Application of Waste Polymers as Basic Material for Ultrafiltration Membranes Preparation

Round 1

Reviewer 1 Report

The manuscript "Application of waste polymers as basic material for ultrafiltration membranes preparation" involves reasearch for utilizing waste consisting of polystyrene into filtration media. This is a very interesting subject and the methods used are scientifically sound. The main drawback of this manuscript is the proor use of English which needs from moderate to extensive editing. Other comments are:

1) The authors could combine both Figures 3 and 6, 4 and 7, 5 and 10 to make easy comparisongs. The lines could be omitted since they indicate a trend which might be false. Experimental data are usually depicted with symbols and line are used to represent model results, but here this is not the case.

2) I wonder about the durability of these membranes with respect to the volume of water they can treat in total at an acceptable level of permeate quality. Additionally, the reuse of these membranes after cleaning is another aspect which could be considered.

3) Some economical data would be useful to be incorporated in the discusion.

   

Author Response

Reviever 1

1) The authors could combine both Figures 3 and 6, 4 and 7, 5 and 10 to make easy comparisongs. The lines could be omitted since they indicate a trend which might be false. Experimental data are usually depicted with symbols and line are used to represent model results, but here this is not the case.

2) I wonder about the durability of these membranes with respect to the volume of water they can treat in total at an acceptable level of permeate quality. Additionally, the reuse of these membranes after cleaning is another aspect which could be considered.

3) Some economical data would be useful to be incorporated in the discusion.

Ad.1. Unfortunately, I can't agree with this suggestion. Indeed, the combination of these charts would make it easier to compare them, however the assumption of the article was to create two distinctive parts: part with the selection of the appropriate concentration of the polymer, and the second one with modification of membrane chosen in first part. In addition, I think that too much data on one chart could makes its unclear. Lines were removed.

Ad. 2. As part of the research and preparation for them, the quality of the permeate was tested every half hour of the experiment. No deterioration of water quality was observed, although they were not qualitatively identical. Similarly, no degradation in permeate quality was seen after membrane cleaning processes. Regarding permeate quantity and process time, no deterioration of membrane quality was observed

Ad.3. These are only preliminary experimental studies, no economic considerations have been carried out. As mentioned in the introduction, there are very few publications on the subject using waste as a raw material. However, the use of waste materials will naturally reduce the cost of purchasing pure polymer, as well as reduce production costs. This could be used in large scale commercial membrane production.

Reviewer 2 Report

See attached file

Comments for author File: Comments.pdf

Author Response

Reviever 2

Comments:

Page 6, line 176, is relative permeability estimated via experiments performed with pure water? Idem for figure 3 and figure 6, filtration of pure water? For pure water, permeate flux vs. transmembrane pressure is a straight line passing through the origin, comments? In this case, calculation of a water permeability would make it easier to compare hydraulic membrane performances. Contact angle: interest?

Rps 16  decrease of contact angle A small decrease of contact angle shall not imply that there is no modification due to nanotubes and addition of hydroxyl groups. It should be interesting to perform experiments with 3 solvents for determine polar and apolar contributions of free surface energy and the components (electron donor and receptor) of surface tension. It exists different methods, often implemented in the software (as for example OWRK, …).

Modification with OH groups should significantly modify components of the polar contribution. Figure5: a decline of permeability of 20-40% was observed during filtration, but this result cannot express that membrane fouling occurs because experiments were performed in dead-end mode (modification of physical properties of the solution, i.e. viscosity, …). Only additional filtration experiment of pure water after membrane rinsing can provide information about membrane fouling.

Response:

In the tests in Figures 5 and 10, the value 0 was the value of clean water flow through the membrane - while conditioning the same membrane. Then the feed was exchanged for river water and the experiment was continued. In charts 3 and 6, pure water was filtrated using membranes with the same composition but from different sheet. Due to the fact that it was an experiment conducted in the range of 0.05 - 0.2 MPa, it was decided to use another sheet to avoid irreversible expansion of the membrane pores at a higher pressur. The expanding pores do not have to give a straight line, and cause, in increasingly high pressure, a curve on the chart could have an exponential shape. The decrease in membrane permeability during the experiment was only to check which membrane would show the highest resistance to clogging. Next article is being prepared, where a cross-flow system was used to study membrane fouling.

Indeed, due to the fact that membranes made only of rPS, despite different concentrations, should have the same contact angle because they are made of the same material. The differences in Table 6 are caused by imperfections of the measuring device. The addition of nanotubes to the membrane slightly reduced the wettability angle. The idea of ​​using 3 different solvents is very interesting and I will gladly check this relationship in further studies.

All other comments have been taken into account and corrected in the article.

Reviewer 3 Report

The authors could consider a few comments and recommendations:

Please check the manuscript for spelling, lack of spaces, errors, etc., e.g. page 2, line 46 (waste waste), page 2 line 63 (wad), page 2 line 64 (undertakenmembranes) and so on. The meaning of the acronym CNT is not explained in the Introduction section, nor the abbreviation SWCNT-OH in the Membrane Preparation subsection. Please correct both inaccuracies. Table 3. Please check the conductivity value “for the second part of study”. It should probably be 640 μS/cm, otherwise, please explain this drastic increase in conductivity. Please add wavelength value for the parameter “absorbance”. Table 5. Could you comment on why DI water (feed) has a TOC value of 3.49 mg/L? Was feed water contaminated? DI water usually has a TOC below 1 mg/L. Subsections 3.3 and 3.4 can be easily combined.

Author Response

Reviever 3

Comment:

Please check the manuscript for spelling, lack of spaces, errors, etc., e.g. page 2, line 46 (waste waste), page 2 line 63 (wad), page 2 line 64 (undertakenmembranes) and so on. The meaning of the acronym CNT is not explained in the Introduction section, nor the abbreviation SWCNT-OH in the Membrane Preparation subsection. Please correct both inaccuracies. Table 3. Please check the conductivity value “for the second part of study”. It should probably be 640 μS/cm, otherwise, please explain this drastic increase in conductivity. Please add wavelength value for the parameter “absorbance”. Table 5.

Could you comment on why DI water (feed) has a TOC value of 3.49 mg/L? Was feed water contaminated? DI water usually has a TOC below 1 mg/L. Subsections 3.3 and 3.4 can be easily combined.

Response:

Thank you for your comments, they have been corrected in the text. High TOC value is probably due to an error on the calibration curve. The second reason may also be the fact that this DI water was kept too long in the open air. However, in relation to the obtained TOC values for permeate, this is not a quantity that will significantly affect it.