Volatile Fatty Acid Production from Food Waste Leachate Using Enriched Bacterial Culture and Soil Bacteria as Co-Digester

Round 1

Reviewer 1 Report

This study presents an interesting application of soil organisms along with an adapted strain for volatile fatty acid production from food waste. Overall the approach is simple and the authors analyse the volatiles over a 15 day fermentation period. I have a few minor suggestions to improve the manuscript-

The genus and species names of bacteria throughout the manuscript should be consistently in italics.

Some sentences are incomplete- line 17, 85

Statistics should be presented for figure 1 and 2 to show significant effects of the Bacillus strain in combination with soil bacteria on degradation processes

It would be useful to have consistency in referring to conditions where pH was not controlled. Currently 4 different styles are being used- uncontrolled pH, pH no control, pH no-adjustment, non-adjusted pH. This gets confusing for the reader. 

Table 2 the "-1" needs to be a superscript

Figure 4 caption needs to be edited, at the moment it is the same as figure3 but the data indicates otherwise. 

More discussion would be appreciated on the reason for the loss of diversity in VFAs after the 2 day of fermentation. The AM5 strain seems to be the source of this diversity so indicating which metabolic pathways are activated would be helpful. Also some speculation on why butyric acid production in this strain increases in the presence of soil community would be useful. 

Author Response

Dear Chief Editor and Reviewer,

We would like to thank you for your insightful comments and valuable suggestions on our manuscript. We have responded to the decision letter in the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

The aim of this study is to enhance the VFA production from food waste leachate using an effective bacterial strain isolated from soil under non-strict anaerobic condition in the contribution of soil facultative bacteria as an additive.

From my point of view, the work has potential but requires a thorough revision, reorganisation of the main sections of the manuscript and numerous corrections. Please see below my suggestions in order to give a better shape, structure and content to this paper.

Mandatory shape requests

Please check the Instruction for authors, Sustainability journal, regarding the structure/sections of a research article. https://www.mdpi.com/journal/sustainability/instructions Actual text of section 2 can be partially moved to Introduction, and partially to Discussion section. Additionally, Results and Discussion are recommended to be 2 separate sections. Please proceed in this regard. Actual section 5. Figures and Tables MUST be moved to the future 3. Results section (figures and tables ARE the RESULTS)

Please replace comma between Keywords with semicolon.

Please use g/L as unit of measure instead of mg l-1. same for g-1. it is not correct. Or use g^-1 Revise the entire manuscript in this regard, as the unit of measures to be correctly written.

Table 1. 1st column. Please use "acid" instead of "Acid"; 2nd column - please check the numerical values, some of them are with point, some of them are with comma. They must to be corrected and expressed in English style.

Table 2, last column. References must be mentioned as number, in brackets ie [1], [1-3],, not with names.

Legend of the figures: Please use "acid" instead of "Acid"

Please check and revise in the entire manuscript the latin names of bacteria to be in Italics.

References must be written in MDPI style, same style for all of them. Please check the Instructions for authors in this regard. https://www.mdpi.com/journal/sustainability/instructions The easiest way to write them as required is EndNoting them and choosing MDPI style.

Content suggestions

1. Introduction

Numerous statements in this section need to be referenced: ie L47-48 , as you stated that "Numerous studies have...". Same for the sentence L53-55: Some studies have investigated...Please check the entire manuscript in this regard. For the Introduction please refer to recent/very recent published data, as Bungau et al. Expatiating the impact of anthropogenic aspects and climatic factors on long term soil monitoring and management. Environ Sci. Pollut. Res. 2021, 202, 30528-30550. https://doi.org/10.1007/s11356-021-14127-7 ; Samuel et al. Effects of long term application of organic and mineral fertilizers on soil enzymes, Rev. Chim., 69(10), 2018, 2608-2612. https://doi.org/10.37358/RC.18.10.6590 and Samuel et al. Enzymatic indicators of soil quality. J. Environ. Prot. Ecol. 2017, 18(3), 2017, 871-878.

L95-97 is presented the aim of the study. Very briefly. If the authors will consider to respond to the following questions, this aim of the study will be much more relevant: Which are the novelty/special aspects that this paper brings to the field? Why the authors have chosen this topic? How does this research differ from other similar ones in the topic?

2. The importance of soil microorganisms

Again, please reference better your statements: both paragraphs L105-110 and 116-122 are not referenced at all (L116: Numerous molecular biological... Please exemplify and reference them)

Future 4. Discussion section must contain comparisons between the results of this study and other similar studies, as to highlight as better is possible the relevance of the current research.

  

Author Response

Dear Chief Editor and Reviewer,

We would like to thank you for your insightful comments and valuable suggestions on our manuscript. We have responded to the decision letter in the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

From my point of view, the revision of this paper is poorly done, being done just to be done not for providing a better manuscript. Some shape corrections were done, but the manuscript still needs major improvements, especially regarding the content with remained poorly developed and presented.

Shape requests

Red background paragraph cannot be read. Or if they must be removed, please remove them.

Please remove empty spaces between paragraphs (i.e. section 4), giving to your paper a much more neat appearance. The ASPECT is very important also for a paper, as well as its content.

Please check and remove duplicate information. Some data are mentioned as well in the text form and in figures/tables. One information must be provided in a single/unique form.

 

Content requests

Introduction section

The authors responded that they "have rewritten and combined the section 2 “The importance of soil microorganisms” into the Introduction to point out more clearly the aim of this study." But the relevance of the study is still missing, no novelty character of this research was not highlighted, no reason supporting the fact that this paper is better than other (already published) in the same topic, no reason for choosing this topic, etc. AIM of the study is missing! Please add it as the last separate paragraph of this section

The authors have not developed and chose not to refer to the published paper I suggested. Introduction still need improvements. Please check my 1st report and apply (references I suggest were not for my personal purpose but for your better information). Not referencing just the text, but also developing it further.

Results section must be drastically reorganised. 

• an entire subsection title for a sentence? - please revise 3.6. L 291 and merge it with other subsection.
• NO section must to exist with the title Figures and Tables. Each Figure or table must be inserted at its right place, in the main text, being introduced before its insertion by : Figure x presents.., or Table y summarises.... or Data regarding... are depicted in the Figure/Table z.

Discussion section.

Still very poor. Not developed enough. Just 9 References supporting this part, which is the main part of a study highlighting / making similarities and parallels between the results of your own study and those of other studies in topic. Very limited number of other studies were mentioned, and almost no comparative discussion.

L388. "To date, limited studies...". Please reference those limited studies. As I already mentioned in my previous report. ALL statements must be referenced.

Conclusion section. Not understandable. All is red backgrounded - what is the meaning of it?

 L412 has not a beginning for that phrase.

References section. The authors have chosen to add some references older than 15-20 years! Why?, if there are plenty of references considering the same statements but more recent and updated regarding information provided.

Author Response

Dear Chief Editors and Reviewers,

We appreciate the time and effort that you and the reviewers have dedicated to providing your valuable feedback on my manuscript on round 2. We have highlighted the changes within the manuscript in yellow that any change can be easily viewed. We hope that the Reviewers and Editors will be satisfied with the further amendments which we have made to the manuscript. Please find the attachment for our response letter to Editors and Reviewers.

Thank you very much for your kind consideration and valuable time.

Sincerely,

Corresponding author: Woo Jin Chung

Department of Environmental Energy Engineering, Kyonggi University

154-42 Gwanggyosan-ro, Yeongtong-gu, Suwon-si, Geonggi-do, South Korea

Tel: +82 31 249 9755/Fax: +82 31 244 6300

E-mail: cine23@kyonggi.ac.kr

Author Response File: Author Response.docx

Round 3

Reviewer 2 Report

Authors responded to all my requests.