Application of Radiation Technology in Removing Endocrine Micropollutants from Waters and Wastewaters—A Review

Round 1

Reviewer 1 Report

The topic of the manuscript is timely and very important. The presence of non-biodegradable micropollutants in surface waters and even in drinking waters faces mankind with a great problem. Radiation technology seems to be an appropriate method to solve this problem. As compared to other AOP methods a further advantage of irradiation technology is that, as the established large-scale facilities show, the technology can be scaled up to the 10,000-100,000 m³/day level. In spite of these facts, radiation technology is not well known. Therefore, with this manuscript the author intends to fill a gap.

General comments

I have a problem with the title that is a bit different from the content of the manuscript. “Application of radiation technology in removing endocrine micropollutants from waters and wastewaters – a review” is the title. Until chapter 3.6. the compounds included in the text are really endocrine micropollutants. In chapter 3.7. Non-steroidal anti-inflammatory drugs (NSID) degradation – the compounds discussed are toxic, badly biodegradable, but it is not clear if they are endocrine disruptors. I have similar problem with the next chapter, 3.8. Antibiotics degradation. Antibiotics in the wastewater are really dangerous. They may cause the spread of antibiotic resistant bacteria and resistance genes. The author should either explain why NSID and antibiotics belong to the endocrine micropollutants, or change the title of the manuscript. In the latter case an additional problem occurs. The author should justify why did she choose just two from the NSID and some from the antibiotics. The number of both NSID and antibiotics is high and many articles deal with their radiation-induced degradation.

Endocrine micropollutants are defined at two places, (line 33-38: endocrine disrupting compounds (EDCs) merit special attention. They include: and line 211-218: Contaminants that cause endocrine disruption include:). I suggest omitting one of the two listings.

The English of the manuscript is rather good but at some places it needs improvement. I suggest some corrections.

References:

Some of the references contain abbreviations (journals titles), some of them do not contain. The numbering of the references is not consistent (e.g., after Ref. [27] the next Ref. in Table 2 is [108]). I suggest making the Reference list consistent. The formats of Ref. [32], [91] are unusual. Ref. 42 should be corrected: Rivera-Utrilla, J.; Abdel Daiem, M.M.;

Rate constants (k) of the reactions of OH radicals, hydrated electrons and H-atoms are cited without mentioning the methods used for the determination. It would be necessary to mention the method because the accuracies of the various methods are different. There are large discrepancies in reported values in some cases. Therefore, it would be useful to compare the methods and estimate their accuracy. This could help a critical evaluation of the k values obtained in different laboratories for the same compounds.

Chapter 2.1. Type of radiation sources. Due to the low dose rate they produce the industrial application of gamma sources in wastewater treatment is out of question. Therefore, it should be emphasized in the manuscript that gamma sources, mainly Co-60 sources are frequently used for scientific purposes in laboratory experiments but for industrial applications electron beam (EB) accelerators are applied. Besides, it is not necessary to emphasize that the results were obtained by the application or a gamma source or by EB, because it has no significance. All the results mentioned in the manuscript were obtained in laboratory experiments; in these cases the treatment time is not important. However, at a sewage treatment plant the purification of hundreds of thousands m³ is requested. Due to its low dose rate this requirement cannot be fulfilled by using gamma source only by EB accelerator. The fact that for industrial application in China (see Re. 22) EB accelerators are used support this statement. Therefore, I suggest modifying chapter 2.1. with more details about of EB accelerators and shorter description of gamma sources.  

Based on the above mentioned facts the modification of the Conclusions is also suggested, emphasizing that for industrial applications EB accelerators are suggested.

Specific comments:

Line 7: AOP will not be an alternative to conventional wastewater treatment but rather a post-treatment after the conventional one as it is written in the manuscript later on (line line 171.). Please correct the abstract accordingly.

Line 119: they are generated only in situ during – delete the word during

Line 861: 25. Directive 2000/60/EC of the European Parliament and of the Council of 23 October 2000

Table 1: use the English version for the names of pharmaceuticals, e.g., amoxicillin, tetracyclin.

Line 274: decreased with increasing absorbed dose;

Line 298-300: In our study on the BPA degradation using gamma radiation it was found that in the primary reaction of •OH radicals with BPA two isomers of hydroxycyclohexadienyl radicals (1,2) and phenoxyl-type radical (3) (Figure 2) are formed.

Line 313: In the case of BPA 10 mg dm-3, a dose of 0.3 kGy is needed to achieve 100% degradation, - matrix should be mentioned here.

Line 315-317: The obtained data indicate that the determination of the required absorbed dose in each case should be preceded by an investigation of matrix effects on water or wastewater. This sentence is confusing, correct please. I suppose that the matrix effect on the required absorbed dose should be investigated.

Line 322: what do you mean when mentioning wide pH range?

Line 338-340: The results obtained showed that the effectiveness of both MDHB and total organic carbon (TOC) removal in the irradiation process increased with the absorbed dose, regardless of the initial concentration of MDHB (in the range from 1-10 mg dm-3) at the absorbed dose of 800 Gy.

Line 361: The numerous industrial applications of perfluoroalkyl substances (PFAS) combined

The abbreviations should be defined at the first place they are mentioned. In this page there are some abbreviations which are not defined.

Line 374: and - 3.0x10⁷ M^-1s^-1 and 7.3x10⁷ M^-1s^-1, respectively, for PFOS.

Line 502: in Figure 6, hydroxyl radical provided

Line 502: As presented in Figure 6, hydroxyl radical •OH provided a powerful impact on CBZ degradation. This statement is supported by the facts neither in this paragraph nor in the figure. The figure shows a proposed mechanism. Correct the sentence.

Line 561: Degradation pathway was proposed that includes the electrophilic

Line 624: It has been shown that in the γ/N2O system, the dose needed to decompose 480 μM was reduced from 7.4 to 1.47 kGy [89]. Reduced as compared to what?

Line 631: which is in agreement with data presented previously [91,92]. It is necessary to cite all the presented data.

Line 754: non-beta-lactams – such group of antibiotics is not known. I suggest using the term other antibiotics.

 

Author Response

Dear Sirs

Please find my answers for revison in attachment

your sincerely

Anna Bojanowska

Author Response File: Author Response.docx

Reviewer 2 Report

The paper is a well-written review of application possibilities of gamma and electron beam radiation for the degradation of endocrine micropollutants in the field of water treatments. The topic is actual and the article is well-constructed. There are only a few questions and remarks, which should be taken into consideration by the author.

• Line 120-122: Besides ionizing radiation based processes other AOP methods are also able to generate hydrated electrons and hydrogen atoms simultaneously with the hydroxyl radicals.
• At line 143-147: Only tertbutyl alcohol is given as a hydroxyl radical scavenger. It would be worth to list some other options.
• In Table 2 what is the difference between the degradation results of SMX based on the 110^th article?
• In the text it would be better to define the meaning of decomposition, degradation and mineralization, whether it is transformation of the initial compound or TOC degradation. E.g. at line 250-253 it is not clear what is complete degradation.
• It would be worth mentioning the length of the separate treatment times (when possible), e.g. in the case of the combined irradiation and biological treatment [51].

Editing problems:

• Abbreviations of the compounds (SMX, LMC, TCN, SD, SMT) should be on the same page with Table 2.
• The readability of Figure 3., 4., 7., 8. and 9. should be improved.
• The picture and the title of Figure 5. are too far apart from each other.
• The title of Figure 7. is misplaced.
• Figure 8. is misplaced.
• There is no space after the title of Figure 9.
• Figure 10 is too far from the relevant text.

Please also check English grammar and correct typos throughout the manuscript:

• Line 31: “among which or generally”
• Line 139: “H₂O₂ is present in the solution”
• Line 304: “% OH-induced” the hydroxyl radical sign is not correct
• Line 451: instead of “about 50% larger” higher would be more appropriate
• Line 561-546: “It was proposed degradation pathway…” sentence is not clear
• Line 619: “indicated, thus indicating” repetition
• Line 692-694: “Due to the fact that sulfonamides…” sentence should be revised
• Line 709: “the process is higher, the lower the starting concentration”
• Line 735: “In the first step…”
• Line 757: missing point “(see Table2.). The use…”
• Line 797: ”being carried out to all over”
• Line 798: “wastewaters and waters with this type”

After the modification of the manuscript, it is recommended to be published.

Comments for author File: Comments.docx

Author Response

Dear Sirs

Please find my answers for revison in attachment

your sincerely

Anna Bojanowska

Author Response File: Author Response.docx

Reviewer 3 Report

The present review is a detailed and well structured literature study regarding radiation technologies for removal of micropollutants. This a very relevant and actual topic, and the revision of the literature on gamma radiation and electron beam might be a significant contribution to the field. Through the structure of the review by different compounds it is possible to have a broad view of the possibilities of these radiation-based oxidation processes. However, the review lacks on a critical comparison of the reviewed technologies with current technologies that are already widely implemented for removal of micropollutants – e.g. ozone oxidation and activated carbon adsorption. In fact, along the text is possible to find some few references to such comparative studies e.g. as the finding regarding energy consumption of electron beam and UV/H2O2 (in lines 528 to 531). Nonetheless, by the end of the reading is still not possible to visualize the implementation potential of these radiation technologies, nor of their potential advantage and drawbacks regarding other existing treatment methods – e.g. what should be expected regarding energy consumption, costs, operational complexity, etc.; or how mature are these technologies and what still need to be investigated. These considerations could be used to reformulate the conclusion which is still very vague, and with an improvement potential.

Additional revision points:

Lines 66 to 70: Here are indeed some considerations regarding the advantages and disadvantages of these technologies. In these two sentences, it is mentioned the risk of radiation contamination followed by the acceptance problem, that might due to the fear of using radioactivity. It is maybe possible to expand this discussion here? It could be shortly commented of this fear corresponds to a real risk, or if there are experiences from other fields that could be used here. This would be very helpful for readers not used to work with such technologies to better access the safety and further implications of using gama radiation and electron beam.     

Lines 177 – 179: Please consider the possibility of revising this phrase, even because this plant is probably not proving drinking water.

Table 2: Please check the spelling of some compounds.

Table 2: It is possible to add some information here regarding the water matrix (e.g.: wastewater, river water, pure water)?

Line 298: Please consider to include an indication that this a past study (e.g. “our previous”) and does not refer to this current review.

Lines 305 to 309: Very long sentence and also difficult to understand, please consider revising it.

Line 756: what is meant by “to utilize infusion bottles?”.

Author Response

Dear Sirs

Please find my answers for revison in attachment

your sincerely

Anna Bojanowska

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The reasoning of the authors is sound, I accept them. I suggest considering the publication of the manuscript in the present form. 

I call the attention of the authors to some typo.