Metal Cation and Surfactant-Assisted Flocculation for Enhanced Dewatering of Anaerobically Digested Sludge

Round 1

Reviewer 1 Report

Overall manuscript and findings are interesting and provide ample information to contribute to the field. 

However,  it needs to modify with major revision to improve it soundness to be a great finding.

1. Abstract is not very interacting. Use of bracket  , name of the chemicals or chemical formulas are not taken care. It should be either name or formula....

2. Introduction and discussion part do not contain the discussion and comparison with recent literature.

3. Figure 2 to 4 must also be plotted in a comparative manner to see the effect at a glance.

 

4. Similarly in other sections also, results should be summarized in effective manner.

Author Response

the recommended changes have been made and the comments given have been addressed

Author Response File: Author Response.docx

Reviewer 2 Report

The manuscript, entitled “Metal Cation and Surfactant Assisted Flocculation for Enhanced Dewatering of Anaerobically Digested Sludge” is an interesting paper. According to me, this manuscript merits to be accepted in the journal Sustainability. However, the below changes should be addressed before taking it further.

Abstract:

-The abstract should be improved.

-It is not suitable to begin the abstract by (This research work focuses), you should show the problem at the beginning.

 - Describe the abbreviation where it is used first; For example, CTAB and SDS.

The introduction:

1.     The novelty statement should be added clearly in the paper.

2.     The aim of the study of this paper should be improved.

Methodology and results &discussions:

·        There is a missed section (materials) which describes the sources and properties of used chemicals.

·        Why do the authors abbreviate dewaterability by (CST)?; CST is the abbreviation of capillary suction time.

·        There is a problem in references (Error! Reference source not found).

·        Table 1. (authors should add the Zeta potential value and the dissolved metals value)

·         The effect of reaction time should be added.

·        The standard deviation should be mentioned in all of manuscript.

·        How do the author determine the improvement in dewaterability?; the equation of CST reduction percentage and results should be added.

·        Did authors measure cell lysis in sludge samples?

·        The authors should make a statistical analysis of their results.

·        The performance of the recovered salts used in system to enhance dewaterability should be investigated (reusability).

·        Can the authors investigate the application of sludge cake? For example, as a fertilizer,…etc.

·        Please correct the chemical formula in figures and text (numbers must be subscript).

·        Please, revise the manuscript and correct the written errors.

Author Response

all the responses to the reviewers comments are in the attachment

Author Response File: Author Response.docx

Reviewer 3 Report

The article “Metal Cation and Surfactant Assisted Flocculation for Enhanced Dewatering of Anaerobically Digested Sludge” represents the application of metal conditioning agents (ferric chloride, calcium chloride and magnesium sulphate) to improve the digested sludge dewaterability. The article results are important for sludge handling and treatment; however, some points should be considered before final decision:

1-  Please add a line related to novelty of this work in abstract

2-  Please resolve spacing issue between letters/words

3-  Reference/citation should be fixed throughout the manuscript.

4-  The authors should explain why they selected dose (ml/50 ml DS).

5-  Some figures such as 11 and 12 should contain y-axis label

6-  The effect of varying flocculant types on the dewatering process still not clear; and this variation should be justified by statistical analysis, flocculant characterization by SEM, EDX, XRD, FTIR, etc.

7-  What about recovery and regeneration of flocculants

8-  Please add a couple of points at the end of conclusions, which need further investigation in future studies.

Author Response

Please kindly see the attachment

Author Response File: Author Response.docx

Reviewer 4 Report

The aim of this work is to study alternative dewatering performance enhancement options, using different metal-based conditioning coupled with polymers and surfactants to reduce cost of dewatering, enhance flocculation, and improve quality of biosolid coming out of the process.

However, the description of methods is very poor.

It is an interesting research work, and it is within the scope of the journal’s topics.

 

1) Grammar should be checked by a native English speaker. There are several grammar errors in the text. For example, in section 2.3 some methods are explained in the past, other in the future.

 

2) Methodology (section 2.2.) should include a table with the quantities of sludge and metal-based conditioning reagents, number of trials/assays, description of operational conditions in jar test (velocity in rpm, time of mixture, time of sedimentation, ect.). The quantities are only mentioned in the Results section.

FTIR is not mentioned here, is described in Results.

The Methods section needs a major revision.

 

3) References in the text need to be checked. Many “errors” in the references.

 

4) Fig. 11 to 13, particle size. Particle size was not mentioned in the Methods section. These figures have no legend in the YY axis.

Tables 2 to 4. Again, the parameters presented in this table were not mentioned in the Methods section.

 

5) The discussion must be improved by including a comparison with results from similar studies.

Author Response

Please see the attachment for the comments

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

I found that at many places the source file is missing statement ,"Error! Reference source not found." Please remove

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

-I think the statistical analysis is still important.

-The measure of cell lysis in sludge samples is important.

-The effect of reaction time is also important.

-The chemical formula should be corrected. (Please, see Fig.7)

-The authors should relate their findings to other research results.

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

The text contains a lot of "Error! Reference source not found" which should be fixed.

Author Response

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Author Response File: Author Response.docx

Reviewer 4 Report

Authors made the changes requested in the first review. However, when reading this second version of the manuscript, I got the impression that the "Introduction" is weak regarding matters that may be interesting to add for improving the quality of the manuscript. Bibliographic references are few.

 

Suggestions:

1) “Introduction” section: as the objective of the work is to increase the dewatering of anaerobically digested sludge, other alternative methods that may lead to the same objective must be mentioned.

The following works can be useful and can be added after referencing the work [1] (approximately after L. 20 of the “Introduction” section):

DOI: https://doi.org/10.3390/pr7040228 

DOI: https://doi.org/10.3390/su13168783 

DOI: https://doi.org/10.3390/en13246753 

DOI: https://doi.org/10.3390/cleantechnol4030052 

2) Emphasize the advantages of adding metal cation and surfactant assisted flocculation in relation to other technologies and treatment processes.

 

Author Response

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Author Response File: Author Response.docx

Round 3

Reviewer 4 Report

The authors have made a good improvement to the manuscript.