Strategies for Controlling Filamentous Bulking in Activated Sludge Wastewater Treatment Plants: The Old and the New

Round 1

Reviewer 1 Report

-The submitted review describes the problem of sludge bulking and foaming in WWTPs. The problems and control strategies for sludge bulking caused by excessive growth of filamentous bacteria have been finely covered. On the other hand, factors promoting sludge foaming have been given less attention. 

-Factors favoring the growth of filamentous bacteria are due to wastewater characteristics , failure in desing configuration and or operational  practices. This has to be considered in proposing control measures by manipulating operational parameters.

- Paragraph 3.1.4 Toxic metals

Most toxic metals are usually (not mineralized in WWTPs ) please change this sentence.  

Author Response

The submitted review describes the problem of sludge bulking and foaming in WWTPs. The problems and control strategies for sludge bulking caused by excessive growth of filamentous bacteria have been finely covered. On the other hand, factors promoting sludge foaming have been given less attention. 

-Factors favoring the growth of filamentous bacteria are due to wastewater characteristics , failure in desing configuration and or operational  practices. This has to be considered in proposing control measures by manipulating operational parameters.

Thank you for your comment. We are unsure whether you are making a comment, or whether you need us to make a particular change to the text. If the latter, kindly indicate in which section we should make an amendment.

- Paragraph 3.1.4 Toxic metals

Most toxic metals are usually (not mineralized in WWTPs ) please change this sentence. 

We have amended this sentence

Reviewer 2 Report

The manuscript titled ‘Strategies for controlling filamentous bulking in activated sludge wastewater treatment plants: the old and the new’ is a pretty well written review paper. Manuscript is divided into short paragraphs describing various physicochemical factors influencing bulking and foaming of activated sludge during wastewater treatment. Authors present traditional and new strategies of dealing with the stated problem, supported by references. In general, there is no major issues influencing paper quality. The one can expect more graphs related to the presented problems from cited papers.

Other issues:

1) caption for Fig.1 is slightly unclear, please make it more reader-friendly

2) please check the manuscript very carefully to avoid various mistakes as: H2O2 (page 10 line 394

 

Author Response

The manuscript titled ‘Strategies for controlling filamentous bulking in activated sludge wastewater treatment plants: the old and the new’ is a pretty well written review paper. Manuscript is divided into short paragraphs describing various physicochemical factors influencing bulking and foaming of activated sludge during wastewater treatment. Authors present traditional and new strategies of dealing with the stated problem, supported by references. In general, there is no major issues influencing paper quality. The one can expect more graphs related to the presented problems from cited papers.

Thank you for your comment. We did consider adding more figures when we wrote the manuscript, but the content did not lend itself to arranging into graphical format. On reconsideration, we still feel that this is the case. If you have an ideas about where graphs may be added, kindly indicate.

Other issues:

1) caption for Fig.1 is slightly unclear, please make it more reader-friendly

We have amended the caption and hope that the content is now clear to the reader.

2) please check the manuscript very carefully to avoid various mistakes as: H2O2 (page 10 line 394)

We realise that the formatting changed when we uploaded the document onto the ‘Water’ template. Italics were lost as well as superscripts and subscripts among others. We did not pick up all of these in our initial proofing, but are confident that we have now addressed all of these issues.

Reviewer 3 Report

This review on old and new strategies for controlling filamentous bulking in activated sludge wastewater treatment plants delivers what its title promises. I was skeptical at the start (“is there indeed enough ‘new’ to highlight”) but I was very happily surprised and learned a lot. I might have to update my lecture slides on this phenomenon in my basic wastewater treatment course ;-) Apart from some typos (still some species names that need to be in italics or some subscripts in chemical compthat are missing), I do not have any major suggestion for improvement. (typos are indicated in red, all other highlights are just for me)

Just out of curiosity,

è I do not understand why NaCl would impact filamentous bulking and what the link with ‘chlorination’ (in that paragraph) is. To be honest, I looked up reference 123 and I do not see any link with NaCl (or NaOCl?) but, admittedly, I only did a diagonal check ...

è I did not immediately infer why ‘skilled operators are required to deal with upsets’ when selectors are applied. Or otherwise said: do you require even more skilled operators when selectors are there than usual when having to deal with filamentous bulking?

 

Comments for author File: Comments.pdf

Author Response

This review on old and new strategies for controlling filamentous bulking in activated sludge wastewater treatment plants delivers what its title promises. I was skeptical at the start (“is there indeed enough ‘new’ to highlight”) but I was very happily surprised and learned a lot. I might have to update my lecture slides on this phenomenon in my basic wastewater treatment course ;-) Apart from some typos (still some species names that need to be in italics or some subscripts in chemical compthat are missing), I do not have any major suggestion for improvement. (typos are indicated in red, all other highlights are just for me)

Thank you for your comments. We have addressed all of the typographical errors indicated on the MS.

Just out of curiosity,

I do not understand why NaCl would impact filamentous bulking and what the link with ‘chlorination’ (in that paragraph) is. To be honest, I looked up reference 123 and I do not see any link with NaCl (or NaOCl?) but, admittedly, I only did a diagonal check ...

Thank you for pointing this out, much appreciated. The same group of researchers published 2 papers in Biotechnology in the same year. All of the details, including the DOI were correct, but the incorrect title was loaded. We have amended the reference list to reflect the correct paper entitled: “Use of sodium chloride to rapidly restore polydroxyalkanoates production from filamentous bulking without polyhydroxyalkanoates productivity impairment.”  

I did not immediately infer why ‘skilled operators are required to deal with upsets’ when selectors are applied. Or otherwise said: do you require even more skilled operators when selectors are there than usual when having to deal with filamentous bulking?

We agree that this may be seen as a debatable point, but any additional operational variables add to the skills burden at WWTPs, so we have left the table as is.