Review Reports - Biochars Derived from Diverse Local Tunisian Feedstocks for Environmental Remediation: Physicochemical Properties and Adsorption Behaviour

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Thank you for considring me to review the manuscript "Production and characterization of Biochar issued from diverse local feedstocks in Tunisia". The manuscript assesed the physical and chemical charcteristics of biochars from different types of local biomass feedstocks in Tunisia and and their adsorption propertes. The study is well justified due to environmental issues in Mediterranean agricultural settings, especially pesticide pollution and soil quality issues. The authors combined experimental biochar production with physicochemical and adsorption analyses.

Suggestions

The manuscript needs careful language editing to improve the general language.

The title

The title is clear but could be imbroved by highlighting "environmental remediation" or "adsorption behavior" “Biochar from local Tunisian biomass: Physicochemical properties and adsorption behavior for environmental remediation

Abstract

The abstract is well-written but could be improved by focusing more on the key findings.

Introduction

The introduction needs to be extended and would benefit from citing more recent key reviews on biochar environmental applications. The rationale for choosing the specific biomass feedstocks could be more explicitly justified in terms of availability, composition and relevance in Tunisia.

Material and methods

The description of the biochar production kiln should include more technical details to enhance reproducibility.

Table 2 is presented before its mention in the text

Results

Any of the measures of dispersion should be presented with the results values in Tables and Figures.

Table 4 is presented before its mention in the text

Line 284 and 446, replace Fig. 3 with Figure 3 to be the same as the others throughout the text, also Fig. 7 in lines 425 and 444

Revise the used abbreviations, such as XCa and XMg in Table 3, and CE in line 387. Ensure that all abbreviations are defined on first appearance in the text.

Adding schematic diagrams of production and application workflow could enhance the manuscript.

The resolusion of Figure 6 needs to be improved

Discussion

Consider summary comparison of adsorption affinities by biochar type and molecule.

Extend how the obtained findings align and differ from previous studies globally or regionally.

Potential practical applications and limitations should be elaborated, including the suitability of specific biochars for particular contaminants or field conditions.

References

The reference list needs to be carefully revised, Journal names are abbrivated in some as J. Geotech. Geoenviron. Eng." in line 553 while the remaining are not. Please verify consistency and formatting according to the journal guidelines.

Author Response

We are very grateful for the thorough review of our manuscript and for all the insightful comments and suggestions provided.

Reviewer 1

Comments and Suggestions for Authors

Suggestions

The manuscript needs careful language editing to improve the general language.

Response:

The manuscript has been edited by a native english speaking reader.

The title

The title is clear but could be improved by highlighting "environmental remediation" or "adsorption behavior" “Biochar from local Tunisian biomass: Physicochemical properties and adsorption behavior for environmental remediation ✓

Response:

The title of the manuscript has been modified : Biochar issued from diverse local tunisian feed-stocks: Physicochemical properties and adsorption behavior for environmental remediation.

Abstract

The abstract is well-written but could be improved by focusing more on the key findings.✓

Response:

The findings have been highlighted in the abstract mainly about the type of interactions between the different biochars and organic dyes.

Introduction

Response:

The introduction has been enhanced with current citations and expanded discussions on the issues of pesticides and agricultural waste. The rationale for choosing the specific biomass feedstocks in terms of availability and relevance in Tunisia.

Material and methods

The description of the biochar production kiln should include more technical details to enhance reproducibility. ✓

Response:

The description of the kiln with more technical details in the manuscript.

Table 2 is presented before its mention in the text ✓

Response:

LaTeX automatically positions tables and figures based on available space. However, this matter will likely be handled by the printing department.

Results

Any of the measures of dispersion should be presented with the results values in Tables and Figures.

Response:

Dispersion measures have been presented in the tables of adsorption parameters.

Table 4 is presented before its mention in the text ✓

Response:

LaTeX automatically positions tables and figures based on available space. However, this matter will likely be handled by the printing department.

Line 284 and 446, replace Fig. 3 with Figure 3 to be the same as the others throughout the text, also Fig. 7 in lines 425 and 444 ✓

Response

We changed it directly in the manuscript.

Revise the used abbreviations, such as XCa and XMg in Table 3, and CE in line 387. Ensure that all abbreviations are defined on first appearance in the text. ✓

Response:

The abbreviation was defined in the manuscript.

Adding schematic diagrams of production and application workflow could enhance the manuscript.✓

Response:

A schematic diagram of production and application workflow was added to the materials and methods section.

The resolution of Figure 6 needs to be improved ✓

Response:

The resolution has been improved.

Discussion

Consider summary comparison of adsorption affinities by biochar type and molecule.

Response:

To summarize the various affinities between biochars and organic dye types, a schematic diagram has been included in the manuscript.

Extend how the obtained findings align and differ from previous studies globally or regionally

Response:

The results have been compared to several recent studies but we didn’t find any relevant publications dealing with this topic at a regional scale. Though numerous studies tackle the adsorption of methylene blue and Uranine on biochar only very few deal with SRB.While our results were compared to several recent studies, we did not find any relevant regional-scale publications on this topic. Although numerous studies address the adsorption of methylene blue and Uranine on biochar, very few focus on SRB.

Potential practical applications and limitations should be elaborated, including the suitability of specific biochars for particular contaminants or field conditions.

Response ;

The conclusion was slightly modified according to the recommendations of the reviewers, mentioning the limitations and outlined future research directions to address the questions raised by this study..

References

Response

The whole reference list had been revised carefully and formatted according to the journal guidelines.

Reviewer 2 Report

Comments and Suggestions for Authors

This study investigates the properties and sorption behaviours of biochars produced in a low-cost metallic kiln using local biomass residues, to evaluate their potential for environmental remediation with special focus on the mobility and retention of emerging contaminants. The subject holds major research value for the Mediterranean region, with sufficient data presented in a clear structure. However, the methodological rigour, protocol standardisation, and erroneous descriptions require further revision.

1. Lines 117–119: Should "1000 g/L stock solution" be "1000 mg/L"? Alternatively, specify preparation details for high concentrations and provide solubility rationale.
2. Lines 134–137: The Freundlich equation notation and symbols are non-standard. n is an empirical parameter; its definition and reference should be provided. Similarly, provide the dimensionless or actual units for relevant parameters.
3. MED is used simultaneously as the abbreviation for Molarity of Ethanol Droplet and Median pore diameter, causing semantic conflict. Median pore diameter could be modified to MPD. The full term and abbreviation for MED appear in multiple locations. Note that abbreviations require definition only once. Please consult the Author Guidelines.
4. Lines 146–160: Thermodynamic units are poorly defined. Kl from Langmuir is used as a constant in Equation 5. If the unit for Kl is L g⁻¹ (as shown in Table 5), verify whether it can be directly substituted into the standard free energy equation. Alternatively, this should be standardised as a dimensionless equilibrium constant.
5. Lines 138–143: Verify the calculation of SSA using a monolayer MB (the origin of the constant 2446.5 and the unit conversion process are not explained).
6. Lines 161–176, 255–269: Logic of PZC experimental procedure and environmental pH. The description states pHi is measured first, followed by KCl addition and then pHf measurement. Add rationale and references for selecting this modified ionic strength method.
7. Table 3 and Lines 230–249: Verify CEC units and reference cations. Examine the validity of "saturation SR >1000%". Does this require further explanation and discussion of extreme high or low adsorption?
8. I recommend adding a schematic diagram to contrast the mechanisms, for example highlighting MB and UR/SRB regarding electrostatic attraction, coordination, charge shielding, and π–π interactions.
9. Formatting and language issues
Unify the unit notation for L g⁻¹ and L/g.
"electrolyte.30 mL" lacks a space.
Check capitalisation of Latin names (Washingtonia robusta).
Both EC and CE denote electrical conductivity in the text.
"2.1. biochar production", check capitalisation.
Line 132 and 324, "adsorbtion" → adsorption.
Table 1 title: "physico-chimical" → physicochemical.
Consistent capitalisation throughout: "Methylene blue/Blue" and "Fourier Transform InfraRed" require uniform spelling.
Multiple duplicate DOIs "https://doi.org/https://doi.org/...", please remove.

Author Response

Reviewer 2

We are very grateful for the thorough review of our manuscript and for all the insightful comments and suggestions provided.

Lines 117–119: Should "1000 g/L stock solution" be "1000 mg/L"? Alternatively, specify preparation details for high concentrations and provide solubility rationale. ✓

Response:

It’s 1g/L = 1000 mg/L . We corrected it in the text.

Lines 134–137: The Freundlich equation notation and symbols are non-standard. n is an empirical parameter; its definition and reference should be provided. Similarly, provide the dimensionless or actual units for relevant parameters.✓

Response:

Though formally Freundlich equation should be written with exponent of 1/n, it is more and more common to simplify the notation to n, which is dimensionless. The units of the distribution factor Kf where described more clearly in the manuscript.

MED is used simultaneously as the abbreviation for Molarity of Ethanol Droplet and Median pore diameter, causing semantic conflict. Median pore diameter could be modified to MPD. The full term and abbreviation for MED appear in multiple locations. Note that abbreviations require definition only once. Please consult the Author Guidelines. ✓

Response:

We corrected the text ( there’s no median pore diameter relation mentioned) the MED and all the abbreviation redundancy was deleted in the text.

Lines 146–160: Thermodynamic units are poorly defined. Kl from Langmuir is used as a constant in Equation 5. If the unit for Kl is L g⁻¹ (as shown in Table 5), verify whether it can be directly substituted into the standard free energy equation. Alternatively, this should be standardised as a dimensionless equilibrium constant. ✓

Response:

This issue was corrected directly in the manuscript, by introducing a dimensionless parameter K0 derived from Kl, providing a clear explanation of the different parameters involved.

Lines 138–143: Verify the calculation of SSA using a monolayer MB (the origin of the constant 2446.5 and the unit conversion process are not explained). ✓

Response

The units for each factor have now been explicitly mentioned in the manuscript, addressing this point.

Lines 161–176, 255–269: Logic of PZC experimental procedure and environmental pH. The description states pHi is measured first, followed by KCl addition and then pHf measurement. Add rationale and references for selecting this modified ionic strength method.✓

Response

To be sure that our measurements accurately reflect the intrinsic properties of the biochar, we opted to determine the PZC at varying ionic strengths. This approach helps us identify any PZC derivations that might be caused by ionic specific adsorption.

Table 3 and Lines 230–249: Verify CEC units and reference cations. Examine the validity of "saturation SR >1000%". Does this require further explanation and discussion of extreme high or low adsorption?

Response:

The very high saturation ratio (SR) observed is most likely related to the intrinsic characteristics of the biochar and the presence of ash within its structure. Biochar generally contains a substantial proportion of inorganic constituents originating from the mineral fraction of the feedstock. Therefore, the elevated SR mainly reflects the presence of soluble minerals present in the ash, rather than the true long-term exchange capacity of the material. Once these easily soluble cations are leached out, the measured cation exchange capacity (CEC) becomes more representative of the stable surface functional groups associated with the carbon matrix.

I recommend adding a schematic diagram to contrast the mechanisms, for example highlighting MB and UR/SRB regarding electrostatic attraction, coordination, charge shielding, and π–π interactions. ✓

Response:

The schematic diagram was added to the manuscript.

Formatting and language issues✓

Response:

all the typos and recommendation were modified directly in the manuscript

Unify the unit notation for L g⁻¹ and L/g.✓

Response:

We changed it directly in the manuscript.

"electrolyte.30 mL" lacks a space.✓

Response:

We changed it directly in the manuscript.

Check capitalisation of Latin names (Washingtonia robusta).✓

Response:

We changed it directly in the manuscript.

Both EC and CE denote electrical conductivity in the text.✓

Response:

We changed it directly in the manuscript.

"2.1. biochar production", check capitalisation.✓

Response:

We changed it directly in the manuscript.

Line 132 and 324, "adsorbtion" → adsorption.✓

Response:

We changed it directly in the manuscript.

Table 1 title: "physico-chimical" → physicochemical.✓

Response:

We changed it directly in the manuscript.

Consistent capitalisation throughout: "Methylene blue/Blue" and "Fourier Transform InfraRed" require uniform spelling.✓

Response:

The manuscript was directly amended.

Multiple duplicate DOIs "https://doi.org/https://doi.org/...", please remove.✓

Response:

All references were revised.

Reviewer 3 Report

Comments and Suggestions for Authors

This MS discusses the Production and characterization of Biochar issued from diverse local feed-stocks in Tunisia.

Here the comments:

- Please do not write the name of plants in capital form in abstract and whole MS:

This study …..rosemary, giant reed, St. John’s wort, olive, cypress, and palm trees….

- In abstract, it is recommended to present your findings as an increase/decrease rate according to the control.

- Keywords, please avoid repeating any word already mentioned in the title, please

- Introduction needs more improvements, please by adding update the citations (mainly 2026, 2025, 2024 and 2023). All paragraphs (mainly 3-4) in this section can be one on pollution by pesticides, second on the agro-wastes, and third on the biochar

- Section Materials:

Please, correct the scientific names of plants (mainly Cypress (Cupressus)

It is recommended to start any sentence with written number like

21 glass bottles were divided in 3 groups ….

Please change the 2.8. Statistics, to Statistical Analyses

Please change the unit of EC from µS/cm to the unit dS m-1

Table 3, or any table or figure, should mention any information without referring to the text

Any abbreviation in all tables and figures should be clarified, please

All figures, each column should carry out the bar of SE and Duncan letter (if any)

- Conclusions should be one paragraph please

Minor revision is needed

Thanks

Comments on the Quality of English Language

Author Response

Reviewer 5

We are very grateful for the thorough review of our manuscript and for all the insightful comments and suggestions provided

This MS discusses the Production and characterization of Biochar issued from diverse local feed-stocks in Tunisia.

Here the comments:

- Please do not write the name of plants in capital form in abstract and whole MS:

This study …..rosemary, giant reed, St. John’s wort, olive, cypress, and palm trees…. ✓

Response:

All the names of plants were revised all through the manuscript.

- In abstract, it is recommended to present your findings as an increase/decrease rate according to the control. ✓

Response:

The findings have been highlighted in the abstract mainly about the type of interactions between the different biochars and organic dyes.

- Keywords, please avoid repeating any word already mentioned in the title, please ✓

Response:

We made sure that no word in the keywords already mentioned in the title.

Response

The introduction has been enhanced with current citations and expanded discussions on the issues of pesticides and agricultural waste, as well as the benefits of biochar.

- Section Materials:

Please, correct the scientific names of plants (mainly Cypress (Cupressus) ✓

Response:

We corrected the scientific name of plant cypress ( Cupressus serpenvirens)

It is recommended to start any sentence with written number like 21 glass bottles were divided in 3 groups …. ✓

Response:

We changed it directly in the manuscript text.

Please change the 2.8. Statistics, to Statistical Analyses ✓

Response:

We changed it directly in the manuscript text.

Please change the unit of EC from µS/cm to the unit dS m-1 ✓

Response:

We changed it from µS/cm to dS/m.

Table 3, or any table or figure, should mention any information without referring to the text✓

Response:

All the information in table 3 was mentioned in the caption, to be understandable in its own.

Any abbreviation in all tables and figures should be clarified, please✓

Response:

To address this, we clarified abbreviations in tables and figures where needed.

All figures, each column should carry out the bar of SE and Duncan letter (if any)✓

Response:

For the adsorption parameters, we included the standard error (SE) in each table, as these analyses were conducted with three replicates. However, for other parameters such as CEC, exchangeable cations, pH, and MED, the analyses were performed with only a single measurement.

- Conclusions should be one paragraph please ✓

Response:

The conclusion format was modified to one single paragraph

Minor revision is needed. Thanks YOU ARE WELCOME ?

Reviewer 4 Report

Comments and Suggestions for Authors

The manuscript in general is well-written, well-organized, and tackles a topic of regional and global importance. There are sections that need to be revised to further improve the scientific merit and contextual relevance.

Major Concerns

Abstract

The abstract is materials- and methods-oriented, while the results section is concise. For better balance, the abstract should provide the main findings to allow the readers to better appreciate the study's outcomes.

Results

Although statistical significance testing was mentioned in the manuscript, this is not provided in the results section. Differences in statistical treatment ought to be designated, both textually and in tables. Inclusion of the p-values, standard error (SE) or standard deviation (SD), and/or lettering of significance would render the study transparent and scientifically credible.

Section 3.7. It could be better to merge this section into the related sections. include numbers and data for showing statistical analysis.

Discussion

The authors do not sufficiently situate the findings within the broader literature. The authors reference only 8 sources, only one of which is from 2023 and two of which are from 2020; the others are from before 2020. To strengthen the manuscript, the authors must more actively interact with recent studies and compare their findings with those studies critically. This would also make the discussion more novel and contextually relevant.

Conclusion

The conclusion now overstates the findings. Lines 474 and 494, for example, say that biochar can "improve soil quality in Mediterranean agricultural systems" or "improve soil quality." These are not explicitly supported by the data presented, as no validation on the soil basis was conducted. The conclusions must be more precisely worded, adhering to the laboratory-scale evidence provided, and making no claims to field-level impacts.

Minor Concerns

Materials and Methods

The units are expressed irregularly in the manuscript (e.g., "mg/L" and "cmolc · kg-1"). The writing style of units should be made uniform for better readability.

Lines 208-210: “As only few replicates could be measured for most of the experiments (between three and five)…”, it worth mentioning which parameters.

References

Approximately 40% of the references used are 2020 and newer. While this is acceptable, the reference list would benefit from the inclusion of more recent publications.

Author Response

Reviewer 4

We are very grateful for the thorough review of our manuscript and for all the insightful comments and suggestions provided.

Major Concerns

Abstract

Response:

We improved the abstract by adding more findings in the manuscript.

Results

Response:

Standard errors for the adsorption parameters have been incorporated into their respective tables. This was possible because three replicates were used for each concentration point on the isotherms. The average Freundlich and Langmuir parameters were calculated from the averaged values for each concentration, while the standard deviation and error were computed from the parameters determined for each replicate.

Section 3.7. It could be better to merge this section into the related sections. include numbers and data for showing statistical analysis.

Response:

We attempted to merge the statistical results of this section with related sections; however, it proved most efficient and straightforward to keep them separate.

Discussion

Response:

While our study has its own unique points, we're really focusing on local biomass here. Our first step is to describe the biochar we get, just to build a solid base of info on how its core characteristics vary and how consistently we can reproduce them, all depending on what's available..

Conclusion

Response:

The manuscript has been updated to reflect the comments. The conclusion now includes expanded results and future perspectives, carefully avoiding over-interpretation.

Minor Concerns

Materials and Methods

The units are expressed irregularly in the manuscript (e.g., "mg/L" and "cmolc · kg-1"). The writing style of units should be made uniform for better readability.✓

Response

We have revised all units and harmonized their notation throughout the manuscript.

Lines 208-210: “As only few replicates could be measured for most of the experiments (between three and five)…”, it worth mentioning which parameters. ✓

Response:

Actually all the adsorption experiments were conducted in triplicate. The mistake has been corrected in the manuscript.

References

Approximately 40% of the references used are 2020 and newer. While this is acceptable, the reference list would benefit from the inclusion of more recent publications. ✓

Response

New references were added to the manuscript.

Reviewer 5 Report

Comments and Suggestions for Authors

Abstract: more results should be added

Article name: should be revised as organic contaminats were investigated

Introduction: could be enlarged, more uptoday references and main research question should be added

Material and methods: where the biomasses were grown, disbre more which parts were taken

As the ph value in table 3 was higher than 7 why the ph metr was calibrated to 4 and 7 points and not 10 point?

2.2 missing the references

Why Sulforhodamine was chosen?

Table 2: try to avoid abbreviation in the figure caption

Results and disccusion: this part is well written but more the newest refferences should be added

Conslusion: could be more descriptive and more results could be added

Author Response

Reviewer 5

We are very grateful for the thorough review of our manuscript and for all the insightful comments and suggestions provided.

Abstract: more results should be added ✓

Response:

As required by most of the reviewers, the abstract now includes several key findings.

Article name: should be revised as organic contaminants were investigated ✓

Response:

The title of the manuscript has been modified : Biochar issued from diverse local tunisian feed-stocks: Physicochemical properties and adsorption behavior for environmental remediation.

Introduction: could be enlarged, more uptoday references and main research question should be added ✓

Response:

The introduction was enriched with more information on pollution by pesticides, on the agro-wastes specific to Tunisia context, and third on the biochar adsorption interest.

Material and methods: where the biomasses were grown, disbre more which parts were taken ✓

Response:

The specific plant parts used for biochar production are detailed in the text. Generally, whole plants were utilized, with the exception of wood-sourced biochar, for which only branches or, in the case of palm trees, midribs were pyrolyzed.

As the ph value in table 3 was higher than 7 why the ph metr was calibrated to 4 and 7 points and not 10 point? ✓

Response:

The pH meter was, in fact, also calibrated for pH 10; the omission in the manuscript was an error, that we corrected

2.2 missing the references ✓

Response:

We added relevant and recent references in the text.

Why Sulforhodamine was chosen? ✓

Response:

SRB is a zwitterionic molecule featuring both hydrophobic aromatic regions and hydrophilic ionized sites. This dual nature allows it to interact through various mechanisms, including electrostatic interactions, π–π stacking, and hydrogen bonding. SRB behaves similarly to organic pollutants such as Metolachlor.This point was developed in the manuscript.

Table 2: try to avoid abbreviation in the figure caption ✓

Response:

This point was corrected in the manuscript

Results and disccusion: this part is well written but more the newest refferences should be added ✓

Response:

New references were added to the discussion, providing to cite the most recent studies in this field.

Conslusion: could be more descriptive and more results could be added✓

Response:

We incorporated additional findings into the conclusion and outlined future research directions to address the questions raised by this study..