Optimization of Chitosan Surface Response Methodology (Natural and Commercial) Used for Chromium Ion Removal from Wastewater across Different Parameters
Round 1
Reviewer 1 Report
In this work, commercial and prepared natural chitosan was treated, and applied for the removal of Cr6+ in the water solution across studying the effect of different variables, and isotherm, and kinetic models of the adsorption process were considered. And, adsorption capacity with different factors such as time, concentration, and temperature using Box-Behnken Design (BBD) was studied. I think it needs a minor revision before it is accepted.
- Authors can re-think about the title of the manuscript.
- The English of the manuscript should be carefully polished, and some expression should be improved.
- A lot of data about prediction analysis was disclosed, hence the significance, necessity and relevant works should be added in Abstract.
- The research background is not well summarized, so the “Introduction” of this manuscript should be reorganized. Flotation may be an effective method for the removal of Cr6+ in the water solution, and it has been widely used in the efficient recovery of minerals, solid waste, heavy metal ions in water, etc. Thus, several relevant references should be added to the “Introduction” section of your manuscript to support this point, such as Miner. Eng. 169 (2021) 106982.
- The authors should explain why chitosan was chosen in this work.
- A flowchart could have been added to the article to show the research methodology.
- It is suggested to compare the results of the present research with some similar studies which is done before.
Author Response
"Please see the attachment"
Author Response File: 
Author Response.pdf
Reviewer 2 Report
While the topic is interesting, the manuscript has many grammatical errors. I recommend it is revised by a native English writer or someone with better English writing experience; some sentences are very difficult to understand the authors' intent.
Authors must carefully check the manuscript for typographical and grammatical mistakes. Do not put a space before commas and full stops. Put space after them.
Line 38: what is CrO42-
What percentage of chitosan is contained in shrimp’s shells?
Line 95: What do you mean with 2wt%?
Do not use first person (we, our, us) in text (lines 15, 26, 245, 306, 362).
The section 2.2 Preparation of grafted (commercial and natural) chitosan is confused and difficult to understand. Use 2 different subsections to describe separately the preparation of grafted commercial (2.2.1) and natural chitosan (2.2.2). This way, it will be easy and clear to understand.
Line 99: Convert to SI units 0.12 M. Generally use a uniform way of unit expression.
Lines 114-115: at 30◦C instead of…. at temperature of (30◦C).
Line 116: at different concentrations of which?
Line 117: There is not any reference in Materials and Methods section about the different adsorbent doses and pH.
Line 129: Put the title of the section 2.5 in bold
Line 238: what is 1gm?
What is the difference between commercial chitosan and grafted commercial chitosan?
Author Response
"Please see the attachment"
Author Response File: Author Response.pdf
Reviewer 3 Report
The paper deals with Cr(VI) removal by commercial and natural Chitosan and also with modified commercial and natural Chitosan. Prior to this paper, numerical studies, for instance, https://doi.org/10.1016/j.seppur.2012.12.028, have been carried using a variety of Chitosans for Cr(VI) removal. Thus in this paper, the modification done on Chitosan as a base material is a repetition in my opinion. Further, the Cr(VI) concentrations used from 20-100 mg/L, whereas, the total Cr(VI) concentrations encountered in groundwater are in the range 50-1000 microgram/L. Hence, the study does not have practical relevance. In addition, Figure 1(D) shows that the adsorption behavior of all four adsorbents based on Chitosan is the same. Also, Language shall be improved. This is a must since some phrases in the manuscript contain some grammatical and writing mistakes and are even incomplete, for e.g., lines 19-20.
Author Response
"Please see the attachment"
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
The authors responded to the authors' comments and revised the manuscript so it is accepted in present form.
