The Potential of the Co-Recycling of Secondary Biodegradable Household Resources Including Wild Plants to Close Nutrient and Carbon Cycles in Agriculture in Germany

Round 1

Reviewer 1 Report

The topic of this paper is timely and essential for decoupling. However, several points need to be revised.

1. The introduction section seems to be too long, and it is not easy to know what the author(s) tries to make points. The section starts without a proper introduction, so readers are left wondering where this argument goes. Then, finally, in section 1.7, the aim and object are suddenly discussed, which is too late. This introduction seems to need to have a proper introduction.
2. What is more, it is unclear what the existing literature's research gaps are even after the long literature review from section 1.1 to 1.6. In other words, this means that it is not clear what the contribution of this paper is. It would be better to identify the research gap in the existing literature. 
3. Probably, because of the above, the objective of this paper, mentioned in section 1.7, is too broad and without focus. Therefore, it would be better to revise. Once revised in this section, the following sections also need to revise to answer the questions identified.
4. Section 1.6 explains circular concepts, but it explains only concept one, not other concepts. The readers are again left wondering what the concepts are? (The concepts appears in section 2.2). In this regard, the abstract is also challenging for readers to understand as there is no explanation "concept".
5. Section 2.1 starts by mentioning concepts 1, 2 and 3 without explaining what those concepts are. The structure of this paper needs to be revised.
6. Table 1 needs more information, such as the year of data collection and the data collection method. The author(s) need to explain the abbreviation and others used for the table, such as "p*a" and "*". p*a is explained in the conclusion section. The issue is not only in table 1 but also in other tables. Please check and explain the tables carefully.
7. Section 2.2 introduce concepts, but the explanation is flat. What are the new to examine these three? 
8. Why does the author(s) use the term "concept"? As far as it is understood from section 2.2, this seems not a concept but a scheme or something like that.
9. Section 3 presents data but is unclear when, where and how the data was generated.

(Minor point)

1. There are two types of expression for "concept one" and "concept 1" in the abstract. The author(s) needs to use only either one of the two. 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Dear Authors:

I have the following comments and suggestions to which I expect answers:

1. „The estimation for biopolymers orientates on literature calculations and own investigated COD values.” Please justify why you used COD and not BOD? PHA is produced mainly by bacterial methods. Not all carbon determined by COD can be used by bacteria.
2. „Substitution of fossil-based plastics”. Some assumptions are not very realistic. You have determined that it is possible to substitute 19% of plastic consumption by producing PHA. Is this a theoretical idea only or is it feasible? You report that "In agriculture in Germany 1.1 million tons of plastics are used every year". 19% of this is 209,000 tons, while the worldwide PHA production capacity (according to G.-Q. Chen (ed.), Plastics from Bacteria: Natural Functions and Applications, Microbiology Monographs, Vol. 14, DOI 10.1007 / 978-3 -642-03287_5_6, © Springer-Verlag Berlin Heidelberg 2010) are 10,000 tons only!
3. „There is a lack of investigation of joint exploitation of household resources” . Literature in this area requires supplementing, important items are missing, e.g.
   
   RijutaGanesh Saratale^aSi-KyungCho^bGaneshDattatraya Saratale^cAvinash A.Kadam^aGajanan S.Ghodake^bManuKumar^dRamNaresh Bharagava^eGopalakrishnanKumar^fDongSu Kim^gSikandar I.Mulla^hHanSeung Shin^c „A comprehensive overview and recent advances on polyhydroxyalkanoates (PHA) production using various organic waste streams”; Bioresource Technology, Volume 325, April 2021, 12468

4. Future research. The research should be supported with LCA analyses, also SLCA, LCC, which would show not only ecological aspects but also socio-economic ones.
   
   
5. References:

1.I propose to consider quoting international ISO standards which are equivalents of German DIN standards: [39] - [42].

2. Items 13, 23, 24, 49, 52, 53, 58, 62 require corrections and additions.

Good luck !

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

I understand the authors tried to revise the paper and appreciated the effort. However, the introduction section was written very poorly (because of this, the same as the subsequent sections). The section gave me the impression that this paper is an institutional report rather than a research paper. 

As mentioned in my first reviewer's report, the introduction is too long (not in the sense of actual word numbers). Especially the arguments from sections 1.1 to 1.6 are too general and are not a critical literature review. So, even if the authors mentioned in section 1.7 that there is a research gap and objectives, it is difficult to follow your argument. The stated research objective looks pretty general and does not sound attractive to continue reading. 

Here, I am not saying actual research does not worth reading. I am simply saying that the authors need to revise this section to convince readers that your research is worth reading and attractive.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

My point by point position to authors' responses

Ad. 1 The factors influencing the biogas production are: COD, BOD and TOC. There is a lot of literature on this topic. COD and BOD value are not comparable. In most cases BOD is half of COD. This wil strongly affect your estimation.
The reference [45] which you based on is not possible to reach by an international reader. YOU SHOULD EXPLAIN IN THE MANUSCRIPT WHY YOU DIDN'T TAKE BOD INTO ACCOUNT.

Ad.2 In that case, I propose that the title of the manuscript should include the word "theoretical", i.e. THE THEORETICAL POTENTIAL OF THE CO-RECYCLING…

Ad.3 this explanation is at least trivial! In the age of the Internet, access to literature is practically unlimited, especially for a scientist from the University of Stuttgart. I RECOMMEND THAT YOU UPDATE YOUR LITERATURE.

Ad. 4 let it be

Ad.5. Comply with the German DIN standards: [39] - [42], but also state the international ISO standards for which the DIN’ ones are equivalent. It will be more convenient for the international reader.

Ad. 6. Many German-language literature references are virtually unattainable for an international reader!

The missing aspects of the references are among others:

[13], [24], [33], [49], [53], [54], [55], [58], [62], [67], = source not given (name, publisher)

[23 ], [42],  Accessed = what ?

[46 ], [69] – when Accessed ?

Author Response

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Author Response File: Author Response.pdf

Round 3

Reviewer 1 Report

With the extensive revision of the introduction section, it became much better than before. The research gap and aims of the research could be improved but can be accepted as a present form. Therefore, I think this article is now ready to publish.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

I read your's explanations and the changes introduced. However, despite the assurances, not all suggestions were taken into account, e.g. you declared corrections:"  I have added the website in the reference list." = where ?    1839.Deutsches Institut für Normung e.V. Deutsche Einheitsverfahren zur Wasser-, Deutsche Einheitsverfahren zur Wasser-, Abwasser- und Schlammuntersuchung; Schlamm und Sedimente; Beuth Verlag GmbH (38414-12) (accessed on 14 May 2021). 1940.Deutsches Institut für Normung e.V. Schlamm, behandelter Bioabfall und Boden - Bestimmung des Gesamt Stickstoffgehalts mittels trockener Verbrennung; Beuth Verlag GmbH (16168). Available online: 14.05.2021. 2041.Deutsches Institut für Normung e.V. Wasserbeschaffenheit - Anwendung der induktiv gekoppelten Plasma Massenspektrometrie; Beuth Verlag GmbH (17294-2) (accessed on 14 May 2021). 2142.Deutsches Institut für Normung e.V. Deutsche Einheitsverfahren zur Wasser-, Abwasser- und Schlammuntersuchung; Summarische Wirkungs- und Stoffkenngrößen; Beuth Verlag GmbH (38409-41) (   but still no ISO equivalent for DIN as I asked for as well as adding accessed on 14 May 2021) or Available online: 14.05.2021 without providing web address is useless!    I suggested clarifying the title of the article by adding "theoretical potential" = not done!

Author Response

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Author Response File: Author Response.pdf

Round 4

Reviewer 2 Report

It looks like you don't want to understand my comments and recommendations.

Specifically:

Ad.  1) I added the web pages to the reference list where they were missing according to your suggestion. But in the case of the DIN documents, I accidentally added “access to” beforehand. Since I did not get these documents online but from our library, I changed the type of DIN references from internet document to norm dokument.

But author only changed for one standard - [38]. The rest: [39-42] are unchanged.

Ad.2. I wrote in the text that the DIN standards correspond to the international ISO standards. I hope this makes it easier for the international reader to under stand.

From the beginning, I applied for the number and titles of international ISO standards, the equivalents of which are DIN standards [38-42]. Why does the author insist on not providing it?

Ad.3 Last time I made a mistake when I changed the title. I changed it in the wrong document. I am sorry for this mistake. This time the title change proposal is included.

In the last version of the manuscript I see:

The Theoretical Potential of the Co-recycling of Secondary Bio[1]degradable Household Resources Including Wild Plants to Close Nutrient and Carbon Cycles in Agriculture in Germany

 the word theoretical is deleted, what kind of change is this?