Technically Enhanced Biological Carbon Sequestration

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To achieve Net Zero, the use of Negative Emission Technologies on a global scale is essential. In this project, a pilot-scale photobioreactor (SDG 13) is realized to produce microalgae with ambient air. The produced algae will be buried as dried biomass. This plant will directly remove tons of atmospheric CO2 per year. The overall goal of this plant is to pave the way for larger reactors with CO2 removal rates of thousands of tons per year to make a significant contribution to reverse climate change. Background: In order to counteract anthropogenic climate change, not only anthropogenic CO2 emissions must be reduced quickly and significantly, but also Negative Emission Technologies (NET) must be used on a large scale (see e.g. IPPC Special Report: Global Warming of 1.5°C, https://www.ipcc.ch/sr15/). In 2019, Switzerland also committed to a net zero target for 2050, which includes long-term Carbon Dioxide Removal (CDR) from the atmosphere. Net zero means that from 2050 onwards, CO2 may still be emitted, but CO2 at the same time must be removed from the atmosphere by natural and engineered storages at the same scale. The NET include numerous approaches such as afforestation of forests, ocean fertilization, replacement of concrete and metals with woods, etc. The growth of plants on land through photosynthesis sequesters CO2 from the atmosphere and store it long-term if the biomass is removed from the natural cycle. If the goal is to maximize the production rate of biomass with high energy and space efficiency, photosynthesis of microalgae in water is significantly superior to photosynthesis of land plants by a factor of 10 to 50 under suitable conditions (see e.g. Khan, S.A. et al., “Prospects of biodiesel production from microalgae in India”, Renewable and Sustainable Energy Reviews). The biomass consisting of the elements C, H, O, N, P and S binds on average 1.66 kg CO2 per kg microalgae (see e.g. Williams, P.J.l.B., L.M.L. Laurens, “Microalgae as biodiesel & biomass feedstocks: Review & analysis of the biochemistry, energetics & economics.”, Energy and Env. Science) . It is expected that an area-related production rate of up to 287 t/ha/a biomass can be achieved with photobioreactors, where today already up to 155 t/ha/a can be reached. With open ponds a rate of roughly 60 t/ha/a can be achieved (see e.g. Stephens, E. et al., “An economic and technical evaluation of microalgal biofuels.”, Nature Biotechnology.) The specific costs of producing microalgae with photobioreactors when additionally adding pure CO2 instead of just air as feed to the reactors currently start at about 0.5 US$ to about 0.68 EUR per kg dry biomass, which corresponds to about 0.3 US$ to 0.41 EUR per separated kg CO2 (see e.g. Norsker, N.H. et al., “Microalgal production – a close look at the economics.”, Biotechnology Advances). The demand for technical energy as a differentiation to ambient heat and solar irradiation starts at almost zero, if one accepts relatively low growth rates compared to systems optimized to maximize the production rate. Almost all large and widely cited studies and reviews of NET list biomass production by plants on land and algae in oceans, but overlook algae production in bioreactors. It should be noted that technologies referred to as Bioenergy with CCS (BECCS) intend the complete energetic use of the renewably generated biomass with subsequent sequestration and storage, and Direct Air CCS (DACCS) describe a technological CO2 removal with filters and subsequent storage. CCS involves only technological capture at power plants with subsequent storage. If artificial photobioreactors are used instead of large-scale fertilization of sea surfaces, e.g. with iron (see e.g. Powell, H., “Fertilizing the Ocean with Iron: Should we add iron to the sea to help reduce greenhouse gases in the air?”, Woods Hole Oceanographic Institution), the advantages of high efficiency can be used without the dangers for marine ecosystems. Microalgae photobioreactors (MAPBR) are being studied in the field of research and development and are used commercially almost exclusively for the production of high valuable products (HVP) like pharmaceuticals, cosmetics and food supplements based on special algae, for which relatively high prices can be charged in contrast to biomass for energy purposes. After biomass production, two sequestration paths are conceivable: long-term anaerobic storage of the complete biomass or partial combustion under deoxygenation to use part of it for energy and to store the largest part as biochar long-term. This process is also known as Pyrogenic Carbon Capture and Storage (PyCCS). Approach: The project team has studied the processes of microalgae cultivation in photobioreactors with natural and artificial light theoretically and practically in numerous variants and now wants to provide experimental proof of this Negative Emission Technology on a pilot plant scale. A bulk reactor with a water volume of 4 m3, operated with forced convection of suspension and ambient air and supported by artificial light for photosynthesis, will be designed and commissioned. This bulk reactor will provide new insights into the energy, mass balances, and maximization of algae production and its cost structure, paving the way for improved implementation options. Outcome: It is expected that this pilot-scale prototype alone will remove about 15 tons of CO2 from the atmosphere per year. However, the overall goal for the medium term is to operate larger and optimized reactors in very large numbers to make a significant contribution to CO2 removal from the atmosphere. If, for example, bulk reactors with a water volume of an indoor swimming pool with a length of 50 m, a width of 15 m and an average depth of 2.5 m were used as a bioreactor, CO2 removals from the atmosphere of more than 7000 tons per year per reactor would be possible at a feasible productivity of 6.5 g of new algae per liter and day and an CO2 intake factor of 1.66.

Project Idea Metadata

Project Idea Name: Technically Enhanced Biological Carbon Sequestration
Date: 3/10/2022 9:41:18 AM
Administrators:
- Reto Tamburini

Project Idea Description

Background: In order to counteract anthropogenic climate change, not only anthropogenic CO2 emissions must be reduced quickly and significantly, but also Negative Emission Technologies (NET) must be used on a large scale (see e.g. IPPC Special Report: Global Warming of 1.5°C, https://www.ipcc.ch/sr15/). In 2019, Switzerland also committed to a net zero target for 2050, which includes long-term Carbon Dioxide Removal (CDR) from the atmosphere. Net zero means that from 2050 onwards, CO2 may still be emitted, but CO2 at the same time must be removed from the atmosphere by natural and engineered storages at the same scale. The NET include numerous approaches such as afforestation of forests, ocean fertilization, replacement of concrete and metals with woods, etc. The growth of plants on land through photosynthesis sequesters CO2 from the atmosphere and store it long-term if the biomass is removed from the natural cycle. If the goal is to maximize the production rate of biomass with high energy and space efficiency, photosynthesis of microalgae in water is significantly superior to photosynthesis of land plants by a factor of 10 to 50 under suitable conditions (see e.g. Khan, S.A. et al., “Prospects of biodiesel production from microalgae in India”, Renewable and Sustainable Energy Reviews). The biomass consisting of the elements C, H, O, N, P and S binds on average 1.66 kg CO2 per kg microalgae (see e.g. Williams, P.J.l.B., L.M.L. Laurens, “Microalgae as biodiesel & biomass feedstocks: Review & analysis of the biochemistry, energetics & economics.”, Energy and Env. Science) . It is expected that an area-related production rate of up to 287 t/ha/a biomass can be achieved with photobioreactors, where today already up to 155 t/ha/a can be reached. With open ponds a rate of roughly 60 t/ha/a can be achieved (see e.g. Stephens, E. et al., “An economic and technical evaluation of microalgal biofuels.”, Nature Biotechnology.) The specific costs of producing microalgae with photobioreactors when additionally adding pure CO2 instead of just air as feed to the reactors currently start at about 0.5 US$ to about 0.68 EUR per kg dry biomass, which corresponds to about 0.3 US$ to 0.41 EUR per separated kg CO2 (see e.g. Norsker, N.H. et al., “Microalgal production – a close look at the economics.”, Biotechnology Advances). The demand for technical energy as a differentiation to ambient heat and solar irradiation starts at almost zero, if one accepts relatively low growth rates compared to systems optimized to maximize the production rate. Almost all large and widely cited studies and reviews of NET list biomass production by plants on land and algae in oceans, but overlook algae production in bioreactors.

It should be noted that technologies referred to as Bioenergy with CCS (BECCS) intend the complete energetic use of the renewably generated biomass with subsequent sequestration and storage, and Direct Air CCS (DACCS) describe a technological CO2 removal with filters and subsequent storage. CCS involves only technological capture at power plants with subsequent storage.

If artificial photobioreactors are used instead of large-scale fertilization of sea surfaces, e.g. with iron (see e.g. Powell, H., “Fertilizing the Ocean with Iron: Should we add iron to the sea to help reduce greenhouse gases in the air?”, Woods Hole Oceanographic Institution), the advantages of high efficiency can be used without the dangers for marine ecosystems. Microalgae photobioreactors (MAPBR) are being studied in the field of research and development and are used commercially almost exclusively for the production of high valuable products (HVP) like pharmaceuticals, cosmetics and food supplements based on special algae, for which relatively high prices can be charged in contrast to biomass for energy purposes. After biomass production, two sequestration paths are conceivable: long-term anaerobic storage of the complete biomass or partial combustion under deoxygenation to use part of it for energy and to store the largest part as biochar long-term. This process is also known as Pyrogenic Carbon Capture and Storage (PyCCS).

Approach: The project team has studied the processes of microalgae cultivation in photobioreactors with natural and artificial light theoretically and practically in numerous variants and now wants to provide experimental proof of this Negative Emission Technology on a pilot plant scale. A bulk reactor with a water volume of 4 m3, operated with forced convection of suspension and ambient air and supported by artificial light for photosynthesis, will be designed and commissioned. This bulk reactor will provide new insights into the energy, mass balances, and maximization of algae production and its cost structure, paving the way for improved implementation options.

Outcome: It is expected that this pilot-scale prototype alone will remove about 15 tons of CO2 from the atmosphere per year. However, the overall goal for the medium term is to operate larger and optimized reactors in very large numbers to make a significant contribution to CO2 removal from the atmosphere. If, for example, bulk reactors with a water volume of an indoor swimming pool with a length of 50 m, a width of 15 m and an average depth of 2.5 m were used as a bioreactor, CO2 removals from the atmosphere of more than 7000 tons per year per reactor would be possible at a feasible productivity of 6.5 g of new algae per liter and day and an CO2 intake factor of 1.66.