Microalgae has been touted for the last few decades as a panacea for the world’s energy crisis, specifically our dependency on oil. At first, there was good reason to be optimistic. Compared to other biofuels, microalgae promises to be highly efficient based on its yield, as defined by the biomass in a given unit of surface area (5 to 10 grams of biomass per meter squared of surface area is typical.) Additionally, microalgae is relatively easy to produce because it can be harvested in a natural environment similar to the one in which it grows (microalgae can flourish in ponds one feet deep). The oil content in microalgae is also extremely high compared to other crops. Studies indicate that approximately 15,000 square miles, or roughly half the size of Maine, is required to sustain all the microalgae needed for the U.S. energy needs for an entire year. Nevertheless, microalgae has yet to become a viable commercial alternative to fossil fuels mainly because of the costs of providing for even a small biomass. Regardless of the method used, problems include the difficulty of ensuring that the same species thrives in a given culture (other species can form a colour gradient leading to a difficulty in photosynthesis and a reduction in output) and the relatively low yield of algal oil when used as a biofuel.

Microalgae has been used successfully to deal with other environment-related issues. As one example, microalgae can be grown in ponds where it can collect runoff fertiliser; this “fertiliser-enhanced” microalgae can then be used as fertiliser, thereby leading to a reduction in overall crop-production costs. Other uses of microalgae relate to eco-efficiency, meaning that it helps reduce the negative environmental impact that inevitably results from certain industrial processes. For example, microalgae can be used in water-treatment facilities to limit the amount of chemicals needed. More significantly, microalgae is able to absorb the CO2 emissions from coal factories, one of the world’s most commonly used fossil fuels, and one that is most damaging to the environment. Again, convenience explains much of microalgae’s appeal; in this case, a microalgae farm needs to be placed in close proximity to coal-producing plant to absorb much of the CO2 emissions.

Because of such multifaceted uses, microalgae has continued to be part of the conversation around biofuel production over the last several decades, despite the lack of any innovations in microalgae production that might lead to a viable commercial product.  The best established methods of traditional microalgeal oil harvesting, centrifugation, filtration, and flocculation, all have issues with cost and efficiency. Centrifugation requires the rapid rotation of water containing microalgae, via a spinning motor which consumes energy at a high rate. Filtration is not-so energy intensive, but only larger species of microalgae can be caught in filters for the purposes of oil separation. Flocculation, the adding of chemicals in the algae to separate them from both water and oil through a sedimentation process in which the microalgae sinks to the bottom of the water, poses a different problem: the chemicals, once added, make the energy yield of the oil much lower, and flocculation agents are very hard to remove after the fact.  While it might be easy to be skeptical of any new innovations and discount microalgae as a perennial allurement, a number of recent breakthroughs are showing a far more promising path to full-scale viability.

Perhaps the most promising method of utilising microalgae’s biofuel potential is “floatation harvesting,” in large part because of its low energy cost and ease of maintenance. Other methods require frequent harvesting and are known to researchers as being “extensive and expensive”. Floatation, by contrast, involves the creation and injection of microscopic gas bubbles that stick to destabilised molecules in the microalgae, “pulling” these molecules to the surface to form a concentrate. The efficiency of floatation is also aided by the effect of gravity, which pulls water from the concentrate. In this sense, floatation is an inversion of sedimentation; floatation is preferable in that it works in conjunction with nature, since microalgae tends to float rather than settle, thereby requiring far less oversight yet leading to a thicker microalgeal concentrate.

Given the history of converting microalgae into a biofuel, researchers are reluctant to hail floatation as the “magic bullet” that has long eluded scientists. In addition to the problems outlined above, researchers cite several other issues, including the reduction of efficacy when diverse species of microalgae are present and the need for coagulants to neutralise the surface charge of microalgae to make it hydrophobic, so as to prevent toxicity of the biomass.