Harnessing the Potential of Sludge Fermentation Liquid to Induce Partial Nitrification

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The work is theoretical in nature and uses a lot of numerical data.

This review aims to provide insights into the synergistic integration of WAS fermentation and PN for sustainable and energy-efficient wastewater treatment.

The aim of the work was achieved.

Proportions between particular chapters, the presence of methodological assumptions of work including methods, techniques and research tools, and the interpretation of results is correct and consistent with the accepted rules of editing and performing work.

In general, the paper is well written, the results are conclusive and of interest for this topic.

The results of the research may be of interest to some readers of Fermentation.

I did not notice any stylistic or substantive errors in the work.

The bibliography is sufficient.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

I was about to suggest rejection, but Section 4.3 is quite interesting. I liked the experiences described within. However, this article needs a drastic improvement in terms of language. English proof reading by the journal would not be enough for this. You need to use more proper terminology throughout the paper. Described experiences and results obtained thereby are not clear. It took me a second reading before I could grasp some valuable content. There is also a lack of critical comments on the literature about the topic dealt with in this work. Are there opposing findings? What are the research gaps in the field? Section 4.3 is the most interesting and novel section, it should be expanded further. If you don’t improve the language drastically, I will have to suggest rejection in an eventual second review: language in this manuscript is far from being acceptable for publication and it’s not just the English, it’s due to the use of exaggerated terminologies, the unclearness of sentences. Sometimes concepts proposed seem wrong.

Detailed comments to be addressed are as follows:

Avoid extravagant terminology such as “immense”, “massive”. I don’t think AS process produces massive wastage sludge. It produces excess sludge, but not massively. Avoid “dramatically”, “proliferation”.

Verb tenses are sometimes not properly chosen, making the reading of the text awkward in several instances. The use of past tense is in most cases unsuitable in this manuscript. Please revise English thoroughly.

“novel nitrogen removal technologies based on partial nitrification (PN) (e.g. anammox)” Anammox and PN are two different processes

“supplementing anaerobic WAS fermentation liquid to induce PN” where should we supplement this liquid?

L29 “comprehensively”: your review is not comprehensive; it doesn’t take into account the huge amount of research carried out in North America and Western Europe, which should be largely implemented. Take personalities such as Gizem Mutlu Scopus ID 8656085700 , Barth Smets Scopus ID 7006949747, Yang Liu Scopus ID 55899989000, Eveline Volcke Scopus ID 6507108691. These are just few examples, there are many others you should consider and incorporate in your review. This paper should be cited given the very similar topic to yours: https://doi.org/10.2166/wst.2022.131

Too few keywords have been chosen.

“Unfortunately, the by-products in fermentation liquid have not been managed appropriately for now.” Why not? Why are you saying so? Usually, they are recycled back to the main stream for further treatment or have had several chemical and biological options for side stream treatment. This sentence is therefore quite inappropriate.

L81: Instead of “denitrification” you should use the term “denitritation” which indicates nitrite instead of nitrate reduction into N2.

L86 “secondary pollution”?

“methods for achieving PN, such as adjusting pH and DO or treating sludge with chemical substances how are two correlated?

How does recirculation of “fermentation” liquid residue on top of activated sludge system induce PN?

L115-116: “Ammonia oxidizing reaction is catalyzed by ammonia monooxygenase encoded by the amoA” the enzyme HAO is also very much needed to convert NH2OH into nitrite

L179-181: this lacks references. I need at least 2-3 references in support for that sentence

 L188: “proliferation”? Did you mean growth?

L266-267: there is a confusion with respect to what fermentation is. In general, fermentation is a biological process which transforms sugars, amino acids and fatty acids into volatile fatty acids. I wouldn’t include hydrolysis nor methanogenesis. Those are surrounding processes that could occur along with fermentation but are not part of fermentation. You should replace “fermentation” with “digestion” or “stabilization”. Up to you if the adjective “anaerobic” should be included as well.

L297 “several thousand milligrams”? I think this is a bit too much. Ammonium concentration can range from several hundreds to 1000 o 2000 mg/L. No more than 2000 mg/L.

L328: replace “REALIZING” with “RELEASING”

L329: it may be “effectively” but “not completely” nor “sufficiently”

L334: “were”?

L349: we are more interested in the conversion percentage than in the actual final concentration value.

L353: I don’t know how C/N could be too low in wastage sludge from domestic wastewater treatment plants. Usually, nitrogen is sufficient for digestion purposes.

“leading to a decrease in biogas production”? Why would nitrogen transformation into protein lead to lower biogas production? There is something missing here.

L366-375: what does it have to do with partial nitritation?

L366-368: this is an interesting practice; I have never thought about it before.

What’s NAR?

L380-387: and what was the role of fermentation liquid effluent on that?

L396: Polit? You meant pilot, I guess.

L399-400. This is not clear. Actually, side stream fermentation water can be recycled to the main stream without ammonia removal. Simply, the main stream will be more loaded with ammonium but it can still be handled.

Comments on the Quality of English Language

English must be improved drastically. Comments are provided above

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

1) Provide justification how the presented research covers under the scope of the journal. Since the work is on sludge fermentation liquid, it could not satisfy the minimum requirements of the journal. Process also needs to involve fermentation.

2) Abstract: Provide full name of WAS at its first sight.

3) Introduction: Organized well and provided all aspects related to review.

4) Microbial Basis and Establishment Methods of Partial Nitrification: Microbial basis and factors affecting PN were elaborated well. Providing title as conventional methods for PN, methods were not mentioned and explained. Organization could be improved for more clarity.

5) Anaerobic Fermentation of Waste Activated Sludge: Results could be provided here in the form of Tables and Figures.

6) Combination of PN and sludge fermentation: Discussion is not sufficient.

7) The length of manuscript is not enough for a review on PN.

8) References from 2024 have to be updated

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

Dear authors, I think some of the comments have addressed while others have not. Therefore, I am listing here what should be still changed before acceptance:

Comment 4. “supplementing anaerobic WAS fermentation liquid to induce PN” where should we supplement this liquid? Replace "for inducing" with "to induce". Secondly, when you say "fermentation liquid" you are just talking about the digestate. I have already commented about it but I still see this mistake throughout the text. You are confusing fermentation with anaerobic digestion. Fermentation is just a process that converts sugars, amino acids and fatty acids into VFAs, but it doesn't involve methane production. Secondly, the mechanisms through which the recycle of digestate in the mainstream AS tanks induces partial nitritation are not explained, though crucial for clear understanding, although this is somehow explained unclearly only later in the text. This way of organising the content leaves the reader with a question in his/her mind unanswered for a very long time.

L70 "this stage was consuming": again, a lot of mistakes with improper verb tense., which have been already pointed out in the previous review. Please check the entire text and correct this mistake

L75-76 "For promoting the fermentation performance": again, replace "for promoting" with "to promote". Secondly, it's not really the fermentation that needs to be promoted, rather the hydrolysis step. Fermentation and hydrolysis are two different and separate processes taking part during anaerobic digestion. Please revise carefully

  Comment 5. L29 “comprehensively”: your review is not comprehensive; You have just added three more references. Cited works on PN and anammox are still few. This comment could have been addressed much better.

L139: replace "depression" with "repression"

L141: what do you mean by "independent"?

L230: "FA refers to free ammonia as NH4OH": Really? I thought free ammonia is NH₃

Title of Chapters 3 and 3.1 are still quite wrong, pointing at fermentation as the key process while in the reality we are talking about anaerobic digestion

L390-391 "The concentration of ammonium in fermentation liquid can range from a few hundred to two thousand milligrams per liter"; can you add some references in support?

In Section 4.1, there is a lot of confusion about what fermentation is and what anaerobic digestion is. I think you haven't revised the manuscript properly and these two process concepts "fermentation" and "anaerobic digestion" are still mistakenly interchanged between each other throughout the text.

L448: it's not really due to the too high C/N ratio, rather it's due to the organic overloading, i.e. the loading beyond the design capacity. 

When you talk about C/N ratio influence on methanogenesis, is the sludge or wastewater municipal or industrial? I think N and P are important and can affect anaerobic digestion only in case of industrial wastewaters

L470-473: you mean that by adding fermentation effluent to a mainstream activated sludge system performing nitrification, the short cut nitrogen removal via nitritation (i.e. ammonium conversion to nitrite) will take place instead of nitrification (i.e. ammonium conversion to nitrate). Is that what you mean? What were the underlying mechanisms leading to this? Was the extra organic carbon suppressing NOB activity? All of this needs to be clarified and talked more linearly in the text. Content needs to be properly organised. Sometimes you make statements that are explained only after a while. Content within sections should more logically organized.

Regarding Figure 2, there are cases in literature where the KO2,AOB is larger than KO2,NOB: 10.1016/j.watres.2005.09.020, 10.1016/j.watres.2014.03.035,  You should make a broder search for KO2,AOB and KO2,NOB values if you wanna be comprehensive in your review work

Comments on the Quality of English Language

English is still quite poor. There's plenty of wrong verb tenses. 

Readability is still poor

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

As I am satisfied with the response to my comments, I would like to recommend the manuscript for publication in its present form. 

Author Response

 On behalf of my co-authors, thanks for your kind comments on our manuscript deeply.