Comparison between Different Technologies (Zerovalent Iron, Coagulation-Flocculation, Adsorption) for Arsenic Treatment at High Concentrations

Round 1

Reviewer 1 Report

Suggest a more concise title: 

 

Comparison of low-cost removal technologies for high concentration of arsenic

 

 

Need an objective statement at the end of the introduction.  Suggest: 

 

The objective of this study was to compare low-cost treatment systems to remove high concentrations of As(V) and As(III) from aqueous solutions. Following treatment leaching of As(III) back into solution was also studied.

 

 

Methods:

 

Start the methods section by describing the treatment technologies chosen for evaluation: Fe(0), coagulation with Al2(SO4)3 and FeCl3, and adsorption on a natural clay

 

Need more detail about the chemistry of the clay minerals evaluated. Why is it special? Could a different clay be used?

 

I like the evaluation pointing to an application as a household filter. Worth pursuing in another paper

 

The leaching experiment was very interesting and an important contribution in this paper.

 

Well written but would benefit from some English editing.

Author Response

Please see the attachment

Author Response File: Author Response.docx

Reviewer 2 Report

Article entitled Comparison between different technologies (zero-valent iron, coagulation-flocculation, adsorption) for arsenic treatment at high concentrations written by Luis E. Lan, Fernando D. Reina, Graciela E. De Seta, Jorge M. Meichtry, Marta I. Litter and submitted to Water journal as a draft no. 2305716 deals with an important issue of selection and comparison two technologies aimed on arsenic removal.

The article is in journal’s scope. Therefore, it could be considered for publication in Water journal.

As English is not my native language, I am not able to assess language correctness. However, while reading, I found some statements missing, confusing or unclear. Below I enclose the list of my comments.

I have a feeling that there are some formatting issues with the file and the current form is not compatible with template.

In Supplementary Information, I propose to standardize the method of notation of reactions, using superscript for ion charges. I propose not to use fractional stoichiometric coefficients and check all reactions to balance, e.g. S7, S10, etc.

Why in table S1 only 3 metals were mentioned? What about other elements? All properties should be given, as at least citation from [64, 65].

What does the symbol “*” (asterisk) mean in table S2?

Since the removal of As(V) was more effective than As(III), why didn't the Authors use an oxidant to support corrosion, eg hydrogen peroxide, activating the Fenton process? Maybe it's worth trying at least in the course of further research?

What was the source of micron-sized zero-valent iron?

There are some error bars eg. on Fig 1. Information about experiment duplication should be in Materials and methods.

3.1 Why no agitation was used to simulate filtration? Why real filter was not used? I do not understand the idea of this experiment. Fe(0) will just settle down at the bottom of the beaker. The concentration of As should then change in a gradient. How and where were samples taken for As determinations?

I suggest enlarging the figures, in the current version it is difficult to read anything from them.

Fig 1 and 2 what is RT? All abbreviations should be explained at first appearance.

Fig 3: why only 1 measurement for pre oxidation – green line was done?

Fig 3 why only 2 pH values were tested? Other pH values, especially in acidic region, supporting corrosion should be checked.

Why in coagulation pH was adjusted to 7.0?

It is well known that, depending on the coagulant used, different pH values allow optimal removal of impurities. Check the pH at which the process should be carried out and complete it in the article.

The entire Materials and methods chapter needs to be supplemented with detailed descriptions. Not only is the previously mentioned information about the doubling of all experiments missing, but even information about the times of fast and slow mixing for coagulation. There is no word about the sedimentation kinetics of the resulting sludge.

Since the coagulation process commonly used in the preparation of drinking water is 100% effective in removing As (table 3) while clay and Fe are not, as it can be concluded that Fe is a promising method - this needs to be clarified by the Authors.

The dose of 5g of coagulant is unexpectedly large in the case of drinking water preparation. How do the authors explain the use of such a large dose? Even the smallest doses are unexpectedly high. Since the lowest dose of coagulant used completely removed As, why were lower doses not tested? This should be supplemented.

Lines 107-110 -  5x10=50g. I have never heard of using coagulant doses of 50g/L, even in wastewater treatment. Not to mention the preparation of drinking water, where the doses used in practice are orders of magnitude smaller. Please accurately quote the data from the cited references.

Wouldn't it be simpler to oxidize As(III) to As(V) and coagulate it? it is worth conducting such tests and completing the results in the article.

The clay experiment is the use of only 2 doses. why only 2? again what is the point of no agitation?

There is no economic analysis, no costs of running the process.

I have many other doubts, but this list is enough to make a decision. The article needs to be thoroughly supplemented. Due to the fact that the Authors use a model solution, corrections are possible. Based on these comments and overall impression, I suggest a major revision.

 

 

 

 

 

Author Response

Please see the attachment

Author Response File: Author Response.docx

Reviewer 3 Report

Summary

In this study, the authors investigated three different methods, namely, powdered iron (μFe(0)) and iron wool (wFe(0)) treament, coagulation-flocculation with Al2(SO4)3 or FeCl3 treatment, and adsorption with natural clay, to remove the As that presents in fresh water. After the comprehensive study and comparison, the authors identified the Fe(0) treatment is the optimal method. The As pollution is big issue which is needed to be solve, particularly, in a low-cost and house-hold scale. People who live in poor places or off-grid remote places may benefit from this study because their drinking water are poor in quality. In addition, this manuscript is well-written. In this regard, this work is suitable to be published in Water after addressing the following issues.  

List of comments:

1.     For cases of Fe(0) treatments and coagulation processes, the As ions were removed but the side effects or by-products such as Fe ions and Al ions are introduced into the treated water. The excessive amount of Fe and Al present in drinking water is harmful as well. It means you solve one issue and create another issue. Please clarify and discuss this dilemma.

2.     As mentioned by the authors, the presence of other species or ions may and can affect the As removal. Have you used the real As contaminated water to perform the experiments and study their effects?

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

This is my second review of this article. The Authors answered all of my questions comments. Suggested corrections have been applied. Second version of the manuscript is better than the first one.

However, there are still some minor technical issues to be solved. There are errors in the reactions added to the article. An example would be reactions S5 or S10. This should be corrected before publication.  These are technical issues that can be corrected at the stage of editing the final version for publication. For this reason, I suggest you accept this article for publication.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf