In the global effort to wean ourselves from fossil fuels, scientists have been looking towards algal biofuels as renewable sources of energy. Microalgae is capable of using sunlight and carbon dioxide to produce energy-rich molecules, create bioplastics, and act as a replacement to petroleum. Most current methods of growing the tiny plants are inefficient due to the large amounts of water and energy required, but Dr. Hail Berberoglu and Thomas Murphy from the University of Texas at Austin have developed a system that mimics the structure of trees called the Surface Adhering Bioreactor (SABR). By imitating the way vascular plants transport water and nutrients, they were able to greatly increase the efficiency of the cultivation process.
In the SABR, algae cells are grown as photosynthetic biofilms that are located on porous surfaces that keep them hydrated and supplied with nutrients. Once the biofilms have matured, nutrients are taken away and growth is stopped. The algae is then given the necessary inputs to photosynthesize and create the molecules desired by the researchers, such as fatty acids for fuel production. The energy-laden molecules are then transported away from the cells in a manner similar to how the veins of plants use evaporation to generate flow. After the biofilms have reached the end of their lifespans within a couple of months, new films replace them and the cycle continues over again. This allows solar energy, water and nutrients to be concentrated toward generating fuel and less on overall algal growth.
In several experiments comparing the SABR with a traditional suspended growth bioreactor, the scientists found that the SABR required 25 times less water. The suspended growth reactor needed 40 watts of power per cubic meter to mix the liquid culture of algae while the SABR needed none at all. In certain parts of the SABR, the growth rate of the cells were four times greater. However, the researchers are still working on minimizing water loss from the reactor, a challenge that even real trees face. Evaporation is responsible for much of the transport of nutrients and water, and the quicker evaporation moves the faster nutrients can be cycled. They hope to design the reactor to better retain water while also maximizing productivity.