A new – ambitious – experiment demonstrating the ability of “wet” human waste (so like rotting food and sewerage) to power airplanes has just dropped. Pun intended.
The paper, undertaken by the U.S. National Renewable Energy Laboratory (NREL), claims that recycled fuel could vanquish airline emissions and reduce waste, creating a “165 [percent] reduction” overall. That represents about 4 percent of total greenhouse gases.
Apparently the secret is volatile fatty acids (VFA), converted from a waste product into paraffin, a popular combustible jet fuel ingredient.
“Over 21 billion gallons of jet fuel are consumed in the United States annually, with demand expected to double by 2050,” the researchers explain.
“Sustainable aviation fuels (SAF) comprise a significant portion of the aviation sector’s strategy for CO2 reductions given the limited near-term prospects for electrification. In addition, the low aromatic content of current SAF routes has been shown to reduce soot formation and aviation-related aerosol emissions by 50 to 70 [percent]. Soot is the primary nucleator of contrails, which have a larger effective radiative forcing (57.4 mW/m2) than aviation-emitted CO2 alone (34.3 mW/m2).”
Wet waste, which includes everything from flushed toilet water, to rotting food waste, to yes, your poop, is typically biodegradable, but still generates further waste—like the methane generated by landfills. This is harvested, but the process is inefficient. In their new study, the NREL scientists describe draining wet waste of water and then catalysing it into fungible (virtually identical and swappable one-to-one) hydrocarbons for airplane fuel.
“Wet waste is a low-cost, prevalent feedstock with the energy potential to displace over 20% of US jet fuel consumption; however, its complexity and high moisture typically relegates its use to methane production from anaerobic digestion. To overcome this, methanogenesis can be arrested during fermentation to instead produce C2 to C8 volatile fatty acids (VFA) for catalytic upgrading to SAF.”
So basically, in order to extract and blend to get more efficient, better-burning jet fuel that can safely replace a higher percentage of hydrocarbons in the final blend, the scientists took wet waste that’s typically turned into methane and slowed the process so that more complex hydrocarbons emerged.
It’s a huge improvement, and the cost is reasonable: “Techno-economic analysis for VFA catalyst upgrading determined VFAs can be produced at $0.30/kg to achieve a Fast Track minimum fuel selling price of $2.50/gallon,” the scientists explain.
So there you have it, you trip to the toilet could help your trip in the skies.