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?

All four listed materials can be used as feedstock for producing Sustainable Aviation Fuel (SAF). SAF is a biofuel used to power aircraft, designed to reduce aviation's carbon emissions, and can be produced from diverse biomass and waste streams.

1. Agricultural residues: Correct. Crop residues (corn stover, wheat straw, bagasse) are lignocellulosic biomass and a major SAF feedstock via Biomass-to-Liquid (BtL) or Alcohol-to-Jet (AtJ) pathways.

2. Corn grain: Correct. Sugar/starch crops can be converted to ethanol and then to SAF via the Alcohol-to-Jet (AtJ) pathway, despite the food-vs-fuel debate.

3. Wastewater treatment sludge: Correct. Sewage sludge and MSW can be converted to SAF through thermochemical routes such as gasification followed by Fischer-Tropsch synthesis.

4. Wood mill waste: Correct. Sawdust, wood chips and mill bark are lignocellulosic feedstocks suitable for SAF production through processes similar to those used for agricultural residues.

Hence, all four are valid SAF feedstocks.