With the exception of chemosynthetic life forms such as many of those who reside at the openings of deep-sea hydrothermal vents, the vast majority of biological energy has the sun to thank for its origins. Whether it be thermal, or through photonic collisions within the chloroplasts of plant cells, the energy of life comes from the sun. At a certain scale, the nonrenewable energy we use to meet our industrious needs, for the most part, can also be traced back to our solar system’s star. Even some of our renewable methodologies like solar, of course, or wind, more transitively. But what if there was a way to harness that biological energy, too? As odd as it may sound, that may not be too much a stretch of reality, and no, we aren’t talking about corn.
Algae, or simple photosynthetic aquatic plants, are believed to be a good source of renewable energy because of its rapid growth rate and its ability to be cultivated in wastewater or wasteland. Potential algal candidates double in as few as 6 h, and many exhibit two doublings per day. At the moment, one of the largest barriers, as is the case with virtually any new energy endeavor, lies in nonexistent infrastructure, operating costs, and commercial viability. That hasn’t stopped governments and corporations alike from working to make this a reality. As far as plants are concerned, algae are the fastest growing. That’s bullet point one in the “pro’s” column. Hypothetically, the potential exists for algae to produce more oil or biomass per acre when compared to other crops and plants. That’s fantastic news, but there are still questions of efficiency ratios and other possible ecological footprints of this developing technology such as water use.
Interest in accessing the energetic potential of algae first arose during the second world war when desperation and need were driving all sorts of innovations in technology and agriculture. It was during this time that algae began making their ways into our food and medical supply. Through years of study, it was deemed that their lipids would be an ideal feedstock for high energy density transportation fuels such as biodiesel, green jet fuel and green gasoline. The best part? Algae don’t require vast swaths of land like agricultural sources, there is no effect on food prices like there are with corn and ethanol. In addition, algae can grow in brackish or saltwater, therefore not depleting freshwater resources like corn does. Of course, algae also possess an intrinsic ecological function that appears to make them the golden goose of renewable energy–carbon sequestration. But how exactly does this sort of thing work?
Algae are a diverse group of single-celled microorganisms made up of the basic stuff of life: proteins, lipids, and carbohydrates. These lipids are especially valuable, able to be refined down to their composite fatty acids which could be further refined to biodiesel fuels. Biogas could be harvested from the process of anaerobic digestion. Fermentation of their carbohydrates could produce bioethanol. Heating up their biomass could produce different usable gasses, liquids, and solids. They can be used to produce usable methane gas. Or, of course, their biomass could be combusted directly to generate power. Clearly a plethora of opportunities, but not opportunities without cost—especially when looking at economical scale production.
Closing the cost gap requires an identification of most useful organisms or an alteration of desired traits, one of which is high lipid content. One such way of making high lipid content biomasses involves growing them under nutrient-limited conditions (especially nitrogen, phosphorous, or silicon). The problem then becomes that the organism within the biomass then sees reduced productivity. Then there is the question of production and cultivation scale. While some extremophile species are capable of handling more alkaline environments. Outside of those, mass cultivation of algae on open ponds has not been scaled up beyond 25 acres. Still, that’s 25 football fields of bioenergy production. Still, a less area-intensive approach is the real goal. Some have worked on developing closed photobioreactors, but their operation and maintenance costs are far too high to be economical. At this point, the potential is known and exists, but the unanswered questions haven’t exactly shrunk.
Nevertheless, no one is talking about an all-or-nothing approach to algal biofuels. Climate change solutions are just as multifaceted as its causes. Reversing and minimizing the effects of a changing climate will require a combination of strategies that can be employed that will substantially decrease our dependence on fossil fuels, and algae just may be a part of that solution. Algae is without a doubt the best option available for the production of biodiesel. In the US, total diesel needs could be entirely met by algae grown in an area of about 100,000 km^2, or about the land area of Iceland or South Korea with current levels of productivity and efficiency. When looking at the typical annual productivity of biodiesel from different plants per unit area of farming, algae leads by a landslide at 1700 10^3 L/km^2. That’s compared to the next highest being palm oil at 475, and coconut at 215. Time after time, new technologies arise with seemingly insurmountable barriers to true or attractive economical viability. Time and time again, innovation wins. No matter your measure, algae deserves serious consideration in the future of biofuel production.