Which Configuration of Photocatalytic Membrane Reactors Has a Major Potential to Be Used at an Industrial Level in Tertiary Sewage Wastewater Treatment?
Round 1
Reviewer 1 Report
Authors are requested to revise the manuscript according to the suggested concerns.
Comments for author File: 
Comments.pdf
Should be proofread by a native English speaker or use professional language editing services.
Author Response
Reviewer 1
Dear Reviewer,
thank you very much for the work done and for your very useful and helpful comments addressed to improve the quality of our manuscript. Below the answer to each one of your comments is reported (in green).
Overview
The review highlights the need for the scale up of photocatalytic membrane reactors from laboratory setup to industrial scale. Further it also emphasizes the role of operational parameters in the sewage treatment.
Major Comments
- Figure 2, 3, and 4 are low quality.
The quality of the figures was improved by uploading higher definition files.
- Rewrite the conclusion focusing on the future perspectives.
The future perspectives have been highlighted in the conclusions.
- Should include more figures and tables as literature on the topic is abundantly available.
As suggested, we added five new figures that, in this new version, are numbered: 1, 2, 6, 8 and 9.
- Should also highlight the stability aspects of photocatalytic membranes.
The stability aspects of photocatalytic membranes were described by adding, after the line 512, the following sentences: “For example, a PVDF membrane was used in various studies for immobilizing the photocatalyst [105,106] but in a study of Dzinun et al. [107] it was concluded that UV irradiation has some effect on the stability of the TiO2/PVDF membrane within 30 days exposure. Therefore, the use of polymeric membranes is limited for their low photostability and resistance against oxidative species, so a membrane material (e.g. inorganic membranes) with shows adequate stability against the oxidative species under light irradiation should be used.”
- As Authors are highlighting the lab scale to industrial scale PMRs, they should include the Sustainability assessments of the processes and membranes covering economics associated with overall configuration and design of both reactors (fixed and slurry).
As suggested, a summary on this topic was included at end of section 4 from line 993.
- Papers published by leading research groups in the field are missing. Should review the relevant literature.
More references by some leading research groups were added.
Minor Comments
- Line 34: “so it results crucial for worldwide development”. Rewrite.
The sentence was rewritten as follows:
“so it results crucial for economical and healthy reasons considering the worldwide population growth.”
- Line 40: “present” instead of “available”.
This word was modified as suggested.
- Line 59: Use updated statistics, as new data is available for the same.
The statistic has been updated, line 60.
- Line 64: Its is “Advanced Oxidation Processes” not “Advanced Oxidation Technologies”.
This sentence was modified as suggested as well as related acronims.
- Line 78: “the immobilized photocatalysts are usually recommended because of some disadvantages”. Incomplete sentence.
This sentence has been modified as follows: “A slurry photoreactor offers a high surface area for the reactions, but although it is more efficient than an immobilized system, [21] there are some drawbacks such as : i) difficulty of separation of the photocatalyst at the end of a batch photocatalytic process; ii) particle aggregation and agglomeration at high photocatalyst concentration; and iii) difficulty of operating a continuous process.”
- Line 79: Remove “Indeed”.
As suggested “indeed” was removed.
- Line 90: “can be retained in the reaction ambient until they are completely mineralized”. What is “reaction ambient”.
We changed “reaction ambient” with “reaction zone”
- Line 96: “none of them” instead of “none of they”.
This sentence was modified as suggested.
- Line 141 to 142: Should be rewritten.
This sentence was rewritten as follows: “The choice of the most appropriate tertiary treatment is a complex matter, since each method has certain strengths and weaknesses. On the bases of the required final quality of the treated water it is possible to choose the combination in multi-step process for the removal of target contaminants.”.
- Line 143: “Photocatalytic membrane reactors” should be “PMRs”.
As suggested, we writted PMRs.
- Line 156: “to relate them” instead of “to relate they”.
This sentence was modified as suggested.
- Line 160: “WWTPs operates continuously”.
This sentence was writted as suggested.
- Line 218: representation of superoxide anion.
We adjusted in all places as O2•-
- Line 246: “due to the pH”. Funny sentence “Thanks to the pH”.
This sentence has been modified as suggested.
- Line 256: Tan et al. Remove “Yik”. “
Yik” was removed.
- Line 284: LH mechanism. Abbreviated in Line 188.
Langmuir-Hinshelwood was replaced by the acronym LH.
- Line 333 to 336: Rewrite.
This sentence has been rewritten as follows: “Following is reported an overview of some reactor configurations with or without membrane and the differences between these two systems are also described. This study of the literature can give a lot of useful information to improve the design of membrane photoreactors.”
- line 468: PMR. Already abbreviated.
“Photocatalytic membrane reactors” was replaced by the acronym PMRs.
- Line 474: PM should be abbreviated in Line 94.
The abbreviation PM was added as suggested.
- Line 480: ROS. Already abbreviated.
“Reactive oxygen species” was replaced by the acronym ROS
- Table 1: “ . ” are used at the end of few sentences within the table. Either use it or don’t. Be consistent.
The dots were removed.
- Line 664: OH, O2, H2O2 already abbreviated.
Hydroxyl radical and hydrogen peroxide were replaced by their abbreviations.
Remark
Even though the manuscript is informative and lengthy, lack of technical aspects related to the configuration setup and overall economics involved in the upscale of reactors from lab to industrial scale is a setback. Authors should include more tables or quality figures. Manuscript should be proofread by a native English speaker.
Some figures were added as well as a discussion on assessment.
Author Response File: 
Author Response.docx
Reviewer 2 Report
I would be very glad to review this paper because the subject is interesting. In this manuscript, the authors have reviewed the recent advances in photocatalytic membrane reactor to be used at industrial level in tertiary sewage wastewater treatment. In this review, the two main PMRs configurations have been analysed as requirements of a tertiary treatment of sewage wastewater considering six design and operational parameters of various plants. Some characteristics of photocatalysis and that of membranes have been considered. This review can give a push to switch research from laboratory to industry in using the photocatalytic membrane reactors.
Totally, the paper can be considered for publication after a minor revision.
1. The Keywords is needed to be changed. It seems that the keywords are repeated. Wastewater appears for 3 times, and photocataly* appears for 2 times.
2. The fee and cost of photocatalytic technology is needed to be compared with other technology for wastewater treatment.
3. Is the reaction atmosphere and pressure as an important parameter for the photocatalytic efficiency?
4. Is it possible to remove nuclear radiation wastewater by photocatalytic membrane reactor?
5. What kind of light is more useful? Sunlight, UV light, Vis light or NIR light?
Author Response
Reviewer 2
Dear Reviewer,
thank you very much for the work done and for your very useful and helpful comments addressed to improve the quality of our manuscript. Below the answer to each one of your comments is reported (in red).
I would be very glad to review this paper because the subject is interesting. In this manuscript, the authors have reviewed the recent advances in photocatalytic membrane reactor to be used at industrial level in tertiary sewage wastewater treatment. In this review, the two main PMRs configurations have been analysed as requirements of a tertiary treatment of sewage wastewater considering six design and operational parameters of various plants. Some characteristics of photocatalysis and that of membranes have been considered. This review can give a push to switch research from laboratory to industry in using the photocatalytic membrane reactors.
Totally, the paper can be considered for publication after a minor revision.
- The Keywords is needed to be changed. It seems that the keywords are repeated. Wastewater appears for 3 times, and photocataly* appears for 2 times.
As suggested the keywords have been revised, however some words appear in different context.
- The fee and cost of photocatalytic technology is needed to be compared with other technology for wastewater treatment.
The photocatalytic technology is still young, so trusted information to make a cost comparison with other technology for wastewater treatment is still insufficient. However, at the end of sec. 4 of the revised version, some aspects on the use of the sustainability assessment for comparing different technologies are included with some costs also.
- Is the reaction atmosphere and pressure as an important parameter for the photocatalytic efficiency?
For reactions in aqueous phase the pressure does not influence the photocatalytic efficiency. For gas phase reactions the pressure increase increases the adsorbed target species on the photocatalyst surface so the pressure becomes an important parameter.
- Is it possible to remove nuclear radiation wastewater by photocatalytic membrane reactor?
The photocatalytic technology is generally applied for destroying (mineralize) organic pollutants in aqueous media and in some cases also reduction of metal ions (e.g. Cr(VI) to Cr(III), As(V) to As(III)); the coupling with membranes sinergically increase the power of both technologies. For nuclear wastewater treatment the radionuclides are generally removed (adsorption and membranes are the most mature technologies) but not destroyed (or successively are disactivated). We are not expert of the nuclear field but we think that photocatalytic membrane reactors could not be suitable for such a type of application. If of interest, the oxidation state of a radionuclide could be reduced (e.g. by using a PMR) to facilitate then its removal by a chemical technology.
- What kind of light is more useful? Sunlight, UV light, Vis light or NIR light?
The activation of a photocatalyst is done by the energy of photons that are present in a radiation of suitable wavelength because the bandgap energy is generally different for different photocatalysts (see Fig. 9 of the revised version). So, the most useful kind by light is the one that corresponds to a max absorption of the photocatalyst (that also maximize the performance of a certain photocatalyst).
Author Response File: Author Response.docx
