Enhanced Nitrate Nitrogen Removal from Wastewater Using Modified Reed Straw: Adsorption Performance and Resource Utilization

Round 1

Reviewer 1 Report

This paper describes a method to remove nitrate nitrogen (NN) using modified reed straw (MRS). A series of characterization were performed to demonstrate the dynamic adsorption capacity of MRS for a maximum NN 14.76 mg/g. The authors also demonstrated the recycled use of these NN in promoting plant growth. In general, I find this work interesting and worth publishing. However, I do have some concerns which are needed to be addressed before its acceptance.

11.   Page 1, line 25, the first term “Nitrate (NO3--N)” has two dash line. Is this correct?

22.   Page 2, line 66 to 71, what are the purity level of all the purchased chemicals?

33.   Page 4, figure 1, I believe these images were generated from the SEM software. Image quality is fine, however the bottom parameters are beyond my eyesight. I suggest either remove these too small to be seen parameters, or present the images with clear texts.

44. Page 5, figure 2, the “1240 cm^-1” peak line is too far away the 1250 cm^-1 axis tick. Are the authors sure about the reading?

55.  Page 6, figure 3, the XPS data simply doesn’t make sense to me. The top C-N is marked 400.2 eV, which is clearly off the mark. And I don’t believe the other two C-N peak readings are correct either. The authors need to double check the XPS data.

66.  Page 8, table 1. I understand that the authors want to demonstrate the goodness of the model fitting using R² value. However, simply listing R² from the least-square fitting doesn’t provide this information with confidence at all. I can tell the goodness of the fitting by looking at the overlapping of the fitting curve and raw data. Listing R² data only make readers confused about the meaning of these data.

77.  Page 10, figure 6. This figure needs redraw. The quality of these figures are not consistent with the others.

88.  Page 12, figure 7. This figure panel is so confusing. First, I don’t understand the legend in (a). Second, what is the point of green and yellow color? At first glance, I though they are from a single variable data set, then I found that was not the case. And what do “a” and “b” mean?

99.  Following last comment, I can see the error bars on the corresponding data. But where do these statistical information come from?

Author Response

Thank you for your valuable suggestions. Please refer to the attachment for our response to your suggestions.

Author Response File: Author Response.pdf

Reviewer 2 Report

This work reported the use of NaOH modified reed biomass as adsorbent to removal aqueous NO3-. Both batch and column experiments were performed to evaluate the adsorption capacity. The material was characterized using SEM, XRD, FTIR, and the NO3- loaded material was also analyzed. Obviously, the topic is not new, since acid/alkali modification of biomass has been intensely reported in literature. However, this work is a comprehensive study including both batch and column experiments, analysis of mechanisms, and the desorption process. Therefore, I think this work may be considered after major revisions.

The specific comments are as follows:

1. The background of the use of reed biomass should be intensely introduced in the introduction section.

2. Further, the use of NaOH treatment of reed should also be introduced to highlight the novelty of this work.

3. In the batch experiments, several factors that affect the adsorption of NO3- were ignored in the present work. Such as the effect of pH, adsorbent dosage, coexisting competing anions, should be studied.

4. In the adsorption kinetics experiments, only one NO3- concentration was considered, which was very poor. Generally, different concentrations of NO3- should be studied in the adsorption kinetics.

5. The adsorption mechanisms should be discussed in a separate paragraph, and the possible mechanisms should be inferred and combined in a figure.

6. In the dynamic adsorption experiments, Fig. 6 is not clear and should be re-drawed. And the desorption and reuse of adsorbents should be considered.

 7. Adsorption data did not contain error bars, experiments should be repeated.

Overall, it is not acceptable in the present form, significant revisions are needed.

Author Response

Thank you for your valuable suggestions. Please refer to the attachment for our response to your suggestions.

Author Response File: Author Response.pdf

Reviewer 3 Report

Dear Authors, 

Very interesting article. Great experiment, very relevant.

A few observations:

1. The formatting of the article is very bad. Text must be formatted in Justufy. No need for tares between faragraphs.

2. Literature sources are listed incorrectly in the text - they must be of normal size like the text.

3. There is no statistical data processing methodology.

4. The title of Figure 7 must not be bold.

5. It is not clear what is on the x-axis in Figures 7 b - 7 d.

6. The discussion is missing.

Author Response

Thank you for your valuable suggestions. Please refer to the attachment for our response to your suggestions.

Author Response File: Author Response.pdf

Reviewer 4 Report

The manuscript provides interesting results with applicable potential. However, several issues must be improved before potential publication in the journal. The main issue is a poorly organized discussion. Moreover, the experiment setup description and the motivation of the chosen plant must be improved. The specific comments to the authors You find in the attached file.

Comments for author File: Comments.pdf

Author Response

Thank you for your valuable suggestions. Please refer to the attachment for our response to your suggestions.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

All my concerns have been addressed. I recommend its acceptance now.

Author Response

Thank you for your valuable input!

Reviewer 2 Report

The paper has been improved. however, comment 5 was not clearly replied.

5. The adsorption mechanisms should be discussed in a separate paragraph, and the possible mechanisms should be inferred and combined in a figure.

Author Response

Thank you for your valuable suggestions. Please refer to the attachment for our response to your suggestions.

Author Response File: Author Response.pdf

Reviewer 3 Report

Dear Authors, 

In my opinion, the article has been supplemented and corrected according to the comments. May be published.,

Author Response

Thank you for your valuable input!

Reviewer 4 Report

The authors responded adequately to most of my critical comments. However, I am not satisfied with the discussion of the obtained results. The authors still omitted the discussion about the novelty of this study in contrast to the others. They responded that they cited two types of study but they still have not discussed it results thus it does not satisfy me enough. Thus, I still recommend some minor revisions to the discussion of this study.

Author Response

Thank you for your valuable suggestions. Please refer to the attachment for our response to your suggestions.

Author Response File: Author Response.pdf