues to rise, and fossil fuel supply remains relatively stagnant, every alternative source of energy must be explored. Biofuels are a viable source, and can be produced from cultivating algae. Like other sources of biofuels, the burning of algae produces large amounts of carbon dioxide, which in turn is used in the photosynthetic process of growing more algae, and thereby creating a closed system. [1]
While biofuels still encompass about 1% of global energy production, they are still a reliable option for some level of replacement of fossil fuels. However, scaling the production of biofuels, especially from algae, is costly, and thus the stunted expansion of a shift towards microalgal biodiesel.
Algae has always been perceived as a promising source of protein, and has been cultivated mainly for the purpose of human consumption. German scientists at the time of World War II were the first to begin cultivating algae on a large scale in open ponds, and in the early 1950s, the first attempts in the U.S. were led by the Stanford Research Institute. Under certain conditions, algae can produce lipids that are suitable for chemical transformation to liquid fuels. The oil embargo of the 1970s sparked a 20-year research endeavor for biofuel production from algae. [2]
For various reasons, algal biofuels are considered advantageous in contrast to fossil fuels. While a lot of the advantages could be true for most biofuels, some of the key arguments specifically using algal biofuels are listed below: [3]
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| Fig. 2: The transesterification of triglycerides using alcohol. |
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| Fig. 3: The entire process map of producing biodiesel from algae. Source: Nadiv Rahman |
High biomass productivity. Microalgae have been demonstrated to possess higher efficiency is photosynthesis and adaption to stressful conditions. Many microalgal species exist as single cells, or simple clusters of cells, and this simpler structure allows the species to grow lipid production and starch collection at a faster rate.
High oil yields. Microalgae contain storage oils at more than 50% of dry cell weight. They are also capable of producing more lipids under stress conditions, such as a nitrogen deficiency.
Less usage of arable land and fresh water. The ability to cultivate microalgae in a diverse range of atmospheres means less arable land and fresh water sources have to be used up in its production.
Besides these benefits, the reliability of algae as a consistence source of fuel, and reduction in greenhouse gas emissions, make algae an attractive option. Furthermore, considering that most algae would be cultivated in rural areas, it adds economic incentives in the way of more jobs, and possible tax revenue.
The chemical process by which lipids in microalgae are converted to biodiesel is known as transesterification. The process, using alcohol as a catalyst, is described by the equations to the right (Fig. 2). The entire process itself is made up of several stages, as delineated in the diagram below that (Fig. 3) [2]
The fraction of world fuel supply made up of biodiesel has been decreasing ever since the 18th century. However, with energy scarcity an ubiquitous problem, biofuels, and especially those produced from microalgae, are still an important source to consider. Algae can produce up to 300 more oil per acre than other tradition vegetation sources (such as palm, soy etc.), and with a harvest cycle of about 1-10 days, it can have a very speedy production schedule. [4]
Algae can be produced in wastewater, sewage, oceans, rivers, and ponds, and have no environmental consequences if burned or spilled, making it a truly "green" alternative. However, the high cost of production keeps it from being further developed, and the Aquatic Species Program funded by the US Department of Energy (1978) was shut down in 1996, closing down a large initiative for research towards exploiting microalgae for our energy needs.
© Nadiv Rahman. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] F. H. Cocks, Energy Demand and Climate Change (Wiley-VCH, 2009).
[2] A. Demirbas and M. F. Demirbas, Algae Energy: Algae as a New Source of Biofuel (Springer, 2010).
[3] Y.-F. Chen and Q. Wu, "Production of Biodiesel from Algal Biomass: Current Perspectives and Future," in Biofuels: Alternative Feedstocks and Conversion Process, ed. by A. Pandey et al. (Academic Press, 2011), p. 399.
[4] H. C. Greenwell et al., "Placing Microalgae on the Biofuels Priority List: a Review of the Technological Challenges," J. Roy. Soc. Interface 7, 703 (2010).
