Question 62 from UPSC CSE 2024 - Environm ent

Question

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?

IASCODEX · Accepted Answer

Correct Option: C. 1, 2, 3, and 4

Strategy: Analyze each listed material for its eligibility as a feedstock in SAF production. Both agricultural residues and wood mill waste are classic lignocellulosic sources widely utilized in biofuel industry. Corn grain is a conventional feedstock, commonly processed to produce ethanol and advanced aviation fuels. Wastewater treatment sludge is included under 'wet wastes,' recognized in recent SAF production pathways. Since all four entries are validated feedstocks, option C is correct.

Key Info: Sustainable Aviation Fuel (SAF) refers to renewable or waste-derived liquid fuels designed to replace conventional jet fuel with lower lifecycle greenhouse gas emissions. SAF can be produced from a broad range of feedstocks:

* Agricultural residues: Non-food parts of crops left after harvest, like straw, husks, or stalks. Rich in lignocellulosic biomass, extensively researched and used in biofuel production.
* Corn grain: A primary feedstock for ethanol, which can be upgraded to SAF via various biochemical and thermochemical processes. Corn-based ethanol-to-jet technologies are established.
* Wastewater treatment sludge: 'Wet wastes' such as biosolids from sewage treatment contain high organic content and are emerging as alternative biofuel feedstocks. Technologies exist for converting this sludge into biogas or advanced liquid fuels, including SAF, through hydrothermal liquefaction or anaerobic digestion.
* Wood mill waste: Leftovers from timber processing—sawdust, shavings, and bark—serve as reliable lignocellulosic biomass feeds for biofuel conversion.

Global standards such as ASTM allow for SAF production via multiple recognized pathways, for example: Fischer–Tropsch synthesis, Alcohol-to-Jet, and Hydroprocessed Esters and Fatty Acids (HEFA). The expansion to utilize municipal solid waste, algae, oil seeds, fats, and even industrial CO2 reflects growing feedstock flexibility. The U.S. Department of Energy and global aviation authorities emphasize diversified feedstock supply, including all the examples above, to meet ambitious decarbonization targets for the sector.

IASCODEX · Answer

Option A: 1 and 2 only

IASCODEX · Answer

Option B: 3 and 4 only

IASCODEX · Answer

Option D: 1, 3, and 4 only

Consider the following materials: Agricultural residues Corn grain Wastewater treatment sludge Wood mill waste Which of the above can be used as feedstock for producing Sustainable Aviation Fuel?

Consider the following materials:

Agricultural residues

Corn grain

Wastewater treatment sludge

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