ECHA awarded contract by the Energy Institute to investigate the susceptibility of Sustainable Aviation Fuel to microbial growth.
The aviation industry is committed to achieving net zero carbon emissions by 2050, and it is believed that the use of Sustainable Aviation Fuels (SAF) will play an essential role in the decarbonisation journey.
It has been estimated that by 2025, 62% of the carbon emissions reduction would need to be realised through the use of SAF. (IATA SAF Handbook, May 2024)
What is Sustainable Aviation Fuel (SAF)?
Sustainable Aviation Fuels are synthetic hydrocarbon fuels that can be derived from many different production pathways using various feedstocks, such as energy crops, algae, and municipal and agricultural wastes.
Eight SAF production pathways already have ASTM D1655 approval for use in jet fuel as a synthetic blend component (SBC), typically up to 50%, and even more pathways and processes are under development.
Because SBCs consist of molecules which share similarities in chemistry to those found in conventional jet fuels, there does not need to be any modification of the fuel supply chain or aircraft, and they are sometimes referred to as “drop-in” fuels.
A specification for 100% Sustainable Aviation Fuel is under consideration. In November 2023, Virgin Atlantic operated the world’s first 100% SAF flight from London to New York on a commercial aircraft. Read the full article.
Background to Microbial Growth in Aviation Fuels
Microbial contamination and growth in conventional jet fuels is a well-known problem in the aviation industry and can occur at any stage of the supply and distribution chain – from the refinery to end-user tanks.
Microbial growth may occur wherever any water accumulates in aviation fuel tanks and systems. The presence of water allows heavy microbial growth to occur and fuel quality can be affected due to particulate contamination of fuel with microbial biomass, and contamination with by-products of microbial growth such as biosurfactants and sulphide. Microbial growth can cause potentially severe problems which can compromise aircraft operational safety, including Fuel Quantity Indicator System malfunction, clogging of engine filters and corrosion of airframe and fuel system components.
The aviation industry is extremely diligent when it comes to controlling microbial contamination and has developed guidance documents detailing good practice below. Housekeeping measures focus on regular removal of water form storage tanks, filter vessels and aircraft fuel tanks.
- International Aviation Transportation Association (2023) Guidance Material on Microbiological Contamination in Aircraft Fuel Tanks, 6th ed., IATA, Montreal.
- Joint Inspection Group (JIG) Bulletin 83 & Technical Information Document, Microbial Monitoring Strategies (2023).
Early work by ECHA investigating the susceptibility of Sustainable Aviation Fuels to microbial growth
In 2012, ECHA was commissioned to conduct laboratory research to investigate the susceptibility of some alternative jet fuels to microbial growth. The investigation formed part of the ALFA-BIRD Alternative Fuels and Biofuels for Aircraft Development Project, a multi-partner, partially EU funded project coordinated by the European Virtual Institute for Integrated Risk Management (EEIG). The study included assessment of one of the first SBCs to be developed – Fischer-Tropsch Hydroprocessed Synthesized Paraffinic Kerosene (FT-SPK). Conventional jet fuel can be blended with up to 50% FT-SPK. When we tested FT-SPK at 100% in our study, it was shown that it did support some microbial growth but to a significant less degree than in a conventional jet fuel, MEROX treated Jet A-1, that was tested alongside. The paper is available on the Commercial Aviation Alternative Fuels Initiative (CAAFI) Website. Read the full paper.
In the time since this study was completed, a further seven SAF production pathways have been approved.
How is ECHA helping to address industry concerns about microbial growth in Sustainable Aviation Fuels?
Because Sustainable Aviation Fuel and conventional jet fuels share similarities in their properties and chemistries, one could assume that the susceptibility of SAF to microbial growth would also be similar. However, the relative proportions of chemical constituents in SBCs are not the same, or as wide ranging, as those found in conventional fuels, and this could impact overall fuel properties, which in turn could influence the susceptibility to microbial growth. The relative susceptibility of SAF and SBCs to microbial growth compared to conventional jet fuels has not been thoroughly investigated and remains a pressing industry concern.
ECHA Microbiology have been awarded a contract by the Energy Institute to investigate the susceptibility of Sustainable Aviation Fuels to microbial growth. This will comprise of a desktop study where we will review the existing information addressing microbial growth in SAF, for instance field test data and the scientific literature. There are several general properties of fuel that are known to affect susceptibility to microbial growth and we will be considering how they vary for conventional jet fuel and SAF. We are engaging with the industry to assess current knowledge on microbial growth in Sustainable Aviation Fuels and the degree to which this is being assessed in the field.
The aim of the study is to provide a provisional assessment on likely impacts, if any, on incidence of microbial growth in jet fuels with increasing use of Sustainable Aviation Fuels and the extent to which it might lead to an increase or decrease in operational risks. We will also consider whether additional or alternative control and monitoring measures may be appropriate with increasing use of SAF.
If you have any research work relevant to this project or any field data pertaining to the microbiological testing of Sustainable Aviation Fuels or their synthetic blend component, we would be keen to speak to you! Please get in touch with us at marketing@echamicrobiology.com.