Low-Temperature Hydrothermal Treatment (HTT) Improves the Combustion Properties of Short-Rotation Coppice Willow Wood by Reducing Emission Precursors
Round 1
Reviewer 1 Report
Dear editor,
The manuscript entitled "Low Temperature Hydrothermal Treatment (HTT) Improves the Combustion Properties of Short Rotation Coppice Willow Wood by Reducing Emission Precursors" has been reviewed. It is recommended minor revision. The intrinsic characteristics of low H/C ratio and large ash content limit the energy utilization of biomass. In this paper, the possibility to upgrade short rotation oppice willow biomass by low temperature hydrothermal treatment (HTT) was conducted. It has some novelties seeking and can be accepted after some revisions. The comments are listed as follows:
- Materials and Methods. More basic analysis was illustrated and some contents can be deleted.
- Results. More depth analysis and comparison need be added based on some updated references about hydrolysis and trace element behavior, such as [Green Chemistry, 2019, 21(6): 1292-1304; Industrial Crops and Products, 2021, 173: 114135; Fuel, 2021, 285: 119090; Fuel, 2019, 239: 1194-1203.].
- Fig. 1. Is any references for these data for coal, lignite, etc.
Author Response
Dear editor,
The manuscript entitled "Low Temperature Hydrothermal Treatment (HTT) Improves the Combustion Properties of Short Rotation Coppice Willow Wood by Reducing Emission Precursors" has been reviewed. It is recommended minor revision. The intrinsic characteristics of low H/C ratio and large ash content limit the energy utilization of biomass. In this paper, the possibility to upgrade short rotation coppice willow biomass by low temperature hydrothermal treatment (HTT) was conducted. It has some novelties seeking and can be accepted after some revisions. The comments are listed as follows:
- Materials and Methods. More basic analysis was illustrated and some contents can be deleted.
Reply: The method section was shortened and for 2.6 – 2.9. another study of the authors was cited were the same methods were applied.
- More depth analysis and comparison need be added based on some updated references about hydrolysis and trace element behavior, such as
Reply: Green Chemistry, 2019, 21(6): 1292-1304; The paper was added referring to the solid acid catalyzer induced increase of the hydrolysis of corn cob, which complements the increase of acids during HTT as biomass-based catalyzer. Also, it was cited in the context of the sulfonation of carbonated cellulose at relatively low temperatures that complement the temperatures in this study.
Reply: Industrial Crops and Products, 2021, 173: 114135; The paper was cited referring to the detected phenol in the process water in relation to a suppressed condensation of the biomass.
Reply: Fuel, 2021, 285: 119090; This paper was cited referring to the high impact of calcium on ash slagging.
Reply: Fuel, 2019, 239: 1194-1203. This paper was cited in the introduction to open the perspective of condensation reactions catalyzed by the increasing mineral content in the solid phase at high temperatures.
- 1. Is any references for these data for coal, lignite, etc.
Reply: Thank you for reminding us, the carbonized material shapes are drawn according to Reza et al., which was included in the caption.
Reviewer 2 Report
The authors showed that the hydrothermal treatment has the potential to enlarge the availability of biomass for the increasing worldwide demand in the future in view of the transition from fossil to sustainable energy sources.
The work is overall good even if it has shortcomings that can be improved.
Here are some of my suggestions for the authors:
1) Why did you choose to investigate this process, i.e. low temperature hydrothermal treatment (HTT)?
It would be advisable to justify this choice and discuss any improvements in this study compared to previous works.
2) In Materials and Methods there are many paragraphs that indicate processes or techniques of analysis. In my opinion, it might be useful to describe some of these in more detail. I think that these analyzes have already been done by your group for other works, you could cite them as references.
3) I suggest reorganizing the results better because they are unclear, also English should be improved.
In the caption of Figure 2, it is temperature no temperatur.
4) In Figure 3, the lines represent error bars? If so, they should be mentioned.
5)The authors limit themselves to making a list of the results achieved in the "conclusions" section. In my opinion, they should try to report the main results but also the improvements obtained if there are any compared to other similar works, enhancing this part.
Author Response
The authors showed that the hydrothermal treatment has the potential to enlarge the availability of biomass for the increasing worldwide demand in the future in view of the transition from fossil to sustainable energy sources.
The work is overall good even if it has shortcomings that can be improved.
Here are some of my suggestions for the authors:
- Why did you choose to investigate this process, i.e. low temperature hydrothermal treatment (HTT)?
It would be advisable to justify this choice and discuss any improvements in this study compared to previous works.
Reply: In the introduction water leaching was described more precisely in the beginning (Line 32-41) in order to conclude at the end of the introduction, why HTT was chosen (intermediate process severity to combine both positive effects of water leaching and HTC, Line 71-77. In the conclusion the advantage of the HTT method was outline more detailed, referring to results of other studies on water leaching and HTC. Line 402-404 and Line 410-420
- In Materials and Methods there are many paragraphs that indicate processes or techniques of analysis. In my opinion, it might be useful to describe some of these in more detail. I think that these analyzes have already been done by your group for other works, you could cite them as references.
Reply: The material method section was improved by citing another paper that includes the respective method descriptions. Especially the GC-MS and the ICP-OES parts were shortened, while referring to the already published work.
- I suggest reorganizing the results better because they are unclear, also English should be improved.
Reply: The result section was reorganized by adding more subchapters, which should increase the readability. The English was checked throughout the manuscript and many sentences or wordings were changed in order to increase the readability and the correctness of the language.
In the caption of Figure 2, it is temperature no temperatur.
Reply: Thank you, this was changed accordingly
- In Figure 3, the lines represent error bars? If so, they should be mentioned.
Reply: The shapes of the boxplots were assigned to the respective elements of the descriptive statistics in this caption.
5)The authors limit themselves to making a list of the results achieved in the "conclusions" section. In my opinion, they should try to report the main results but also the improvements obtained if there are any compared to other similar works, enhancing this part.
Reply: The conclusion was strengthened by relating to concise literature studies on HTC and water leaching. The respective results were stated and it was shown that HTT of wood biomass is advantageous over HTC and water leaching. Line 398-426
Reviewer 3 Report
This is an interesting article where authors have reported their work on Low Temperature Hydrothermal Treatment (HTT) . The article is nicely written. Following corrections are needed: -Introduction should be strengthened to highlight the current state of the art -How the work is differet from others -Some of the relevant references may be cited such as: https://www.sciencedirect.com/science/article/pii/S1364032121007644 https://www.sciencedirect.com/science/article/pii/S0960852419317110Author Response
Comments and Suggestions for Authors
This is an interesting article where authors have reported their work on Low Temperature Hydrothermal Treatment (HTT) . The article is nicely written. Following corrections are needed: -
Introduction should be strengthened to highlight the current state of the art –
Reply: The introduction was strengthened by adding relevant literature sources on water leaching (Line 34-41). Also, the objective of the study was highlighted (Line 71-77)
How the work is different from others –
Reply: This was outlined in the introduction as stated above (reply to your first comment) and also in the conclusion (Line 402-404 and Line 416-420)
Some of the relevant references may be cited such as:
Reply: https://www.sciencedirect.com/science/article/pii/S1364032121007644 This review was added in the introduction referring to general waste treatment approaches.
Reply: https://www.sciencedirect.com/science/article/pii/S0960852419317110 This review was unfortunately not available for the authors and, therefore, could not be included. The topic is gasification in general and the factors that influence the process. At least in the abstract there is no mentioning about relevant topics related to this manuscript.
Round 2
Reviewer 2 Report
Thanks to the authors for their answers.
I only suggest improving the English of the paper as a last effort before possible publication.
Author Response
The Englisch language was improved throughout the text:
Line 34, "solve" to "dissolve"
Line 88, "carried out" to "done"
Line 109, "measured by" to "determination of"
Line 120-121, sentence split in two sentences
Line 129, "with" deleted, brackets added
Line 143, "is the value for" to "indicated"
Line 238, "leads to" to "causes"
Line 246, "heated" to "heat"
Line 280, "yielded biomass with an" to "caused"
Line 281 "caused" to "induced"
Line 358, "In water it can oxidize" to "It can oxidize in water"
Line 383, "probable" was deleted
Line 389, "the effects reducing the solubility of sodium and zinc" to "the solubility reduction of sodium and zinc"
Author Response File: 
Author Response.docx
