Mesophilic, Anaerobic Digestion in a Full-Scale, Commercial Biogas Reactor Kills Seeds More Efficiently than Lab-Scale Systems
Round 1
Reviewer 1 Report
Comments for author ：
The content of the article is very interesting and informative, but the question arises for the authors, why the research data were conducted in 2015-2016 and only now described the entire process and methodology. Has nothing changed in the methodology of fermentation or inactivation in 7-8 years? Please respond.
What is the object and subject of research?
Please tell me how relevant it is for agricultural production?
Also, in the structure of the article submission, there is no subsection "conclusion"
Literary references have an outdated retrospective: references: 14-15, 17, 24, 33-34, 43-45, 51-52. Please respond to the appropriateness of these links.
Author Response
Dear Reviewer 1,
please find our response to your questions below. Your questions are in italics, our responses in blue.
Kind regards,
the authors
___________________________________________________________________________________
The content of the article is very interesting and informative, but the question arises for the authors, why the research data were conducted in 2015-2016 and only now described the entire process and methodology. Has nothing changed in the methodology of fermentation or inactivation in 7-8 years? Please respond.
>>> Yes, our experiments were conducted in 2015/16. However, given the use of digestate in the circular bioeconomy (e.g., Theuerl et al. 2019, source 11) as well as the expanding and diversifying portfolio of energy cropping systems (e.g., Yang et al. 2018, Englund et al. 2020), our results are relevant again right now. This is addressed in the first paragraph of the introduction.
>>> Regarding a possible change in methodology: (1) We are aware of the fact, and we name it in the discussion, that each biogas plant is an individual (lines 609-611), so it has its own unique milieu, which can have a seed-inactivating effect. This environment may be changed by innovations in biogas technology. In fact, we pointed out in our introduction, how much biogas plants can differ in terms of their process technology and mode of operation. Nevertheless, we do not consider this to be of concern for our study as our focus was to determine whether seed inactivation in anaerobic digestion can be reproduced in laboratory systems. In terms of process technology, there have been no significant changes in agricultural biogas plants over the past 8 years. (2) In determining seed viability, we used both germination and metabolic activity. This already sets us apart from the majority of studies on seeds in anaerobic digestion, most of which only determine germinability (see discussion in Hahn et al. 2022, source 20). We are not aware of a more reliable method to determine whether a seed is viable after treatment in anaerobic digestion. However, if you were thinking of a newer method when you asked your question, we would be more than happy to include it in our discussion.
- Englund, O., Börjesson, P., Berndes, G., Scarlat, N., Dallemand, J.-F., Grizzetti, B., et al. (2020). Beneficial land use change: Strategic expansion of new biomass plantations can reduce environmental impacts from EU agriculture. Global Env. Change 60, 1–13. doi: 10.1016/j.gloenvcha.2019.101990
- Yang, Y., Tilman, D., Lehman, C., and Trost, J. J. (2018). Sustainable intensification of high-diversity biomass production for optimal biofuel benefits. Nat Sustain 1, 686–692. doi: 10.1038/s41893-018-0166-1
What is the object and subject of research?
>>> We assume that by "object and subject of the research" you mean the objective of the paper. This is clearly stated in the last paragraph of the introduction: “The objective of this study was to determine the survival of seeds in full-scale, commercial biogas reactors using the six species that had best survived mesophilic, anaerobic digestion in lab-scale, experimental reactors [20]. Five of the species were hardseeded, one was not. Seed survival was explored as a function of exposure time and additionally tested in pH-buffered water-baths. By comparing the three systems, we aimed to gain insight into the dynamics of seed inactivation and evaluate whether experimental reactors and water baths are suitable as less complex and costly options for estimating seed survival in commercial biogas reactors” (lines 93-100).
Please tell me how relevant it is for agricultural production?
>>> The importance of seed survival in agricultural production is explained in the first paragraph of the introduction (lines 28-42). In short, the sustainable use of digestate in agricultural (or other) production requires that the digestate is free from contaminants such as seeds. Because “[a]ny such contamination will result in additional costs and labor that will compromise sustainability of digestate use“ (lines 41-42).
Also, in the structure of the article submission, there is no subsection "conclusion"
>>> According to the Instructions for Authors a conclusions “… section is not mandatory but can be added to the manuscript if the discussion is unusually long or complex“ (https://www.mdpi.com/journal/fermentation/instructions, accessed 28.04.2023 and 09.05.2023). Thus, we have refrained from formulating explicit conclusions. Instead, we have included our considerations in this regard, citing the relevant literature, in the final section of the discussion ("4.3 Estimating seed survival in commercial reactors”, lines 590-622). We believe that repeating the ideas presented there in an additional Conclusions section would not add value, but would only lengthen the manuscript.
Literary references have an outdated retrospective: references: 14-15, 17, 24, 33-34, 43-45, 51-52. Please respond to the appropriateness of these links.
>>>Unfortunately, we do not understand what you mean by "outdated retrospective”. In order to be able to interpret our results, we aimed to give the interested reader a comprehensive insight into the relevant literature on seed survival in anaerobic digestion. Of course, this includes recent studies (e.g., source 20) as well as pioneer studies (e.g., source 14) and basic literature (e.g., source 24). In fact, we specifically point out that the literature on seed survival is limited (lines 60-63). We almost get the impression that you consider literature published before 2005 to be outdated, since all the references you mention (14-15, 17, 24, 33-34, 43-45, 51-52) are from that time. However, that would lack any justification, because among them there is, for example, a law which, although amended in 2022, was nevertheless published in 1998 (reference 45). Or cornerstone publications by Baskin and Baskin (reference 24) or Thompson (reference 43), which according to Scopus have been cited 425 or 284 times (as of 09.05.2023). Thus, we are convinced that the cited references are absolutely appropriate. Nevertheless, we would be grateful if you could provide us with references from your insight into the topic to current, relevant literature that we may have overlooked. This would certainly improve the quality of our manuscript.
Reviewer 2 Report
Dear Authors,
your manuscript "Mesophilic, anaerobic digestion in a full-scale, commercial bio-2 gas reactor kills seeds more efficiently than lab-scale systems", based the experiments is well presented.
The used methods are state of the art. Modelling of v(t) supported the finding results.
The manuscript show the different effect of bioreactor-scales on inactivating of seeds.
Maybe the followed paper could be integrated:
Schrade, S., Oechsner, H., Pekrun, C., & Claupein, W. (2003). Einfluss des Biogasprozeses auf die Keimfähigkeit von Samen. LANDTECHNIK, 58(2), 90–91. https://doi.org/10.15150/lt.2003.1404
Author Response
Dear Reviewer 2,
Thank you for your positive review of our manuscript. The reference you suggest integrating is already included in our manuscript: Reference number 31 (line 728).
Kind regards,
the authors
Reviewer 3 Report
The manuscript is of great interest in implementing a circular economy scheme in the anaerobic digestion of agricultural residues containing seeds. The research demonstrates the need to apply special control in the anaerobic digestion process to avoid contamination of the digestate with the presence of viable seeds.
The presentation of the manuscript is clean and consistent.
The description of the methodology is clear and easy to assimilate.
The manuscript meets the quality to be published in Fermentation, and there are only a couple of recommendations in the edition:
It is recommended that Figure 1 include labels indicating the type of reactor in each image.
It is recommended that the size of Figures 2 and 3 be adjusted so that their description remains on one page.
In Figure 2, it is necessary to include the trend lines of the graphs corresponding to A. theophrasti, as it is presented with the other studied seeds.
Author Response
Dear Reviewer 3,
Thank you for your positive and encouraging feedback on our manuscript. Please find below our reply (in blue) to your recommendations (in italics) on editing.
the authors
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The manuscript is of great interest in implementing a circular economy scheme in the anaerobic digestion of agricultural residues containing seeds. The research demonstrates the need to apply special control in the anaerobic digestion process to avoid contamination of the digestate with the presence of viable seeds.
The presentation of the manuscript is clean and consistent.
The description of the methodology is clear and easy to assimilate.
The manuscript meets the quality to be published in Fermentation, and there are only a couple of recommendations in the edition:
It is recommended that Figure 1 include labels indicating the type of reactor in each image.
>>> Now, Figure 1 includes labels indicating the type of reactor in each panel.
It is recommended that the size of Figures 2 and 3 be adjusted so that their description remains on one page.
>>> We agree with you and hope that this will be implemented by the publisher in the layout process. We have inserted our illustrations into the MDPI template to the best of our ability.
In Figure 2, it is necessary to include the trend lines of the graphs corresponding to A. theophrasti, as it is presented with the other studied seeds.
>>> The lines in the graphs in Figure 2 are not trend lines, but viability models. No viability models could be fitted for A. theophrasti. However, we have followed your suggestion and added trend lines for A. theophrasti to make the progression of inactivation easier to see for the reader.
