Arundo donax Refining to Second Generation Bioethanol and Furfural

Round 1

Reviewer 1 Report

1. Objective of the paper is not clearly described.
2. In the Introduction section and the Discussion section there are no references to the papers describing the economic aspects of bioethanol production, since the conclusions mentioned the aspect of economic profitability.
3. Materials and Methods section - the hydrolysis test should be expanded, the steps and test conditions should be clearly indicated.
4. The paragraph starting with Saccharomyces cerevisiae - is probably the fermentation part, but its edition indicates a new sub-item. Please correct.
5. Methodology for the separation of ethanol and its measurement should be expanded.
6. The discussion of the results is mainly related to ethanol production efficiency, please expand the discussion of the other results.
7. Editorial mistakes, especially regarding the editing of tables figures, and titles.
8. Fig. 4 - illegible, probably the second axis describing the temperature is missing.
9. Some references seem to have incomplete details such as the missing volume, issue and page numbers.

Author Response

I would like to thank the reviewer 1 for their comments which certainly improved the quality of the manuscript.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments for processes-1000079:

 

This manuscript presents a very attractive pathway to convert non-food Arundo donax biomass to more valuable products, furfural and ethanol. Acid-catalysed steam explosion was used for the biomass pretreatment and fractionation. Thereafter, hydrolysis-fermentation followed by simultaneous saccharification and fermentation was carried out. Biomass-derived xylose was then subjected to dehydration to produce furfural on solid acid catalyst (Amberlyst 15) in microwave-irradiated media. Although the beginning of the manuscript provides great impression to the reader, it suffers from lack of presentation in many aspects. Therefore, the current version of the manuscript is not recommended for publication before several major revision have made. The following concerns must be addressed point-to-point, clearly, and coherently in order for the manuscript to be reconsidered for publication.

1- The abstract: it is stated that the optimized HSSF process produced ethanol titers in the range 43- 51g/L depending on the enzymatic dosage. The authors must include the ethanol production under unoptimized conditions to highlight their contribution. In addition, the type of catalyst/acid in the acid-catalyzed steam explosion must be stated in the abstract.

2- This paper provides relatively well introduction on biochemical conversion of lignocellulosic biomass conversion. However, the manuscript will be improved significantly if some recent papers that include both optimization and thermochemical process as a more robust conversion alternative are cited. The following articles are suggested to be referred to in the revised version:

https://doi.org/10.1016/j.ces.2020.116249

https://doi.org/10.1371/journal.pone.0231045

https://doi.org/10.1016/j.colsurfa.2020.125791

https://doi.org/10.1021/acs.iecr.0c02902

3- What does DM stand for? The full terminology must be used as it first appear in Section 2.1 with DM in parentheses. Additionally, the steam explosion process must be elaborated on as the process matrix has significant influence on chemical structure of lignocellulosic biomass. It is not clear how the researchers performed steam explosion in this work. Also, the type and nature of acid catalyst is not clear. Is this a heterogeneous catalytic process or a homogeneous one or a combination of both?

4- Where was Amberlyst 15 obtained from? Was it synthesized in the lab or purchased from chemical suppliers? No information on this acid catalyst including catalyst characterization is provided.

5- A clear block diagram and schematic diagram of the process including steam explosion, hydrolysis, dehydration test, and microwave irradiation is required. There is even no previous publication from which the procedure was adopted has been cited.

6- In Figure 4, what is the reason for labeling subfigures A, B, …,F while they are not mentioned in the caption?

7- A major shortcoming of this work is the fact that there is no information on side products after the entire integrated process. What is the fate of solid residues? Is there a way of valorizing the side products?

8- Units of numeric values (degree C and g/L) are missing from X-axis in Figure 6.

9- Surprisingly, It looks like there is not much difference in ethanol production while yield dosage increases by approximately 45% from 4 to 7 g/L. Is it due to mass transfer limitation? Microorganism inactivation? A 3D representation of temperature, pH, and dosage might help to better visualize these effects.

Author Response

I would like to thank the reviewers for their comments which certainly improved the quality of the manuscript.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

1. The paper is well structured and logically organised.
2. I suggest accepting the chapter for the Processes since its relevance, but it needs minor revisions.
3. The introduction section of the paper suitably motivates the readers in the subject of the paper but it should be developed further.
4. Conclusions section needs to be developed further in order to highlight the unique contributions of the paper and limitations of the research.

Author Response

Additions have been made in the manuscript. Details can be viewed in the attached file. Thanks again to the reviewer 1 for the additional suggestions that improved the  reading of the manuscript.

Author Response File: Author Response.docx

Reviewer 2 Report

The revised manuscript has been improved significantly and all concerns have been addressed properly. I would recommend publication of this manuscript in present form.

Author Response

Thanks again to Reviewer 2 for making the purpose of the this work clearer and more understandable.