Low Cost Activated Carbon for Removal of NOM and DBPs: Optimization and Comparison

Round 1

Reviewer 1 Report

The manuscript concerns an interesting issue which is the obtaining of metal-modified activated carbons from pulp and paper waste materials, and then using them for removal of natural organic matter (NOM) and disinfection byproducts (DBPs) from water samples. The Authors prepared active carbons modified with iron and aluminum salts from inexpensive carbon-rich materials, and then characterized the obtained sorbents using various methods. Subsequently, the Authors used sorbents to remove NOM from natural and synthetic water samples. The Authors also performed kinetic studies. Therefore, the submitted study can be suitable for publication in Water.

The objectives of the study are clearly defined. The introduction provides a good background of the topic. The methods are described in a proper way. However, there are points which need to be clarified or improved. The description of the results seems to be prepared in a hurry and there are many small errors and understatements. The Authors should read this section one more time and write it in a clearer manner. Some examples of the most obvious shortcomings are presented below:

• There is a sentence “However, N₂ adsorption tests are time-consuming and costly” in section 3.1.1.2 which is out of the context. Please correct this section.
• What does it mean: “…mixture of pure CO₂ (>99.99%) and steam at 80°C for two hours at optimum temperature of 850^oC…”? Please describe the preparation of gas mixture for carbon activation in a more clear and detailed way.
• Figure 3 – please increase the size of experimentally measured points. The fitted curve (only for four experimentally measured points!) is probably incorrect, because the Authors did not take into account that experimentally measured points have some uncertainties, so therefore an equally good fit can be e.g. linear relationship. The good practise is to put in the drawing equation of the fitted model and add an explanation of why such a model was used. If you have only used some spline curve from graphical software, it only misleads the reader. Such a curve means nothing and if the Authors have any additional information, the better way is to use linear interpolation.
• Figure 4 is unreadable. It is too small. Please improve the size of the figure.
• Figure 9 - please increase the size of experimentally measured points (currently they are almost invisible) and as in the case of Figure 3 please explain how kinetic lines were fitted. Moreover, in Fig. 9 in the cases of kinetic curves for 0.75%Fe-Ac and 1%Al-Ac there are plateaux at about 150 min. Sorption is stopped for some time and after about 200 min it speeds up again. Please explain this issue. Is this a real observation or just a consequence of the type of  fitted curve used in the drawing?
• In the section 3.1.2, there is no information which type of AC was used for impregnation with Fe and Al. Please add this information.
• In reviewer opinion, in the case of impregnation of AC with Fe there is no statistically significant difference in DOC removal efficiency for samples with different Fe loading. Such small observed differences are probably normal uncontrolled variability (originated e.g. from AC sample variability).
• Please add the results of measurements of the particle size distribution using Zetasizer Nano.
• Line 43, 315, 333, 340, 341, 357 and 404: The dot after “Fig” is missing.
• Line 162: In the formula of aluminum sulfate, there should be a multiplication dot, not a comma.
• Table 5: Please use the superscript in m² and cm³.
• There are two tables entitled “Table 6”.
• Second Table 6: Please use the superscript in m².
• Line 413 and 450: There are two section entitled “3.2.1. optimization of dose”.
• Line 558: The “Conclusions” section is number 5, while there is no section 4. Please correct the section numbers.
• There are two equations (2) and (3). Please correct equation numbers.

Overall, the manuscript shows some interesting results but must be improved before publication.

Author Response

Response to Reviewer 1 Comments

 

 

 

• Point 1: The objectives of the study are clearly defined. The introduction provides a good background of the topic. The methods are described in a proper way. However, there are points which need to be clarified or improved. The description of the results seems to be prepared in a hurry and there are many small errors and understatements. The Authors should read this section one more time and write it in a clearer manner.

 

Response 1: We appreciate your time and valuable comments. We completely understand your concerns. The changes are made in the manuscript as per your recommendations as follows:

Page 3, lines 74, 93-97, 104-109 and 115.

Page 4, line 175.

Page 5, Fig. 2b.

Page 6, lines 183-185, 196 and 201.

Page 8, lines 306 and 310.

Page 9, lines 359-355.

Page 10, lines 386, 390, 391, Fig.3,

Page 11 and 12, Fig. 4 and lines 432-434, 438, 443, 444 and 446.

Pahe 13, line 454 and Table 4 (minor edits of adding second decimal wherever was missing).

Page 14, lines 473 and 486, and Table 5 (Size (d.nm)).

Page 15, lines 503, 504, 507, 510, 512, 520-521.

Page 16, Fig 7 (c-d), lines 541-545, 555.

Page 17, lines 572-574, 586, 589-595.

Page 18, lines 637, 641, 643, and 646.

Page 19, Table 7 (minor edits of heading line), line 657, 662,664, 665, 669-671, and 677.

Page 20, Fig 9, lines 712, 717-719, 721, 728-733, 734.

Page 21, lines 789-792, 801, 803, 804, 807, 808, 823, and 824.

Page 22-26, reference list (formatting).

 

Point 2: There is a sentence “However, N2 adsorption tests are time-consuming and costly” in section 3.1.1.2 which is out of the context. Please correct this section.

 

Response 2: We appreciate your valuable comment. The sentence is removed from the manuscript as per your recommendation.

 

• Point 3: What does it mean: “…mixture of pure CO2 (>99.99%) and steam at 80°C for two hours at optimum temperature of 850oC…”? Please describe the preparation of gas mixture for carbon activation in a more clear and detailed way.

Response 3: Steam has changed to water vapor in section 3.1.1.2. More details are added to the materials and methods (page 9, lines 349-355). Fig 2(b) is added to the manuscript to clarify further.

 

• Point 4: Figure 3 – please increase the size of experimentally measured points. The fitted curve (only for four experimentally measured points!) is probably incorrect, because the Authors did not take into account that experimentally measured points have some uncertainties, so therefore an equally good fit can be e.g. linear relationship. The good practise is to put in the drawing equation of the fitted model and add an explanation of why such a model was used. If you have only used some spline curve from graphical software, it only misleads the reader. Such a curve means nothing and if the Authors have any additional information, the better way is to use linear interpolation.

Response 4: The type of plot has been changed to column type in the new revision (New Fig. 3). Also, the fitted tangent line to the curve and its interpretation is edited (page 10, line 390-391).

 

• Point 5: Figure 4 is unreadable. It is too small. Please improve the size of the figure

Response 5: The size of Fig 4 (a-c) has been increased in the new revision. Also, high resolution figures are uploaded with the new revision.

 

• Point 6: Figure 9 - please increase the size of experimentally measured points (currently they are almost invisible) and as in the case of Figure 3 please explain how kinetic lines were fitted. Moreover, in Fig. 9 in the cases of kinetic curves for 0.75%Fe-Ac and 1%Al-Ac there are plateaux at about 150 min. Sorption is stopped for some time and after about 200 min it speeds up again. Please explain this issue. Is this a real observation or just a consequence of the type of  fitted curve used in the drawing?

Response 6: We appreciate your suggestion for increasing the size of the measured points. The size of marks is increased to improve the visual quality of the figures. The observed data showed an increase in the removal of NOM (without any stop at Time=150min). The effect of smooth curve is removed from the new Fig. 9 to avoid any misunderstanding for the readers. Also, according to the recommendation by reviewer 3, the figure has been changed to time and qe.

• Point 7: In the section 3.1.2, there is no information which type of AC was used for impregnation with Fe and Al. Please add this information.

Response 7: Thank you for your comment. It was the fly ash based activated carbon as demonstrated in the methodology (section 2.1)

To clarify, we have also included the following sentence in lines 432-433, page 12:

“Adsorption tests …… metal impregnation on the fly ash based AC-A10 using ferric chloride and aluminum sulfate.”

AC in the text is an abbreviation to activated carbon. However, wherever the authors illustrated non modified activated carbon, AC has changed to “AC-A10” in the new revision (lines 434, 435, and 438).

 

• Point 8: In reviewer opinion, in the case of impregnation of AC with Fe there is no statistically significant difference in DOC removal efficiency for samples with different Fe loading. Such small observed differences are probably normal uncontrolled variability (originated e.g. from AC sample variability).

Response 8: Thank you for your concerns. Fe loading in Water sample 2 shows apparent difference in the efficiency for samples. Moreover, the samples were tested in triplicate and average values were used for plotting purposes. However, the discussion has been revised in section 3.1.2.1 in the new revision (page 12, lines 443-444).

• Point 9: Please add the results of measurements of the particle size distribution using Zetasizer Nano

Response 9: Thank you for your suggestion. The measured particle size results by Zetasizer are added in Table 5 (last column on the right).

 

• Point 10: Line 43, 315, 333, 340, 341, 357 and 404: The dot after “Fig” is missing

Response 10: Thank you for your comment. The manuscript was checked again for the new revision and dot after Fig. is added wherever it was missing.

 

• Point 11: Line 162: In the formula of aluminum sulfate, there should be a multiplication dot, not a comma.

Response 11: Thank you for your comment. It is changed to a dot in the new revision (page 6, line 201 of the new manuscript):

• Point 12: Table 5: Please use the superscript in m²and cm³.

Response 12: The subscript for m² and cm³ are corrected in the new revision in Table 5 (page 14).

 

• Point 13: There are two tables entitled “Table 6”.

Response 13: Table numbers are updated in the new revision (Tables 7 and 8 in the new revision)

 

• Point 14: Second Table 6: Please use the superscript in m².

Response 14: the subscript for m² is revised in the new revision (New Table 7).

• Point 15: Line 413 and 450: There are two section entitled “3.2.1. optimization of dose”.

Response 15: the numbering and titles are revised in the new revision.

 

• Point 16: Line 558: The “Conclusions” section is number 5, while there is no section 4. Please correct the section numbers.

Response 16: the numbering is revised in the new revision.

 

• Point 17: There are two equations (2) and (3). Please correct equation numbers.

Response 17: the numbering is revised in the new revision

 

 

 

Author Response File: Author Response.docx

Reviewer 2 Report

Authors have developed a metal coated activated carbon to remove the natural organic matter and disinfection byproducts from water. Research is sound interesting following points must be addressed before further processing

1. Reason for the development of Al coated AC is explained in the introduction. similarly explain the reason of using Fe coated AC
2. For the experiment, what is the reason for using different ratio for Al-AC and Fe-AC? (Al: AC of 1.00% and Fe: AC of 0.75%).
3. Why developed activated carbon is more effective for the natural water and synthetic water.
4. Further, discuss the results appropriately using suitable literatures.

 

Author Response

Response to Reviewer 2 Comments

Author Response File: Author Response.docx

Reviewer 3 Report

At present, this referee does not recommend that the manuscript can be published. The manuscript needs major revision.

1. The q_e is sufficient to evaluate the adsorption capacity, and it is only dependent on equilibrium concentration (C_e). But, removal rate (R) is dependent on dosage of adsorbent and volume of solution. It’s not necessary to use R to evaluate the adsorption capacity. Please delete all of these data.
2. Please provide the whole ANOVA for the model including F-values and P-values of items (Time, Dose, pH, Time×Dase, Time×pH, Dose×pH, Time², Dose² and pH²).
3. Please delete the 3-D surface plot of DOC removal rate (Figure 7a). Besides, please provide 3-D surface plots illustrating the effects of Dose and pH on the q_e, and the effect of pH and Time on the q_e.
4. The adsorption kinetics (Figure 9) should be presented as the effect of Time on q_e.

Author Response

Response to Reviewer 3 Comments

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The manuscript has been revised by the Authors but there are two points which need to be improved:

• Line 172: In the formula of aluminum sulfate, there should be a middle dot Al₂(SO₄)₃·18H₂O.
• There are two equations (8). Please correct equation numbers.

The other comments and corrections made by the Authors are satisfactory.

Author Response

Response to Reviewer 1 Comments

 

 

 

• Point 1: Line 172: In the formula of aluminum sulfate, there should be a middle dot Al₂(SO₄)₃18H₂O

Response 1: We appreciate your valuable comments. The formula has been corrected.

 

• Point 2: There are two equations (8). Please correct equation numbers.

Response 2: The equation numbers are modified.

Reviewer 3 Report

No more comments and suggestions for authors.

Author Response

Your input is highly appreciated.