What if sewage sludge from wastewater treatment could be used as a feedstock? A solution to waste disposal issues and a means of providing an additional revenue stream for water companies? Cranfield University – academic partner to Green Fuels Research and energy services company Petrofac — has already proven its viability as Dr Ying Jiang reports.
The world’s aviation industry urgently needs low-carbon liquid fuels — now seen as the only practical means of meeting its targets for reducing carbon emissions by 2050. These kinds of Sustainable Aviation Fuels (SAFs) emit 80% less carbon over their life cycle compared with conventional jet fuels. There’s no need for expensive investment in new aircraft or new infrastructure, SAFs are a plug-and-play solution for the industry.
The global market for SAFs is huge, due to be worth $6.2 billion by 2028. The problem for the moment is solely production capacity. Like all other types of biofuels, SAFs need feedstocks, and these are either in short supply or come loaded with other environmental issues.
SAFs boom
Levels of interest in SAFs are growing exponentially. Last year saw the first commercial flight with a full load of passengers using 100% SAF for one of its two engines. Rolls-Royce has confirmed that all its engines will be SAF-ready by 2023. The US government has taken a lead on incentivising the use of SAFs through its Inflation Reduction Act (IRA) 2022 and has a goal of enabling the production of 3 billion gallons of SAF by 2030, with a trajectory of growing production facilities to deliver 35 billion gallons a year by 2050.
In 2020, the industry was reporting $7bn worth of SAF offtake agreements (arrangements where buyers agree to purchase goods that will be available in the future). This figure has increased to $25bn and rising.
Current production rates of approved SAF technologies, however, only meet a small fraction (less than 1%) of the actual fuel demand from commercial airlines.
Feedstock dilemmas
Biofuels in general are in demand. The UK government and many others have signalled their support for the increased use of biofuels as a stepping stone technology until electric and hydrogen alternatives for transport become viable. This just means a constantly growing pressure on supplies of feedstocks — and higher unit costs — which make transition to low carbon transport a challenge.
The UK continues to be a net importer of biofuels, with most of its supply (traditionally at least) coming from Ukraine, China, the US and the EU. With government plans to increase the mandate for ‘biofuel blending’ in transport fuels to 14.6% by 2032, there is only going to be more competition over land use internationally: more land being turned over to bioenergy crops rather than food; weakening food security; damage to local economies; and higher prices for biofuels.
The Intergovernmental Panel on Climate Change (IPCC) has warned that the shift to using land for bioenergy crops is leading to deforestation, land degradation, increased use of chemicals, water pollution, and is a serious threat to wildlife and biodiversity. A controversial crop like palm oil — with its significant contribution to carbon emissions — is increasingly being grown as a biofuel. It will be critical for the aviation industry not to simply shift its carbon impact onto agricultural businesses that are growing palms for example.
Flying on sewage
Using municipal sewage sludge to produce SAFs will be a genuinely sustainable foundation, addressing both waste management and low-carbon energy demand. As a feedstock, the scale of supply more than works. It is estimated that around 53m tonnes of sewage sludge are produced every year that require to be treated in the network of around 200 sludge treatment centres in the UK. The UK’s wastewater system is heavily over capacity, meaning storm events (or even, in some locations, just a light rain) regularly lead to raw sewage ending up in rivers and seas. According to Environment Agency figures, there has been a 37% increase year-on-year in incidents: meaning 9 million hours of sewage being pumped into rivers and seas since 2016. Finding alternative uses for sewage sludge will be a huge benefit to businesses, to the environment and society as a whole.
The FIREFLY project, funded by Department for Transport as part of its Green Fuels, Green Skies competition, has shown how this can work; it has proved that the quality of the resulting biofuel will meet strict industry standards; and led to the engineering design and construction of a demonstrator plant for production. With further industry investment, the project is due to lead to a first-of-a-kind commercial refinery and the development of a network of UK sites close to airports, pipeline terminals and wastewater treatment works. The integrated processes involved will also reduce the processing costs involved and help keep unit costs low. Alongside other development pathways, the FIREFLY technology is expected to become a strategic asset for the UK as part of the broader national SAF portfolio.
Costs for SAFs will remain relatively high, at least for the short-term. Which is why the huge potential for SAFs — and the opportunity for a circular economy approach to their production — will only be realised with a clear mandate from governments, stimulating mass uptake of SAFs, more investment from finance institutions and a rolling cycle of lower costs for every stakeholder involved.
Dr Ying Jian is Senior Lecturer in Bioenergy, Centre for Renewable and Low Carbon Energy, Cranfield University, cranfield.ac.uk
