Consider the following materials :
1. Agricultural residues
2. Corn grain
3. Wastewater treatment sludge
4. Wood mill waste

Which of the above can be used as feedstock for producing Sustainable Aviation Fuel?

The correct option is 1, 2, 3 and 4.

Sustainable Aviation Fuel (SAF) is a cleaner alternative to conventional fossil-based jet fuel. It can be produced from a wide variety of renewable resources, known as biomass or feedstocks. Let us analyze each of the given materials to see if they can serve as feedstocks for SAF production:

1. Agricultural residues: These include leftover plant materials from agricultural harvests, such as stalks, husks, and straw. They are rich in lignocellulosic biomass, which can be processed through biochemical or thermochemical pathways (like gasification followed by Fischer-Tropsch synthesis) to yield SAF. Therefore, agricultural residues are viable feedstocks.
2. Corn grain: Corn grain is high in starch, which can be fermented into alcohol (ethanol or isobutanol) and then converted into jet fuel using the Alcohol-to-Jet (ATJ) pathway. Therefore, corn grain can be used as a feedstock.
3. Wastewater treatment sludge: Wet waste resources, such as sewage sludge from wastewater treatment facilities, contain organic compounds and lipids. These wastes can be converted into hydrocarbons suitable for aviation fuel via hydrothermal liquefaction (HTL) or anaerobic digestion followed by upgrading pathways. Therefore, wastewater treatment sludge is a valid feedstock.
4. Wood mill waste: Forestry residues and wood processing waste (like sawdust and wood chips) are abundant sources of cellulosic biomass. They can be converted into synthetic kerosene through gasification and synthesis, or by converting wood sugars to hydrocarbons. Therefore, wood mill waste can be used as a feedstock.

Since all four listed materials can be utilized as feedstocks to produce Sustainable Aviation Fuel, the correct combination is 1, 2, 3 and 4.