Simultaneous Arsenic and Fluoride Removal from Contaminated Water Using Powder Reagents of CaO, Ca(OH)₂, and CaCO₃ as Calcium-Based Adsorbents

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Paper ID, Sustainability-3777321

Thanks for giving me the opportunity to review this paper. The paper titled “Simultaneous Arsenic and Fluoride Removal from Contaminated Water using Calcium-based Adsorbents” is an interesting topic, and well written. However, before publication in sustainability, it needs some minor improvements.

 Here I am writing some minor comments for improvement.

1. Is there any need to get copy right permission of table 1 in your paper?
2. Clarifying the type of calcium-based adsorbents have used by the reviewer in the title (e.g., "natural," "engineered," or a specific material like "calcium alginate" or "calcium carbonate") if space permits. This would improve clarity and relevance for targeted readers.
3. Please clarify the adsorbent can be regenerated or reused, which is important for practical applications.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This study addresses the use of Ca-based adsorbents for the simultaneous removal of As and
F from contaminated water. The authors conducted a comprehensive series of experiments to
evaluate the efficiency of different Ca-based adsorbents in removing these contaminants and
investigated the underlying removal mechanisms.
Based on the experimental results, the paper provides valuable insights into the adsorption
behavior of As and F, as well as the adsorption mechanism. It offers relevant guidance on
optimizing these processes for practical application in wastewater treatment. The authors also
propose that a two-cycle treatment process using Ca-based adsorbents may be necessary to
consistently meet environmental standards.
This study contributes useful recommendations for the application of Ca-based adsorbents in
waters with elevated concentrations of As and F. It also highlights important challenges, such
as the influence of solution pH on removal efficiency.
Overall, the paper presents a well-structured investigation with meaningful findings that
advance understanding in this field. However, further validation of the proposed two-cycle
treatment and exploration of residue management strategies would strengthen the practical
applicability of the study.
I have a few comments and suggestions that might be helpful in further improving the
manuscript or guiding future research studies:
1. It might be helpful to provide additional details on the rationale for choosing the
specific concentrations of As and F used in the experiments.
2. While the experiments were conducted with 24-hour stirring clarification on
whether the effects of contact time and adsorption kinetics on removal efficiency were
investigated would be valuable.
3. Has the potential influence of temperature on the adsorption process been
examined, even if only through preliminary testing?
4. Finally, it would be important to consider the management of adsorbent materials
after As and F adsorption, such as possible recycling or safe disposal, due to potential
environmental risks

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Sugita et al. studied the removal of Arsenic and Fluoride from Contaminated Water using Calcium-based Adsorbents, but some modification is needed from a publication point of view.

1. What is the novelty of the present work? Rewrite it at the end of the introduction section.
2. The author should add an error bar where it is necessary.
3. The author should compare its own application results with other researchers' work in a table form.
4. To enrich literature, the author should refer or add some references. i. Materials Today Communications 26, (2021), 102101, ii. Recent Patents on Nanotechnology 17 (1), (2023), 5-7, iii. Ultrasonics Sonochemistry 58, (2019), 104663
5. The conclusion section section much longer. Make it short.

Author Response

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Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

1. The data presentation must be improved. Conventional plot with x-axis as equilibrium concentration Ce and y-axis as Qe(mass of adsorbed molecule/mass of adsorbent) should be used. Current plots e.g., figure 1 shows a certain amount of Wad0/V must be reached to reduce the concentration of CAS to a low enough level. But this conclusion will change if the initial concentration of CAS0 changes.
2. The mechanism of adsorption should be discussed more. It's highly unnecessary to prove you cannot fit the data with Langmuir or Freundlich isotherm. Move it to the supporting doc if you really want to present it. Especially you excluded data points that deviate significantly which makes the fitting step even less meaningful. The table 3 even reports negative max uptake. I appreciate you present actual data but if the data apparently is not explained by the isotherms, there is no need to try fitting it which gives meaningless parameters. 
3. Authors tried explaining some adsorption is by interacting with leached Ca2+. Please add more reference to that theory. The majority of adsorption is with the solid framework. Please add references and comments about the adsorption with the solid framework. Is it adsorbed to the cations or the dispersion forces etc. 
4. The solubility study should be combined into the section with leached Ca measurement and justify the plateau of leached Ca concentration with increased solid quantity. 

Author Response

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Author Response File: Author Response.pdf