Review Reports

Reviewer

Query

Responses

1

Abstract

The abstract consists mainly of empty phrases and grandiose terminology, such as eco-friendly, valorisation, maximum impact, and optimum delivery, which do not provide specific technical information or define the study scope. Furthermore, it condenses too many disparate topics into a single paragraph (definition of biochar, technological challenges, policy opportunities, artificial intelligence, co-combustion, scale-up, and aviation biofuels), which are unconnected. The text mentions elements such as AI and aviation fuels as if they were central themes but does not develop them in the article. There are phrases such as “has the potential to make a significant impact on reducing greenhouse gas emissions,” which are more typical of promotional texts than technical ones.

We acknowledged the reviewer’s comment on the abstract session with mentioning of our 1. Use many empty phrases and grandiose terminology; 2. Condensation of many disparate topics into a single paragraph; 3. AI and aviation fuels mentioning as if they were central themes; 4. Use of promotional texts phrases.

All of these comments have been addressed in lines 13-18, and 21-31 of corrected manuscript.

1

Literature review

The literature review was not organized by topic or to compare approaches, results, and limitations. The text redundantly repeats authors, especially Afshar and Mofatteh (2024), who are cited in almost every section, without drawing conclusions or providing interpretations. There are numerous decontextualized citations where numerical data or statements from other works are reproduced without evaluating their validity, methodological consistency, or relevance. Thus, the paragraphs become a descriptive compendium without a common thread, more akin to a list of references than a conceptual framework with analysis. Furthermore, the selection of sources lacks temporal and quality criteria; old studies are mixed with recent reports, and some references of dubious credibility are included without justification. Finally, although the text mentions that “research gaps are identified,” it does not specify any, omitting the analysis of real gaps in the literature (such as limitations in co-pyrolysis, experimental conditions or industrial scalability).

Thank you for these observations in our article introduction and literature review section. This session has now been organized into sessions and right paragraphing style as can be seen in lines 35, 41, 52, 59, 69, 74, 80, 85, 92, 97, and 101; which highlighted: demand for this review, bioenergy definition, main biomass for bioenergy, other useful biomass, biochar production, biochar feedstocks, temperature for Biochar production, oxygen requirement for biochar production, by-products of biochar production, biochar market, and research focus and gap to be filled by the research respectively.

Also we have reduced the redundant repeat of certain authors especially Afshar and Mofatteh (2024) to just 3 times, and contextualized valid and relevant information and citations in the literature review section. These can be seen in lines 34-74, 80-84, 92-100. The paragraphs are no longer descriptive but the synthesis of each work have been highlighted in the paragraphs. Example is in lines 47-51.

More so, the paragraphs now connect with each other in an orderly sequence. Old references are now situated before recent ones and

With regards to this comment “some references of dubious credibility are included without justification”

some statement like that by Alhazmi and Loy (2021) “Although solar and wind energy projects can lessen greenhouse effects, their carbon dioxide emissions into the atmosphere is significantly higher than the Intergovernmental Panel on Climate Change's (IPCC) recommended global safe limit” formerly line 38 to 41 has been withdrawn.

The research gaps we meant here are the prospects already discussed, such as prospect of biochar in air and water pollution control, Ai in biochar production, etc.

1

The manuscript claims that solar and wind energy “emit more CO₂ than the safe global limit recommended by the IPCC,” a statement that is technically incorrect and unfounded. The IPCC does not set “safe limits” for emissions by specific technology but rather global carbon budgets and target atmospheric concentrations (e.g., 450 ppm CO₂ for 1.5–2 °C scenarios). Furthermore, life cycle analyses show that emissions associated with solar and wind power generation are minimal compared to fossil fuels; therefore, claiming otherwise without data, context, or reference is technically incorrect and potentially misleading.

Thank you. This assertion has been withdrawn.

1

The section on flash pyrolysis presents an internal technical contradiction regarding the yields and objectives of this process. Initially, it correctly describes that flash pyrolysis, at temperatures above 1000 °C and very short residence times, favors the production of bio-oil; however, the text then states that “the purpose of flash pyrolysis is to produce as much biochar as possible” and cites a yield of 60% biochar and 40% volatiles, which contradicts both the theory and the manuscript's own data. Table 3 of the same article reports a typical yield of 75% bio-oil, 12% biochar, and 15% gas, confirming that this process is mainly oriented towards the liquid fraction.

The manuscript correctly defines fast pyrolysis as a process with residence times of 0.5–2 s and high heating rates (10–100 °C/s); however, the tables and examples that follow include cases labeled as “fast” with residence times of several minutes (3–30 min). These values correspond more to slow or intermediate pyrolysis conditions than fast pyrolysis.

The contradiction in the section highlighted has been recasted (lines 260-262 and lines 320-322) to capture the different thoughts of the researchers referenced in table 3. However, we can remove the table if the thoughts from all these researchers mentioned could be misleading.

1

The manuscript sets out among its objectives the analysis of “advances in biofuels for aircraft and spacecraft” derived from biochar, and even mentions in the summary the “transition to biofuels in aviation” as a key strategy for mitigating climate change. However, the text does not present any technical link between biochar and aviation fuels, as it does not explain the conversion routes (e.g., bio-oil obtained by fast pyrolysis → hydrotreatment → sustainable aviation fuel) or discuss the hydrogen balances, product purity, or fuel stability.

This comment has been addressed. See lines 925-951 and 954-957

1

The paper claims that applying biochar to soil “mitigates 12% of CO₂ emissions from land use per year,” but does not provide sources to justify this figure, nor is it elaborated on in the text.

Thank you for the observation. The references have been provided in lines 469-471

1

This work presents abundant quantitative information (pyrolysis temperatures, biochar, bio-oil, and syngas yields, feedstock types, and various applications), but lacks comparative or interpretive analysis. The results of different studies are listed without establishing trends, correlations, or conclusions derived from the data. Aspects such as the relationship between temperature and yield, optimal operating ranges, and raw materials that offer the best energy performance have not been analyzed. Furthermore, no statistical treatment (if possible) or visual representation, such as comparative graphs or frequency analyses, is included, making it impossible to identify patterns or general behavior in the data.

This comment has been addressed. See lines 374-380

1

The conclusions merely reiterate generic statements about sustainability, such as “biochar can contribute to a sustainable future” or “this article provides insights into bioenergy production.” The main results are not summarized, nor are more efficient processes, technological gaps, or industrial scaling requirements identified. The conclusion lacks forward-looking projections or applied recommendations, limiting itself to declarative statements that do not derive from the review.

This comment has been resolved. See lines 975-1016

1

Comments on the Quality of English Language

I see misspelled words and grammatical problems such as subject-verb agreement errors (“Thermochemical conversion is a process that employ...” → employs), omitted articles (“pollutants to atmosphere” → to the atmosphere), and pluralization errors (“Various type” → Various types). There is also misuse of verb tenses (“Biochar production valued at...” → was valued at), and errors in prepositions and collocations, such as “Plugging the system of biomass underuse,” which does not make idiomatic sense. I see redundancies, for example, “carbon-rich material” repeated twice in a row, as well as incorrect constructions such as “Biochar characteristics performance” instead of Biochar performance characteristics.

These remarks has been corrected. See lines 86, 406-407, 139 (various feedstock types), 241(variety of biomass types), 97 (was valued at), 3(wastage for underuse) 561(biochar performance),

2

The article presents a comprehensive, qualified review. The authors used a broad, up-to-date, and adequate number of references.

Thank you for the response

The article successfully mapped and discussed the processes, raw materials, production conditions, and application in biochar production.

Thank you for the response

Furthermore, the review presents the environmental and market implications of utilizing biochar.
The analysis of biochar's integration with other energy systems highlights the research contribution.

Thank you for the response

The text describing the manuscript's conclusion could be improved to highlight the research's contributions better.

Its research contributions have  been recast (lines 975-1016)

3

Torrefaction should be mentioned as a conversion technique to obtain biochar.

Torrefaction has been added as a conversion technique to obtain biochar (lines 342-373)

Section 2.2.3, since Bridgwater has a positive opinion about bio-oil produced by fast pyrolysis, it would be better to add more detailed information about him in this chapter.

The positive opinion by Bridgwater  has been detailed (lines 275-278)

Section 2.2.4, the various reports by Prof. Michael Jerry Antal at the University of Hawaii at Manoa are very informative. Therefore, authors should check them; if possible, these reports might be added to the revised manuscript.

Prof Jerry Antal co-authored the manuscript with Nunoura and we have added their information lines 310-314

Section 6.4, this is an interesting topic, but the text is lengthy. I would suggest adding a description of the Biomass-to-Liquid (BTL) technology, which converts biochar into liquid fuel.

Conversion of biochar into aviation biofuel has been detailed (lines 925-951 and 954-957)

Reviewer

Query

Responses

1

Literature review

Although the first part was reorganized into thematic subsections (lines 35–101), the synthesis remains weak. Citations continue to be descriptive rather than analytical. Example: Lines 47–51: Fan et al. (2021) and Domínguez et al. (2022) are cited, but only what they did is reported without discussing methodological differences, limitations, or implications.

We acknowledged the reviewer’s further comment on the article introduction and literature review section. This section has now been modified capturing the understanding from each paragraph with thematic bridges in lines 39-40, 51-53,70-73, 78-80 and 87-89

The example and references mentioned are not contained in our work.

1

The transition between lines 74 and 80 is abrupt; it moves from feedstocks to temperature without a thematic bridge.

The research gap that it claims to cover is poorly defined.

Line 101 mentions that it addresses “gaps such as AI-assisted biochar production,” but that is not a specific gap, but rather a topic.

Thank you for these observations: Thematic bridges have been added (lines 87-89)

Also we have outlined in detail the gap that this study covered. These can be seen in lines 121-141.

The mention in line 101 of AI-assisted biochar production has been addressed is in lines 138-140.

1

In lines 260–262, it is clarified that flash pyrolysis tends to generate bio-oil, but some authors report more biochar.

In lines 320–322, it is mentioned that the heating rate and time affect the yield, but Table 3 continues with erroneous classification. A process with a 15-minute residence time (row 3, feedstock “Corn stalk”) is labeled as “Fast pyrolysis,” which corresponds to slow or intermediate pyrolysis, not fast. There are also processes with temperature ranges of 300–550 °C classified as flash, without specifying the heating rate or exact time.

Thank you. This misinformation has been withdrawn.

The classification has been modified as can be seen in table 1 under intermediate pyrolysis in rows 6 and 7

1

Lines 374–380: A paragraph is included that briefly discusses how increased temperature decreases biochar yield and increases gas and bio-oil yield, but with minimal and generic interpretation: There are no graphs or comparative tables to visualize trends or statistical correlations. I suggest including a comparative summary table (e.g., temperature vs. typical yield) or boxplot or scatterplot graphs to show the relationships.

Although the lines mentioned does not contain what was described, we have included a section on the effect of temperature on biochar production as we felt it was necessary to add it with an accompanying graphical representation in lines  431-432

1

Abstract

The abstract in lines 13–31 maintains a markedly promotional tone; expressions such as “eco-friendly and affordable material” allude to positive qualities without technical justification or quantifiable parameters.

Similarly, the term “optimum delivery of biochar application” is ambiguous, as it does not specify whether it refers to agronomic efficiency in the application of biochar, its distribution logistics, or its integration into industrial processes, which falls outside the scope of biomass recovery and biochar application.

In addition, references are made to topics such as “transition to biofuels in aviation” and “application of AI,” without adequately developing their technical and operational links to the use of biochar in the body of the article, creating dissonance between the elements highlighted in the abstract and the content analyzed. Statements such as “make a significant impact on GHG emissions” are declarative and lack empirical support or specific citations. Likewise, the abstract does not explicitly state the study’s focus, research questions, or the main contributions of the analysis.

Although some of these remark seem to be pointing to phrases that were not used in this study abstract section, we have reduced the use of these general phrases marking the quality of biochar in both the abstract and the entire work as can be seen in lines 18, 128 -129.

Applications of biochar in industries has been modified as can be seen in line 28

The references made to these topics has been modified to present them as prospects not as a technically discussed topic. These can be seen in lines 25-30

1

Comments on the Quality of English Language

Line 267: “moisture content of the biomass is observed to influenced...” is incorrect. It should be “to influence.”

Line 924: “high viscosity and acidic nature” → ambiguous phrase, nature of what? Of the bio-oil? A definite noun is missing.

Line 942: “which pose technical and economic”–what? Missing noun (“challenges,” “barriers,” etc.).

Inconsistent use of capital letters (“BioChar” in line 558) → should be biochar.

Thank you for the observation. But the lines mentioned do not exist in this work.

This line also does not match any line in our work.

The same with this line, it does not match with any line in our work.

This also, does not match any line in our work.