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Bibliometric Analysis of Hydrothermal Wastewater Treatment in the Last Two Decades

Water 2025, 17(5), 746; https://doi.org/10.3390/w17050746

by Abel Santillan-Angeles¹, Candido Mendoza-Perez¹

, Edwin Villagrán²

, Francisco Garcia¹ and Jorge Flores-Velazquez^1,*

Reviewer 1: Anonymous

Reviewer 2:

Fajun Zhao

Reviewer 3:

Zakaria Al-Qodah

Water 2025, 17(5), 746; https://doi.org/10.3390/w17050746

Submission received: 16 January 2025 / Revised: 26 February 2025 / Accepted: 28 February 2025 / Published: 4 March 2025

(This article belongs to the Special Issue Urban Water Pollution Control: Theory and Technology)

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The publication is initially interesting, but written at a very low level. It requires significant expansion, especially in terms of discussing the results.

The review should also discuss the substantive content of the analyzed works, and here it is done in a very limited way. If this review is to be useful for the reader, it cannot block 14 or 10 citations in one place. This is not a report, but a scientific publication. Please expand the discussion - the question should be asked - what results from this review? The name of the main scientist and the place of research and the number of publications do not contribute much to science without in-depth analysis. Please significantly deepen the analysis. For example, it can be related to future directions of research and indicate research gaps...

The illustration side requires refinement. The article lacks formulas, calculations (e.g. annual increase), statistical analysis should be added. Detailed comments are provided below, which should help the Authors improve the manuscript.

1. The time range given in the abstract is inconsistent with that given in the title…

2. The key abbreviation for the article – is not explained anywhere, appears in different configurations, once as THAR, and once as HTAR, and is created from the name in Spanish, not English – this is unacceptable;

3. Do not use combined references at the end of the paragraph – only a specific indication of which data comes from which source – e.g. lines 50 – 55 – US reports (which?), what references for the data? [5-6] – please separate and indicate exactly;

4. Why is the number of references smaller when the table shows 97 articles????

5. Don't start a sentence with [10]….. Maybe it would be better to be “Source [10]…” or “Authors of work [10]….” – applies to the entire article;

6. If keywords are given in Spanish and then in English, it would be good to maintain the order of keywords;

7. Table 1 – keywords – please add that keywords are in English;

8. Please provide a justification for not including articles without open access. The fact that an article is available using the university library or interlibrary loan does not mean that it does not exist.

9. MOZILA browser? Line 104

10. Please provide more information about the BIBLIOMETRIX tool.

11. Subtitle 3.1. – please check if this title is 100% adequate to the content?

12. Table 2 – since the result is 97, and the number of authors of these publications and journals are included in table – at this point they should all be included in the list of references.

13. The figures require refinement – Figure 1: No. or NO – there is a difference; you can make a cumulative graph on the same graph (it is cumulative on the next graph, but in a different context)

14. A statistical study, trend line, R and R2 and confidence level and a comment on the correlation coefficient should be added to Graph No. 1.

15. Figure 2 should be superimposed on Figure 1 or bars with the number of publications in a given year should be added – if there are few publications, a smaller number of citations should be expected, the comment should be expanded and possible reasons for the small number of publications should be provided;

16. Line 143 – why is 2023 being analyzed?

17. Figure 3 – the full name of the Journal should be; No of documents

18. Figure 4 – indicate that it is cumulative

19. Chapter 3.6. – how the frequency was calculated, provide the formula and description of the components, provide the period in which the frequency was calculated for the authors;

20. Figure 5 – no legend, why were these 12 analyzed, why not 15 or 20 out of 328? Are these the authors of 97 documents or 72? Please provide justification;

21. Lines 186 - 189 - does not fit, to be moved or supplemented, what other group is this, what countries, not really on topic in this subsection;

22. Figure 7 – the text should state what % of all articles the top 10 is; the title of the chart should indicate that this is the top 10;

23. Figure 8 – no information in Material and method about the type of chart used, please expand the information about this tool;

24. Chapter 3.11 – incomprehensible – paragraphs 244 – 247 and 253 – 254 need to be rewritten.

25. “[36] generated…” – the publication did not generate anything except tinning, rather the Authors’ Team did it…..

26. Line 278 – 288 – please separate the references and provide one after the other, sentences like this can be used at the end in the summary;

27. Line 300 – incorrectly formulated conclusion, the average itself does not indicate that something is growing, I suggest calculating the annual increase;

Comments for author File: Comments.pdf

Comments on the Quality of English Language

The editing of the article leaves much to be desired;

Author Response

Reviewer(s)' Comments to Author:

Reviewer: 1

General Comments

the publication is initially interesting, but written at a very low level. It requires significant expansion, especially in terms of discussing the results.

Dear Reviewer: Many thanks for your thoughtful suggestions. All of them were addressed and integrated into the new version of the manuscript, which is detailed below.

Introduction

In general, hydrothermal treatments facilitate the generation, synthesis, or recovery of compounds from biomass or contaminants found in wastewater and sludge. Chand et al., [10] reported that modern wastewater treatment plants using Hydrothermal Liquefaction (HTL) can retain up to 99 % of microplastics in wastewater streams. Similarly, Zijlstra et al. [11] produced biochar with a dry matter content of 38 % through HTC using the patented TORWASH® process on sludge from the paper industry. They demonstrated that this treatment enhances dewatering biological paper sludge without the need for additives such as fibers or polyelectrolytes. Aragón et al. (2019) also generated biochar with TCH, from organic materials present in sludge subjected to 250°C and 5 MPa of pressure.

Regarding TGH Cengiz et al. (2017) generated hydrogen and methane from opium alkaloid (Papaver somniferum) wastewater supplied from the Afyon treatment plant in Turkey. The treatment consisted of subjecting the wastewater to temperature ranges of 400-600°C and 23-45 MPa pressure and found that the yields of H2 and CH4 increased from 11.3 to 28.5 mol/kg C and from 3.5 to 7.4 mol/kg C, when comparing the treatment intervals. In turn, Onwudili et al. (2013) in the United Kingdom, obtained the same gases, from pharmaceutical wastewater and treated water sludge, which were subjected to 450°C and 34 MPa pressure; The wastewater produced more methane than hydrogen and the sludge produced more hydrogen than methane.

Dear Reviewer: The main reason for the current redaction was due to the paper is a bibliometric study and not a paper review, in fact is in the objective “the objective of this work was to analyze the bibliographic information to assess the evolution of HTAR at the beginning of the 21st century” .Tthat is why, discussion was not deep expanded with specific results. Even that, we integer cites in the introduction and discussion was complemented

Results

3.11 Reading Analysis

Experimentation analysis using HTL

The analysis reveals that [12-14] carry out experiments using HTL to produce bio-oil from biomass developed in wastewater (Lemna minor) and biomass contained in urban organic waste. In this regard, in all cases organic material was used as raw material, such that, through the application of heat as part of the thermochemical process, the transformation of biomass is achieved by decomposing the molecules through dehydration and decarboxylation reactions at temperatures between 200 and 350 ◦C, and pressures between 5 and 25 MPa (Al-juboori et al., 2023).

[15-17, 5, 18-19] aimed to generate bio-crude from biomass produced by algae, microalgae, fungi, bacteria, and cyanobacteria. Because considerable fractions of lipids, proteins, carbohydrates and lignin are present in biomass, biocrude is easily formed by ionic reactions at temperatures of 280–374 ◦C and 8–22 MPa due to the subcritical conditions to which the water in the biomass is subjected (Liu et al., 2021).

Additionally, [20-22] primarily focused on generating hydrocarbons from sludge.

The production of the aqueous phase from wastewater, biomass, and sludge was explored by Jesse and Davidson [23-25]. In this sense, Watson et al., 2020, mention that the aqueous phase consists of a large amount of process water, with high levels of organic carbon, chemical oxygen demand, ammonium and toxic compounds (aromatic and nitrogenous organic compounds) useful in the formation of biocrude.

To recover the aqueous phase, [26-27] applied HTL to biomass derived from algae and purified sludge, respectively. Zhou et al. (2015) point out that the aqueous phase produced in TLH contains high concentrations of nutrients and organic carbon, which represent, respectively, up to 80% and 40% of its content in the raw material. However, the composition of the aqueous phase will depend at all times on the composition of the wastewater.

Since Sayegh et al. (2021) carried out an extra process to recover 88% of the ammonium immersed in the aqueous phase of the TLH, it was demonstrated that a second process was needed to recover the contaminants that the TLH fails to remove. For their part, Chand et al. (2022) achieved a 99% recovery of microplastic from wastewater using TLH. In this regard, it should be mentioned that TLH refers specifically to a thermochemical process in subcritical conditions where the dehydration stage is omitted, so that solid compounds are easily recovered.

3.12 Reported Experimental Methods in HTC

[28] used HTC to synthesize modified montmorillonite as a pesticide adsorbent in wastewater, using dextrose, cellulose, and corn starch as biomass. In this sense, Fang et al., 2018, mention that because the temperatures in TCH are moderate, it allows the pressure to be generated autogenously; which allows the water contained in the sludge to function as a solvent, reagent or even catalyst in the synthesis reactions.
Similarly, [29,11] used sludge and wastewater, respectively to generate hydrocarbons. Hydrochar is mainly studied as a solid biofuel from TCH and is normally produced at a temperature range of 180–280 ◦C; so that several authors establish a difference between the production of hydrochar with TLH and TCH because the wet biomass as raw material in TCH does not go through the dehydration process (Fang et al., 2018).

[30] used this treatment to generate an aqueous phase to study the effect of Thraustochytrium striatum on wastewater treatment. The same authors mention that as a result of TCH, hydrocarbon, CO2 and a liquid or filtered product are produced from which nutrients present in the raw material can be extracted and which serve as food for the microorganisms present in it.

3.13 Experimental methodology in HTG

[31] studied the types of gases generated from HTG of wastewater containing opium alkaloids. It can be concluded that hydrothermal gasification of wastewater with alkaloids for the production of hydrogen and methane was achieved as a result of high COD removal efficiencies in terms of treatment.
[26] applied this treatment to the aqueous phase obtained from HTL to remove phosphorus and nitrogen. Onwudili et al. [32] also applied HTG to the aqueous phase from a HT process to obtain hydrogen and methane.

3.14 Experimental methods in HT

In general, HT aims to generate or synthesize materials used in wastewater treatment or to recover or remove materials, compounds, or elements present in wastewater.

[33-35] In this regard, generated hydrocarbons from organic compounds, biomass, and wastewater from the paper industry, respectively. Wang et al. (2023) indicate that TH can convert organic biomass into carbon-rich hydrochar, accompanied by more fractions responsible for adsorption reactions. On the other hand, studies on the use of TH for lignocellulosic biomass have mainly focused on virgin materials and agricultural or food waste (Fang et al., 2018), and little attention has been paid to waste paper sludge and lignocellulosic pulp.
[36] generated an aqueous phase using HT from woody organic compounds to conduct electrochemical reactions and decompose I-butanol present in wastewater.
[37] produced tobermorite using eggshells, rice, and glass fragments.
[38] decomposed carbamazepine, metoprolol, and sulfamethoxazole. These authors agree in pointing out that the chemical transformation reactions that occur during the TH process include hydrolysis, dehydration, decarboxylation, decomposition, condensation, bond cleavage, formation of new bonds and isomerization of hemicellulose, cellulose and lignin derivatives.

[39-53] synthesized titanium oxide, tungsten trioxide/titanium dioxide nanostructures, AgInS2/SnIn4S8 heterojunctions, CdS/SnIn4S8 heterojunctions, reduced graphene oxide, oxidized graphite, iron-based materials, MnO, copper selenide nanocrystals, zinc metasilicate nanocrystals, zeolite, mesoporous titanium oxide particles, iron-based nanocomposites, manganese oxide, titanium dioxide, and zinc oxide. These compounds are useful in removing wastewater contaminants generated from chemical compounds. The use of TH for the synthesis of visible light-active compounds and photocatalysts useful in the absorption of contaminants present in wastewater (Abdelraheem et al., 2019).

[54-55] focused on recovering phosphorus/nitrates and phosphorus from wastewater.
[56-65] removed contaminants such as tungsten, boron, chromium, hexavalent chromium, kaomicin, boron, 2,4-dichlorophenoxyacetic acid, arsenic sulfide, and crystallized glyphosate salts, primarily from wastewater. In this regard, Sun et al. (2020) mention that TH-produced hydrochar can adsorb heavy metals and pesticides from wastewater and sludge. In turn, Yang et al. (2024) found that molybdenum disulfide synthesized by TH is capable of adsorbing Chromium VI particles present in wastewater.

Discussion

Technological development regarding wastewater has proven to be useful in mitigating environmental impacts and after the pandemic, research has increased on water reuse. Critical situations have been detected such as the presence of antibiotics in the effluents, but in general procedures for water treatment. In this sense, reviewing the databases in 2024, the SCOPUS catalog records that 21 documents related to Hydrothermal Treatment were published. Highlighting the country of China, which has established itself as a leader in related research and its publication in indexed journals [74-77].

The perspective in the development of research around water treatment and separation methodologies maintains a growth rate whose results will be presented in publications in 2024. During the year 2024, the results of research aimed at addressing problems of mixing and permanence of contaminating compounds present in the solid and liquid phases derived from hydrothermal treatment (HTL, HTC and HTG) in their different modalities were published [78-81].

Regarding the liquid phase Liu et al. 2024, [78] studied the decomposition of the substances contained in the aqueous phase of HTC, and found that heavy metals can be eliminated by coagulation as a secondary process to the hydrothermal process. For their part, Zhang et al. 2024 [74] investigated the aqueous phase of a HT as a source of denitrified carbon without affecting beneficial microorganisms in wastewater decomposition.

The synthesis of compounds useful in the adsorption of contaminants present in sludge and wastewater was also carried out; In this regard, Yang et al. (2024) [81] worked on the formation of chromium VI adsorbent compounds that were found present in the liquid phase prior to HT. In turn, Liu et al. (2024) [84] managed to improve the contents of protein, polysaccharides and volatile fatty acids of the aqueous phase of HTL.

However, in the research and use of HT, short-term aspects such as: technical challenges, pollution and social impact, economic cost must be considered; as well as policy management. In such a way that the use of HT processes is useful in water recovery phenomena that promote forms of sustainable economy and with adaptability to specific treatment conditions and not those of a country.

The illustration side requires refinement. The article lacks formulas, calculations (e.g. annual increase), statistical analysis should be added.

All illustrations were adapted based on your suggestions

specific suggestions

Detailed comments are provided below, which should help the Authors improve the manuscript.

Position	Reviewer observation	Author corrections	comments
Title	The time range given in the abstract is inconsistent with that given in the title…	Bibliometric Analysis of Hydrothermal Wastewater Treatment in the las two decades	Time in the title was deleted in order to remark the topic
2	The key abbreviation for the article – is not explained anywhere, appears in different configurations, once as THAR, and once as HTAR, and is created from the name in Spanish, not English – this is unacceptable;	HTAR	Authors toughs explain how the key words in Spanish homologue in English were
lines 50 – 55	Do not use combined references at the end of the paragraph – only a specific indication of which data comes from which source – e.g. lines 50 – 55 – US reports (which?), what references for the data? [5-6] – please separate and indicate exactly;	the United States reports an annual sludge production of approximately 12 million dry tons and 56 million wet tons [5],	There is a 1998 US Environmental Protection Agency Report (6.8 millons dry tons, https://www.epa.gov/sites/default/files/2018-12/documents/biosolids-generation-use-disposal-us.pdf). But there is no recently published information. Por otro lado, Liu et al 2022 redirecciona a Marrone et al 2018, cuyo artículo tiene costo.
4	Why is the number of references smaller when the table shows 97 articles????		97 documents were found in the SCOPUS database, only 72 open access documents were read and analyzed. A file with total references was added. After this review, these numbers were changed, but same, in the original bibliometric analysis these numbers were worked, after that, have been include 2024 cites and discussion cites were added
5	Don't start a sentence with [10]….. Maybe it would be better to be “Source [10]…” or “Authors of work [10]….” – applies to the entire article;	Chand et al., [10] reported that modern wastewater treatment plants using Hydrothermal	Good points were changed in all manuscript
6	If keywords are given in Spanish and then in English, it would be good to maintain the order of keywords;		Do it, Thanks a lot To start the work Spanish term were used, without results, so were changed in English. All manuscript was generated with the English keywords
7	Table 1 – keywords – please add that keywords are in English;		SAME, To start the work Spanish term were used, without results, so were changed in English. All manuscript was generated with the English keywords
8	Please provide a justification for not including articles without open access. The fact that an article is available using the university library or interlibrary loan does not mean that it does not exist.		The support staff of the educational institution's library conducted a search and determined that documents of Chinese origin are impossible to obtain, while others have an unauthorized cost for their acquisition. Unfortunately, non-free access articles involve a cost.
Line 104	MOZILA browser?	Mozilla Firefox web browser
10	Please provide more information about the BIBLIOMETRIX tool.	Bibliometric it is a statistical tool that compile published research in journals around the world. The program has a series of tabs and subtabs that directly provide the results of the bibliometric analysis on the screen. . In the background, the NNUAL SCIENTIFIC PRODUCTION subtab provides a graph on the screen that can be replaced by a table. Its information gets analyze some statistical parameters such as quantity and temporal evolution and trending. Is useful in the remark items in specific area of science, in this case HTAR.	Integrate, thanks The program has a series of tabs and subtabs that directly provide the results of the bibliometric analysis on the screen, these are: OVERVIEW, which in the foreground and, through the MAIN INFORMATION subtab, displays a box with the main information on the screen; In turn, you can consult a table with the same information. In the background, the NNUAL SCIENTIFIC PRODUCTION subtab provides a graph on the screen that can be replaced by a table. The Average Citations Per Year subtab also displays a graph that can be replaced by a table of information. In the THREE-FIELD PLOT subtab and the Parameters selection in three options (middle field, left field and right field) provides graphical information of the respective parameters (author, affiliation, country, among others.). SOURCES, allows interaction in the tabs: Most Relevant Sources, Bradford's law, Sources Local Impact and Sources production over Time; All of them provide graphs and tables with the results of the respective analysis. AUTHORS is divided into Authors, Affiliations and Countries.
11	Subtitle 3.1. – please check if this title is 100% adequate to the content?	3.1 Information analyzed by BIBLIOMETRIX tool	Ok, was adapted
12	Table 2 – since the result is 97, and the number of authors of these publications and journals are included in table – at this point they should all be included in the list of references		Missing references were added in an Anexo file (All references, divided by groups, all references in the manuscript, cites in 2024 and not reviewed)
13	The figures require refinement – Figure 1: No. or NO – there is a difference; you can make a cumulative graph on the same graph (it is cumulative on the next graph, but in a different context)	Figure 1. Temporal Trends ( ---- ) in Scientific Production within the Selected Range, accumulate (O) and normal data	Ok. new graph added
14	A statistical study, trend line, R and R2 and confidence level and a comment on the correlation coefficient should be added to Graph No. 1.		Ok, new graph added
15	Figure 2 should be superimposed on Figure 1 or bars with the number of publications in a given year should be added – if there are few publications, a smaller number of citations should be expected, the comment should be expanded and possible reasons for the small number of publications should be provided;		Ok. new graph added
Line 143	– why is 2023 being analyzed?		Because this magazine (Bioresource Technology) is the one that reached the maximum number of publications, and it did so in that year.
17	Figure 3 – the full name of the Journal should be; No of documents		The graphics are replaced.
18	Figure 4 – indicate that it is cumulative		Yeap, good idea Es la 3 o la 4
19	. Chapter 3.6. – how the frequency was calculated, provide the formula and description of the components, provide the period in which the frequency was calculated for the authors;		The frequency value is provided by BIBLIOMETRIX
20	Figure 5 – no legend, why were these 12 analyzed, why not 15 or 20 out of 328? Are these the authors of 97 documents or 72? Please provide justification;		Because the interest of any reader is to know who the author with the maximum number of publications is.
Lines 186 - 189	- does not fit, to be moved or supplemented, what other group is this, what countries, not really on topic in this subsection;		Yes, delete
22	Figure 7 – the text should state what % of all articles the top 10 is; the title of the chart should indicate that this is the top 10;		Good point. Falta porcentaje
23	Figure 8 – no information in Material and method about the type of chart used, please expand the information about this tool;	In the methodology it will be specified that because the graphs provided by BIBLIOMETRIX are not specific, the data obtained was graphed using excel. And that only the xxxxx figures are a direct source of BIBLIOMETRIX.
24	Chapter 3.11 – incomprehensible – paragraphs 244 – 247 and 253 – 254 need to be rewritten.
25	“[36] generated…” – the publication did not generate anything except tinning, rather the Authors’ Team did it…..		Ok
26	Line 278 – 288 – please separate the references and provide one after the other, sentences like this can be used at the end in the summary;	Sasaki et al. [36] generated an aqueous phase using HT from woody organic compounds to conduct electrochemical reactions and decompose I-butanol present in wastewater. Loryuenyong et al. [37] produced tobermorite using eggshells, rice, and glass fragments. Falamarzian et al. [38] decomposed carbamazepine, metoprolol, and sulfamethoxazole. On the other hand, Abdelraheem et al., Bhagwat et al., Deng (a) et al., Deng(b) et al., Ikram et al., Liu et al., Mahmoud et al., Masrat et al., Qiaoa et al., Somerset et al., Sun et al., Wang et al., Xu et al. and Yang et al. [39-53] synthesized titanium oxide, tungsten	Ok
Line 300	– incorrectly formulated conclusion, the average itself does not indicate that something is growing, I suggest calculating the annual increase;	Ok	Good idea.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

(1) The abstract provides a clear summary of the paper’s objectives and the methods employed, although it could benefit from a more detailed discussion on the practical implications of the findings.The introduction effectively sets up the context, particularly regarding the global need for efficient wastewater treatment methods. However, it would be helpful to briefly mention key gaps in the existing literature on hydrothermal treatments to better justify the study's importance.The use of the SCOPUS database and BIBLIMETRIX software for bibliometric analysis is well-justified. However, more details could be provided on the selection criteria for the documents used in the analysis. For example, it would be useful to explain why only certain documents were included or excluded, as this can influence the reliability and comprehensiveness of the results.It might be beneficial to clarify the process of filtering data and how this aligns with the study’s goals to improve transparency.

(2) The results section is thorough and provides detailed insights into the growth of research on hydrothermal treatments over time. The inclusion of various bibliometric indicators, such as citation counts, author networks, and journal trends, adds significant value to the analysis.The inclusion of charts and figures enhances the readability and understanding of the trends. However, some of the figures, such as the network collaboration graphs, could use clearer labels or legends for ease of interpretation.

(3) The discussion does a good job interpreting the findings and aligning them with broader trends in scientific research. However, it could benefit from a more in-depth critique of the methodologies used in the cited studies. Are there any notable weaknesses or inconsistencies in the studies included in the analysis that could affect the overall conclusions?

(4) The implications of these results on future research directions are well-explored. It would be interesting to see more specific recommendations on how the research community could address identified gaps, particularly regarding the integration of hydrothermal treatments in wastewater management at a global scale.

(5) The conclusion effectively summarizes the study's findings and highlights the significance of bibliometric tools in tracking scientific progress. It could be strengthened by more direct recommendations on how policymakers or researchers can apply these insights in the context of improving global wastewater treatment practices.The statement on the gap in research in Mexico is a valuable addition, but further elaboration on potential solutions or future research agendas in this area would be useful.

(6) The references section is comprehensive and includes many relevant studies. However, it may benefit from the inclusion of more recent publications (post-2023) to ensure that the analysis reflects the most up-to-date trends in the field.

(7) This is a solid bibliometric study that contributes valuable insights into the growth of research on hydrothermal wastewater treatment. It effectively uses bibliometric analysis to explore trends and identify key contributors in the field.The paper would benefit from a more critical evaluation of the methodologies used in the reviewed articles and a deeper discussion of the practical applications of hydrothermal treatments. Additionally, the overall clarity and readability of the figures and charts could be improved.

Comments on the Quality of English Language

Suggestions for Improvement: Sentence Length: Break long sentences into shorter ones to improve clarity. Try to avoid over-complicated sentences. Use of Articles and Prepositions: Ensure that articles ("a," "an," "the") are used correctly and consistently. Consistency in Terminology: Review and ensure that technical terms are consistently used throughout the paper, especially in terms like “homogeneous catalysis,” “heavy oil,” and “aquathermolysis.” Punctuation: Improve punctuation use, especially in complex sentences, by using commas, semicolons, and periods more effectively to clarify ideas. Active vs. Passive Voice: While passive voice is commonly used in scientific writing, ensure it doesn't make the writing unnecessarily complex. Using active voice can often make the writing clearer and more direct. In conclusion, the quality of English in this article is generally strong, but minor revisions to sentence structure, punctuation, and consistency will improve its clarity and flow.

Author Response

Reviewer: 2

General Comments to the Author

Detailed discussion on the practical implications of the findings (ABSTRAC).

The analysis will allow us to know who the researcher is, the country, the technology or type of treatment that is developing the research in THAR to the greatest extent:The author with the highest number of contributions on the topic is Yuanhui Zhang. The countries most involved in this issue are China, the U.S.A. and Japan; China being the one with the highest number of publications. The scientific and technological development regarding the THAR is shown; and that, technology is aimed at the use and generation of energy. In addition, Hydrothermal Liquefaction Treatment is being investigated to gener-ate biocrude and bio-oils; the Hydrothermal Carbonization Treatment for the generation of hydrochar; and the Hydrothermal Gasification Treatment to produce methane and hy-drogen; all from biomass with high moisture content.

Key gaps in the existing literature on hydrothermal treatments to better justify the study's importance (INTRODUCTION).

Aragon et al. (2019) also generated biochar with TCH, from organic materials present in sludge subjected to 250°C and 5 MPa pressure.

Regarding TGH Cengiz et al. (2017) Hydrogen and methane generation from opium alkaloid (Papaver somniferum) wastewater supplied from the Afyon treatment plant Turkey. The treatment consisted of subjecting the wastewater to temperature intervals of 400-600°C and 23-45 MPa of pressure, and they found that the yields of H2 and CH4 increased from 11.3 to 28.5 mol/kg of C and from 3.5 to 7.4 mol/kg of C, when comparing the treatment intervals. In turn, Onwudili et al. (2013) in the United Kingdom, obtained the same gases from pharmaceutical wastewater and treated water sludge, which were subjected to 450°C and 34 MPa of pressure; The wastewater produced more methane than hydrogen and the sludge produced more hydrogen than methane.

Criteria for the documents used in the analysis

In the foreground, SCOPUS searches within 26 registry parameters, in such a way that the number of documents found exceeds the reading capacity of each of them. In the background, and because the SCOPUS database provides as search results an endless number of documents related by word, the set of words that best describe the desired topic of the search must be specified. (2) The results section is thorough and provides detailed insights into the growth of research on hydrothermal treatments over time. The inclusion of various bibliometric indicators, such as citation counts, author networks, and journal trends, adds significant value to the analysis.The inclusion of charts and figures enhances the readability and understanding of the trends. However, some of the figures, such as the network collaboration graphs, could use clearer labels or legends for ease of interpretation.

The figures, such as the network collaboration graphs, could use clearer labels or legends for ease of interpretation.

BIBLIOMETRIX provides image output that in some cases can be adjusted. In the case of collaborations, the graphs were adjusted as representatively as possible.

The SCOPUS database has a record of the authors' names, where the first name is abbreviated; in such a way that, when the comparison analysis of the authors is done, their name influences the quantification. For example, the name of the author Zhang Yuanhui is registered in SCOPUS as Zhang Y., and is confusing when quantified with the authors Zhang Yu, Zhang Yishu, and Zhang Yan who have the same first initial (Y). In order to carry out the respective comparative and quantification analysis, the names are reviewed document by document. However, the conclusions are not affected. (4) The implications of these results on future research directions are well-explored. It would be interesting to see more specific recommendations on how the research community could address identified gaps, particularly regarding the integration of hydrothermal treatments in wastewater management at a global scale.

The intention of the document is to make known to the world and mainly in Mexico the enormous advantage that THARs present as processing processes and utilization of highly energetic products and by-products.

(5) The conclusion effectively summarizes the study's findings and highlights the significance of bibliometric tools in tracking scientific progress. It could be strengthened by more direct recommendations on how policymakers or researchers can apply these insights in the context of improving global wastewater treatment practices. The statement on the gap in research in Mexico is a valuable addition, but further elaboration on potential solutions or future research agendas in this area would be useful.

The statement on the gap in research in Mexico is a valuable addition, but further elaboration on potential solutions or future research agendas in this area would be useful.

INCLUDE 2024

Akbari, H.; Akbari, H.; Fanaei, F.; Adibzadeh, A. 2024. Optimization of parameters affecting the hydrothermal carbonization of wastewater treatment plant sewage sludge. Biomass Conversion and Biorefinery, 14(21): 27335–27346 pp. https://doi.org/10.1007/s13399-022-03427-8

AlObaid, A.A.; Nazir, G.; Modi, A.; Thakur, S.; Malik, J.H. 2024. Hydrazine hydrate free one pot rapid hydrothermal synthesis of crystalline Zn1−xNdxSe nanostructures for wastewater treatment. Inorganic Chemistry, Communications; 161, 112060. https://doi.org/10.1016/j.inoche.2024.112060

Awan, A.M.; Khalid, A.; Ahmad, P.; (...); F. Dawood, A.; H. Zyoud, S. 2024. Defects oriented hydrothermal synthesis of TiO2 and MnTiO2 nanoparticles as photocatalysts for wastewater treatment and antibacterial applications. Heliyon, 10(3): e25579. https://doi.org/10.1016/j.heliyon.2024.e25579

Basar, I.A.; Stokes, A.; Eskicioglu, C. 2024. Evaluation of on-site biological treatment options for hydrothermal liquefaction aqueous phase derived from sludge in municipal wastewater treatment plants. Water Research, 252, 121206. https://doi.org/10.1016/j.watres.2024.121206

Cabrera, D.V.; Adema-Yusta, I.; Santibañez, M.J.; (...); Tester, J.W.: Labatut, R.A. 2024. Grease trap waste valorization through hydrothermal liquefaction and anaerobic digestion: a circular approach to dairy wastewater treatment. Energy and Environmental Science, 17(22): 8926–8941 pp. DOI: https://doi.org/10.1039/D4EE02245A

Gao, K.; Shi, Y.; An, K.; (...); Yu, W.; Lin, H. 2024. Rapid synthesis of pollucite by hydrothermal method for the treatment of cesium in wastewater. https://doi.org/10.1007/s10967-024-09554-y

Kanoo, B.; Garg, A. 2024. Characterization of the Hydrochar and Process Wastewater Recovered after Hydrothermal Pre-Treatment of Diaper Waste. Waste and Biomass Valorization. DOI: 10.1007/s12649-024-02579-0

Karka, P.; Johannsen, I.; Papadokonstantakis, S. 2024. Hydrothermal liquefaction integrated with wastewater treatment plants - life cycle assessment and technoeconomic analysis of process system options. Sustainable Energy and Fuels, 8(15): 3438–3451 pp. https://doi.org/10.1039/D3SE01211E

Kaur, H.; Kumar, S.; Kumar, P.; Ghfar, A.A.; Bouzid, G. 2024. Tailoring ZnS nanostructures through precipitation-cum-hydrothermal synthesis for enhanced wastewater purification and antibacterial treatment. Environmental Research, 259, 119534. https://doi.org/10.1016/j.envres.2024.119534

Kossińska, N.; Grosser, A.; Kwapińska, M.; (...); Jouhara, H.; Krzyżyńska, R. 2024. Co-hydrothermal carbonization as a potential method of utilising digested sludge and screenings from wastewater treatment plants towards energy application. Energy, 299, 131456. https://doi.org/10.1016/j.energy.2024.131456

Liu, C.; Yue, Z.; Ma, D.; (...); Yang, M.; Wang, J. 2024a. Integration of hydrothermal liquefied sludge as wastewater for anaerobic treatment and energy recovery: Aqueous phase characterization, anaerobic digestion performance and energy balance análisis. Journal of Water Process, Engineering, 60, 105096 . https://doi.org/10.1016/j.jwpe.2024.105096

Liu, G.; Xu, Q.; Abou-Elwafa, S.F.; Alshehri, M.A.; Zhang, T. 2024b. Hydrothermal Carbonization Technology for Wastewater Treatment under the “Dual Carbon” Goals: Current Status, Trends, and Challenges. Water (Switzerland), 16(12): 1749. https://doi.org/10.3390/w16121749

Liu, L.; Zhao, L., Jin, S.; (...); Zhai, Y.; Luo, P. 2024c. Treatment of sludge hydrothermal carbonization wastewater by ferrous/sodium percarbonate system: Effect of wastewater composition and role of coagulation and oxidation. Water Research, 267, 122531. https://doi.org/10.1016/j.watres.2024.122531

Liu, M.; Mahata, C.; Wang, Z.; Kumar, S.; Zheng, Y. 2024d. Comparative exploration of biological treatment of hydrothermal liquefaction wastewater from sewage sludge: Effects of culture, fermentation conditions, and ammonia stripping. Journal of Environmental Management, 349, 119527. https://doi.org/10.1016/j.jenvman.2023.119527

Silva Thomsen, L.B.; Anastasakis, K.; Biller, P. 2024. Hydrothermal liquefaction potential of wastewater treatment sludges: Effect of wastewater treatment plant and sludge nature on products distribution. Fuel, 355, 129525. DOI: 10.1016/j.fuel.2023.129525

Xiao, L.; Meng, Y.; Jin, H.; (...); Shen, D.; Long, Y. 2024. Conversion of waste-activated sludge from wastewater treatment plants to 5-hydroxymethylfurfural by microwave hydrothermal treatment. Biomass Conversion and Biorefinery, 14(9); 10389–10397 pp. https://doi.org/10.1007/s13399-022-03076-x

Yang, T.; Gao, N.; Li, B. 2024. Biomass hydrothermal carbonization solution-assisted synthesis of intercalation-expanded core–shell structured molybdenum disulfide for efficient adsorption of Cr (VI) in electroplating wastewater treatment. Bioresource Technology, 401, 130761. https://doi.org/10.1016/j.biortech.2024.130761

Yu, Y.; Zhao, K.; Li, W.; (...); Jia, X.; Sun, J. 2024. Reaction pathway of hydrothermal liquefaction of duckweed for wastewater treatment based on major model compounds. Biomass and Bioenergy; 182, 107106. https://doi.org/10.1016/j.biombioe.2024.107106

Zeb, H.; Hussain, M.A.; Javed, M.; (...); Abbas, R.; Siddiqi, M.H. 2024. Study of biooil production from sewage sludge of a municipal wastewater treatment plant by using hydrothermal liquefaction. Thermal Science, 28(3): 2683–2692 pp. https://doi.org/10.2298/TSCI230728262Z

Zhang, H.; Li, G.; Li, W.; (...); Zhang, S.; Nie, Y. 2024. Biochemical properties of sludge derived hydrothermal liquid products and microbial response of wastewater treatment. Process Biochemistry, 144: 294–305 pp. https://doi.org/10.1016/j.procbio.2024.06.007

Zheng, Q.; Ma, Y.; Wan, J.; (...); Xia, X.; Sun, X. 2024. Hydrolysate derived from sugarcane bagasse by hydrothermal and enzymatic treatment as an external carbon source for wastewater nitrogen removal. Journal of Water Process Engineering, 59, 105039. https://doi.org/10.1016/j.jwpe.2024.105039

(7) This is a solid bibliometric study that contributes valuable insights into the growth of research on hydrothermal wastewater treatment. It effectively uses bibliometric analysis to explore trends and identify key contributors in the field. The paper would benefit from a more critical evaluation of the methodologies used in the reviewed articles and a deeper discussion of the practical applications of hydrothermal treatments. Additionally, the overall clarity and readability of the figures and charts could be improved.

Results and discussion section was expended with more details about, additionally figures were improved

Discussion of the practical applications of hydrothermal treatments

3.11 Reported Experimental Methods in HTL

The analysis reveals that [12-14] carry out experiments using HTL to produce bio-oil from biomass developed in wastewater (Lemna minor) and biomass contained in urban organic waste. In this regard, in all cases organic material was used as raw material, such that, through the application of heat as part of the thermochemical process, the transformation of biomass is achieved by decomposing the molecules through dehydration and decar-boxylation reactions at temperatures between 200 and 350 ◦C, and pressures between 5 and 25 MPa (Al-juboori et al., 2023).

[15-17, 5, 18-19] aimed to generate bio-crude from biomass produced by algae, microalgae, fungi, bacteria, and cyanobacteria. Because considerable fractions of lipids, proteins, car-bohydrates and lignin are present in biomass, biocrude is easily formed by ionic reactions at temperatures of 280–374 ◦C and 8–22 MPa due to the subcritical conditions to which the water in the biomass is subjected (Liu et al., 2021).

Additionally, [20-22] primarily focused on generating hydrocarbons from sludge.

To recover the aqueous phase, [26-27] applied HTL to biomass derived from algae and pu-rified sludge, respectively. Zhou et al. (2015) point out that the aqueous phase produced in TLH contains high concentrations of nutrients and organic carbon, which represent, re-spectively, up to 80% and 40% of its content in the raw material. However, the composition of the aqueous phase will depend at all times on the composition of the wastewater.

Since Sayegh et al. (2021) carried out an extra process to recover 88% of the ammonium immersed in the aqueous phase of the TLH, it was demonstrated that a second process was needed to recover the contaminants that the TLH fails to remove. For their part, Chand et al. (2022) achieved a 99% recovery of microplastic from wastewater using TLH. In this re-gard, it should be mentioned that TLH refers specifically to a thermochemical process in subcritical conditions where the dehydration stage is omitted, so that solid compounds are easily recovered.

3.12 Reported Experimental Methods in HTC

Similarly, [29,11] used sludge and wastewater, respectively to generate hydrocarbons. Hy-drochar is mainly studied as a solid biofuel from TCH and is normally produced at a tem-perature range of 180–280 ◦C; so that several authors establish a difference between the production of hydrochar with TLH and TCH because the wet biomass as raw material in TCH does not go through the dehydration process (Fang et al., 2018).

[30] used this treatment to generate an aqueous phase to study the effect of Thrausto-chytrium striatum on wastewater treatment. The same authors mention that as a result of TCH, hydrocarbon, CO2 and a liquid or filtered product are produced from which nutri-ents present in the raw material can be extracted and which serve as food for the microor-ganisms present in it.

3.13 Experimental methodology in HTG

[31] studied the types of gases generated from HTG of wastewater containing opium alka-loids. It can be concluded that hydrothermal gasification of wastewater with alkaloids for the production of hydrogen and methane was achieved as a result of high COD removal efficiencies in terms of treatment.

[26] applied this treatment to the aqueous phase obtained from HTL to remove phospho-rus and nitrogen. Onwudili et al. [32] also applied HTG to the aqueous phase from a HT process to obtain hydrogen and methane.

3.14 Experimental methods in HT

In general, HT aims to generate or synthesize materials used in wastewater treatment or to recover or remove materials, compounds, or elements present in wastewater.

[36] generated an aqueous phase using HT from woody organic compounds to conduct electrochemical reactions and decompose I-butanol present in wastewater.

[37] produced tobermorite using eggshells, rice, and glass fragments.

[38] decomposed carbamazepine, metoprolol, and sulfamethoxazole. These authors agree in pointing out that the chemical transformation reactions that occur during the TH pro-cess include hydrolysis, dehydration, decarboxylation, decomposition, condensation, bond cleavage, formation of new bonds and isomerization of hemicellulose, cellulose and lignin derivatives.

[39-53] synthesized titanium oxide, tungsten trioxide/titanium dioxide nanostructures, AgInS2/SnIn4S8 heterojunctions, CdS/SnIn4S8 heterojunctions, reduced graphene oxide, oxidized graphite, iron-based materials, MnO, copper selenide nanocrystals, zinc metasil-icate nanocrystals, zeolite, mesoporous titanium oxide particles, iron-based nanocompo-sites, manganese oxide, titanium dioxide, and zinc oxide. These compounds are useful in removing wastewater contaminants generated from chemical compounds. The use of TH for the synthesis of visible light-active compounds and photocatalysts useful in the ab-sorption of contaminants present in wastewater (Abdelraheem et al., 2019).

[54-55] focused on recovering phosphorus/nitrates and phosphorus from wastewater.

[56-65] removed contaminants such as tungsten, boron, chromium, hexavalent chromium, kaomicin, boron, 2,4-dichlorophenoxyacetic acid, arsenic sulfide, and crystallized glyphosate salts, primarily from wastewater. In this regard, Sun et al. (2020) mention that TH-produced hydrochar can adsorb heavy metals and pesticides from wastewater and sludge. In turn, Yang et al. (2024) found that molybdenum disulfide synthesized by TH is capable of adsorbing Chromium VI particles present in wastewater.

Figures and graphs will be modified for greater clarity and readability.

Current graph. Adjusted graph.

specific suggestions

Suggestions for Improvement: Sentence Length: Break long sentences into shorter ones to improve clarity.

Try to avoid over-complicated sentences. Use of Articles and Prepositions: Ensure that articles ("a," "an," "the") are used correctly and consistently. Consistency in Terminology: Review and ensure that technical terms are consistently used throughout the paper, especially in terms like “homogeneous catalysis,” “heavy oil,” and “aquathermolysis.”

Thank you so much for your excellent suggestion; the manuscript was reviewed and we think the redaction was improved

In chemistry, homogeneous catalysis¹ is that catalysis in which the catalysts are in the same phase as the reactants. While, Hyne (1986) defined aquathermolysis² as the chemical interaction that takes place between water vapor and hydrocarbons present in the formation. Heavy oil³, characterized by its high density and viscosity, contains higher levels of impurities such as waxes, suspended solids and heavy metals compared to lighter crude oils.

¹ https://es.wikipedia.org/wiki/Cat%C3%A1lisis_homog%C3%A9nea

² https://energyandcommerce.com.mx/acuatermolisis-catalitica-en-procesos-de-inyeccion-de-vapor/#:~:text=Hyne%20(1986)%20defini%C3%B3%20la%20acuaterm%C3%B3lisis,hidrocarburos%20presentes%20en%20la%20formaci%C3%B3n

³ https://www.watertechnologies.mx/blog/what-heavy-oil-look-how-refineries-can-overcome-mixing-challenges

Punctuation: Improve punctuation use, especially in complex sentences, by using commas, semicolons, and periods more effectively to clarify ideas. Active vs. Passive Voice: While passive voice is commonly used in scientific writing, ensure it doesn't make the writing unnecessarily complex.

Using active voice can often make the writing clearer and more direct.

In conclusion, the quality of English in this article is generally strong, but minor revisions to sentence structure, punctuation, and consistency will improve its clarity and flow.

Thank you

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The objective of this review is to evaluate the growth and development of science in the THAR through bibliometric analysis. The keywords directly obtained from the treatment method were used in order to carry out the integration of related published research, the terms used in the search both separately and crossly were “treatment, hydrothermal, wastewater” in the database from SCOPUS. The review is well written and gives important information about the growth of publication in the THAR. However, some comments should be addressed before any further recommendations:

1- Some abbreviation are not defined such as HTAR. For this reason all abbreviations should be clearly defined.

2- Since in 2023 there are 17 references concerning the subject, I expect in 2024 there are more references. For this reason, I suggest to add the references published in 2024.

3- It is necessary to give a short information about the online interface program BIBLIMETRIX and the reasons for using it rather than other models.

4- The keywords are poor. None of them contain wastewater. the keywords should be linked by some words with the subject of the manuscript.

5- The organization of the manuscript should be revised. The discussion of any figure or table must be after the figure or the table. Their discussion should be after them.

6- Some recommendations for future work can be added after the conclusions..

7. The authors stated that the objective of this work was to analyze the bibliographic information to assess the evolution of HTAR at the beginning of the 21st century. Actually the first four years are missed. It is better to write in the last two decades.

8- There are many reviews concerning the subjects but not listed in the references such as :

Environmental Research, 212, Part D, 2022, 113532.

and many others. Accordingly, the literature survey should be improved. and this will affect the whole analysis.

9- The quality of some figures like fig. 4, 8, and 9 should be improved.

Author Response

Reviewer: 3

General Comments to the Author

specific suggestions

However, some comments should be addressed before any further recommendations:

No	Reviewer observation	Author corrections	comments
1	Some abbreviation are not defined such as HTAR. For this reason all abbreviations should be clearly defined.	HTAR	The reviewer has reason, abbreviation was homologue
2	Since in 2023 there are 17 references concerning the subject, I expect in 2024 there are more references. For this reason, I suggest to add the references published in 2024		21 References in 2024 were integrated at bibliography and some of one in the manuscript
3	It is necessary to give a short information about the online interface program BIBLIMETRIX and the reasons for using it rather than other models.	Bibliometric it is a statistical tool that compile published research in journals around the world. The program has a series of tabs and subtabs that directly provide the results of the bibliometric analysis on the screen. . In the background, the NNUAL SCIENTIFIC PRODUCTION subtab provides a graph on the screen that can be replaced by a table. Its information gets analyze some statistical parameters such as quantity and temporal evolution and trending. Is useful in the remark items in specific area of science, in this case HTAR.	Thanks, was included The program has a series of tabs and subtabs that directly provide the results of the bibliometric analysis on the screen, these are: OVERVIEW, which in the foreground and, through the MAIN INFORMATION subtab, displays a box with the main information on the screen; In turn, you can consult a table with the same information. In the background, the NNUAL SCIENTIFIC PRODUCTION subtab provides a graph on the screen that can be replaced by a table. The Average Citations Per Year subtab also displays a graph that can be replaced by a table of information. In the THREE-FIELD PLOT subtab and the Parameters selection in three options (middle field, left field and right field) provides graphical information of the respective parameters (author, affiliation, country, among others.). SOURCES, allows interaction in the tabs: Most Relevant Sources, Bradford's law, Sources Local Impact and Sources production over Time; All of them provide graphs and tables with the results of the respective analysis. AUTHORS is divided into Authors, Affiliations and Countries. Authors, presents subtabs such as: Most Relevant Authors, in which case you can select the number of graphed values using Options; Authors’ Production over Time, Author Productivity through Lotka’s Law and Authors’ Local Impact Also graphs and tables with analyzed information. Affiliations, has the Most Relevant Affiliations and Affiliations'Productions over Time subtabs. Countries, presents subtabs such as Corresponding Author's Countries, Production, Countries' production over Time and Most Cited Countries that provide graphs and tables; In turn, the Countries' Scientific production sub-tab displays a world map on the screen in which the countries with productive importance regarding the topic appear. DOCUMENTS, is divided into Documents, Cited References and Words. Documents only presents the Most Local Cited References subtab that displays a graph or table adjustable through Options to determine the number of values presented. Cited References has Most Local References and References Spectroscopy subtabs. Words has the Most Frequency Words, Words Frequency over Time and Trend Topics subtabs that display graphs and tables that can be modified using Options; In turn, WordCloud and TreeMaps show figures in which the most recurrent word in the analysis appears in larger size and percentage of appearance respectively. CLUSTERING has a tab that groups and presents a figure on the screen, in which the number of response values can be modified using Options, Cloustering by Couping. CONCEPTUAL STRUCTURE is divided into Network Approach and Factorial Approach. Network Approach has three subtabs: Co-occurrence Network, Thematic Map and Thematic Evolution that display a series of thematic figures and graphs that can be modified using Options. The Factorial Approach subtab displays a graph, a dendrogram and tables with the grouped values. SOCIAL STRUCTURE, allows you to identify the collaboration regarding authors, institutions and countries, through the Collaboration Network subtab, when using Options. The Countries Collabotration World Map subtab displays a world map on the screen in which the respective collaboration between countries is graphically indicated and which is adjustable through Options.
4	The keywords are poor. None of them contain wastewater. the keywords should be linked by some words with the subject of the manuscript.	Hydrothermal liquefaction-carbonization-gasification, biomass, wastewater treatment, reuse of treated water	Because it's in the title. However, some keywords were added to approximate the importance of the objective method of this study.
5	The organization of the manuscript should be revised. The discussion of any figure or table must be after the figure or the table. Their discussion should be after them		Good point, include
6	Some recommendations for future work can be added after the conclusions..	It is recommended for Mexico to apply by replicating some methodology investigated in another country, to do HTWW and consider concentrated solar radiation as a source of energy.	Yes, we are agreeing and added
7	The authors stated that the objective of this work was to analyze the bibliographic information to assess the evolution of HTAR at the beginning of the 21st century. Actually the first four years are missed. It is better to write in the last two decades	Bibliometric Analysis of Hydrothermal Wastewater Treatment in the las two decades	Good idea, changed
8	There are many reviews concerning the subjects but not listed in the references such as : 1- Current challenges of hydrothermal treated wastewater (HTWW) for environmental applications and their perspectives: A review. Environmental Research, 212, Part D, 2022, 113532. 2- A perspective on hydrothermal processing of sewage sludge, Current Opinion in Environmental Science & Health 14, 2020, 63-73 and many others. Accordingly, the literature survey should be improved. and this will affect the whole analysis.	Muhammad Usman, Zhijian Shi, Nalok Dutta, Muhammad Awais Ashraf, Bushra Ishfaq, Mohamed Gamal El-Din. 2022. Current challenges of hydrothermal treated wastewater (HTWW) for environmental applications and their perspectives: A review. Environmental Research, 212 (D), https://doi.org/10.1016/j.envres.2022.113532 Chen WT, Haque MA, Lu T, Aierzhati A, Reimonn G. 2020. A perspective on hydrothermal processing of sewage sludge. Curr Opin Environ Sci Health. 2020 Apr;14:63-73. doi: 10.1016/j.coesh.2020.02.008	Was include 18 cites more, also include your warm suggestion
9	The quality of some figures like fig. 4, 8, and 9 should be improved		Was doit

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors did not make any fundamental changes to the text of the manuscript. The manuscript still contains essential errors, from confused abbreviations (once THAR, and ONCE HTAR) and also abbreviations from the Spanish name, up to the blocked citations (line 348).There is still a mess in the number of articles analyzed, because the abstract mentions 98 articles, while the text mentions 97. The response to the reviewer is chaotic, and does not contain a precise indication of where the changes were applied. In addition, there are many explanations that I do not find in the text. It is not me who needs an explanation, but the reader.

Deatile comments:

I have noted still inconsistent with the abbrevations - in abstract THAR, line 89 HTAR? And this abbrevation is still in Spanish! Aqua residual is spanish words not english!!! Wastewater!

In abstract, there are: 98 response records were filtered to 87 documents

Later: 97 documents were obtained as "article" and "final," as shown in Table 1.

MOZILA line 120, still incorrect; (but in the response to reviewer is ok);

Bibliometric or Bibliometrix? In the response to the Reviewer there are these two names. I can not find the explanation about the tool from response to the reviewer in the text. I as a reviewer not need it - it is needed in the text!

"The support staff of the educational
institution's library conducted a search and
determined that documents of Chinese origin
are impossible to obtain, while others have an
unauthorized cost for their acquisition.
Unfortunately, non-free access articles
involve a cost." - where it is in the text?

Comments on the Quality of English Language

The abbreviation from Spanish name AGUA RESIDUAL in English text is not acceptable! How many times I should repeat the same comments?

Author Response

Dear Reviewer 1

Many thank you for your scientific support in the reviewed of this manuscript; our really apologize for the confusion and mistakes during the correction process. We are agreeing with the chaotic of the process, due the long corrections, but we really concentrate in the corrections process, We hope to complement the suggestions and really sorry again

Reviewer: 1

General Comments

ANSWER: HTAR was homologue in all manuscript; Was eliminated all words in Spanish and we have not found abbreviations from the Spanish name. Regarding blocked citations, as were exposed, this is bibliometric analysis in order to know the evolution of method along time, remarking authors, countries, collaborations etc. that is why, in some specific cases several authors are cluster. Was corrected in 97 cites.

The response to the reviewer is chaotic: Our apologize, was very (very)difficult the correction of the 3 reviewers, practically was other manuscript. Was necessary to include publications in 2024 (21 articles) suggested by reviewer 2 and specific cites suggested by reviewer 3. So, we decided to include all the suggestions, the current publications but without doing the bibliometric analysis again. If we did, we would practically have to rewrite the entire article, it would be another article. Really apologize.

The explanation column is to help the reviewer how the correction was and/or in some cases to clarify the confusion. We have not sure if in the manuscript is adequate explain the cost of manuscript or open access articles

Deatile comments:

Position	Reviewer observation	Author corrections	comments
	I have noted still inconsistent with the abbrevations - in abstract THAR, line 89 HTAR? And this abbrevation is still in Spanish! Aqua residual is spanish words not english!!! Wastewater!	.The objective of this work was to evaluate the growth and development of science in the Hydrothermal Wastewater Treatment (HTAR) through… The scientific and technological development regarding the HTAR) is shown; and that, technology… Keywords: Hydrothermal liquefaction-carbonization-gasification, biomass, wastewater treatment, wastewater reuse.	ABSTRAC AND KEYWORDS
	In abstract, there are: 98 response records were filtered to 87 documents	carry out the integration of related published research, the terms used in the search both separately and crossly were “treatment, hydrothermal, wastewater” in the database from SCOPUS. 97 response records were filtered to 87 documents that were analyzed using BIBLIMETRIX
	Later: 97 documents were obtained as "article" and "final," as shown in Table 1.	This record set was filtered by document type ("DOCTYPE") and publication stage ("PUBSTAGE"). From this, 97 documents were obtained as "article" and "final," as shown in Table 1.
	MOZILA line 120, still incorrect; (but in the response to reviewer is ok);	…command was requested to be executed, which automatically linked to the BIBLIOMETRIX interface from the Mozilla Firefox web browser.
	Bibliometric or Bibliometrix? In the response to the Reviewer there are these two names. I can not find the explanation about the tool from response to the reviewer in the text. I as a reviewer not need it - it is needed in the text!	Bibliometrix it is a statistical tool that compile published research in journals around the world. The program has a series of tabs and subtabs that directly provide the results of the bibliometric analysis on the screen. In the background, the NNUAL SCIENTIFIC PRODUCTION subtab provides a graph on the screen that can be replaced by a table. Its information gets analyze some statistical parameters such as quantity and temporal evolution and trending. Is useful in the remark items in specific area of science, in this case HTAR.	Bibliometrix is the tool, and bibliometric is the analysis or method used to identify the evolution of researcher in the time Paragraphs is include in materials and methods , line 97 Our apologize for the mistake; it is being really difficult to maintain order and structure with too much adequations, with each one correction lines are moved
	"The support staff of the educational institution's library conducted a search and determined that documents of Chinese origin are impossible to obtain, while others have an unauthorized cost for their acquisition. Unfortunately, non-free access articles involve a cost." - where it is in the text?	After that, bibliography was actualized with 16 more cites not include in the first bibliometric analysis, some of they have been published in until 2024, which was included in the analysis of results. 88 cites is the score of articles reviewed in this paper. The support staff of the educational institution's library conducted a search and determined that documents of Chinese origin are impossible to obtain, while others have an unauthorized cost for their acquisition. Unfortunately, non-free access articles involve a cost. 2.1 Bibliometric analysis	We insist, we do not know if this information must be the text. Now was include in line 120

Comments on the Quality of English Language

The abbreviation from Spanish name AGUA RESIDUAL in English text is not acceptable! How many times I should repeat the same comments?

Our really apologize

Keywords: Hydrothermal liquefaction-carbonization-gasification, biomass, wastewater treatment, wastewater reuse.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

I have completed the re-review of the manuscript submitted by Abel Santillán-Ángeles's. The author has carefully addressed the comments and suggestions I provided in the initial review, making significant improvements to the manuscript. The previously raised issues have been adequately revised and supplemented.

After this second review, I believe the manuscript now meets the standards required for publication. The content is clear, logically sound, and aligns with the journal's academic requirements. Therefore, I recommend the manuscript for acceptance.

If the editorial board has any further suggestions or concerns, I remain available to assist as needed.

Thank you for the opportunity to review this manuscript.

Best regards,

Author Response

Reviewer: 2

General Comments to the Author

Comments and Suggestions for Authors

If the editorial board has any further suggestions or concerns, I remain available to assist as needed.

Thank you for the opportunity to review this manuscript.

Best regards,

Dear reviewer 2

Many thank you for your scientific support

Beste regards

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The authors successfully considered the reviewers comments. The manuscript is significantly improved and become suitable for publication. I recommend its acceptance.

Author Response

Reviewer: 3

General Comments to the Author

Comments and Suggestions for Authors

The authors successfully considered the reviewers comments. The manuscript is significantly improved and become suitable for publication. I recommend its acceptance.

Dear reviewer 3

Really thanks for your kind support

Author Response File: Author Response.pdf

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Bibliometric Analysis of Hydrothermal Wastewater Treatment in the Last Two Decades

Environmental Research, 212, Part D, 2022, 113532.

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Bibliometric Analysis of Hydrothermal Wastewater Treatment in the Last Two Decades

1- Current challenges of hydrothermal treated wastewater (HTWW) for environmental applications and their perspectives: A review.

Environmental Research, 212, Part D, 2022, 113532.

2- A perspective on hydrothermal processing of sewage sludge, Current Opinion in Environmental Science & Health 14, 2020, 63-73

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