Modified Hydrothermal Pretreatment Conditions Enhance Alcohol Solubility of Lignin from Wheat Straw Biorefining

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Biomass: 3513522

This manuscript brings a relatively new concept of further processing of previously fermented biomass for additional recovery of sugars for fermentation to alcohol as well as lignin byproducts.  Others have previously tried this but not so effectively. The current study investigates how industrially relevant modifications to hydrothermal processing of previously used biomass can effectively solubilize alcohol from residual lignin fraction as well as the total sugar recovery. The study explores the effects of temperature, surfactants, oxidizing agents, organic acids, alkali, and capping agent for this purpose.  The experimental methods are fully described and the results obtained are significant and useful to the scientific community. As such there is no need for further modification of the manuscript with the exception of the following comments. Given the above I strongly recommend that this manuscript should be considered for publication.

Comments:  

1. Table 1 – First two columns – Name and the temperature used are the same for the 1^st three items. Designate them distinguishably. Further, adjust the names used correctly in various figures and tables, as well as the text. Include a brief description of the experimental conditions in the footnote. 
2. Figure 1 – what does Glucan 7d mean? Describe it in the figure description. What do letters “a-f” on the bars in the diagram represent? Describe them in the figure lagend description.
3. Figure 2 – what do letters “a-c” on the bars represent? Describe them in the figure lagend description.
4. Figure 3, Panel A and B - what do letters “a-e” on the bars represent? Please describe them in the figure legend.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript proposes to evaluate different modifications to Hydrothermal pretreatment to optimize saccharification and the alcohol solubility of lignin. The experiments were carefully conducted, and the findings are interesting.  However, some issues should be addressed before being considered for publication.

1. It would be interesting to provide some literature review to compare the results.
2. It is not clear what is the novelty of the work
3. Line 61 – 62. Cite relevant findings from these studies. What types of acids, bases, and oxidizers were used? In what kind of pretreatment were they employed? For what purposes were they conducted? What type of biomass were they performed on?
4. What is the benefit of catalyzed HTP over using an alkaline, acid method, etc?  What are the benefits of HTP?
5. What is the molecular weight of lignin?
6. Line 134. How was the content of lignin measured? Was it measured the soluble and insoluble lignin? 
7. What is the conclusion of the evaluation process? Which additive does the author suggest for HTP? Which one is potential, and which one is not?

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

I find this manuscript to be excellently written, with a clear and concise presentation of the research subject. The study addresses an important scientific challenge in the energy sector, particularly the underutilization of lignin-rich residues in lignocellulosic biorefineries. The authors effectively demonstrate how modifying hydrothermal pretreatment with temperature and additives enhances lignin solubility in alcohol, offering promising implications for biofuel and material applications. The findings are significant, with the potential to optimize lignin utilization while maintaining high carbohydrate conversion in biorefinery processes. Only one detail I would like to clarify.

• What was the main reason for choosing 190 ⁰C as the control, a short explanation in the text would be helpful. Wouldn’t overall efficiency be higher with lower temperature, maybe? Has that been tested before?
• Maybe a more detailed discussion is needed on why H2O2 could reduce saccharification yield despite previous studies showing positive effects would strengthen the argument. https://doi.org/10.1016/j.energy.2021.120324, https://doi.org/10.1016/j.biortech.2021.126162.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have addressed some of the necessary changes, and the manuscript has been greatly improved. However, some aspects could still be considered before publication, such as comparing the findings with others reported in the literature. This will be important to provide an idea of the efficiency of the proposed experiments. 

Also, In the introduction, avoid using more than one citation per statement unless it is extremely necessary. 

Author Response

Comment 1)  Regarding the suggestion to compare our findings with previous literature, we would like to emphasize that, to the best of our knowledge, this study is the first to systematically evaluate how hydrothermal pretreatment modifications affect both alcohol solubility of lignin-rich residues and enzymatic saccharification in a unified experimental framework. As such, no directly comparable studies exist. This has now been explicitly stated in the manuscript (lines 11, 100, and – 300–303) to clarify the novelty of our work. The Changes are highlighted in yellow.

Comment 2) Concerning the comment on citation density in the introduction, we have carefully considered this and retained multiple citations in certain cases where they reflect consensus or provide complementary insights from different research groups. We believe this strengthens the credibility of key background statements and demonstrates the broader relevance of the topic, without introducing redundancy.