Aviation Fuel Developers Ponder Macro vs. Microalgae

by Jacob Dykes, geographical.co.uk

The 23 countries participating at the inaugural meeting of the International Aviation Climate Ambition Coalition at COP26 in Glasgow last November committed to reducing aviation’s CO₂ emissions in line with a 1.5º C future. Now, the race is on to achieve carbon-neutral flight.

Thomas Brück, professor of synthetic biotechnology at the Technical University of Munich (TUM) is leading a collaboration between TUM’s AlgaeTec Center and Airbus to produce aviation biofuel from microalgae.

Dr. Brück’s team has already tested its fuel with Airbus’s planes. “There’s an efficiency advantage as the fuel can be co-designed with lightweight carbon-fiber materials, capable of achieving carbon-neutral flight,” he says. When algae-based biofuels are burned, they will release greenhouse gases into the atmosphere, but the process is touted as carbon neutral because that carbon is drawn down during the algae’s growth phase.

Kelp is another frontrunner as a fuel solution. It can be grown at sea, removing the need to convert arable land, and advocates point to the fact that it can be put to work using the petrochemical industry’s existing refining infrastructure. “Kelp forests also support diverse marine ecosystems, which in turn remove additional carbon from the atmosphere, enriching coastal areas with marine life,” says Cindy Wilcox, co-founder, president, and chief engineer at California-based Marine BioEnergy, which is currently working on kelp-based biofuels.

Through what it calls a “depth cycling” technique — in which kelp is grown in the nutrient-rich oceanic depths — Ms. Wilcox’s company claims to have quadrupled traditional kelp yields. She claims that a mere 0.5 percent of the world’s ocean would be required to cultivate enough kelp to replace all fossil-fuel-driven long-haul road vehicles and airplanes.

Dr. Brück, however, is sticking to the smaller organisms. “Macroalgae such as sea kelp are very good carbon sources. However, because of the seasonal growth, there’s a time period in which there’s little productivity,” he says. “Microalgae have three to four times higher photosynthetic efficiency than terrestrial plants, and if grown in a saline environment, will be less prone to contamination.”

Whether either of these approaches will really work is likely to come down to cost. Most people believe that scaling up any clean aviation fuel will require a green premium placed on it by governments. According to Dr. Brück, algae-based biofuels are becoming increasingly cost-competitive, but “mass cultivation means new infrastructure. That’s the major economic hurdle for the industry right now.”

With aviation innovation stated as an ambition at COP26, technologists such as Dr. Brück and Ms. Wilcox hope that governments will inject the sector with support in 2022 in order to get clean planes airborne.