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It sounds very absurd: kerosene from feces. Even for a cheap advertising slogan – which some budget airlines are not too keen on – it doesn’t seem very tempting. So what’s behind the announcement with which Europe’s third largest low-cost airline is attracting attention in expert circles? 

First the facts: Wizz Air, the rapidly expanding Hungarian low-cost airline, announced in April that it plans to use up to 525,000 tons of climate-neutral kerosene made from faeces from 2028. The company has contractually agreed this with the British start-up Firefly. Firefly has developed a process to produce sustainable fuel for aircraft from sewage sludge. Wizz Air wants to be the first airline to do this in four years. The number three behind Ryanair and Easyjet currently operates a good 200 Airbus aircraft, and the number is expected to reach 500 by the end of the decade.

This makes you sit up and take notice, because the enormous CO2 emissions are one of the biggest problems in aviation. Most experts see the solution to this in the use of sustainable fuel. Research institutions and companies have been working on the production of so-called Sustainable Aviation Fuels (SAF) for years. Many different processes are being tested, and the first aircraft with SAF additives are in use – including at Lufthansa. However, there is still no industrial standard and no large-scale production either. 

However, this will have to change in the foreseeable future, as the EU Commission has now massively increased the pressure: from next year, airlines in Europe will have to cover at least two percent of their fuel requirements with sustainable fuel. From 2030 it should be six percent, and then 70 percent in 2050. The production of sustainable fuel must therefore get going soon. To date, around 600 million liters of SAF have been produced worldwide, which corresponds to only around 0.2 percent of kerosene consumption. 

Fossil kerosene can be replaced – even with unusual substances such as chip fat or algae. In addition to plant-based raw materials, complex synthetic processes that do not use any natural resources are also being tested. While some waste materials or raw materials are only available in limited quantities or are simply too expensive, there are large quantities of faeces from households everywhere. “I don’t find this approach at all absurd,” says Ulf NEUE, project manager for fuels at the Agora Verkehrswende initiative, when asked by Capital. Sewage sludge is currently used as fertilizer in fields, but also to produce biological fuels.

Also aviation expert Dirk Niemeier, Director at Strategy

It is therefore worth taking a look at the process that Wizz Air’s British partner wants to use. Firefly plans to treat sludge from Britain’s sewage treatment plants using hydrothermal liquefaction. The wet waste is treated with high pressure and heat and is thus separated into crude oil and a powder. This powder can be used as fertilizer in the agricultural industry. The crude oil, in turn, is to be processed into sustainable aviation fuel. The start-up explained at the presentation that it is very similar to fossil kerosene and has been tested by expert laboratories in Great Britain, the EU and the USA. The fuel’s CO2 emissions are 92 percent lower than fossil fuels.

However, it still needs to be certified for use in aviation. The process is currently ongoing. If the authorities give their permission, it could well mean a breakthrough for feces in the tank. “The process is promising, well-tested in research and relatively inexpensive,” said Agora representative NEUER. “That would be progressive.” 

The product is not yet ready for the market. “Currently, the process is certainly still in its early stages and proof of economical large-scale implementation and approval for air traffic is still pending,” says Strategy

The question remains whether there is enough sewage sludge – or to put it another way: How far can the feces carry us? In Europe, according to Strategy