Decarbonisation Technology November 2025 Issue

Waste carbon is key to scaling sustainable fuels Developers that build Alcohol-to-Jet capacity around ethanol from waste carbon position themselves for large-scale, policy-favoured SAF production tomorrow

Freya Burton LanzaTech

Introduction: feedstocks as the hidden lever The aviation sector faces one of the hardest decarbonisation challenges of any industry. Sustainable aviation fuel (SAF) has emerged as a critical solution, but its real climate benefit hinges on one question: what it is made from. Feedstocks are the invisible backbone of SAF production, determining not only lifecycle emissions but also scalability, cost, and public perception. The decarbonisation potential of SAF is only as beneficial as the feedstock that makes the fuel. As demand for low-carbon fuels accelerates across aviation and shipping, the competition for sustainable feedstocks is intensifying. One promising route reshaping this landscape is using waste carbon as a feedstock. By converting captured carbon into ethanol – a versatile, energy-dense intermediate – producers can enable a new generation of feedstocks to bypass many of the traditional constraints. Ethanol produced from these waste inputs can then be upgraded via the Alcohol- to-Jet (AtJ) process into SAF, while also serving as a next-generation marine fuel. Historically, ethanol has been utilised as a biofuel in ground transportation, predominantly produced from food crops, such as corn and sugarcane. However, the production of ethanol for aviation fuel, particularly from non-food sources, provides a pathway to greater sustainability including waste agricultural residues without competing with food supplies or causing indirect land-use changes. This approach not only decouples fuel production from food crops and land use but also valorises what would otherwise be

considered waste carbon into a high-value, drop-in solution for hard-to-abate sectors. However, sustainability in this context goes far beyond reducing greenhouse gas emissions. It also encompasses the ability to consistently produce, scale, and supply the volumes needed to meet growing demand in the aviation sector. Feedstock choice is therefore not just an environmental decision but a strategic one, directly influencing the resilience, scalability, and long-term viability of SAF production. Comparing feedstock pathways When assessing future fuel supply, it helps to think in terms of carbon intensity, availability, and maturity. Used cooking oil and tallow score well on carbon intensity, but poorly on “ As policy criteria tighten, the market will increasingly reward feedstocks that can prove real, additional greenhouse-gas reductions at scale – exactly where waste-carbon routes shine ” availability. Agricultural and forestry residues are more abundant but may require new collection and preprocessing systems for some fuel pathways. Ethanol produced from waste carbon potentially offers the lowest carbon intensity and the highest theoretical availability – any concentrated CO₂ stream plus hydrogen made from clean power could become a fuel source. The contrast underscores why feedstock strategy matters. Developers that build AtJ