Coagulation Enhanced with Adsorption and Ozonation Processes in Surface Water Treatment

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This paper presented their research on coagulation and absorption process of surface water. The authors demonstrated that by combining ozonisation and adsorption processes can improve the removal efficiencies of various characteristics including OXI, DOC, TOC, UV at 254nm and ion removal efficiencies. The overall structure is very clear and the datapoints collected are well-presented. Below are my comments:

1. Figure 6 shows that removal efficiencies for both Zinc and Copper ions are 10% ~ 25% for initial concentrations at 0.5 mg/L using different procedures. These numbers don't align with previous figure 3 and 4, which has removal rate at 50% ~ 60%. I am not sure if I missed anything. If would great if authors can provide some explanations on this.

2. It would be nice if all the axis's names of the figures are consistent. For example, Figure 3, 4 and 6 have y-axis name as "Metal removal efficiency:" whereas others are presented as "Metal removal efficiency %".

3. Figure 5, y-axis name is not in bold.

4. Line 283, it should be "PAC" instead of "PCA".

 

Overall, I think this paper can be accepted with minor text revision. The experiments were well-designed and the results are supporting with their conclusions. 

Author Response

We would like to thank very much for the professional, helpful an useful Reviewer comments and suggestions. We are grateful to the Reviewer’s careful reading and whole work put into improving our manuscript. Corrections were made according to the comments.

 

This paper presented their research on coagulation and absorption process of surface water. The authors demonstrated that by combining ozonisation and adsorption processes can improve the removal efficiencies of various characteristics including OXI, DOC, TOC, UV at 254nm and ion removal efficiencies. The overall structure is very clear and the datapoints collected are well-presented. Below are my comments:

1. Figure 6 shows that removal efficiencies for both Zinc and Copper ions are 10% ~ 25% for initial concentrations at 0.5 mg/L using different procedures. These numbers don't align with previous figure 3 and 4, which has removal rate at 50% ~ 60%. I am not sure if I missed anything. If would great if authors can provide some explanations on this.

Thank you very much for the suggestion. We would like to inform, that on Figure 6 data previously indicate the ratio of actual concentration of metal to initial concentration. In actual version of manuscript y-axis is changed to removal efficiency in %. The data on Fig.6 refers to metals ion concentration in modified water (surface water dotted with zinc and copper). Data on figures 3 and 4 reflects metal behavior during adsorption process with using modeling water (distilled water dotted with zinc and copper) and were used for adsorption process optimization. So differences were effect of another material used for experiments as well as using of additional processes (Fig.6).

2. It would be nice if all the axis's names of the figures are consistent. For example, Figure 3, 4 and 6 have y-axis name as "Metal removal efficiency:" whereas others are presented as "Metal removal efficiency %".

Thank you very much for the comment. We would like to inform, that Figures 3,4 and 6 illustrate metals behavior, Figures 2 and 5 for NOM indicators removal. According to Reviewers suggestions and to clarify data interpretation, additional axis for efficiency of metal removal was added to Figures 3 and 4 and Figure 6 was changed.

3. Figure 5, y-axis name is not in bold.

The obvious mistake has been corrected, thank you very much for indicating it.

4. Line 283, it should be "PAC" instead of "PCA".

The obvious mistake has been corrected, thank you very much for indicating it.

Overall, I think this paper can be accepted with minor text revision. The experiments were well-designed and the results are supporting with their conclusions. 

Thank you very much for all comments, suggestions and opinions about ours report.

Reviewer 2 Report

Comments and Suggestions for Authors

in this paper, the authors reported the effect of adsorption and ozonation processes to enhance the main coagulation process for finding the desirable methods and technologies of removing pollutants from surface water.

The reduction of natural organic matter (NOM) was analyzed as change of color, turbidity, oxidizability (OXI), total and dissolved organic carbon (TOC, DOC), and absorbance at UV₂₅₄ for four stage of studies, coagulation, coagulation + adsorption, ozonation + coagulation, and ozonation + coagulation + adsorption.

Additionally, the concentration change of heavy metal ions such as Cu(II) and Zn(II) were measured by atomic adsorption spectrometry method.

The obtained data were discussed carefully referring the previously reported data.

They concluded that the obtaining additional removal of OXI, TOC, DOC, and UV₂₅₄ were 12%, 12%, 11% and 11% respectively for simultaneous coagulation and adsorption preceded by ozonation process compared to coagulation conducted as single process, and the best results were obtained for removing of Cu(II) and Zn(II) ions during combining initial ozonation with coagulation and adsorption.

The results reported in this paper didn’t show dramatic progress of coagulation study, however, they showed new direction for the study of coagulation by combining with adsorption and ozonation systematically.

I think that this paper is useful to develop the field of coagulation for removing pollutants from surface water.

There are some minor comments as follows.

1.     P. 3, line 137

zinc → zinc(II)

2.     P. 8, line 263

by 60% → by 40%        ?

3.     P. 9, line 284

“uneven structure of…”

The meaning is not clear to me.

4.     P. 12, fig. 6

 

The figure shows the same data with the data of table 9 (ion concentration).

Author Response

We would like to thank very much for the professional, helpful an useful Reviewer comments and suggestions. We are grateful to the Reviewer’s careful reading and whole work put into improving our manuscript. Corrections were made according to the comments.

 

in this paper, the authors reported the effect of adsorption and ozonation processes to enhance the main coagulation process for finding the desirable methods and technologies of removing pollutants from surface water.

The reduction of natural organic matter (NOM) was analyzed as change of color, turbidity, oxidizability (OXI), total and dissolved organic carbon (TOC, DOC), and absorbance at UV₂₅₄ for four stage of studies, coagulation, coagulation + adsorption, ozonation + coagulation, and ozonation + coagulation + adsorption.

Additionally, the concentration change of heavy metal ions such as Cu(II) and Zn(II) were measured by atomic adsorption spectrometry method.

The obtained data were discussed carefully referring the previously reported data.

They concluded that the obtaining additional removal of OXI, TOC, DOC, and UV₂₅₄ were 12%, 12%, 11% and 11% respectively for simultaneous coagulation and adsorption preceded by ozonation process compared to coagulation conducted as single process, and the best results were obtained for removing of Cu(II) and Zn(II) ions during combining initial ozonation with coagulation and adsorption.

The results reported in this paper didn’t show dramatic progress of coagulation study, however, they showed new direction for the study of coagulation by combining with adsorption and ozonation systematically.

I think that this paper is useful to develop the field of coagulation for removing pollutants from surface water.

There are some minor comments as follows.

1. P. 3, line 137: zinc → zinc(II)

Thank you very much for the suggestion. We would like to inform, that in the context of inorganic compounds naming, because zinc in chemical compounds exists only on oxidation state +2, the name of its salt does not need addition of the valency in the bracket.

2. P. 8, line 263: by 60% → by 40%?

The obvious mistake has been corrected, thank you very much for indicating it.

3. P. 9, line 284: “uneven structure of…”. The meaning is not clear to me.

Thank you very much for the careful reading of our manuscript. We would like to explain that term “uneven structure” was proposed by professional translation office. Unfortunately, we did not detect such not clear translation. We thought about irregular or heterogenous structure. We made the proper correction in the manuscript body.

4. P. 12, fig. 6: The figure shows the same data with the data of table 9 (ion concentration).

Thank you very much for the suggestion. We would like to inform, that Figure 6 was changed according to yours as well as other Reviewers comments. Actually figure presents metal removal efficiency given in %, what seems to be better for interpretation of results.

Reviewer 3 Report

Comments and Suggestions for Authors

The reviewed work is quite interesting and correctly written. However, according to the reviewer, certain issues require clarification/extension:

1. Authors should be more explicit about what is new in their work. This is not entirely clear, because all the single operations presented in the article and their combinations have long been used in many fields related to industry, environmental protection, etc.,

2. What does the phrase "typical laboratory conditions at 20 - 25°C"  (line 202) mean? Adsorption processes are quite sensitive to temperature changes, so the use of constant measurement temperature in basic (laboratory) research is of key importance in both kinetic and static research and facilitates the transfer of the scale of the process - please explain this approach.

3. The authors presented the results of kinetic studies and it is OK. But to use adsorption processes in practice, it is also necessary to determine adsorption isotherms for individual substances. This is clearly missing in the reviewed work and should be presented/supplemented in some way.

4. The presented conclusions are too laconic. They do not indicate what makes the proposed methodology better than others already used - please explain.

Author Response

We would like to thank very much for the professional, helpful an useful Reviewer comments and suggestions. We are grateful to the Reviewer’s careful reading and whole work put into improving our manuscript. Corrections were made according to the comments.

 

The reviewed work is quite interesting and correctly written. However, according to the reviewer, certain issues require clarification/extension:

1. Authors should be more explicit about what is new in their work. This is not entirely clear, because all the single operations presented in the article and their combinations have long been used in many fields related to industry, environmental protection, etc.,

Thank you very much for the comment. We would like to inform, that according to Reviewer suggestion we added more explanation in the Summary section. What more we would like to explain that the combination of ozonation and PAC adsorption processes with coagulation are not commonly used in treatment of water for human consumption purposes. Water treatment plants (WTP) sometime introduce ozonation module before the coagulation process, but this is not a standard approach. The adsorption process is most often carried out at WTP using granulated activated carbon (GAC) in adsorption columns. Powdered activated carbon is rarely used during coagulation, most often in emergency situations. The biggest advantage of PAC, compared to GAC, is the ability to quickly and easily change the type and dose depending on the type of water pollution. At the same time, it should be noted that the order of processes in the sequence may affect the removal of contaminants

2. What does the phrase "typical laboratory conditions at 20 - 25°C"  (line 202) mean? Adsorption processes are quite sensitive to temperature changes, so the use of constant measurement temperature in basic (laboratory) research is of key importance in both kinetic and static research and facilitates the transfer of the scale of the process - please explain this approach.

Thank you very much for the careful reading of our manuscript. We would like to explain that adsorption experiments were driven at constant temperature about 22°C. But whole experimental data were collected during 2 – 3 weeks, when temperature in our laboratory changed, but still was in the range 20 – 25ºC. The temperature was not regulated in the laboratory in any way.

3. The authors presented the results of kinetic studies and it is OK. But to use adsorption processes in practice, it is also necessary to determine adsorption isotherms for individual substances. This is clearly missing in the reviewed work and should be presented/supplemented in some way.

Thank you very much for the suggestion. We would like to inform, that the general topic of our study was the coagulation process ant its intensification. That why we did not describe other processes (adsorption and ozonation) in more detailed way. We absolutely agree, that adsorption isotherm (for example the Langmuir or Freundlich) would be valuable for adsorption description. We will use the Reviewer idea in our future work concerned on adsorption as a main topic. Thank you very much for the valuable suggestion.

4. The presented conclusions are too laconic. They do not indicate what makes the proposed methodology better than others already used - please explain.

We would like to thank the Reviewer for valuable comments, which we certainly use when planning and driving further research. Taking into account the comments of Reviewer 4 and the other three Reviewers, we have made some changes to the Summary, which should more clearly present the achievements of our work.

Reviewer 4 Report

Comments and Suggestions for Authors

Dear Authors,

The paper titled "Coagulation enhanced with adsorption and ozonation processes in surface water treatment" has been carefully read and reviewed. The primary focus of the research work is to improve the coagulation process by integrating it with adsorption and/or ozonation for treating surface water. The scope and subject is an ever-important field of environmental science (and sustainability as well), and although the global research interest towards water treatment is extensive, there are still numerous gaps to fill. 

Please find my comments, suggestions and questions below. 

- The Introduction section provides a broadly detailed description of some of the methods and technology in surface water treatment (regarding coagulation and its possible combinations). What I do lack a bit is a brief comparison with existing technologies: how does this combined treatment process compare with existing water treatment technologies in terms of efficiency, cost, and environmental impact?

- The general description of materials and applied methods is well detailed and logical, only found some minor parts that should be clarified. How exactly was the different parameters selected, e.g. the PAX/PAC dosage, the metal ion concentration, duration of ozonation, etc. 

Without thorough statistical analysis, the accuracy of the analytical techniques and equipments (sensitivity, or resolution power if you like) should be provided - some of the results are quite close to each other, and therefore it is hard to see whether these differences are statisctially significant. 

Authors mention that the analyses were carried out in three parallels: does this mean that each and every experiment was done three times, or a given sample was measured three times with the same equipment? If the former, values for SD should be submitted. 

- During the discussion of the results, some of the Figures need a bit improvement. Figure 2 in my point of view is a bit small, especially the textual part of it. In Figure 3 & 4 , the unit of the independent variable (time) should be put in brackets [], instead of using / - "time/min" is not an appropirate labeling. Minor issue, but in Figure 5 the 3 would look better if but in lower index, regarding the ozone molecule. 

I found it quite interesting that the aluminium concentration in the surface water sample systematically increased when using lower concentrations (in case of ALS and C1 even higher concentrations), but decreased when applying >3 mg/L. The reason behind is of course quite obvious (as the concentration of the coagulant increases, it becomes more effective at removing aluminum and other impurities from the water), but this observation underscores the importance of optimizing coagulant dosage to balance treatment efficacy with potential increases in certain contaminants.

Regarding Figure 6, I think it would be better to depict the factual removal efficacy (in %) on the y-axis for better comprehensibility and comparability. For example, Authors state (line 384-386) that the removal efficiencies were higher for lower initial Zn²⁺ concentrations, which can seem contradictroy at a first glance of Figure 6 - the bars are higher for the 1 mg/L concentrations, and the y-axis is labeled as "metal removal efficiency". 

 

Comments on the Quality of English Language

Overall, the paper demonstrates a good level of scientific rigor and use of scientific formulation. There are occasional grammatical errors and unusual phrasings that could be refined for clarity and precision. These include minor issues with verb tenses, subject-verb agreement, and sentence structure.

Author Response

The paper titled "Coagulation enhanced with adsorption and ozonation processes in surface water treatment" has been carefully read and reviewed. The primary focus of the research work is to improve the coagulation process by integrating it with adsorption and/or ozonation for treating surface water. The scope and subject is an ever-important field of environmental science (and sustainability as well), and although the global research interest towards water treatment is extensive, there are still numerous gaps to fill.

Dear Reviewer,

we would like to thank very much for the professional, helpful an useful Reviewer comments and suggestions. We are grateful to the Reviewer’s careful reading and whole work put into improving our manuscript. Corrections were made according to the comments.

Please find my comments, suggestions and questions below. 

- The Introduction section provides a broadly detailed description of some of the methods and technology in surface water treatment (regarding coagulation and its possible combinations). What I do lack a bit is a brief comparison with existing technologies: how does this combined treatment process compare with existing water treatment technologies in terms of efficiency, cost, and environmental impact?

It is very difficult to compare combined processes with unit processes in terms of their efficiency, costs or environmental impact. This is primarily due to the lack of available data, the diversity of technical solutions for a given technology, as well as the wide commercial offer of available coagulants, activated carbons and ozone generators, as well as the changing costs of the above. It would be very interesting, but also very difficult, to compare environmental costs, for example, by using LCA (life cycle assessment) for individual technological processes. We would like to thank the Reviewer for valuable comments, suggestions and recommendations, which we certainly use when planning and driving further research.

- The general description of materials and applied methods is well detailed and logical, only found some minor parts that should be clarified. How exactly was the different parameters selected, e.g. the PAX/PAC dosage, the metal ion concentration, duration of ozonation, etc. 

Zinc and copper initial concentration was selected on the base of levels determined in low regulations for water intended for human consumption and detection limit of flame AAS spectrophotometer. We decided for concentration low enough not to exceed the permissible limits of these metals in drinking water and high enough to make changes in concentration during the processes possible to notice and analyze. The selection of the ozonation time and the dose of activated carbon was based on previous research:

1. Karwowska, B.; Sperczynska, E.; Dąbrowska, L. Water Treatment in Hybrid Connection of Coagulation, Ozonation, UV Irradiation and Adsorption Processes. Water 2021, 13(13), 1748; https://doi.org/10.3390/w13131748
2. Karwowska, B.; Sperczyńska, E. Organic matter and heavy metal ions removal from surface water in processes of oxidation with ozone, UV irradiation, coagulation and adsorption. Water 2022, 14, 3763; DOI:10.3390/w14223763
3. Dąbrowska L; Karwowska B.; Rosińska A; Sperczynska E.;. Oczyszczanie wody w procesach hybrydowych/Water purification in hybrid processes Częstochowa 2021. (in Polish)

Without thorough statistical analysis, the accuracy of the analytical techniques and equipments (sensitivity, or resolution power if you like) should be provided - some of the results are quite close to each other, and therefore it is hard to see whether these differences are statisctially significant. 

Authors mention that the analyses were carried out in three parallels: does this mean that each and every experiment was done three times, or a given sample was measured three times with the same equipment? If the former, values for SD should be submitted. 

We would like to inform, that each single experiment was driven in triplicate and figures were prepared on the base of average value of data from tables. The SD values have been added to the tables. Thank you very much for the suggestion, which will be valuable in the future during next reports preparation.

- During the discussion of the results, some of the Figures need a bit improvement. Figure 2 in my point of view is a bit small, especially the textual part of it. In Figure 3 & 4 , the unit of the independent variable (time) should be put in brackets [], instead of using / - "time/min" is not an appropirate labeling. Minor issue, but in Figure 5 the 3 would look better if but in lower index, regarding the ozone molecule. 

Thank you very much for the careful analysis of tables and figures in our manuscript. The figures were improved according to all four Reviewers suggestions and comments.

 

I found it quite interesting that the aluminium concentration in the surface water sample systematically increased when using lower concentrations (in case of ALS and C1 even higher concentrations), but decreased when applying >3 mg/L. The reason behind is of course quite obvious (as the concentration of the coagulant increases, it becomes more effective at removing aluminum and other impurities from the water), but this observation underscores the importance of optimizing coagulant dosage to balance treatment efficacy with potential increases in certain contaminants.

Thank you very much for the comment.

Regarding Figure 6, I think it would be better to depict the factual removal efficacy (in %) on the y-axis for better comprehensibility and comparability. For example, Authors state (line 384-386) that the removal efficiencies were higher for lower initial Zn²⁺ concentrations, which can seem contradictroy at a first glance of Figure 6 - the bars are higher for the 1 mg/L concentrations, and the y-axis is labeled as "metal removal efficiency". 

Thank you very much for the suggestion. We would like to inform, that Figure 6 was changed according to yours as well as other Reviewers comments. Actually figure presents metal removal efficiency given in %, what seems to be better for interpretation of results.

 

 

Comments on the Quality of English Language

Overall, the paper demonstrates a good level of scientific rigor and use of scientific formulation. There are occasional grammatical errors and unusual phrasings that could be refined for clarity and precision. These include minor issues with verb tenses, subject-verb agreement, and sentence structure.

Thank you very much for the professional, helpful an useful comments and suggestions. We are grateful for the Reviewer’s careful reading. The professional language agency was employed for language correction and whole manuscript was examined according to the comments of Revivers.

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

No comments