The search for sustainable aviation fuel (SAF) has led researchers into the realm of lavatories with the intent of exploiting sewage as an aviation propellant.

U.K.-based Firefly Green Fuels is sourcing sewage sludge from water companies to be refined through a hydrothermal liquefaction process. The resulting bio-crude can be refined into jet fuel and the biochar produced can be exploited by the agricultural sector as a fertilizer.

Testing has confirmed that the fuel has a carbon intensity of 7.97 g of carbon dioxide/megajoule, which represents a 90% lower carbon footprint relative to conventional aviation fuels. Assays have also demonstrated that the waste-derived SAF is nearly identical to standard A1 jet fuel.

While not yet available commercially, the company is on track to deliver this fuel to the global market and expects to have its first commercial plant operating within five years. Firefly Green Fuels has also entered into a partnership with the aptly named airline Wizz Air to supply it with fuel starting in 2028.