What Is the Carbon Footprint of Biofuel? A Life-Cycle Assessment

What Is the Carbon Footprint of Biofuel? A Life-Cycle Assessment

Grace Smoot

Read Time:14 Minutes


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Fossil fuels, specifically gasoline and diesel fuel, still remain the two most widely used transportation fuels. But as of late, biofuel has emerged as an alternative fuel source with lower levels of carbon dioxide (CO2) emissions and climate change mitigation properties. So, we had to ask: What is the carbon footprint of biofuel?

On a life-cycle basis, biofuel (ethanol and biodiesel) has a low carbon footprint. Ethanol emits 18.92 pounds (lb) and biodiesel 5.87 lb of CO2 per gallon combusted, and driving one mile on average emits 315 (for ethanol) or 404 (for biodiesel) grams of CO2.

Keep reading to learn about the overall carbon footprint of biofuel, its carbon footprint throughout its life-cycle, and how environmentally friendly it is.

Here’s What the Carbon Footprint of Biofuel Is

The carbon footprint is one of the ways we measure the effects of human-induced global climate change. It primarily focuses on the GHG emissions associated with consumption, but also includes other emissions such as methane (CH4), nitrous oxide, and chlorofluorocarbons.

“Carbon footprint: the amount of greenhouse gases and specifically carbon dioxide emitted by something (such as a person’s activities or a product’s manufacture and transport) during a given period”

Merriam Webster

Basically, it is the amount of carbon emitted by an activity or an organization. This includes GHG emissions from fuel that we burn directly (e.g., heating a home, driving a car) and GHG emissions from manufacturing the products that we use (e.g., power plants, factories, and landfills).

A biofuel is any liquid fuel derived from biomass

“Biofuel: a fuel (such as wood or ethanol) composed of or produced from biological raw materials”

Merriam-Webster Dictionary

Biomass is renewable organic material from plants and animals that can be used to produce a wide range of products including energy, everyday products that contain plastics, and fuel.

“Biomass: natural materials from living or recently dead plants, trees and animals, used as fuel and in industrial production, especially in the generation of electricity”

Oxford Dictionary

The two most common biofuels used for transportation are ethanol and biodiesel, which are commonly blended with petroleum fuels (gasoline and diesel fuel). They are an alternative to these petroleum fuels and come with lower carbon monoxide (CO), sulfur (S), air toxics (benzene), and CO2 emissions.

“Ethanol: a colorless volatile flammable liquid C2H5OH that is the intoxicating agent in liquors and is also used as a solvent and in fuel”

Merriam-Webster Dictionary

Like gasoline, ethanol is used in engines, which use a spark to ignite the fuel. Ethanol can be blended with gasoline in any percentage up to 83% to produce finished ethanol fuel. Pure ethanol is referred to as E100, and E10 (10% ethanol and 90% gasoline) is the most common blend. Other common forms of ethanol include E15 and E85. 

One gallon of ethanol produces 4% fewer emissions than gasoline, 8,595 grams of CO2 (gCO2) compared to 8,887 gCO2.

“Biodiesel: a type of fuel made from plant or animal material and used in diesel engines”

Oxford Dictionary

Like petroleum diesel, biodiesel is used in diesel engines, which use compressed air in a cylinder to ignite the fuel rather than a spark. Biodiesel can be blended with petroleum diesel in any percentage to produce finished biodiesel. Pure biodiesel is referred to as B100, and B20 (20% biodiesel and 80% petroleum diesel) is the most common blend. 

One gallon of biodiesel produces 74% fewer emissions than petroleum diesel, 2,661 gCO2 compared to 10,180 gCO2

Burning of biofuelCarbon footprint
Burning one gallonEthanol: 8,595 gCO2 emitted (when E10 is combusted)Biodiesel: 2,661 gCO2 emitted
Driving one mile (on average)Ethanol: 315 gCO2 emitted (when E85 is combusted)Biodiesel: 404 gCO2 emitted
Per million British thermal units (Btu)Ethanol: 150.88 lb of CO2 emitted (when E100 is combusted)Biodiesel: 162.8 lb of CO2 emitted (when B100 is combusted)

Global biofuel production in 2019 was 156 billion liters (bl), and this number is expected to increase to 165 bl in 2025.

Illustration of lobal biofuel production in 2019 and forecast to 2025
International Energy Agency: Global biofuel production in 2019 and forecast to 2025

Oil (including gasoline and diesel fuel) is the world’s primary fuel source for transportation. But since the turn of the century, there has been a push towards cleaner-burning transportation fuels with fewer negative effects on the environment. This is one major reason the markets for ethanol and biodiesel are expected to increase to $155.6 billion (b) and $307 b, respectively, by 2030.

To understand the total carbon footprint of biofuel, we must assess its life-cycle and each stage’s carbon footprint. This life-cycle assessment (LCA) is a method to evaluate the environmental impacts of products and materials. Over the years, companies have strategically used LCA to research and create more sustainable products. So, let’s have a look at the LCA of biofuel!

The life-cycle stages of biofuelEach stage’s carbon footprint
Building of biofuel production facilities and refineriesEthanol: CO2 emissions from building the components of the ethanol power plantBiodiesel: CO2 emissions from building the components of the biorefinery
Extracting of biofuelEthanol: CO2 emissions from the milling and fermentation processesBiodiesel: CO2 emissions from the transesterification process
Transportation of biofuelCO2 emissions from transporting ethanol and biodiesel by barges, tankers, pipelines, trucks, and railroads across distances
Building back of biofuel production facilities and refineriesCO2 emissions from utilizing construction equipment to demolish the buildings and construct new buildings in the old production facility/ biorefinery’s place

The total carbon footprint of biofuel would equal the carbon footprint from building + the carbon footprint from extracting + the carbon footprint from transportation + the carbon footprint from building back.

What Is the Carbon Footprint of Building Biofuel Production Facilities and Refineries

Ethanol is made in ethanol production facilities, and biodiesel is produced in biodiesel refineries (biorefineries). Both convert organic material into chemicals for making products that are otherwise made from fossil fuels. 

“Biorefinery: a facility that processes biological material (such as crop waste) to produce fuel (such as ethanol and biodiesel), electricity, and commercially useful chemicals (such as succinic acid)”

Merriam-Webster Dictionary

Ethanol production facilities and biorefineries have many components, and constructing these components requires machinery that emits CO2

What Is the Carbon Footprint of Extracting Biofuel

The extraction process is different for ethanol and biodiesel. For ethanol, ethanol feedstocks (corn) are grown, harvested, and transported to an ethanol production facility. The feedstocks are then converted to ethanol via biological conversion, specifically the process of fermentation. Fermentation converts sugars (glucose, fructose, sucrose) into ethanol and produces CO2 as a byproduct.

There are two main ways to produce ethanol from sugar or starch-based crops: dry and wet mill; plus there’s a distant third: cellulosic biomass. Approximately 90% of today’s ethanol is produced via dry milling, with the remainder largely via wet milling. The difference between the two is the initial treatment of the grain. 

  1. Dry mill: In dry milling, the grain kernel is first ground before being mixed with water to form a “mash”. Enzymes are then added to the mash to convert starch into sugar. The mash is cooked, cooled, and sent to fermenters where yeast is added and the sugars begin to convert to alcohol. After fermentation, the ethanol is distilled, dehydrated, and blended with a small percentage of gasoline before it is transported to gas pumps.
  1. Wet mill: In wet milling, the grain is first soaked to separate it into its basic parts. Grinders separate the corn germ from the fiber, gluten, and starch components, which are then further separated to isolate the starch. The remaining starch is sent to fermenters where yeast is added and the sugars begin to convert to alcohol. After fermentation, the ethanol is distilled, dehydrated, and blended with a small percentage of gasoline before it is transported to gas pumps. 
  1. Cellulosic biomass: Converting cellulosic feedstock (grass, wood, crop residue) to ethanol is a more involved process with two pathways, biochemical and thermochemical. In the former, biomass is pretreated to release hemicellulose sugars. Hydrolysis then breaks cellulose into sugar which is fermented into ethanol. In the latter, heat and chemicals are added to biomass to produce syngas, a mix of hydrogen and CO. Syngas is then mixed with a catalyst and reformed into ethanol. 

On the other hand, biomass sources are extracted and converted to biodiesel via chemical conversion, specifically the process of transesterification. In this process, vegetable oil, animal fat, and grease are converted into fatty acid methyl esters (FAME), producing biodiesel. 

Generally, 100 pounds of oil or fat reacts with 10 pounds of short-chain alcohol (methanol or ethanol) in the presence of a catalyst (sodium hydroxide [NaOH] or potassium hydroxide [KOH]) to form 100 pounds of biodiesel and 10 pounds of glycerin (or glycerol). 

What Is the Carbon Footprint of Transportation of Biofuel

In 2018, 160 bl of biofuels were produced globally from biomass. North and South America accounted for 75% and Europe 14% of global biofuel production. 

Illustration of biofuel energy production
Our World in Data: Biofuel Energy Production

The six largest biofuel-producing countries (amount per year) in the world are: 

  1. United States – 374 billion kilowatt-hours (bKWh)
  2. Brazil – 245 bKWh
  3. Indonesia – 78 bKWh
  4. Germany – 40 bKWh
  5. China – 39 bKWh
  6. Thailand – 27 bKWh

Calculating the carbon footprint of biofuel transportation involves knowing where the biofuel is produced, where it is being consumed, and the distance between the two. 

The United States exports 40% of its ethanol to Brazil and Canada. Transporting ethanol from the US to Brazil, for example, is an approximate 6,790 kilometer (km) (4,219 miles) transportation distance. Transporting biodiesel from the world’s largest biodiesel refinery, the Neste Singapore Refinery, to the US is a 15,299 kilometer (km) (9,500 miles) transportation distance. The carbon footprint of transportation for these circumstances would be high because it is a long distance that would require multiple modes of transportation. 

On the flip side, if biofuels are produced in one country and are consumed in that same country, the transportation distance is much shorter and would require fewer modes of transportation, leading to a lower carbon footprint for this stage. 

What Is the Carbon Footprint of Building Back Biofuel Production Facilities and Refineries

Since ethanol and biodiesel are relatively new industries, there is not much historical data available on the life expectancy of ethanol production facilities and biorefineries. Experts estimate that dry-mill ethanol production facilities can last anywhere from 30-60 years if maintained properly. And as a guesstimate, the average age of today’s oil refineries is around 40 years

CO2 emissions at this stage occur when utilizing construction equipment to demolish the buildings and construct new buildings in the old production facility or refinery’s place.

What Role Does Biofuel Play in Combating Climate Change

Ethanol and biodiesel can potentially play a crucial role in combating global climate change. Ethanol can reduce GHG emissions by 32-62% when compared with gasoline, and fuel made from cellulosic biomass can reduce GHG emissions by more than 100%. And B20 can reduce emissions from CO by 12.6%, hydrocarbons 11%, particulates 18%, and air toxics 12-20% although it may produce 1.2% more nitrogen oxide (NOx) emissions.

“Climate Change: changes in the world’s weather, in particular the fact that it is believed to be getting warmer as a result of human activity increasing the level of carbon dioxide in the atmosphere:”

Cambridge Dictionary

Climate change is arguably the most severe, long-term, global impact of fossil fuel combustion. Every year, approximately 36 billion tons (bt) of CO2 are emitted from burning fossil fuels. 12 bt (34%) of this comes from oil. The carbon found in fossil fuels reacts with oxygen in the air to produce CO2 which warms the earth by acting as a heating blanket.

Reduced CO2 emissions from ethanol and biodiesel combat climate change in the following ways:

  • Melting of sea ice: Since 1979 arctic sea ice has declined by 30%. Sea ice plays a major role in regulating the earth’s climate by reflecting sunlight into space and providing habitat for animal species. If all of the glaciers on Earth melted, sea levels would rise by approximately 70 feet, effectively flooding out every coastal city on the planet. 
  • Changing precipitation patterns: Extreme weather events (e.g., hurricanes, floods, droughts) are becoming more common and more intense. Storm-affected areas will experience increased precipitation and flooding whereas areas located further from storm tracks will experience decreased precipitation and droughts.
  • Ocean acidification: The ocean absorbs 30% of the CO2 released into the atmosphere, which decreases the pH (increases the acidity) of the ocean. In the past 200 years, the pH of oceans has decreased by 0.1 pH units, which translates to a 30% increase in acidity. Aquatic life unable to adjust to this rapid acidification will die off. A prime example of this is coral bleaching, where coral expel the algae (zooxanthellae) living in their tissues as a result of changes in temperature, light, or nutrients. 

Climate change results in global warming, when CO2 and other air pollutants absorb sunlight and solar radiation in the atmosphere, thereby trapping the heat and acting as an insulator for the planet. Since the Industrial Revolution, Earth’s temperature has risen a little more than 1 degree Celsius (C), or 2 degrees Fahrenheit (F). Between 1880-1980 the global temperature rose by 0.07C every 10 years. This rate has more than doubled since 1981, with a current global annual temperature rise of 0.18C, or 0.32F, for every 10 years. 

Experts claim that to avoid a future plagued by rising sea levels, acidified oceans, loss of biodiversity, more frequent and severe weather events, and other environmental disasters brought on by the hotter temperatures, we must limit global warming to 1.5C by 2040

The more we reduce CO2 emissions, the more we slow the rate of temperature rise, sea-level rise, ice melting, and ocean acidification. When these rates are slowed, the earth’s biodiversity does not have to struggle to adapt to temperature and pH changes. People will not be displaced due to the flooding of coastal areas. And icebergs will continue to provide climate regulation. 

How Environmentally Friendly Is Biofuel

Ethanol and biodiesel are biofuels that come with lower levels of GHG emissions compared to gasoline and petroleum diesel fuel. 

“Environmentally friendly: (of products) not harming the environment.”

Cambridge Dictionary

Both the environmental benefits and drawbacks of ethanol and biodiesel must be taken into consideration when discussing the issue of climate change.

What Are Environmental Benefits of Biofuel

The environmental benefits of both ethanol and biodiesel include:

  1. Climate change mitigation: In 2020, the use of ethanol in gasoline reduced CO2 emissions from the transportation industry by 47.3 million metric tons. This is the equivalent of removing 10.1 million cars from the road for 1 year or negating the emissions from 12 coal-fired power plants for a year! Biodiesel can decrease GHG emissions between 56-96%, the equivalent of planting 1.9 billion trees. It can also cut global warming pollution by 80-90% when compared to petroleum diesel. 
  1. Improves air quality: Blending ethanol into gasoline reduces tailpipe emissions from several pollutants including CO, hydrocarbons, benzene, and particulate matter. Biodiesel produces 1.0%, 8.3%, and 13% of the agricultural nitrogen, phosphorus, and pesticide pollutants, respectively, per net energy gain. These pollutants can reduce oxygen delivery to bodily organs, contribute to harmful ozone formation, and cause cancer and reproductive/birth defects. 

If made from waste materials or used cooking oil and operated at a small scale, biodiesel comes with other environmental benefits including: 

  1. Increases engine efficiency: Biodiesel yields 93% more energy than the energy used in its production. 
  1. Reduces wastewater: Biodiesel production, compared to petroleum diesel production, reduces wastewater by up to 79%.
  1. Reduces hazardous waste: Biodiesel is nontoxic, biodegradable, and can reduce hazardous waste by up to 96%. It will degrade quicker in the case of an oil spill, and it will not cause as many environmental problems compared to petroleum diesel. It also degrades when it comes into contact with water.

What Are Environmental Drawbacks of Biofuel

Some research suggests that by 2050, bioenergy (biomass and biofuel) could meet 20% of the world’s total annual energy demand. But ethanol and biodiesel cannot replace gasoline and diesel fuel as the world’s primary transportation fuels because it would require using ALL of the world’s crop harvests, plant residues, timber, and grass consumed by livestock. 

The main environmental drawbacks of ethanol and biodiesel are the amount of land needed to grow the biomass material and the source of that material. If made from unused cooking oil (canola, soybean, palm), instead of used cooking oil or waste material, biodiesel comes with environmental drawbacks. Some claim that biofuel is carbon neutral because the plants that are the source of the ethanol and biodiesel absorb CO2 as they grow, thereby offsetting the CO2 released when they are burned. But in some parts of the world, large swaths of forests have been cleared and burned to plant needed to make ethanol and biodiesel. Dedicating land for the sole purpose of biofuel production leads to deforestation, which in turn expedites global climate change. 

Our forests absorb 2.6 bt of CO2 every year. The main threat to them is deforestation, which occurs at roughly 10 million hectares (~ 25 million acres) per year. The world has lost more than 1/3 of its forest since the last ice age, which occurred about 2.6 million years ago. Trees combat climate change, purify the air, provide housing for millions of plant and animal species, protect against floods and water pollution, and improve mental health. Chopping these trees to make space for crops has a devastating effect on the environment because it reduces the amount of trees that can capture our CO2 emissions. Protecting forest habitats increases carbon sequestration and decreases the effects of global climate change. 

The best ways to avoid the environmental drawbacks associated with ethanol and biodiesel are to avoid dedicating land for the sole purpose of biofuel production and to use waste products and used cooking oils instead of unused cooking oils. The scale of ethanol and biodiesel production is also important to consider because the land needed to produce these is also needed for food and carbon storage.

Final Thoughts

Ethanol and biodiesel emit less CO2 than their fossil-fuel counterparts, gasoline and petroleum diesel, when burned and also come with lower levels of harmful air pollutants. They have a low carbon footprint across their building, extraction, transportation, and building back stages. Besides combating climate change, they also help improve air quality and reduce hazardous waste. Deforestation is the environmental drawback that must be taken into consideration when discussing using biofuel as an alternative fuel source.

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