Carbon Capture and Utilization Through Microalgae and Carbonic Anhydrases: Opportunities, Challenges and Future Directions

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript adresses a relevant topic by reviewing the potential integration of microalgae and immobilized carbonic anhydrases for biological carbon capture and utilisation. Sections 4.1 and 4.2 are relatevely genric and disproportionate in lenght compared with the manuscript's contribution. I suggest shortening such sections, or merging them into a concise introductory subsection, while giving  emphases to section 4.3, which adds the most value by focusing directly on CA immobilisation for CCU applications. The citation style in section 2 should be revised, as several claims related to costs, market size, and projected growth are currently supported by raw hyperlinks instead of numbered references consistent with the rest of the manuscript. The manuscript would benefit from a clearer conceptual distintion between the role of microalgae and that of carbonic anhydrases in bio-CCU. Microalgae perform the biological utilisation of inorganic carbon through photosynthetic fixation, whereas carbonic anhydrases facilitate inorganic carbon interconversion and availability. Therefore, immobilized CAs should be presented as auxiliary tools to enhance CO₂ delivery and uptake in microalgal bio-CCU systems, rather than as the main biological agents responsible for carbon utilisation.

 

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Comments and Suggestions for Authors:

The manuscript addresses a relevant topic and consolidates a large amount of technical material on carbonic anhydrase, immobilization strategies, and microalgal cultivation. The Conclusions section is notably candid about the gap between what is commonly claimed in this field and what the evidence actually supports. That said, some points need to be raised.

1. The novelty claim

The Abstract suggests that, unlike previous reviews addressing these applications separately, this work is the first to offer a comprehensive assessment of their combined implementation. A literature search brings up elements suggesting that this claim may be, at the very least, partially incorrect. Sen and Mukherjee (2024, Crit. Rev. Environ. Sci. Technol., 54(24), 1777–1802) appear to have already introduced the "bio-CCU" terminology this manuscript adopts as its own framework, and Mukherjee, Sen, Ralph, and Poddar (2025, J. Clean. Prod., 505, 145461) specifically address carbonic anhydrase immobilization in microalgal cultivation systems — an intersection very close to the one this manuscript presents as its distinctive contribution. Neither appears in the reference list. A further review by Xia et al. (2026, Clean Technol., 8(3), 63) is also absent, covering similar ground in terms of CA engineering and immobilization. It would be necessary for the authors to review this literature and clarify in what respects their contribution differs from or extends beyond it.

Along the same lines, Table 4 would appear to be missing some primary studies relevant to its own scope, such as You et al. (2020, Bioresour. Technol., 318, 124072), Salbitani et al. (2020, J. Enzyme Inhib. Med. Chem., 35(1), 913–920), and Kim et al. (2020, J. CO2 Util., 38, 291–298).

2. Section 5.2

This appears to be the section carrying the manuscript's most original contribution, yet it is comparatively brief relative to the central place it occupies in the work's contribution. Could the authors expand it, adding a further layer of depth or analysis? It would be necessary to develop this section further given what it represents for the manuscript as a whole.

3. The "n.r." pattern in Tables 2 and 4

The primary literature cited shows a fairly frequent absence of data on immobilization yield and specific activity. What do the authors make of this pattern? It would be necessary to explore this further — quantifying it, if possible — given what it appears to reveal about the current state of the field.

4. Language

Overall, the writing is clear. The phrase "represents a promising/valuable strategy" recurs fairly often throughout the text, and it would be worth varying it in places. Additionally, in Section 2, where it reads "the faith of captured CO2," it should read "the fate of captured CO2."

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

 1. Although limitations like "high cost" are noted for encapsulation, the file lacks a detailed techno-economic analysis to support these qualitative claims.

2. The manuscript focuses on hydrogels and resins but fails to explore the potential of modified biochar as a sustainable and low-cost alternative support for enzyme immobilization.

3. While some catalysts show stability over 10 to 20 cycles, the report does not define the specific loss mechanisms (leaching vs. denaturation) occurring during these cycles.

4. The sensitivity to pH fluctuations is noted as a limitation for adsorption, but the manuscript lacks a clear profile of the isoelectric point interactions for the listed data.

5. In contrast, the manuscript lacks a clear roadmap for the total utilization of fixed carbon into high-value components like pigments or lipids.

6. Conclusion can be reduced to 200 words by highlighting the important outcomes and future direction

7. Check spelling and grammatical  mistakes throughout the manuscript

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have implemented my suggestions.

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have comprehensively addressed all points raised during the review of the original manuscript. The statement regarding novelty has been appropriately reformulated, the missing references have been incorporated—with clear justification for their inclusion in or exclusion from Table 4—, Section 5.2 has been expanded, and the "n.r." pattern has been quantified in a way that adds real value to the discussion.