‘All pieces in place’ for commercial sewage-based SAF

A COMPANY planning to produce sustainable aviation fuel (SAF) from sewage says it has “all the pieces now in place” to commercialise the technology after selecting a provider for a critical hydrothermal liquefaction (HTL) process.

Signed at a ceremony at the British Embassy in Türkiye, the agreement will see engineering firm Altaca provide its CatLiq-based HTL technology for Firefly Green Fuels' forthcoming commercial-scale plant. The facility will convert sewage-derived biosolids into jet fuel and is expected to be in operation from 2028/29.

HTL is a key part of Firefly’s process, converting wet sewage sludge into crude oil. In an interview with TCE earlier this year, Firefly CEO James Hygate described HTL as “like a pressure cooker”, pressurising and heating the water until it acts as both a reactant and reagent. Under these conditions, biosolids in the sewage break down into biocrude oil and biochar.

Sewage sludge is around 80% water, removal of which has historically been a significant barrier to using it as a feedstock for SAF. Altaca says their CatLiq process is optimised for wet alkaline waste.  

Firefly said it now possesses all the necessary components to scale production at its planned facility at the Harwich oil refinery in Essex, owned by Haltermann Carless, where Chevron Lummus Global technology will be used to refine biocrude into jet fuel. Hygate said the deal with Altaca allows them to “get to work on saving carbon by the gigatonne”.

Hygate added: “We’ve looked around the world and undertaken extensive testing to find the best-in-class supplier for this key technology – and found it in Altaca. Firefly exists to combat climate change by decarbonising aviation. With all the pieces now in place, we have an end-to-end platform and a new category of waste-to-fuels infrastructure.”

Altaca president Alper Önoğlu said: “We are thrilled that our hydrothermal liquefaction technology has been recognised as the final, crucial link in Firefly’s innovative supply chain. Our engineering solution provides the essential upstream step required to transform sewage sludge into high-quality bio-crude oil, enabling the production of truly sustainable aviation fuel.”

Fuelling debate

The deal between Firefly and Altaca was signed shortly after researchers warned that European Union legislation risks discouraging innovation in SAF production from biobased feedstocks.

The EU SAF programme mandates that 70% of all jet fuel used in aircraft departing European soil by 2050 must be SAF, of which 50% must be synthetic fuel, or so-called “power-to-liquid” SAF, typically produced from captured CO2 and green hydrogen generated through water electrolysis.

However, in a paper published in Fuel, researchers at Chalmers University of Technology in Sweden found that power-to-liquid production methods are more expensive and less energy efficient than pathways using biobased feedstock such as Firefly’s. The researchers compared three production pathways to turn biomass into methanol: post-combustion carbon capture with and without integrated power and heat generation, and gasification. They found that gasification was significantly cheaper, costing €820 (US$955) per tonne of methanol compared to up to €1,495 using carbon capture and green hydrogen, and achieved energy efficiency of 46% compared with 37% for the carbon-capture routes.

The EU argues that synthetic SAF mandates will help stimulate the renewable electricity and hydrogen sectors. However, Henrik Thunman, a co-author on the paper and a professor of energy technology at Chalmers, said: “Instead of driving innovation towards the most efficient solutions, we risk locking ourselves into less resource-efficient production methods.”

Firefly strategy director Paul Hilditch said “projects using Altaca’s technology are expected to be deployed in multiple locations, both inside and outside of the EU”.

The European Commission declined to comment.