Environmental Impact Assessment of a Plant Cell-Based Bio-Manufacturing Process for Producing Plant Natural Product Ingredients

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript "Environmental Impact Assessment of a Plant Cell-Based Biomanufacturing Process for Plant Natural Product Ingredients Production" describes the results of modeling the impact of different production stages, as well as different raw materials manufacturing on the environment. As an example, the plant cell culture biomanufacturing of tannine was chosen. Expectedly, the most environment-impactful was the stage of biomanufacturing as it was the most energy-consuming. Raw materials production made a negligible contribution. Unexpected was the observation made by the Authors that such renewable sources of energy as solar and geothermal were even more hazardous than the mixture of fossil fuels and renewable sources. Unfortunately, no explanation (even speculative) is given within the paper to this fact. So why does solar energy perform so badly?

The analysis of the material circularity index revealed a relatively low level of material circularity, which was caused by the lack of reused or recycled components among raw materials and the short lifetime of a product.

The wild harvest approach, anyway, was worse in terms of environmental impact.

In general, I feel that the model used might be, perhaps, too idealized as it sets, for example, the same recycled fraction for all different types of raw materials. In addition, I feel it necessary to provide more details about the assessment of the environmental impact of the different energy sources.

Author Response

Comment 1: The manuscript "Environmental Impact Assessment of a Plant Cell-Based Biomanufacturing Process for Plant Natural Product Ingredients Production" describes the results of modeling the impact of different production stages, as well as different raw materials manufacturing on the environment. As an example, the plant cell culture biomanufacturing of tannine was chosen. Expectedly, the most environment-impactful was the stage of biomanufacturing as it was the most energy-consuming. Raw materials production made a negligible contribution. Unexpected was the observation made by the Authors that such renewable sources of energy as solar and geothermal were even more hazardous than the mixture of fossil fuels and renewable sources. Unfortunately, no explanation (even speculative) is given within the paper to this fact. So why does solar energy perform so badly?

Response 1: Thank you for pointing out. Figure 3 represents the normalized scores for the various environmental impact categories associated with the plant cell culture based biomanufacturing process across production stages A1 – A3, as listed in Table 1. The normalized scores are calculated based on energy consumption during each production stage. The embodied environmental factors for the different energy source were obtained from the database that we listed in the methodology section. Solar energy and geothermal energy have relatively higher embodied environmental factors resulting in them having relatively higher environmental impacts compare to other energy sources. To make this clearer, we have added a new Table 2 that lists the embodied environmental factors from different energy sources and added a corresponding description in the main body of the text.

 

Comment 2: The analysis of the material circularity index revealed a relatively low level of material circularity, which was caused by the lack of reused or recycled components among raw materials and the short lifetime of a product. 

Response 2: Thanks for comment. We agree and feel no revision required to address this comment.

 

Comment 3: The wild harvest approach, anyway, was worse in terms of environmental impact. 

Response 3: Thanks for comment. We agree and feel no revision required to address this comment.

 

Comment 4: In general, I feel that the model used might be, perhaps, too idealized as it sets, for example, the same recycled fraction for all different types of raw materials. In addition, I feel it necessary to provide more details about the assessment of the environmental impact of the different energy sources.

Response 4: Thanks for the comment. We have added more information in Section 3.1 to provide more detail about the environmental impact of the different energy sources. Additionally, we have added Table 2 to give more details on the embodied environmental factors from different energy resources.

Reviewer 2 Report

Comments and Suggestions for Authors

The article “Environmental Impact Assessment of a Plant Cell-Based Bio-Manufacturing Process for Plant Natural Product Ingredients Production” describes a Life Cycle Assessment methodology for evaluating the relative sustainability of a bio-production process using plant feedstocks. It also provides insights into potential areas for improvement in these processes. The authors assessed the environmental impact of plant cell culture-based bioproduction, identified critical process steps that contribute to environmental stress, and compared the environmental impact of this approach with that of traditional wildlife-based methods. While the research is of good quality, there are areas that require improvement, as outlined below:

1. How much confidence can we place in the data presented in Tables 1 and 3? Are these energy values per kilogram of finished product?

2. Why is the recycled fraction consistently 0.19 in Table 4 for all processes?

3. What is the increased environmental risk associated with solar and geothermal energy, as shown in Fig. 3?

4. Which energy sources are preferred in the UK to reduce environmental risks while maximizing efficiency?

5. What is the increased global warming potential associated with the production PVP-10 (Fig. 4)?

 

6. What are the uncertainties for all the diagrams?

Author Response

The article “Environmental Impact Assessment of a Plant Cell-Based Bio-Manufacturing Process for Plant Natural Product Ingredients Production” describes a Life Cycle Assessment methodology for evaluating the relative sustainability of a bio-production process using plant feedstocks. It also provides insights into potential areas for improvement in these processes. The authors assessed the environmental impact of plant cell culture-based bioproduction, identified critical process steps that contribute to environmental stress, and compared the environmental impact of this approach with that of traditional wildlife-based methods. While the research is of good quality, there are areas that require improvement, as outlined below:

 

Comment 1: How much confidence can we place in the data presented in Tables 1 and 3? Are these energy values per kilogram of finished product?

Response 1: Thanks for the comment. The data in Tables 1 and 3 have high confidence as these were generated from industry analysis, as stated in Section 2.2.4. Energy values indicated in Table 1 represent the energy consumption for each step in the biomanufacturing process necessary to produce 1 kg of plant extract for each extraction scenario, as stated in Section 2.2.5. To improve the clarity here, we added additional explanatory text in Section 2.2.4.

 

Comment 2: Why is the recycled fraction consistently 0.19 in Table 4 for all processes?

Response 2: Thanks for the question. Table 5 (Table 4 in original manuscript) outlined the media composition of the plant cell culture formulation used for the biomanufacturing production system. The plant cell culture media were made with all listed components and were regarded as waste after completion of the biomanufacturing process. Only a small fraction (19%) of the post-biomanufacturing media waste can currently be recycled, thus we assume that the recycled fraction for all biomanufactured extracts to be the same. We have updated the text in Section 3.2 to provide more clarity here.

 

Comment 3: What is the increased environmental risk associated with solar and geothermal energy, as shown in Fig. 3?

Response 3: Thanks for the question. Figure 3 represents the normalized scores for the various environmental impact categories associated with the plant cell culture-based biomanufacturing process across production stages A1 – A3, as listed in Table 1. The normalized score is calculated based on energy consumption during each production stage and the embodied environmental factors of different energy source were obtained from the database that we listed in the methodology section. Solar energy and geothermal energy have higher embodied environmental factors resulting in them having a higher environmental impact compare to other energy sources. To make this clearer, we have added a new Table 2 to list the embodied environmental factors from different energy sources and added a corresponding description in the main body of the text.

 

Comment 4: Which energy sources are preferred in the UK to reduce environmental risks while maximizing efficiency?

Response 4: Thanks for the question. Wind driven energy is the most widely installed renewable energy source in Scotland, where the plant cell culture based biomanufacturing site is located. However, in our manuscript, the energy source used to compare with the tannin extraction process is a mixed energy blend comprising 70% fossil fuel derived energy sources and 30% renewable energy sources as indicated in Section 3.3. We have added additional text here to improve the clarity of this part of the manuscript.

 

Comment 5: What is the increased global warming potential associated with the production PVP-10 (Fig. 4)?

Response 5: Thanks for the question. PVP-10 is one of the material inputs used during the biomanufacturing process with higher embodied carbon factors. The normalized global warming potential associated with the PVP-10 is 1.804e-5, as we showed in Figure 4. To provide more context, we have added new Table 4 to outline the embodied environmental factors for material in the biomanufacturing process in section 2.2.4.

 

Comment 6: What are the uncertainties for all the diagrams?

Response 6: Thanks for the question. The uncertainty for the diagrams is addressed by the description of the system boundaries and the data provided for the study in terms of energy consumption during the biomanufacturing process. Additionally, uncertainty during the biomanufacturing process has been addressed by a consideration of different scenarios during the extraction and post-extraction processes as listed in Table 1 and described in Section 2.2.3.

Reviewer 3 Report

Comments and Suggestions for Authors

10.09.2024

A review to evaluate its suitability for publication Type of manuscript in Sustainability:

Article Title: Environmental Impact Assessment of a Plant Cell-Based Bio- manufacturing Process for Plant Natural Product Ingredients Production

Authors: Gbenga F. Oluyemi, Richard Afolabi, Samuel Casasola Zamora, Yuan Li, David McElroy

The peer-reviewed manuscript is based on the problems of assessing and comparing the environmental impact of a bioproduction process, identifying critical process stages with environmental impact and comparing the proposed bioproduction approach with the traditional wild harvesting method in terms of the strength of environmental impact.

The manuscript gives the impression of a deeply thought-out work with practical realisation of the assigned results: in the Introduction section the authors indicate the current status and unresolved problems related to ecological and economic problems of plant cell culture technology. The Materials and Methods section presents a ready-made scenario for bioproduction, life cycle inventory of materials and energy, life cycle impact assessment and material cycling.

The Results section discusses in detail several categories of environmental impacts with the justified choice of the research object being the extraction of tannin from spruce.

Comments and suggestions made by the reviewer are aimed at clarifying some unclear points and improving the quality of the material for publication in Sustainability:

1.      Is there permission from the authors [20]: Ding, T., et al, Life cycle assessment of tannin extraction from spruce bark. iForest - Biogeosciences and Forestry, 2017. 10(5): p. 504 on the authors' use of Figure 2 for their own purposes?

2.      Does the grinding of the raw materials specified in the extraction scheme have to be accompanied by particle size control? Does the grind size matter for further extraction?

3.      The graph in Figure 3 should carry information on the statistical analysis of the results - sample size in determining normalised scores standard deviation. If no statistical analysis is necessary, give justification.

4.      Same in Figures 4, 5, 6 and 7.

5.      Table 4 is presented with very sparse data and does not, in my opinion, carry useful information. The content of Table 4 should either be supplemented with meaningful and differentiating figures or presented as a text with enumerations.

6.      On the basis of which results is the life span of the extracts in Table 5 given? Were these results from accelerated ageing or practical review data?

 Respectfully, reviewer

Comments for author File: Comments.pdf

Author Response

Comments and suggestions made by the reviewer are aimed at clarifying some unclear points and improving the quality of the material for publication in Sustainability:

 

Comment 1: Is there permission from the authors [20]: Ding, T., et al, Life cycle assessment of tannin extraction from spruce bark. iForest - Biogeosciences and Forestry, 2017. 10(5): p. 504 on the authors' use of Figure 2 for their own purposes?

Response 1: Thanks for the question. We have re-drawn Figure 2 based on the original figure and updated the figure legend accordingly.

 

Comment 2: Does the grinding of the raw materials specified in the extraction scheme have to be accompanied by particle size control? Does the grind size matter for further extraction?

Response 2: Thanks for the question. Grinding of the raw material is a crucial step for tannin extraction from spruce bark.  However, in the available referenced study that we used, there is no mentioning of particle size control. In the plant cell culture based biomanufacturing, grinding is not part of the process.

 

Comment 3: The graph in Figure 3 should carry information on the statistical analysis of the results - sample size in determining normalised scores standard deviation. If no statistical analysis is necessary, give justification.

Response 3: Thanks for the comment. Figure 3 considered the environmental impact during the biomanufacturing process in all scenarios within the system boundary using different energy resources. The uncertainty/variables are addressed by the scenario approaches. We used a model-based assessment where repeated trials to establish variance isn’t possible. Instead, we have addressed the uncertainty through alternative scenario analysis.

 

Comment 4: Same in Figures 4, 5, 6 and 7.

Response 4: Thanks for the comment. In Figure 4, 5, 6 and 7, we have addressed potential system uncertainty through scenario analysis.

Figure 4 showed the environmental impacts associated with producing the various input materials associated with the plant cell culture based biomanufacturing process. The material input is constant during biomanufacturing process.

Scenario-based approaches were used for Figure 5, 6 and 7. In Figure 5, we considered the environmental impact of all individual scenarios within the system boundary. In Figure 6, we compared the environmental impact of the biomanufacturing process versus natural extraction process under all scenarios. In Figure 7, we have analysed the greenhouse gas emission under different post extraction scenarios to address the uncertainty.

 

Comment 5: Table 4 is presented with very sparse data and does not, in my opinion, carry useful information. The content of Table 4 should either be supplemented with meaningful and differentiating figures or presented as a text with enumerations.

Response 5: Thanks for the comment. Table 6 (Table 4 in original manuscript) is pivotal for the context of Material Circularity Index as it showed that all raw material used during the biomanufacturing process does not including any recycled or reused material and that most of process waste is neither recyclable nor reusable. Such illustration provided solid evidence to estimate the current MCI. We have added more text in Section 3.2 to make a stronger connection between the text and the table here.

 

Comment 6: On the basis of which results is the life span of the extracts in Table 5 given? Were these results from accelerated ageing or practical review data?

Response 6: Thanks for the question. The figure of product life span from biomanufacturing process is provided by Green Bioactives Limited based on in-house assessment.

Reviewer 4 Report

Comments and Suggestions for Authors

The article is nicely written, however It would be great to include  1) Global sensitivity analysis.

Also, Could you please explain LCA as a flowchart other than Figure1

Author Response

Comment 1: The article is nicely written, however It would be great to include  1) Global sensitivity analysis.

Response 1: Thanks for the positive response and suggestion.  We plan to incorporate a global sensitivity analysis in future studies.

 

Comment 2: Also, Could you please explain LCA as a flowchart other than Figure1

Response 2: Thanks for the comment. The Figure 1 showed the system boundary for the biomanufacturing process, the relevant context is explained in Section 2.2.3. Additionally, we have further refined the text to provide more clarity.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The Authors made necessary corrections to the text and provided the detailed answers to my questions. I believe the revised manuscript is suitable for publishing.

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Authors,

I am satisfied with your response to my comments.