NEW YORK - Humans dump an estimated 10 billion gallons of potential biofuel into landfills every year. Researchers found a way to capitalize on it.

For many uses, liquid fuels remain the most practical energy supply—aircraft and large ships being obvious examples. It's possible to produce biofuels for these applications. But so far no one's been able to do that at a competitive price, leaving fossil fuels as the dominant option.

With the increasing demand for net-zero sustainable aviation fuels (SAF), new conversion technologies are needed to process waste feedstocks and meet carbon reduction and cost targets. 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.

Here, we evaluate the catalytic conversion of food waste–derived VFAs to produce n-paraffin SAF for near-term use as a 10 vol% blend for ASTM “Fast Track” qualification and produce a highly branched, isoparaffin VFA-SAF to increase the renewable blend limit. VFA ketonization models assessed the carbon chain length distributions suitable for each VFA-SAF conversion pathway, and food waste–derived VFA ketonization was demonstrated for >100 h of time on stream at approximately theoretical yield. Fuel property blending models and experimental testing determined normal paraffin VFA-SAF meets 10 vol% fuel specifications for “Fast Track.”

Synergistic blending with isoparaffin VFA-SAF increased the blend limit to 70 vol% by addressing flashpoint and viscosity constraints, with sooting 34% lower than fossil jet. Techno-economic analysis evaluated the major catalytic process cost-drivers, determining the minimum fuel selling price as a function of VFA production costs. Life cycle analysis determined that if food waste is diverted from landfills to avoid methane emissions, VFA-SAF could enable up to 165% reduction in greenhouse gas emissions relative to fossil jet.

Over 21 billion gallons of jet fuel are consumed in the United States annually, with demand expected to double by 2050. The aviation sector accounts for 2.5% of global greenhouse gas emissions, with airlines committing to reduce their carbon footprint by 50% before 2050. 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%, which can significantly impact the net global warming potential. Soot is the primary nucleator of aviation-induced contrails, which have a larger effective radiative forcing (57.4 mW/m2) than aviation-emitted CO2 alone (34.3 mW/m2).

The one issue here is that there are many circumstances where the food waste wouldn't be allowed to release methane into the atmosphere anyway. A lot of it serves as feedstock for biodiesel production, so it would be diverted before it reached a landfill. And there are now landfills that capture the methane they would otherwise release and use that for power generation. So the jet fuel production might end up in competition with the food waste being used for other carbon-neutral fuel processes.