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| Fig. 1: Biofuel production from algae. (Source: Wikimedia Commons). |
Burning fossil fuels has been the worlds primary method of meeting our energy demands since the early 1900s. However, research into the use of coal, crude oil, and natural gas has revealed fossil fuels to be an increasingly problematic energy source and a primary driver of climate change. Further, fossil fuel supplies are both finite and declining given escalating energy needs. Climate change has driven rising environmental threats and resulting consequences on human health have prompted an ongoing pursuit for sustainable energy alternatives. One of the emerging possibilities is biofuels; in particular, algae offers a promising opportunity to leverage natures powerful process of harvesting the suns energy.
Algae is a photosynthetic organism which comes in two forms macroalgae, which are multicellular seaweeds including green, brown, and red algae, and microalgae, which are unicellular and exist independently or in a chain. Requiring only light, sugar, carbon dioxide, phosphorus, and potassium to grow, microalgaes are a particularly promising energy source given their high concentrations of energy-rich lipids, hydrocarbons, sugars, and carbohydrates. [1]
Third generation biofuels based on algal matter and cyanobacteria present a myriad of exciting advantages. Thriving in a variety of diverse and often otherwise unusable environments, algae can grow in non-arable land, freshwater, saltwater, brackish water, marine water, or even wastewater. [2,3] Their rapid growth rates and short harvesting cycle (~one to ten days) outpace many other biofuel alternatives, making them a promising opportunity to meet the worlds rising energy demands. Further, they have a higher photon conversion efficiency than many traditional biofuel sources. Algae biofuels also have an exceptional capacity to convert CO2 into biomass as well as liberate oxygen into the environment, producing both biofuels and desirable byproducts. [4]
Per unit area, microalgae produce roughly 15 - 300 times more oil for biodiesel production than conventional crops. [5] A multistep process is required to convert the organism to a usable biofuel, illustrated in Fig. 1. The remarkable versatility, rapid growth, and prolific biofuel production capabilities of algae present a promising solution to the global energy crisis.
In 2022, North America's energy consumption reached a staggering 113.7 exajoules. [6] Using Chlorella vulgaris as an exemplar species of microalgae, the following calculations demonstrate the quantity of algae required to store the energy equivalent to powering the globe. One kilogram of Chlorella vulgaris holds 21.3 MJ of energy. [7]
| Calculation 1: Quantity of algae required to store energy needed to power North America | ||||
| 113.7 Exajoules | = | 1.137 × 1020 J | ||
| 21.3 MJ kg-1 × 106 J MJ-1 | = | 2.13 × 107 J kg-1 | in Chlorella vulgaris | |
| 1.137 × 1020 J / (2.13 × 107 J kg-1) | = | 5.34 × 1012 kg | Chlorella vulgaris needed to meet North America's energy consumption |
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| Calculation 2: Quantity of algae required to store energy needed to replace natural gas in the United States. | ||||
| 29.76 Exajoules | = | 2.976 × 1019 J | ||
| 2.976 × 1019 J / (2.13 × 107 J kg-1) | = | 1.397 × 1012 kg | Chlorella vulgaris needed to replace United States natural gas as an energy source. |
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Algae remains a promising contender in the search for sustainable energy sources. However, its viability is constrained by the finite availability of solar energy and the massive scale of the worlds energy consumption. While algae-based biofuel production may be feasible on a smaller scale, the current limitations in solar energy flux render it impractical as a primary alternative to fossil fuels. Further, the demanding costs of agricultural management, harvesting, and processing restricts its ability to serve as an economically effective solution. Nevertheless, the prospect of utilizing algae as a biofuel presents the opportunity for further research and innovation to leverage this phylum to meet the worlds growing energetic needs.
© Mia Bennett. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. 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] M. A. Borowitzka and N. R. Moheimani, "Sustainable Biofuels From Algae," Mitig. Adapt. Strateg. Glob. Change 18, 13 (2013).
[2] M. Mofijur et al., "Recent Development in the Production of Third Generation Biodiesel From Microalgae," Energy Procedia 156, 53 (2019).
[3] S. P. Singh and P. Singh, "Effect of Temperature and Light on the Growth of Algae Species: A Review," Renew. Sustain. Energy Rev. 50, 431 (2015).
[4] P. M. Schenk et al., "Second Generation Biofuels: High-Efficiency Microalgae For Biodiesel Production," Bioenergy Res. 1, 20 (2008).
[5] Y. Chisti, "Biodiesel From Microalgae," Biotechnol. Adv. 25, 294 (2007).
[6] "BP Statistical Review of World Energy 2022," British Petroleum, June 2022.
[7] T. Minowa and S. Sawayama, "A Novel Microalgal System For Energy Production With Nitrogen Cycling," Fuel 78, 1213 (1999).
