Biofuels explained Biofuels and the environment

Biofuels may have fewer effects on the environment than fossil fuels

Production and use of biofuels is considered by the U.S. government to have fewer or lower negative effects on the environment compared to fossil-fuel derived fuels. There are also potential national economic and security benefits when biofuel use reduces the need to import petroleum fuels. Government programs that promote and/or require biofuels use, such as the U.S. Renewable Fuel Standard (RFS) and California's Low Carbon Fuel Standard (LCFS), define the types of biofuels and processes or low-carbon pathways by which biofuels can be produced in order for them to qualify for use under the programs. While biofuels have environmental benefits, their production and use do have effects on the environment.

Pure ethanol and biodiesel are nontoxic and biodegradable, and if spilled, they break down into harmless substances. However, fuel ethanol contains denaturants to make fuel ethanol undrinkable. Similar to petroleum fuels, biofuels are flammable (especially ethanol) and must be transported carefully.

When burned, pure biofuels generally produce fewer emissions of particulates, sulfur dioxide, and air toxics than their fossil-fuel derived counterparts. Biofuel-petroleum blends also generally result in lower emissions relative to fuels that do not contain biofuels. Biodiesel combustion may result in slightly higher amounts of nitrogen oxides relative to petroleum diesel.

Ethanol and ethanol-gasoline mixtures burn cleaner and have higher octane levels than gasoline that does not contain ethanol, but they also have higher evaporative emissions from fuel tanks and dispensing equipment. These evaporative emissions contribute to the formation of harmful, ground-level ozone and smog. Gasoline requires extra processing to reduce evaporative emissions before blending with ethanol.

Burning biofuels results in emissions of carbon dioxide (CO₂), a greenhouse gas. However, according to international convention, CO₂ emissions from biofuel combustion are excluded from national greenhouse gas emissions inventories because growing the biomass feedstocks used for biofuel production may offset the CO₂ produced when biofuels are burned.

The effect that biofuel use has on net CO₂ emissions depends on how the biofuels are produced and whether or not emissions associated with cropland cultivation are included in the calculations. Growing plants for fuel is a controversial topic because some people believe the land, fertilizers, and energy used to grow biofuel crops should be used to grow food crops instead. In some parts of the world, large areas of natural vegetation and forests have been cleared or burned to grow soybeans and palm oil trees to make biodiesel. The processes for producing ethanol, renewable diesel, renewable heating oil, and renewable aviation fuel require a heat source, and most producers of these biofuels currently use fossil fuels. Some U.S. ethanol producers burn corn stalks for heat and ethanol producers in Brazil use sugar cane stalks (called bagasse) to produce heat and electricity.

The U.S. government is supporting efforts to produce biofuels with methods that use less energy than conventional fermentation and that use cellulosic biomass, which requires less cultivation, fertilizer, and pesticides than corn or sugar cane. Cellulosic ethanol feedstock includes native prairie grasses, fast-growing trees, sawdust, and even waste paper. However, there is currently no commercial cellulosic ethanol production in the United States because of technical and economic challenges.

Lipid feedstocks—waste/used cooking oil and animal fats/tallow and grease—have relatively low carbon intensities as feedstocks for biofuels production and they have been used to meet the targets for advanced biofuels under the federal RFS program. The total process (or life-cycle) emissions for lipid feedstocks are low because lipids were previously used for another purpose and the emissions related to transportation of these biofuels feedstocks only account for emissions that occur after the waste oil/grease is collected. Because of their potentially lower carbon intensities, some state governments provide more support for biofuels production from lipid feedstocks than for raw, unused vegetable oil feedstocks. In California, lipids account for the majority of the feedstocks for U.S. non-fuel ethanol biofuels production and also for the majority of credits generated under California's LCFS. The federal RFS currently does not differentiate between lipid and vegetable oil feedstocks as it does with cellulosic and other renewable fuels. At scale, hydrogenated lipid-based biofuels production requires a significant amount of hydrogen, which if produced from fossil fuels, may increase process emissions and thus increase their carbon intensity.

Last updated: April 13, 2022