Carbon Sequestration: Methodology, Benefits and Risks

Satyesh Bhandari

Carbon dioxide is the most commonly produced greenhouse gas. Carbon sequestration is?the process of capturing and storing atmospheric carbon dioxide.

Carbon sequestration or CO2 sequestration is?the process of capturing, removal and permanent storage of CO2?from the earth's atmosphere. It's recognised as a key method for removing or reducing carbon from the earth's atmosphere, which is a major contributor to global warming and climate change.

There is a difference between carbon storage and Carbon sequestration. ?Carbon sequestration refers to the process of removing carbon from the atmosphere and depositing it in a reservoir, while carbon storage refers to the quantity of carbon stored in a reservoir. Carbon sequestration refers to?the storage of CO2, after it is captured from industrial facilities and power plants or removed directly from the atmosphere. Those captured CO2 emissions are then safely transported and permanently stored in geologic formations.

Carbon sequestration: Methodology

There are two primary methods of CO2 sequestration:

1. Geological Sequestration: Once CO2?has been captured using CCUS technology,?it's pressurised and turned into a liquid-like form known as 'supercritical CO2'. From there it's transported via pipeline and injected into the rocks found in the formations deep below the earth's surface. This is a process called geological sequestration. These formations can include depleted oil and gas fields, deep saline aquifers, ?un-mineable coal seams, Oil- and gas-rich organic shale and basalt. The CO2 is stored in the pore spaces of the rocks, effectively removing it from the atmosphere for potentially millions of years.
2. Biological Sequestration: This involves capturing CO2 through natural processes such as photosynthesis. Plants, trees, and other vegetation absorb CO2 from the atmosphere and store it as carbon in biomass (trunks, branches, roots, and leaves) and in soils. Forests, grasslands, and agricultural lands can serve as significant carbon sinks.

CO2 sequestration is considered a crucial strategy for mitigating the effects of climate change, alongside reducing greenhouse gas emissions and increasing the use of renewable energy sources.

Materials for CO2?capture and sequestration

The most widely used solid materials for CO2?capture are silica, zeolites, alumina, amine-based materials, metal oxides, metal-organic frameworks (MOFs), polymers, and carbon materials (activated carbon, graphite, graphene, fullerene, carbon nanotubes, biochar, and hydrochar).

Carbon sequestration involves a variety of materials and technologies depending on the method used. Here are some of the key materials involved in different types of carbon sequestration:

Geological Sequestration

1. CO2 Capture Materials: Amine-based solvents: These are used to chemically absorb CO2 from flue gases in power plants and industrial processes. Ionic liquids: Salts in a liquid state that can dissolve CO2 at certain temperatures and pressures. Metal-organic frameworks (MOFs): Porous materials that can adsorb CO2 due to their high surface area.
2. Injection Materials: Pipelines: Steel or composite materials are used for transporting captured CO2 to storage sites. Well Cements: Specialized cements are used to seal wells and prevent CO2 leakage. Reservoir Rocks: Porous and permeable rock formations such as sandstone or limestone that can store injected CO2.

Biological Sequestration

1. Vegetation: Trees and Forests: Various species of trees are planted in reforestation and afforestation projects to absorb CO2 through photosynthesis. Crops and Grasses: Agricultural practices can enhance carbon storage in plants and soil.
2. Soil Additives: Biochar: Charcoal-like substance made from biomass that can be added to soil to increase carbon storage. Compost and Organic Matter: Adding organic materials to soil can improve its carbon content.

Ocean Sequestration

1. Alkaline Materials: Limestone and other carbonates: These can be added to the ocean to enhance the natural process of carbon mineralization. Alkaline wastes: Industrial by-products that can increase the ocean's capacity to absorb CO2.

Chemical Sequestration

1. Mineral Carbonation Materials: Magnesium and calcium silicates: These minerals react with CO2 to form stable carbonates. Olivine and serpentine: Specific types of silicate minerals used in mineral carbonation processes.

Each of these materials plays a crucial role in the capture, transportation, and storage of CO2, contributing to the overall effectiveness of carbon sequestration strategies.

Benefits of CO2 Sequestration ?

CO2 sequestration offers several benefits, primarily related to mitigating climate change and improving environmental health. Here are some key benefits:

1. Reduction of Atmospheric CO2 Levels: By capturing and storing CO2, sequestration helps reduce the concentration of this greenhouse gas in the atmosphere, thus mitigating global warming and climate change.
2. Enhanced Climate Stability: Lower atmospheric CO2 levels contribute to more stable global temperatures, reducing the risks associated with extreme weather events, sea-level rise, and other climate-related impacts.
3. Improved Air Quality: Reducing CO2 emissions can also lower the presence of other pollutants, such as particulate matter and nitrogen oxides, which are often released alongside CO2 from fossil fuel combustion. This leads to better air quality and public health benefits.
4. Economic Opportunities: The development and deployment of CO2 sequestration technologies can create new jobs and industries. This includes roles in research, engineering, construction, and maintenance of sequestration projects.
5. Enhanced Soil and Forest Management: Biological sequestration methods, such as reforestation and improved agricultural practices, can improve soil health, increase biodiversity, and enhance ecosystem services.
6. Sustainable Energy Production: CO2 sequestration can be integrated with energy production methods, such as bioenergy with carbon capture and storage (BECCS), to create a net-negative carbon impact, meaning more CO2 is removed from the atmosphere than is emitted.
7. Extension of Fossil Fuel Use: While the ultimate goal is to transition to renewable energy, CO2 sequestration can help manage emissions from existing fossil fuel infrastructure, allowing for a more gradual and economically feasible transition.
8. Regulatory Compliance: Companies and countries can use CO2 sequestration to meet regulatory requirements and international commitments to reduce greenhouse gas emissions, such as those outlined in the Paris Agreement.

About?two billion tonnes?of carbon dioxide are being removed from the atmosphere every year, scientists have calculated for the first time. But nearly all of it is down to forests, despite growing investments in new technologies. Top of Form

Risks Involved in CO2 sequestration

CO2 sequestration, while beneficial for reducing greenhouse gas emissions, carries certain risks that need to be managed carefully. Here are some of the key risks associated with CO2 sequestration:

Geological Sequestration

1. Leakage: There is a risk that stored CO2 could leak from geological formations back into the atmosphere through faults, fractures, or improperly sealed wells. This would negate the benefits of sequestration and could pose environmental and safety hazards.
2. Induced Seismicity: Injecting CO2 into underground formations can increase pressure and potentially trigger earthquakes. This is a particular concern in areas with active fault lines.
3. Groundwater Contamination: There is a risk that CO2, or brine displaced by CO2 injection, could migrate and contaminate underground sources of drinking water.

Ensuring that CO2 remains securely stored over long periods requires robust monitoring and verification technologies, which can be costly and complex.

Biological Sequestration

1. Land Use Changes: Large-scale afforestation or reforestation projects can lead to changes in land use, potentially displacing agricultural activities and affecting food security.
2. Biodiversity Impacts: Planting monocultures or non-native species for carbon sequestration can harm local biodiversity and disrupt ecosystems.
3. Forest Fires and Pest Outbreaks: Sequestered carbon in forests can be released back into the atmosphere through forest fires or pest outbreaks, reducing the effectiveness of sequestration efforts.
4. Soil Carbon Release: Changes in land management practices intended to enhance soil carbon sequestration can sometimes lead to unintended release of soil carbon if not properly managed.

Ocean Sequestration

1. Ocean Acidification: Adding CO2 to the ocean can increase its acidity, which can harm marine life, particularly organisms with calcium carbonate shells or skeletons, such as corals and shellfish.
2. Ecosystem Disruption: Large-scale ocean sequestration projects could disrupt marine ecosystems and food webs, with uncertain and potentially harmful consequences.

Chemical Sequestration

1. Energy Intensive Processes: Many chemical sequestration methods require significant energy input, which can offset the benefits if the energy comes from fossil fuels.
2. Material Availability: The availability and extraction of minerals required for chemical sequestration, such as magnesium and calcium silicates, can have environmental impacts.

General Risks

1. Economic Costs: The costs associated with CO2 capture, transportation, and storage can be high, and economic viability depends on regulatory frameworks, carbon pricing, and technological advancements.
2. Regulatory and Legal Issues: Uncertainties in regulatory frameworks and legal liabilities regarding long-term storage and potential leaks can pose challenges for widespread adoption of CO2 sequestration technologies.
3. Public Acceptance: Public perception and acceptance of CO2 sequestration projects can influence their implementation. Concerns about safety and environmental impact can lead to opposition from local communities.

Addressing these risks requires careful planning, robust monitoring, regulatory oversight, and continuous research and development to improve the safety and effectiveness of CO2 sequestration technologies.