How Activated Carbon Can Help You—Processes, Properties and Technological Applications

Round 1

Reviewer 1 Report

This article is a chapter of the book, which systematically introduces the definition, structure, and preparation process of activated carbon, as well as the main applied adsorption processes, characterization methods, and practical applications, and its content is very comprehensive. However, I have only one problem, the references are rather old and some new research progress needs to be summarized and concluded.

Author Response

Reply to Reviewer 1

Note that all page numbers within the below reply statements refer to the revised article with highlighted track changes switched on.

To “Quality of English Language English language fine. No issues detected”

Reply: No comment required.

To “Does the introduction provide sufficient background and include all relevant references? Yes”

Reply: No comment required.

To “Are all the cited references relevant to the research? Yes”

Reply: No comment required.

To “Is the research design appropriate? Yes”

Reply: No comment required.

To “Are the methods adequately described? Yes”

Reply: No comment required.

To “Are the results clearly presented? Yes”

Reply: No comment required.

To “Are the conclusions supported by the results? Yes”

Reply: No comment required.

To “This article is a chapter of the book, which systematically introduces the definition, structure, and preparation process of activated carbon, as well as the main applied adsorption processes, characterization methods, and practical applications, and its content is very comprehensive.”

Reply: The official article type is Tutorial. However, it is rather similar to a book chapter or handbook as explained in the abstract (page 1) and conclusion (pages 29 and 30).

To “However, I have only one problem, the references are rather old and some new research progress needs to be summarized and concluded.”

Reply: Seven new references have been added to the handbook-style tutorial (pages 29 and 30). The reference section includes now six review papers. However, this handbook has been written for professionals and a lot of background information has therefore been omitted as outlined in the abstract (page 1).

Reviewer 2 Report

The manuscript is well written.  The paper spends the most time on PFOA/PFAS, which is perhaps intentional considering the global concern surrounding these compounds.  If this is the case, more references on this topic would be appropriate.

Additional comments:

1.  Why discuss sub-micropores that are not accessible for 99.9% of compounds?

2. The literature continually discusses activated carbons as graphite-like, however, we know that biomass derived activated carbons are honeycomb shaped and possess more aliphatic versus aromatic carbon-carbon bonds.

3. The distance between the raw material and manufacturing site is critical, for shipping can be a significant cost since yields are typically very low.

4. At Line 90, including economics about raw material will be misleading since the cost of raw materials vary world-wide.  

5. At Line 191, biological reactivation can only occur if the compounds are desorbed (i.e., microbes cannot enter the pores).

6. In all methods, ASTM and other standards should be included.

7. 3.2.4 is a replicate of 3.2.3.

8. Table 3. Dichloromethan should be Dichloromethane.

9. Section 6.5 should include PAC, which is used at the head of water treatment plants.

10. There are countless reviews on activated carbon.  Some of these should be cited.

11. The manuscript should include the importance of performance based testing.

Author Response

Reply to Reviewer 2

Note that all page numbers within the below reply statements refer to the revised article with highlighted track changes switched on.

To “Quality of English Language English language fine. No issues detected”

Reply: No comment required.

To “Does the introduction provide sufficient background and include all relevant references? Must be improved”

Reply: Note that there is no introduction as this is a tutorial and not an original research article. Therefore, the question is not relevant.

To “Are all the cited references relevant to the research? Can be improved”

Reply: Seven new references have been added to the handbook-style tutorial (pages 29 and 30). However, this handbook has been written for professionals and a lot of background information has therefore been omitted as outlined in the abstract (page 1).

To “Is the research design appropriate? Not applicable”

Reply: No comment required.

To “Are the methods adequately described? Not applicable”

Reply: No comment required.

To “Are the results clearly presented? Can be improved”

Reply: Note that this not an original research article. Therefore, the question is not relevant.

To “Are the conclusions supported by the results? Not applicable”

Reply: No comment required.

To “The manuscript is well written”

Reply: No comment required.

To “The paper spends the most time on PFOA/PFAS, which is perhaps intentional considering the global concern surrounding these compounds.  If this is the case, more references on this topic would be appropriate. Additional comments:”

Reply: Only about 2.5 out of 30 pages are concerned with PFAS and related compounds. The recent and relevant reference Catoni et al. (2001) has been added.

To “1.  Why discuss sub-micropores that are not accessible for 99.9% of compounds?”

Reply: Submicropores are only shown in Table 1 for reasons of completeness. No detailed discussion takes deliberately place for the reason highlighted. However, an explanation of their relationship to micropores has been given to support the understanding of practitioners (page 3).

To “2. The literature continually discusses activated carbons as graphite-like, however, we know that biomass derived activated carbons are honeycomb shaped and possess more aliphatic versus aromatic carbon-carbon bonds.”

Reply: This important information has been added to subsection 1.2 (page 3).

To “3. The distance between the raw material and manufacturing site is critical, for shipping can be a significant cost since yields are typically very low.”

Reply: This specific point has been highlighted in the revised text (page 21).

To “4. At Line 90, including economics about raw material will be misleading since the cost of raw materials vary world-wide.”

Reply: The corresponding sentence has been rewritten (made more relative) and a new sentence has been added highlighting the variability of material costs world-wide (page 5).

To “5. At Line 191, biological reactivation can only occur if the compounds are desorbed (i.e., microbes cannot enter the pores).”

Reply: This point has been added to the discussion (page 7).

To “6. In all methods, ASTM and other standards should be included.”

Reply: Note that all standards relevant in practice have already been included where appropriate. More references and explanations have also been provided.

To “7. 3.2.4 is a replicate of 3.2.3.”

Reply: The duplicated section has been deleted.

To “8. Table 3. Dichloromethan should be Dichloromethane.”

Reply: The spelling mistake has been corrected (page 18).

To “9. Section 6.5 should include PAC, which is used at the head of water treatment plants.”

Reply: The section has been rewritten, and the use of powdered activated carbon has been discussed as well (page 24).

To “10. There are countless reviews on activated carbon. Some of these should be cited.”

Reply: The revised article refers to six review articles (pages 29 and 30)

To “11. The manuscript should include the importance of performance based testing.”

Reply: A new subsection has been included to briefly highlight this type of test (page 16).

Reviewer 3 Report

Undertaking the task of describing sorption processes in this form is a challenge. Usually, in textbooks for students, the subject is described on a dozen or so pages in a very brief manner or on a few dozen pages in a detailed manner, then limiting the considerations to, for example, adsorption from water. However, scientific studies on such a broad subject are books of several hundred pages. In this case, the author wanted to describe the adsorption process on activated carbons in broad terms, but quite generally. However, such a goal is very difficult to achieve. The number of issues covered is very large.  In some parts of the work, the issues are discussed very briefly, in others in too much detail. The author should read through the work again and consider which information should be shortened because it is described in too much detail. All the more so, however, as the paper omits many aspects that are quite important for adsorption on activated carbons (e.g. the chemical structure of the activated carbon surface).  It seems, however, that despite the reviewer's incomprehensible high degree of detail (or lack of detail) on certain issues, this work can be a valuable addition to the available literature.

Nevertheless, I believe that the author should respond to the following comments:

General comments

1. this item is mainly aimed at students (in my opinion as a supplement to the information in other textbooks). However, there is a lack of diagrams and drawings in many places, which would allow a better understanding of the described problem.

- e.g. illustrative drawing of the structure of activated carbon to chapter 1.2

- e.g. diagrams in chapter 2.5.1

The work and the possibility of introducing more diagrams should be analysed.

2. lack of reference to literature sources in many places where very specific information is given e.g.

- Table 1, Table 2, Table 3, Table 4,

- line 477-479

- No literature citation in the description of the pH of the aqueous extract (section 4.5)

- no literature citation in the description of methylene blue adsorption (chapter 5.2.1.)

The entire paper should be analysed for literature sources

(3) I believe that in the case of a very cursory treatment of certain topics, it would be good to refer the reader to literature sources that describe the topic in more detail, e.g.

- literature sources on activated carbon furnaces

- Chapter 3.2.1; 3.2.3; 3.2.5; 3.3.1; 3.3.2.; 3.5; 5.1.3. etc.

4. a table of contents would be beneficial.

Specific comments

1 Section 2.6 The information below applies to all types of cookers. There is no point in repeating this information for each cooker. Reword content.

"The residence time in the fluidized bed furnace depends on the number of trays and 325

the allocation. The reaction rate rests on the temperature and the concentration of the ac- 326

tivation media (water vapour and carbon dioxide)."

2 There is no information on the chemical structure of the activated carbon surface

3. in Chapter 1 "Activated Carbon" there is a subsection 1.2 Chemical Structure. There is no subsection e.g. Porous Structure. It is true that part of the message is contained in chapter 1.1. but the porous structure is in many cases decisive for the amount of sorption and more important than the chemical structure of the surface.

4. line 234 Chapter 2.4 should probably be titled Adsorption Kinetics

5. line 261 subsection is numbered 2.1.1 should be 2.5.1.

6. line 334 is section number 3.3 should be 3

7. subclause 3.2.4 is a repeat of 3.2.3.

8. subclause 4.5 has the title "pH". Consideration should be given to whether the title should not read, for example, "pH of aqueous extract"?

9. line 101 and 159 is subsection 2.7 should be subsection 2.6

10. line 254 is probably a mistake

11 The author devotes a lot of space to the mechanical properties of activated carbons. As these are of minor importance for the adsorption rate it would be beneficial to explain why these properties are important. (e.g. grain destruction during filter operation, large carbon losses during regeneration....)

12 Line 459-460 Remove definition of desiccator. The paper is aimed at people well versed in various chemical issues, the definition of desiccator is unnecessary here.

13) I do not understand how the information in line 546-547 connects to the topic of the paper (adsorption on activated carbons).

"The iodine number is often used as a fat index to characterize fats and oils."

14 The following sentence should be placed in the chapter on porous structure, not in section 5.1.2.

"Most adsorbents have a wide pore radius distribution with various maxima. The

macro- and mesopores mainly serve the transport processes, while the adsorption mainly

takes place in the micropores."

15. section 6.4. unnecessarily expanded with irrelevant information.

- Delete as irrelevant information lines 776-779.

- Move information from lines 780-795 to Chapter 6.1. as it is repetitive.

17. in the chapter "Design of Adsorbers" there should be an introduction with a general description of batch and flow adsorption.

18. chapter 1.5 - it might be more beneficial to call this chapter "Regeneration".

Author Response

Reply to Reviewer 3

Note that all page numbers within the below reply statements refer to the revised article with highlighted track changes switched on.

To “Quality of English Language English language fine. I am not qualified to assess the quality of English in this paper”

Reply: No comment required.

To “Does the introduction provide sufficient background and include all relevant references? Can be improved”

Reply: Note that there is no introduction as this is a tutorial and not an original research article. Therefore, the question is not relevant.

To “Are all the cited references relevant to the research? Must be improved”

Reply: Seven new references have been added to the handbook-style tutorial (pages 29 and 30). However, this handbook has been written for professionals and a lot of background information has therefore been omitted as outlined in the abstract (page 1).

To “Is the research design appropriate? Can be improved”

Reply: As this is a tutorial (similar to a handbook), no original research has been performed. Therefore, this question is not applicable.

To “Are the methods adequately described? Must be improved”

Reply: This is a tutorial-style handbook. No original research requiring a methodology section has been performed. Therefore, this question is not applicable. However, all tests and methods described have been referenced, where appropriate.

To “Are the results clearly presented? Must be improved”

Reply: The article type is a tutorial (similar to a handbook). No original research has been performed. Therefore, this question is not applicable.

To “Are the conclusions supported by the results? Must be improved”

Reply: Note that this is a tutorial-style handbook and not an original article based on results obtained, for example, from experiments.

To “Undertaking the task of describing sorption processes in this form is a challenge. Usually, in textbooks for students, the subject is described on a dozen or so pages in a very brief manner or on a few dozen pages in a detailed manner, then limiting the considerations to, for example, adsorption from water. However, scientific studies on such a broad subject are books of several hundred pages. In this case, the author wanted to describe the adsorption process on activated carbons in broad terms, but quite generally. However, such a goal is very difficult to achieve. The number of issues covered is very large.  In some parts of the work, the issues are discussed very briefly, in others in too much detail. The author should read through the work again and consider which information should be shortened because it is described in too much detail.”

Reply: The article type proposed by the Editorial Office is a Tutorial, which suggests that the target readership are students. The original submission stated Handbook, which would be more fitting, but it not recognised by the publisher. The target group are professionals and practitioners. Therefore, the content focuses on practical topics relevant for the industry.

To “All the more so, however, as the paper omits many aspects that are quite important for adsorption on activated carbons (e.g. the chemical structure of the activated carbon surface).  It seems, however, that despite the reviewer's incomprehensible high degree of detail (or lack of detail) on certain issues, this work can be a valuable addition to the available literature. Nevertheless, I believe that the author should respond to the following comments: General comments”

Reply: This article is a handbook-style tutorial that has been written for professionals and a lot of background information not of relevance for practitioners has therefore been omitted as outlined in the abstract (page 1). See below for responses to general comments.

To “1. this item is mainly aimed at students (in my opinion as a supplement to the information in other textbooks). However, there is a lack of diagrams and drawings in many places, which would allow a better understanding of the described problem.”

Reply: This is a misunderstanding. The article type proposed by the Editorial Office is a tutorial, which suggests that the target readership are students. The original submission stated Handbook, which would be more fitting, but it not recognised by the publisher. The main target groups are professionals and practitioners in industry benefitting also from the selected open access publication method as they have no direct access to libraries. Therefore, the content focuses on practical topics as now better explained in the abstract (page 1) and conclusion section (page 29).

To “- e.g. illustrative drawing of the structure of activated carbon to chapter 1.2”

Reply: The proposed illustration has been provided (page 4).

To “- e.g. diagrams in chapter 2.5.1”

Reply: There are many valuable diagrams that could be used. However, including them would deter the target group (professionals and practitioners in industry) to read this handbook-style tutorial as they get the impression that this article is too academic and not useful for them. This is the experience the author has made when working in the activated carbon industry on a daily basis. However, four new references have been provided to those who wish to know more (page 8 and 9).

To “The work and the possibility of introducing more diagrams should be analysed.”

Reply: Two easy-to-understand figures have been added to the article to support practitioners (pages 4 and 23).

To “2. lack of reference to literature sources in many places where very specific information is given e.g.”

Reply: Seven new references and more explanations have been provided throughout the revised handbook-style tutorial.

To “- Table 1, Table 2, Table 3, Table 4,”

Reply: References and, where appropriate, also more explanations have been provided (pages 3, 4, 17, 18 and 24).

To “- line 477-479”

Reply: Two references and more explanations have been provided (page 13).

To “- No literature citation in the description of the pH of the aqueous extract (section 4.5)”

Reply: A reference and further explanations have been added (page 14).

To “- no literature citation in the description of methylene blue adsorption (chapter 5.2.1.)”

Reply: A reference together with further explanations have been supplemented (page 16).

To “The entire paper should be analysed for literature sources”

Reply: The article has been supplemented with more literature sources where appropriate.

To “(3) I believe that in the case of a very cursory treatment of certain topics, it would be good to refer the reader to literature sources that describe the topic in more detail, e.g.”

Reply: The entire article has been strengthened with more literature.

To “- literature sources on activated carbon furnaces”

Reply: Two references and more explanations have been provided (pages 9 and 10).

To “- Chapter 3.2.1; 3.2.3; 3.2.5; 3.3.1; 3.3.2.; 3.5; 5.1.3. etc.”

Reply: References and/or further explanations have been provided where appropriate.

To “4. a table of contents would be beneficial.”

Reply: A table of contents has been added to the revised article (pages 1 and 2).

To “Specific comments 1 Section 2.6 The information below applies to all types of cookers. There is no point in repeating this information for each cooker. Reword content. "The residence time in the fluidized bed furnace depends on the number of trays and 325

the allocation. The reaction rate rests on the temperature and the concentration of the ac- 326

tivation media (water vapour and carbon dioxide)."”

Reply: The sub-section has been rewritten, accordingly (page 9).

To “2 There is no information on the chemical structure of the activated carbon surface”

Reply: The updated subsection 1.3 is concerned with the chemical structure (page 3). Moreover, subsections 1.4.2, 1.5, 2.1, 5.1.1, 5.2.1 and 5.2.2 also discuss this topic.

To “3. in Chapter 1 "Activated Carbon" there is a subsection 1.2 Chemical Structure. There is no subsection e.g. Porous Structure. It is true that part of the message is contained in chapter 1.1. but the porous structure is in many cases decisive for the amount of sorption and more important than the chemical structure of the surface.”

Reply: Two paragraphs concerned with pore structure have been added to subsection 1.1 (page 4)

To “4. line 234 Chapter 2.4 should probably be titled Adsorption Kinetics”

Reply: The chapter title has been revised as proposed (page 8).

To “5. line 261 subsection is numbered 2.1.1 should be 2.5.1.”

Reply: The numbering has been corrected (page 8).

To “6. line 334 is section number 3.3 should be 3”

Reply: The section numbering has been updated (page 10).

To “7. subclause 3.2.4 is a repeat of 3.2.3.”

Reply: One subsection has been deleted.

To “8. subclause 4.5 has the title "pH". Consideration should be given to whether the title should not read, for example, "pH of aqueous extract"?”

Reply: The proposed renaming has been performed (page 13).

To “9. line 101 and 159 is subsection 2.7 should be subsection 2.6”

Reply: Renumbering was performed (page 9).

To “10. line 254 is probably a mistake”

Reply: The spelling mistake has been corrected (page 6)

To “11 The author devotes a lot of space to the mechanical properties of activated carbons. As these are of minor importance for the adsorption rate it would be beneficial to explain why these properties are important. (e.g. grain destruction during filter operation, large carbon losses during regeneration....)”

Reply: Not even 2.5 out 30 pages are concerned with the characterization of mechanical properties of activated carbon (Section 3). As the article has been written for practitioners, it has now been highlighted that the mechanical properties are important for producers, suppliers and customers of different activated carbon products (page 10).

To “12 Line 459-460 Remove definition of desiccator. The paper is aimed at people well versed in various chemical issues, the definition of desiccator is unnecessary here.”

Reply: The definition has been removed, but the previous sentence has been revised to support practitioners with the understanding of the process (page 13)

To “13) I do not understand how the information in line 546-547 connects to the topic of the paper (adsorption on activated carbons). "The iodine number is often used as a fat index to characterize fats and oils."”

Reply: The sentence has been deleted.

To “14 The following sentence should be placed in the chapter on porous structure, not in section 5.1.2. "Most adsorbents have a wide pore radius distribution with various maxima. The macro- and mesopores mainly serve the transport processes, while the adsorption mainly takes place in the micropores."”

Reply: The paragraph has been moved to subsection 1.1 (page 3).

To “15. section 6.4. unnecessarily expanded with irrelevant information.”

Reply: The information regarding the customer details is not directly relevant for the actual design and has therefore been deleted.

To “- Delete as irrelevant information lines 776-779.”

Reply: The proposed lines have been deleted.

To “- Move information from lines 780-795 to Chapter 6.1. as it is repetitive.”

Reply: The indicated information has been merged with that in subchapter 6.1 (pages 16 and 17).

To “17. in the chapter "Design of Adsorbers" there should be an introduction with a general description of batch and flow adsorption.”

Reply: An introduction paragraph has been added following the proposal made (page 22).

To “18. chapter 1.5 - it might be more beneficial to call this chapter "Regeneration".”

Reply: The subsection title has been revised accordingly (page 6).

Reviewer 4 Report

The article “How Activated Carbon Can Help You? – Processes, Properties 2 and Technology Applications” is a general overview about activated carbon properties, preparation methods and adsorption and regeneration conditions, written in a Handbook style article, and from my point of view, very useful for researchers which can start working in this field.

The description of the content of the article (numbered sections) should not be provided in the abstract. The abstract has to resume most important points, findings and conclusions of the paper. Could be good to include an index in this article after the abstract and keywords. The abstract needs to include goals and some numerical important data/values, for example, surface area, pore size, regeneration temperature, etc.

First reference is cited in page 5. Please, include 4-6 references in the first 5 pages of the article. There is a broad knowledge which is not referred to other authors work.

Line 51: Last sentence is not clear. Please, explain better.

Lines 427-435: Could be good to include units in Ergun equation, with the order of magnitude related to activated carbon.

Line 449: subindex in density.

Section 6.4 (Design of adsorbers) is complex to read because it has been written in points and the essentials are not well understood. I suggest to rewrite this part (lines 748-835) with more explanation sentences and subsections in the main points. It would be much more valuable to include in this section a graphical scheme.

Author Response

Reply to Reviewer 4

Note that all page numbers within the below reply statements refer to the revised article with highlighted track changes switched on.

To “Quality of English Language English language fine. No issues detected”

Reply: No comment required.

To “Does the introduction provide sufficient background and include all relevant references? Not applicable”

Reply: No comment required.

To “Are all the cited references relevant to the research? Yes”

Reply: No comment required.

To “Is the research design appropriate? Yes”

Reply: No comment required.

To “Are the methods adequately described? Yes”

Reply: No comment required.

To “Are the results clearly presented? Not applicable”

Reply: No comment required.

To “Are the conclusions supported by the results? Not applicable”

Reply: No comment required.

To “The article “How Activated Carbon Can Help You? – Processes, Properties 2 and Technology Applications” is a general overview about activated carbon properties, preparation methods and adsorption and regeneration conditions, written in a Handbook style article, and from my point of view, very useful for researchers which can start working in this field.”

Reply: Moreover, the handbook-style tutorial targets practitioners working in industry.

To “The description of the content of the article (numbered sections) should not be provided in the abstract.”

Reply: The numbered sections have been removed as proposed (page 1).

To “The abstract has to resume most important points, findings and conclusions of the paper.”

Reply: Note that this is a handbook-style tutorial type of article that does not describe original research.

To “Could be good to include an index in this article after the abstract and keywords.”

Reply: Instead of an index, a table of contents has been included as proposed by another reviewer. This table has a similar function to an index (pages 1 and 2). Keywords have already been included after the abstract (page 1).

To “The abstract needs to include goals and some numerical important data/values, for example, surface area, pore size, regeneration temperature, etc.”

Reply: The purpose and aim of the article have been clearly stated (page 1). As this is a handbook-style paper and not an original article, no data findings can be presented. Value ranges for the proposed parameters are wide for literally hundreds of different activated carbon types.

To “First reference is cited in page 5. Please, include 4-6 references in the first 5 pages of the article. There is a broad knowledge which is not referred to other authors work.”

Reply: The initial pages of the revised article contain now more than the requested number of references (pages 3 to 8).

To “Line 51: Last sentence is not clear. Please, explain better.”

Reply: The sentence has been rewritten (page 3).

To “Lines 427-435: Could be good to include units in Ergun equation, with the order of magnitude related to activated carbon.”

Reply: Units have been included in the modified Ergun equation (page 12).

To “Line 449: subindex in density.”

Reply: The formatting mistake has been corrected (page 12).

To “Section 6.4 (Design of adsorbers) is complex to read because it has been written in points and the essentials are not well understood. I suggest to rewrite this part (lines 748-835) with more explanation sentences and subsections in the main points. It would be much more valuable to include in this section a graphical scheme.”

Reply: It has been clarified in the subsection title that a design checklist has been provided (page 21). An introduction paragraph as proposed by another reviewer has been added (page 22). The list on customer information has been deleted to make this subsection less complex. Subsection 6.4 has been split into two further subsections to improve its readability (pages 22 to 24). A complex graphical scheme would certainly look good but would be less comprehensive than a checklist and therefore less relevant to practitioners. Moreover, it is not allowed to show content both as text and as a figure. Nevertheless, a new figure has been added also to improve the readability and visually stimulate the reader.

Round 2

Reviewer 2 Report

no comments

Reviewer 3 Report