Algae in Biologic Carbon Sequestration

Introduction

The study of carbon sequestration as it relates to global climate change dates back to the early 1990s.  With carbon sequestration, scientists study how the planet removes carbon dioxide, a greenhouse gas, from the atmosphere by storing it in the oceans and in other ways.  In doing so, these natural cycles help cleanse the atmosphere of carbon dioxide, mitigating the effects of climate change.  Since the 1990s, efforts have centered on developing ways to augment these naturally occuring cycles.  And as it turns out, research conducted on advancing bioregenerative life support technology has proven valuable to those searching for global climate change remediation solutions.

In the opening chapter of Algae Across the Decades, Algae in Bioregenerative Life Support, a paper by Tew, Sane and Geckler was the centerpiece, as it proves a connecting tissue between the use of algae in bioregenerative life support and in biological carbon sequestration.  Though the research conducted by the team was intended for air revitalization in space environments, their paper is currently being cited by researchers interested in biologic carbon sequestration for global climate change remediation.

Concepts

Biologic Carbon Sequestration

Carbon sequestration is the process of storing carbon in a carbon pool.  Carbon sequestration can be broken down into two general categories, geologic and biologic.  Geological sequestration refers to the storage of CO2 underground in depleted oil and gas reservoirs, saline formations, or deep coal beds unsuitable for mining. ("Carbon sequestration", 2025).  Biological carbon sequestration is a naturally occurring process as part of the carbon cycle ("Carbon cycle", 2025).

While biological carbon sequestration is a naturally ocurring process, it plays a critical role in limiting climate change by reducing the amount of carbon dioxide in the atmosphere.  As such, scientists are engaged in research to find ways to enhance and accelerate this natural process.

Biosequestration of Carbon Dioxide - Cleaning Our Atmosphere

Introduction

Present day researchers are reexamining the function of algae previously viewed through a life support framework and expanding it to global climate mitigation.

Algae are plant-like organisms, are photosynthetic and mostly found in the sea, land and freshwater.   It multiplies rapidly and has a great potential to sequester carbon from the atmosphere and recycle it into bioenergy. This biological method of capturing and sequestering carbon from the environment is more cost effective and environment friendly than physical methods of ameliorating environmental pollution. (Tarafador, A., Sowmya, G., Yogeshwari, K., Rattu, G., Negi, T., Awasthi, M.K., Hoang, A., Sindhu, R. & Sirohi, R., 2023)

It is pretty easy to imagine the use of algae to revitalize the air inside a space vehicle or base being expanded in scale by untold magnitudes to revitalize an entire planetary atmosphere.

One may ask why not a concerted effort at planting trees (reforestation and afforestation) or other terrestrial plants rather than utilizing microalgae's air revitalization and carbon sequestering function, which seems to present challenges.  Although reforestation and afforestation are accepted strategies in a climate change mitigation strategy it turns out that algae has an advantage that is hard to ignore: 

Terrestrial plants are able to sequester vast amounts of CO2 from the atmosphere. However, when compared to terrestrial plants, microalgae and cyanobacteria have faster growth rates, and their CO2-fixation efficiency is also between 10 and 50 times higher (Bhola, V., Swalaha, F., Kumar, R. R., Singh, M. & Bux. F., 2014)

Another factor is that all those challenges around the use of microalgae in space life support are mostly resolved when applied in a terrestrial application.

Comparison

Dovetailing off the challenges of using algae in bioregenerative air revitalization in space applications that are detailed in the first chapter of our Algae Across the Decades story, we can compare those challenges to the use of algae in biological carbon sequestration and see that they do not align.

First of all, with regards to algae maintenance, in space applications, the responsibility either falls to the astronaut, who sacrifices valuable time in doing so, or to earth-bound remote systems, which provide opportunities for communication disruption.  But the staff assigned to a biological carbon sequestration effort would essentially be employed specifically to maintain algae and would not have the multitasking concerns of space travelers.

With regards to reliability, the use of algae in biological carbon sequestration does not present the literal "life-or-death" concerns of a bioregenerative air revitalization system.  If adjustments or tweaks to the system are needed there is no risk of a fatal result.  Indeed, the need to take a biological carbon sequestration system offline for hours, days, weeks or months may be unfortunate, but would be completely achievable.

Connectivity is just not applicable to biological carbon sequestration.  While bioregenerative air revitalization is just one piece of an overall bioregenerative life support system that needs to be coordinated with other pieces, a biological carbon sequestration system does not have other functions that it depends on or are dependent on it.

Likewise, the weight and/or volume of a biological carbon sequestration system presents almost nothing comparable to the challenges of these factors in space applications.  An earth-bound system does not need to be launched into space and therefore does not have the same weight considerations, and with regards to volume, land acquisition would be impacted but would not present the same scale of difficulty as a system's footprint within a space vehicle or station.

Finally, in bioregenerative air revitalization, the need to approach a 100% closed system to the greatest degree possible is essential to success.  The further from a 100% closed system one gets, the greater the need for resupply, which the whole concept of bioregenerative life support is dedicated to eliminating.  Meanwhile, with regards to a closed system and bioregenerative air revitalization, the problem is solved to begin with:

Ignoring the small amounts of matter that enter Earth's system as meteorites and possibly water ice and also the few hydrogen and, perhaps, other molecules (and today, spacecraft) that may reach escape velocity and leave Earth forever, Earth is a system that is closed to matter, but open to energy. (Salibury, Gitelson & Lisovsy, 1997)

In fact, arguments are made that assert that the concept of closed systems is the key not only to space travel, but to stabilizing Earth's atmosphere:

the scientific community is increasingly convinced of the importance of developing artificial, closed ecosystems, not only for future life support in space, but primarily as tools to study the fundamental problems of biospherics - that is to better understand the regularities of stable existence of Earth's biosphere. (Salisbury, Gitelson & Lisovsky, 1997)

If we recall, the whole goal of a bioregenerative life support system is to try to replicate in miniature the closed system of planet Earth.  This shows how closely related the two technologies are.

Open raceway ponds and closed photobioreactors

Unlike bioregenerative life support applications, in which a closed algae growth bioreactor is the only realistic approach, biological carbon sequestration efforts have two potential paths: closed bioreactors and open bioreactors known as raceway ponds.  The easiest comparison between space applications and carbon sequestration is between the use of closed bioreactors in space and on Earth, and though some algae research related to closed life support bioreactors could also be applicable to open raceway ponds, this direct comparison will be our focus.

Photosynthetic microorganisms can be cultivated in open or closed photobioreactors. The closed systems are characterized by elevated photosynthetic efficiency associated with a precise control of the operational variables, showing a lower risk of contamination and minimization of water loss by evaporation, highly significant factors in open systems. On the other hand, closed systems are more expensive, since they must be constructed with transparent materials, and are more complicated to operate and more difficult to scale up. (Jacob-Lopes, E. & Franco, T. T., 2010)

Photograph of a raceway pond.

Raceway pond for cultivating microalgae
JanB46, CC BY-SA 3.0 , via Wikimedia Commons

Photograph of a photobioreactor.

Photobioreactor for use in cultivating spirulina microalgae
IGV Biotech, CC BY-SA 3.0, via Wikimedia Commons

A closed system has several advantages over an open raceway pond:

  • Smaller size
  • High density of algae
  • Greater control on such parameters as temperature and pH
  • Greater gas transfer
  • Lower chances of contamination (Ndleve, L., Hausberger, B. & Jalama, K., 2016)

A closed system has one major drawback when compared with open raceway ponds: higher capital investment. (Ndleve, L., Hausberger, B. & Jalama, K., 2016)

Biomass

The costs of biological carbon sequestration can be an impediment to its introduction:

(I)f governments are serious about addressing carbon emissions, and promoting the uptake of any technology to make energy production cleaner, the mitigation of CO2 must be economically favorable for the companies (Ndleve, L., Hausberger, B. & Jalama, K., 2016)

According to researchers, biomass utilization is integral to the financial success of a bioreactor based biological carbon sequestration.  Biomass ("Biomass", 2025), in this scenario, would be the harvested algae that have sequestered the carbon.  The harvested algae would provide value as a product, potentially as biofuel ("Biofuel", 2025).  Proponents of algae bioreactors hope to make carbon sequestration economically viable by bringing to market the byproducts created:

microalgae systems have emerged as a particularly promising route for atmospheric CO2 capture due to their high efficiency, scalability, and potential to generate valuable co-products. (Ashour, M., Mansour, A. T., Alkhamis, Y. A. & Elshobary, M., 2024)

The use of biofuels in lieu of fossil fuels could augment the carbon sequestration in mitigating global warming:

Biofuels derived from biomass have gained recognition as significant alternatives to fossil fuels owing to their environmentally friendly nature. (Ahmad, A. & Ashraf, S. S., 2024)

The combination of carbon sequestration and alternative fuel production makes an algae-based solution attractive:

Thus, the reproduction of biofuels together with the capture of carbon dioxide is an elegant and high-potential solution to the problem of global warming. (Iglina, T., Iglin, P., & Pashchenko, D., 2022)

Maturation of the technology

The economic viability of a biological carbon sequestration system is central to the technology's success, but there are technical hurdles as well.

Past research initiatives suggest that practical CO2 utilization using microalgae still requires innovative scientific and technological breakthroughs to render this a feasible technology. (Bhola, V., Swalaha, F., Kumar, R. R., Singh, M. & Bux. F., 2014)

Demonstrating the challenge of bringing the technology to fruition, compare the assessment ten years on:

Microalgal cultivation has been identified as an excellent method for large-scale carbon capture.  However, existing microalgal cultivation systems have not yet reached the production levels necessary for effective carbon capture and storage. (Ahmad, A. & Ashraf, S. S., 2024)

More specifically there is a need for:

(T)echnological advancements and improved cultivation methods to increase efficiency and lower production costs. This could unlock the full potential of microalgae in carbon sequestration and other applications. (Ahmad, A. & Ashraf, S. S., 2024)

Indeed, any way it is sliced, the economic viability and the overcoming of technical hurdles are directly coupled.  It is the technical advancements that will achieve economic viability.  The path forward seems daunting (emphasis added):

Several steps must be taken to harness the potential of microalgae for carbon sequestration on a commercial scale.  These include deepening our understanding of the mechanisms underlying carbon fixation, selecting strains that produce high levels of biomass, developing effective cultivation and harvesting techniques, integrating carbon fixation with the development of value-added products and conducting comprehensive techno-economic analysis. (Ahmad, A. & Ashraf, S. S., 2024)

Though five separate pieces to the puzzle are articulated, we'll be most interested in the second in the list, selecting strains (of algae) that produce high levels of biomass, as we'll see below.

Review articles 1966 and 2014

It is illuminating to compare two of the articles that cite the Tew, Sane & Geckler paper.  The two articles are review articles, essentially literature reviews gathering research on specific topic(s).  One article is from the period of heavy bioregenerative life support research in the 1960s referenced above, the other from the period of twenty-first century carbon sequestration research.

1966

A review article contemporary to the paper's presentation at the conference and publication in the proceedings grouped the Tew, Sane and Geckler experiment with a half dozen others as addressing the concept of closed ecological systems:

applicable to a regeneration of oxygen and fixation of carbon dioxid (sic) and hydrogen in space missiles (sic) are described. The cell material produced can serve as a source of food or a food supplement (Malek, I. & Ricica, J., 1966)

Though this review presented an overview of microorganism cultivation, the authors saw fit to identify the paper as being directly related to the specific application of bioregenerative life support by grouping it under closed ecological systems, and mentioning two of the hoped for benefits of a potential algae-based system.

2014

However, a review article specific to the potential of algae in carbon dioxide sequestration presented the results of the Tew, Sane and Geckler experiment and noted that the resulting mean biomass cell concentrations achieved were

reasonably similar to those achieved with other Chlorella species (Bhola, V., Swalaha, F., Kumar, R. R., Singh, M. & Bux. F., 2014)

The focus of the review article was a comparison of various strains of algae with respect to their viability in a carbon sequestration application, in this case specifically mentioning biomass production.

This review article recounts experiments with various strains of algae that scientists and engineers may consider when looking to maximize biomass production in biological carbon sequestration applications.  The Tew, Sane & Geckler paper represents in this context a source of data regarding one particular strain.

With biomass production one of the factors that would help make biological carbon sequestration financially viable, determining which strain(s) are most productive would be central to that effort. 

Indeed, with the possibility that existing strains may not be up to the task, creating new strain(s) may be a way to get to financial viability (emphasis added).

Genetic engineering presents significant potential for creating microalgal strains that thrive under elevated CO2 levels and adverse environmental conditions while maintaining efficient carbon fixation. Considering the potential benefits and obstacles that may surface, it is crucial to evaluate these advancements carefully and analytically (Ahmad, A. & Ashraf, S. S., 2024)

This passage illustrates two facts simultaneously, 1) the importance of optimizing the performance of the algae in recycling carbon dioxide, to the degree that the creation of entirely new strain(s) may be necessary to achieve desired results and 2) that technical barrier(s) may persist for decades blocking the realization of theoreticallly possible achievements until new development(s) - perhaps genetic engineering - create the conditions for the theoretical to become possible. 

Summary

To recap our discussion, there are two yet unrealized technologies, bioregenerative life support and biological carbon sequestration, which if they become realized, will quite possibly utilize the function of microalgae as a recycler of carbon dioxide.  The Tew, Sane and Geckler article was presented at a symposium discussing bioregenerative life support, and after the Contrails paper level indexing and digitization was likely "rediscovered" and applied to biological carbon sequestration.

This anecdotal research scenario demonstrates the following:

  • Decades old scientific and technical research can still be relevant
  • Research conducted with one application in mind may be used in alternate applications
  • Paper level indexing and digitization efforts such as Contrails provide enhanced discovery for gray literature that increases the chance that twentieth century resources can prove their value in current research

For decades now researchers have pursued the realization of both technologies due to the vast potential rewards should they ultimately become realized. Perhaps at this moment scientists are working on a game-changing gene edit that will create an algal "super" strain that will prove determininative in stabilizing Earth's atmosphere and creating a self-sustaining atmosphere for a Martian outpost!

References

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