Review Reports - Utility Aspects of Sugarcane Bagasse as a Feedstock for Bioethanol Production: Leading Role of Steam Explosion as a Pretreatment Technique

Round 1

Reviewer 1 Report (Previous Reviewer 3)

Comments and Suggestions for Authors

The second version of Article "Utility aspects of sugarcane bagasse as a feedstock for bioeth-anol production: Leading role of steam explosion as a pretreat-ment technique" was revised, it was complicated to understand the document with all the corrections and changes.

1) The document improved in its structure and content.

2) The topic is relevant in the field of study, however it requires improvements again, line 106, 108, the symbol for degrees centigrade, it is suggested to review the whole document.

3) The figures and tables are correct.

4) The authors left comments on the revision process on line 420.

Author Response

The second version of Article "Utility aspects of sugarcane bagasse as a feedstock for bioethanol production: Leading role of steam explosion as a pretreatment technique" was revised, it was complicated to understand the document with all the corrections and changes.

1) The document improved in its structure and content.

Response: Thank you for taking the time to review our manuscript a second time. We are very grateful.

2) The topic is relevant in the field of study, however, it requires improvements again, line 106, 108, the symbol for degrees centigrade, is suggested to review the whole document.

Response: Thank you very much. We have already corrected the centigrade symbol throughout the manuscript. We have attached a new version with the two versions, CLEAN and the TRACK & CHANGES tool active so that the document can be followed easily.

3) The figures and tables are correct.

Response: Thank you very much for all your remarks.

4) The authors left comments on the revision process on line 420.

Response: Please, note that we are sorry to have left the comment there. It has been removed.

Reviewer 2 Report (Previous Reviewer 4)

Comments and Suggestions for Authors

The authors have diligently revised the manuscript, thoroughly addressing all the issues previously highlighted by the reviewer. It appears that the manuscript is now in a state suitable for publication.

Author Response

Response: We are very thankful to the reviewers for giving us the opportunity to work on improving the quality of the paper. We have done our utmost to ensure that the manuscript is suited for the journal. Thank you for your feedback.

Reviewer 3 Report (New Reviewer)

Comments and Suggestions for Authors

The review “Utility aspects of sugarcane bagasse as a feedstock for bioethanol production: Leading role of steam explosion as a pretreatment technique” is devoted to the conversion of lignocellulosic raw materials – sugarcane bagasse into ethanol via steam explosion. The production of bioethanol is a hot topic. Steam explosion as a method of pre-treatment of sugarcane bagasse has a number of advantages and a number of disadvantages. The following are concerns that should be addressed.

1. It is not clear from the introduction how a review on this topic differs from reviews on a similar topic published previously.

2. Among the disadvantages of steam explosion as a pretreatment method, the possibility of re-condensation of lignin on cellulose fibers is not discussed.

3. Information describing the catalyzed steam explosion set out in paragraph 3. Sugarcane bagasse as a potential raw material for bioethanol production should be moved to paragraph 2. Steam explosion as lignocellulosic biomass pretreatment

Author Response

It is not clear from the introduction how a review on this topic differs from reviews on a similar topic published previously.

Response: Thank you for your comment. To clear up the differences between this review and other similar reviews already published, the ending of the introduction section has been slightly changed. Please, check the new file, we have updated one document with the two versions (CLEAN and with TRACK & CHANGES tool) to make much easy the revision.

In addition, we have introduced the following sentence to respond to your concerns:

“Thus, this review aims to compile current information regarding second-generation biofuels production focusing on two parameters: the pretreatment technique applied (steam explosion) and the feedstock used (sugarcane bagasse).”

Among the disadvantages of steam explosion as a pretreatment method, the possibility of re-condensation of lignin on cellulose fibers is not discussed.

Response: Yes, many thanks for your note. It is true that steam explosion could be a susceptible process for lignin re-condensation. We have found an article where this factor was mentioned by the authors and we have added it to our manuscript accordingly.

“For example, one study evaluated the hydrothermal humification and decomposition effects of SE using broccoli as a vegetable waste. The results showed that SE affected the physicochemical properties of broccoli residues, such as lignin re-condensation and degradation of the amorphous cellulose region, which were accompanied by porous structure destruction and browning phenomena. However, it was concluded that SE promotes the degradation of easily biodegradable feedstocks and the subsequent reactions of polycondensation, aromatization, and nitrogen fixation”.

Information describing the catalyzed steam explosion set out in paragraph 3. Sugarcane bagasse as a potential raw material for bioethanol production should be moved to paragraph 2. Steam explosion as lignocellulosic biomass pretreatment.

Response: Thank you very much. We have implemented your suggestion.

Round 2

Reviewer 1 Report (Previous Reviewer 3)

Comments and Suggestions for Authors

The authors improved the quality of the document by editing the information. The contribution of the article is significant to the field of knowledge.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript “Insight into a steam explosion pretreatment of sugarcane bagasse for bioethanol production”.

I appreciate the opportunity to review your manuscript titled "Insight into a Steam Explosion Pretreatment of Sugarcane Bagasse for Bioethanol Production." Overall, the paper addresses a pertinent theme, presents interesting arguments, and reports valuable results. However, I recommend the following MINOR revisions:

1- Grammar and Language: It's important to carefully proofread the manuscript to correct any grammatical errors and ensure that the English is clear and coherent.

2- Highlighting Challenges: Consider expanding on the challenges associated with using steam explosion as a biomass pretreatment method. Addressing these complexities is crucial for the successful application of steam explosion in diverse biorefinery processes.

3- Quantitative Data in Conclusion: In the conclusion, rather than mentioning "positive results" and "positive outcomes," consider providing specific quantitative data or findings from relevant studies. Including figures or tables that show sugar conversion rates, lignin removal percentages, and bioethanol yields would add credibility to your argument.

4- Acknowledging Limitations: It's essential to acknowledge potential challenges or limitations associated with steam explosion pretreatment. Discuss any drawbacks or issues that researchers have encountered to present a more balanced perspective.

5- Comparative Analysis: While you discuss steam explosion as a promising method, it would be beneficial to briefly compare it to other pretreatment techniques for lignocellulosic biomass. Analyze how steam explosion compares in terms of efficiency, cost-effectiveness, and environmental impact with methods like acid or enzymatic pretreatment.

6- Market Demand and Economic Prospects: Explore the potential market demand for bioethanol produced using steam explosion-pretreated sugarcane bagasse. Are there existing or emerging markets for this biofuel? Discuss the economic prospects for producers to provide a more holistic view.

Incorporating these revisions will enhance the quality and completeness of your manuscript. I wish you success in further developing your work.

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript of the review article "Insight into a steam explosion pretreatment of sugarcane bagasse for bioethanol production” would presumably provide an up-to-date view of “steam explosion pretreatment”, “sugarcane bagasse”, and “bioethanol (i.e., cellulosic ethanol) production”. In my vision, the manuscript fails in this task. Therefore, I cannot recommend its publication.

Although the manuscript presents a reasonable summary of setam explosion pretreatment technology, there are a few recent reviews of steam explosion pretreatment that are more accurate and complete than the manuscript. So, at this point, I do not see any new added value in the manuscript.

In addition, the manuscript fails to contextualize the specificities of sugarcane bagasse, considering agroindustrial characteristics and multiscale biomass structure. The compositional data informed in the manuscript (Table 2) is insufficient to delineate the specificities of sugarcane bagasse as a lignocellulosic feedstock.

Finally, cellulosic ethanol from sugarcane bagasse reached commercial scale and commercial facilities are now being replicated. This commercial reality should serve as a benchmark for the discussion of bioethanol production, but the manuscript misses this point.

Comments on the Quality of English Language

There are problems in the article preparation.

Examples:

line 116 and others, reference error.

line 218 and others, incomplete text.

Reviewer 3 Report

Comments and Suggestions for Authors

The article entitled "Insight into a steam explosion pretreatment of sugarcane bagasse for bioethanol production"

The article contains editing and organizational errors between information and figures.

It requires improvements in the temperature units.

A high percentage of similarity is identified between the document and the one reported in: Eng. Proc. 2023, 37(1), 113; https://doi.org/10.3390/ECP2023-14673

Comments on the Quality of English Language

Not applicable

Reviewer 4 Report

Comments and Suggestions for Authors

I have reviewed the manuscript titled "Insight into a Steam Explosion Pretreatment of Sugarcane Bagasse for Bioethanol Production" submitted to the "Processes" journal.

The topic of steam explosion pretreatment for bioethanol production from agricultural wastes is highly relevant in the context of sustainable biofuel production. As the demand for renewable energy sources grows, research into efficient pretreatment methods is essential.

The manuscript is well-written and comprehensive in its coverage of the subject. It provides a clear and detailed overview of steam explosion pretreatment, its principles, and its application in converting sugarcane bagasse and other sources of lignocellulose into bioethanol. The manuscript successfully combines recent research findings with a broader understanding of the field.

The authors have demonstrated a thorough examination of recent literature related to steam explosion pretreatment, bioethanol production, and sugarcane bagasse utilization. The inclusion of figures and tables aids in conveying complex information to the readers.

While the manuscript is generally well-structured and informative, I recommend addressing the following minor issues for further improvement.

Line 36. Since global warming is a part of climate change, I would recommend choosing only one term here.

Line 39. Typo: with.

Line 46. “Anything that is useless” seems to be too broad, isn't it?

Lines 48, 56 and others. Clarify please what “matrix to obtain biofuel” did you mean. I do not understand why is it a matrix.

Line 51. “…is necessary so plant specific...” So or to?

Lines 52-56. I would recommend paraphrasing this sentence, it is not clear enough. The first claim relates to economy, the second - to the discourse about a competition between food and fuel, but the meaning of the third should be explained better. What means pretreatment as animal feed?

Lines 63-64. The second part of the sentence "or if not accumulated..." should be paraphrased. What is environmental health?

Line 71. Footprint, not just print. Carbon print is something different.

Line 82. Bleaching mixtures sounds better.

Lines 90-91. Please check the reference. What did the authors mean by yields of pure cellulose 81.4 and 79? From what are these percent? From the total cellulose content or from biomass composition (which is unreal)? It sounds ambiguous now. The same in Line 93. Yield of what from what?

Lines 94-97. This conclusion seems to be not logic from above discussion. There are chemical methods with examples of effectiveness, and suddenly the authors conclude that despite these examples, SE is one of the most efficient. Give an example here to set the logic.

Lines 97-98. Provide the references.

Line 100-102. Which studies? Provide the references.

Lines 103-104. Regarding bioethanol, or regarding the techniques of its production? It seems that the accent was put inaccurately in the aim.

Titles of the sections 2 and 3. You have already introduced the abbreviations, there is no need to duplicate it.

Errors in figure number in lines 116, 150, 170, 211.

Line 139. Provide the reference for the eq.1, define R0 (how a parameter may be a scaling strategy?), and explain the numbers 100 and 14.75 in the eq.1. Also, in the equation is written T, while in the line below it is a Greek letter tau.

Lines 143-146. Was the optimal combination determined in [31] via statistical analysis? More detailed information would be appreciated here.

Lines 196-198. It would be better to provide some numbers or at least limits for the yields, probably, in a table.

Line 208. Even?

Table 1.

Use the word by-products consistently throughout the text. Now there are by products and by-products.

It could be environmentally friendly or environment friendly, no other forms. I suppose that in this particular case (the line with ref. [30]), the term environment friendly is too broad and water-saving technique would be more precise. Note that in the next line, - low-energy- is also environment friendly, but it is specified there.

The line with refs [9,10,44]. Energy efficiency has been already mentioned above. Do not duplicate the benefits.

The last advantage is a duplication of the first line in the table.

The line with ref [23]. What are effective components? Why are they effective?

The line with ref [45]. Isn't the second disadvantage controversial to the second advantage? The last and the third from the end disadvantages definitely sounds the opposite of what is written in the advantages. Energy effective and low energy treatment contra high energy requirements, commercial applications has not been proved, but the technique is easy to scale up.

Line 218. Check the C figure name.

Line 225. Sugar cane or sugarcane?

Line 243. How or by whom it has been established? It needs a little more detail.

Line 245. Note the units for the components.

Table 2. No treated and non-treated, make them similar.

Line 252. Is enzymatic hydrolysis the obligatory stage after SE?

Lines 254, 261. Provide the references.

Lines 391,400. Thermos-mechanical?

Line 392. Wide and broad are too much together, choose one of these words.

In conclusion, I recommend the manuscript "Insight into a Steam Explosion Pretreatment of Sugarcane Bagasse for Bioethanol Production" for publication with minor changes to address the above recommendations. The manuscript offers valuable insights into the use of steam explosion pretreatment for sustainable biomass conversion.