Sulphate Removal in Industrial Effluents Using Electrocoagulation Sludge as an Adsorbent

Round 1

Reviewer 1 Report (Previous Reviewer 3)

The manuscript entitled “Sulphate removal in industrial effluents using electrocoagulation sludge as an adsorbent”

1-    Introduction # Section : You can explain the novelty of this work

2-    In the materials section, you say that the table shows the composition of the battery wastewater, while in the manuscript, Table 1 is Comparison of surface area and pore size analysis with Brunauer Emmett Telle literature. this should be corrected

3-    The quality of the figures  is low, and the resolution must be increased.

4-    The equations to rewrite.

5-    The mechanism of sulphate adsorption must be well detailed.

6-    a comparison of the adsorption capacity with the literature should be added.

7-    The references were well matched to the research topic but need to update (2022).

 

8-     Conclusion needs to be improved with novelty and the importance of the investigation in the present work.

Author Response

Dear Reviewer

We highly appreciate the time and the comments that you made you made to improve our manuscript. Please find our comments in the attached document.

Kind regards

Author

Author Response File: Author Response.pdf

Reviewer 2 Report (New Reviewer)

Review of paper ‘Sulphate removal in industrial effluents using electrocoagulation sludge as an adsorbent’ prepared by Siyanda Yamba, Tunde L. Yusuf, Nomso C. Hintsho-Mbita, Richard Moutloali and Nonhlangabezo Mabuba.

Manuscript sustainability-1892676 is focused on the presentation of the waste management method for removing sulfates from sewage. The authors presented studies on both model and real systems. I have some suggestions that authors may consider prior to publishing this work.

1. There are numerous editing errors in the work. For example:

- no subscripts in the names of chemical formulae, see, i.e. Al(OH)3 in line 73 and ions SO42- in line 88,

- all equations require editing, see for example eq. 1 lines 149-150,

- Table 1 needs to be corrected, columns have moved.

The paper requires detailed proofreading by the authors.

2. The notation of the equations is not fully understood (lines 82-83). Please explain:                            5.

- Al13 complex

- difference between FeOH2+  and Fe(OH)2+

- value of complex Fe(OH)45+

3. Problems with figures:

- Figure 1: provide an explanation for Figures a and b. At present there is no clear distinction as to what they refer to.

- Schema 1, Figure 6, Figure 7 are blurred. It should be improved.

- The description in the text does not correspond to the markings in Figure 2. This should be corrected. Also, replace comma with dot in the description of the y-axis.

- The figure on page 11 should be numbered 7. Additionally, the results shown in Figure b do not correspond with the results in Figure 6. In Figure 7 b the efficiency for 40 mg is below 90% and in figure 6 it is almost 100%. Explain the differences.

- Since, as the authors point out, the efficiency of the adsorption process depends on many factors, e.g. time, pH, etc., all parameters should be clearly indicated in the description of the experiments presented in figures. For example, Figure 8 lacks information in this respect.

- Replace the comma with dot in Figure 8.

4. The authors should compare the proposed adsorbent with other adsorbents for the removal of sulphate ions. As an example, such a comparison could be presented in the context of the obtained parameters for the adsorption isotherms. At the same time, the presented adsorption parameters should be discussed in more detail.

5. From an ecological as well as an economic point of view, it is worth pointing out the potential for sorbent recycling after triple use. Can the resulting waste pose a risk to the environment? Is a possible release into the environment to be expected? How should it be stored?

6. There are no conclusions in the article. The authors have again copied section from Chapter 3.4.

7. English needs to be corrected throughout the manuscript. Examples from the abstract:

- The BET shows that the surface area of the sludge is 231.247m2 / g with total pore volume of 0.632 cm3 g-1

- The two isotherm models (Langmuir and Freundlich) were fitted, and the results show that the Langmuir equation was better fitted than the Freundlich isotherm. This confirms the homogenous distribution of the active sites on the EC sludge. At different EC’s sludges, the pseudo-second order kinetic model produced the best fitting experimental result which confirms the removal of sulphate ions by chemisorption.

 

 

 

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Author Response

Dear Reviewer

 

We highly appreciate the time and the effort you took to provide us with comments to improve our manuscript. Please find our responses in the attached document.

 

Kind regards

Author

Author Response File: Author Response.pdf

Reviewer 3 Report (New Reviewer)

The manuscript is interesting however, there are some suggestions which can improve the quality of manuscript.

1) The English language needs careful attention.

2) Line 13 in the abstract is incomplete and can not be understood.

3) Line 35, Revise the sentence with appropriate scientific language.

4) The objectives written in the introduction section are not clear. Authors should describe what actually they have done in this research.

5) Line 108, It should be subscript.

6) The quality of Figure 1 is very poor. Improve it with high resolution

7) How time 120 mins was selected for adsorption study? 

8) The formatting of all equations should be corrected.

9) The authors should report the FTIR results before and after sulfate loading.

10) The discussion in SEM section is not enough to describe the Image of EC sludge.

11) The equilibrium was achieved at 10-20 mins of contact time then why authors selected 120 mins as equilibrium time in other parameters?

Overall, the manuscript is not properly formatted and there are many grammatical mistakes which should be corrected. 

  

Author Response

Dear Reviewer

 

We highly appreciate the comments that you provided to improve our manuscript. Please find our comments in the attached document.

 

Kind regards

Author

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report (Previous Reviewer 3)

The revised version of the manuscript may acceptable to the journal standard.

Author Response

Dear Reviewer

 

Thank you for your contribution.

 

Kind regards

Author

Reviewer 2 Report (New Reviewer)

The authors have improved the work, which has significantly improved its quality, but the work still needs to be corrected.
In accordance with the recommendations sent, I asked for a correction of Figure 8: there is no indication of the process conditions for the results shown. at the same time, there are commas instead of dots. I would like to reiterate my remark that, due to the fact that adsorption depends on a number of factors, which are mentioned by the authors in the paper and which are investigated by the authors, the indication of these parameters in the figure description is very important.

Author Response

Dear Reviewer

 

Thank you very much for the contribution that you have made to our manuscript. Please find the responses in the attached document.

 

Kind regards

Author Response File: Author Response.docx

Reviewer 3 Report (New Reviewer)

Accept

Author Response

Dear Reviewer

 

Thank you very much for your contribution.

 

Kind regards

Author

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

The manuscript is devoted to investigate the high content of iron-based material from recycled electro-coagulated (EC) sludge for the adsorptive removal of sulphate, and the properties of the material were characterized. The adsorption performance of the material is determined using batch adsorption tests and kinetic and equilibrium data is obtained. The manuscript is not well-written and there are still many fundamental scientific problems to be solved, For example, how the adsorbent is prepared, and how to deal with the unwanted impurities from EC sludge. Moreover, the adsorption efficiency of the EC sludge is not impressive at and above all, the material cannot be fully regenerated after using as an adsorbent, which means the material has to disposed of, leading to secondary pollution after 2-3 adsorption cycles. Overall, this work has no importance to the academy and industry.

Reviewer 2 Report

The sludge from electrocoagulation (EC) process was used as adsorbent to remove industrial sulfate wastewater. The sludge properties including structure and morphology were characterized. The removal efficiency, kinetic and adsorption isotherm was clearly presented. However, the electrocoagulation process (i.e., wastewater source and composition) to obtain the sludge should be more explained.

There are some specific comments as following

1.      The battery wastewater represented that sulfate wastewater that further treated by sludge adsorption or it was the wastewater treated by electrocoagulation. Please clarify in the manuscript. In addition, the composition of battery wastewater is presented in Table 1, however there was no this table in the manuscript.

2.      In section of continuous electrocoagulation,

-          “..initial concentration = 100 mg/L”, what pollutant?

-          The Fe was used as material electrodes, however Al was also in the sludge. Where was Al from? Explain in the manuscript

3.      Explain more on sludge appearance such as color, yield (g sludge / L  treated wastewater by EC)

4.      In Fig 2, are there any C bonding peaks? If yes, it was likely as activated carbon absorbent

5.      In Fig 3, match the possible structures of iron and aluminum complexes in the XRD peaks.

6.      In Page 11, change Fig 6 to Fig 7

7.      The adsorption performance was tested in high sulfate wastewater. Explain why it was interesting pollutant.   

8.      There were equations for “energy consumption” and “theoretical amount of ions produced by current I”. Are there any discussion on these two points?

9.      In section of reusability of adsorbent, explain more on the washing process such as ratio of absorbent and deionized water, how many times for washing and period for each washing, any stirring or heating?  

“..the number of the cycle increased while the pH also increase in solution” Explain the reason in the manuscript

Reviewer 3 Report

The manuscript entitled “Reuse of electrocoagulation sludge as adsorbent for sulphate removal in industrial effluents”.

1-    Introduction # Section : You can explain the novelty of this work because in the literature we found a lot of works that deal with the same subject with the same adsorbent material Explain how you found the optimum conditions for the preparation of the adsorbent.

2-    The quality of the schematics is low, and the resolution must be increased.

3-    The equations to rewrite.

4-    FT-IR and DRX parts, references must be added to the interpretation.

5-    In the table of comparison of the specific surface, it is necessary to add more references to make a good comparison.

6-    The units must be in the same style

 

7-    Conclusion again needs re-organized with the study findings and what it cause etc.. not what they do.