Fluoride Removal from Aqueous Medium Using Biochar Produced from Coffee Ground

Round 1

Reviewer 1 Report

Dear authors,

Your topic is not current, and I would also point out mistakes and give you some suggestions below.

Why did you take coffee grounds to obtain biochar and not some other precursor, when it turned out that biochar obtained from coffee grounds does not show any results for fluoride removal.

Also, why didn't you try your material to use it to remove, for example, some heavy metals or organic pollutants?

Row 51, Biochar is a solid product, enriched with carbon obtained in inert conditions at elevated temperatures, change reference 16

You said that biochar is porous, and your sample is not porous.

I don't understand the sentence: In comparison to conventional activated carbon, biochar offers environmental sustainability, lower production costs, and increased precursor material availability [17] ?

Line 78, explain, The coffee grounds used were obtained after the domestic preparation of the beer-age ?

What does ultrapure water mean? is it room temperature (± 26 °C)?

The carbonization process was conducted at a temper-86 ature of 500 °C for 2 h, with a heating rate of 10 °C.min-1, did the process last for 2 h or is the 2 h retention time?

Section 3.1 What happens in the temperature range from 0 to 200C?

You said: Furthermore, 180 degradation of hemicellulose, cellulose, and lignin occurs in the temperature ranges of 181 220-315 °C, 315-400 °C, and 100-900 °C, respectively [43,44]. Why didn't you determine the proportion of hemicellulose, cellulose and lignin in the coffee grounds?

Table 1 shows the share of sulfur and oxygen

Why didn't you do XRD of coffee grounds as a precursor and then compare with BC

Figure 2 is blurry, especially under b)

Figure 3. Mark under a and b

Give a table with distribution, pore volume as well as other parameters

Figure 4. State where the AU comes from?

EDS also shows Ca, MG... it should be seen or marked on the XRD diagram

Figure 5, mark the essential functional groups on the diagram

Table 3, did you do the adsorption model according to Temkin?

Section 3.6 table 1. The table tells you that your sample has a very low adsorption capacity

Author Response

Review 1

Your topic is not current, and I would also point out mistakes and give you some suggestions below.

1) Why did you take coffee grounds to obtain biochar and not some other precursor, when it turned out that biochar obtained from coffee grounds does not show any results for fluoride removal.

R: Coffee grounds were selected as a precursor material due to their abundant production and lack of potential for reuse or economic value in their natural form, resulting in their disposal in the environment.

The overarching project in which this study is included focuses on the utilization of coffee grounds as a precursor material for fluoride removal in water. In this context, different methods of biochar production can be proposed. However, the initial objective was to produce non-activated biochar in order to avoid the use of chemical reagents, which also generate waste and production costs. I believe that the low adsorption capacity exhibited by the produced biochar does not invalidate the research but rather indicates the need to employ activation methods to attempt to increase the removal efficiency.

2) Also, why didn't you try your material to use it to remove, for example, some heavy metals or organic pollutants?

R: The removal of metals or organic pollutants was not assessed because the main research project in which this study was included focuses on the use of coffee grounds as a precursor material for fluoride removal.

3) Row 51, Biochar is a solid product, enriched with carbon obtained in inert conditions at elevated temperatures, change reference 16

R: Modified to: Biochar is a porous, carbon-rich material that is produced through the carbonization of cellulosic or non-cellulosic biomass in an anaerobic environment or under limited oxygen conditions (XIANG et al., 2020).

4) You said that biochar is porous, and your sample is not porous.

R: The text does not mention that the obtained material is non-porous. What was presented in the text is that according to the results of the N₂ adsorption and desorption isotherms tested at a temperature of -195.85 °C, the material exhibited a type III isotherm classification, indicating the presence of pores with different sizes. The obtained surface area and pore volume for the mesoporous adsorbent were 12.94 m².g^-1 and 0.0349 cm³.g^-1, respectively.

5) I don't understand the sentence: In comparison to conventional activated carbon, biochar offers environmental sustainability, lower production costs, and increased precursor material availability [17] ?

R: Modified to:  In comparison to conventional activated carbon, commonly generated from nonrenewable coal and requiring energy-intensive thermal activation to develop adsorption properties [THOMPSON et al, 2016], biochar offers environmental sustainability, lower production costs, and increased precursor material availability [1722].

6) Line 78, explain, The coffee grounds used were obtained after the domestic preparation of the beer-age ?

R: Modified to:  The coffee grounds used were obtained from the domestic preparation of the beverage without the addition of other substances such as sugar or sweetener to the water or coffee powder.

7) What does ultrapure water mean? is it room temperature (± 26 °C)?

R: Modified to: To remove water-soluble substances and impurities, the coffee grounds were rinsed with ultra-pure water (GEHAKA, Master System) with a conductivity of 1.35 µS.cm^-1 at a temperature of 80 ± 5 °C and subsequently at room temperature (26 ± 2 °C) [3446].

8) The carbonization process was conducted at a temper-86 ature of 500 °C for 2 h, with a heating rate of 10 °C.min-1, did the process last for 2 h or is the 2 h retention time?

R: Modified to; The BC was produced by pyrolyzing the PM in a rotary bipartite tubular furnace (approximately 7.25 rpm), Sanchis®, under an inert atmosphere created by a nitrogen flow of 200 mL.min^-1. Pyrolysis was carried out for 2 h at a temperature of 500 °C with a heating rate of 10 °C.min^-1 [3446].

9) Section 3.1 What happens in the temperature range from 0 to 200C?

R: Modified to: The yield of BC production from the precursor material (PM) was 16.72%, which is attributed to the loss of mass caused by the release of water from the coffee grounds and light volatile molecules that occurs at temperatures below 200 °C, as well as the release of volatile hydrocarbons, hemicellulose, cellulose, and some part of lignin in the temperature range of 200 to 650 °C, as reported in the literature on thermogravimetric analysis of coffee grounds [3446,4254, SINGH; MAHANTA; BORA (2017)].

10) You said: Furthermore, 180 degradation of hemicellulose, cellulose, and lignin occurs in the temperature ranges of 181 220-315 °C, 315-400 °C, and 100-900 °C, respectively [43,44]. Why didn't you determine the proportion of hemicellulose, cellulose and lignin in the coffee grounds?

R: The determination of the proportion of these compounds was not the focus of this study as it would provide limited information for the discussion of the obtained adsorption results. Typically, what is observed in the literature is the elemental analysis of the precursor material and the produced biochar, as presented in the article (Table 1). Paragraph adjusted according to question 8.

11) Table 1 shows the share of sulfur and oxygen

R: There is not such an information

12) Why didn't you do XRD of coffee grounds as a precursor and then compare with BC

R: The purpose of the assay was to verify if the produced material exhibited the typical amorphous structure of charcoal, rather than comparing different materials.

13) Figure 2 is blurry, especially under b)

R: Adressed

14) Figure 3. Mark under a and b

Adressed

15) Give a table with distribution, pore volume as well as other parameters

R: Since the data is only for one material, the table would consist of two rows (headings and results), which aesthetically doesn't look good. Therefore, it was decided to describe the obtained characteristics in the text.

16) Figure 4. State where the AU comes from?

R: For scanning electron microscopy analysis, the sample is coated with a thin layer of gold, which is the reason why the element appears. However, this information is typically not presented and discussed in the results section, as it is a specificity of the analysis rather than a characteristic of the sample. However, it was mentioned in Section 2.4. that the samples were previously coated with gold before obtaining the images

17) EDS also shows Ca, MG... it should be seen or marked on the XRD diagram

R: The XRD technique characterizes the formation of crystalline planes. In the present study, it was not possible to identify crystal peaks of these elements, possibly due to their low quantity.

18) Figure 5, mark the essential functional groups on the diagram

R: Attended. However, the Figure becomes overloaded with information, especially when the peaks are close together. For this reason, it was decided to only mark the wavelength and present the groups in the text.

19) Table 3, did you do the adsorption model according to Temkin?

R: The Temkin model was not used as satisfactory fits were obtained with commonly employed models such as Langmuir and Freundlich

20) Section 3.6 table 1. The table tells you that your sample has a very low adsorption capacity

R: When compared to other studies reported in the literature, the adsorption capacity was found to be low. Therefore, it is suggested to employ activation or functionalization techniques to explore the possibility of increasing the adsorption capacity.

Author Response File: Author Response.pdf

Reviewer 2 Report

In manuscript, aiming the water pollution, authors applied coffee derived biochar for the fluoride removal from aqueous medium. Comprehensive characterizations have been performed. In general, the manuscript is well organized and the conclusion is supported by the experimental and results. However, there are still some issues to be addressed. A moderate revision is required before its acceptance.

1.     The keyword fluorine can be removed because of another keyword defluorination.

2.     The introduction section contains too many paragraphs. Authors are suggested to rearranged this section with better logic. The same issue with conclusion section. Please revise.

3.     The last paragraph in introduction should spent more contents on briefly introduce the novel strategy, methods and results.

4.     More background on the sources, structure, preparation, properties and applications should be further provided with some more recent supporting articles: CHEN Yangyang, ZHANG Qingtong, CHI Mingchao, GUO Chenyan, WANG Shuangfei, MIN Douyong. Preparation and performance of different carbonized wood electrodes.Journal of Forestry Engineering,2022,7(03):127-135.doi:10.13360/j.issn.2096-1359.202107025; Biochar derived from non-customized matamba fruit shell as an adsorbent for wastewater treatment; etc.

5.     One subsection on the raw materials can be added in materials and methods section.

6.     One scheme to show the experimental procedure is suggested for better understanding of this work to readers.

7.     How about the defluorination effect when comparing with commercial activated carbon?

8.     The scale bar in SEM images can be rebuilt to have a better readability.

9.     Some of the figures should be added with error bars for better scientific expression.

10.  It is better to make a table in the main manuscript to compare the defluorination effect with different materials. Please consider the following recent articles: Molecules 28 (8), 3492, 2023; Polymers 14 (24), 5417, 2022; New Journal of Chemistry 46, 490-497, 2022; Separation and Purification Technology 314, 123562, 2023; Composites Communications 33, 101194, 2022; RSC Advances 12 (47), 30522-30528, 2022; etc.

11.  There are still some typos and grammar issues in the manuscript. Authors should carefully recheck the whole manuscript.

Author Response

Review 2

Comments and Suggestions for Authors

In manuscript, aiming the water pollution, authors applied coffee derived biochar for the fluoride removal from aqueous medium. Comprehensive characterizations have been performed. In general, the manuscript is well organized and the conclusion is supported by the experimental and results. However, there are still some issues to be addressed. A moderate revision is required before its acceptance.

1. The keyword fluorine can be removed because of another keyword defluorination. R: Adressed

2. The introduction section contains too many paragraphs. Authors are suggested to rearranged this section with better logic. The same issue with conclusion section. Please revise. R: The text has been revised and reorganized to achieve a more suitable logical sequence.

3. The last paragraph in introduction should spent more contents on briefly introduce the novel strategy, methods and results. R: Adressed

4. More background on the sources, structure, preparation, properties and applications should be further provided with some more recent supporting articles: CHEN Yangyang, ZHANG Qingtong, CHI Mingchao, GUO Chenyan, WANG Shuangfei, MIN Douyong. Preparation and performance of different carbonized wood electrodes.Journal of Forestry Engineering,2022,7(03):127-135.doi:10.13360/j.issn.2096-1359.202107025; R: The text has been improved, and it was possible to use the reference: "Biochar derived from non-customized matamba fruit shell as an adsorbent for wastewater treatment," etc.

5. One subsection on the raw materials can be added in materials and methods section. R: Adressed

6. One scheme to show the experimental procedure is suggested for better understanding of this work to readers. R: The scheme was created and included as a graphical abstract. However, if the reviewers believe it is more appropriate to include it in the Materials and Methods section, it can be done.

7. How about the defluorination effect when comparing with commercial activated carbon? R: In the present study, adsorption tests with activated carbon for comparison were not conducted. However, data from scientific literature were used to make the comparison.

8. Comparison of Adsorptive Removal of Fluoride from Water by Different Adsorbents under Laboratory and Real Conditions. R: The comparison of fluoride removal with different adsorbents is made in the introduction as well as in Table 5 (Results and Discussion). The comparison of results with those obtained from samples under real conditions was not made because we believe it would not have practical value due to the difference in the nature of the solutions.

9. The scale bar in SEM images can be rebuilt to have a better readability. R: The image has been improved.

10. Some of the figures should be added with error bars for better scientific expression. R: Error bars have been added whenever possible.

11. It is better to make a table in the main manuscript to compare the defluorination effect with different materials. Please consider the following recent articles: Molecules 28 (8), 3492, 2023; Polymers 14 (24), 5417, 2022; New Journal of Chemistry 46, 490-497, 2022; Separation and Purification Technology 314, 123562, 2023; Composites Communications 33, 101194, 2022; RSC Advances 12 (47), 30522-30528, 2022; etc. R: The suggested articles feature adsorbents that are quite different from the ones used in this study. We believe that the comparison would not be appropriate.

12. There are still some typos and grammar issues in the manuscript. Authors should carefully recheck the whole manuscript. R: Another revision has been conducted.

Author Response File: Author Response.pdf

Reviewer 3 Report

Summary and general comments

In this study, the authors investigate the use of biochar derived from spent coffee as an adsorbent for the removal of fluoride from aqueous solution.

The overall work seems alright, and the results and discussion section support the conclusion. However, the Introduction and methodology sections can be improved. Numerous minor errors were also observed. Please, see the specific comments section for details.

Specific Comments

1.   Abstract: the minus charge for F should be superscripted

2.   Line 30. The maximum adsorption capacity should be ‘qm’, not qemax. See Equation 6. While in Table 3 qmax is used

3.   Recheck the total number of keywords.  I suggest the author to mention the spent coffee biochar

4.   In the Introduction, the authors only focus on agricultural wastes. There are also various BC that can be a source of highly available material such as bamboo and leaves. Here are some of my recommendations. doi.org/10.1155/2022/8245797
doi.org/10.1080/03067319.2021.1884238

5.   Section 2.1. What is the nature of biochar? What is the particle size?

6.   In Section 2.2 the experimental detail of fluoride analysis should be provided. This is to ensure that the experiment can be reproduced. The authors should describe the amount of sample and amount of TISAB added, waiting time, etc.

7.   Section 2.4. A brief experimental procedure of the point of zero charge should be provided. Gold is detected in Fig. 4. The authors should include that gold sputtering was carried out prior to obtaining the SEM images.

8.   Section 2.5 can be written more concisely. Please refer to the reference on how to write it more concisely.

9.   All the symbols in the main text from the isotherm or kinetic models should match those in the equations exactly. The symbols should be in superscript, subscripted, and italicised.

10.             Figure 6 caption spelling error “effecto of…”

11.             The expression of unit should be consistent. In the text authors used mg.g-1, however, in the figure mg/g was used.

12.             Error bars should be included in the figure wherever applicable

13.             Table numbering error at line 443

See comments to authors

Author Response

Review 3

Comments and Suggestions for Authors

Summary and general comments

In this study, the authors investigate the use of biochar derived from spent coffee as an adsorbent for the removal of fluoride from aqueous solution.

The overall work seems alright, and the results and discussion section support the conclusion. However, the Introduction and methodology sections can be improved. Numerous minor errors were also observed. Please, see the specific comments section for details.

 Specific Comments

1. Abstract: the minus charge for F should be superscripted. R: The entire text has been revised, and subscripts and superscripts have been corrected.

2. Line 30. The maximum adsorption capacity should be ‘qm’, not qemax. See Equation 6. While in Table 3 qmax is used. R: Revised as mentioned.

3. Recheck the total number of keywords.  I suggest the author to mention the spent coffee biochar. R: The suggestion has been implemented.

4. In the Introduction, the authors only focus on agricultural wastes. There are also various BC that can be a source of highly available material such as bamboo and leaves. Here are some of my recommendations. doi.org/10.1155/2022/8245797 doi.org/10.1080/03067319.2021.1884238. R: The introduction has been restructured for better understanding.

5. Section 2.1. What is the nature of biochar? What is the particle size? R: We do not understand what the reviewer meant by "the nature of biochar." The particle size has been mentioned in the text.

6. In Section 2.2 the experimental detail of fluoride analysis should be provided. This is to ensure that the experiment can be reproduced. The authors should describe the amount of sample and amount of TISAB added, waiting time, etc. R: The analysis was performed according to procedure 4.500-F-C presented in the Standard Methods for the Examination of Water & Wastewater. This information has been added to the text with the proper reference.

7. Section 2.4. A brief experimental procedure of the point of zero charge should be provided. Gold is detected in Fig. 4. The authors should include that gold sputtering was carried out prior to obtaining the SEM images. R: Addressed.

8. Section 2.5 can be written more concisely. Please refer to the reference on how to write it more concisely. R: Some changes have been made to the text, but we believe that making it more concise may result in the loss of information. The order of headings and subheadings has been adjusted based on the presentation of other articles suggested by the reviewer.

9. All the symbols in the main text from the isotherm or kinetic models should match those in the equations exactly. The symbols should be in superscript, subscripted, and italicised. R: Addressed.

10. Figure 6 caption spelling error “effecto of…” R: Addressed.

11. The expression of unit should be consistent. In the text authors used mg.g-1, however, in the figure mg/g was used. R: Addressed.

12. Error bars should be included in the figure wherever applicable. R: Error bars have been added.

13. Table numbering error at line 443. R: Addressed.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Dear,

the authors adequately responded to the questions, remarks and suggestions, therefore I give a positive opinion that the paper should be accepted in the journal.

Best Regards

Author Response

Response: Dear reviewer, we appreciate your comments and suggestions, which have greatly improved the work.

Reviewer 2 Report

Authors did not treat the reviewers comments seriously. There are only response, but without corresponding revisions. In addition, this reviewer suggested many previous published examples for comparison, but authors did not included them, which is difficult to find the novelty of this work. In addition, there are many typos and grammar issues in the manuscript, making it out of the scientific standards of this journal. 

 In addition, there are many typos and grammar issues in the manuscript, making it out of the scientific standards of this journal. 

Author Response

1. Authors did not treat the reviewers comments seriously. There are only response, but without corresponding revisions. In addition, this reviewer suggested many previous published examples for comparison, but authors did not included them, which is difficult to find the novelty of this work

R: The authors regret that the corrections made did not meet the reviewer's expectations. We acknowledge that all suggestions are valid and important for improving the work. However, in some cases, it was not possible to accommodate the suggestion, but we have provided a detailed explanation for not implementing them. Twelve new references have been included, incorporating the suggested ones.

A new revision has been conducted, and to the best of our abilities, the suggestions have been addressed, as outlined in the following considerations:

2. In addition, this reviewer suggested many previous published examples for comparison, but authors did not included them, which is difficult to find the novelty of this work

R: The novelty of this work has been explained throughout the text as follows:

1. Obtaining information on biochar produced from coffee grounds for fluoride removal, which, according to the literature, has limited available information. The following paragraph has been included: "Studies investigating the use of biochar produced from coffee grounds for anion removal are limited (SHADU et al., 2022)."
2. In the literature, most biochars (and adsorbents) used for fluoride removal have their surface structure modified using chemical reagents, which can increase production costs. Therefore, the following explanation has been provided in the text:

[...] In recent years, various adsorbent materials have been proposed to improve the removal efficiency of anionic compounds. These include metal-organic frameworks (MOFs) (SONG et al., 2023; HU et al., 2023), nanofibers composed of multivalent metals (JIAN et al., 2022a; JIAN et al., 2022b), and chemically modified biochars using acid compounds, basic compounds, polymers, and metals (ZHANG et al., 2021 [19]; OBEY; ADELAIDE; RAMARAJ, 2022). However, the utilization of these materials, as well as the chemical modification techniques of biochar, can significantly impact the production costs of the adsorbents (BIANCO et al., 2022), making it challenging to implement large-scale biochar usage in developing countries, as these costs represent a determining factor in the practical application of these materials (SHIN et al., 2023a). Therefore, further research is needed to explore alternative precursor materials and optimize the parameters for biochar production [...].

iii. Specifically, regarding biochar produced from coffee grounds for fluoride removal, an article was identified: OGATA, F. et al. "Removal of Fluoride Ions from Water by Adsorption onto Carbonaceous Materials Produced from Coffee Grounds." Journal of Oleo Science, v.60(12), p.619-625, 2011. However, in that study, the biochar produced was modified with 6M HCl.

Furthermore, the biochar produced in the present study took into consideration the biomass stabilization temperature determined through thermogravimetric analysis. Most articles in the literature use higher temperatures. The following explanation has been added to the text to address this:

[...]The efficiency of contaminant removal is primarily associated with the physico-chemical properties of biochar, which are influenced by factors such as the raw material used and the conditions of pyrolysis [22], including residence time, heat transfer rate, gas flow, and pyrolysis temperature. Pyrolysis temperature, in particular, has been extensively studied due to its influence on the surface area and porous structure of biochar. Researchers can optimize the pyrolysis conditions according to the desired results (LUO et al., 2022). Typically, biochar studies are conducted within the temperature range of 300 °C to 700 °C (KEERTHANAN et al., 2020), with increasing temperature generally leading to improved surface characteristics through the removal of alcoholic (-OH), aliphatic, and ester (-CO-) groups from the biomass during decomposition until stabilization (SHAKIA; VITHANAGE; AGARWAL, 2022).

However, it is important to note that increasing pyrolysis temperature does not al-ways result in improved surface characteristics of biochar. Some studies (JUNG et al., 2016) have observed a significant decrease in both porosity (0.112 cm³g⁻¹, 0.078 cm³g⁻¹, and 0.057 cm³g⁻¹) and surface area (70.290 m²g⁻¹, 61.809 m²g⁻¹, and 44.491 m²g⁻¹) of bio-char produced from marine macroalgae residues and almond/nut shells at temperatures of 400 °C, 600 °C, and 800 °C, respectively. Biochars prepared from almond and nut shells at temperatures of 400 °C, 500 °C, and 800 °C also had reduced surface areas, measuring 0.840 m²g⁻¹, 0.440 m²g⁻¹, and 0.370 m²g⁻¹ for almond biochar and 2.410 m²g⁻¹, 0.350 m²g⁻¹, and 0.130 m²g⁻¹ for the respective temperatures (ORTIZ et al., 2020). This phenomenon can be attributed to pore widening, coalescence of adjacent pores, and partial pore blockage caused by the softening, melting, fusing, and carbonization of the biochar structure at high temperatures (ANGIN, 2013). Conversely, performing pyrolysis at temperatures lower than the stabilization temperature of biochar can lead to incomplete carbonization of the biomass, resulting in reduced loss of volatiles and a lower surface area (SHAKYA; VITHANAGE; AGARWAL, 2022).

Therefore, the pyrolysis temperature plays a crucial role in determining the production costs and adsorption efficiency of biochar. Careful optimization of this parameter is necessary to strike a balance between cost-effectiveness and the desired adsorption performance. [...].

Therefore, in light of the need to obtain potential precursor materials for the production of cost-effective adsorbents targeting fluoride removal from water, as well as the limited technical information available on biochar production from coffee waste for fluoride removal, this study presents the results of the physicochemical characteristics and fluoride removal capacity of biochar derived from coffee grounds. The biochar was produced at the biomass stabilization temperature without any chemical or physical modification, aiming to enhance economic and environmental sustainability during the production process. The pyrolysis temperature was determined using thermogravimetric analysis, followed by adsorption tests that involved manipulating the physicochemical parameters of the system to establish ideal sorption conditions. Additionally, the adsorption mechanism was investigated through kinetic, thermodynamic, and surface characterization studies.

Comments on the Quality of English Language

In addition, there are many typos and grammar issues in the manuscript, making it out of the scientific standards of this journal. 

R: The text has been revised.

Author Response File: Author Response.pdf

Reviewer 3 Report

Following the comments from Reviewer 1, the novelty remains low as there are similar publications on coffee ground biochar on removing fluoride.

Ogata F, Tominaga H, Yabutani H, Kawasaki N. Removal of fluoride ions from water by adsorption onto carbonaceous materials produced from coffee grounds. Journal of Oleo Science. 2011;60(12):619-25.

Ayaz I, Rizwan M, Ullman JL, Haroon H, Qayyum A, Ahmed N, Elesawy BH, Askary AE, Gharib AF, Ismail KA. Lignocellulosic based biochar adsorbents for the removal of fluoride and Arsenic from aqueous solution: isotherm and Kinetic modeling. Polymers. 2022 Feb 12;14(4):715.

The authors should highlight how this study can be different.

Minor errors are still observed throughout the manuscript. Recheck and correct whenever possible.

Authors should use a grammar check. Some words are without spacing.

Author Response

1) 

Following the comments from Reviewer 1, the novelty remains low as there are similar publications on coffee ground biochar on removing fluoride.

Ogata F, Tominaga H, Yabutani H, Kawasaki N. Removal of fluoride ions from water by adsorption onto carbonaceous materials produced from coffee grounds. Journal of Oleo Science. 2011;60(12):619-25.

Ayaz I, Rizwan M, Ullman JL, Haroon H, Qayyum A, Ahmed N, Elesawy BH, Askary AE, Gharib AF, Ismail KA. Lignocellulosic based biochar adsorbents for the removal of fluoride and Arsenic from aqueous solution: isotherm and Kinetic modeling. Polymers. 2022 Feb 12;14(4):715.

The authors should highlight how this study can be different.

R: The novelty of this work has been explained throughout the text as follows:

1. Obtaining information on biochar produced from coffee grounds for fluoride removal, which, according to the literature, has limited available information. The following paragraph has been included: "Studies investigating the use of biochar produced from coffee grounds for anion removal are limited (SHADU et al., 2022)."
2. In the literature, most biochars (and adsorbents) used for fluoride removal have their surface structure modified using chemical reagents, which can increase production costs. Therefore, the following explanation has been provided in the text:

[...] In recent years, various adsorbent materials have been proposed to improve the removal efficiency of anionic compounds. These include metal-organic frameworks (MOFs) (SONG et al., 2023; HU et al., 2023), nanofibers composed of multivalent metals (JIAN et al., 2022a; JIAN et al., 2022b), and chemically modified biochars using acid compounds, basic compounds, polymers, and metals (ZHANG et al., 2021 [19]; OBEY; ADELAIDE; RAMARAJ, 2022). However, the utilization of these materials, as well as the chemical modification techniques of biochar, can significantly impact the production costs of the adsorbents (BIANCO et al., 2022), making it challenging to implement large-scale biochar usage in developing countries, as these costs represent a determining factor in the practical application of these materials (SHIN et al., 2023a). Therefore, further research is needed to explore alternative precursor materials and optimize the parameters for biochar production [...].

iii. Specifically, regarding biochar produced from coffee grounds for fluoride removal, an article was identified: OGATA, F. et al. "Removal of Fluoride Ions from Water by Adsorption onto Carbonaceous Materials Produced from Coffee Grounds." Journal of Oleo Science, v.60(12), p.619-625, 2011. However, in that study, the biochar produced was modified with 6M HCl.

Furthermore, the biochar produced in the present study took into consideration the biomass stabilization temperature determined through thermogravimetric analysis. Most articles in the literature use higher temperatures. The following explanation has been added to the text to address this:

[...]The efficiency of contaminant removal is primarily associated with the physico-chemical properties of biochar, which are influenced by factors such as the raw material used and the conditions of pyrolysis [22], including residence time, heat transfer rate, gas flow, and pyrolysis temperature. Pyrolysis temperature, in particular, has been extensively studied due to its influence on the surface area and porous structure of biochar. Researchers can optimize the pyrolysis conditions according to the desired results (LUO et al., 2022). Typically, biochar studies are conducted within the temperature range of 300 °C to 700 °C (KEERTHANAN et al., 2020), with increasing temperature generally leading to improved surface characteristics through the removal of alcoholic (-OH), aliphatic, and ester (-CO-) groups from the biomass during decomposition until stabilization (SHAKIA; VITHANAGE; AGARWAL, 2022).

However, it is important to note that increasing pyrolysis temperature does not al-ways result in improved surface characteristics of biochar. Some studies (JUNG et al., 2016) have observed a significant decrease in both porosity (0.112 cm³g⁻¹, 0.078 cm³g⁻¹, and 0.057 cm³g⁻¹) and surface area (70.290 m²g⁻¹, 61.809 m²g⁻¹, and 44.491 m²g⁻¹) of bio-char produced from marine macroalgae residues and almond/nut shells at temperatures of 400 °C, 600 °C, and 800 °C, respectively. Biochars prepared from almond and nut shells at temperatures of 400 °C, 500 °C, and 800 °C also had reduced surface areas, measuring 0.840 m²g⁻¹, 0.440 m²g⁻¹, and 0.370 m²g⁻¹ for almond biochar and 2.410 m²g⁻¹, 0.350 m²g⁻¹, and 0.130 m²g⁻¹ for the respective temperatures (ORTIZ et al., 2020). This phenomenon can be attributed to pore widening, coalescence of adjacent pores, and partial pore blockage caused by the softening, melting, fusing, and carbonization of the biochar structure at high temperatures (ANGIN, 2013). Conversely, performing pyrolysis at temperatures lower than the stabilization temperature of biochar can lead to incomplete carbonization of the biomass, resulting in reduced loss of volatiles and a lower surface area (SHAKYA; VITHANAGE; AGARWAL, 2022).

Therefore, the pyrolysis temperature plays a crucial role in determining the production costs and adsorption efficiency of biochar. Careful optimization of this parameter is necessary to strike a balance between cost-effectiveness and the desired adsorption performance. [...].

At the end of the introduction, before the objective, the following text was added: Therefore, in light of the need to obtain potential precursor materials for the production of cost-effective adsorbents targeting fluoride removal from water, as well as the limited technical information available on biochar production from coffee waste for fluoride removal, this study presents the results of the physicochemical characteristics and fluoride removal capacity of biochar derived from coffee grounds. The biochar was produced at the biomass stabilization temperature without any chemical or physical modification, aiming to enhance economic and environmental sustainability during the production process. The pyrolysis temperature was determined using thermogravimetric analysis, followed by adsorption tests that involved manipulating the physicochemical parameters of the system to establish ideal sorption conditions. Additionally, the adsorption mechanism was investigated through kinetic, thermodynamic, and surface characterization studies.

2) Comments on the Quality of English Language

Minor errors are still observed throughout the manuscript. Recheck and correct whenever possible.

R: The text has been revised.

Round 3

Reviewer 2 Report

 Accept in present form