Pilot-Scale Anaerobic Co-Digestion of Food Waste and Polylactic Acid
Round 1
Reviewer 1 Report (Previous Reviewer 2)
The current paper can be considered to be published.
Author Response
We would like to thank the reviewers for their support to our research.
Author Response File: 
Author Response.pdf
Reviewer 2 Report (Previous Reviewer 4)
Thank you for your corrections.
Author Response
We would like to thank the reviewers for their support to our research.
Author Response File: Author Response.pdf
Reviewer 3 Report (New Reviewer)
Dear Authors,
In general, I think it is a very interesting manuscript that fits into the circular economy. In order to improve the quality of this manuscript, please note the few corrections I have included below.
Line 73: It is worth adding that digestate (waste from agricultural biogas plants) can also be reused to produce biodegradable materials, e.g. based on TPS thermoplastic starch. You will review the following publications: "Properties of Biocomposites Produced with Thermoplastic Starch and Digestate: Physicochemical and Mechanical Characteristics". In addition, you continue to write about the decomposition of PLA bioplastic. Also add a publication where the biodegradation of TPS thermoplastic starch was tested. In my opinion, this is very important because these materials are increasingly used to produce new biodegradable plastics: "The anaerobic degradability of thermoplastic starch: Polyvinyl alcohol blends: Potential biodegradable food packaging materials". I think there may be even more such publications in the literature.
Line 89: Try to justify why your research is innovative. This will underline the validity of your research. Of course, filling the research gap is important, but in my opinion this justification should be approached more broadly.
Line 103: That last sentence is unnecessary. They can be placed somewhere in the methodology.
Line 113: Add a deviation from the average temperature, e.g. +/- (…..).
Line 147: Consider inserting an anaerobic digester image. I assume that this is a device of my own design?.
Line 150: Each test apparatus should have a description (name: manufacturer, city, country). Review the entire methodology in this respect.
Line 252 Are the results close or far from the expected values. This generally applies to all results obtained. Try to justify it.
Line 300: Add one more conclusion outlining the prospects of your research. Forward-looking conclusions. That's what's missing here.
Line 307: In my opinion, the citations are well chosen, but you should add a few more publications. 25 publications is a bit too little in my opinion, especially since the topic concerns biodegradable materials (commonly described in the literature. I suggest giving about 30 items.
Author Response
We would like to thank the reviewer for their thoughtful comments. We have revised the manuscript based on their feedback. Please see attachement.
Author Response File: Author Response.pdf
Reviewer 4 Report (New Reviewer)
This paper, entitled Pilot-scale anaerobic co-digestion of food waste and polylactic acid, is a scholarly work and can increase knowledge on this domain. The authors provide an interesting and original study, the content is relevant to Sustainability.
I have some general and specific comments:
- abstract and keywords are meaningful
- why some parts of text are written in red?
- the manuscript doesn't respect the MDPI
- About BMP tests, please check and consider Holliger et al., 2016 Water Science and Technology; Hafner et al., 2020 Water about recommendations and modalities for BMP tests.
- What is the S/X (or I/S) ratio for BMP tests?
- Is there any positive control for BMP tests allowing to validate the tests?
- Please express results of methane production in normo-milliliters of biogas or methane per gram of VS (this unit is widely used for results in anaerobic digestion).
- Is the blank (inoculum) substracted for biogas or methane production in Figure 1?
- Same comments about expression of unit for Figure 2 (NL / kg VS)
- Please check colours and legends for Figure 2.
As it, the manuscript is not fully acceptable for publication and require some amendments and additional information. I recommend the following decision: RECONSIDER AFTER MAJOR REVISION.
Author Response
We would like to thank the reviewer for their thoughtful comments. We have revised the manuscript based on their feedback. Please see attachement.
Author Response File: Author Response.pdf
Round 2
Reviewer 4 Report (New Reviewer)
The authors provide a revised version of their manuscript taking into account all the comments and requests of amendments. The authors provide also detailed answers in their response and I agree with all the answers. I recommend the following decision: ACCEPT IN PRESENT FORM.
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
The authors present scientifically sound work in a concise manner. Two areas where improvement could be made:
1. Figures 1 and 2 showcase no error bars (perhaps indicating there were no replicates run?)
2. All the figures could use more instructive captions
Reviewer 2 Report
The authors provide very simple data that can not sustain a full length paper. Normally, the anaerobic digestion refers to continuous operation of a reactor not a batch experiment. The results obtained in this study was based on batch test.
Reviewer 3 Report
In this paper, the authors have obtained a lot of data or information from their research work. However, I don't support the acceptance of this paper published in this journal. Here are my several comments. I can't tell what kind of scientifical questions the authors try to address in this research, as well as the meaningness of this research. As to the introduction section, it's also difficult for readers to understand the intentions of the authors. For example, on Page 2 lines 65-67, how to get this conclusion for the authors? Regarding the presence of the data, it's not comparable for different groups using the volume of total biogas production since there are differences in terms of methane content among different digesters., taking an example of Figure 1. For these reasons, the article cannot be allowed to be published in this journal.
Reviewer 4 Report
The significance of the paper is that the pilot scale experimental results allow to optimise the parameters for the combined anaerobic treatment of organic waste and bio-based plastics for the best biogas yield.
According to the article, the research aims to investigate the impact of PLLA on methane production under different substrate and experimental conditions. The experiment was not carried out with biodegradable plastics already produced, but the effect of PLLA produced from food waste was investigated.
It would be useful to provide the key characteristics of the production of PLLA from waste. It is not clear what parameters were used to produce PLLA from waste and what characterises these PLLAs besides molecular weight.
It is concluded that higher methane yields can be achieved with PLLA, which may improve the economics of such treatment. However, it appears that degradation does not take place completely. In the future, attention should also be paid to the microplastics generated.
The article contains a lot of abbreviations which should be highlighted in a list for ease of reference. In addition to PLLA, PLA is used several times in the article. It is not clear what the difference is between the two? This should be explained!
In the first sentence of the abstract, the abbreviation (AD) is misplaced in line 13. And in the later parts of the text he uses both anaerobic digestion and the abbreviation together, which is unnecessary.
