Nickel (Ni2+) Removal from Water Using Gellan Gum–Sand Mixture as a Filter Material
Round 1
Reviewer 1 Report
This manuscript did a good job in investigating heavy metal adsorption capacities of a gellan gum biopolymer-sand mixture with different gellan gum contents treating contaminants at different flow rate. After moderate revisions, it will be a valuable contribution to the studies of soil treatment and ground improvement.
Specific comments:
P10 line 251-252 “The difference in the amount of … GG content” should consider the flow rate of the contaminated water.
“The potential Ni2+ absorbability of 1m3 was suggested”: more details about how to come to this conclusion will be very helpful.
Besides, more discussion about how to use this mixture as hydraulic barrier material would be a great improvement for this paper.
Author Response
Please see the attachment
Author Response File: 
Author Response.pdf
Reviewer 2 Report
- Line 81, change to "barrier liner (HBL) of 0.0, 0.5, 1.0 and 2.0 %,
- Lines 163-164, change to "Figs. 4b and 4c show"
- Lines 169-177, qmax is an important parameter. Explain how qmax was defined based on the experimental results, such as those shown in Fig. 4a.
- Line 181, change to "Table 3."
- Line 189-196, explain the implication of C (Carbon?) and O (oxygen?) peak increases as seen in Figure 6.
- Figure 5, indicate GG content for this experiment
Author Response
Please see the attachment
Author Response File: Author Response.pdf
Reviewer 3 Report
The topic of the manucript is interesting from theorethical and
ecological point if view. It describes a method for Ni2+ removal from
water samples.
However the described methos was tested only with standart nickel solutions.
To make the study more valuable, I would suggest to provide results from real
astewate samples.
I suppose that the process if nickel removal will depend on its speciation.
In addition, the following corrections need to be made:
Page 3, row 80 - delete are
Page 4, rows 107-108 - replace is with was
Page 4, row 104 - I would suggest to replace flowrate with flow rate in Table 2 and everywhere in the text
Page 5, row 146- use standard instead standardized
Page 7, row 181 - I suppose, it should be Table 3
Author Response
Please see the attachment
Author Response File: Author Response.pdf
Round 2
Reviewer 3 Report
Dear Authors,
Thank you for complying with some of my comments.
I have also suggested to test the method and provide results for Ni2+ removal from real wastewater
samples. I did not mean other types if chemical pollutants?
As a result you added that "Implemented in-situ GC-treated sand layers (or barriers)
are expected to enhance the ground strength in therms of shear strength and bearing capacity,
as well as reducing the ground water flow and adsorbing hazardous
Ni2+ from contaminated ground water."
I really recommend to confirm this statement with data for real contaminated
with Ni2+ water. This will show the possibility for the application of the method
for real samples and contribute much more interest on the study.
Author Response
Authors understand the Reviewer’s concern, and apologies for the inappropriate response in our prior rebuttal.
Authors want to ask Reviewer’s understanding on the difficulty of conducting new experimental programs using a new material (real waste water). The authors understand that the Reviewer wants us to prove the removability of Ni2+ from a wastewater sample. In our previous answer (Round 1), we wanted to emphasize that wastewater does not contain only Ni2+. Wastewater contains so many other heavy metal ions which may have different adsorption mechanisms with gellan gum.
In this study, Authors mainly address and regard this study as a preliminary attempt to assess the feasibility of gellan gum biopolymer for heavy metal adsorption and removal from water. Thus, instead of including additional experimental data, we are suggesting and emphasizing the importance of advanced further research.
Regarding the statement "Implemented in-situ GC-treated sand layers (or barriers) are expected to enhance the ground strength in terms of shear strength and bearing capacity, as well as reducing the ground water flow and adsorbing hazardous Ni2+ from contaminated ground water.”, it was the answer for another Reviewer who asked how gellan gum-treated sand is used as a hydraulic barrier material. The author thought that our answer to the Reviewer would have been more apparent if we had put it in a whole paragraph. Authors feel sorry if it misleadings you.
Since the shear strength, bearing capacity, and hydraulic conductivity were not tested in this study, the authors decided to cite references (Chang and Cho 2019 [14] and Chang et al. 2016 [9] in the revised manuscript as:
(Lines 287-297)
“This study aimed to remove a concerned heavy metal with two valence electrons, nickel (Ni2+), using GG-treated sand. One of the biggest advantages of the newly suggested GG-sand material is that it can be easily implemented in field via direct mixing (e.g., GG-soil column mixing using an auger) or ground injection (e.g., GG solution grouting into porous ground). Implemented in-situ GG-treated sand layers (or barriers) are expected to enhance the ground strength in terms of shear strength and bearing capacity [14], as well as reducing the ground water flow [9] and adsorbing hazardous Ni2+ from contaminated ground water. In order to enhance the practical feasibility of the investigated GG-treated sand material into practice, further studies are requested to consider other types of heavy metals and actual wastewater that contains different kinds of chemical pollutants.”
Round 3
Reviewer 3 Report
Dear Authors,
My proposal was to apply the developed method by standard nickel solutions to a sample of wastewater, which in my opinion is not a “new experimental programs” . It is application of a theoretical approach in practice, which makes sense of its development.
I think it is not time consuming to check the concentration of nickel in wastewater before and after treatment. The yield could also be checked by a standard addition method.
As far as the presence of other metals is concerned, a large number of other metals may be present in wastewater at much higher concentrations than nickel, but this cause no difficulty for nickel determination by ICP-OES, except that the presence of matrix and spectral interferences must be taken into account.
In conclusion, I believe that without data for real sample treatment, the work is not complete, would not be of interest and is not ready for publication.
Author Response
Dear Reviewer
Authors totally understand your concern. As you can recognized the variety of the Authors affiliation, the experimental program described in this study has been mainly conducted by the 1st and 2nd authors during their Ph.D. studies at KAIST. Now they have graduated and moved to their own institution as an independent researcher. As the Corresponding Author of this submission, I totally agree with your viewpoint about the importance of conducting verification on real wastewater. However, we also want to ask the Reviewer’s kind understanding on the difficult situation for conducting a new experimental program at this stage.
Indeed, real wastewater contains different kinds of chemical pollutants including heavy metal cations, hydrocarbons, pesticides, nitrogenous compounds, pharmaceutical residues, detergents, and phosphorus. Conducting the removal test with actual wastewater right now is thought to be overburdened for a newly suggested gellan gum – sand.
For this study, the authors first wanted to see the mechanism inside this new material (GG-sand) as it contacts heavy metals with two valence electrons like nickel. Once this study is successfully published to the academia field, then further studies will be conducted for more heavy metal types and actual wastewater.
The authors think it would be better if we emphasize the thought mentioned above in the Discussion section. The manuscript has been revised as:
(Lines 287-296)
This study aimed to remove a concerned heavy metal with two valence electrons, nickel (Ni2+), using GG-treated sand. One of the biggest advantages of the newly suggested GG-sand material is that it can be easily implemented in field via direct mixing (e.g., GG-soil column mixing using an auger) or ground injection (e.g., GG solution grouting into porous ground). Implemented in-situ GG-treated sand layers (or barriers) are expected to enhance the ground strength in terms of shear strength and bearing capacity [14], as well as reducing the ground water flow [9] and adsorbing hazardous Ni2+ from contaminated ground water. However, in order to bring GG-treated sand into practice, further study needs to be considered for other types of heavy metals and actual wastewater that contains different kinds of chemical pollutants.
