Skip to main content

Significant quantities of fertilizer, water, microorganisms, hydrogen and catalysts are required to support the production of sustainable aviation fuels at a large scale

Summary​

Beyond land use, producing biofuels at scale requires vast quantities of other inputs including fertilizer, water, energy, microorganisms, and hydrogen with catalysts. Cultivating 179 million dry tons of switchgrass would require approximately 1.6 million tons of nitrogen fertilizer annually which represents a significant portion of current U.S. ammonia consumption. Water usage for ethanol production requires roughly 592 billion liters and the alcohol-to-jet conversion process requires an additional 94 billion liters. Microorganisms present another scaling challenge, requiring approximately 892,000 tons of yeast and 5.5 million tons of enzymes yearly. Hydrogen consumption for jet fuel production ranges from 500,000 to 1.15 million tons annually.

The most consequential input economically and environmentally for the production of biofuels is the actual land used to produce biomass and the indirect land use change (ILUC) that is a consequence of this. Nonetheless, there is a considerable amount of other inputs that are required in large quantities such as fertilizer, water, energy, microorganisms, and hydrogen and catalysts to support the industry. Shown below are some rudimentary estimations of these key inputs that show the scale required to sustain an advanced biofuel industry to produce sustainable aviation fuel.

Fertilizer​

Fertilizer usage is the primary input of concern for the cultivation of any biomass, specifically nitrogen fertilizers. Nitrogen is the most abundant element in the atmosphere and is readily available however, it needs to be converted into a form that can be used by plants such as ammonia (NH₃) and urea (CO(NH₂)₂). A key component for the production of ammonia is hydrogen, which is almost exclusively produced from the fossil fuel methane (CH₄) through a process known as steam methane reforming (SMR) and a water-gas shift reaction. Beyond relying on a fossil fuel feedstock, the water-gas shift reaction produces a significant amount of carbon dioxide (CO₂), which is usually released directly into the atmosphere.

Although fertilizer is used for the cultivation of most of the crops whose residue can be used as feedstock for biofuels, the focus will just be placed on the fertilization requirements for switchgrass, which requires nitrogen fertilizer. Fertilizer requirements vary with region and soil type, but as a general rule for maximizing yields, nitrogen (N) is applied at a rate of 20 pounds per acre per year for every ton of anticipated biomass 1. For marginal and productive land, as the total desired biomass production is the same, the estimated fertilizer requirement is the same for both land types. Nitrogen can be applied in a solid or liquid form, with the most common solid form being urea, which is approximately 46% nitrogen by weight, and the most common liquid form being ammonium nitrate (NH₄NO₃), which is approximately 34% nitrogen by weight 2. Shown below in table 1 is a summary of fertilizer requirements using three different nitrogen fertilizer forms for the cultivation of switchgrass.

Table 1: Summary of fertilizer requirements for the cultivation of 179.17 million dry tons of switchgrass

Crop typeBiomass production (tons/year)Total Nitrogen (N) required (tons/year)Total ammonia (NH₃) required (tons/year)Total Urea (CO(NH₂)₂) required (tons/year)Total Ammonium nitrate (NH₄NO₃) required (tons/year)
Switchgrass179,170,0001,625,4301,982,2323,533,5444,780,677

Annual US domestic consumption of ammonia and its derivatives are shown below in table 2. In order to meet the switchgrass demands, a significant portion of the United States' domestic ammonia consumption would need to be diverted to the cultivation of switchgrass, which is understandable given the enormous scale of the switchgrass cultivation required.

Table 2: Annual domestic consumption of ammonia and its derivatives as of 2022 2

ProductConsumption (tons/year)
Ammonia (NH₃)14,938,000
Urea (CO(NH₂)₂)6,505,000
Ammonium nitrate (NH₄NO₃)2,819,000

Water​

Water is a significant input for biofuels as it is needed for irrigation during initial cultivation as well as for various steps in the production of ethanol and jet fuel for chemical cleaning and cooling. For switchgrass cultivation, irrigation is generally only required for the initial cultivation but is less necessary once the crop is established 1. Switchgrass, being a C4 photosynthesizer with deep roots, is generally considered a highly efficient water user whose yield has low sensitivity to precipitation levels once established 3. The degree of irrigation required is highly dependent on climate, region, and seasonal variations.

For the ethanol production stages, water usage becomes much more significant, as many of the steps (pretreatment, hydrolysis, fermentation) require water for cleaning away solvents and microbes, as well as for cooling to maintain optimal temperatures. Additionally, as the ethanol production process requires energy, there is a significant portion of indirect water usage used for cooling in energy generation facilities. A summary of water usage for ethanol and gasoline production is shown below in table 3. It should be noted that the majority of process water for ethanol production, and to a similar degree gasoline production, is recycled and fed back into the production process, meaning that the water is not directly consumed in the production process. Therefore, the majority of water usage is tied to energy usage and generation, which could be reduced if non-fossil fuel energy sources are used.

Table 3: Summary of water usage for ethanol and gasoline production

ProcessGallon of water per gallon of fuel (same value for L/L) 4
Ethanol (corn)3 – 4
Ethanol (lignocellulosic non-optimized)6
Gasoline2 – 2.5

These values can be extrapolated up to the scale of ethanol production required for sustainable aviation fuel production (49.3 billion L of jet fuel), which would require approximately 98.65 billion L of ethanol. Thus requiring 591.9 billion L of water. As a comparison, water consumption in the United States is approximately 1,218 billion liters/day 5. If renewable energy sources were used for power generation, this water usage value could decrease significantly.

For the conversion of ethanol into jet fuel, water is not used as a feedstock and is often produced as a byproduct of the production process. Therefore, in the same vein as the ethanol production process, water consumption is primarily tied to energy generation and cooling. Estimates for water consumption in the alcohol-to-jet production process are roughly 1.9 liters of water per liter of jet fuel produced 6. Care needs to be taken when utilizing this value as it is obscured by the fact that in the jet production process, other products like diesel and gasoline can be and are often produced as co-products. The 1.9 liter of water value is derived from a process that involves approximately 75% jet fuel and 25% co-product breakdown on an energy basis. Extrapolating this value to the sustainable aviation fuel requirement of 49.3 billion L, approximately 93.7 billion L of water would be required for the alcohol-to-jet conversion process.

Energy​

Energy usage values for ethanol and jet fuel conversion can be difficult to quantify due to the wide range of factors that can affect energy usage. Key factors include the degree of on-site energy production from co-products such as lignin, whether hydrogen is produced on-site for the alcohol-to-jet conversion, whether natural gas is utilized to meet heating requirements, and the type of pretreatment utilized to break down the biomass. Pretreatments such as liquid hot water (LHW) treatment involve a significant energy burden to support the high temperatures required. Energy usage values vary greatly in the literature, with some analyses reporting that on-site co-production of energy is greater than the total energy requirement 6, whereas others report an energy requirement multiple times greater than the on-site energy production (but not greater than an order of magnitude) 7 8. Due to the wide variation of reported external energy consumption values, it is reasonable to assume that energy will be required from the grid, albeit at a level that excludes energy requirements as a limiting factor for production. As with most industrial processes, if renewable energy is utilized to meet the heating and energy requirements, large emissions reductions can be achieved.

Microorganisms (enzymes and yeast)​

The high requirement for microorganisms in the biochemical conversion process for lignocellulosic biomass to ethanol is one of the key limiting factors for scaling up ethanol production to meet the demands of a commercial sustainable aviation fuel industry. Microorganisms can be grown on-site at ethanol plants utilizing biomass, inoculating agents, and other inputs to feed their growth, or they can be grown off-site and delivered. The type and quantity of microorganisms used is tailored to the biomass and production process, and can include genetically modified strains of yeast that are able to ferment pentose sugars that cannot be fermented by naturally occurring strains of yeast. A generalized estimate of microorganism requirement for conversion of cellulosic biomass to ethanol is 15.5 grams of enzymes and 2.49 grams of yeast per dry kilogram of cellulosic biomass 9. Extrapolation of total yeast and enzyme requirements are shown in table 4 that give a rough estimate of the scale of the microorganism requirements for conversion of cellulosic biomass to ethanol.

Table 4: Summary of microorganism requirements for conversion of cellulosic biomass to ethanol

Total processed biomass (million dry tons/year)Yeast requirement (kg/ ton of dry biomass)Enzyme requirement (kg/ton of dry biomass)Total Yeast requirement (tons/year)Total Enzyme requirement (tons/year)
358.32.4915.5892,1675,553,650

Hydrogen and catalysts​

Hydrogen and catalysts are the primary inputs of the fuel upgrading stages of the alcohol-to-jet conversion process and are used in most stages of the fuel upgrading process (dehydration, oligomerization, hydrogenation). Dehydration is the process of removing any oxygen molecules that are present in the alcohol molecules such as ethanol (C₂H₅OH). Oligomerization is the process of breaking down the double bonds of short-chained hydrocarbons into longer-chained hydrocarbons via the use of a catalyst. Hydrogenation is the process of breaking down any remaining double bonds still present in the hydrocarbon by attaching hydrogen atoms to the hydrocarbon via the use of a catalyst (typically platinum) and hydrogen gas. Catalysts slowly break down over time and need to be replaced or regenerated to maintain efficiency. Because of the wide variety of catalyst options, it can be difficult to place an exact estimate on the amount of catalyst required for the fuel upgrading process. One estimate for the amount of generalized catalyst consumption in the fuel upgrading process is 0.107 (g/MJ jet) 6. Given that the energy density of jet fuel is approximately 34.5 MJ/L 10, the total catalyst consumption for the production of 49.3 billion L of jet fuel would be approximately 182,075 tons of generalized catalyst.

With regard to hydrogen consumption, the amount of hydrogen used depends on the desired jet fuel yield in the hydrogenation process. Put simply, if higher jet fuel yields and less co-product yields (such as gasoline and diesel) are desired, then more hydrogen is required. Analysis of fuel upgrading tends to focus on a 70% – 75% jet fuel yield and 25% – 30% co-product yield 6 11. Rough calculations of hydrogen consumption place the hydrogen requirement between 500,000 and 1.15 million tons per year to produce 49.3 billion L of jet fuel 6 11. To put this number in perspective, the total hydrogen produced in the United States in 2019 was approximately 10 million tons, of which 99% was sourced from fossil fuels 12.

Sources​

Footnotes​

  1. Downing, M., Eaton, L. M., Graham, R. L., Langholtz, M. H., Perlack, R. D., Turhollow, A. F., ... & Brandt, C. C. (2011). U.S. billion-ton update: Biomass supply for a bioenergy and bioproducts industry (No. ORNL/TM-2011/224). Oak Ridge National Laboratory. ↩ ↩2

  2. Williams, A., Collins, L. A., & Boline, A. (2025, September). Drivers of fertilizer markets: Supply, demand, and prices (Economic Research Report No. ERR-354). U.S. Department of Agriculture, Economic Research Service. https://www.ers.usda.gov/sites/default/files/_laserfiche/publications/113324/ERR-354.pdf?v=83545 ↩ ↩2

  3. Wright, L. (2007, August). Historical perspective on how and why switchgrass was selected as a "model" high-potential energy crop (ORNL/TM-2007/109). U.S. Department of Energy, Office of Energy Efficiency & Renewable Energy. https://www.energy.gov/eere/bioenergy/articles/switchgrass-high-potential-energy-crop ↩

  4. Aden, A. (2007). Water use in ethanol production and implications for biofuels policy. [Factsheet]. Southwest Hydrology. https://ethanolrfa.org/file/1795/waterusagenrel-1.pdf ↩

  5. Mytton, D. (2021). Data centre water consumption. npj Clean Water, 4(1), 11. https://doi.org/10.1038/s41545-021-00101-w ↩

  6. Han, J., Tao, L., & Wang, M. (2017). Well-to-wake analysis of ethanol-to-jet and sugar-to-jet pathways. Biotechnology for Biofuels, 10(1), 21. https://doi.org/10.1186/s13068-017-0698-z ↩ ↩2 ↩3 ↩4 ↩5

  7. Maga, D., Thonemann, N., Hiebel, M., et al. (2019). Comparative life cycle assessment of first- and second-generation ethanol from sugarcane in Brazil. International Journal of Life Cycle Assessment, 24, 266–280. https://doi.org/10.1007/s11367-018-1505-1 ↩

  8. Kourkoumpas, D.-S., Sagani, A., Hull, A., Hull, A., Karellas, S., & Grammelis, P. (2024). Life cycle assessment of an innovative alcohol-to-jet process: The case for retrofitting a bioethanol plant for sustainable aviation fuel production. Renewable Energy, 228, 120512. https://doi.org/10.1016/j.renene.2024.120512 ↩

  9. Wang, M., Han, J., Dunn, J. B., Cai, H., & Elgowainy, A. (2012). Well-to-wheels energy use and greenhouse gas emissions of ethanol from corn, sugarcane and cellulosic biomass for US use. Environmental Research Letters, 7(4), 045905. https://doi.org/10.1088/1748-9326/7/4/045905 ↩

  10. Holladay, Johnathan, Abdullah, Zia, & Heyne, Joshua (2020). Sustainable Aviation Fuel: Review of Technical Pathways. https://doi.org/10.2172/1660415 ↩

  11. Geleynse, S., Brandt, K., Garcia-Perez, M., Wolcott, M., & Zhang, X. (2018). The Alcohol-to-Jet Conversion Pathway for Drop-In Biofuels: Techno-Economic Evaluation. ChemSusChem, 11(21), 3728–3741. https://doi.org/10.1002/cssc.201801690 ↩ ↩2

  12. Hydrogen Production: Overview and Issues for Congress. (2025, November 14). https://www.congress.gov/crs-product/R48196 ↩