Life Cycle Assessment of Biochar from Residual Lignocellulosic Biomass Using Kon-Tiki Kilns: Applications in Soil Amendment and Wastewater Filtration

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This is an interesting paper about life cycle assessment of biochar produced from residual lignocellulosic biomass and its applications in soil amendment and wastewater treatment. The subject is very interesting, and is very well written.

It seems that something is missing in the tile like: “Life cycle assessment of biochar produced from residual lignocellulosic biomass”?

 The main question is why the use of BC is considered as water filtering. BC, due to its characteristics, large surface area and surface properties, adsorbs pollutants. Filtration is only the retention of solid particles. Why use this terminology?

One major issue is the missing analysis of the impact of energy consumption in the pyrolysis process. Why was it not considered?

Other questions are highlighted in the document attached.

Comments for author File: Comments.pdf

Author Response

Reviewer 1:

This is an interesting paper about life cycle assessment of biochar produced from residual lignocellulosic biomass and its applications in soil amendment and wastewater treatment. The subject is very interesting, and is very well written.

It seems that something is missing in the tile like: “Life cycle assessment of biochar produced from residual lignocellulosic biomass”?

The title has slightly changed due to another reviewer’s comment. It now reads:  Life cycle assessment of biochar from residual lignocellulosic biomass using Kon-Tiki kilns: applications in soil amendment and wastewater filtration. The wording “biochar from residual lignocellulosic biomass” is equivalent to the proposed reviewer wording.

 The main question is why the use of BC is considered as water filtering. BC, due to its characteristics, large surface area and surface properties, adsorbs pollutants. Filtration is only the retention of solid particles. Why use this terminology?

BC certainly has good adsorption properties, but it can also be used as a filtration medium (small particle removal). The overall filtration efficiency measured in this work is in fact the sum of the two effects (filtration and adsorption), although given the nature of the particles in wastewater (organic matter) the filtration component is expected to dominate. This application was analyzed as the pig farms that generate the residues also require filtration agents for their wastewater treatment, so reusing the BC to this end adds to the circular economy strategy. This is explained in lines 39-45, 64-68, and 98-99. For this reason, the term “filter, filtration” and so on is correct throughout the document.

One major issue is the missing analysis of the impact of energy consumption in the pyrolysis process. Why was it not considered?

The Kon Tiki kiln operation does not require an external energy source. The energy is taken from the combustion of the biomass on the top layers. That’s why there are also no indirect emissions for the kiln operation, just the direct ones.

Other questions are highlighted in the document attached.

Nitrates (NO₃^- ) are now correctly written throughout the document.

Other minor remarks and comments have been considered and changed using track changes in the text, when appropriate:

• • The BM abbreviature has been eliminated from the manuscript. It reads now “biomass”.
  • Figure 1 has been modified to represent better the avoided emissions and the outputs of the system.
  • There is no transport stage because the BC is used in the same plots where the residual biomass is generated. The Kon Tiki kiln is an onsite transformation technology, specifically convenient to farmers. This is clarified in lines 374-375.
  • All the mentioned standards are now cited and included in the reference list.
  • When using the BC from water treatment, it was considered the impact of the pollutants leaching from this BC to the soil?
  • The pollutants are organic matter, and their impact is not considered after they finish their used life, as the main assumption is that they will remain trapped within the biochar until they’re degraded. The reviewer is right in noting that throwing organic matter to soil will have potential impacts of eutrophication, and we also note in lines 427-429 that the potential benefits on soil enhancement are not considered, precisely because of the lack of data regarding the interactions of the used material with the environment. This is an assumption that will need more study in the future, and it has been added in the perspectives of the work, lines 310-315.
  • Figure 6 has been modified for consistency with Figure 5.
  • The IBI reference has been fixed.

Reviewer 2 Report

Comments and Suggestions for Authors

Please find the review in attached file.

Comments for author File: Comments.pdf

Author Response

Reviewer 2:

Note: Please consider that, when the reply cites a line number, it will correspond only to the TRACKED CHANGES version of the NEW manuscript.

 

Therefore I recommend to publish the manuscript after minor revision. I have two overall technical comments:

1. If technically feasible, please provide figures in higher quality, as the letters are unclear. Increasing the resolution may help address this issue.

The figures have been reworked, hoping they read better now.

2. Additionally, please check and unify the notation for ions (e.g., NO₃⁻, PO₄³⁻ or NO3, PO3) throughout the entire manuscript.

The correct notation of the ions is used now throughout the manuscript.

Minor remarks:

Figure 1: Please explain the abbreviation DAP.

The abbreviation is now defined in line 294. Also, Figure 1 is Figure 7 now, after modifying the manuscript’s sections order, as per the editor’s request. The abbreviations used in the figure are now explained in the Figure’s caption. This adds clarity to the figure.

Line 207: It appears that "macronutrients" should be used instead of "micronutrients."

Thank you, that’s correct. It’s been corrected now.

Line 214: Please use a subscript for NO3. In Line 325, "NO₃⁻" is used; please standardize throughout.

The correct notation of the ions is used now throughout the manuscript.

Line 231: Ensure there is a space between “with” and “carbon.”

Corrected

Lines 348, 349, 350, 354: Please standardize the spelling of "co-product" and "coproduct."

The term “coproduct” is used now consistently throughout the manuscript.

Lines 360–362 and 368–370: This sentence is repeated; please revise.

Thank you for noticing this. We have revised and rewritten these paragraphs to avoid repetition.  These are now in lines 225-231

Line 394 and Table 6: Please also standardize the method of wri?ng ions in units for EP.

The correct notation of the ions is used now throughout the manuscript.

Reviewer 3 Report

Comments and Suggestions for Authors

Very interesting and well done work. I found a few errors which I will report later. In general I recommend spending a few words explaining what kon tiki is. in my case, for example, I couldn't explain why the electricity to start the pyrolysis wasn't counted and only after watching some videos did I understand. Perhaps you could also introduce a link to the video you deem appropriate, or you could add a diagram of the device.

Please be more generous in describing graphs and tables. better explaining the abbreviations, the scope of the results and how they should be read

I also ask you to carefully review all the result numbers reported in the text and in figures.

Title

Can be improved, in my opinion. For example can be important to understand the production technology:

“Life cycle assessment of Kon Tiki kilns biochar from residual lignocellulosic biomass: applications in soil amendment and wastewater filtration”

 

Introduction

Weel done in my opinion. I just want to leave some suggestions or ideas for improvement.

-          In table 1 maybe is possible to specify also cradle and gate on each analysis?

-          Can you improve information about Kon Tiki? And about quenching?

Materials and methods

Line 133: “Branches with a diameter of led than 2 m…” ! maybe in 2 mm or 2 cm?

Line 136 and 165: BM? Maybe biomass?

Table 2: it seem that table 2 is incomplete (data about PP bags?) and has some errors (38 t per each km of transport seems very high! Describing Water filtration scenario the water from well is calculated in m3 and in the text in L.

Results and discussion

Please, in the captions of Figures 2 and 3 please repeat the name of categories, it is more convenient for the reader.

In the Figure 4 maybe you can use ‘BC production’ instead of ‘BC transformation’, to match the previous graph.

Conclusions

Can be improved.

Author Response

Reviewer 3:

Note: Please consider that, when the reply cites a line number, it will correspond only to the TRACKED CHANGES version of the NEW manuscript.

Very interesting and well done work. I found a few errors which I will report later. In general I recommend spending a few words explaining what kon tiki is. in my case, for example, I couldn't explain why the electricity to start the pyrolysis wasn't counted and only after watching some videos did I understand. Perhaps you could also introduce a link to the video you deem appropriate, or you could add a diagram of the device.

Thank you for the suggestion. We have added a paragraph explaining the operation of the Kon Tiki kiln and a diagram (Figure 8), hoping it’s useful for those not familiar with the technology.

Please be more generous in describing graphs and tables. better explaining the abbreviations, the scope of the results and how they should be read

We have added the abbreviations meanings to the figures’ descriptions. We also added some text to the beginning of section 2.2 to explain how to read Figure 1, hoping this helps to clarify the meaning of the following similar figures. These figures are pretty much standard on LCA results, so we’re hoping this won’t be an issue for the target audience.

I also ask you to carefully review all the result numbers reported in the text and in figures.

We made a small correction to the Biochar transportation flow in Table 2, and the corresponding corrections in the text. All the other results and units seem correct.

Title. Can be improved, in my opinion. For example can be important to understand the production technology: “Life cycle assessment of Kon Tiki kilns biochar from residual lignocellulosic biomass: applications in soil amendment and wastewater filtration”

We agree to include the transformation technology in the title. The title has slightly changed due to another reviewer’s comment. It now reads:  Life cycle assessment of biochar from residual lignocellulosic biomass using Kon-Tiki kilns: applications in soil amendment and wastewater filtration.

Introduction. Weel done in my opinion. I just want to leave some suggestions or ideas for improvement. In table 1 maybe is possible to specify also cradle and gate on each analysis?

The three papers cited in Table 1 are cradle to grave analysis. This has now been explicitly stated in the Table caption.

-   Can you improve information about Kon Tiki? And about quenching?

Thank you for the suggestion. We have added a paragraph explaining the operation of the Kon Tiki kiln and a diagram (Figure 8), hoping it’s useful for those not familiar with the technology.

Materials and methods

Line 133: “Branches with a diameter of led than 2 m…” ! maybe in 2 mm or 2 cm?

It should be 2 cm. It’s changed now.

Line 136 and 165: BM? Maybe biomass?

The BM abbreviature has been eliminated from the manuscript. It reads now “biomass”.

Table 2: it seem that table 2 is incomplete (data about PP bags?) and has some errors (38 t per each km of transport seems very high! Describing Water filtration scenario the water from well is calculated in m3 and in the text in L.

Thank you for your comments. Clarifying these issues:

1) The inventory includes the PP bags as part of the first stage (biochar production in KonTiki Kiln). The last items for this stage are the PP material required and the energy used to produce the bags. As the BC bagging process is manual, there are no more inputs related to the bags.

2) The unit tkm is standard in LCA to measure transportation work. It means tonnes transported *times* km of distance traveled. In this work, as the numbers in Table 2 are referred to 1 t of biochar, it means that the BC is transported from the parcels to the pig farms only 34 km away, in average (this is described in line 451). There was, however, a mistake on the number in the table, which is now corrected (it reads 34 now).

3) In lines 424-427 it is explained the water demand of washing and rinsing the BC before use. We corrected a mistake in the text and adjusted the wording to clarify. It reads now that it is required 7.18 L per kg of BC. Since the number in Table 2 is referred to tonne of BC, the water demand is 7.18 m3.

Results and discussion

Please, in the captions of Figures 2 and 3 please repeat the name of categories, it is more convenient for the reader.

The captions of Figures 1-3 have been modified to include the abbreviations of the impact categories.

In the Figure 4 maybe you can use ‘BC production’ instead of ‘BC transformation’, to match the previous graph.

This was changed, it now reads BC production

Conclusions. Can be improved.

The conclusions were revised and improved. Be believe the revised text, although short, gives answer to all the research questions of the paper.