Hydrothermal Treatment of Residual Forest Wood (Softwood) and Digestate from Anaerobic Digestion—Influence of Temperature and Holding Time on the Characteristics of the Solid and Liquid Products

Round 1

Reviewer 1 Report

This article presents research on hydrothermal treatment with microwaves at different temperatures and holding times, which allows influences the quality of the final products. In the process of reviewing the paper, several recommendations have been made:

1. It is recommended to add the aim of the paper at the end of the Introduction.
2. Conclusions do not show the main results of the study. It is recommended to summarize all the results that have been obtained.
3. There are some minor typos in the text.

Author Response

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Reviewer 2 Report

The manuscript (Ms.) describes of hydrothermal treatment of residual forest and digestate from anaerobic digestion. The subject of the Ms. is interesting.  The paper includes minor errors which have no significant impact on the whole manuscript. It's recommended to see Guide for Authors carefully.
Minor comments to the Ms. are provided below:
Why did the Authors not carry out statistical analyzes? e.g. analysis of variance and post-hoc tests.
Could the authors explain the high values of the following elements: Ca and K.

Author Response

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Reviewer 3 Report

There are following comments:

1. Section “Abstract”. The first sentence is not informative. Please add information about weight or volume of biomass sample and sizes of fuel particles.
2. Section “1. Introduction”. If microwave heating is one of the main arguments for present study novelty, please add a paragraph with critical analysis of previous studies deal with microwave pyrolysis of solid fuels.
3. Section “1. Introduction”. Please state more specifically the purpose of the study at the end of the section.
4. Section “2. Materials and Methods”. Please briefly describe the need for the analysis described below and the significance of obtained results in order to achieve the formulated purpose.
5. Section “3. Results and Discussion”. Please give at the end of the section practical recommendation for hydrothermal treatment based on one of criterion. Authors can formulate an original criterion or choose one of the following criteria: maximum yield of useful products; minimal economic costs for waste processing; maximum technology performance, etc.
6. Section “4. Conclusions”. Please avoid Refences.

Author Response

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Reviewer 4 Report

The article submitted by the authors deals with an important issue at the present time, namely the production of biofuels from renewable raw materials. 

The introduction, despite being a separate part with the abstract, seems to be a continuation of it. I would suggest that this section be rewritten as it is difficult for the recipient to assimilate. There is no unifying thought explaining why such and not other research was done.

"In the context of a sustainable energy supply and an ecological economy, further improvements are required in these sectors. " - Why is this important and in which sectors? 

The literature review lacks information on the types of biofuels, pretreatment methods and the desirability of these treatments. 

In the abstract I did not find how the individual treatments affect the biomass components. Where according to the literature, the process of high temperature treatment without addition of an alkaline substance leads first to degradation of hemicelluloses, low molecular weight amorphous cellulose and only at higher temperatures (above 200 deg C) leads to degradation of lignin. Treatment with alkaline substances can be carried out at lower temperatures and has a greater effect on lignin. 

In the material chapter the abbreviation FR is explained, other abbreviations are given without explanation of their meanings, so one can only guess from the text what the authors had in mind and what they refer to. 

Why was the drying process carried out for at least 24 h? The thermal decomposition of the biomass results in an increase in the mass of the material (2.2).  

What gas has been used as a carrier gas in gas chromatography (nitrogen, hydrogen, helium,...) (2.5). What chromatography column was used in the GC-MS analysis. What did the temperature program look like (temperature spread, etc.).

In the figure: 2, 3, 4, 5, 6, 7: the presented numbering of the peaks is not consecutive, which makes it difficult for offices to arrive. Additionally, the mean retention time and peak area are not included in Table 6.

The values given in figures 8, 9, 10 are very unreadable. I would propose to present them in the form of a table.

The conclusions should not contain an explanation of what the research material was used for (it may be in the material or at the end of the literature review with an explanation that it is great material). The applications should contain the most important summarized CONCLUSIONS that have been developed on the basis of the research. E.G. HTT treatment significantly increases the carbon content of the biomass ...

Sample literature on biomass conversion and metal content:

DOI:10.5604/01.3001.0015.3633

DOI:10.37763/wr.1336-4561/66.1.3948

DOI:10.1007/s00226-021-01350-1

DOI:10.12841/wood.1644-3985.C19.20

Author Response

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Round 2

Reviewer 4 Report

Thank you very much for reading and referring to my comments. As regards clarity of publication, Figures 2,3,4,5,6,7 could be made with a shift of the chromatograms in the Y axis to make them more visible. Additionally, in subsequent publications, the percentage of compounds in relation to all identified substances can be specified. However, this is not necessary to be introduced in this publication. 

 

Author Response

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