Imagine a world in which your poo could become one of the most sought-after resources on the planet.
There are some strong mental images flying around in all the talk around sustainable aviation fuel (SAF). One report for campaign group Transport and Environment has noted that just one transatlantic flight’s worth of biofuel would require 8,800 dead pigs worth of fat. No matter how you feel about vegetarianism, 8,800 pig carcasses is surely an unpleasant idea. But, if you thought that was a striking notion, how about jets burning human excrement?
Firefly Green Fuels, an aviation company based in the idyllic rural county of Gloucestershire, UK, is proposing powering planes with poo. Human poo. And it’s a concept making people sit up and pay attention.
Sewage is a relatively unexplored resource when it comes to the production of SAF, but, as Firefly Green Fuels CEO James Hygate put it, talking to CNN: “There’s loads of it, it’s everywhere in the world and there’s not really any good use for it at the moment which makes a very low-value material.”
Of course, you can’t just burn raw sewage to fuel jet planes. To turn human excrement into a usable fuel, you need to process it, through “hydrothermal liquefaction”. Exposed to high pressure and heat, sewage convertsinto carbon-rich “biochar” (a powder that can be used as a crop fertilizer) and crude oil.
Laboratory tests, while small scale, have demonstrated positive early outcomes. Independent analysis by EU and US university researchers have shown poo biochar to have almost identical properties to standard fossil jet fuel. The UK’s Cranfield University has found through life cycle analysis that it also has a 90% lower carbon footprint than standard jet fuel.
It’s often pointed out that “sustainable” aviation fuel could be argued to be a misleading misnomer, since burning SAF produces the same quantity of emissions while a plane is flying, as fossil fuel.
However SAF does actually have a smaller carbon footprint. This is because burning traditional fossil fuels releases C02 that would otherwise remain locked away in fossils. Burning plant matter or human poo made from plants and other products eaten by humans, simply re-releases C02 that has been absorbed during their lifecycle.
Scaling up is a big problem when it comes to SAF, but Firefly is set to apply for the necessary processing permissions from ASTM International this year. If they are awarded, a UK processing facility will be built and come into operation by 2030.
Hygate says that from 100,00 tons of biocrude oil, Firefly could produce 40 million litres of SAF, enough for 800 flights from London to New York. According to current market data, that’s less than a month’s worth of the long-haul journeys, so we will all need to up our fibre intake if we want to carry on flying as much as we do now.