Study of the Potential Uses of Hydrochar from Grape Pomace and Walnut Shells Generated from Hydrothermal Carbonization as an Alternative for the Revalorization of Agri-Waste in Chile
Round 1
Reviewer 1 Report
Manuscript ID - sustainability-1370191
The manuscript is very relevant to ongoing research on hydrochar. Therefore, the manuscript is relevant to the scope of the Journal. However, some minor issues need to be addressed adequately before accepting this manuscript for the Journal. Therefore, I strongly recommend that the manuscript publishes after a minor revision.
Detailed comments:
- The authors should explicitly specify the novelty of their work. For example, what progress against the most recent state-of-the-art similar studies was made in this study? Mention this in the revised manuscript sections, including abstract, introduction, and conclusions.
- It is recommended to discuss and explain the appropriate policies based on the findings of this study. In addition, the results should be further elaborated to show how they could be used for real applications.
- It is much recommended to provide a comparative studies table (literature review table) with similar factors/parameters used in this study.
- Please eliminate those multiple references. After that, please check the manuscript thoroughly and eliminate all the lumps in the manuscript. Also, check with the Journal for reference formatting/style.
- It is recommended to extend the comparison of the study findings with other similar published work under the results and discussion section.
- It is strongly recommended to add a new subsection under results and discussion, 'Practical implications of this study,' outlining the challenges in the current research, future work, and recommendations.
- Currently, the conclusion section contains both the concluding marks and recommendations. The future work-related points can be grouped under the newly added subsection, as mentioned above.
- Overall, the manuscript is too short and contains very little information in the Introduction and Discussion sections, which need to be extended by following the examples of good related articles published in similar and other high-impact journals.
Author Response
Please see the attachment
Author Response File: 
Author Response.docx
Reviewer 2 Report
Overall the level of study is good, following are few suggestions
- Improve the introduction work by showing the research gaps and novelty. author can take guidance from following studies; https://doi.org/10.1016/j.chemosphere.2021.131730, https://doi.org/10.1016/j.rser.2021.111451, https://doi.org/10.1016/j.chemosphere.2021.131382
- results should be discussed comprehensively.
Author Response
Please see the attached
Author Response File: Author Response.docx
Reviewer 3 Report
The paper presents data regarding the HTC of two biomasses, grape marc and walnut shells. The paper is quite basic, and the English should be definitively improved. The objectives reported by the authors at the end of the Introduction section << Consequently, this research fills this knowledge gap by producing a comprehensive, up-to-date characterization of this organic waste in Chile, estimating the resource potential. Furthermore, this study conducts a potential review of opportunities for hydrochar from these organic wastes to determine barriers, and potential regulatory solutions, to enable greater utilization of the bioresources.>> are not addressed in the paper: The authors should spend efforts on this regard, to increase the quality and the significance of the paper, which as it is now seems (as I already stated) quite basic.
Line 37 <<Through thermochemical conversion and hydrothermal carbonization grape pomace and walnut shells become hydrochar which has several uses such as soil amendment, energy as pellets, or low-cost adsorbent.>>. The authors should add some relevant references.
Line 62 <<Hydrothermal carbonization HTC), also known as wet torrefaction or wet pyrolysis, is the decomposition process of organic matter through changes in water temperature. The water is at a temperature above its boiling point and the pressure in the system is autogenous.>>. Replace “through changes in water temperature” with “occurring in liquid water generally in the temperature range 180-250°C”. The following sentence should be accordingly modified, as it is not true that “The water is at a temperature above its boiling point” – the sentence would be correct only if adding “at ambient pressure”. Rephrase.
Line 65 <<This process simulates the natural formation of carbon>>. Coal, not carbon. Correct here and elsewhere in the text.
Line 73 <<More specifically walnut shell and grape pomace have received great attention regarding HTC processing to study myriad variables, such as residence time, temperature, and biomass-water ratio, obtaining results that help to determine the potential use that can be given to the waste, being reused and preventing it from being considered solely as a waste but as a bioresource [30-39].>> Actually some relevant and recent papers should be added as references: Basso et al., In deep analysis on the behavior of grape marc constituents during hydrothermal carbonization, Energies, 11 (2018) 1379 https://www.mdpi.com/1996-1073/11/6/1379; Purnomo et al., Granular activated carbon from grape seeds hydrothermal char, Applied Sciences 8 (2018) 331 http://doi.org/10.3390/app8030331; Saha et al., Cationic Dye Adsorption on Hydrochars of Winery and Citrus Juice Industries Residues: Performance, Mechanism, and Thermodynamics, Energies, 13 (2020) 4686 https://www.mdpi.com/1996-1073/13/18/4686. Ref 49 is not reported correctly; instead of: Fiori L, Basso D, Castello D, Baratieri M. Hydrothermal Carbonization of Biomass: Design of a Batch Reactor and Preliminary Experimental Results. Iconbm: International Conference on Biomass, Pts 1 and 2. 2014;37:55-+ It should be Fiori L, Basso D, Castello D, Baratieri M. Hydrothermal carbonization of biomass: design of a batch reactor and preliminary experimental results. Chemical Engineering Transactions. 2014;37:55-60.
Line 79 <<… there remains a need for an efficient method to obtain hydro-char specially from grape pomace>>. I do not understand this sentence. I suggest to be more specific or to delete it.
Line 86 <<No animals or humans were tested on or harmed in the research performed for this study.>>. Remove it.
Line 88 <<Grape pomace was collected from Undurraga vineyard, Talagante, Región Metropolitana, Chile. The samples were collected right after harvesting time (April) when the grape pomace was sun drying before final disposal.>>. Authors should be clearer. Did the authors deal with bunches of grapes harvested during the harvest (but in fact it would not make sense, the grapes must be destined for human consumption or for the production of wine or grape juices) or rather the residual pomace of vinification or extraction of grape juice?
Line 119, Table 1. A biomass to water ratio of 5:1 does not allow HTC to be performed. Would it not be 1:5?
Line 149 <<As anticipated, the increase of residence time significantly reduces the ash content to approximately 2% – 3% compared to the 10% for GP and 23% from WS.>> Anticipated where?
There are two figs 1: line 154 and line 174. The second should be corrected in Fig. 2.
Line 169 << Additionally, the mass loss depends heavily on the reaction severity and the composition of biomass [53].>>. The Basso et al. Energies, 11 (2018) 1379 paper I mentioned above presents a specific section where the effect of reaction severity on grape marc constituents is addressed.
Line 174, Figure 2. The elemental analysis data is unclear. Is the complement to 100% represented by ashes? But this should not be the case looking at what reported at line 149 <<As anticipated, the increase of residence time significantly reduces the ash content to approximately 2% – 3% compared to the 10% for GP and 23% from WS.>>. The figure should be revised and explained in the text. Actually, looking at line 170 << Figure 2. Displays the elemental composition of hydro-char as a function of the yield…>>, so the authors combined the yield and the compositional data (reported as a percentage): this is not correct. I suggest replacing Figure 2 with a table reporting all the data in the correct way and clear: hydrochar yields, HHV, elemental composition data, H/C and O/C. I see some of this data are reported in Table 3: another good reason for avoiding to report the solid yield data (i.e. the hydrochar yield) in Fig. 2, which causes confusion.
Line 199 Table 3. Why the authors did not report the Severity values for the HTC treatment on walnut shells?
Line 215 << several hydrothermal variables were studied…>>. Actually, only temperature and reaction time.
Line 223 << In addition, HTC process was proven successful to reduce inorganic matter from feedstocks.>>. Data should be presented in the paper regarding this, is too less to write (Line 149) <<As anticipated, the increase of residence time significantly reduces the ash content to approximately 2% – 3% compared to the 10% for GP and 23% from WS.>>.
Author Response
Please see attachments
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
The authors have verified the usefulness of the results and data and significantly improved the manuscript after revision. The manuscript is within the scope of the Journal. The manuscript is important to publish because of the topic/contents importance, precise methodology, clarity, and novelty. Based on my comments, I recommend the manuscript to publish as it is.Author Response
The reviewer 1 does not provide more comments to be added in the manuscript, but the overall english languaje and style was revized and minor spell checks were taken care of.
Reviewer 3 Report
The paper was improved with the revision. One point to be addressed: Table 3: The authors should use the dot, not the comma, as a separator for decimal digits.
Author Response
Response to Reviewer 3 Comments
Point 1: Table 3: The authors should use the dot, not the comma, as a separator for decimal digits.
Response point 1: We have acknowledge the reviewers comment and made the arrangements as needed.
