A Performance Comparison of Pilot-Scale Sand Filtration and Membrane Filtration of Glafkos River Water

Round 1

Reviewer 1 Report

In this study, the authors compared pilot-scale sand filtration and membrane filtration of river water. The authors mentioned that ζ-potential, conductivity, TS, TSS were measured, but no such data in the manuscript. The authors should provide such data.

In addition, the reviewer has several comments need to be further clarified.

• It suggests changing the title to “A performance comparison of pilot-scale sand filtration and membrane filtration of Glafkos River water”.
• Abstract: the results and brief conclusion should be presented instead of description experimental procedure.
• Introduction: the authors should shorten the Introduction and focus on the previously-reported studies associating with (i) performance comparison of sand filtration and membrane filtration, (ii) challenges of sand filtration and membrane filtration in treating surface water.
• Line 207, “clean water permeability”.
• Section 3.2, the first two paragraphs should be moved to “materials and methods” part.
• During sand filtration, the feed water with initial turbidity at 15, 70 and 150 NTU was used, but for membrane filtration, the feed water with initial turbidity at 150 NTU was not tested. The authors should give an explanation on it.
• Figure 8, the axis title is not clear. It suggests to present the real TMP data instead of TMP/TMP0. It should be pressure increase instead of pressure drop as TMP increased with membrane fouling. What is time ratio and particle concentration rate? Please present the real time scale.
• Figure 9, permeability unit should be “m3/bar m2h” (i.e., flux/TMP).
• Figure 10, axis titles are missing. The titles and figure contents are not consistent.
• Section 3.3., it suggests list the cost and environmental impacts in a table for such a comparison.
• The conclusion part should be shortened.

Author Response

Response to Reviewer 1 comments

We thank very much the Reviewer for the comments and suggestions. Please find below our responses in Italic Fonts

Comment 1: In this study, the authors compared pilot-scale sand filtration and membrane filtration of river water. The authors mentioned that ζ-potential, conductivity, TS, TSS were measured, but no such data in the manuscript. The authors should provide such data.

Response: ζ-potential, conductivity, TS and TSS measurements were done in a previous work, they also have been measured during this study but they were not useful for the interpretation of the current data, and the corresponding sentences were corrected as following:

Lines 152-153:  Moreover, parameters such as ζ-potential and pH, conductivity and suspended solids concentration were examined. Phrase was deleted

Lines 195-197: Phrase was changed ‘Samples were collected along the filter tube for turbidity, ζ-potential, conductivity, TS, TSS and particle concentration and particle size distribution measurements’.

Lines 214-215: Phrase was changed ‘During the experiment, samples of the permeate and the concentrate were collected for turbidity, ζ-potential, conductivity, TS, TSS and particle size distribution and particle concentration measurements’.

Lines 220-221: Phrase was deleted For the zeta potential and conductivity measurements a Zetasizer NanoS (by Malvern Co.) device was used.

Comment 2: It suggests changing the title to “A performance comparison of pilot-scale sand filtration and membrane filtration of Glafkos River water”.

Response: The title was changed as proposed.

Comment 3: Abstract: the results and brief conclusion should be presented instead of description experimental procedure.

Response: The abstract was changed as the Reviewer proposed as follows:

Lines 14-16 were deleted: Membrane filtration can also help to the reduction of chemical reagents in water and wastewater treatment (electrolytes, polyelectrolytes, etc.), to the reduction of produced waste sludge and the use of less hazardous and more innovative treatment methods.

Lines 23-31 were deleted and text was added: Thae optimum values of operational parameters were identified and filtration efficiencies of the two cases were compared. Water produced from UF membrane was of better quality, meeting the EU regulations, than in the case of deep bed filtration process. A discussion in terms of the operational cost and environmental impacts was performed. Filtration capacity of the sand filter is a decreasing function of the flow rate and it was found less efficient than membrane ultrafiltration for increased turbidity or increased particle concentration values. Membrane ultrafiltration could achieve long term economical profit while it is characterized by minimum environmental impact since the use of chemical reagents and the production of waste sludge are limited.

Comment 4:  Introduction: the authors should shorten the Introduction and focus on the previously-reported studies associating with (i) performance comparison of sand filtration and membrane filtration, (ii) challenges of sand filtration and membrane filtration in treating surface water.

Response: Lines 43-48, 60-75, 158-160 were deleted as the Reviewer proposed.

Comment 5:  Line 207, “clean water permeability”.

Response: “Clean “ was added in Line 212

Comment 6: Section 3.2, the first two paragraphs should be moved to “materials and methods” part.

Response: The first paragraph was moved to Materials and methods section Lines 207-213, the second one was deleted.

Comment 7:  During sand filtration, the feed water with initial turbidity at 15, 70 and 150 NTU was used, but for membrane filtration, the feed water with initial turbidity at 150 NTU was not tested. The authors should give an explanation on it.

Response: The 150NTU data were missing by mistake and now are added.

Comment 8: Figure 8, the axis title is not clear. It suggests to present the real TMP data instead of TMP/TMP0. It should be pressure increase instead of pressure drop as TMP increased with membrane fouling. What is time ratio and particle concentration rate? Please present the real time scale.

Response: The Figure was corrected.

Comment 9: Figure 9, permeability unit should be “m3/bar m2h” (i.e., flux/TMP).

Response: The figure was corrected.

Comment 10:  Figure 10, axis titles are missing. The titles and figure contents are not consistent.

Response: The figure was corrected.

Comment 11: Section 3.3., it suggests list the cost and environmental impacts in a table for such a comparison.

Response: Three tables were added as Reviewer suggested.

Comment 12: The conclusion part should be shortened.

Response:  We shortened the conclusion as the Reviewer noticed.

We have also done extended changes in English, according to Reviewer suggestion.

Author Response File: Author Response.docx

Reviewer 2 Report

The article writing should be improved in some parts:

optimal should be used as an adjective (e.g. the optimal concentration) and optimum as an substantive (e.g. the optimum is ...).

Lines 191 and 192: "The manometer panel was used for pressure difference measurements along the column and was consisted of 9 Hg manometers made of glass with internal diameter 3 mm". Here "was consisted" should be "consisted", wiithout was.

Lines 258 and 259: "This section may be divided by subheadings. It should provide a concise and precise description of the experimental results, their interpretation, as well as the experimental conclusions that can be drawn". This text might be deleted. It looks as part of the intruction text for authors.

Lines 364 and 365: "the transmembrane pressure rate (TMP/TMP0) were measured at five different input turbidity's". Here "turbidity's" should be Turbidities.

Author Response

Response to Reviewer 2 comments

We thank the Reviewer for the comments and suggestions. Please find below our responses in Italic Fonts.

Comment 1: optimal should be used as an adjective (e.g. the optimal concentration) and optimum as an substantive (e.g. the optimum is ...).

Response: It was corrected based on Reviewer’s suggestions.

Comment 2: Lines 191 and 192: "The manometer panel was used for pressure difference measurements along the column and was consisted of 9 Hg manometers made of glass with internal diameter 3 mm". Here "was consisted" should be "consisted", wiithout was.

Response: “was consisted” was corrected to “consisted”.

Comment 3: Lines 258 and 259: "This section may be divided by subheadings. It should provide a concise and precise description of the experimental results, their interpretation, as well as the experimental conclusions that can be drawn". This text might be deleted. It looks as part of the intruction text for authors.

Response: The phrase was part of the template document of the journal and it was deleted.

Comment 4: Lines 364 and 365: "the transmembrane pressure rate (TMP/TMP0) were measured at five different input turbidity's". Here "turbidity's" should be Turbidities.

Response: It was corrected.

We have also done extended changes in English, according to Reviewer’s suggestion.

Author Response File: Author Response.docx

Reviewer 3 Report

The paper titled "Depth and membrane filtration performance and perspectives:  A study for the implementation to Glafkos River surface water 
Fotios K. Katrivesis et al. meanly deals with the comparison between the two methods for water treatment of ultra-filtration (UF) and deep bed filtration process. Moreover, the Authors would like to focus the comparison on the operational cost and environmental impacts was performed.

The work describes the performed experiments for the two methodologies and reports their performances without any direct comparison outlining the difference in efficiency or other parameters. This aspect has also a relevant consequences on the environmental impact/pressure assessment in order to give useful information about the best efficiency comparison between the two investigated methodologies.

In the figures 8 (a, b) the "time ratio" is used but it is not defined in the text as well as in the figures 9 (a, b) the "time rate" is used but not defined.

Finally the economic and environmental impacts assessment/comparison is provide basing on literature review without supply further useful and usable information arising from the previous experimental analysis.

The general suggestion is to try to re-organize the paper calibrating the results in line with the declared objectives of comparison in terms of cost and sustainability efficiency.

Author Response

Response to Reviewer 3 Comments

We thank the Reviewer for the comments. Below please find our responses in Italic Fonts.

Comment 1: The paper titled "Depth and membrane filtration performance and perspectives:  A study for the implementation to Glafkos River surface water 
Fotios K. Katrivesis et al. meanly deals with the comparison between the two methods for water treatment of ultra-filtration (UF) and deep bed filtration process. Moreover, the Authors would like to focus the comparison on the operational cost and environmental impacts was performed. The work describes the performed experiments for the two methodologies and reports their performances without any direct comparison outlining the difference in efficiency or other parameters. This aspect has also a relevant consequences on the environmental impact/pressure assessment in order to give useful information about the best efficiency comparison between the two investigated methodologies.

Response: We thank the reviewer for his comments and remarks.

Comment 2: In the figures 8 (a, b) the "time ratio" is used but it is not defined in the text as well as in the figures 9 (a, b) the "time rate" is used but not defined.

Response: The figure was corrected, and the real time was used.

Comment 3: Finally the economic and environmental impacts assessment/comparison is provide basing on literature review without supply further useful and usable information arising from the previous experimental analysis.

Response: We understand reviewer’s question, however we tried to do a bibliographically approach of the costs of the two methods and the technoeconomic analysis is in progress.

Comment 4: The general suggestion is to try to re-organize the paper calibrating the results in line with the declared objectives of comparison in terms of cost and sustainability efficiency.

Response: In the current version, a significant number of corrections, changes and re-arrangements have been done according the comments of all reviewers to improve the manuscript. We hope that the comparison is more comprehensive now.

We have also done extended changes in English, according to Reviewer suggestion.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The authors have improved the manuscript and responded my questions.

Reviewer 3 Report

The Authors have improved the paper and the final version sounds better than the previous in terms of contents but fine/minor spell check is still required.