Harnessing potential of biological CO2 capture for Circular Economy

Absorption: Carbon capture technology (see CCUS) where a fluid (CO₂) is dissolved by a liquid or a solid (absorbent). Can be distinguished as natural and chemical.

Acetoclastic methanogens: Group of microorganisms belonging to methanogens. They utilize acetate (CH₃COOH) as an electron acceptor in order to produce methane (CH₄). [1]

Acetogenesis: Process of anaerobic digestion, where acetate is produced by the reduction of CO₂ or the reduction of organic acids [2]

Acidogenesis: The fermentation process where acidogenic microorganisms break down the hydrolyzed compounds (soluble organic monomers of sugars and amino acids) to create alcohols, aldehydes, volatile fatty acids (VFAs), and acetate along with H₂ and CO₂. [3]

Adsorption: Carbon capture technology (see CCUS). Process in which, molecules of a fluid (CO₂) adhere to the surface of the adsorbent.

Alkaline Water Electrolysis (AWE): Electrolysis technology (see Electrolysis). Alkaline water electrolysis is used to split water into hydrogen and oxygen gases. At the cathode, water (H₂O) molecules are reduced by electrons to hydrogen (H₂) and negatively charged hydroxide ions (OH^–). At the anode, hydroxide ions are oxidized to oxygen (O₂) and water (H₂O) while releasing electrons. [4]

Anaerobic Digestion: The biological degradation of organic matter (with the aid of microorganisms) in the absence of Oxygen (O₂), releasing the product in the form of biogas composed mainly of methane. [5]

Anthropogenic removals: The withdrawal of GHGs from the atmosphere because of deliberate human activities. (e.g. planting trees).[6]

Archaea: Group of microorganisms. Similar to bacteria but with evolutionary distinction from them. Archaea can be spherical, rod, spiral, lobed, rectangular, or irregular in shape. Some species may exist under extreme conditions (temperature and pressure). They can exist as single cells, others form filaments or clusters. [7]

Bibliography

[1]  D.E. Holmes, J.A. Smith, Chapter One – Biologically Produced Methane as a Renewable Energy Source, in: S. Sariaslani, G. Michael Gadd (Eds.), Advances in Applied Microbiology, Academic Press, 2016: pp. 1–61. https://doi.org/10.1016/bs.aambs.2016.09.001.

[2]  I. Angelidaki, D. Karakashev, D.J. Batstone, C.M. Plugge, A.J.M. Stams, Chapter sixteen – Biomethanation and Its Potential, in: A.C. Rosenzweig, S.W. Ragsdale (Eds.), Methods in Enzymology, Academic Press, 2011: pp. 327–351. https://doi.org/10.1016/B978-0-12-385112-3.00016-0.

[3]  R. Kamusoko, R.M. Jingura, Z. Chikwambi, W. Parawira, Chapter 25 – Biogas: microbiological research to enhance efficiency and regulation, in: S. Sahay (Ed.), Handbook of Biofuels, Academic Press, 2022: pp. 485–497. https://doi.org/10.1016/B978-0-12-822810-4.00025-7.

[4]  J. Brauns, T. Turek, Alkaline Water Electrolysis Powered by Renewable Energy: A Review, Processes. 8 (2020) 248. https://doi.org/10.3390/pr8020248.

[5]  S. Kumar, S. Ankaram, Chapter 12 – Waste-to-Energy Model/Tool Presentation, in: S. Kumar, R. Kumar, A. Pandey (Eds.), Current Developments in Biotechnology and Bioengineering, Elsevier, 2019: pp. 239–258. https://doi.org/10.1016/B978-0-444-64083-3.00012-9.

[6]  Glossary — Global Warming of 1.5 ^oC, (n.d.). https://www.ipcc.ch/sr15/chapter/glossary/ (accessed July 27, 2022).

[7]  M. Society, Archaea | What is microbiology?, (n.d.). https://microbiologysociety.org/why-microbiology-matters/what-is-microbiology/archaea.html (accessed July 27, 2022).

Bacteria: Procaryotic single-celled organisms. They are vital to the planet’s ecosystem. They can be spherical, rods, or they can be spiral in shape. [1]

Biodiversity: The variety of life on earth. All creatures, species, and populations, as well as their genetic variation and complex assemblages of communities and ecosystems, are included.[2]

Bioenergy with carbon dioxide capture and storage (BECCS): Geoengineering technique that, in addition to replacing fossil fuel energy, eliminates carbon dioxide (CO₂) from the atmosphere. [3]

Bioenergy: It is a type of renewable energy obtained from recently lived organic materials known as biomass, and it may be utilized to generate transportation fuels, heat, power, and goods. [4]

Biofuel: Any fuel that is derived from biomass (see biomass).

Biogas: Biogas is a methane-rich gas that is created by anaerobic digestion (see anaerobic digestion) of wastes (agricultural, sewage, and landfill) and may be utilized to generate electricity. The composition of biogas varies depending on the source, although it typically has a high carbon dioxide (CO₂) level (30-50%) and in small amounts hydrogen sulfide (H₂S). [5]

Biological methanation (BM): Synonym of hydrogenotrophic methanogenesis (see hydrogenotrophic methanogenesis)

Biomass: Plant-based material (for example, wood, energy crops, residues, and so on) used as a fuel to generate heat or power.

Bioreactor: A vessel-like device that offers a homogeneous environment for microorganisms to flourish while maintaining a continuous balance in the metabolic processes carried out by these microorganisms in order to create desired products.[6]

[1]  Bacteria, Genome.Gov. (n.d.). https://www.genome.gov/genetics-glossary/Bacteria (accessed July 27, 2022).

[2]  What is biodiversity?, (n.d.). https://www.unesco.pl/fileadmin/user_upload/pdf/BIODIVERSITY_FACTSHEET.pdf (accessed July 27, 2022).

[3]  Preventing Climate Change with BECCS: Bioenergy With Carbon Capture and Storage, PSCI. (n.d.). https://psci.princeton.edu/tips/2020/11/15/preventing-climate-change-with-beccs-bioenergy-with-carbon-capture-and-storage (accessed July 27, 2022).

[4]  Bioenergy Basics, Energy.Gov. (n.d.). https://www.energy.gov/eere/bioenergy/bioenergy-basics (accessed July 27, 2022).

[5]  I. Angelidaki, L. Treu, P. Tsapekos, G. Luo, S. Campanaro, H. Wenzel, P.G. Kougias, Biogas upgrading and utilization: Current status and perspectives, Biotechnology Advances. 36 (2018) 452–466. https://doi.org/10.1016/j.biotechadv.2018.01.011.

[6]  P. Jaibiba, S. Naga Vignesh, S. Hariharan, Chapter 10 – Working principle of typical bioreactors, in: L. Singh, A. Yousuf, D.M. Mahapatra (Eds.), Bioreactors, Elsevier, 2020: pp. 145–173. https://doi.org/10.1016/B978-0-12-821264-6.00010-3.

Carbon cycle: The movement of carbon through Earth system pathways. It is one of the main biochemical cycles of the earth’s ecosystem. From the atmosphere to autotrophic organisms in order to produce glucose and with respiration back to the atmosphere. [1]

Carbon dioxide (CO₂): A colorless and non-flammable gas at normal temperature and pressure. Although less abundant than nitrogen (N₂) and oxygen (O₂) in Earth’s atmosphere, CO₂ is an important component of the planet’s air. It is an important greenhouse gas (see GHG) that aids in the trapping of heat in the atmosphere. Without it, the planet would be inhospitably cold. However, an increase in CO₂ concentrations in the atmosphere causes an increase in the average global temperature, disrupting the Earth’s climate. [1]

Carbon Dioxide Capture, Utilization, and Storage (CCUS): Involve the capture of CO₂ from large point sources, including power generation or industrial facilities that use either fossil fuels or biomass for fuel. If not being used on-site, the captured CO₂ is compressed and transported by pipeline, ship, rail, or truck to be used in a range of applications or injected into deep geological formations (see EOR) for permanent storage. [2]

Carbon Dioxide equivalent emission (CO₂e): The number of metric tons of CO₂ emissions with the same global warming potential as one metric ton of another greenhouse gas. [3]

Carbon neutrality: The balance between carbon emissions and the absorbed carbon from the atmosphere in carbon sinks.

Carbon sinks: Anything that removes more carbon from the atmosphere than it absorbs. Examples include soil, plants, and the ocean. [4]

Carbon sources: Anything that releases more carbon into the atmosphere than it absorbs. For example, the burning of fossil fuels or volcanic eruptions. [4]

Catalytic methanation (CM): The production of methane (CH₄) with the use of catalysts. Known as the Sabatier process and is carried out at high temperature (300°C) and high pressure (5-20 MPa) [5]

Climate change: Long-term change in temperature and weather patterns. This change might be caused by natural processes, such as variations in the solar cycle. But since the 1800s, human activities—primarily the combustion of fossil fuels like coal, oil, and gas—have been the primary cause of climate change. [6]

Climate-resilient development pathways (CRDPs): Paths that outline directions that aim to increase sustainable development, while keeping global warming to 1.5°C. [7]

Continuous Stirred Tank Reactor (CSTR): A Continuous Stirred Tank Reactor (CSTR) is a reaction vessel in which continuous input (reagents, reactants and often solvents) flow into the reactor while the output (product(s) of the reaction) concurrently exit(s) the vessel. The CSTR is well mixed with no dead zones. [8]

Cryogenics: Carbon capture technology (see CCUS). It is a gas separation process that uses the method of distillation at very low temperatures and high pressure. [9]

Bibliography

[1]  G.T. Farmer, J. Cook, Carbon Dioxide, Other Greenhouse Gases, and the Carbon Cycle, in: G.T. Farmer, J. Cook (Eds.), Climate Change Science: A Modern Synthesis: Volume 1 – The Physical Climate, Springer Netherlands, Dordrecht, 2013: pp. 199–215. https://doi.org/10.1007/978-94-007-5757-8_9.

[2]  Carbon capture, utilisation and storage – Fuels & Technologies, IEA. (n.d.). https://www.iea.org/fuels-and-technologies/carbon-capture-utilisation-and-storage (accessed July 27, 2022).

[3]  EPA, Carbon footprint calculator-Definitions, (n.d.). https://www3.epa.gov/carbon-footprint-calculator/tool/definitions/co2e.html (accessed July 27, 2022).

[4]  What is a carbon sink?, (n.d.). https://www.clientearth.org/latest/latest-updates/stories/what-is-a-carbon-sink/ (accessed July 27, 2022).

[5]  M. Götz, A. McDaniel Koch, F. Graf, State of the Art and Perspectives of CO2 Methanation Process Concepts for Power-to-Gas Applications, in: International Gas Union Research Conference, Copenhagen, 2014.

[6]  U. Nations, What Is Climate Change?, United Nations. (n.d.). https://www.un.org/en/climatechange/what-is-climate-change (accessed July 27, 2022).

[7]  Special Report-Glossary-Global Warming of 1.5 ^oC, (n.d.). https://www.ipcc.ch/sr15/chapter/chapter-5/faq-5-2-2/ (accessed July 27, 2022).

[8]  R. Meyers, Encyclopedia of Physical Science and Technology | ScienceDirect, 3d ed., Academic Press, San Diego, 2002. https://www.sciencedirect.com/referencework/9780122274107/encyclopedia-of-physical-science-and-technology (accessed July 27, 2022).

[9]  D.Y.C. Leung, G. Caramanna, M.M. Maroto-Valer, An overview of current status of carbon dioxide capture and storage technologies, Renewable and Sustainable Energy Reviews. 39 (2014) 426–443. https://doi.org/10.1016/j.rser.2014.07.093.

Decarbonization: This term refers to the process of reducing carbon dioxide (CO₂) emissions.

Digestate: The remaining material of anaerobic digestion.

Ecosystem: An ecosystem, also known as an ecological system, is made up of all the creatures and the physical setting in which they live. The nutrition cycles and energy fluxes connect these biotic and abiotic elements. [1]

Enhanced Oil Recovery: Carbon utilization process, where CO₂ can be injected into depleted oil/gas wells to increase their pressure and provide the driving force to extract the remaining oil/gas, while the injected CO₂ remains stored there permanently. [2]

Ex situ biomethanation: Biomethanation that takes place outside the anaerobic digester, in a new reactor. External addition of hydrogen (H₂) and carbon dioxide (CO₂). [3]

Bibliography

[1]  S. Chapin, P. Matson, P. Vitousek, Principles of Terrestrial Ecosystem Ecology, 2nd ed., Springer, New York, n.d. https://doi.org/10.1007/978-1-4419-9504-9 (accessed July 27, 2022).

[2]  D.Y.C. Leung, G. Caramanna, M.M. Maroto-Valer, An overview of current status of carbon dioxide capture and storage technologies, Renewable and Sustainable Energy Reviews. 39 (2014) 426–443. https://doi.org/10.1016/j.rser.2014.07.093.

[3]  I. Angelidaki, L. Treu, P. Tsapekos, G. Luo, S. Campanaro, H. Wenzel, P.G. Kougias, Biogas upgrading and utilization: Current status and perspectives, Biotechnology Advances. 36 (2018) 452–466. https://doi.org/10.1016/j.biotechadv.2018.01.011.

Gas Retention Time (GRT): Retention time measures how long a gas remains in the system. The lower the retention time, the more compact a system achieved due to the shorter travel path of gases within the reactor system. [1]

Global warming: Consequence of climate change.

Greenhouse Gases (GHG): Gases that trap heat in the atmosphere.

Bibliography

[1]  D. Rusmanis, R. O’Shea, D.M. Wall, J.D. Murphy, Biological hydrogen methanation systems – an overview of design and efficiency, Bioengineered. 10 (2019) 604–634. https://doi.org/10.1080/21655979.2019.1684607.

Homoacetogenesis: The reduction of carbon dioxide (CO₂) with hydrogen (H₂) to acetate. [1]

Hydrogen (H₂): The lightest element. At standard conditions, hydrogen is a gas of diatomic molecules. It is colorless, odorless, tasteless, non-toxic, and highly combustible. It is the most abundant chemical substance in nature, constituting roughly 75% of all normal matter. [2]

Hydrogenotrophic methanogenesis: Is called also biomethanation. The conversion of carbon dioxide (CO₂) and hydrogen (H₂) to methane (CH₄₎ by means of specialized microorganisms, called hydrogenotrophic methanogens. [3]

Hydrogenotrophic methanogens: Microorganisms that carry out hydrogenotrophic methanogenesis. Strictly anaerobic. They belong to the Archaea species. [3]

Bibliography

[1]  R. Ye, Q. Jin, B. Bohannan, J.K. Keller, S.D. Bridgham, Homoacetogenesis: A potentially underappreciated carbon pathway in peatlands, Soil Biology and Biochemistry. 68 (2014) 385–391. https://doi.org/10.1016/j.soilbio.2013.10.020.

[2]  Hydrogen | Properties, Uses, & Facts | Britannica, (n.d.). https://www.britannica.com/science/hydrogen (accessed July 27, 2022).

[3]  D. Rusmanis, R. O’Shea, D.M. Wall, J.D. Murphy, Biological hydrogen methanation systems – an overview of design and efficiency, Bioengineered. 10 (2019) 604–634. https://doi.org/10.1080/21655979.2019.1684607.

in-situ biomethanation: Biomethanation that takes place in the anaerobic digester, with internal addition of CO₂ that comes out from the degradation of the organic matter, and external addition of Hydrogen (H₂). The opposite of ex-situ biomethanation. [1]

Bibliography

[1]  I. Angelidaki, L. Treu, P. Tsapekos, G. Luo, S. Campanaro, H. Wenzel, P.G. Kougias, Biogas upgrading and utilization: Current status and perspectives, Biotechnology Advances. 36 (2018) 452–466. https://doi.org/10.1016/j.biotechadv.2018.01.011.

Kyoto Protocol: An international agreement that commits the industrialized nations to set limits on greenhouse gas emissions, based on the scientific consensus that firstly global warming is occurring and secondly that human-made CO₂ emissions are driving it. The Kyoto Protocol was adopted in Kyoto, Japan, on 11 December 1997 and entered into force on 16 February 2005. [1]

Bibliography

[1]  O. Geden, S. Fischer, Moving Targets – Negotiations on the EU’s Energy and Climate Policy Objectives for the Post-2020 Period and Implications for the German Energy Transition, 2014.

Maladaptive actions (Maladaptation): Actions that might result in increased susceptibility to climate change, higher risk of unfavorable climate-related consequences, or decreased welfare, either now or in the future. [1]

Membrane separation: Carbon capture technology, where carbon dioxide is separated from the other gaseous components, due to a concentration gradient and the selective permeability of the membrane. [2]

Mesophilic methanogens: Biomethanation systems can be either mesophilic or thermophilic, characterizing the methanogenic population. Mesophilic methanogens range from 30 to 45 ^oC. [3]

Methanation: The reaction between carbon dioxide (CO₂) and hydrogen (H₂) with the main product methane (CH₄) and byproduct water (H₂O). It is distinguished in biological and thermocatalytic.

Methane (CH₄): Colorless and odorless gas that is produced both naturally and because of some human activities. One of the most potent greenhouse gases. The product of hydrogenotrophic methanogenesis. [4]

Methanogens: Microorganisms that carry out methanation.

Methylotrophic methanogens: Methanogens group, that use methylated substrates (methanol, methylamines, and methyl sulfides) in order to reduce CO₂ and form CH₄. [5]

Bibliography

[1]  S. Huq, Y. Anokhin, J. Garmin, D. Goudou, F. Lansigan, B. Osman-Elasha, H. Wright, Adaptation Needs and Options, IPCC, 2018.

[2]  N. Norahim, P. Yaisanga, K. Faungnawakij, T. Charinpanitkul, C. Klaysom, Recent Membrane Developments for CO2 Separation and Capture, Chemical Engineering & Technology. 41 (2018) 211–223. https://doi.org/10.1002/ceat.201700406.

[3]  M.B. Jensen, L.D.M. Ottosen, M.V.W. Kofoed, H2 gas-liquid mass transfer: A key element in biological Power-to-Gas methanation, Renewable and Sustainable Energy Reviews. 147 (2021) 111209. https://doi.org/10.1016/j.rser.2021.111209.

[4]  Methane | Definition, Properties, Uses, & Facts | Britannica, (n.d.). https://www.britannica.com/science/methane (accessed July 27, 2022).

[5]  D.E. Holmes, J.A. Smith, Chapter One – Biologically Produced Methane as a Renewable Energy Source, in: S. Sariaslani, G. Michael Gadd (Eds.), Advances in Applied Microbiology, Academic Press, 2016: pp. 1–61. https://doi.org/10.1016/bs.aambs.2016.09.001.

Negative emissions: Term used for activities that remove carbon dioxide from the atmosphere. Other terms include Carbon Dioxide Removal (CDR) and Greenhouse Gas Removal (GGR). [1]

Non-CO₂ emissions and radiative forcing: The radiative forcing associated with non-CO₂ emissions. The term “radiative forcing” refers to a change in a driver of climate change, such as a change in the concentration of carbon dioxide (CO₂) or the output of the Sun, that results in a change in the net, downward minus upward, radiative flux (expressed in W m^-2) at the troposphere or top of the atmosphere. Non-CO₂ emissions include all anthropogenic emissions that have a radiative forcing effect but are not CO₂, such as methane (CH₄), certain fluorinated gases, and precursors to ozone (O₃). [2]

Bibliography

[1]  What are negative emissions?, Fern. (n.d.). https://www.fern.org/publications-insight/what-are-negative-emissions-2175/ (accessed July 27, 2022).

[2]  Glossary — Global Warming of 1.5 ^oC, (n.d.). https://www.ipcc.ch/sr15/chapter/glossary/ (accessed July 27, 2022).

Packing materials: Main component of the trickle bed reactors. The point where the methanogenic biofilm is immobilized.

Paris agreement: At the major conference of United Nations Framework Convention on Climate Change (UNFCCC) members in Paris in 2015, the successor to the Kyoto Protocol, commonly known as the Paris Agreement, was approved. The key resolution was a commitment to limit temperature rise below 2°C compared to pre-industrial levels, with efforts to limit it to 1.5°C. It entered into force in November 2016. [1]

Power to Gas (PtG): Any process that uses renewable sources or excess electricity to produce hydrogen (H₂) (Power-to-Hydrogen) through water electrolysis. This H₂ can be used directly through injection into the gas grid or used to convert carbon dioxide (CO₂) to methane (CH₄) (Hydrogen-to-Gas). [2]

Pressure Swing Adsorption (PSA): In this procedure, CO₂ is selectively adsorbed on the surface of a solid adsorbent under high pressure, after which the adsorbent is desorbed at low pressure (typically atmospheric pressure), releasing CO₂ for further transport. [3]

Proton Exchange Membrane Electrolysis (PEM): Water electrolysis technology, in which proton-conducting polymer thin membranes, with proton selective conductivity, are used as solid electrolytes instead of liquid electrolytes. [2]

Purchasing power parity (PPP): A theory contending that exchange rates between currencies are in equilibrium when their purchasing power is the same in each of the two countries. This means that the exchange rate between two countries should equal the ratio of the two countries’ price level of a fixed basket of goods and services. [4]

Bibliography

[1]  R. Madurai Elavarasan, R. Pugazhendhi, M. Irfan, L. Mihet-Popa, I.A. Khan, P.E. Campana, State-of-the-art sustainable approaches for deeper decarbonization in Europe – An endowment to climate neutral vision, Renewable and Sustainable Energy Reviews. 159 (2022) 112204. https://doi.org/10.1016/j.rser.2022.112204.

[2]  B. Zhang, L. Fan, R.B. Ambre, T. Liu, Q. Meng, B.J.J. Timmer, L. Sun, Advancing Proton Exchange Membrane Electrolyzers with Molecular Catalysts, Joule. 4 (2020) 1408–1444. https://doi.org/10.1016/j.joule.2020.06.001.

[3]  D.Y.C. Leung, G. Caramanna, M.M. Maroto-Valer, An overview of current status of carbon dioxide capture and storage technologies, Renewable and Sustainable Energy Reviews. 39 (2014) 426–443. https://doi.org/10.1016/j.rser.2014.07.093.

[4]  Purchasing Power Parity, (n.d.). https://fx.sauder.ubc.ca/PPP.html (accessed July 28, 2022).

Renewable energy: Energy derived from natural sources (e.g., sunlight and wind).

Solid Oxide Electrolysis (SOE): Water electrolysis technology, a solid oxide fuel cell that runs in regenerative mode to achieve the electrolysis of water (and/or carbon dioxide) by using a solid oxide, or ceramic, electrolyte to produce hydrogen. [1]

Sustainability: The concept of living within the limits of physical, environmental, and social resources in a way that ensures the long-term viability of the living systems in which people are embedded.

Sustainable Development Goals (SDGs): Also known as the Global Goals, that were adopted by the United Nations in 2015 as a universal call to end poverty, protect the planet, and ensure that by 2030 all people enjoy peace and prosperity. [2]

Bibliography

[1]  Y. Zheng, J. Wang, B. Yu, W. Zhang, J. Chen, J. Qiao, J. Zhang, A review of high temperature co-electrolysis of H2O and CO2 to produce sustainable fuels using solid oxide electrolysis cells (SOECs): advanced materials and technology, Chem. Soc. Rev. 46 (2017) 1427–1463. https://doi.org/10.1039/C6CS00403B.

[2]  Sustainable Development Goals | United Nations Development Programme, UNDP. (n.d.). https://www.undp.org/sustainable-development-goals (accessed July 28, 2022).

Temperature Swing Adsorption (TSA): The adsorption process, where the adsorbent that is saturated is heated to conditions, in which the physical and chemical bond is broken leading to the detachment of the adsorbed CO₂ molecules. [1]

Thermophilic methanogens: Thermophilic methanogens range from 55 to 70 ^oC. [2]

Trickle Bed Reactor (TBR): A three-phase reactor (liquid phase-gas phase-biofilm) that uses the downward movement of a liquid and the downward (co-current) or upward (counter-current) movement of gas over a packed bed of packing materials. [3]

Bibliography

[1]  X. Wang, C. Song, Carbon Capture From Flue Gas and the Atmosphere: A Perspective, Frontiers in Energy Research. 8 (2020). https://www.frontiersin.org/articles/10.3389/fenrg.2020.560849 (accessed July 28, 2022).

[2]  M.B. Jensen, L.D.M. Ottosen, M.V.W. Kofoed, H2 gas-liquid mass transfer: A key element in biological Power-to-Gas methanation, Renewable and Sustainable Energy Reviews. 147 (2021) 111209. https://doi.org/10.1016/j.rser.2021.111209.

[3]  M.V. Wegener Kofoed, M.B. Jensen, L.D. Mørck Ottosen, Chapter 12 – Biological upgrading of biogas through CO2 conversion to CH4, in: N. Aryal, L.D. Mørck Ottosen, M.V. Wegener Kofoed, D. Pant (Eds.), Emerging Technologies and Biological Systems for Biogas Upgrading, Academic Press, 2021: pp. 321–362. https://doi.org/10.1016/B978-0-12-822808-1.00012-X.

United Nations Framework Convention on Climate Change (UNFCCC): The first global joint effort to control and stabilize the concentration of greenhouse gases (GHG) in the atmosphere took place at the Earth Summit in Rio de Janeiro in 1992. The goal of this convention was to achieve stabilization of greenhouse gas concentrations in the atmosphere to a level that will prevent dangerous anthropogenic interference with the climate. [1]

Bibliography

[1]  E. Papadis, G. Tsatsaronis, Challenges in the decarbonization of the energy sector, Energy. 205 (2020) 118025. https://doi.org/10.1016/j.energy.2020.118025.

Volatile Fatty Acids (VFA): Short-chain fatty acids composed mainly of C2–C6 carboxylic acids, produced in the anaerobic digestion process. [1]

Bibliography

[1]  N.-J. Kim, S.-J. Lim, H.N. Chang, Volatile Fatty Acid Platform: Concept and Application, in: Emerging Areas in Bioengineering, John Wiley & Sons, Ltd, 2018: pp. 173–190. https://doi.org/10.1002/9783527803293.ch10.

Water electrolysis: A process where electricity from renewable energy sources is used to split water (H₂O) into hydrogen (H₂) and oxygen (O₂) [1]

Bibliography

[1]  S. Shiva Kumar, V. Himabindu, Hydrogen production by PEM water electrolysis – A review, Materials Science for Energy Technologies. 2 (2019) 442–454. https://doi.org/10.1016/j.mset.2019.03.002.