Influences of Management Practices and Methodological Choices on Life Cycle Assessment Results of Composting Mixtures of Biowaste and Green Cuts

Round 1

Reviewer 1 Report

The authors of the article present an example of LCA modeling of composting of a selected product with reduction of global warming potential. The effect of treatment processes on the effect of chemical composition changes is considered.  The impact of composting management practices and the effect of the selected marginal product on the overall environmental impact of the composting system were examined.

The composting system in Germany was adopted from the base model.

Unfortunately, the methodology did not substantiate the average distance of compost deliveries to 21.9km. Such information is only confirmed in line 453 for literature item 42. The source of the adopted distance affecting the OFP indicator should be indicated in the methodology.

. Methodological justification for the adopted mixing ratio of 70% by weight of biowaste and 30% of green matter is not indicated.

The modeling was based on the introduction of compost, taking into account CH4, N2O and NH3, and organic matter as an alternative to peat. The contribution of the composting product as a substitute for mineral and marginal fertilizers was taken into account.

Analyzed LCA for 9 bio-waste blending scenarios. Selected ingredient participation systems and different compost preparation procedures were considered.

The results present emission levels and chemical composition analysis of the by-product resulting from biowaste processing (compost).

The results of the study are discussed in relation to the available literature on the subject.

The results relate directly to the obtained research results. They are a comprehensive presentation of the results of selecting a scenario for the production of fertilizer from compost.

The authors accurately demonstrated the changes in the production of natural fertilizers from civilization waste. The validity of replacing fossil fuels with available waste materials is indicated

The research and literature review should emphasize the validity of separating the LCA for production indicating the obtained computational results in the selected OpenLCA v.2 algorithm, No justification for the choice of the selected model and the source of the license.

The article prepared at a good scientific level. The lack of a deeper statistical analysis of the significance of differences for the presented scenarios can be taken as a shortcoming.

Author Response

The detailed observations and constructive critiques not only identified areas that needed improvement but also provided clear guidance on how to address them. We genuinely appreciate the time and effort invested by reviewer 1 in evaluating my manuscript and helping to bring it to its best possible version.

We have carefully considered and addressed all the comments, and we believe that the revised manuscript has now been significantly improved. I am hopeful that the changes will meet reviewer 1’s and the journal's expectations.

Issue 1: Unfortunately, the methodology did not substantiate the average distance of compost deliveries to 21.9km. Such information is only confirmed in line 453 for literature item 42.

• It is literature value that was estimated based on the average distance travelled by a waste collection truck in the region of Heidelberg, Germany. The distance was estimated to be 7.4 km for collection from households and a 14.5 km to the composting plant.

Issue 2: The source of the adopted distance affecting the OFP indicator should be indicated in the methodology.

• The OFP impact category is affected by the NOx emissions arising from the transport. The underlying impact mechanism on how NOx affects OFP is covered in the ReCiPe 2016 method, and this is mentioned in the methodology.

Issue 3: Methodological justification for the adopted mixing ratio of 70% by weight of biowaste and 30% of green matter is not indicated.

• The default ratio of 70:30 was assumed based on the data from the composting facility in Heidelberg. This is based on the certification document from “RAL-Gütesicherung Kompost Chargenuntersuchung”.

Issue 4: The research and literature review should emphasize the validity of separating the LCA for production indicating the obtained computational results in the selected OpenLCA v.2 algorithm, No justification for the choice of the selected model and the source of the license.

• OpenLCA is a freeware tool that is able to operate with various LCI-databases; in this case the most recent version of Ecoinvent. Ecoinvent is mentioned in line 112,
  OpenLCA v2 is an advanced tool for the evaluation of LCA results, the model selected for the evaluation is ReCiPe 2016 and is one of the latest methodologies. This is mentioned in 2.2.4 (line 161).

General comment: The article prepared at a good scientific level. The lack of a deeper statistical analysis of the significance of differences for the presented scenarios can be taken as a shortcoming.

• Thank you for the complement – much appreciated. You are right that varying the transport distance would alter the results, but that belongs to all model parameters. The influence of the transport distance does not correspond with the aims of this study; therefore, we kept the transport distance constant for all scenarios.

Reviewer 2 Report

Dear authors,

The research is generally insightful. However, the scenario-based work it is partially very difficult to follow, and the clarity is insufficient. In the current form, therefore, overall, the work lacks transparency.

1. A clear and easy-to-follow nomenclature for the different scenarios should be introduced and applied. The current structure is not logical, distorts the attention of the reader and makes it very difficult and partially impossible to follow the actual contents and results. It makes no sense to have an a-b-c-d structure if there are no “a” or “b” etc. in some of the settings, and in addition in section 2.3.2 this is not even properly explained, and a clear overview of the scenarios is lacking/the presentation is deficient and lacks clarity and completeness. In addition, partially you talk about scenario groups (1, 2, 3) and partially about scenario only (4, 5, 6), but still seem to stick to the a-b-c structure, no matter if it is a “scenario group” or a “scenario”. And for example, it seems that in scenario 4 only 4b exists, while scenario 6 seems to have 6b and 6c, but this is not clear and confusing. Furthermore, scenarios 4, 5, and 6 are generally not clearly presented, very little information is provided.

2. There also seem to be mistakes in applying the own structure, or in reporting what was done with precision. For example, according to Table 2, the “b” elements would have a BW:GW mixing ratio of 60:40 and the “c” elements a BW:GW mixing ratio of 90:10, but then Table 3 ignores this and the “b” and “c” elements all have an indicated BW:GW mixing ratio of 70:30.

3. Figure 6: unclear what the reference scenarios (the claimed “default scenarios”) are here.

4. Figure 6b: typing error in word “Sceanrio”.

no specific comment

Author Response

The detailed observations and constructive critiques not only identified areas that needed improvement but also provided clear guidance on how to address them. We genuinely appreciate the time and effort invested by reviewer 2 in evaluating my manuscript and helping to bring it to its best possible version.

We have carefully considered and addressed all the comments, and we believe that the revised manuscript has now been significantly improved. I am hopeful that the changes will meet reviewer 2’s and the journal's expectations.

Issue 1: The scenario-based work it is partially very difficult to follow, and the clarity is insufficient. In the current form, therefore, overall, the work lacks transparency.

The current structure is not logical, distorts the attention of the reader and makes it very difficult and partially impossible to follow the actual contents and results.

It makes no sense to have an a-b-c-d structure if there are no “a” or “b” etc. in some of the settings, and in addition in section 2.3.2 this is not even properly explained, and a clear overview of the scenarios is lacking/the presentation is deficient and lacks clarity and completeness. In addition, partially you talk about scenario groups (1, 2, 3) and partially about scenario only (4, 5, 6), but still seem to stick to the a-b-c structure, no matter if it is a “scenario group” or a “scenario”. And for example, it seems that in scenario 4 only 4b exists, while scenario 6 seems to have 6b and 6c, but this is not clear and confusing. Furthermore, scenarios 4, 5, and 6 are generally not clearly presented, very little information is provided.

• We have amended chapter 2.3.2. The default scenario is now shown in table 2 and the previous scenario groups 4 and 5 have been merged to scenario group 4. The former Scenario group 6 has become scenario group 5. Thus the a-b-c structure is now consistently applied upon all scenario groups.

Issue 2: There also seem to be mistakes in applying the own structure, or in reporting what was done with precision. For example, according to Table 2, the “b” elements would have a BW:GW mixing ratio of 60:40 and the “c” elements a BW:GW mixing ratio of 90:10, but then Table 3 ignores this and the “b” and “c” elements all have an indicated BW:GW mixing ratio of 70:30.

• Section 2.3.2 has also been restructured to clearly distinguish between the SG1 to SG3 which investigate the impact of controllable composting management practices and scenarios SG 4 and SG 5 which investigate the impact of using alternative substituted products.

Issue 3: Figure 6: unclear what the reference scenarios (the claimed “default scenarios”) are here.

• The default scenario for scenario group 4 has been redefined in table 2 to make the scenario definition more clear

Issue 4: Figure 6b: typing error in word “Sceanrio”.

• It has been corrected

Round 2

Reviewer 2 Report

Dear Authors,

The contents of the revised manuscript are now clear and insightful. Some minor issues only should find your attention:

1. Heading of Table 2 required updating, as there are no longer 6 scenarios. Instead of "Description of scenario 1 to 6 groups." one option is "Description of scenario groups 1 to 5.", or simply "Description of scenarios under study."

2. There are 11 scenarios in this work, but the abstract refers to 9 scenarios studied, which is potentially confusing to the reader. This could be improved in the abstract.

3. In Table 3, there is inconsistent usage of decimal numbers. For example, where you indicate "62.0" you should also indicate "59.0" instead of "59", "17.0" instead of "17", etc.

Author Response

Dear Reviewer,

We hope this message finds you well. We would like to express our sincere gratitude for your continued commitment to the improvement of our manuscript. As suggested by you, we have made the following changes:

1. The heading of Table 2 has been modified to include only 5 scenarios
2. The number of scenarios in the abstract has been modified
3. The decimal units have been made uniform