Phosphorus Recovery and Simultaneous Heavy Metal Removal from ISSA in a Two-Compartment Cell

Round 1

Reviewer 1 Report

 

I have reviewed the manuscript entitled “Phosphorus recovery and simultaneous heavy metal removal 2 from ISSA through electrodialysis” and I don’t recommend its publication mainly because the manuscript lack to highlight its novelty vs the already published literate, and there is a lack of comparison of this approach vs other approaches in terms of specific energy consumption. The author should mention up to what levels of purity for the P rich stream this process can be considered successful; also, what is the expected downstream process for the recovered P stream, what can be done with a 2000 ppm of P solution?

Other comments:

·       Check English, some minor errors can be found in the manuscript.

·       Graph quality is low.

·       Typically, a electrodialysis a unit cell is a combination of one cation-exchange membrane and one anion-exchange membrane. In your setup you only use one cation-exchange membrane, can it still be called electrodialysis?

·       Page 1 line 44 “ method not only” missing the word “that”.

·       Chemical formulas do not have subscripts

·       Electrode areas are not reported.

·       Report current densities.

·       Page 4 lines 133 to 142 can go in methods section.

·       Concentration of P seems to be constant during the experiments

·       Xrd figure missing legend for a and b graph.

·       Energy consumption should be expressed as specific energy (by volume or weight of target element).

Author Response

Reviewer 1：

I have reviewed the manuscript entitled “Phosphorus recovery and simultaneous heavy metal removal 2 from ISSA through electrodialysis” and I don’t recommend its publication mainly because the manuscript lack to highlight its novelty vs the already published literate, and there is a lack of comparison of this approach vs other approaches in terms of specific energy consumption. The author should mention up to what levels of purity for the P rich stream this process can be considered successful; also, what is the expected downstream process for the recovered P stream, what can be done with a 2000 ppm of P solution?

Response: Thanks for your comment. More relative recent publishes have been reviewed and critically compared in updated version for better clarification of novelty. The P purity was assessed and the downstream process was added in updated version.

 

Other comments:

 

• Check English, some minor errors can be found in the manuscript.

Response: Thanks for your comment. We have reviewed this manuscript several times to avoid minor errors.

 

• Graph quality is low.

Response: Thanks for your comment. The Gragh has been reconstructed for higher quality.

 

• Typically, a electrodialysis a unit cell is a combination of one cation-exchange membrane and one anion-exchange membrane. In your setup you only use one cation-exchange membrane, can it still be called electrodialysis?

Response: Thanks for your comment. Strictly speaking, an electrodialysis system contains both cation-exchange membrane and anion-exchange membrane, therefore, we have deleted the expression of “electrodialysis”.

 

• Page 1 line 44 “ method not only” missing the word “that”.

Response: Thanks for your comment. This error has been corrected as in line 51.

 

• Chemical formulas do not have subscripts

Response: Thanks for your comment. We have corrected this mistake in the whole manuscript.

 

• Electrode areas are not reported.

Response: Thanks for your comment. The electrode area has been added in line 111.

 

• Report current densities.

Response: Thanks for your comment. The current densities were added in methods section (line 108).

 

• Page 4 lines 133 to 142 can go in methods section.

Response: Thanks for your comment. This part has been moved into methods section.

 

• Concentration of P seems to be constant during the experiments

Response: Thanks for your comment. As you can see in Figure 3, the concentration of P has a slightly increase tendency, however, because the volume of anolyte was decreasing, the P was escaped and detected in cathoyte (Figure 8).

 

• Xrd figure missing legend for a and b graph.

Response: Thanks for your comment. The legend for a and b graph has been added.

 

• Energy consumption should be expressed as specific energy (by volume or weight of target element).

Response: Thanks for your comment. The energy consumption was counted by treating 200 mL P-extract, which has been added in title of table 4.

Reviewer 2 Report

Reviewer's Comments

December 19^th, 2022

Water (ISSN 2073-4441)

Manuscript ID: water-2096167

Title: Phosphorus recovery and simultaneous heavy metal removal from ISSA through electrodialysis

 

The manuscript is well written, and the experimental design is well planned and executed, and I have just one concern:

           

1-   The novelty of the study is not clear and the introduction is very short. Please include recent studies related to the extraction of phosphorus from different sludge, especially the incinerated sewage sludge ash.

2-   No report at all regarding the error analysis and no error bars were included in the figures. I wonder if the reported values based on one measurement or many measurements?

3-   Please discuss the effect of pH on the removal of phosphorous in more details based on the speciation diagram of phosphorous in addition to the other removed heavy metals.

4-   The XRD figures need smoothing and indexing as well as the JCPDs reference numbers for each chemical compounds.

5-   Figures 7 and 8 are amazing.

6-   The authors have to pay attention to the way they write the chemical formulas especially the subscripts.

 

After a clear thought, I highly recommend the publication of the manuscript after taking into consideration the above mentioned comments.

Sincerely,

Comments for author File: Comments.pdf

Author Response

Reviewer 2:

The manuscript is well written, and the experimental design is well planned and executed, and I have just one concern:

 

1-The novelty of the study is not clear and the introduction is very short. Please include recent studies related to the extraction of phosphorus from different sludge, especially the incinerated sewage sludge ash.

Response: Thanks for your comment. More studies related to the P extraction from ISSA were reviewed and added in introduction part. And the introduction was re-constructed for better clarification of novelty.

 

2-No report at all regarding the error analysis and no error bars were included in the figures. I wonder if the reported values based on one measurement or many measurements?

Response: Thanks for your comment. As shown in line 124, each of these currents was carried out twice for trend line rectification. The overall results are shown in one trend line. And the error bars of bar diagram (Figure 3) were added, as per your suggestion.

 

3-Please discuss the effect of pH on the removal of phosphorous in more details based on the speciation diagram of phosphorous in addition to the other removed heavy metals.

Response: Thanks for your comment. The speciation diagram of phosphorus has been studied in our previous researches: L. Fang, J.-s. Li, S. Donatello, C.R. Cheeseman, C.S. Poon, D.C.W. Tsang, Use of Mg/Ca modified biochars to take up phosphorus from acid-extract of incinerated sewage sludge ash (ISSA) for fertilizer application, Journal of Cleaner Production 244 (2020) 118853. In short, at pH 2, the P was dominantly in forms of H₂PO₄^- and H₃PO₄ (mass ratio of 1:1), while pH lower than 1, the P was dominantly in form of H₃PO₄. Therefore, when pH of anolyte lower than 1, the P was more easily escaping to anolyte with other cations. And these discussion has been added in part 3.3.

 

4-The XRD figures need smoothing and indexing as well as the JCPDs reference numbers for each chemical compounds.

Response: Thanks for your comment. We have smoothed the XRD figures, re-analyzed them and added the JCPDs reference numbers for each chemical compounds.

 

5- Figures 7 and 8 are amazing.

Response: Thanks for your comment.

 

6-The authors have to pay attention to the way they write the chemical formulas especially the subscripts.

Response: Thanks for your comment. These errors have been corrected in updated version.

 

After a clear thought, I highly recommend the publication of the manuscript after taking into consideration the above mentioned comments

Author Response File: Author Response.pdf

Reviewer 3 Report

This investigation combined the acid extract and electrodialytic method to recover P. It is an excellent trial to recover P, and the manuscript topic is suitable for Water. However, the manuscript should be polished further before consideration for publication.

1.      The English should be checked carefully.

2.      The are many superscripts and subscripts mistakes. Please check!

3.      There are many format mistakes as well. When the authors used the template, it is better to change the content accordingly and delete the unnecessary text.

4.      L143： Both the C/C₀ and the absolute concentration change should be considered.

5.      Why Fe-PO4 precipitate? The authors stated that the shift of Fe is negligible.

6.      L171: The lowest P concentration at 1.5 h is not agreed with the drop of metals.

7.      ‘This is because….’ Here, ‘this’ is not clear.

8.      Table 3: What are the conditions for table 3, especially the current?

9.      Fig 2 and Fig 3: The captions are similar to each other. How about the evolution of catholyte? The discussion could be more profound if the authors had the catholyte chemistry evolution data.

10.   I suggest the authors directly show the currents in the figures (Fig 2-4).

11.   Fig 4(f): Use the same width for all lines.

12.   What’s the Si concentration in the anolyte?

13.   The initial Mn concentration is relatively small. Is it possible to precipitate enough Mn-bearing phase for XRD detection? The EDS data showed no Mn signal. Thus the XRD results are questionable. The crystalline phase and the corresponding discussion should focus on the dominant element, i.e., Ca, P, Al, Na, Si.

14.   Are there any precipitates in the cathode? If yes, what are the chemical and crystalline compositions?

15.   How could the precipitates, e.g., Ca3(PO4)3(OH), keep stable at a solution with a pH of 0.087?

 

16.   More comments have been added to the manuscript; please check them.

Comments for author File: Comments.pdf

Author Response

Reviewer 3：

This investigation combined the acid extract and electrodialytic method to recover P. It is an excellent trial to recover P, and the manuscript topic is suitable for Water. However, the manuscript should be polished further before consideration for publication.

 

1. The English should be checked carefully.

Response: Thanks for your comment. The manuscript has been revised several times to avoid errors.

 

2. The are many superscripts and subscripts mistakes. Please check!

Response: Thanks for your comment. The superscripts and subscripts have been paid special attention when revised the manuscript, as per your suggestion.

 

3. There are many format mistakes as well. When the authors used the template, it is better to change the content accordingly and delete the unnecessary text.

Response: Thanks for your comment. We have changed the content accordingly and deleted the unnecessary text, as per your suggestion.

 

4. L14 Both the C/C0 and the absolute concentration change should be considered.

Response: Thanks for your comment. The absolute concentration of P-extract before EDR has been shown in Table 1 (refers to C₀), thus the absolute concentration change can be counted according to the value of C/C₀.

 

5. Why Fe-PO4 precipitate? The authors stated that the shift of Fe is negligible.

Response: Thanks for your comment. As statement, this precipitate is temporary, it would be re-dissolved quickly. But the example here (Fe) may be misleading, thus we have changed for a more exact example (Pb).

 

6. L171: The lowest P concentration at 1.5 h is not agreed with the drop of metals.

Response: Thanks for your comment. The lowest P concentration can be corresponding to the drop of heavy metals, especially Pb, as in Figure 2 b.

 

7. ‘This is because….’ Here, ‘this’ is not clear.

Response: Thanks for your comment. The ambiguous description has been deleted.

 

8. Table 3: What are the conditions for table 3, especially the current?

Response: Thanks for your comment. The current was 50 mA and this has been added in the title of table 3, as per your suggestion.

 

9. Fig 2 and Fig 3: The captions are similar to each other. How about the evolution of catholyte? The discussion could be more profound if the authors had the catholyte chemistry evolution data.

Response: Thanks for your comment. The Figure 2 and Figure 3 were focused on different time periods; we have clarified this in title of Figure 2. The discussion here was more focused on anolyte, which is because this study aims to purity the P-extract in anolyte. Heavy metals/metals were immigrating to catholyte and forming with flocculent sediment, thus the we characterized this sediment afterwards. In addition, we have the pH evolution data of catholyte in Figure 4.

 

10. I suggest the authors directly show the currents in the figures (Fig 2-4).

Response: Thanks for your comment. The figures 2-4 have 2 or 3 kinds of results in every figure, take figure 2 as an example, there are results of heavy metals/metals, P concentration and pH changes in anolyte, thus, it is still necessary add subheadings (a, b, c, etc.) to explain.

 

11. Fig 4(f): Use the same width for all lines.

Response: Thanks for your comment. Same width has been applied, as per your suggestion.

 

12. What’s the Si concentration in the anolyte?

Response: Thanks for your comment. Anion of SiO₂^2- was released from ISSA, as in our previous study:

83. Fang, J.-s. Li, S. Donatello, C.R. Cheeseman, Q. Wang, C.S. Poon, D.C.W. Tsang, Recovery of phosphorus from incinerated sewage sludge ash by combined two-step extraction and selective precipitation, Chemical Engineering Journal 348 (2018) 74-83.

The Si concentration cannot be detected by ICP and it was not the focus of this study, thus no specifically detection was carried out.

 

13. The initial Mn concentration is relatively small. Is it possible to precipitate enough Mn-bearing phase for XRD detection? The EDS data showed no Mn signal. Thus the XRD results are questionable. The crystalline phase and the corresponding discussion should focus on the dominant element, i.e., Ca, P, Al, Na, Si.

Response: Thanks for your comment. The Mn-bearing phase was one of the overlapped minerals but the Mn concentration was relatively small, as in your comments. We have re-analyzed this XRD results based on the dominant elements in EDS data and the update findings has been shown in Figure 6. In addition, the reference codes of these three kinds of minerals were added in figure title.

 

14. Are there any precipitates in the cathode? If yes, what are the chemical and crystalline compositions?

Response: Thanks for your comment. As you can see in part 2.4, there were two kinds of precipitates in catholyte and no precipitates were found on the cathode.

 

15. How could the precipitates, e.g., Ca3(PO4)3(OH), keep stable at a solution with a pH of 0.087?

Response: Thanks for your comment. The precipitates were formed in catholyte, which were alkaline (pH around 14).

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

If the electrode area is 1x1cm2 , how the current densities are the values reported. There is an error on the calculation ??

Author Response

If the electrode area is 1x1cm2 , how the current densities are the values reported. There is an error on the calculation ?

Reply: Thanks for your comment. In electromagnetism, current density is the amount of charge per unit time that flows through a unit area of a chosen cross section. For this study, the electrode was in anolyte, and the cross section of anolyte was: 6*5 cm². The current densities was counting by currents (15 mA, 35 mA and 50 mA) divided by cross section (6*5 cm²), which were 0.5 mA/cm², 1.17 mA/cm², and 1.67 mA/cm², respectively. Similar counting method can be found in a reference we have cited:

G.M. Kirkelund, C. Magro, P. Guedes, P.E. Jensen, A.B. Ribeiro, L.M. Ottosen, Electrodialytic removal of heavy metals and chloride from municipal solid waste incineration fly ash and air pollution control residue in suspension – test of a new two compartment experimental cell, Electrochimica Acta 181 (2015) 73-81.

Reviewer 3 Report

The authors have greatly improved the manuscript and answered most of the questions. However, I still have other worries.

1. All figures quality is still low. Higher resolution figures must be provided.

2. I'm afraid I have to disagree with the discussion in L185-190. There might be 100 reasons for the P drop, but not the precipitation of Fe-P or Pb-P compounds since Fe/Pb concentrations are much lower than P. If any precipitation could impact the P concentration, it should be Ca-P or Al-P. Anyhow, it is better to provide evidence.

3. Figures 6&8. The XRD results and the EDS are mutually contradictory. The XRD results said all precipitates are Ca-P/Ca-Si dominated, but the EDS data supported Al-P is dominated. The authors should recheck the XRD data and provide evidence (i.e., reference patterns) to show which kind of crystalline material they are.

P.S. Please remove the grid lines in Figure 6.

 

 

Author Response

1. All figures quality is still low. Higher resolution figures must be provided.

Reply: Thanks for your suggestion. I have uploaded a higher quality figures, as per your suggestion.

 

2. I'm afraid I have to disagree with the discussion in L185-190. There might be 100 reasons for the P drop, but not the precipitation of Fe-P or Pb-P compounds since Fe/Pb concentrations are much lower than P. If any precipitation could impact the P concentration, it should be Ca-P or Al-P. Anyhow, it is better to provide evidence.

Reply: Thanks for your suggestion. The temporary P drop can be related to lots of reasons. Referring to other studies, the temporary drop here was more related to the escape of H₂PO₄^-/H₃PO₄ with heavy metals. And the discussion here has been updated and cited to references, as per your suggestion.

 

3. Figures 6&8. The XRD results and the EDS are mutually contradictory. The XRD results said all precipitates are Ca-P/Ca-Si dominated, but the EDS data supported Al-P is dominated. The authors should recheck the XRD data and provide evidence (i.e., reference patterns) to show which kind of crystalline material they are. P.S. Please remove the grid lines in Figure 6.

Reply: Thanks for your comments. The “contradictory” is because the amorphous structure of Al-P. As we all know, the XRD only can detect the crystallized cell. And there were many small peaks in the XRD results, which identified the amorphous structure of these two precipitates. Still, after carefully contrasting, we marked out the peaks of AlPO₄ in figure 6, which were relatively weak than other three substances, as you can see. The reference codes have been added in the title of figure 6 and the gird lines have been deleted, as per your suggestion.

Author Response File: Author Response.pdf