Sustainable aviation fuel: Can waste help the industry reach ‘jet zero’?

The aviation sector is one of the fastest-growing contributors to greenhouse gas emissions worldwide. Globally, the industry is responsible for 2.1 per cent of total emissions, whilst accounting for 12 per cent of all transport-based emissions.

With the demand for air travel rapidly increasing – the sector is forecasted to grow by 33 per cent in the next decade – various strategies have been proposed in attempts to make the industry cleaner and mitigate the high levels of emissions.

Some have suggested limiting the number of flights as a solution, whilst others advocate for market-based policies, such as emission trading schemes or taxation, to lower greenhouse gas emissions within the aviation industry. However, use of sustainable aviation fuels is perhaps the strategy that is gathering the most attention within the sector and from politicians.

Sustainable aviation fuels are thought of as more sustainable than conventional jet fuels since they originate from waste; various waste feedstocks, such as used cooking oils or agricultural residues, are used to produce the fuel.

Following this strategy, notably, the UK has announced ambitious plans to divert its EfW plants from electricity production, to instead produce SAFs as efforts to achieve its target of ‘jet zero’ by 2050 are increased.

The question is, are the fuels truly sustainable and is the usage of SAFs achievable at the scale necessary to mitigate the aviation industry’s heavy emissions?

Why has the uptake of sustainable aviation fuels been so slow?

Sustainable aviation fuels have long been seen as a solution to the emissions of the aviation industry, however, uptake has been slow with SAFs representing less than 0.1 per cent of fuel consumption within the sector.

Sustainable aviation fuel is a waste technology that already exists. Indeed, industry experts estimate that the fuels could reduce greenhouse gas emissions in the aviation industry by up to 94 per cent dependent on the chosen waste feedstock and technological pathway. So, what exactly is holding the aviation industry back from fully embracing these new waste-derived fuels?

Both the availability and costs of the necessary waste feedstocks required for the production of SAFs provide an obstacle to the fuel’s proliferation. Crucially, sustainable aviation fuel currently costs three to five times more than kerosene, leading to a reluctance from the industry to absorb this additional cost.

The uptake of waste-derived fuels is also faced with the hurdle of requiring significant investment and infrastructure. SAFs are unique fuels and therefore require specialised equipment, facilities and storage solutions to ensure they are handled optimally, at a high cost to both airlines and airports alike.

What are the different types of sustainable aviation fuels?

A number of different feedstocks can be used in sustainable aviation fuels production. Non-renewable, low-carbon fuels are another type of fuel that are being proposed in SAF policies around the world. Recycled carbon fuels (RCFs) are created from fossil wastes that cannot be avoided like unrecyclable plastics or industrial gases. This EfW-based type of fuel can help provide greenhouse gas emission savings as they are less polluting than conventional jet fuels.

Synthetic fuels, such as renewable fuels of non-biological origin (RFNBO) or fuels from nuclear energy, have also been proposed by the UK government for SAFs. Also known as ‘power-to-liquid’, these are renewable fuels in which none of the content comes from biological sources.

This type of SAF is seen as optimal by the UK government due to its likely low land-use impact, though critics question whether there is enough renewable energy generation in place to power this pathway.

The use of agricultural crops to produce sustainable aviation fuels has also previously been used to produce SAFs. However, both the EU and the UK have recently voted to exclude crop-driven biofuels from SAF production. This is due to the modest greenhouse gas emissions savings they provide alongside high indirect land-use change risks. It is argued that producing this type of SAF could potentially hinder food security for communities around the world.

How is waste used to produce sustainable aviation fuels?

Biofuels derived from waste currently represent the most commonly used feedstop for the creation of sustainable aviation fuels, with a majority of Europe’s SAF production coming from this pathway.

These fuels are wholly derived from biomass and are created using a range of feedstocks. The feedstocks used include: used cooking oils (UCOs) and animal fats, agricultural residues, forestry residues and household waste.

Despite the merits of waste-driven biofuels, the sustainability of many of the feedstocks used has been questioned. UCOs and animal fats are one of the prime waste sources used for SAF production, with over a third of the 400,000 bottles of oil collected in Japan in 2021 used for fuel production.

However, concerns have been raised regarding the sustainability of UCOs. A UK Government consultation document has suggested putting a cap or ban on the use of UCOs, due to fears that portions of the 26 million litres of UCOs imported into the UK from Asia in 2021 may in reality be virgin palm oil – a feedstock that contributes to tropical deforestation.

Similar questions of sustainability surround the use of agricultural residues. These residues contribute moisture and nutrients to the soil, therefore sparking concerns regarding the impact on soil quality should they be harvested to a high level for SAF production. Critics have similar concerns regarding the use of forestry residues.

What is the future of sustainable aviation fuel production?

Though growth appears slow currently, efforts to increase the scale of sustainable aviation fuel production across the world are increasing.

Notably, 370,000 flights have taken to the air using sustainable aviation fuels since the year 2016 and this is expected to grow further in the coming years.

In the UK, eight companies were selected to share £15m of investment to go towards developing EfW production plants across the country. The aim of the investment is to turn standard household waste – the kind you could find in a black bin bag – into jet fuel.

The UK government hopes that by using waste to create jet fuel through these new plants, it will be able to take considerable steps towards its target of 10 per cent SAF use by the year 2030.

Globally, if scaled adequately, it is believed that the use of waste-derived sustainable aviation fuels could provide approximately 65 per cent of the emissions reductions necessary for the industry to reach net zero by the year 2050.

However, the question of whether SAF truly holds the key to unlocking ‘jet zero’ by 2050 remains to be seen. The technology certainly exists and has demonstrated its ability to cut greenhouse gas emissions on commercial flights.

Ultimately, the impact of SAFs on achieving ‘jet zero’ will come down to how quickly it can be scaled to meet the needs of the aviation industry and whether the industry can bypass the potential challenges – such as feedstock selection – that may arise from its implementation.