Monitoring the Dynamics in Nitrogen and Phosphorus Contents during Aerobic Digestion of Swine Slurry

Round 1

Reviewer 1 Report

A lot of important improvements have been made. The article gained a lot. In my opinion, Table 1 could have remained. It contained important information. 3 my comments were not taken into account. They are still marked in the attached text. Please, think about it. Charts have been nicely improved. 

Comments for author File: Comments.pdf

Author Response

"Please see the attachment."

Author Response File: Author Response.pdf

Reviewer 2 Report

This version of manuscript was slightly improved by the Authors however, still many shortcomings could be highlighted and in my opinion should not be published in Agronomy.

Despite clear declaration of improvements mentioned in the Author's response attached to the Cover letter, many important comments from previous review were ignored. 

The list of ignored comments from the previous review (the lines relate to old version of the manuscript, file attached) is presented below:

• Comment 5. Line 41. The phosphorus and nitrogen forms especially beneficial for plans should be highlighted as not all of them are present in raw swine slurry.
• Comment 9. Line 73. What is the optimal ratio range?
• Comment 18. Line 110. Does the TN measured this way equal to N-NH4+N-org? What about samples containing nitrate/nitrite? This is unclear.
• Comment 19. Line 139-142. The range of obtained results is huge. Deeper analysis of the process configurations should be proposed (i.e. including the pretreatment method, size of the facility, swine slurry farm description etc.) as all of these could affect the swine slurry composition
• Comment 20. Table 2. The results should be presented in more attractive way. I recommend to move the table to supplementary materials and graphically present the most important data.
• Comment 21 Line 154.  How exactly the mean pH value was calculated?
• Comment 23 Line 161-163. Comparison of these values should be followed by deeper discussion than presented
• Comment 24 Line 168-170. Nitrogen removal through "nitrification - denitrification" rather that "denitrification" should be mentioned. The process should be discussed in more detail. The role of all nitrogen transformations is poorly discussed which significantly decrease the value of this article.
• Comment 25 Line 177. Can it be estimated how much of the nitrogen load is lost this way in comparison do denitrification? It should be considered in discussion of the results presented in Table 4 (lines 190-217). This part of discussion should describe deeper analysis focused of nitrogen transformations and provide more literature data if available
• Comment 28 Lines 232-238. Deeper discussion is needed.
• Comment 30 Line 267-269. What is the reason of poor removal of PO4(3-) using coagulants?
• Comment 31 Table 5. Discussion of this data is very brief and poor

Furthermore, the new comments to the current version of the manuscript are:

1. Lines 57-58. What are the main products of nitrification and denitrification processes? Why NH3 and N2O are mentioned?
2. Lines 77-78. Abbreviations should be explained once in the text.
3. Lines 77-88. This part describes process, not the sample collection.
4. Lines 89-90. This text is repeated in lines 100-101
5. Lines 211-224. This part does not sufficiently explain the nitrogen loss which is crucial for this study. The nitrification / denitrification impact on emission should be verified by the authors and compared with the other products of these processes as presented approach seems to be wrong.

 

 

 

Comments for author File: Comments.pdf

Author Response

"Please see the attachment."

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

In my feeling there is still a long list of unresolved comments from  previous revisions.

In the author's response please highlight the exact lines and describe applied response to the certain comments, as I feel that some of them were ignored and marked in the response as "changed".

After this is completed I'll further revision will be possbile.

Author Response

 "Please see the attachment." 

Author Response File: Author Response.pdf

Round 3

Reviewer 2 Report

The manuscript has been improved. Below the list of comments to the previous review and some additional questions.

• Comment 5

For example the role of ammonium and nitrate are different in plant cultivation process. I think it should be taken into consideration in this article.

 

• Comment 9

Ok.

 

Comment 18

Thank you for this explanation. In this way,  sentence: „The total nitrogen (TN) content of the sample was determined using the Kjeldahl method (…)” should be rewritten to make it clear that is the sum of TKN+NO3 as no NO2 were detected.

 

• Comment 19

It is a big miss for this paper that detailed information about facility specification could not relate to the results of the samples analysis.

 

• Comment 20

Ok.

 

• Comment 21

Ok.

 

• Comment 23

Ok.

 

• Comment 24

Why the article mentions only N2O as denitrification product? Does the N₂ should be mentioned as the main product of this process? Based on the information in the text, the aeration during each phase of treatment was intermittent, thus in my opinion anoxic conditions occurred facilitating denitrification process. Please make these things clear.

 

• Comment 25

Should be re-considered together with comment 24.

 

• Comment 28

Ok.

 

• Comment 30

Ok. Such information in the text could be helpful for the audience.

 

• Comment 31

Ok.

 

Other suggests (lines corresponds to the current numeration):

Line 376-378. Please rewrite this sentence using nitrogen form names or symbols rather than names and symbols (do not use “ammonium NH₄”)

Line 382-384: Please select one: anoxic or anaerobic conditions are suitable for denitrification? What is the main product of this process? This part suggests that N₂O is equally produced as N₂.

Line 411-412: Denitrification accounts for NO3 (and thus TN) decrease rather than ammonium decrease.

Line 413-423: This part is confusing. It is stated that TN loss was due to ammonia (through stripping) and N2O emission (which states for ca. 1%  TN removal as presented later), while denitrification is omitted (while intermittent aeration and thus anoxic conditions occurred). Please better explain presented approach.

 

Please provide detailed information in the Authors response file attached to the cover letter.

Author Response

"Please see the attachment."

Author Response File: Author Response.pdf

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

General comment:

The paper entitled "Variation in the Forms and Concentrations of Nitrogen and Phosphorus in Swine Slurry across Aerobic Digestion Stages in Public Livestock Waste Recycling Centers" presents the results of study on nitrogen and phosphorus concentration changes during aerobic digestion process of swine slurry. Presented data was gathered from multiple swine slurry aerobic digestion facilities at different process stages. The amount of gathered data which is an undisputed strength of this paper, however, number of shortcomings can be pointed. The background of the problem is poorly presented, without highlighting the essence of the selected topic and thus the importance of this study. The discussion of the results is not providing sufficient scientific insights and requires much deeper analysis.

In my opinion, in its current form, the article is not suitable for publication in Agronomy.

 

Specific comments:

1. The English sometimes seems to be unclear, those parts are listed below.
2. Some words are repeated very often (i.e. in abstract; lines 54-57).
3. Title. Title seems to be too long.
4. Lines 35-38. Unclear, the sentence is too long.
5. Line 41. The phosphorus and nitrogen forms especially beneficial for plans should be highlighted as not all of them are present in raw swine slurry.
6. Lines 54-57. Please re-write this part without using "P" so often.
7. Line 65-66. Will the change of P and N content during the digestion process be interesting for farmers? Maybe the final composition of the digestion product? How the results of this study will affect the current situation?
8. Line 68-69. As previous research is available please highlight the missing gaps in current knowledge that this manuscript is about to fill.
9. Line 73. What is the optimal ratio range? 
10. Introduction. The importance of this study is not highlighted on the background of currently available literature. The aim of this study should be pointed in the context of potential impact on the swine slurry treatment at least at regional level.
11. Materials and methods. This section should be written more concise. The language structure makes this part difficult to read and unclear so this section should be re-written. Maybe a figure presenting the schematic of the swine slurry process and sampling points would be beneficial for the reader?
12. Line 85. Aeration rate (AE) - why not AR?
13. Table 1. seems to be unnecessary and can be presented graphically (see point 11).
14. Table 1. Raw SS. Solids separation greater than 2mm is mentioned while in line 79 is 5mm. Please make it clear.
15. Table 1. Fresh SS. No chemical treatment is mentioned while in previous description such information is provided.
16. Table 1. Please improve the clarity of sampling points digestion times. The description used so far might be unclear.
17. Line 95. From the previous text it can be assumed that Raw SS is pretreated before transferred to the first cell. Please make that clear.
18. Line 110. Does the TN measured this way equal to N-NH4+N-org? What about samples containing nitrate/nitrite? This is unclear.
19. Line 139-142. The range of obtained results is huge. Deeper analysis of the process configurations should be proposed (i.e. including the pretreatment method, size of the facility, swine slurry farm description etc.) as all of these could affect the swine slurry composition.
20. Table 2. The results should be presented in more attractive way. I recommend to move the table to supplementary materials and graphically present the most important data.
21. Line 154. The mean value is incorrect (8.199) and should be 8.19. How exactly the mean pH value was calculated?
22. Line 157. What is smaller fraction of organic matter? How does the mentioned OM breakdown produce CO2?
23. Line 161-163. Comparison of these values should be followed by deeper discussion than presented.
24. Line 168-170. Nitrogen removal through "nitrification - denitrification" rather that "denitrification" should be mentioned. The process should be discussed in more detail. The role of all nitrogen transformations is poorly discussed which significantly decrease the value of this article.
25. Line 177. Can it be estimated how much of the nitrogen load is lost this way in comparison do denitrification? It should be considered in discussion of the results presented in Table 4 (lines 190-217). This part of discussion should describe deeper analysis focused of nitrogen transformations and provide more literature data if available.
26. Table 3. See point 20.
27. Line 221-222. Not clear.
28. Lines 232-238. Deeper discussion is needed.
29. Figure 1 and 2. Maybe a cumulative bar chart can be considered? Color selection should be considered different as in black and white printing it's difficult to differentiate the data series.
30. Line 267-269. What is the reason of poor removal of PO4(3-) using coagulants?
31. Table 5. Discussion of this data is very brief and poor.
32. Conclusions. As the importance of this study is not well highlighted in the introduction nor the discussion, this section is only a brief summary of presented data. Any significant outcome for the swine slurry treatment process could not be noticed.

Reviewer 2 Report

The work was written very carefully. Very correct graphs, well illustrating dependencies. Chemical nomenclature should be corrected in line with IUPCS rules. I have marked some minor comments in the text. 

Comments for author File: Comments.pdf