Modified Lignocellulosic Waste for the Amelioration of Water Quality: Adsorptive Removal of Congo Red and Nitrate Using Modified Poplar Sawdust

Round 1

Reviewer 1 Report

The presented manuscript “Modified lignocellulosic waste for the amelioration of water quality: Adsorptive removal of Congo Red and nitrate using modified poplar sawdust”, is devoted to the removal of dye and nitrate from waters, using an effective adsorbent based on an available and cheap material- poplar sawdust. The topic and results are very meaningful solving of increasingly serious problems about resources and the environment.

The manuscript may be accepted in “Water” after major revision according to following remarks:

1.      The authors presented the Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray (EDX) spectra in Fig. 1. The content of the main elements obtained by EDS analysis should be presented (in at. % or wt %) in a separate table.

2.      According to the adsorption-desorption isotherm of nitrogen for mPWS (Supplementary) adsorbed amounts are extremely low, and such an isotherm is not suitable for discussion of the specific surface area (S_BET) by the method of Brunauer, Emmett, and Teller (BET) and pore size determination. Adsorption/desorption isotherms of nitrogen should be deleted and discussion about pore structure analysis (page 6) should be rewritten using only Mercury Intrusion Porosimetry (MIP) results.

3.      In order to examine the stability and potential regeneration of the adsorbent as well as the mechanism of adsorption, desorption studies should be conducted.

4.      Which pH value was chosen for adsorption experiments and why? Whether the influence of pH value on adsorption capacity was examined?

5.      The discussion can be improved by comparing the obtained adsorption results with the capacities of some similar materials (with adequate references).

6.      There are some mistakes in the numbers of tables and figures. The authors should check the whole text carefully.

Author Response

The authors would like to thank the reviewer 1 for the kind assessment of our manuscript. Please find enclosed the point-by-point replies to the comments regarding the manuscript Water-2641393.

Author Response File: Author Response.pdf

Reviewer 2 Report

In this paper, Velić et al. report the use of a modified poplar sawdust for the removal of Congo Red and nitrate through an adsorption process. In my opinion, the paper can be accepted for publication after Major Revision, and addressing the following questions.

1-      It would help the readers if a brief explanation about lignocellulose is added to the abstract.

2-      The authors claim the development of a low-cost, sustainable purification system. However, in the experimental section they explain the use of N,N-dimethylformamide, ethylenediamine, and triethylamine. Are these solvents toxic? What is their biodegradability? Were the solvents recycled after the treatment steps? This requires further explanation.

3-      The authors mentioned that a pH meter was used to keep the pH at the native value. What was the native pH value of the solution? This value should be reported.

4-      pH is a very important parameter that affects the adsorption behavior of an adsorbent. The effect of changing this value must be reported.

5-      The isoelectric point of the adsorbent should be measured to study the surface charge of the adsorbent, which directly influences its adsorption behavior. And, the mechanism proposed in Fig. 6 is dependent on the pH value and the surface charge of the adsorbent.

6-      What is the importance of studying adsorption kinetics and isotherm? This should be explained before explaining the results.

Author Response

The authors would like to thank the reviewer 2 for the kind assessment of our manuscript. Please find enclosed the point-by-point replies to the comments regarding the manuscript Water-2641393.

Author Response File: Author Response.pdf

Reviewer 3 Report

Reviewer’s comments on the manuscript: Modified lignocellulosic waste for the amelioration of water quality: Adsorptive removal of Congo Red and nitrate using modified poplar sawdust written by Natalija Velić et al.

The reviewed manuscript concerns  adsorptive removal was investigated using a novel biosorbent (mPWS) obtained by modifying poplar (waste) sawdust through quaternisation. Characterisation of mPWS included SEM /EDX, FTIR, BET and MIP analysis was presented. Adsorption of Congo Red and nitrate on mPWS was studied in a batch system as a function of contact time, biosorbent concentration and initial adsorbate concentration. In all experiments, a high removal of both adsorbates from 60 to over 90% was achieved. The manuscript presents qiute interesting data having high application potential. It offers valuable insights into the practicalities of using chemically modified poplar sawdust for water treatment. The data are presented clearly and obtained using variety of analytical techniques. However in the reviewer’s opinion major revision is required.

-          change keyword “poplar sawdust” into “sawdust”.

-          line 68: one extra space.

-          lines 81-85: please add reference to the text: “Poplar sawdust, a wood industry byproduct, stands out due to its wide availability, renewability, and unique structure conducive to absorption and modification. However, despite its potential, it suffers from a few limitations such as hydrophobic nature and limited active sites which might restrict its efficiency as an adsorbent in its raw form.”

-          all text: Please decide if you it should be Congo red or Congo Red.

-          all text: Number and its unit should be always in the same line.

-          line 116: The summary formula of Congo Red is wrong.

-          lines 116, 117 and further: The molecular weight of a chemical compound is not a dimensionless. Please add the missing units.

-          Table 1: Since the concentrations of adsorbates differed significantly and pH is one of the factors influencing the adsorption process, I believe that the pH of the tested systems should be measured and its values accurately reported.

-          Fig. 1: In my opinion, the results of SEM-EDX analyzes are better presented numerically in a table. However, authors can keep the figures if they change it to a universally acceptable form (white background, not blue, and dark numbers and axes, not white). Fig. 1 should be presented in the same way as others figs in the manuscript.

-          Fig. 2: I would like to ask about the band around 1700 - 1750 cm^-1 on the PSW spectrum. What is it? There is no such band on mPSW.

-          Table 2: Please add some information about measurements uncertainties. The same comment Fig. 4.

-          line 238: One extra dot.

-          pages 9-11: (3.3. Isotherm and kinetic modelling of the experimental adsorption data). This part of the text is definitely not a discussion of the results, but a theoretical introduction. The information presented is quite basic and commonly known information about adsorption isotherms and their modeling, this part of the text could be moved to the supplement or significantly shortened to the introduction.

-          I would like to encourage the authors to change Fig. 6. It contains very important information, but it looks quite strange with this fragment of the adsorbent photo in the middle.

Author Response

The authors would like to thank the reviewer 3 for the kind assessment of our manuscript. Please find enclosed the point-by-point replies to the comments regarding the manuscript Water-2641393.

Author Response File: Author Response.pdf

Reviewer 4 Report

Dear author

My suggestions are made in the manuscript.

Thanks.

The referee

Comments for author File: Comments.pdf

Dear Editor

I must say that it is a surprise for me to review a manuscript with a subject already covered by other authors, previously, in Water Journal. For example, the article titled "From Waste to Biosorbent: Removal of Congo Red from Water by Waste Wood Biomass" was published in 2020 in Water. Link: https://doi.org/10.3390/w13030279.

Thus, if one of the criteria for accepting a manuscript for publication in Water Journal is novelty, I did not find it in this manuscript.

Furthermore, there are many imperfections (chemical and mathematical analysis)  in the manuscript that make me refuse to publish it,  I added them all in the manuscript.

Thanks.

The referee

Author Response

The authors would like to thank the reviewer 4 for the kind assessment of our manuscript. Please find enclosed the point-by-point replies to the comments regarding the manuscript Water-2641393.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

I see a lot of improvement comparing to the first version of the manuscript. But the major shortcoming is related to the Table 5. Adsorption capacities of biosorbents made from poplar sawdust. In order to explain the effectiveness of used poplar sawdust, the adsorption capacity should be compared with the capacities of some other adsorption materials for adsorption of Congo Red and nitrate not with the capacities for different adsorbates.

Author Response

Dear Reviewer,

Thank you very much for reviewing our manuscript. Your constructive advice has greatly improved the quality of it.

We have expanded Table 5 to include other adsorbents that have proven to be successful in removing CR and NO3.

On behalf of all authors, sincerely,

Marija Stjepanović

Author Response File: Author Response.pdf

Reviewer 2 Report

The authors have addressed all the comments in a thorough manner. Consequently, I am of the opinion that the manuscript can be accepted for publication in its current state.

Sincerely,

Author Response

Dear Reviewer,

Thank you very much for reviewing our manuscript. Your constructive comments have greatly improved the quality of it.

Just a short note: we have expanded Table 5 to include other adsorbents that have shown to be effective in removing CR and NO3.

On behalf of all authors, sincerely,

Marija Stjepanović

Author Response File: Author Response.pdf

Reviewer 3 Report

Dear Authors,

The changes that you have been made in the mansucript are satisfactory.

Thank you and good luck.

Reviewer

Author Response

Dear Reviewer,

Thank you very much for reviewing our manuscript. Your constructive comments have greatly improved the quality of it.

Just a short note: we have expanded Table 5 to include other adsorbents that have shown to be effective in removing CR and NO3.

On behalf of all authors, sincerely,

Marija Stjepanović

Author Response File: Author Response.pdf

Reviewer 4 Report

Dear author

After manuscript's revision, I believe that your manuscript is enough good to be submitted on the Water journal.

Thanks.

The referee

Author Response

Dear Reviewer,

Thank you very much for reviewing our manuscript. Your constructive comments have greatly improved the quality of it.

Just a short note: we have expanded Table 5 to include other adsorbents that have shown to be effective in removing CR and NO3.

On behalf of all authors, sincerely,

Marija Stjepanović

Author Response File: Author Response.pdf