Phosphate Removal from Polluted Water via Lanthanum-Modified Sludge Biochar

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The study converts sludge into biochar with the potential to remove phosphorus from polluted waters. The manuscript is in line with the journal's sustainability philosophy. I recommend this manuscript for publication in this journal after addressing the following minor corrections:

(1)  The composition of the sludge is not visible in the manuscript. Has the composition of the sludge been measured?

(2)  Did the study run parallel teats? especially pH and dosages.

(3)  You present the mass ratio and temperature in the biochar material preparation experiment. Why they are set in this way.

(4)  The scale on SEM images is not clear. You are advised to label it again.

(5)  Move Tab. S2 into the article.

(6)  This paper considers that the adsorbent is mainly chemisorption. At the same time, the results showed that the adsorbent retained good adsorption effect after adsorption and regeneration. Is that a bit of a contradiction?

(7)  In the conclusions, what do you mean here “…the low ambient temperature and alkaline environment inhibited the adsorption capability of LaSBC”, advised to delete it or re-express it.

Comments on the Quality of English Language

N/A

Author Response

• The composition of the sludge is not visible in the manuscript. Has the composition of the sludge been measured?

Response 1: Thanks for reviewer’s comment. The sludge in the experiment was collected from a sewage treatment plant in Guilin, China. The basic physical and chemical properties of municipal sludge are as follows: water content of municipal sludge is 80%, pH value is 6.5, electrical conductivity is 0.55 mS/cm, organic matter content is 56.8%, carbon nitrogen ratio (C/N) is 5.3.

• Did the study run parallel teats? especially pH and dosages.

Response 2: Thanks for reviewer’s comment. All the experiments were conducted in parallel, including pH and dosages. We averaged three parallel experiments, and there was little difference. For more clarity, additional explanations have been provided in the batch adsorption section of the manuscript. This change can be found – page 4, line 156.

• You present the mass ratio and temperature in the biochar material preparation experiment. Why they are set in this way.

Response 3: Thanks for reviewer’s comment. The mass ratio and temperature of this study refer to the literature [A. Chen, L. Lv, R. Hu, X. Wei, J. Guan, X. Meng, Achieving win-win outcomes with cerium-loaded porous aluminum sludge hydrogel microspheres for enhanced phosphate removal, Science of The Total Environment. 867 (2023) 161530. https://doi.org/10.1016/j.scitotenv.2023.161530.], and our pre-experimental results, and finally determine the range of mass ratio. Therefore, the tedious pre-experiment steps are not reflected in the article, but the final selected materials ratio range is written into the article.

• The scale on SEM images is not clear. You are advised to label it again.

Response 4: Thanks for reviewer’s comment. We agree with the reviewer’s comment and have made corresponding supplements. The scale has been marked out in the SEM image, as shown in Figure 1 in the manuscript.

• Move Tab. S2 into the article.

Response 5: Thanks for reviewer’s comment. We agree with the reviewer’s comment and have moved Tab. S2 into the article, as shown in Table 2. in the manuscript.

 

• This paper considers that the adsorbent is mainly chemisorption. At the same time, the results showed that the adsorbent retained good adsorption effect after adsorption and regeneration. Is that a bit of a contradiction?

Response 6: Thanks for reviewer’s comment. The desorption ability of phosphate in NaCl solution is good. When the bond between the adsorbent and P is weak, neutral salts such as KCl and NaCl can desorb phosphate from some adsorbents. In NaCl solution, due to the strong affinity of Cl^- free radicals, they can occupy the limited active sites of biochar. Therefore, a part of the phosphate can be exchanged, while the rest of the phosphate is strongly bound and deep into the adsorbent, thus there is some desorption efficiency. After prolonged adsorption, phosphate may be located deep inside and firmly bound to the adsorbent, resulting in a decrease in available active adsorption sites [ Q. Yang, X. Wang, W. Luo, J. Sun, Q. Xu, F. Chen, J. Zhao, S. Wang, F. Yao, D. Wang, X. Li, G. Zeng, Effectiveness and mechanisms of phosphate adsorption on iron-modified biochars derived from waste activated sludge, Bioresource Technology. 247 (2018) 537–544. https://doi.org/10.1016/j.biortech.2017.09.136.]. Although the adsorption capacity of LaSBC decreases with the extension of recovery time, the phosphorus removal efficiency is still 72.3% after six consecutive recycles, which indicates that LaSBC has high reusability and is a promising phosphorus removal adsorbent.

• In the conclusions, what do you mean here “…the low ambient temperature and alkaline environment inhibited the adsorption capability of LaSBC”, advised to delete it or re-express it.

Response 7: Thanks for reviewer’s comment. We agree with the reviewer’s comment and have removed “…the low ambient temperature and alkaline environment inhibited the adsorption capability of LaSBC” from the manuscript. This change can be found – page 13, line 440.

Reviewer 2 Report

Comments and Suggestions for Authors

The present manuscript deals with Phosphate Removal in Polluted Waters with Lanthanum Modified Sludge Biochar. From reviewing your work, I found it interesting, and the manuscript was written in an organized manner that makes it easy for the reader to understand the topic, however, some points should be improved, and others clarified so that the work can be accepted in this famous and prestigious journal.

Few observations/suggestions for revision

1-      Although there have been several previous studies on the same topicو hat additional contributions does it relate to the topic area in comparison to previous published materials? And what novel perspectives does the presented work provide?

2-      The manuscript needs careful linguistic review from beginning to end.

3-      It is better to add the section of “Formula and calculation” from supplementary file in the manuscript.

4-      In figure 3, the X-Ray peaks should be indexed and axes units also.

5-      In line 328, “Van’t H off equation” should be written correctly.

6-      In line 363, “Fig. S3 illustrates the possible adsorption mechanisms”, the corrected figure is 9. Furthermore, it is better to move the XPS results after XRD data.

 

 

 

 

Comments on the Quality of English Language

The manuscript needs careful linguistic review from beginning to end.

Author Response

• Although there have been several previous studies on the same topic, that additional contributions does it relate to the topic area in comparison to previous published materials? And what novel perspectives does the presented work provide?

Response 1: Thanks for reviewer’s comment. In this study, phosphorus in polluted waters was absorbed by lanthanum nitrate modified sludge biochar to realize the resource utilization of sewage sludge waste, which is in line with the journal’s sustainability philosophy. In addition, the adsorption capacity of LaSBC in this study is better than that of most metal modified sludge biochar (see Table 2). The maximum experimental adsorption capacity of 140.237 mg/g at 3.0 pH for phosphate. The results showed that the Lanthanum modification enhanced the ion exchange and complexation ability of the sludge biochar, and was convenient and environmentally friendly. Meanwhile, the adsorption and desorption experiments indicated that the modified biochar exhibited satisfying recycling performance and the adsorption capacity retained 72.3% after the sixth desorption. The dynamic adsorption study showed that the modified biochar has a long sustainable treatment time of 7.58 and 9.08 hours in adsorbent dosages of 1 and 2 g, which proves its feasibility as a cost-effective and efficient adsorbent for phosphate polluted water.

• The manuscript needs careful linguistic review from beginning to end.

Response 2: Thanks for reviewer’s comment. We agree with the reviewer’s comment and have carefully reviewed the manuscript from beginning to end. All the grammatical errors in the manuscript have been corrected.

• It is better to add the section of “Formula and calculation” from supplementary file in the manuscript.

Response 3: Thanks for reviewer’s comment. Since the formulas used in this study are commonly used in most biochar adsorption studies, it is not the focus of this study. The results of the calculation are reflected in the tables and figures of the manuscript. Because there are many formulas, to simplify the content of the article, we put them in the supplementary file. And references are added to each formula in the supplementary file.

• In figure 3, the X-Ray peaks should be indexed and axes units also.

Response 4: Thanks for reviewer’s comment. We agree with the reviewer’s comment and have made corresponding supplements. The peaks and axes have been indexed in the X-Ray image, as shown in Figure 3 in the manuscript.

• In line 328, “Van’t H off equation” should be written correctly.

Response 5: Thanks for reviewer’s comment. We agree with the reviewer’s comment and have revised it in the manuscript. This change can be found – page 11, line 349.

• In line 363, “Fig. S3 illustrates the possible adsorption mechanisms”, the corrected figure is 9. Furthermore, it is better to move the XPS results after XRD data.

Response 6: Thanks for reviewer’s comment. We agree with the reviewer’s comment and have revised it in the manuscript. This change can be found – page 12, line 383. The XPS results is also placed after XRD data.

Reviewer 3 Report

Comments and Suggestions for Authors

This work exhibit the potential of lanthanum modified sludge bio-char on P removal from contaminated water. Here are some comments for the authors to address:

1) The key issue of this paper: want to convince readers that La modification enhance P sorption, but no control SBC's sorption data to support it. It is a huge shortcoming in the experiment design. Please provide this control data collected under the same testing condition as your modified adsorbents. This is a must if the authors want to publish this work on our journal. At least the control data should be presented in Figure 4. Since you put the SBC's surface charge information on the right side, it is better to put qe data of SBC's on the left side figure, right? In order to show the advantage of La modification.

2) For SEM in Figure 1, it is better to provide EDX or elemental mapping within the SEM photos in order to convince readers that La is loaded successfully onto the bio-char or P is adsorbed on the surface of the bio-char. It is the easiest way to provide such direct evidence right? In the following Figure 2 and 3, there is no direct evidence to support that La was loaded successfully. Another option is put your figure 8 XPS characterization results into Figure 1, combine the two figure together.

3) For Figure 3,  to collect the carbon structure information and surface functional groups, Raman may be better (e.g., D, G bands), especially for carbon based adsorbents.

4) For Figure 9, For ligand exchange mechanism, to prove it, the pH monitoring data should be provided in your P adsorption kinetics test. But there is no such important data in the manuscript or supporting information. If you cannot provide it, just do not mention this adsorption mechanism.

5) for conclusion, line 415 Careless typo. Anion exchange

6) for introduction, line 125, abstract line 37, conclusion line 418, please delete the word "novel" as is mentioned in Line 111, others have used this strategy to modify their bio-char.

7) For the supporting information, please cite reference behind each of the 8 equations.

8) Line 63 ion exchange resin is well known for regeneration for recycling usage. Why the authors claim it doesn't?

Comments on the Quality of English Language

The writing is very bad with tons of grammar errors and confusing descriptions across the whole manuscript.  I would suggest the authors to do the grammar check in the Word and ask for professional language editing service. The examples shown below are just a tiny part selected:

1) Title, Grammar error, please use by or via or using instead of with

2) line 26 Grammar error : the maximum experimental adsorption capacity is 140.237 mg/g

3) Line 32 grammar error, it is satisfying not satisfactory

4) line 35 Please add phosphate in front of polluted water.

5) line 37 grammar error, comma is missing between novel and inexpensive

6) line 38 improper description. Better if use the following:

Lanthanum modification enhanced the ion exchange and complexion ability of the sludge bio-char

7) line 40 Please delete possessed

8) line 52 Grammar error: should be for "value for discharged effluent of the wastewater treatment plant is"

9) Line 60-61

10) Line 66

 

Author Response

• The key issue of this paper: want to convince readers that La modification enhance P sorption, but no control SBC's sorption data to support it. It is a huge shortcoming in the experiment design. Please provide this control data collected under the same testing condition as your modified adsorbents. This is a must if the authors want to publish this work on our journal. At least the control data should be presented in Figure 4. Since you put the SBC's surface charge information on the right side, it is better to put qe data of SBC's on the left side figure, right? In order to show the advantage of La modification.

Response 1: Thanks for reviewer’s comment. We agree with the reviewer’s comment and have added SBC in Fig 4. This change can be found – page 8, line 261. In this study, the SEM, FTIR, XRD, Zeta Potential and XPS data of SBC were determined under the same testing condition as LaSBC. The main purpose of this study is that compared with previous studies of metal modified sludge biochar, the adsorption performance of LaSBC is significantly improved (see Table 2), so we are sorry that we did not pay attention to this issue.

• For SEM in Figure 1, it is better to provide EDX or elemental mapping within the SEM photos in order to convince readers that La is loaded successfully onto the bio-char or P is adsorbed on the surface of the bio-char. It is the easiest way to provide such direct evidence right? In the following Figure 2 and 3, there is no direct evidence to support that La was loaded successfully. Another option is put your figure 8 XPS characterization results into Figure 1, combine the two figure together.

Response 2: Thanks for reviewer’s comment. We agree with the reviewer’s comment and have made corresponding supplements. The EDS image of LaSBC has been supplemented in Figure 1. to provide more direct evidence of La’s load, as shown in Figure 1. in the manuscript. This change can be found – page 5, line 194.

• For Figure 3, to collect the carbon structure information and surface functional groups, Raman may be better (e.g., D, G bands), especially for carbon based adsorbents.

Response 3: Thanks for reviewer’s comment. We agree with the reviewer’s comment. However, Raman was not performed in this study due to instrument limitations. We performed XRD spectra to collect the carbon structure information and surface functional groups. In the future research process, we will send samples to professional testing institutions for Raman spectrum analysis. Thanks again for the reviewer's suggestions.

• For Figure 9, For ligand exchange mechanism, to prove it, the pH monitoring data should be provided in your P adsorption kinetics test. But there is no such important data in the manuscript or supporting information. If you cannot provide it, just do not mention this adsorption mechanism.

Response 4: Thanks for reviewer’s comment. We agree with the reviewer’s comment. The ligand exchange mechanism was deleted from the possible adsorption mechanisms of phosphate in Figure 9. This change can be found – page 13, line 430.

• for conclusion, line 415 Careless typo. Anion exchange

Response 5: Thanks for reviewer’s comment. We agree with the reviewer’s comment and have made corresponding modifications in the manuscript. This change can be found – page 13, line 407.

• for introduction, line 125, abstract line 37, conclusion line 418, please delete the word "novel" as is mentioned in Line 111, others have used this strategy to modify their bio-char.

Response 6: Thanks for reviewer’s comment. We agree with the reviewer’s comment and have deleted the word "novel" in the manuscript. This change can be found – page 1, line 35; page 3, line 121; page 13, line 440.

• For the supporting information, please cite reference behind each of the 8 equations.

Response 7: Thanks for reviewer’s comment. We agree with the reviewer’s comment and have made corresponding supplements in supplementary file.

• Line 63 ion exchange resin is well known for regeneration for recycling usage. Why the authors claim it doesn't?

Response 8: Thanks for reviewer’s comment. We agree with the reviewer’s comment and delete the words “ion exchange resin” in the manuscript. This change can be found – page 2, line 62.

Comments on the Quality of English Language

The writing is very bad with tons of grammar errors and confusing descriptions across the whole manuscript.  I would suggest the authors to do the grammar check in the Word and ask for professional language editing service.

Response: Thanks for the reviewer's comments, we have checked and revised the language of the full text, and the typos have been corrected. Moreover, the revised manuscript has been sent to an English editing agency for editing, paying special attention to the correctness of words, syntax and grammar. We hope that the revised manuscript can meet the publication standards of the journal and sincerely hope the reviewers to approve our paper. Thanks again to the reviewers.

Reviewer 4 Report

Comments and Suggestions for Authors

The article titled “Phosphate Removal in Polluted Waters with Lanthanum Modified Sludge Biochar” represents the application of sludge biochar modified with lanthanum nitrate to enhance P removal from aqueous solution. The sludge material was characterized by SEM, XRD, FTIR, and XPS. The maximum saturation adsorption capacity of 140.237 mg/g at 3.0 pH for P was noticed.

1-  The Introduction section should be improved because it seems that it states only the results of previous studies about adsorption processes!

2-  What are the primary objectives and novelty of the study in terms of the synthesized biochar material

3-  The legends in “Figure 1. SEM images of SBC (a), LaSBC (b), and LaSBC-P (c).” should be clarified

4-  The FTIR peaks in Figure 2 should be defined based on strong and recent references

5-  The discussion of the temperature variation in “Table 1. Isotherm parameters for the phosphate adsorption of the LaSBC” is insufficient

6-  Compare your results with the phosphate removal mechanisms by nanoparticles (https://doi.org/10.1080/01496395.2018.1504799)

7-  Are there any alternative interpretations of the results that should be considered that could define the suggested removal mechanisms “Figure 9. Possible adsorption mechanisms of phosphate by LaSBC.”

8-  Insert the chemical reactions used to define the removal mechanisms

9-  Reformat the conclusions section to be arranged as follows: A summary of your key findings; A highlight of your hypothesis, new concepts, and innovations; A summary of key improvements compared to findings in the literature

Comments on the Quality of English Language

Moderate editing of English language required

Author Response

• The Introduction section should be improved because it seems that it states only the results of previous studies about adsorption processes!

Response 1: Thanks for reviewer’s comment. We agree with the reviewer’s comment and have revised in the Introduction section in the manuscript. This change can be found – page 3, line 103-108.

• What are the primary objectives and novelty of the study in terms of the synthesized biochar material

Response 2: Thanks for reviewer’s comment. In this study, phosphorus in polluted waters was absorbed by lanthanum nitrate modified sludge biochar to realize the resource utilization of sewage sludge waste, which is in line with the journal’s sustainability philosophy. In addition, the adsorption capacity of LaSBC in this study is better than that of most metal modified sludge biochar (see Table 2). The maximum experimental adsorption capacity of 140.237 mg/g at 3.0 pH for phosphate. The results showed that the Lanthanum modification enhanced the ion exchange and complexation ability of the sludge biochar, and was convenient and environmentally friendly. Meanwhile, the adsorption and desorption experiments indicated that the modified biochar exhibited satisfying recycling performance and the adsorption capacity retained 72.3% after the sixth desorption. The dynamic adsorption study showed that the modified biochar has a long sustainable treatment time of 7.58 and 9.08 hours in adsorbent dosages of 1 and 2 g, which proves its feasibility as a cost-effective and efficient adsorbent for phosphate polluted water.

• The legends in “Figure 1. SEM images of SBC (a), LaSBC (b), and LaSBC-P (c).” should be clarified

Response 3: Thanks for reviewer’s comment. We agree with the reviewer’s comment and have revised, as shown in Figure 1 in the manuscript. This change can be found – page 5, line 194.

• The FTIR peaks in Figure 2 should be defined based on strong and recent references

Response 4: Thanks for reviewer’s comment. We agree with the reviewer’s comment and have added strong and recent references in the manuscript. This change can be found – page 5, line 199, 201, 204, 206, 209, and 212.

• The discussion of the temperature variation in “Table 1. Isotherm parameters for the phosphate adsorption of the LaSBC” is insufficient

Response 5: Thanks for reviewer’s comment. We agree with the reviewer’s comment and have added the discussion in the manuscript. This change can be found – page 10, line 324-332.

• Compare your results with the phosphate removal mechanisms by nanoparticles (https://doi.org/10.1080/01496395.2018.1504799)

Response 6: Thanks for reviewer’s comment. We have added it to the manuscript. This change can be found – page 13, line 427.

• Are there any alternative interpretations of the results that should be considered that could define the suggested removal mechanisms “Figure 9. Possible adsorption mechanisms of phosphate by LaSBC.”

Response 7: Thanks for reviewer’s comment. We agree with the reviewer’s comment and have revised. We have inserted the chemical reactions used to define the adsorption mechanisms in the manuscript. This change can be found – page 12, line 391-395. And the ligand exchange mechanism was deleted from the possible adsorption mechanisms of phosphate in Figure 9. This change can be found – page 13, line 430.

• Insert the chemical reactions used to define the removal mechanisms

Response 8: Thanks for reviewer’s comment. We agree with the reviewer’s comment and have inserted the chemical reactions in the manuscript. This change can be found – page 12, line 391-395.

• Reformat the conclusions section to be arranged as follows: A summary of your key findings; A highlight of your hypothesis, new concepts, and innovations; A summary of key improvements compared to findings in the literature

Response 9: Thanks for reviewer’s comment. We agree with the reviewer’s comment and have revised in the manuscript. This change can be found – page 13, line 433-441.

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

The authors have addressed my comments properly. No other issues detected. 

Reviewer 4 Report

Comments and Suggestions for Authors

The authors' responses to my comments are satisfactory

 

Comments on the Quality of English Language

Minor editing of English language required