Spent Coffee Ground-Based Materials Evaluated by Methylene Blue Removal

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Title: Spent coffee ground-based materials evaluated by methylene blue removal

Manuscript ID: processes-3609751 Journal Name: Processes My comments are given here 1. In abstract also add results of characterization techniques briefly. 2. In introduction you have given "Acetylation, KOH and HNO3 treatment of SCG, evaluated in this study, according to our literature review, haven’t been reported". Revise this sentence. 3. Give state of the art introduction. Give common toxicities of dyes and then focus the toxicity of your MB dye. Also cite these articles. "Water stable graphene oxide metal-organic frameworks composite (ZIF-67@ GO) for efficient removal of malachite green from water"   "Fabrication of CuWO4@ MIL-101 (Fe) nanocomposite for efficient OER and photodegradation of methylene blue". 4. In introduction you have given different methods applied to remove MB and which method you have applied to remove this dye and why? Also discuss in introduction. 5. In water extraction section Time is not mentioned? Briefly describe the procedure with details. 6. In acetylation section Give percentage and Molarity of sulfuric acid. 7. In section 2.3.1 you have given "After this time the sample was left idle for 12h and the water was removed by distillation". Here check carefully water removed by distillation of filtration. 8. In the same section you have given "The obtained material was neutralized with sodium bicarbonate 10% solution".  Briefly give procedure. 9. Give reference for equation used in manuscript. 10. Label the functional groups in the FTIR spectrum. 11. It is good to add FTIR after adsorption of MB to explain adsorption mechanism. 12. In Table 2 Also add other factors like time, pH, concentration and models etc. 13. Explain adsorption mechanism with diagram.
Effect of concentration, pH, Time , regeneration, temperature is not given in the manuscript.

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript here is a fascinating and timely investigation on methylene blue removal from aqueous environments by spent coffee grounds (SCG) as a biosorbent. The experimental design is extensive with different techniques for cleaning and chemical amendment, and data reported are applicable. The manuscript is, nonetheless, affected by various fundamental flaws regarding experimental justification, characterization thoroughness, statistical analysis, and overall congruence between claims and evidence. These flaws need to be resolved for this paper to qualify for publication in Processes.

List of Comments:

1. The abstract needs to emphasize better the novelty of the chemical treatments, e.g., first use of HNO₃/KOH on SCG, and also the application perspectives of the findings, e.g., possibility to use them in real-life wastewater treatment systems. Quantitative data for chemically treated SCG must also be provided, and it has to be stated clearly that treatments with KOH/HNO₃ result in as much as a threefold increase in adsorption capacity.
2. There is also a need to include a brief discussion of the costs/benefits or energy consumption of these methods compared with hot water washing. Although the environmental problem is adequately framed, there is little justification for preferring ASE, SFE and US as cleaning methods. These methods are expensive and only marginally improve on the adsorption efficiency, and the authors should better justify including them.
3. It is not stated whether or not the adsorption tests were replicated. The paper needs to indicate how many replicates were run for all adsorption tests and state whether mean values and standard deviations are given. Although FTIR and SEM utilization is welcome, the research is missing very vital surface characterization information, in this case: BET surface area and pore volume and distribution.
4. While the analysis is comprehensive, the relatively low difference in qmax values among SCG-H₂O and other treatments leaves one wondering about the need for these treatments. A table or bar chart with comparative costs, energy use, and efficiency would provide justification for their utilization or rationale for making simpler treatments a priority.
5. In sections 3.2–3.4, the large increase in qmax, especially for SCG-HNO₃, is not adequately accounted for, particularly with relatively low values for R² and χ². Perhaps consider addressing possibilities for how surface heterogeneity would impact isotherm model fit.
6. Show the standard deviations or error bars on all graphs of the adsorption isotherm, as in Figures 4 and 5: include the error bars on the data points, while in Table 1 specify whether the values are mean ± standard deviation.
7. For added strengths in its introduction, it would be suitable to emphasize recent developments in non-toxic and sustainable solvents in membrane technologies for applications involving removal of dyes (DOI: 10.3390/polym13152579). This would fit into a larger context of advocating sustainable alternatives to traditional materials.
8. The existing arrangement of SEM images in Figure 2 seems to be aesthetically unbalanced and may interfere with comparative examination. I would like to propose rearranging the figure as three rows with two images in each row ((a)–(f)), with image (g) placed in a centered fourth row. This would provide better visual balance as well as clarity for reading.

Comments for author File: Comments.pdf

Author Response

Reply attached

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Accept the paper.

Reviewer 2 Report

Comments and Suggestions for Authors

I would like to thank the authors for their comprehensive revision of the manuscript. The revised version answers the main issues earlier brought forth in the previous review, especially on the justification of treatment techniques, presentation of adsorption data, and general organization of figures and citations. The new figure design, better statistical clarity, and expanded discussion of the chemical treatments greatly enhance the readability and scientific usefulness of the manuscript. One small comment: in Tables 2 and 3, the column titles straddle two lines for some of them, which makes them look unattractive on the page. My preference would be to reformulate the titles or break them up with spaces or abbreviations so that they appear on one line, where possible.