Application of Sequential Combination of Electro-Coagulation/Electro-Oxidation and Adsorption for the Treatment of Hemodialysis Wastewater for Possible Reuse

Round 1

Reviewer 1 Report

1. What is the logic behind it? . Really readers may get confusion. What is the prime novelty of the present investigation (combination between three methods for removing pollutants)?

2. In the section of abstract, there is long introduction for your work, it should be shorter.

3. In Abstract; The first occurrence of an acronym should be interpreted. Such as (COD).

4. By comparing with the other methods for removing pollutants, the combination of three techniques to remove pollutants is a complex system. the authors should clearify that.

5. The authors have used adsorption onto activated carbon, why did they use only AC, although there are a lot of effective materials in this trend.

6. The number of figures is very low, the authors should add some images and photo to confirm their experiments.

7. The authors should add the raw data of their results in the supplementry files.

8. Moderate english change required; please check in line 29 (to leading to), line 381 (as s a strategy), line 400 (as shown in shema1).

Author Response

Dear Reviewer,

We would like to thank you for the review of our manuscript and the constructive indications and comments provided.

Coming to the specific issues raised:

1. What is the logic behind it. Really readers may get confusion. What is the prime novelty of the present investigation (combination between three methods for removing pollutants)?

R1: Thank you for this question.

In fact, the combination of these three techniques was performed to treat HWW in order to enhance the efficacy of removal of all the persistent pollutants present in the wastewater. allowing to a possible reutilization of treated water in irrigation. In fact, in this study the percentage of sodium content which can induce calcium and potassium deficiency in soils low in these nutrients was reduced from 97% to 1.87 % after treatment by the sequential techniques only.

2. In the section of abstract, there is long introduction for your work, it should be shorter

R2: We agreed totally with you, the long sentence in the abstract has been removed.

3. In Abstract; The first occurrence of an acronym should be interpreted. Such as (COD).

R3: Sentence has been corrected.

4. By comparing with the other methods for removing pollutants, the combination of three techniques to remove pollutants is a complex system. the authors should clarify that.

R4: A combination of variable methods that were used in this study was mentioned in details in order to assess the factors influencing the performance of the wastewater treatments  and to encourage the stakeholders to set up such combination for HWW treatment in cities.

5. The authors have used adsorption onto activated carbon, why did they use only AC, although there are a lot of effective materials in this trend.

R5: The AC materials has been used in this study due to its low cost, exceptionally high porosity, tunable pore size and high adsorptive capacities according to Girgis et al.

6. The number of figures is very low, the authors should add some images and photo to confirm their experiments.

R6: Thank you for pointing out this remark. Some photos have been added in the section of materials and methods.

7. The authors should add the raw data of their results in the supplementary files.

R7: A table summarizing our results has been added in the supplementary data.

8. Moderate English change required; please check in line 29 (to leading to), line 381 (as s a strategy), line 400 (as shown in shema1).

R8: English has been corrected.

Reviewer 2 Report

1.      Please add the full name of SAR in abstract.

2.      You should summarize recent researches on the treatment of HWW in ‘Introduction’ and highlight the characteristics of your research.

3.      Please state the brand and model of spectrophotometer in page 3 line 126.

4.      Please analyze the reasons of the degradation of Ca²⁺ does not change within 20 minutes of EC process as figure1.

5.      Please illustrate the parameters and experimental process of EC-EO-AC device in detail.

6.      According to Scheme1, the coupling of EC, EO and AC is EC first, then EO, and finally AC? If so, the efficiency of EC-EO-AC process is good, but increase greatly the treatment cost.

Author Response

Dear Reviewer,

We would like to thank you for the review of our manuscript and the constructive indications and comments provided.

Coming to the specific issues raised:

This study mainly describes the characteristics of HWW treatment by EC, EO and AC processes, and the combination of two or more treatment methods process of HWW wastewater is proposed. It is very valuable and interesting. The description of research center should be improved, the advantages and practicability of this new process and more details should be illustrated. And the manuscript has some problems need to be addressed. 

1. Please add the full name of SAR in abstract.

R1: The description of the abbreviation SAR has been added.

2. You should summarize recent researches on the treatment of HWW in ‘Introduction’ and highlight the characteristics of your research.

R2: Few lines summarizing the previous studies on the HWW have been added

3. Please state the brand and model of spectrophotometer in page 3 line 126.

           R3: Agree,

         It has been added

4. Please analyze the reasons of the degradation of Ca²⁺does not change within 20 minutes of EC process as figure1.

R4: Sentence of the calcium removal have been added

5. Please illustrate the parameters and experimental process of EC-EO-AC device in detail.

R5: Agree

A sentence to describe clearly the parameters and experimental process has been added to the section of “Experimental procedure”.

6. According to Scheme1, the coupling of EC, EO and AC is EC first, then EO, and finally AC? If so, the efficiency of EC-EO-AC process is good, but increase greatly the treatment cost.

R6: In this study, the sequential flow of the processes was EC first, then EO and finally AC. Thus, the efficiency of EC-EO-AC process is good, with no significant energy consumption. In the present study the energy consummation was 0.05 to 0.7 kWh/m³ for EO and EC, respectively.

Reviewer 3 Report

The work is interesting from the point of view of proposed strategy. There are a number of issues that need to be clarified or reconsidered.

First of all, I believe that an important point should be clarified:

Is hemodialysis wastewater collected separately?

I consider that it is the wastewater from hospitals that includes the water from hemodialysis.

The authors must clearly state the purpose of the study.

Introduction.  The statement "Reducing environmental health risks of hemodialysis is particularly important amid the persistence of the COVID-19 pandemic and biological hazardous agents" should be justified. Did you determine the presence of COVID 19 in hospital wastewater?

The paper should be reorganized for example the paragraph in which the phytotoxicity tests are presented (Phytotoxicity Test) is included in 2.1. Energy consumption calculation.

Equation 3 must be rewritten.

Table 1, first line, in addition to references, must be added the water categories for which the parameters are presented.

In case of studying the influence of electrolysis time, why were only 100 minutes were considered? For sodium and magnesium this time is not relevant.

Point 3.3. Effect of electro-oxidation treatment on HWW characteristics

The statement is "According the figure 2 the EO process is efficient for the removal of COD, total nitrogen and Mg" but in figure 2 Mg is not shown.

Author Response

Dear Reviewer,

We would like to thank you for the review of our manuscript and the constructive indications and comments provided.

Coming to the specific issues raised:

The work is interesting from the point of view of proposed strategy. There are a number of issues that need to be clarified or reconsidered.

First of all, I believe that an important point should be clarified:

• Is hemodialysis wastewater collected separately?I consider that it is the wastewater from hospitals that includes the water from hemodialysis.

R1: The wastewater was collected only from at the dialysis facility of Hédi Chaker University Hospital in Sfax, Tunisia

• The authors must clearly state the purpose of the study.

R2: The purpose of this study has been stated in the paper.

• The statement "Reducing environmental health risks of hemodialysis is particularly important amid the persistence of the COVID-19 pandemic and biological hazardous agents" should be justified. Did you determine the presence of COVID 19 in hospital wastewater?

R3: The statement has been justified since the SARS-CoV-2 RNA has been detected in hemodialysis effluent according to Okuhama et al.

• The paper should be reorganized for example the paragraph in which the phytotoxicity tests are presented (Phytotoxicity Test)is included in 1. Energy consumption calculation.

R4: This indication has been carefully considered and addressed.

• Equation 3 must be rewritten.

R5: Equation has been rewritten in the paper

• Table 1, first line, in addition to references, must be added the water categories for which the parameters are presented.

R6: The category of the other wastewaters has been added

• In case of studying the influence of electrolysis time, why were only 100 minutes were considered? For sodium and magnesium this time is not relevant.

 R7: We considered that only 100 min since after this time the removal percentage were stable doesn’t indicate any change, in addition, the cost energetic were increased. For the sodium and magnesium, there removal was stable after 100 min.

• Point 3.3. Effect of electro-oxidation treatment on HWW characteristics: The statement is "According the figure 2 the EO process is efficient for the removal of COD, total nitrogen and Mg" but in figure 2 Mg is not shown.

R8: The value of Mg has been added in the figure

Round 2

Reviewer 1 Report

The manuscript can be accepted in the present form

Author Response

The manuscript can be accepted in the present form

Thank you for your appreciate time.

Reviewer 2 Report

The manuscript is modified carefully according to the reviewers' comments, but some aspects still should be improved.

(1) Moderate English changes are still required.

(2)  Recent report on electro-coagulation should be cited in the manuscript like: https://doi.org/10.1016/j.cclet.2020.03.051

Author Response

(1) Moderate English changes are still required.

The English language has been revised to make easier the analysis and reading of our manuscript. 

The revised manuscript were made and changes, which were highlighted in red.

(2)  Recent report on electro-coagulation should be cited in the manuscript like: https://doi.org/10.1016/j.cclet.2020.03.051

Reference has been cited in the manuscript.

Reviewer 3 Report

The authors' answers to points 1, 2 and 3 are not convincing.

1 and 2. The question was:  Is hemodialysis wastewater collected separately? I consider that it is the wastewater from hospitals that includes the water from hemodialysis.The authors must clearly state the purpose of the study.

Your answer is The wastewater was collected only from at the dialysis facility of Hédi Chaker University Hospital in Sfax, Tunisia -

Please explain how the samples were collected and add it to the manuscript.

Specify how wastewater can be collected from a only unit in a hospital if there is a certain infrastructure.

2.The observation was: The statement "Reducing environmental health risks of hemodialysis is particularly important amid the persistence of the COVID-19 pandemic and biological hazardous agents" should be justified. Did you determine the presence of COVID 19 in hospital wastewater?
Your answer: The statement has been justified since the SARS-CoV-2 RNA has been detected in hemodialysis effluent according to Okuhama et al.

The question was clear, here I believe that the statement should be reformulated with reference to the context.

It is true that I was identified in Japan and we cannot say the same in the case of the present study without analysis to prove this fact.

Author Response

1 and 2. The question was:  Is hemodialysis wastewater collected separately? I consider that it is the wastewater from hospitals that includes the water from hemodialysis.The authors must clearly state the purpose of the study.

Your answer is The wastewater was collected only from at the dialysis facility of Hédi Chaker University Hospital in Sfax, Tunisia -

Please explain how the samples were collected and add it to the manuscript.

Specify how wastewater can be collected from a only unit in a hospital if there is a certain infrastructure.

Replay: We have addressed the explaination of the collected samples in the material and method section.

The sentence has been highlighted in the manuscript in red.

2.The observation was: The statement "Reducing environmental health risks of hemodialysis is particularly important amid the persistence of the COVID-19 pandemic and biological hazardous agents" should be justified. Did you determine the presence of COVID 19 in hospital wastewater?
Your answer: The statement has been justified since the SARS-CoV-2 RNA has been detected in hemodialysis effluent according to Okuhama et al.

The question was clear, here I believe that the statement should be reformulated with reference to the context.

Replay: The sentence in the introduction has been rewritten and indicated in red.