Briquettes Obtained from Lignocellulosic Hemp (Cannabis sativa spp.) Waste, Comparative to Oak (Quercus robur L.) Ones

Round 1

Reviewer 1 Report (Previous Reviewer 2)

Comments and Suggestions for Authors

The work "Briquettes obtained from lignocellulosic hemp (Cannabis sativa spp.) waste, comparative to oak (Quercus robur L.) ones" explores the possibility of using the cannabis residues and Oak sawdust to produce biofuels, and especially Briquettes, through the analysis of their physical, mechanical, chemical and energetic properties. This new version shows a clear improvement, compared to the previous version. However, there are still a few details that would be good to consider before publication.

1. In the introduction, interesting information was added about Quercus, as well as an estimate of the global industrial market for cannabis. However, it would be more pertinent to know what these estimates correspond to, in terms of volume. This could allow to know how reliable the availability of hemp-based raw materials is, to cover the need created by the shortage of wood and wood-based semi-finished products/composites, as mentioned at the beginning.
2. Several fractions of raw material from different sieves were used (lines 105 to 114) to manufacture the briquettes based on each type of small material (lines 133-134). There is only one type of briquette, for both Cannabis and Oak. Although the authors answered this question in the previous review, saying that it was to determine the percentage of mass participation in the total sample, the question remains as to how this could be translated in terms of results, since no result mentions the participation of the different fractions in the characteristics obtained. One would have expected to see different types of briquettes, made with varying proportions of the different fractions obtained, to analyze the effect they would have on the properties of the briquettes...
3. As the title and objective of this work dictate, it is a question of comparing the results of Cannabis-based briquettes with those based on Oak, which was done with several properties analyzed. Except that for the calorific value, one of the most important parameters in the study of energy characteristics, only the results concerning Cannabis still appear (Figure 9). And what about Oak?
4. Also, this same figure 9 claims to present the results of the calorific value. But in view of what is seen, it would seem that it is rather the relationship between the calorific value and the moisture content. However, it is mentioned in methodology that "each briquette (Fig. 2) was conditioned to have a moisture content of around 10%" (line 137). So, where do the various other moisture contents come from to establish this relationship with the energy content?  Fortunately, there is the result of the high calorific value for both Cannabis and Oak on the centralized data in Table 2. Hence the suggestion to modify the title of Figure 9, to adjust it with its content.

Author Response

Reviewer 1

I would like to thank the reviewer for his observations and suggestions. All changes in the new version of the paper are highlighted in blue.

The work "Briquettes obtained from lignocellulosic hemp (Cannabis sativa spp.) waste, comparative to oak (Quercus robur L.) ones" explores the possibility of using the cannabis residues and Oak sawdust to produce biofuels, and especially Briquettes, through the analysis of their physical, mechanical, chemical and energetic properties. This new version shows a clear improvement, compared to the previous version. However, there are still a few details that would be good to consider before publication.

1. In the introduction, interesting information was added about Quercus, as well as an estimate of the global industrial market for cannabis. However, it would be more pertinent to know what these estimates correspond to, in terms of volume. This could allow to know how reliable the availability of hemp-based raw materials is, to cover the need created by the shortage of wood and wood-based semi-finished products/composites, as mentioned at the beginning.

Author response: A new paragraph was added about hemp “Common hemp is a species of the Cannabaceae family, in which the maximum level of tetrahydrocannabinol is very low at around 0.3%. Hemp has a number of advantages, including: storing between 9 and 15 tons of carbon dioxide in five months of vegetation, just like a very young forest, stopping the cycle of some plant diseases in crop rotation, preventing soil erosion and reducing water loss from the soil, and not requiring pesticides. Hemp is sponsored by the European community and is cultivated in many European countries, on an area that has increased from 20,540 hectares in 2015 to 33,020 in 2022, an increase of 60%. Hemp production in the European Union increased from 97,130 tons (about 38,850 m3) to 179,020 tons (about 68,000 m3) between 2015 and 2022, at a rate of 0.4 t/m3, an increase of over 80%. France is the leading European hemp producer with about 60% from total production, followed by Germany and the Netherlands”.

 

1. Several fractions of raw material from different sieves were used (lines 105 to 114) to manufacture the briquettes based on each type of small material (lines 133-134). There is only one type of briquette, for both Cannabis and Oak. Although the authors answered this question in the previous review, saying that it was to determine the percentage of mass participation in the total sample, the question remains as to how this could be translated in terms of results, since no result mentions the participation of the different fractions in the characteristics obtained. One would have expected to see different types of briquettes, made with varying proportions of the different fractions obtained, to analyse the effect they would have on the properties of the briquettes.

Authors response. In order for the issue of granulometry to be much clearer, modifications and additions were made in various areas of the work, namely:

• In the methodology area. “The intention of determining these granulometries was to observe how the two types of wood chips break down, by observing the different fractions. It was also based on the old observation [22-23] that from small chips we obtain briquettes with slightly higher densities but slightly lower resistance and vice versa, from coarse chips we will obtain lower densities and slightly higher mechanical properties, all due to the different com-pression and compaction of the particles”.
• In the result area. “Looking carefully at the two particle size graphs, it is observed that they are quite close, with peaks in the 1.25-2.0 mm area, that slight difference being due to the fact that hemp chips are lighter than oak chips (Fig 3). Therefore, from this observation, we expect that particle size will not have a major influence on the physical and mechanical properties of the briquettes”.
• In the discussions area. “The existence of very close curve peaks in the 1.25-2 mm area demonstrated the weak influence of granulometry on the physical and mechanical properties of the briquettes. In the same sense, even the bulk density of the two categories of materials leads to the conclusion that hemp briquettes have a slight decrease in unit density and mechanical properties. There was no need to obtain briquettes with different granulometry because the granulometry analysis created enough data for us to draw some pertinent conclusions”.

 

 

1. As the title and objective of this work dictate, it is a question of comparing the results of Cannabis-based briquettes with those based on Oak, which was done with several properties analysed. Except that for the calorific value, one of the most important parameters in the study of energy characteristics, only the results concerning Cannabis still appear (Figure 9). And what about Oak?

Author response: We have made some additions in this regard, adding a new figure to the paper. See figure 9 in the revised paper, line 358. Additions have also been made to the description of this figure, lines 366-369. “… and 18.175 MJ/kg in the case of oak briquettes (Fig. 9). Figure 9 also shows the different values of the calorific value for the two types of briquettes and for the two types of calorific values, HCV and LCV”.

 

1. Also, this same figure 9 claims to present the results of the calorific value. But in view of what is seen, it would seem that it is rather the relationship between the calorific value and the moisture content. However, it is mentioned in methodology that "each briquette (Fig. 2) was conditioned to have a moisture content of around 10%" (line 137). So, where do the various other moisture contents come from to establish this relationship with the energy content?  Fortunately, there is the result of the high calorific value for both Cannabis and Oak on the centralized data in Table 2. Hence the suggestion to modify the title of Figure 9, to adjust it with its content.

Author response: In order to clarify the issues raised by the reviewer, a series of additions were made to the paper, as follows:

----a. The 10% moisture content was used to determine the physical-mechanical properties of the briquettes and not to determine the calorific value. In this regard, the following sequence was introduced to the methodology for determining the calorific value.: “Before each determination, small pieces of 0.8 g were detached from the briquettes and dried in an oven until constant mass”.

----b. Explanation for different moisture content: “To observe the influence of moisture content on the calorific value, pieces of briquettes with a moisture content of 50% were used, at which the calorific value was determined. By coupling the values obtained with those for a moisture content of 5%, two points could be obtained, through which the linear equations visible in the figures from the results chapter were plotted”.

----c. To observe all the calorific value values, a new figure 9 has been introduced.

----d. Title of new modified Figure 8 were changed in accordance with the reviewer observation.

 

Reviewer 2 Report (Previous Reviewer 1)

Comments and Suggestions for Authors

The homogeneity of decimal places must be reviewed (tables 1 ad 2, figure 7...)

The correlation coefficient for the linear adjust in Figure 8 must be indicated

Author Response

Reviewer 2

I would like to thank the reviewer for his observations and suggestions. All changes in the new version of the paper are highlighted in blue.

 

1.----The homogeneity of decimal places must be reviewed (tables 1 ad 2, figure 7...)

Authors responses: All changes regarding the uniformity of decimals were made in the paper. For example, the decimals in Table 1 were standardized to 2 decimals, in Table 2 to 3 decimals, Figure 7 to two decimals on the Oy axis and Figure 6 to one decimal on the Oy axis,

 

2----The correlation coefficients for the linear adjust in Figure 8 must be indicated

Authors response: The coefficients of correlation R-square were displayed on the Figure chart number 7, both for a and b positions, pages 307 and 309.

Reviewer 3 Report (New Reviewer)

Comments and Suggestions for Authors

Hemp (Cannabis sativa) was historically an important agricultural crop, primarily due to the production of hemp fiber.
Today, in a modern context, it is considered a fast-growing plant, making it a potential source of cellulose and lignocellulosic residues after processing. These residues can subsequently be used as a renewable source of heat. The article addresses this issue, reflecting a current and relevant topic.

After studying the article, I can conclude that it is methodologically well-structured. It compares the measured properties of briquettes made from hemp residues with those of oak briquettes."

However, the article lacks a new scientific contribution—such as the application of a novel method, an economic analysis, a life cycle assessment of the product, or other original research. The article should not merely serve as a comparative protocol but should also bring new insights.

The article does not address issues related to the combustion of hemp residues, such as CO₂ and NOₓ emissions, problems with storing briquettes made from hemp residues, or the costs of drying.

Similar articles have been published, for example:

• Ivanova, T., Kolacíková, M., Havrland, B., & Hutla, P. (2014). Mechanical and chemical properties of briquettes made of waste hemp (Cannabis sativa var. Finola) biomass. AgriTech Sci, 8, 1–4.
• Roman, K., & Grzegorzewska, E. (2024). The Comparison of Physical and Chemical Properties of Pellets and Briquettes from Hemp (Cannabis sativa L.). Energies, 17(9), 2210. https://doi.org/10.3390/en17092210
• Kraszkiewicz, A., Kachel, M., Parafiniuk, S., Zając, G., Niedziółka, I., & Sprawka, M. (2019). Assessment of the Possibility of Using Hemp Biomass (Cannabis Sativa L.) for Energy Purposes: A Case Study. Applied Sciences, 9(20), 4437. https://doi.org/10.3390/app9204437

 

Several comments and questions:

• Figures 7 and 8 could be combined into a single graph.
• In the conclusions, include the pros and cons of using hemp residues for briquettes compared to other materials.
• Briquettes made from hemp residues produce significantly more ash than oak—what is the implication of this in terms of usability?
• Have you tried combining multiple materials in a single briquette?
• Consider using different bar colors in Figures 3, 5, and 10—one color per material.
• Figure 2 appears unprofessional.
• It would be useful to include the price of oak briquettes and hemp residue briquettes—this would enrich the discussion section.

Author Response

Reviewer 3

I would like to thank the reviewer for his observations and suggestions. All changes in the new version of the paper are highlighted in blue.

1. Hemp (Cannabis sativa) was historically an important agricultural crop, primarily due to the production of hemp fibre. Today, in a modern context, it is considered a fast-growing plant, making it a potential source of cellulose and lignocellulosic residues after processing. These residues can subsequently be used as a renewable source of heat. The article addresses this issue, reflecting a current and relevant topic. After studying the article, I can conclude that it is methodologically well-structured. It compares the measured properties of briquettes made from hemp residues with those of oak briquettes." However, the article lacks a new scientific contribution—such as the application of a novel method, an economic analysis, a life cycle assessment of the product, or other original research. The article should not merely serve as a comparative protocol but should also bring new insights.

 Authors response: In order to respond to these comments of the reviewer, some additions were made to the paper at the following points: a. in the introduction area, when we make the general discussion about briquettes “From an ecological point of view, briquettes are friendly to the environment, being neutral towards carbon dioxide, by eliminating into the atmosphere the same amount that it absorbed during the life of the tree or plant in question through the photosynthesis process. Analyzing further the Life Cycle Assessment, the exclusive use of lignocellulosic residues in obtaining briquettes is a strong point of them that creates a sustainable activity in the long term (BS EN ISO 14040:2006+A1:2020)”; b- highlighting the novel elements found in the paper “Taking into account the objectives and activities of the work, the following original points of the work stand out: a complete analysis of the properties of hemp briquettes was carried out, a comparison was made between hemp briquettes and oak wood briquettes, and an original methodology was used to determine the compressive strength and splitting resistance.s, c- discussions about the prices of briquettes “Regarding the price of briquettes at European level, it is quite low, namely for beech and oak briquettes it is 0.28 euro/kg, for softwood briquettes 0.27 euro/kg and 0.22 for straw briquettes (similar to hemp residues). The manufacturing process is fully automated, so from this point of view the manufacturing labour is negligible. The highest expenses are the cost of raw materials 30% and its drying 24.9%, company expenses 11.9%, raw material storage 8.3%, briquetting 8%, cooling 8.6% and packaging-storage of briquettes 8.3%. The use of briquettes for combustion in residential, commercial or industrial spaces is opportune, successfully replacing firewood, which can be used with greater efficiency in composite materials technology [1,5].”

 

2. The article does not address issues related to the combustion of hemp residues, such as CO₂ and NOₓ emissions, problems with storing briquettes made from hemp residues, or the costs of drying.

Authors response: The environmental issue is found in the introduction chapter, in the general presentation area of ​​briquettes, lines 58-63. “From an ecological point of view, briquettes are friendly to the environment, being neutral towards carbon dioxide, by eliminating into the atmosphere the same amount that it absorbed during the life of the tree or plant in question through the photosynthesis process. Analyzing further the life cycle assessment, the exclusive use of lignocellulosic residues in obtaining briquettes is a strong point of them that creates a sustainable activity in the long term (BS EN ISO 14040:2006+A1:2020).” The cost of drying was written at the lines 469-476 (see also the above issue number1)

 

3. Similar articles have been published, for example:

• Ivanova, T., Kolacíková, M., Havrland, B., & Hutla, P. (2014). Mechanical and chemical properties of briquettes made of waste hemp (Cannabis sativa var. Finola) biomass. AgriTech Sci, 8, 1–4.
• Roman, K., & Grzegorzewska, E. (2024). The Comparison of Physical and Chemical Properties of Pellets and Briquettes from Hemp (Cannabis sativa L.). Energies, 17(9), 2210. https://doi.org/10.3390/en17092210
• Kraszkiewicz, A., Kachel, M., Parafiniuk, S., Zając, G., Niedziółka, I., & Sprawka, M. (2019). Assessment of the Possibility of Using Hemp Biomass (Cannabis Sativa L.) for Energy Purposes: A Case Study. Applied Sciences, 9(20), 4437. https://doi.org/10.3390/app9204437

 Authors response: These   new articles were added to the references paper and cited accordingly in the paper.

 

1. Several comments an Authors response added questions: Figures 7 and 8 could be combined into a single graph.

 Authors response: The two figures were combined into one (the new Fig 7), with positions a and b.

 

2. In the conclusions, include the pros and cons of using hemp residues for briquettes compared to other materials.

 Authors response: A brief SWOT analysis was made in the conclusions chapter. “The use of hemp briquettes is very opportune because its residues are renewable year after year (like any type of biomass) and sustainable. The transformation of lignocellulosic hemp residues into briquettes meets a pressing need of users at an acceptable price (firewood is increasingly scarce and the price increases from year to year). It should be noted that the storage in nature and the natural degradation of these residues will raise the same amount of carbon dioxide in the atmosphere as when used in combustion. The manufacturing flow of hemp briquettes does not require changes. The only disadvantage of hemp briquettes is the higher ash content than wood residues, for which specific storage and efficient use measures must be taken when using them.”

 

1. Briquettes made from hemp residues produce significantly more ash than oak—what is the implication of this in terms of usability?

 Authors response: We added at lines 461-466 “The major implications of the higher ash content in hemp briquettes are related to the more frequent emptying of the ash box and its use as fertilizer. Therefore, if in the case of oak briquettes, the ash is discharged weekly, in the case of hemp briquettes it should be done daily. To remedy this situation, it is recommended to continuously discharge the ash with a screw conveyor into a large container, which will be taken over weekly by the company transforming it into fertilizer. Also, to remedy this situation, it is recommended to burn the two types of briquettes together in a ratio of 1:10 in favour of the oak ones.”

 

1. Have you tried combining multiple materials in a single briquette?

 Authors response: In our preliminary research it seemed that there was a weak adhesion and cohesion between the two residues during their combination into briquettes. Therefore, we proposed to resume this part of the research using additives specific to this briquetting process. An addition was made in the chapter discussing future research in the field. “Also, more research will be done combining oak and hemp residues with some additives, even though in our preliminary research it seemed that there was an incompatibility between these two types of lignocellulosic residues”. 

 

1. Consider using different bar colours in Figures 3, 5, and 10—one colour per material.

 Authors response: Colours were changed, red for hemp in all figures. See figure 3, at line 294, figure 5 at line 324 and figure 10 at line 388, in the new revised paper.

 

1. Figure 2 appears unprofessional.

 Authors response: Another figure was posted.

 

1. It would be useful to include the price of oak briquettes and hemp residue briquettes—this would enrich the discussion section.

 Authors response: A new paragraph regarding briquette prices at European level has been added and detailed by operations, in order to observe their proportion. “Regarding the price of briquettes, it is quite low, namely for beech and oak briquettes it is 0.28 euro/kg, for softwood briquettes 0.27 euro/kg and 0.22 euro/kg for straw briquettes (similar to hemp residues). The manufacturing process is fully automated, so from this point of view the manufacturing the labor cost is negligible. The highest expenses are the cost of raw materials 30% and its drying 24.9%, company expenses 11.9%, raw material storage 8.3%, briquetting 8%, cooling 8.6% and packaging-storage of briquettes 8.3%. The use of briquettes for combustion in residential, commercial or industrial spaces is opportune, successfully replacing firewood, wood which can be used with greater efficiency in composite materials technology”.

 

Round 2

Reviewer 3 Report (New Reviewer)

Comments and Suggestions for Authors

Thank you to the authors for addressing my comments.
The revisions have been implemented to a satisfactory extent, contributing to an improved overall quality of the manuscript. I have no further remarks regarding the content of the article.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The work is interesting and easy and pleasant to read; the results are competitive with the reference and other previously reported. However, the manuscript shows a lack of several formal issues in scientific information presentation (figures and tables) and other aspects which must be reviewed before publication consideration.

 

The HCV scale in Figure 1 should has the the same decimal places for all the values in the Y-axis. 

Additionally, the number of decimal places must be homogeneized in Table 1

In my opinion the information given in Figures 2, 4 and 10 is low, just the bulk density for 2 materials which can be given within the text.

In Figure 3, the labels with the values above the bars must be relocated to avoid overlapping

Figure 8 needs to be reviewed; the axis titles are missing

In Figure 9, the unit of calorifica value (HCV??) must be increase to MJ/kg to avoid so great numbers. In addition, the use of moisture higher than 100% is unclear; the authors must explain and clarified this issue

The discussion sould to be improved; in my opinion is too short and few develped.

I suppose that there is included any limits to  the variability of the briquettes properties (i.e. braking strength) in refered european and other standards (not the absolute value but the variability); in this case, it must be cited and compared to obtained values in this work

If possible, I recommend to include some images/figures/schemes of briquettes and experimental devices

Author Response

Reviewer 1.

We would like to thank the reviewer for his work and pertinent and important observations in the paper.

 

The work is interesting and easy and pleasant to read; the results are competitive with the reference and other previously reported. However, the manuscript shows a lack of several formal issues in scientific information presentation (figures and tables) and other aspects which must be reviewed before publication consideration.

 

1. The HCV scale in Figure 1 should has the the same decimal places for all the values in the Y-axis. Additionally, the number of decimal places must be homogenised in Table 1

Authors: There are differences between the numbers because the Excel program does not take trailing zeros and ignores them. In table 2 we have made the harmonization.

 

2. In my opinion the information given in Figures 2, 4 and 10 is low, just the bulk density for 2 materials which can be given within the text.

Authors: Figure 2 shows the actual values and errors, and the text of the description does not repeat these values but shows how much weaker this property is for hemp than for oak. Besides, a graph is much more expressive than some numbers. The same for Figure 4 and 10. Since the values in the figure and those in the description are not redundant, please allow us to leave everything as is.

 

3. In Figure 3, the labels with the values above the bars must be relocated to avoid overlapping. Authors: In Figure 3, the numbers have been removed away so that they can no longer overlap.

 

4. Figure 8 needs to be reviewed; the axis titles are missing

Authors: In figure 7, 8, the horizontal and vertical axes have been completed. The font of these figures has also been changed to Palatino Linotype.

 

5. In Figure 9, the unit of calorifica value (HCV??) must be increase to MJ/kg to avoid so great numbers. In addition, the use of moisture higher than 100% is unclear; the authors must explain and clarified this issue.

Authors: Figure 9 was completed. The installations we are currently working with have this unit of measurement: kJ/kg. It is also very precise, converting to MJ/kg would mean working with 3 decimal places or approximating the initial value, which would mean a less precise value. Therefore, please allow us to keep this unit of measurement KJ/kg. The abbreviations HCV -high calorific value and LCV- low calorific value have also been explained in the figure legend.

 

6. The discussion sould to be improved; in my opinion is too short and few develped.

Authors: The chapter of “Discussion” was extended with new aspects and ideas.

 

7. I suppose that there is included any limits to the variability of the briquettes properties (i.e. braking strength) in refered european and other standards (not the absolute value but the variability); in this case, it must be cited and compared to obtained values in this work.

Authors: Many mechanical properties of briquettes (splitting, compression) are not specified in international standards. Also, particle size, a very important property of wood particles, is not specified either as a method or as values, this being taken from wood composites sector.

 

8. If possible, I recommend to include some images/figures/schemes of briquettes and experimental devices.

Authors: We introduced new Figure 2 with briquette and its own particles.

The English was improved.

Reviewer 2 Report

Comments and Suggestions for Authors

The work "Briquettes obtained from lignocellulosic hemp (Cannabis sativa spp.) waste, comparative to oak ones" explores the possibility of using the cannabis residues to produce biofuels, and especially Briquettes, through the analysis of their physical, mechanical, chemical and energetic properties. A comparative study is conducted with Quercus, which is referred to only as Oak, both in the title and elsewhere in the text. It is recommended that its scientific name also be provided.

1. As main remarks, the following can be highlighted:

1.1. In the introduction, there is important information about cannabis cultivation and its different uses, especially in the textile industry. It would be good to have an idea of ​​the quantities, to know, for example, how much waste is generated, since the shortage of wood and wood-based semi-finished products/composites is mentioned at the beginning. This would allow us to know how reliable the availability of hemp-based raw materials is.

1.2. On the other hand, only line 82 mentions oak, without much further discussion. For the sake of balance, although several studies have already been conducted with oak species for bioenergy purposes (as the authors indicate), it would be good to include some specific information on this subject. At least the wood shortage mentioned at the beginning refers primarily to oak species, so it would be good to clarify this.

1.3. The authors state that "The main purpose of this work is to make briquettes from hemp ligno-cellulosic waste and to determine their main characteristics" (lines 80-81). However, they only describe how they determined the characteristics and the results obtained, and a littel bit about how they made the briquettes (without clearly stating under what conditions, what pressures, how many samples...), but nothing about the results of the briquettes obtained... (perhaps before selecting those that have the potential to be produced for the intended purpose): Either the objective must be reformulated in relation to what has been developed in the manuscript, or everything that is supposed to be achieved in the objective must be developed.

1.4. In the same way, it seems that several fractions of raw material from different sieves were used (lines 95 to 102) to manufacture the briquettes based on each small material (lines 120-121). However, the results do not show each type of briquette, with the characteristics it presents, according to the different analyses carried out (density, breaking, splitting, ash). Rather, we see, in a global way, briquettes made from Hemp and those from Oak. So what was the purpose of sieving the samples?

1.5. Table 1 is not relevant, and it is not necessary to present the measurements taken during the experimental phase, as shown in that table. You can simply indicate their purpose in the methodology section, along with the respective formulas for the parameters they were used to determine.

1.6. IIt is very confusing to mention in the methodology that the bulk density was determined for the raw material (lines 86 to 96), but in the results, present the bulk density for briquettes (lines 253 to 257), and then in point 3.1, and figure 2.

1.7. Where are the results for the calorific density determined, as mentioned in lines 190 to 197? It would also be good to explain why this parameter is determined, if the calorific value and density are already known separately. These clarifications were made at least for the calorific value. It would be interesting to do the same for the other values.

1.8. A comparison is being made between briquettes obtained from Hemp and those obtained from Oak, but regarding calorific value, one of the most important parameters, it is presented only for Hemp (Figure 9). Interestingly, the oak results are mentioned in the text, without first presenting them in a figure or table.

1.9. Figure 9 shows the higher calorific value (HCV) and lower calorific value (LCV) provided by the calorimeter, as indicated in the methodology, to explain why the briquettes had a moisture content during the test. Therefore, they determined the calorific value for absolutely dry wood (182 - 189). Curiously, the results obtained are not shown.

2. In terms of form, it is important to take into account the following:

2.1. Formula (1) as well as figure 1 are not necessary in the introduction. Their content can simply be summarized on the essential information to be conveyed. Also, the word "Objectives" (line 80) should be deleted, to speak about it directly, without mentioning it, because it is part of the introduction, an outcome of what was previously developed.

2.2. "Balk density" appears on lines 222, 238 (figure), 253, and "bulk density" on lines 225, 239, 240, 254, 256. Please check and standardize.

2.3. Please check line 244 and others, which say "Row material".

2.4. Please use only one form of expression between unit density (lines 259, 260) and unitary density (line 263).

2.5. There are no titles for the different x- and y-axes in Figure 8. And for figures 2 and 4, there is no y-axis.

2.6. Table 2 should be eliminated, not only because it presents data that already appear (unnecessary repetitions should be avoided), but also because it is not cited in the text, unless it was a mistake to have written figure 1 on line 316. Also, it does not enter into the discussion part.

Author Response

REVIEWER 2

We would like to thank the reviewer for his work and pertinent and important observations in the paper.

The work "Briquettes obtained from lignocellulosic hemp (Cannabis sativa spp.) waste, comparative to oak ones" explores the possibility of using the cannabis residues to produce biofuels, and especially Briquettes, through the analysis of their physical, mechanical, chemical and energetic properties. A comparative study is conducted with Quercus, which is referred to only as Oak, both in the title and elsewhere in the text. It is recommended that its scientific name also be provided.

Authors: The scientifical name of oak was provided in the title and text: Quercus robur L.

 

1. As main remarks, the following can be highlighted:

1.1. In the introduction, there is important information about cannabis cultivation and its different uses, especially in the textile industry. It would be good to have an idea of ​​the quantities, to know, for example, how much waste is generated, since the shortage of wood and wood-based semi-finished products/composites is mentioned at the beginning. This would allow us to know how reliable the availability of hemp-based raw materials is.

Authors: We added at lines 38-39: “The global industrial hemp market was estimated at $11.03 billion in 2024, and is expected to be $30.24 billion in 2029”.

      

1.2. On the other hand, only line 82 mentions oak, without much further discussion. For the sake of balance, although several studies have already been conducted with oak species for bioenergy purposes (as the authors indicate), it would be good to include some specific information on this subject. At least the wood shortage mentioned at the beginning refers primarily to oak species, so it would be good to clarify this.

Authors: A generous paragraph on oak was inserted in the introductory part of the work, lines 40-44.

 

1.3. The authors state that "The main purpose of this work is to make briquettes from hemp ligno-cellulosic waste and to determine their main characteristics" (lines 80-81). However, they only describe how they determined the characteristics and the results obtained, and a littel bit about how they made the briquettes (without clearly stating under what conditions, what pressures, how many samples...), but nothing about the results of the briquettes obtained... (perhaps before selecting those that have the potential to be produced for the intended purpose): Either the objective must be reformulated in relation to what has been developed in the manuscript, or everything that is supposed to be achieved in the objective must be developed.

Authors: We added at the briquetting chapter: “The agglomerate compression pressure in the briquetting machine was constant and equal to 20 bars, and the average time to release a briquette was 1 minute”, in order to explain some parameters of briquetting. In the zone of objective chapter, we added: “In order to know the combustion capacity of the studied briquettes, several physical properties (humidity, density), mechanical properties (compression, splitting) and energetic properties (calorific value, calorific density and ash content) were determined”.

 

1.4. In the same way, it seems that several fractions of raw material from different sieves were used (lines 95 to 102) to manufacture the briquettes based on each small material (lines 120-121). However, the results do not show each type of briquette, with the characteristics it presents, according to the different analyses carried out (density, breaking, splitting, ash). Rather, we see, in a global way, briquettes made from Hemp and those from Oak. So what was the purpose of sieving the samples?

Authors: As is the case in composite material technology (OSB, particleboard), the particle size influences the properties of the final product obtained. We completed at lines 372-376, in the discussion zone: “Regarding the particle size, it was observed that there were two differentiating elements between hemp and oak, namely a higher peak for hemp (representing a greater amount of thick chips) and a shift of the graph to the right (representing greater non-uniformity of these particles). Both aspects led to the obtaining of briquettes with slightly lower properties”.

 

1.5. Table 1 is not relevant, and it is not necessary to present the measurements taken during the experimental phase, as shown in that table. You can simply indicate their purpose in the methodology section, along with the respective formulas for the parameters they were used to determine.

Authors:  This table as well as the calculation relationship used is part of other experimental research by the authors and it is intended to clearly show that the ash content influences the calorific value, but only within certain limits. We work with hemp, but it will be noted that it has different chemical constituents, which will influence the calorific value in a certain way. So, please keep this figure, especially since it is an original one, which we do not find in the authors' articles either.

 

1.6. IIt is very confusing to mention in the methodology that the bulk density was determined for the raw material (lines 86 to 96), but in the results, present the bulk density for briquettes (lines 253 to 257), and then in point 3.1, and figure 2.

Authors: Both types of bulk densities have been determined. In this sense, we can give you an example: the bulk density of the fine material is found in lines 119-125 as method and 254-258 as results, and the bulk density of the briquettes in lines 269-273 as method and results.

 

1.7. Where are the results for the calorific density determined, as mentioned in lines 190 to 197? It would also be good to explain why this parameter is determined, if the calorific value and density are already known separately. These clarifications were made at least for the calorific value. It would be interesting to do the same for the other values.

Authors:  we added the next sentences:” The calorific density was determined in order to size the feed silo of a thermal power plant, which is usually expressed in m³. Also, in many thermal calculations this unit of measurement is required, which we must have already calculated. All calculus were made in Excel program with specific formula.

 

1.8. A comparison is being made between briquettes obtained from Hemp and those obtained from Oak, but regarding calorific value, one of the most important parameters, it is presented only for Hemp (Figure 9). Interestingly, the oak results are mentioned in the text, without first presenting them in a figure or table.

Authors: Presenting values in tables or figures and then in text becomes redundant, which is why we tried to avoid redundancy. Moreover, the table would have been so simple (with two rows and 2 columns) that it would not have been well perceived by readers. The presentation of the graph for oak briquettes was not done because the diagram would have been similar, with slightly different values.

 

1.9. Figure 9 shows the higher calorific value (HCV) and lower calorific value (LCV) provided by the calorimeter, as indicated in the methodology, to explain why the briquettes had a moisture content during the test. Therefore, they determined the calorific value for absolutely dry wood (182 - 189). Curiously, the results obtained are not shown.

Authors: We added in the method chapter, lines 188-190. “In order to capture a series of oxides that would negatively influence the combustion of the sample in the calorimetric bomb, the manufacturer of the installation proposes the use of 3 ml of distilled water on the bottom of the bomb, which slightly increases the moisture content of the sample up to 5%, during the initial period of operation of the installation, that is, until the sample is ignited. To determine the calorific value at 0%moisture content, reference relationships can be used, as eq. 7.” Referring to CV for moisture content of 0% of briquettes, we stated “If we refer to the moisture content of 0% (Eq. 7), the calorific value of the two types of briquettes becomes 18,511 KJ/kg for hemp briquettes and 17,839 KJ/kg for oak briquettes”.

 

2. In terms of form, it is important to take into account the following:

2.1. Formula (1) as well as figure 1 are not necessary in the introduction. Their content can simply be summarized on the essential information to be conveyed. Also, the word "Objectives" (line 80) should be deleted, to speak about it directly, without mentioning it, because it is part of the introduction, an outcome of what was previously developed.

Authors: Word “Objectives” was erased. This table as well as the calculation relationship used are important for paper because they are intended to clearly show that the ash content influences the calorific value, but only within certain limits. So, please keep this figure and equation, especially since it is an original one, which is do not find in the authors' articles either.

 

2.2. "Balk density" appears on lines 222, 238 (figure), 253, and "bulk density" on lines 225, 239, 240, 254, 256. Please check and standardize.

Authors: We erase the word “balk” and remain “bulk”

 

2.3. Please check line 244 and others, which say "Row material".

Authors: Expression become “Raw”

 

2.4. Please use only one form of expression between unit density (lines 259, 260) and unitary density (line 263).

Authors: “Unitary” word was erased.

 

2.5. There are no titles for the different x- and y-axes in Figure 8. And for figures 2 and 4, there is no y-axis.

Authors: Figure 8 was completed. Fig 2 and 4 were also completed. The numbering of the figures has changed, as a new figure has been introduced with the image of the types of briquettes.

 

2.6. Table 2 should be eliminated, not only because it presents data that already appear (unnecessary repetitions should be avoided), but also because it is not cited in the text, unless it was a mistake to have written figure 1 on line 316. Also, it does not enter into the discussion part.

Authors: We made a lot of adding in Discussion Chapter, so, please let this table in the paper. The comparative presentation of the two types of briquettes took the following form, following the additions made to the text.

“Following all the values in Table 2, a slight decrease in the properties of hemp briquettes is observed, this being due to the physic-chemical properties of hemp residues. For instance, splitting strength was 0.079 N/mm² for oak briquettes and 0.076 N/mm² for hemp briquettes. However, these small decreases do not have a major impact on the uses of briquettes for combustion purposes, especially due to better calorific properties. The exception to this rule was the calorific value which was slightly higher in the case of hemp residues and the ash content which falls within the range of agricultural residues”.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Some of the authors responses are completely unacceptable; blaming Excel for the inadequate format is what my first-year students usually do. The formal requirements for a figure, table, etc are widely accepted in the scientific community worldwide and this kind of issues is not expected to be corrected in a manuscript

Issue 1.-

You can modify Excel settings or use another application instead of one as inadequate for scientific results discussion as Excel is, for example Origin. 

Issue 2.-

In my opinion is too low information for so great figures bur if this issue is so important for the authors, I leave the decission in Editor's hands.

Issue 9.-

I am not talking about the number you consider for the calculation but just the labels in the Y axis; you have to pay close attention to see how many zeros there are in the numbers so the number format in Y-axis must be improved using scientific notation, MJ instead of kJ...

On the other hand, it is not physically possible any composition higher than 100% so the authors must clarify the meaning of 120, 140, 160...% moisture.

Issue 6.-

the discussion improvement has not been very extense; I encourage the authors to review and improve it

Author Response

Reviewer 1.

Some of the authors responses are completely unacceptable; blaming Excel for the inadequate format is what my first-year students usually do. The formal requirements for a figure, table, etc are widely accepted in the scientific community worldwide and this kind of issues is not expected to be corrected in a manuscript.

 

Issue 1.- Round 1: The HCV scale in Figure 1 should has the the same decimal places for all the values in the Y-axis. Additionally, the number of decimal places must be homogenised in Table 1. Round 2: You can modify Excel settings or use another application instead of one as inadequate for scientific results discussion as Excel is, for example Origin.

Authors response: According to the reviewer's requirements, Figure 1 was changed by assigning three decimal places to each value on the Oy axis. We also moved to the expression of calorific values from KJ/kg in MJ/kg, in order to be consistent with the requirements regarding the figure 9.

 

Issue 2.- Round 1. In my opinion the information given in Figures 2, 4 and 10 is low, just the bulk density for 2 materials which can be given within the text.

Round 2: In my opinion is too low information for so great figures bur if this issue is so important for the authors, I leave the decission in Editor's hands.

Authors response:

 Any reader prefers to see a figure instead of data existing in the text. A figure always shows the difference between the analyzed values and their amplitude. In the written text, only the percentage differences were kept, so as not to be redundant with the values appearing in the figure. Therefore, the authors consider that the form of presentation with figures is more elegant and closer to the journal readers than the one with written text.

 

Issue 9.- Round 1: -

Round 2: I am not talking about the number you consider for the calculation but just the labels in the Y axis; you have to pay close attention to see how many zeros there are in the numbers so the number format in Y-axis must be improved using scientific notation, MJ instead of kJ...

On the other hand, it is not physically possible any composition higher than 100% so the authors must clarify the meaning of 120, 140, 160...% moisture.

Authors response1: The values that exist inside of the figures (including Figure 9) now have the same number of decimal places. Also, the expression of Oy axis has changed from KJ/kg to MJ/kg.

Authors response 2: The definition of moisture content in the case of porous materials such as wood products and coal is not made as a part of the total. The expression of moisture content is made as a percentage ratio between the amount of water in the wood and the absolute dry mass of the wood. Think that we have a 100 g piece of dry wood that will be kept immersed for a long period of time in water, and when reweighed it will have 210 g. By calculation we will obtain (210-100)/100 x100=110%. For example, a spruce wood will reach a maximum moisture of 210% and a beech wood will reach a maximum moisture content of 120%.

 

Issue 6.-Round 1: The discussion sould to be improved; in my opinion is too short and few developed.

Round 2: the discussion improvement has not been very extense; I encourage the authors to review and improve it.

Authors response: The discussion chapter was improved in the new revised paper.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Improvements have been made to the documents.

However, the amount of waste generated by the cannabis processing chain remains to be determined to know whether it could be a good alternative as a readily available raw material.

I still have the same doubts regarding tables 1 and 2.

But for the rest, the clarifications given by the authors are acceptable.

Author Response

Reviewer 2 (Round 2)

• Improvements have been made to the documents.

 

• However, the amount of waste generated by the cannabis processing chain remains to be determined to know whether it could be a good alternative as a readily available raw material.

Authors: There are European programs that encourage the cultivation of hemp for industrial, pharmaceutical and medical uses (see hemp oil) and a lot of money is allocated for development. Therefore, an accelerated growth in the cultivation of common hemp is predicted. Also, there are some estimations  “The global industrial hemp market was estimated at $11.03 billion in 2024, and is expected to be $30.24 billion in 2029”.

 

• I still have the same doubts regarding tables 1 and 2. Round 1; Round 1: Issue1.5 and 2.6

Authors: Table 1 is important for the paper, because it shows the dimensions of the briquettes, respectively the basis for calculating the other properties. European standards limit the dimensions of briquettes and pellets and attaches great importance to them. That is why a large paragraph was introduced in the discussion chapter to analyse them lines 381-390 and the influence on density and compressive strength.

Table 2 is a comparative one, very important for readers, in which the differences in the values of the main properties analysed in the paper are observed and could be discussed.

 

• But for the rest, the clarifications given by the authors are acceptable.

 

Author Response File: Author Response.pdf