PONE-D-20-31065

Removal of cyanobacteria from a water supply reservoir by sedimentation using natural flocculants and water turbidity as ballast: Case of Legedadi Reservoir (Ethiopia)

PLOS ONE

Dear Dr. Habtemariam,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process. In particular, the first reviewer has made several criticisms on some methodological choices that should be addressed in your revision version. In addition to that, I want also to invite you to be more cautionous in the discussion, in the extrapolation of your experimental findings to the real conditions in the lake.

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We look forward to receiving your revised manuscript.

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Jean-François Humbert

Academic Editor

PLOS ONE

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Demeke Kifle

Seyoum Leta

Maíra Mucci

Miquel Lürling '

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Demeke Kifle

Seyoum Leta

Maíra Mucci

Miquel Lürling '

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Partly

Reviewer #2: Yes

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2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: No

Reviewer #2: Yes

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3. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: Yes

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4. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: No

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5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: This study investigated the removal of cyanobacteria from a water supply resevoir by sedimentation using natural flocculants and water turbidity as ballast. This is a meaningful study, however, this manuscript is still not in a publishable state. The manuscript needs to be further improved in research design and analysis. And some sentences in this manuscript are hard to understand, it needs careful editing by someone with expertise in technical English editing paying particular attention to English grammar, spelling, and sentence structure so that the goals and results of the study are clear. Furthermore, some important aspects of this study are confusing.

1. Title: “use water turbidity as ballast”, but there’s no experimental design on how to use the turbidity of water as the ballast in this paper.

2. Grammar check: such as page 5, line 88-90; page 7, line 139-141……

3. Page 5, line 90-91: “Legedadi Reservoir is a very turbid reservoir”, how high is the turbidity? “the high turbidity was considered as a unique feature and expected to act as ballast”, does the high turbidity reservoir only be used as a case study? It should be designed to compare the effects of different turbidity.

4. Section 2.1: The water quality of the reservoir is not explained. Water quality is an important condition for the research, such as the turbidity of the reservoir when the experiment was carried out, the dominant algae and algae concentration, etc.

5. Page 7, line 149: “After dosing, the contents in each test tube were mixed briefly using a glass rod.” It is confusing. Coagulation-flocculation experiments were usually performed by jar test with a six-paddle stirrer. How to control the specific conditions of the mixing operation using a glass rod, so whether the experimental results of the glass rod mixing would be affected by the man-made operation errors?

6. Page 8, line 161-163: The dose design of PAC, Chitosan, and MOS was different, would the difference of coagulation effect be affected by the dosage range of different coagulants? For example, the dose of 8mg/L chitosan as shown in Fig. 3 has not been proved to reach the optimal dose with stable removal efficiency, while the span of MOS dose is larger with 20 mg/L has a relatively high efficiency and 30mg/L has reached the optimal dose.

7. Section 2.4: It is not recommended to use question sentence as subtitle in the experimental methods section.

8. Page 11, line 233-234: What does the “drop” and “remian” of PSII indicate? It should be explained.

9. Page 12, line 253: It is recommended to list the process and results of data analysis in a table or supporting information, and the supporting information in this paper seems to have uploaded the wrong file.

10. Page 13, line 288: The “Linear regression model” is recommended to provide in detail.

11. Page 14, line 297: “8Al/L”, check unit.

12. Page 15, line 330-331: “At higher concentrations of 50 mg/L MOS and above, there was a sign of cell lyses with a high reduction of PSII efficiency”. However, Fig. 3 showed that PSII efficiency had dropped when the MOS dose is 20 mg/L. Confusing.

13. Page 16, line 345: Section 4.2, check subtitle.

14. Fig. 2 is not clear, and there is no directional significance of the actual results. What is the author’s intention to put Fig. 2 ?

15. Fig. 3, “Moringa” in Fig.3B should be consistent with “MOS” in the text.

16. Fig.4, why not put MOS results in the same figure with PAC and chitosan? Using the drawing method of Fig. 3 to distinguish the top and bottom is a better choice.

17. Fig.6 is not clear.

18. References: It would be better to quote more recent references such as in the last three years.

Reviewer #2: The manuscript evaluated the efficiency of the flocculants/coagulants chitosan, Moringa oleifera seed (MOS) and poly-aluminium chloride (PAC) in settling cyanobacterial species in Legedadi Reservoir. The authors suggest that the efficacy of a flocculant/coagulant in the removal of cyanobacteria is influenced by the uniqueness individual lakes/reservoirs, implying that mitigation methods need to consider the unique characteristic of the lake/reservoir.

The manuscript was generally well organized, and the conclusion is constructive to remove cyanobacteria and control the blooms.

Comments for revision and correction:

1) Introduction: the authors give more information and description to support their assumption: water turbidity functions as ballast.

2) The chemical composition of Moringa oleifera seed may change between those collected from different locations. This information is helpful to understand its efficiency.

3) In Fig.3 A &C，Chla concentration was higher in the high treatments than in the control for bottom and surface?

4) In Fig.5，treated with MOS，PSII efficiency decreased at the surface, but increased for cyanobacteria at the bottom. Why?

5) As turbidity is assumed to be ballast, it is better to give more physical and chemical information of the turbidity. Know which kinds of turbidity function better.

6) In Fig.3, Fig.4, Fig.7, adding error bars.

7) Redrawing Fig.6 to be clear for readers.

8) The English needs correction. For example, Line 86: future =feature? Line 88-89: “The availability of local soils with natural P binding capacities was. For

instance, considered…” =” For instance, the availability of local soils with natural P binding capacities was considered… ”.

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Reviewer #1: No

Reviewer #2: No

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.]

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PONE-D-20-31065R1

Removal of cyanobacteria from a water supply reservoir by sedimentation using flocculants and suspended solids as ballast: Case of Legedadi Reservoir (Ethiopia)

PLOS ONE

Dear Dr. Habtemariam,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the minor points raised by one of the two reviewers.

Please submit your revised manuscript by Apr 29 2021 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

Please include the following items when submitting your revised manuscript:

• A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.
• A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.
• An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter.

If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: http://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols

We look forward to receiving your revised manuscript.

Kind regards,

Jean-François Humbert

Academic Editor

PLOS ONE

Journal Requirements:

Please review your reference list to ensure that it is complete and correct. If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references. Any changes to the reference list should be mentioned in the rebuttal letter that accompanies your revised manuscript. If you need to cite a retracted article, indicate the article’s retracted status in the References list and also include a citation and full reference for the retraction notice.

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: All comments have been addressed

Reviewer #2: All comments have been addressed

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2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Yes

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: Yes

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

**********

6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: There are still some problems to be corrected. It is not limited to the problems listed below. Please read the full text carefully and revise the details.

1) Page 4, line 86-87: Grammar check: “it’s” ?

2) Page 6, line 122: 276 µg/L what? Check your parentheses use.

3) Page 6, line 123-124: “The reservoir has a mean total suspended solids (TSS) concentration of 390 mg/L and total suspended solids” ? Check the statement expression and the use of parentheses.

4) Page 6, line 125-126: Sentence is unreasonable, lack of punctuation.

5) Page 6, line 128: Unpublished data is not recommended for citation.

6) Page 7, line 130-133: According to what? “moisture content of 6.1 ± 0.2, oil content of 41.4 ± 1.6,” and “protein content 42.6 ± 1.4,” ? Check your expression.

7) Fig.1 is not clear.

8) Fig. 2a, there are no relevant instructions in the text, and we still feel that Figure 2 has no actual data to point to value.

9) Fig.6 is not clear, the legend in the picture is invisible, and error bars are not clear.

Reviewer #2: I checked the revision of he manusscript, the authors have corrected and well responded to my questions.

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7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

Reviewer #2: No

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org. Please note that Supporting Information files do not need this step.

Removal of cyanobacteria from a water supply reservoir by sedimentation using flocculants and suspended solids as ballast: Case of Legedadi Reservoir (Ethiopia)

PONE-D-20-31065R2

Dear Dr. Habtemariam,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication.

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If your institution or institutions have a press office, please notify them about your upcoming paper to help maximize its impact. If they’ll be preparing press materials, please inform our press team as soon as possible -- no later than 48 hours after receiving the formal acceptance. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org.

Kind regards,

Jean-François Humbert

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Reviewers' comments: