Toward New Value-Added Products Made from Anaerobic Digestate: Part 2—Effect of Loading Level on the Densification of Solid Digestate

Round 1

Reviewer 1 Report

Reviewers  Comments

The overall structure of this paper is good, and the topic is very interesting. I suggest for a major revision of the article before accepting it for publication in the journal. However, I have few comments which are given below;

1.     Introduction is too long. A few recent studies including https://doi.org/10.1007/s10311-022-01510-0, need to be cited.

2.     Some references related to the work are pretty old. Please refer recent references.

3.     It would be better if you mention the experimental conditions in detail here rather than referencing the whole work of your previous study.  (page 4)

4.     Jumping references should be avoided. (Page 13 lines 354-355)

“Several researchers are analyzing the spring back effect, as it is a major factor in the process of compaction of materials [49, 50, 61–63].”

5.     Results and discussions need to be revised as in the current format the results are presented basically. But based on the results more discussion is encouraged. Most of the cases only reference 29 was cited. Need to cite more recent studies.

6.     The paper reports an interesting topic. I believe that there is not much scientific novelty in the manuscript. The manuscript requires corrections, especially in the case of specifying the nomenclature of the studied parameters. The authors should better stress the novelty and the scientific relevance of the study.

Author Response

Dear editor and reviewers

The answers to the reviewer are included in the attached file 

G. Łysiak 

Author Response File: Author Response.docx

Reviewer 2 Report

Sustainability-2310544-peer-review-v1

Comments:

This study investigated the effects of loading level on the densification behavior of anaerobic digestate and pellet strength under different moisture conditions during cyclic confined loading. This paper is informative. However, I feel it isn’t good enough to warrant its publication in Sustainability presently. Here are my comments as follows.

(1) The introduction section of this article is too lengthy in its description, especially from line 77 to line 135. It would be more effective for the authors to concentrate on explaining the significance of their research and how it addresses any existing gaps in knowledge.

(2) The study's objectives, as outlined in lines 159-163, are not sufficiently comprehensive. Also, why do the authors need to verify the previous observations in this study?

(3) The section on Materials and Methods is not easily comprehensible to readers, particularly with regard to the experiment's design and implementation. For example, it is unclear how many groups were included based on their moisture conditions. In addition, why do the authors utilize moisture levels of 10% and 22%, rather than alternative values?

(4) Line 182-183, why ‘its effect was not dependant on moisture content’? Please explain it.

(5) This paper includes several figures displaying fitted equations, but there is no accompanying text to describe them, such as Figure 2 and Figure 3. It is unclear from the article whether these fitting results are relevant or necessary.

(6) Conclusions should be very concise and very clear. Only the main points and important results are provided. The conclusions section of the paper should be concise and clear, focusing only on the main points and significant findings.

(7) Typically, digestate produced from wet digesters is characterized by high moisture content, ranging from 90% to 98%. Therefore, it is reasonable to assume that obtaining solid anaerobic digestate with a moisture level of 10% or 22% would require a significant amount of energy. How to achieve practical utilization of pelleted SAD in consideration of economic feasibility?

 

 

Author Response

Dear editor and reviewer

 

The answers to the comments are included in the attached file.

G. Łysiak

 

 

 

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The author addressed all the concerns. It can go for publications. 

Reviewer 2 Report

I'm happy with the current form. Therefore, there are no further comments on this manuscript.