Removal of Tetracycline from Water by Biochar: Mechanisms, Challenges, and Future Perspectives

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Summary and general comments

 

This review manuscript compiles the use of biochar for the removal of antibiotic tetracycline. While the work is easy to understand, there are a few major errors and a lot of minor errors. Please see the specific comments below for details.

 

Specific Comments

1. Keywords are too general and should be more focused.
2. There are Chinese characters observed in some sections of the manuscript, e.g. Table 1. The language should be consistent and uniform
3. What is the knowledge gap that this review manuscript is addressing?
4. Section 2. Line 110. Authors need to distinguish the differences between biochar and activated carbon. While biochar and activated carbon are similar, but they are different. ZnCl2 is used to treat biomass, and then pyrolysed is the chemical activation that produces activated carbon instead of biochar. These errors should not be propagated.
5. Many of the following examples are chemical activation of biochar. Perhaps activated carbon would be a more suitable title than biochar.
6. As this manuscript is a review manuscript, the description of the measurement of the performance of the activated carbon using “adsorption capacity” and “% removal” should be mentioned. It will be better to provide the equations as well.
7. Line 224-227. An unrealistic value with an adsorption capacity of 1174 mg/g was reported. Upon inspection, the source reported a qm of only 174 mg/g. This kind of error must be avoided.
8. Table 2. If the unit is already given in the first row, so there is no need to repeat in every row. Also, some numbers were out of alignment. The decimal points were not consistent.
9. Table 2 is difficult to understand. There is a “qmax” before and after column.
10. Other minor errors: The scientific name of biological species should be italicised. The chemical formulas are not properly formatted.

Author Response

Reviewer #1: General comments

This review manuscript compiles the use of biochar for the removal of antibiotic tetracycline. While the work is easy to understand, there are a few major errors and a lot of minor errors. Please see the specific comments below for details.

1. Keywords are too general and should be more focused.

Answer: We thank the reviewer for this insightful suggestion. We have revised the keywords to increase their specificity and ensure that they better reflect the core contributions and scope of our study. The updated keywords now emphasize the key methodologies, novel findings, and specific context of our research as follows:

Original keywords: [Wastewater treatment; Organic pollutants; Biochar modification; Adsorption; Scale-up applications]

Revised keywords: [Medical and livestock wastewater; Tetracycline; Biochar; Adsorption mechanisms; Practical application challenges]

1. There are Chinese characters observed in some sections of the manuscript, e.g., Table 1. The language should be consistent and uniform

Answer: We sincerely apologize for this oversight and appreciate the reviewer’s attention to detail. We have thoroughly reviewed the manuscript and ensured that all content, including tables, figures, and text, adheres to a consistent and uniform language (English) throughout. Specifically:

All Chinese characters in Table 1 (and any other sections) have been replaced with their English equivalents or removed if redundant.

We have double-checked captions, labels, and supplementary materials to confirm linguistic consistency.

1. What is the knowledge gap that this review manuscript is addressing?

Answer: We thank the reviewer for these suggestions. We have revised the Introduction section, and some sentences were revised to clarify the research gap that the manuscript was intended to fill at L85–91.

1. Section 2. Line 110. Authors need to distinguish the differences between biochar and activated carbon. While biochar and activated carbon are similar, but they are different. ZnCl2 is used to treat biomass, and then pyrolysed is the chemical activation that produces activated carbon instead of biochar. These errors should not be propagated.

Answer: We thank the reviewer for raising this distinction. Our use of "biochar" aligns directly with the terminology used in reference [38], whose authors described identically prepared ZnCl₂-activated pyrolyzed material as 'biochar'. We acknowledge the importance of precise terminology and will apply this distinction more rigorously in future work.

1. Many of the following examples are chemical activation of biochar. Perhaps activated carbon would be a more suitable title than biochar.

Answer: We appreciate the reviewer's suggestion. We have retained the term "biochar" throughout the manuscript to maintain consistency with the specific terminology used in the foundational literature describing these ZnCl₂-activated, pyrolyzed materials. While we acknowledge that the activation process enhances the material's properties, the cited source authors explicitly classify the resulting material as 'biochar'. We believe that this consistent nomenclature facilitates direct comparison with their work.

1. As this manuscript is a review manuscript, the description of the measurement of the performance of the activated carbon using “adsorption capacity” and “% removal” should be mentioned. It will be better to provide the equations as well.

Answer: We thank the reviewer for this valuable suggestion to enhance clarity. The definitions of "adsorption capacity" and "% removal" have now been explicitly described in the main text (Lines 203–204). The corresponding equations have been added to the Supplementary Material to maintain readability while ensuring full methodological transparency for readers.

1. Line 224-227. An unrealistic value with an adsorption capacity of 1174 mg/g was reported. Upon inspection, the source reported a qm of only 174 mg/g. This kind of error must be avoided.

Answer: We sincerely apologize for this critical error and deeply appreciate the reviewer’s meticulous scrutiny. As highlighted, the manuscript incorrectly cited an adsorption capacity (qₘ) of 1174 mg/g in Lines 224–227, which has now been corrected to 174 mg/g in the revised version (Lines 182–187). In addition, we also verified the data throughout the text to ensure that they were correct.

1. Table 2. If the unit is already given in the first row, so there is no need to repeat in every row. Also, some numbers were out of alignment. The decimal points were not consistent.

Answer: We appreciate the reviewer’s careful evaluation of Table 2 and apologize for the formatting issues. The following revisions have been implemented to address these concerns: units (e.g., "mg/g") have been removed from subsequent rows and retained only in the column header for clarity and conciseness.

1. Table 2 is difficult to understand. There is a “qmax” before and after column.

Answer: We appreciate the reviewer’s feedback and apologize for the confusion. We have revised the expression in the table to clarify these points.

1. Other minor errors: The scientific name of biological species should be italicised. The chemical formulas are not properly formatted.

Answer: We thank the reviewer for their meticulous review. All scientific species names have been italicized, and chemical formulas have been properly formatted throughout the manuscript.

Reviewer 2 Report

Comments and Suggestions for Authors

1. Provide more qualitative information in abstract
2. Novelty, Scope, Aim and Objective of the research is missing - Add in last para of the intro part
3. Provide S.No in Table 1 - add more explanation for table 1
4. Interpretation of the result is missing throughout the manuscript
5. These strategies enable precise control of the surface properties of biochar, making it highly effective for environmental remediation applications - This sentence is not meaningful - rewrite the meaningful.
6. Table 2 need more explanation
7. Figure 3 need high quality - add more explanation
8. There is no quantitative information found in the conclusion - revise it
9. Add recently published manuscript related to your research 

Author Response

Reviewer #2:

1. Provide more qualitative information in abstract

Answer: We appreciate the reviewer’s suggestion to enhance the qualitative depth of the abstract. In response, we have revised lines 21–26 of the abstract to incorporate a richer qualitative context. These additions aim to highlight the study’s contributions beyond quantitative outcomes, ensuring that the abstract better reflects the study’s significance and broader impact.

2. Novelty, Scope, Aim and Objective of the research is missing - Add in last para of the intro part

Answer: We thank the reviewer for these suggestions. We have revised the Introduction section and added the novelty, scope, aim and objective of the manuscript at L85–91.

3. Provide S.No in Table 1 - add more explanation for table 1

Answer: We thank the reviewer for these suggestions. The serial number has been added to Table 1, and expanded explanations of the table's content have been incorporated into the main text (line 57) to enhance clarity.

4. Interpretation of the result is missing throughout the manuscript

Answer: We sincerely appreciate the reviewer’s insightful feedback. We have revised the manuscript to address this gap. Specifically, we have added detailed interpretations and discussions of the key findings in lines 425–446, where we now explicitly clarify the implications of the results, relate them to literature, and highlight their significance for the field.

5. These strategies enable precise control of the surface properties of biochar, making it highly effective for environmental remediation applications - This sentence is not meaningful - rewrite the meaningful.

Answer: We thank the reviewer for their feedback. Upon careful reconsideration, we agree that the original sentence lacked clarity and specificity. To address this, the sentence has been deleted from the manuscript (Lines 187–189).

6. Table 2 need more explanation

Answer: We appreciate this suggestion. Additional explanatory text has been added to clarify Table 2's content in Lines 204–206, providing an enhanced context for the presented data.

7. Figure 3 need high quality - add more explanation

Answer: We thank the reviewer for their feedback. Detailed explanations contextualizing Figure 3’s key findings have been added to the main text (Lines 303–305).

8. There is no quantitative information found in the conclusion - revise it

Answer: We thank the reviewers for bringing this important issue to our attention. We have revised the conclusion at lines 425–446.

9. Add recently published manuscript related to your research

Answer: We have added citations and discussions of the following high-impact studies published in 2025, which directly inform the context and significance of our work:

1. Zhu, Y.; Yan, J.; Sui, F.; Wang, H.; Quan, G.; Cui, L. Interaction mechanism of biochar dissolved organic matter (BDOM) and tetracycline for environmental remediation. Environ Res 2025, 275, 121405, doi:https://doi.org/10.1016/j.envres.2025.121405.
2. Li, Y.; Zhang, J.; Liu, X.; Liu, H.; Wang, L.; Cheng, D.; Wang, Y.; Guo, W.; Ngo, H.H. Efficient antibiotics removal by pig manure-based magnetic biochar-driven catalytic degradation. J Water Process Eng 2025, 70, 107013, doi:https://doi.org/10.1016/j.jwpe.2025.107013.
3. Cui, T.; Xie, Y.; Zhang, M.; Raise, A. Tetracycline removal from aqueous media and hospital wastewater using a magnetic composite of mango lignocellulosic kernel biochar/MnFe2O4/Cu@Zn-BDC MOF. Int J Biol Macromol 2025, 297, 139774, doi:https://doi.org/10.1016/j.ijbiomac.2025.139774.
4. Munuhe, L.N.; Madivoli, E.S.; Nzilu, D.M.; Lemeitaron, P.N.; Kimani, P.K. Advances in Adsorbent Materials for Pharmaceutical Pollutant Removal: A Review of Occurrence, Fate, and State-of-the-Art Remediation. J Chem-Ny 2025, 2025, 17, doi:10.1155/joch/4477822.
5. Hong, G.; Yu, Z.; Kong, D.; Huhe, T.; Shan, R.; Yuan, H.; Chen, Y. Removal of tetracycline from aqueous solution by magnetic biochar modified with different iron valence and K2C2O4: A comparative study and mechanism. J Anal Appl Pyrol 2025, 187, 107005, doi:https://doi.org/10.1016/j.jaap.2025.107005.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

From the previous revision, it was commented that the author needs to distinguish between biochar and activated carbon. 

Biochar is produced by pyrolysis with minimal additives, and usually does not possess high adsorption capacity. Activated carbon is named "Activated" because additives are added to chemically activate it, or it can be physically activated by extreme temperature. The function of activated carbon is to capture targeted compounds.

The function of biochar is vastly different from that of activated carbon. The characteristic between biochar and activated carbon is also different, as biochar has a much lower surface area than AC. 

This information is communicated very clearly; however, the authors choose to label all pyrolysed carbon, whether it is biochar or activated carbon, as biochar regardless of its nature. 

To avoid propagation of error, I cannot recommend this publication.

Author Response

Reviewer #1: General comments

From the previous revision, it was commented that the author needs to distinguish between biochar and activated carbon.

Biochar is produced by pyrolysis with minimal additives, and usually does not possess high adsorption capacity. Activated carbon is named "Activated" because additives are added to chemically activate it, or it can be physically activated by extreme temperature. The function of activated carbon is to capture targeted compounds.

The function of biochar is vastly different from that of activated carbon. The characteristic between biochar and activated carbon is also different, as biochar has a much lower surface area than AC.

This information is communicated very clearly; however, the authors choose to label all pyrolysed carbon, whether it is biochar or activated carbon, as biochar regardless of its nature.

To avoid propagation of error, I cannot recommend this publication

Answer: We sincerely thank for this important insight. We fully agree that distinguishing biochar from activated carbon is important because of the fundamental differences in production methods, properties and functional applications. We have implemented comprehensive revisions throughout the manuscript.

Reviewer 2 Report

Comments and Suggestions for Authors

Accept the manuscript as it is

Author Response

Thank you for your valuable suggestions on the revision of the manuscript. These recommendations are of great importance to us.

Round 3

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have responded sufficiently to the comment. Previously raised issues were corrected /amended.