# Comprehensive LCA of Biobased Sustainable Aviation Fuels and JET A-1 Multiblend
## 4 Discussion  
A detailed look at the GHG emissions of sustainable aviation fuels showed, on the one hand, the clear advantages of the use of residual and waste materials compared to the use of cultivated biomass and, on the other hand, the advantages of the use of renewable energy to meet process-specific energy requirements. Accordingly, the HEFA concept was found to be particularly advantageous because tallow oil, which is declared as waste, was used as a raw material. Due to the waste declaration (e.g., under RED II framework) and the resulting system boundaries, upstream processes associated with the provision of tallow oil (for example, the availability in a rendering plant) were not included. The specific emissions associated with tallow oil supply were thus significantly lower than the emissions associated with the supply of cultivated biomass, which was mainly due to the emissions from fertilizer production, direct emissions from N-fertilization, and emissions from the use of fossil fuels in agricultural machinery.  
Meanwhile, the naphtha provided within the process was used for steam reforming to produce the required hydrogen and for the provision of process steam. The relatively high GHG emissions caused by the conversion processes for ATJ primarily resulted from the use of fossil fuels to cover the process-related energy demand. An increased share of regenerative energy in the process energy mix could lead to a significant reduction in total GHG emissions. This would also be advantageous in view of the corresponding certification in accordance with the Renewable Energy Directive 2018/2001 (RED II) and the associated proof of compliance with defined GHG reduction targets [4].  
This study shows that the results strongly depend on the type of feedstock used in SAF production processes, the declaration of the biomass used, the greenhouse gas emissions associated with the supply of process energy, and the calculation method used.  
The environmental assessment of the considered multiblends, and in particular the assessment of total GHG emissions, showed clear advantages of the multiblends compared to conventional JET A-1. With the mixtures considered here, up to 35% of GHG emissions could be avoided. As most GHG emissions are caused by the combustion of fossil kerosene and GHG emissions from biobased SAF combustion were not included, the fossil part in the multiblend JET A-1 could be identified as the main driver of the total GHG emissions. Multiblend JET A-1 case A thus had the lowest GHG emissions with the highest proportion of renewable kerosene and, at 35%, the highest GHG savings compared to fossil JET A-1.  
Under the assumed conditions and in accordance with the ASTM requirements, biobased SAF as components of so-called multiblends is a potential option to mitigate GHG emissions in the aviation sector.  
Conceptualization, K.O., S.M. and F.M.-L.; methodology, K.O. and S.M.; software, K.O.; validation, K.O., S.M. and F.M.-L.; formal analysis, K.O.; investigation, K.O.; resources, K.O. and S.M.; data curation, K.O.; writing--original draft preparation, K.O.; writing--review and editing, K.O., S.M., F.M.-L. and D.T.; visualization, K.O.; supervision, D.T.; project administration, F.M.-L.; funding acquisition, F.M.-L. and S.M. All authors have read and agreed to the published version of the manuscript.  
This research was financed by the Federal Ministry of Transport and Digital Infrastructure (BMVI) as a model project of the German Mobility and Fuel Strategy (MFS).  
Not applicable.  
The model project on the use of renewable kerosene at Leipzig/Halle Airport (in short, DEMO-SPK) involved the collaboration of more than 20 international partners from industry and science.  
The authors declare no conflict of interest.