Algae: Nature’s Renewable Resource for Fuels and Chemicals

Round 1

Reviewer 1 Report

Dear Authors,

the paper is well written and clear, and the topic is relevant. The research of alternative resources will always be important for academic community, as well as industry and people in general. It was stated that only studies published within the last 5 years will be taken into account, which was done, and it's fine.

My suggestions are next:

1. row 68 - title of Table 1 should bi in separate row, not continued in text (maybe this happened when word file was converted in pdf, but it has to be corrected).

2. Also Table 1. - Does removal efficiency of NH4, NO3 and P, as well as biomass productivity, depend on the used technology (like pyrolysis) or operative parameters? If so, this technology should also be stated in the Table because the amount of biomass produced varies greatly. So, for better understanding of these differences, and to find a connection between the values in the table, you should extend the table and add more information.

3. row 130-132  different font in word Bijerinckia (I know that's because of the hyperlink, but the size of the word should be aligned with the rest of the text).

4. The chapters are not numbered well. First three chapters are not numbered at all. Then there is chapter 3.1, fallowed by 1.1.1 and 3.2.1.... This must be corrected.

6. Chapter Thermal conversion processes - explain why did you decided to describe only pyrolysis and hydrothermal conversion, and not the other methods.

7. row 328 - abbreviation of HTL is used for the first time. Before abbreviation there should be a full description.

8. row 340 different font in word aromatic compounds

9. row 343 different font in word pyrazine

10. row 394-395 the paragraph is broken in the wrong place.

11. - title of Table 3 should bi in separate row

Author Response

The authors of this manuscript appreciate the comments of the Reviewer 1. The response to these comments are provided in details in the file submitted.

Author Response File: Author Response.docx

Reviewer 2 Report

In this study the authors revised papers of the last five years, emphasizing the versatility of microalgae as feedstock for the production of many commodities and high added value products, ranging from aromatic hydrocarbons to lipids for application in biorefinery systems. It was observed that research presents interesting insights for the field; however, need of little adjusts:

 Abstract

1) A good abstract must contain a brief contextualization of what will be addressed in the study, its general objective, the methodology employed in a succinct and direct way, the most relevant results, and a closing/concluding sentence. However, not all the items mentioned were presented by the authors.

Introduction

1) some sentences are very long and with few or no references (e.g., lines 22-30 and 42-44);

2) to improve and expand the understanding of this research, add this recent reference - 10.1016/j.algal.2023.103266;

3) the authors could further explore and expand this Introduction so that it presents more information about the subject that will be covered;

4) Could the authors explain to future readers of this paper, how the articles used were selected to compose this review, what inclusion or exclusion criteria were used? Add this item as a brief methodology;

5) The authors did not make clear the novelty or contribution of this study to the frontier of knowledge or for the application field.

Growing microalgae on wastewater

1) lines 99-102 - add references;

2) In Table 1, why did the references [12] and [13] not present NO₃^- removal efficiency?

3) The authors are encouraged to present more details about the growth steps of microalgae, e.g., growth time/days, luminosity, growing medium, nutrients quantity, among other factors that are extremely essential for this energy production (see 10.1016/j.algal.2023.103266);

4) In Table 1, Biomass productivity (mg L^-1 d^-1) – remove the point and the entire text – this “d” is day? If so, write in full;

5) line 77 – write Oklahoma native in italic;

6) throughout the text, standardize the presentation of units (mg L^-1 d^-1 or °C/min or mS/cm);

7) The article is not very illustrative and attractive; I believe that for a review article the authors could add more figures and/or diagrams that bring better visual understanding to the future reader. The authors are also invited to present some images of the main microalgae species mentioned in this study.

Algal biomass conversion processes

1) Observe the correct numbering for the topics and subtopics presented in this  paper;

2) lines 165-168; 255-262; 284-288; 316-327; 330-346; 366-374; 375-382; 449-456 – add references;

3) lines 184-198, sentence very long with few or no reference – add references;

4) line 251, CV-LS or CV-LH?

5) line 259 - who is ZSM-5? it was not previously defined;

6) In Table 2, why doesn't reference [62] show the catalyst and the catalyst:feedstock ratio used?

7) line 328 - who is HTL? it was not previously defined;

8) line 376, the citation is not correct;

9) In Table 3, we suggest replacing the “dash” indicating the absence of the sulfur - n.d.: not detected or below the equipment's detection limit;

10) In Table 4 and in all other tables of the paper, standardize the number of decimal places;

11) The authors are invited to present some statistical treatments or coefficients that better correlates the main variables demonstrated in this study;

12) How could the authors, of a well-simplified way, highlight the main contributions, innovations, and/or applications of the results presented in this study for use in more practical applications in developing countries?

Conclusions and Outlook

1) They are good, simple, and direct. Congratulations!

References

1) Observe the correct form (citations and references) in the journal template;

2) the names of microalgae and fungus species must all be written in italics;

3) only 19.47% of the references used in this paper have more than 5 years (excellent percentage for a review paper).

Author Response

The authors of this review article appreciate the attention to details provided by Reviewer 2 in his/ her comments. Please find the detail response to these comments in the file attached.

Author Response File: Author Response.docx

Reviewer 3 Report

Review Report of manuscript ID Number” Biomass-2884665”  

The research article entitled “Conversion of Algal Biomass to Fuels and Industrial Chemicals” submitted for publication in the journal “Biomass” with manuscript ID Number “biomass-2884665” seems quite interesting topic and could be attractive to the researchers all around globe. The review article contains interesting findings about the Algal biomass production and its potential applications in fuel and chemical industries but there are several technical areas which could be improved and need revisions:

 My comments on the manuscript are incorporated as follows:

The title “Conversion of Algal Biomass to Fuels and Industrial Chemicals” seems to be a casual and common for this important review. The title aims to intrigue readers and conveys the relevance and significance of review article on algal biomass conversion for fuels and industrial chemicals. Choose a title that best reflects the focus and impact of your research, while also being catchy and engaging to potential readers. There are some suggested/ potential topics those could be selected or modified for the title of this review article:

Potential Long titles

Title 1-Harnessing Green Gold: Exploring Algal Biomass for Sustainable Energy and Chemical Production"

Title 2"From Pond Scum to Profit: Unlocking the Potential of Algal Biomass for Fuel and Chemical Industries"

Title 3"Green Solutions: The Role of Algal Biomass in Renewable Fuels and Chemical Synthesis"

Potential Short Titles

"Algae: Nature's Renewable Resource for Fuels and Chemicals"

"The Algal Revolution: Transforming Biomass into Valuable Fuels and Chemicals"

Author could take any of the above for make it more reader’s attractive.

Abstract:

In abstract, some sentences could be clearer and more concise. For example, the phrase "emphasizes the versatility of microalgae as feedstock for production of many commodities and high value products ranging from aromatic hydrocarbons to lipids within biorefinery systems" could be simplified for better readability.

Suggestion: Consider rephrasing as: "Highlights microalgae's versatility as feedstock for producing various commodities and high-value products, including aromatic hydrocarbons and lipids in biorefinery systems."

The abstract mentions "properties of algal biomass cultivated in various media" but lacks specific details. Providing examples of these properties and how they impact the conversion process would enhance the clarity and depth of the abstract.

Suggestion: Add specific examples of properties such as lipid content, carbohydrate composition, and nutrient requirements, along with their relevance to biomass conversion techniques.

The abstract transitions abruptly between different topics, such as properties of algal biomass and conversion techniques and smooth transitions between these sections would improve coherence.

Suggestion: Use transition phrases or sentences to connect different sections logically. For example, "After discussing the properties of algal biomass, the review delves into various conversion techniques, including..."

While the abstract mentions a discussion of opportunities and challenges, it could be more explicit about the specific insights or conclusions drawn from this discussion.

Suggestion: Provide a brief summary of the key opportunities and challenges identified in the conclusion, offering readers a clear takeaway from the review.

Line 44 and 45” This article reviews the latest developments in utilization of algal biomass for bioproduct manufacturing via thermal processes.” Is there any other process/method than thermal? If yes than mention and if not then explain why?

·         The author should explain why other methods are not valuable for fuel and chemical production such as

·         1) Anaerobic/Aerobic Digestion. .. 2) Fermentation. .3) Enzymatic/Acid Hydrolysis. ...

4) Combustion. ... 5) Gasification. ...

Table 1 explains only six strains of algae with only 6 references which are not enough. There are many other relevant references for other references could be mentioned.

Also are there other engineered strains or modified strains (genetically modified) for the effective removal of N, P and NH4 and biomass production? Please mention.

Line 143 and 144 Chemical composition of the algal biomass used in any 143 conversion process is the key factor determining final product properties. The author gave references but didn’t present the reason for this specification and requires elaborations.

Table 2. described the Yield of aromatic hydrocarbons (area %) in bio-oil obtained from pyrolysis and co-pyrolysis  of microalgae (catalytic and non – catalytic) with various feedstocks from different literature reports.

Could it be further refined with respect to nature of aromatic compound and any other additional findings of the referred articles could be columned to make it more informative and attractive.

Table 3. Yield of biocrude (wt %) and its characteristics 398 from HTL of microalgae with different feedstocks from various reports.

This table also requires some crucial and key additional findings to make its more informative and conducive.

Table 4. Yield of hydrochar (wt %) and its characteristics from HTC of microalgae as compared with 480 that of various feedstocks from different literature reports.

This table requires thorough findings of other algal species for comparison. Only one chlorella species comparison is not enough to prove your stance and theme.

Please include examples or references to studies that demonstrate how variations in processing techniques and parameters impact the composition and yield of product streams. Providing concrete evidence would strengthen the conclusion.

The review suggests customization of feedstock chemical composition by preparing mixtures of biomass from various sources, it does not elaborate on the specific benefits or challenges of this approach.

Expand on the discussion of feedstock customization by addressing factors such as feedstock availability, compatibility of different biomass sources, and potential effects on product properties and process economics. Providing insights into the feasibility and implications of feedstock customization would enhance the depth of thearticle and its  conclusion.

Expand on the discussion of environmental impact and sustainability by addressing factors such as energy efficiency, waste management, and resource utilization. Additionally, discuss potential strategies for mitigating environmental impacts and enhancing the overall sustainability of algal biomass conversion processes.

The review briefly mentions logistical problems associated with the storage and handling of wet feedstock for hydrothermal processing but does not explore potential solutions or alternative approaches.

Suggestion: Provide a more detailed analysis of the logistical challenges of hydrothermal processing and discuss potential strategies for overcoming these challenges. This could include technologies for feedstock preprocessing, transportation, and storage, as well as considerations for commercial-scale operations. Offering practical insights into addressing logistical challenges would strengthen the conclusion and provide valuable guidance for future research and development efforts.

The language of the article is not smooth and systematic as some sentences are overly long and could be broken down for better clarity and readability.

Suggestion: Divide long sentences into shorter, more digestible chunks, each focusing on a specific point or aspect of the topic.

The plagiarism of the review is only 13% which is a good sign for its genesis and AI is also too low and a healthy sign for its originality.

Provide a brief summary of the key opportunities and challenges identified in the conclusion, offering readers a clear takeaway from the review.

By addressing these technical faults and implementing the suggested improvements, the abstract can enhance its quality and readability, making it more accessible and engaging for a diverse audience.

Comments for author File: Comments.pdf

The language of the article is not smooth and systematic as some sentences are overly long and could be broken down for better clarity and readability.

Suggestion: Divide long sentences into shorter, more digestible chunks, each focusing on a specific point or aspect of the topic.

The plagiarism of the review is only 13% which is a good sign for its genesis and AI is also too low and a healthy sign for its originality.

Provide a brief summary of the key opportunities and challenges identified in the conclusion, offering readers a clear takeaway from the review.

By addressing these technical faults and implementing the suggested improvements, the abstract can enhance its quality and readability, making it more accessible and engaging for a diverse audience.

Author Response

The detailed analysis of the review article by Reviewer is strongly appreciated by the authors of this manuscript. Please find the detailed response to the comments in the file attached.

Author Response File: Author Response.docx

Reviewer 4 Report

This study introduces a groundbreaking biorefinery method, utilizing Microalgae to commodities and valuable chemicals. Its significance is underscored by the conversion performance, sustainable process optimization, and versatility across various substrates. Nevertheless, there are further inquiries related to this manuscript, and it is recommended that the author address these concerns before publication in this journal.

1.     Pictorial representation should be incorporated in the revised manuscript, particularly synthesis protocols.

2.     Table .1 title is included in the main manuscript. Revise it accordingly.

3.     Table .3 title is included in the main manuscript. Revise it accordingly.

4.     Applications of bio-oil and biochar or hydrochar should be incorporated.

5.     Line 161, the indexing should be 3.1.1. not the 1.1.1.

6.     Line 306, the indexing should be 3.2 not 1.1.

English quality should be improved.

Author Response

The authors of this manuscript appreciate and thank Reviewer 4 for providing his/her time in going through this review article. Please find the detailed response to the comments in the file attached.

Author Response File: Author Response.docx

Round 2

Reviewer 3 Report

The manuscript has enormously improved and is in good state to be published. The author approximately addressed all of my questions raised during the first round of review so i am satisfied, but if the author could make a list/table/graph to mainfest the rising global trend/shift of algal biomass research in recent times to highlight the importance and scope of the study then it will be further polished and improved.

Some minor editing is still required in many sections due to grammatical errors.

Author Response

The reviewers request for further refining and polishing of the revised manuscript is strongly appreciated. Please find the response to your comments and suggestions attached in this email. With regards to the main manuscript, all corrections are highlighted in green.

Author Response File: Author Response.docx