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

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

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Grace Smoot

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Biogas is a combustible gas created by anaerobic decomposition or thermochemical conversion. It is a subset of biomass that some say is more sustainable and has more greenhouse gas (GHG) reduction benefits than solid biomass. So we had to ask: What is the carbon footprint of biogas?

Biogas is a form of biomass energy with a lower carbon footprint than fossil fuels and solid biomass. On a life-cycle basis, biogas energy emits between -81 and 251 grams of CO2 equivalent per kWh of electricity produced. Biogas helps combat climate change and has various environmental benefits.

Biogas energy makes up an ever-growing amount of total energy consumption and plays a vital role in combating climate change. Keep reading to learn about the overall carbon footprint of biogas energy, its carbon footprint throughout its life-cycle, and its environmental impact. 

How is Biogas Energy Defined

Biogas is an energy-rich form of biomass. Biomass is renewable organic material that comes from plants and animals. It is incredibly versatile and can be used to produce fuel, energy, and everyday products that contain plastics. 

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

Sources of biomass energy include:

  • Wood and wood processing wastes
  • Agricultural crops and waste materials
  • Municipal solid waste
  • Animal manure
  • Human sewage

Biomass includes solid biomass for traditional use (cooking and heating), solid biomass for modern use (transportation), biofuels, and biogas. 

Biogas is a gas composed of 45% to 75% methane (CH4) and the remainder as CO2. Created through anaerobic decomposition or thermochemical conversion of biomass, biogas is either burned to create electricity or can be further purified. This purified biogas is known as renewable natural gas, or biomethane, and can be used in place of conventional natural gas.

Biogas: a gas containing methane that can be burned as a fuel, produced by dead plants and animals as they decay”

Cambridge Dictionary

Biogas is inherently biomass, but not all biomass can be converted into biogas. 

Sources of biogas energy include:

  • Crop residue
  • Landfills
  • Sewage and industrial wastewater treatment
  • Animal waste

Biogas production has increased substantially since the start of the 21st century. Global production increased from 77 terawatt-hours (TWh) in 2000 to 378 TWh in 2018

What is the Carbon Footprint of Biogas Energy 

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 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). 

What Is the Overall Carbon Footprint of Biogas Energy

Solid biomass energy emits 230 grams of carbon dioxide equivalent per kWh (gCO2 per KWh), the fourth-highest amount out of all of the fuel types, and the highest amount out of all of the renewable fuel types. Biogas energy emits between -81 and 251 gCO2 per KWh, lower than that of solid biomass and potentially lower than all other fuel types.

Illustration of CO2 equivalent per energy source
World Nuclear Association: Average life-cycle CO2 equivalent emissions

In 2018, 637 Terawatt hours (TWh) of electricity were produced globally from biomass. Solid biomass accounted for 66% (420 TWh), municipal and industrial waste accounted for 19% (121 TWh), and biogas accounted for 14% (89 TWh) of total biopower. 

International Energy Agency: Biogas production by region and by feedstock type, 2018

Globally, biogas has developed unevenly due to the uneven availability of materials and policies between countries. For example, most parts of Europe use crop residue, sequential crops, animal waste, and landfill methane as sources of biogas. China uses household-scale digesters which account for over 70% of their installed biogas capacity. The US mainly uses landfill methane and some animal waste as sources of biogas which account for 90% of their biogas production. Together, Europe, China, and the US account for 90% of global biogas production

The top 6 bioenergy producing countries (amount per year) in the world are:

  1. China – 18,687 megawatts (MW)
  2. Brazil – 15,650 MW
  3. US – 12,372 MW
  4. India – 10,532 MW
  5. Germany – 10,364 MW
  6. United Kingdom – 7,250 MW

Because biogas production and consumption have steadily increased since 2000, it is important to understand what its carbon footprint is and how its carbon emissions affect the global climate change process.

To understand the carbon footprint of biogas, 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 biogas!

The life-cycle stages of biogasEach stage’s carbon footprint
Building of biogasCO2 emissions from harvesting and extracting biomass, constructing the biogas power plant, and transporting the biomass material to the power plant
Operating of biogasCO2 emissions from conversion of biomass into biogas and operation of equipment at biogas power plants
Building back of biogasCO2 emissions from utilizing construction equipment to demolish the buildings and construct new buildings in the old power plant’s place

The total carbon footprint of biogas energy would equal the carbon footprint from building + the carbon footprint from operating + the carbon footprint from building back.

What Is the Carbon Footprint of Building Biogas

Building biogas energy includes harvesting and extracting the biomass, constructing the power plant, and transporting the biomass material to the power plant. 

Biomass sources are extracted and converted to biogas energy via the following two processes:

  • Thermochemical Conversion: Gasification and pyrolysis, thermal decomposition processes where biomass is heated in a closed and pressurized vessel, are used to produce synthetic gas (syngas) or charcoal, bio-oil, renewable diesel, methane, and hydrogen, respectively. The two processes differ in the temperature and amount of oxygen in the reaction.

Once the biomass has been harvested, it is transported to biomass power plants by rail or truck, which run on diesel fuel. Burning one gallon of diesel fuel produces 22.38 pounds of CO2

Biogas power plants also have many components, and constructing these components requires machinery that emits CO2. Fuel storage and handling equipment, combustors/furnaces, boilers, pumps, fans, turbines, generators, condensers, cooling towers, and emission controls are all components with a carbon footprint. 

What Is the Carbon Footprint of Operating Biogas

Emissions at this stage occur upon conversion of biomass into biogas and are associated with the operation of the mechanical equipment (e.g. turbines and generators) at the Biogas power plant.

Biomass is converted into biogas via one of the following processes:

  • Biological conversion: Biomass material is collected in digesters, tanks without oxygen. Anaerobic bacteria break down the biomass and produce methane and other byproducts to form biogas (renewable natural gas) which are then purified and combusted to produce electricity. 

Combustion of biogas does release CO2, however, the amount is much less when compared to fossil fuels and even solid biomass. 

CO2 emissions at this stage occur upon biomass conversion processes and are also associated with the operation of the mechanical equipment (e.g., turbines and generators) at the biogas power plant. 

What Is the Carbon Footprint of Building Back Biogas

Similar to biomass power plants, biogas power plants have a historical life expectancy of 20-30 years. CO2 emissions at this stage occur when utilizing construction equipment to demolish the buildings and construct new buildings in the old power plant’s place. 

What Role Does Biogas Play in Combating Climate Change

Fossil fuel combustion is the main contributor to atmospheric CO2 levels. Climate Change occurs when CO2 and other air pollutants absorb sunlight and solar radiation in the atmosphere, 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). The current global annual temperature rise is 0.18C, or 0.32F, for every 10 years. 

Using biogas energy instead of fossil fuel energy helps mitigate the following negative effects of climate change:

  • 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. 

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

Per kWh energy produced, regular biomass power plants emit 150% the CO2 of coal and between 300% – 400% the CO2 of natural gas, making them a major contributor to climate change. Biogas, on the other hand, could reduce global GHG emissions by 10-13%.

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 Biogas

Biogas is a subset of biomass with GHG reduction potential because it is more sustainable compared to solid biomass. 

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

Cambridge Dictionary

Biogas is a sustainable alternative to fossil fuels with CO2 reduction benefits and various other environmental benefits. 

What Are the Environmental Benefits of Biogas

The environmental benefits of biogas include:

  1. Climate Change Mitigation: Using biogas avoids fossil fuel combustion emissions, captures methane from animal manure that would have otherwise entered the atmosphere, creates green fertilizer (digestate) which negates the need to chemically produce mineral fertilizer, and enables soils to act as carbon sinks. This reduction in CO2 emissions, in turn, reduces the effects of global climate change including increasing temperatures, rising sea levels, melting of sea ice, changing precipitation patterns, and ocean acidification.
  1. Improved Air Quality: Using biogas instead of fossil fuels in vehicles and for cooking and heating decreases the amount of CO2, toxic chemicals, and particulate matter released into the atmosphere. Capturing methane from landfills that would otherwise escape into the atmosphere uncontrolled protects the ozone layer thereby improving air quality. 
  1. Improved Solid Waste Management: One of the sources of biogas energy is sewage and industrial wastewater treatment. Biogas energy generation helps prevent the spread of disease from uncontrolled dumping through proper collection and management of organic waste. Improved sanitation, hygiene, and recycling of organic wastes are also benefits of biogas energy. 
  1. Improved Food Security: Using biogas increases nutrient (i.e. carbon, organic matter, phosphorus) cycling through soils and decreases our dependence on inorganic fertilizers. 
  1. Reduced Deforestation:  Our forests absorb 2.6 billion tons 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. By using biogas-derived biomass instead of wood and wood processing waste-derived biomass we can maintain the amount of trees that can capture our CO2 emissions, thereby increasing carbon sequestration and reducing deforestation. 
  1. Energy Independence: Being able to produce our own electricity in the U.S. without the aid of foreign countries is an important step to help us become more self-sufficient instead. Former President George W. Bush signed the Energy Independence and Security Act of 2007 to reduce U.S. dependence on oil, expand the production of renewable fuels (and confront global climate change). 
  1. Employment Opportunities: The renewable energy sector employed 11.5 million people worldwide in 2019, with biogas being one major contributing sector. Renewable energy jobs continue to increase as we start to realize just how beneficial renewable energy is for our environment. 

Whereas solid biomass contributes to global warming, biogas does the opposite. It aids in the fight against climate change and creates jobs while promoting energy independence. 

What Are the Environmental Drawbacks of Biogas

Well, here’s the main environmental drawback of biogas (comparatively speaking):

  1. Relative CO2 Emissions Compared to Clean Energy: Biogas does still emit some CO2 and methane when it is combusted – while this is not much in absolute terms, it is still a multiple of what the cleanest of energies emit.

However, the amount of CO2 emissions is much less compared to the amount emitted when combusting solid biomass and fossil fuels.

Final Thoughts

Biogas is a subset of biomass that has a lower carbon footprint across its building, operating, and building back phases when compared to solid biomass. It mitigates climate change, improves air quality and waste management, creates jobs, and promotes energy independence. 

Although the combustion of biogas does release CO2 and methane, the amount is much less than solid biomass and fossil fuels, making it environmentally friendly overall. As we begin to transition away from fossil fuels and towards renewable energy, biogas is a sustainable option that should be utilized in the transition. 

Stay impactful,

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