Modeling and Optimization of Biochar Based Adsorbent Derived from Kenaf Using Response Surface Methodology on Adsorption of Cd²⁺

Round 1

Reviewer 1 Report

Summary of the Work:

• Preparation of Biochar-based adsorbent and its applicability for cadmium removal has been studied.
• DOE has been applied to reduce the number of experiments.
• RSM approach has been applied to determine the optimal reaction parameters for biochar preparation and subsequent cadmium removal from water.

Abstract: 

The abstract should be more concise and well structured. Need English language corrections.

Introduction:

1. Line #44: “The technological progress..” this sentence needs to be restructured.
2. Line #49: “Heavy metal might be..” the English of this sentence needs to be corrected.
3. Line # 51: It is saying “as long as they are not present under optimum threshold”, this is not correct. It should be present under optimum threshold. Please check.
4. Line #57: How it is being leached?
5. Line #59: “Due to cadmium’s persistent..” Provide references.
6. Line #66: “The environmental impact of cadmium..” this sentence does not mean any sense and needs to be restructured.
7. Line #77-81: This paragraph is extremely vague and needs clarity. Also needs line reconstruction.
8. Line #77: “Many adsorbents have been proven..” What kind of adsorbents are being pointed here?
9. Line #78: “However, extensive developments have..” what is need of an agricultural waste based adsorbents? Needs clarification.
10. Line #79: what is the relevance of renewable energy generation from agricultural waste in this paper?
11. Line #80: “Agricultural waste can be converted..” how these waste are used for water purification? How the value is being increased? Needs calirification
12. Line #85: “Recently, numerous attempts..” Provide references.
13. Line #91: “Biochar usually has an excess..” Please mention clearly what does this sentence mean.
14. Line #96: “A response surface methodology..” line needs reconstruction.
15. Line #107: “To date, there has been no..” What does this sentence mean?

General comment: The structure of the introduction should be more concise and clearer. The sentences need clarity and should be structured properly. The novelty of the work is not mentioned evidently. Using RSM for biochar preparation is not exactly a novelty for the work. The significance of biochar-based adsorbents should be mentioned.

Materials and Methods:  

1. Materials should be stated first before going to the method part.
2. Line #116: “The kenaf fiber was..” this sentence should be under material section.
3. Line #118: What kind of oven is used here?
4. Line #118: “The dried sample was crushed..” How the sample was crushed? Please specify.
5. Table 1: In Line #121 it is mentioned that the reaction condition is stated in table 1. However, Table 1 shows the DOE parameters, and their actual and coded values. Please provide a separate table for reaction parameters.
6. Table 1: Why these particular values for the parameters were chosen? Needs justification.
7. Line #125: “The pyrolysis was performed..” This sentence should be under “Biochar preparation”.
8. Line #127: “For the development of the biochar..” How RSM and CCD can be used for the development of the biochar. DOE and RSM are just statistical tools to minimize the number of experiments and determine the optimal condition for the process. Please explain properly.
9. Line #132: “The parameters were pyrolysis..” Why these parameters were chosen? Needs justification.
10. Line #140: How these limits were chosen, needs to be mentioned clearly.
11. Table 2: Why table 2 is placed here? It should be in the result section.
12. Line #147: “To eliminate the unpredictable impacts..” what is meant by unpredictable impacts?
13. The “Batch Study” should have been mentioned before “Design of experiments”.

General Comment: The structure of “materials and methods” section is not very precise. Needs correction on that. Few points need further clarification as mentioned above. Further explanation needed on the selection of the values of experimental parameters for DOE.

Results and Discussion:  

1. Line #177: “The heating temperature is..” Incomplete sentence.
2. Section 3.1: The details of this experiment is not mentioned anywhere, either in the materials and methods section or in the results section. What was the rection conditions for this study? What is the relevance of this study? Needs further clarification and explanation.
3. Figure 2: it is better not to paste a picture of results like this.
4. Section 3.2: Again, the experimental conditions and relevance is missing here.
5. Section 3.3: Similarly, needs further details on experimental conditions. The explanation of experimental result is unclear.
6. Section 3.4: Again, the experimental conditions and relevance is missing here.
7. Section 3.5: Similarly, needs further details on experimental conditions. The explanation of experimental result is unclear.
8. Section 3.6: Same as no. 4 & 6.
9. Line #299: What is the significance of these regression coefficients? Needs further explanation.
10. More clear and concise explanation on ANOVA and their values are required.
11. Line #479: Where is table 7?

General Comment: The result and discussion section should be more concise and to the point. Few sections lack the required experimental details which is absolutely necessary. Needs to state the relevance of few experiments as stated above. The section could have been structured in a more accurate way.

Comments for author File: Comments.docx

Author Response

 

Response to Reviewer 1

Authors would like to thank the reviewer for the valuable comments and suggestions that contribute to improve our manuscript. Amendments were provided accordingly, and all modifications were highlighted as red tracked change in the revised version of the manuscript. Response to the comments is given below.

Reviewer 1

Summary of the Work:

• Preparation of Biochar-based adsorbent and its applicability for cadmium removal has been studied.
• DOE has been applied to reduce the number of experiments.
• RSM approach has been applied to determine the optimal reaction parameters for biochar preparation and subsequent cadmium removal from water.

Response to Reviewer: Thank you for the positive feedback from reviewer. Below we address point-by-point of each comment raised by reviewer.   

 

Abstract:

The abstract should be more concise and well structured. Need English language corrections.

Response: Thank you for the suggestion. The abstract has been revised to enhance its conciseness and to improve its structure.

 

Introduction:

No	Comments	Response to reviewer comments
1	Line #44: “The technological progress.” this sentence needs to be restructured.	The sentence has been restructured. Please see pages (Line 44 -47) in the revised manuscript.
2	Line #49: “Heavy metal might be.” the English of this sentence needs to be corrected.	Complied, as requested. The sentence has been restructured. Please see line 49 in of the revised manuscript.
3	Line # 51: It is saying “as long as they are not present under optimum threshold”, this is not correct. It should be present under the optimum threshold. Please check.	It has been amended accordingly. Please see line 51 in the revised manuscript.
4	Line #57: How it is being leached?	The authors tried to explain in this sentence that the leaching behaviour of cadmium varies from the other metals due to cadmium's derivatives are highly used in the industries. That is the source of excessive leaching to the environment. Leaching might be naturally in the form of evaporation or alkali leaching and acid leaching.
5	Line #59: “Due to cadmium’s persistent.” Provide references	References is provided now. Please see the revised manuscript (line 60).
6	Line #66: “The environmental impact of cadmium.” this sentence does not mean any sense and needs to be restructured.	The sentence has been restructured. Please see (line 66-68) in the revised manuscript.
7	Line #77-81: This paragraph is extremely vague and needs clarity. Also needs line reconstruction.	The paragraph has been rewritten. Please see (line 77-81) in the revised manuscript.
8	Line #77: “Many adsorbents have been proven.” What kind of adsorbents is being pointed here?	The information requested has been added accordingly. Please see (lines 77-81).
9	Line #78: “However, extensive developments have.” what is the need for an agricultural waste-based adsorbent? Needs clarification.	The sentence has been modified. Please see (lines 77-81).
10	Line #79: what is the relevance of renewable energy generation from agricultural waste in this paper?	This section has been rewritten. The relevance of renewable energy generation from agricultural waste in this paper is that biomass is converted to biochar (Biochar As a Renewable Energy Source) through pyrolysis, which then can be modified chemically or physically and used as an adsorbent for wastewater pollutants.
11	Line #80: “Agricultural waste can be converted.” how these wastes are used for water purification? How the value is being increased? Needs clarification.	As explained in comment 10, agricultural waste (Kenaf) is converted to biochar by pyrolysis and using different input parameters such as temperature, heating time, heating rate, and impregnation ratio of raw materials to alkali or acid, those input parameters have a significant impact on the responses parameters is fully described in the manuscript. The value-added in this study is producing biochar-based adsorbent derived from agricultural waste which considered as abundance waste in Malaysia, which means that kenaf waste is often dumped on landfills, which causes storage and operation problems. Additionally, poor management of kenaf waste causes serious environmental problems, as it is typically burned in the open air. The use of the bulk of biomass residue as biochar can minimize the wastage of valuable products by obeying the 3R concept (Reduce, reuse, and recycle).
12	Line #85: “Recently, numerous attempts.” Provide references.	A reference has been provided. Please see line 86 in the revised manuscript.
13	Line #91: “Biochar usually has an excess.” Please mention clearly what does this sentence mean.	The sentence has been modified. Please see line 91 in the revised manuscript.
14	Line #96: “A response surface methodology.” line needs reconstruction.	The sentence has been reconstructed. Please see line 96 in the revised manuscript.
15	Line #107: “To date, there has been no..” What does this sentence mean?	It means that RSM-CCD Modelling for producing biochar-based adsorbent for cadmium removal is still a new model. Furthermore, the used raw materials (Kenaf waste) for producing biochar are still not used before. It has been used before but for others.

 

General comment: The structure of the introduction should be more concise and clearer. The sentences need clarity and should be structured properly. The novelty of the work is not mentioned evidently. Using RSM for biochar preparation is not exactly a novelty for the work. The significance of biochar-based adsorbents should be mentioned.

Response to the general comment: Thank you for the input. The structure of the introduction is well reconstructed according to the comments provided by the reviewers. The novelty of the work is described in the introduction as well, which is producing biochar-based adsorbent using new promising raw materials using economic technology (producing Biochar based adsorbent with a high yield of biochar then using a specific surface modification adequate to adsorb the targeting pollutant). Surface modification will be investigated in great detail in future work. This study as mention in the introduction is to investigate the effect of input parameters of biochar-based adsorbent production on the response parameters using RSM which is considered a well-recognized mathematical and statistical tool that can be used to evaluate the effects of different factors on a response of interest.

 

Materials and Methods:

 

NO	Comment	Responses
1.	Materials should be stated first before going to the method part.	Materials sources and pre-treatment process has been added accordingly in the biochar preparation section. Please see (line119-125) in the revised manuscript.
2.	Line #116: “The kenaf fiber was.” this sentence should be under the material section.	A new subsection "Collection, Purification, and Preparation of materials" has been added to the materials and method section as recommended. Please see (lines 115-124) in the revised manuscript.
3.	Line #118: What kind of oven is used here?	The detail has been provided. Please see line 118 in the revised manuscript.
4.	Line #118: “The dried sample was crushed.” How was the sample crushed? Please specify.	The raw materials were ground by using a mechanical shredder machine (Granulator WSGP-230) and sieved using a Vibratory sieve shaker to the desired mesh size of 1–2 mm. The sentences has been reconstructed. Please see line 119 in the revised manuscript.
5.	Table 1: In-Line #121 it is mentioned that the reaction condition is stated in table 1. However, Table 1 shows the DOE parameters, and their actual and coded values. Please provide a separate table for reaction parameters.	Complied as suggested, the sentence is changed in the text to another description.
6.	Table 1: Why these values for the parameters were chosen? Needs justification	The justification of selecting the input parameters value range has been added to the revised manuscript (please see lines 132-148). Some justifications were taken from the previously published study by the same author entitled “Physicochemical characterization of different agricultural residues in Malaysia for biochar production.”
7.	Line #125: “The pyrolysis was performed.” This sentence should be under “Biochar preparation”.	Complied as requested
8.	Line #127: “For the development of the biochar...” How RSM and CCD can be used for the development of the biochar. DOE and RSM are just statistical tools to minimize the number of experiments and determine the optimal condition for the process. Please explain properly.	The sentences have been changed as suggested. Please see lines 127-131 in the revised manuscript. .
9.	Line #132: “The parameters were pyrolysis.” Why were these parameters chosen? Needs justification.	Complied as recommended. The justification has been added in the revised manuscript (please see line 132-148).
10.	Line #140: How these limits were chosen, needs to be mentioned clearly.	The authors did not choose factor values limit, they were suggested by the design expert. Those limit values came because the author selects the rotatable central composite design (CCD). CCD is the most widely used experimental design for modelling a second-order response surface. A design is called rotatable when the variance of the predicted response at any point depends only on the distance of the point from the centre point of the design. The rotatable design provides the uniformity of prediction error and it is achieved by proper choice of α. In rotatable designs, all points at the same radial distance (r) from the centre point have the same magnitude of prediction error.
11.	Table 2: Why table 2 is placed here? It should be in the result section.	Table 2 has been replaced to the result section as recommended.
12.	Line #147: “To eliminate the unpredictable impacts.” what is meant by unpredictable impacts?	Clarification has been made in the revised manuscript. Please see lines 293-294.
13.	The “Batch Study” should have been mentioned before “Design of experiments”.	The subsection “Batch study” has been merged with biochar preparation and renamed as biochar-based adsorbent preparation.

 

General Comment: The structure of the “materials and methods” section is not very precise. Needs correction on that. Few points need further clarification as mentioned above. Further explanation is needed on the selection of the values of experimental parameters for DOE.

 

Response to the general comment: Thank you for the feedbacks. The structure of the “materials and methods” section has been reconstructed as recommend, please see (lines 115-185). For the suggested comments and corrections, amendment and justification improvement have been added accordingly.

 

Results and Discussion

General Comment: The result and discussion section should be more concise and to the point. Few sections lack the required experimental details which are necessary. Needs to state the relevance of few experiments as stated above. The section could have been structured more accurately.

Response: Thank you for the detail. Overall text on the Results and Discussion Section has been revised to improve clarity and conciseness.

 

NO	Comments	Responses
1	Line #177: “The heating temperature is.” Incomplete sentence.	Complied as recommended. Please see the line 189 in the revised manuscript.
2	Section 3.1: The details of this experiment are not mentioned anywhere, either in the materials and methods section or in the results section. What were the reaction conditions for this study? What is the relevance of this study? Needs further clarification and explanation.	The experiment process is explained well in the subsection "Biochar based adsorbent preparation (Design of experiments)” which stated that the kenaf powdered was tightly placed in a ceramic pot, then pyrolyzed in an Alumina Tube Furnace under N2 atmosphere. The pyrolysis was programmed to raise the internal biomass chamber under different pyrolysis temperatures and different times as summarized in Table 1, at a rate of 10°C/min. The significance of this study is to study how pyrolysis temperature (as dependent parameter) impact the biochar yield and cadmium removal, where in this section the temperature was changed while the other parameters such as time and impregnation ratio were kept constant. The same scenarios were done to other sections (3.2,3.3,3.4 etc) to change one parameter while keeping the other parameters constant. Then the impact of process parameters as Combined came at section 3.8.
3	Figure 2: it is better not to paste a picture of results like this.	Figure 2 has been redrawn. Please see figure 2 in the revised manuscript.
4	Section 3.2: Again, the experimental conditions and relevance are missing here.	Experimental conditions have been added and the relevance of this study is answered in the comment reply above.
5	Section 3.3: Similarly, needs further details on experimental conditions. The explanation of the experimental result is unclear.	The reply to this comment is the same as the reply on comment reply #2.
6	Section 3.4: Again, the experimental conditions and relevance are missing here.	The reply to this comment is the same as the reply on comment reply #2.
7	Section 3.5: Similarly, needs further details on experimental conditions. The explanation of the experimental result is unclear.	The reply to this comment is the same as the reply on comment reply #2.
8	Section 3.6: Same as no. 4 & 6.	The reply to this comment is the same as the reply on comment reply #2.
9	Line #299: What is the significance of these regression coefficients? Needs further explanation.	Complied as recommended. As explained in the text (lines 323-340) in the revised manuscript, the sign of a regression coefficient tells whether there is a positive or negative correlation between each independent variable the dependent variable. A positive coefficient indicates that as the value of the independent variable increases, the mean of the dependent variable also tends to increase.
10	More clear and concise explanations on ANOVA and their values are required.	The detail information on ANOVA results have been provided in Tables 4-7 under column of “Comment”
11	Line #479: Where is table 7?	Table 7 has been added. It was there, but the title of the table was missing and has been incorporated in the revised manuscript..

 

Author Response File: Author Response.docx

Reviewer 2 Report

Уважаемые авторы, ваша рукопись написана очень хорошо. В этом есть интересная наука.

На мой взгляд, ваша рукопись требует исправления / дополнения.

1. Строка 159-168, вы пишете: «… фиксированными параметрами были доза адсорбента, pH раствора, скорость перемешивания…». Пожалуйста, напишите значение этих параметров.

2. Таблица 4, как вы рассчитываете SD, Среднее, R ² , CV, AP? Думаю, это должно быть в разделе " Материалы".
3. Строка 524: вы пишете, что адсорбционная способность Cd ²⁺ на сорбенте составляет 23,48 мг / г. У меня есть вопросы: «Как вы рассчитываете адсорбционную способность? Используете ли вы какие-либо модели для определения адсорбционной способности Cd ²⁺ на сорбенте? »

Author Response

aResponse to Editor and Reviewers

The authors would like to thank the Reviewers for the valuable comments and suggestions that contribute to improve our manuscript. Amendments were provided accordingly, and all modifications were marked as Track red in the revised version of the manuscript. Point-by-point response to each comment is given below.

Reviewer 2

 Dear Authors, your manuscript is very well written. This is an interesting topic. In my opinion, your manuscript needs correction / addition.

Response: Thank you for the positive feedback. The information and the correction you suggested are taken into consideration and highly appreciated. Below we address point-by-point of each comment raised by reviewer.

 

Following are the comments:

Comment1: Line 159-168, you write: "... the operating dose of the adsorbent, pH solution, stirring speed ..." are fixed. Please write the meaning of these parameters

Response: Complied, as requested. Please see (lines 176-180).     

Comment 2:  Table 4, how do you calculate SD, Average, R2, CV, AP? I think it should be in the Materials section.

Response:  Those are terms used when performing analysis of variance. The full description of the abbreviation has been provided in the footnote of each table when they appeared. They are common parameters in ANNOVA and does not need further explanation in the methodology.

 

Comment 3: Line 524: you write that the adsorption capacity of Cd ²⁺ on the sorbent is 23.48 mg / g. I have questions: “How do you calculate the adsorption capacity? Do you use any models to determine the adsorption capacity of Cd ²⁺ on the sorbent? "

Response:  Actually, the Adsorption capacity was calculated by calculating the amount of adsorbate taken up by the adsorbent per unit mass (or volume) of the adsorbent. Adsorption capacity (mg/gm) = [( Co - Ce) /m] x V, Co - Initial conc in ppm, Ce - Conc at equilibrium, m - mass of the adsorbent , V is the volume of solution containing solute ( adsorbate) .  The only terms which were changed are the final concentration. The kinetics, isotherm, and thermodynamic studies are going to be further investigated after product surface modification.  

 

Author Response File: Author Response.docx

Reviewer 3 Report

Comments to the paper "Modeling and Optimization of Biochar Based Adsorbent Derived from Kenaf Using Response Surface Methodology on Adsorption of Cd2+" by Saeed et al.

The paper presents an interesting experimental design approach to optimize the conditions possibly favoring adsorption of Cd2+ by a biomass derived activated carbon. The introduction clearly state the challenges and the potentials of the study, and the results possibly present important findings which worth publication. However, some lacks in the methods and a too long and not focused discussion of results make hard to observe the main trends to the reader.

A main issue for the characterization and analysis of adsorption performances is the very limited characterization of biochar material. For example, adsorption rate can vary in correlation of the functional groups and surface properties of biochar. Some surface analysis (e.g., IR, raman, see for example Binda et al. 2020 https://doi.org/10.1016/j.algal.2020.102103 and Zhou et al. 2017 https://doi.org/10.1016/j.cej.2016.12.113) can possibly better reconstruct possible chemical (other than physical) adsorption mechanisms. As well, while a strong optimization through experimental design was performed to optimize pyrolisis and activation conditions, batch adsorptions were not as carefully performed. Only a concentration of Cd was used and the time used to equilibrate solution, as well as the concentration of biochar in solution, were not reported. This hampers the possible investigation of adsorption mechanisms.

Moreover, other methods for analyses actually performed in the paper should be state in  the methods section. For examples, methods for proximate and ultimate analysis ( which results are described in Lines 194-196) and methods for reactive surface area (which results are reported in lines 242-247).

Finally I suggest to the authors to abundantly reduce the text in the results section. In fact, the trend qualitatively descripted in the first paragraphs are then marked again with the description of factors treated by experimental design. Moreover, I suggest to reduce the number of graphs and tables, which make the paper confusing and make hard to the reader to highlight the most important results. Authors could possibly add more detailed specifics in a supplementary file.

 

Author Response

Response to Reviewer 3

Authors would like to thank the reviewer for the valuable comments and suggestions that contribute to improve our manuscript. Amendments were provided accordingly, and all modifications were highlighted red tracked change in the revised version of the manuscript. Response to the comments is given below.

 

Comments and Suggestions for Authors

Comments to the paper "Modeling and Optimization of Biochar Based Adsorbent Derived from Kenaf Using Response Surface Methodology on Adsorption of Cd2+" by Saeed et al.

Comment 1: The paper presents an interesting experimental design approach to optimize the conditions possibly favoring adsorption of Cd2+ by a biomass-derived activated carbon. The introduction clearly states the challenges and the potentials of the study, and the results possibly present important findings which worth publication. However, some lacks in the methods and a too long and not focused discussion of results make it hard to observe the main trends to the reader.

Response 1: Thank you, the methods subsections have been merged which let the methods more focused and concise. The too-long description has been reconstructed. Please refer to the revised manuscript.

Comment 2: The main issue for the characterization and analysis of adsorption performances is the very limited characterization of biochar material. For example, the adsorption rate can vary in the correlation of the functional groups and surface properties of biochar. Some surface analysis (e.g., IR, raman, see for example Binda et al. 2020 https://doi.org/10.1016/j.algal.2020.102103 and Zhou et al. 2017 https://doi.org/10.1016/j.cej.2016.12.113) can better reconstruct possible chemical (other than physical) adsorption mechanisms. As well, while a strong optimization through experimental design was performed to optimize pyrolysis and activation conditions, batch adsorptions were not as carefully performed. Only a concentration of Cd was used, and the time used to equilibrate solution, as well as the concentration of biochar in solution, were not reported. This hampers the possible investigation of adsorption mechanisms. Moreover, other methods for analyses performed in the paper should be stated in the methods section. For example, methods for proximate and ultimate analysis (which results are described in Lines 194-196) and methods for reactive surface area (which results are reported in lines 242-247).

Response 2: Thank you for the valuable suggestions, As described in the introduction section the objective of this study is limited to the investigation and optimization of the biochar-based adsorbent using mathematical-statistical tools of RSM-CCD). The authors provided proximate and ultimate analysis presented as Van Krevelen diagram comparing the O/C and H/C to ensure biochar stability. The parameters related to adsorption studies such as solution pH and initial concentration, rotation time, and rotation speed were fixed, the description and justification already added in the revised manuscript (lines 176-180).

Comment 3: Finally, I suggest to the authors to abundantly reduce the text in the results section. The trend qualitatively described in the first paragraphs is then marked again with the description of factors treated by experimental design. Moreover, I suggest reducing the number of graphs and tables, which makes the paper confusing and makes it hard for the reader to highlight the most important results. Authors could add more detailed specifics in a supplementary file.

Response: thank you for the suggestions. We have substantially reduced the text in the results Sections. Some less important tables have been omitted.

 

 

 

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Few English language corrections needed

Author Response

Response to Reviewer 1

The authors would like to thank the reviewer for the valuable comments and suggestions that contribute to improving our manuscript.  

Reviewer 1

Comments and Suggestions for Authors: Few English language corrections needed.

Response to Reviewer: Thank you, the manuscript has been proofread by native speakers accordingly. please see the whole final revised manuscript.

Author Response File: Author Response.docx

Reviewer 3 Report

I carefully read the revised version of the manuscript and the response letter, and I think the paper was improved and the authors carefully checked my comments. The paper is improved regarding the structure and the contents, I suggest just few minor revisions before considering it for publication regarding English style and structure of sentences.

-line 23: when present (it is an adjective in this case)

-line 84: "they are required" instead of "the are required"

-lines 209-210: "avoid the repetition of therefore

-line 458: "Long heating time enhanced the biochar performances of cadmium removal" instead of "Long heating time enhanced the cadmium removal" 

-line 574: "based on the better order polynomials" this sentence is not clear, I suggest  to rephrase it.

-line 715-716: The first sentence is a bit redundant. I suggest to rephrase it as " While temperature negatively affects biochar yields, higher temperatures produced biochar with increased adsorption performances".

-line 729: avoid the repetition of "shows" and "showing"

Author Response

Response to Editor and Reviewers

The authors would like to thank the Reviewers for the valuable comments and suggestions that contribute to improve our manuscript. Amendments were provided accordingly, and all modifications were marked as Track red in the revised version of the manuscript. Point-by-point response to each comment is given below.

Reviewer 3

 Comments and Suggestions for Authors: I carefully read the revised version of the manuscript and the response letter, and I think the paper was improved and the authors carefully checked my comments. The paper is improved regarding the structure and the contents, I suggest just a few minor revisions before considering it for publication regarding English style and structure of sentences.

Response: Thank you for the positive feedback. The information and the correction you suggested are taken into consideration and highly appreciated. Below we address point-by-point of each comment raised by reviewer.

Following are the comments:

Comment1:  Line 23: when present (it is an adjective in this case)

Response: Complied, as requested. Please see line 23 in the revised manuscript.     

Comment 2: line 84: "they are required" instead of "the are required”.

Response:   Complied, as requested.

Comment 3:  Lines 209-210: "avoid the repetition of therefore”.

Response:  Complied, as requested, the sentences have been paraphrased.

Comment 4: Line 458: "Long heating time enhanced the biochar performances of cadmium removal" instead of "Long heating time enhanced the cadmium removal”.

Response:  Complied, as requested,

Comment 5: Line 574: "based on the better order polynomials" this sentence is not clear, I suggest rephrasing it.

Response:  Complied, as requested, please see the revised manuscript

Comment 6: Line 715-716: The first sentence is a bit redundant. I suggest rephrasing it as " While temperature negatively affects biochar yields, higher temperatures produced biochar with increased adsorption performances".

Response:  Complied, as requested, the sentences have been reconstructed accordingly.

Comment 6: Line 729: avoid the repetition of "shows" and "showing”.

Response:   Complied, as requested.

 Notes: please see the final revised manuscript which has been reconstructed and proofread.

Author Response File: Author Response.docx