Photocatalytic ZnO-Assisted Degradation of Spiramycin in Urban Wastewater: Degradation Kinetics and Toxicity
, Giusy Lofrano 2,*, Giovanni Libralato 3, Marco Guida 2,3, Antonietta Siciliano 3, Federica Carraturo 3 and Maurizio Carotenuto 4Round 1
Reviewer 1 Report
Dear Authors,
please reformat the manuscript according to the editorial requirements (tables, citation, reference styles).
Please prepare a solid discussion of the results in the subsection: "3.4. Toxicity data".
Yours faithfully,
Rev
Author Response
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Reviewer 2 Report
The paper is well organized and looks good. The only remark is that conclusions are poor and hace to be extended.
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Reviewer 3 Report
In my opinion, the novelty is limited and data are not enough to publish as a research paper. I cant see any new contribution in the field.Author Response
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Reviewer 4 Report
The article is highly relevant and matches perfectly to the scope of "Water". However, some minor revisions are required:
Abstract:
line 2: Reuse is a term from waste management implying that something never becomes a waste. Waste water has been discarded, so that the term "reuse" is not really correct, so I prefer "utilisation" which has no legal implications.
line 7: Also TiO2 has a photocatalytic activity. What is the advantage of ZnO?
line 11: As the destruction of SPY takes place at the surface of ZnO, the surface area per liter treated waste water would be more interesting than the mass of ZnO used. At least both values should be provided.
line 14: Does this degree of toxicity refer to the treated or untreated sample. It would be great to highlight the effect of the treatment!
line 16: This last sentence sounds as Zn would be toxic. So treating one toxic substance (SPY) by another one sounds not very smart...did I get this right?
Introduction:
What is a "one-health" effect?
Second paragraph (sorry, there are no line numbers in the draft): Sometimes you talk about re-use, sometimes about recycling. Think what matches better as the two terms have different meaning: Re-use implies that something does not become a waste, whereas recycling implies that it becomes a waste and is then treated and finally converted into a new product.
A concern is rather "large" than "great".
Second paragraph: AOPs are a specific kind of physico-chemical methods. So the first two sentences are confusing.
What do you refer to when talking about "recycling ability"? What shall be recycled? According to the grammatical structure it would be the physicochemical methods, but this does not make sense.
Photocatalysis is also a physicochemical process. I suggest to make a diagram to classify the different treatment methods.
Last paragraph: Would "metabolite" be more precise than "by-product", considering also the legal definition of a by-product.
2.1 Experimental Procedure:
What is a "background level of SPY removal"? A level and a rate are two different things.
2.3 Ecotoxicity
"to pregressively dissolve" or "to be progressively dissolved"
Author Response
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Reviewer 5 Report
The manuscript reports on a photocatalytic advanced oxidation process (AOP) based on ZnO to remove a representative macrolide antibiotic, spiramycin (SPY), from different aqueous matrices. The photocatalytic treatments with ZnO of water and urban wastewater spiked with SPY has been evaluated. After 80 min of photocatalysis, 95–99% removal of SPY was achieved at 1 g/L ZnO concentration. The effluent toxicity, tested with different microorganisms: Aliivibrio fischeri bacterium, Raphidocelis subcapitata green alga and Daphnia magna crustacean, ranged between slight acute and high acute hazard. Zn concentrations (filterable and ultrafilterable) were quantified in treated effluents and were shown to be high enough to contribute to the observed toxicity.
The manuscript is suitable for publication in the journal provided some minor corrections are performed.
Minor corrections:
- Page 3: While the terms BOD and COD are well known to the general audience, the term TSS (last paragraph) is more specific and should be clarified.
- Page 4: “Zinc concentrations Zn were determined by Flame Atomic Absorption Spectroscopy (FAAS)…”
Zinc concentrations (Zn) were determined by Flame Atomic Absorption Spectroscopy (FAAS)… Please, make this correction (brackets) in the rest of the manuscript.
- Figure 1. UV spectra of SPY. Please, include the solvent and concentration in the Figure caption.
- Page 6: “These results agree with studies available in scientific literature [22]. For TiO2, superoxide radicals (.O2) and holes (h+) play a key role in the degradation process, while for ZnO superoxide radicals (.O2) and hy-droxyl (.OH) radicals are the predominant reactive species in the degradation process.”
Superoxide is a radical anion (O2·-) with three electrons in the two quasi-degenerated pi* HOMO orbitals, two e- in one of the orbitals and one electron in the other one.
- Page 10: Figure 5 caption: nZnO has not been previously specified.
- Some corrections are required concerning the English text:
P3 paragraph 1: “amount [27].However,…”
P3 paragraph 3: “in a 250 mL magneticALLY stirred cylindrical Pyrex vessel …”
P5 paragraph 1: “Because ZnO nanoparticles are known to progressively DISSOLVE in aqueous matrices, …”
P8 paragraph 2: “SPY are reported in Figure 5and 6, respectively.”
P11 Conclusions: “The future environmental compatibility of ZnO-BASED 13 nanomaterials in...”
Check References 2, 4, 8, 12, 18, 19, 25, 27, 31, 36.
Author Response
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Round 2
Reviewer 1 Report
thank you for the submitted manuscript.
Author Response
We thank you for your revision, English was widely revised by a mother tongue colleague, a spell check was done too.
Reviewer 3 Report
The paper needs language checking as the language is poor in many sentences.
The introduction is too long and can be written in more effective words.
What are the limitations of using zinc oxide?
How zinc oxide improved the system? cost? the performance or something else?
In this sentence which is related to 28 and which one to 33? According to [28,33], the EC50 of SPY per se was of approximately 8000 mg/L for A. fischeri, 4 mg/L for R. subcapitata, and 500 mg/L for D. magna, thus only R. subcapitata could have been directly impaired by the initial experimental SPY concentration (10 mg/L). Also, the English have a problem.
The authors claimed that "It is worth to notice that three different endpoints have been used in this evaluation which is not common in current published papers as well as the toxicity data integration". Can they share which papers they talking about?
It recommended using more recent studies published in 202o and maybe 2021 also to increase the quality of the manuscript.
Author Response
We greatly appreciate the suggestions provided by Reviewer. We improved the paper accordingly. Changes in the manuscript were evidenced with the Word track tool for changes. Reponses to Reviewer were evidenced in blue on a point-by-point basis in the present document. All changes suggested by Reviewer were taken into consideration in this revised and re-submitted version.
The paper needs language checking as the language is poor in many sentences.
English has been widely revised by a mother tongue colleague.
The introduction is too long and can be written in more effective words.
The section introduction has been widely revised and shortened accordingly. See the text.
What are the limitations of using zinc oxide? How zinc oxide improved the system? cost? the performance or something else?
In the section introduction it has been specified: “Zinc oxide (ZnO), with a direct band gap of approximate 3.3 eV, has been suggested as an effective and cheaper alternative to TiO2 because of its strong oxidation ability, good photocatalytic properties, and a large free-excitation binding energy. Moreover, ZnO-based catalysts are considered more suitable for solar-drive photocatalysis because ZnO can absorb a larger fraction of the solar spectrum than TiO2 thanks to its direct and wide band gap in the near-UV spectral region. ZnO is also a good antibacterial agent being stable under harsh processing conditions”. Despite these advantages Zinc oxide can result in higher toxicity respect to titanium oxide, thus its concentration need to be carefully calibrated.
In this sentence which is related to 28 and which one to 33? According to [28,33], the EC50 of SPY per se was of approximately 8000 mg/L for A. fischeri, 4 mg/L for R. subcapitata, and 500 mg/L for D. magna, thus only R. subcapitata could have been directly impaired by the initial experimental SPY concentration (10 mg/L). Also, the English have a problem.
The sentence has been rephrased and the information related to the different papers has been specified.
The authors claimed that "It is worth to notice that three different endpoints have been used in this evaluation which is not common in current published papers as well as the toxicity data integration". Can they share which papers they talking about?
Maybe we were not clear, I am going to explain better. Most papers investigating the behaviours of advanced oxidation processes, including photocatalysis, do not evaluate the effluent toxicity and also when they do this kind of study, it is quite rare to find the use of three different end-points which is very important to assess the process in its whole. Thus, we were not referring to a specific paper, we were highlighting that the study we performed is very complete since the impact on different trophic levels was considered.
It recommended using more recent studies published in 202o and maybe 2021 also to increase the quality of the manuscript.
We checked and we do not find papers published on 2021 dealing with ZnO photocatalysis. The reference n.3 has been published in 2020.
Round 3
Reviewer 3 Report
The paper improved but I have the following concerns:
- The authors said," Most papers investigating the behaviors of advanced oxidation processes, including photocatalysis, do not evaluate the effluent toxicity and also when they do this kind of study, it is quite rare to find the use of three different end-points which is very important to assess the process in its whole". My question is which papers? why the authors didn't mention them? It must be added.
- As the results are not much. I suggest adding the cost-effectiveness of the system comparing to the others.
The language still needs improvement by a native speaker.
Author Response
The paper improved but I have the following concerns:
- The authors said," Most papers investigating the behaviors of advanced oxidation processes, including photocatalysis, do not evaluate the effluent toxicity and also when they do this kind of study, it is quite rare to find the use of three different end-points which is very important to assess the process in its whole". My question is which papers? why the authors didn't mention them? It must be added.
The use of quotation marks seems to imply that the sentence reported above was written as such in the last uploaded revised version of contribution 1104872; which is not the case. This sentence was the reply to a previous question of revision 3.
That said, the question of the reviewer is legitimate and we assumed that it refers to the sentences “Most literature studies established the optimum reaction conditions on the basis of pH, temperature, light intensity, morphological structure and photocatalyst amount 26[27]. However, the ecotoxicity of the final effluents was evaluated only in few cases [Kanakaraju et al. 2018], showing that complete degradation of the targeted chemicals is not enough to ensure that they are free from residual toxicity [28].”
Because this is not a review and because of the need to keep the length of the introduction within reasonable limits we used the review by Kanakaraju et al. (2018) to highlight the need for more regular ecotoxic evaluations of AOP-treated effluents. We also modified the second sentence to avoid ambiguity to: “However, complete degradation of the target chemicals does not ensure that final effluents are free from residual toxicity [Kanakaraju et al. 2018], possibly due to the formation of toxic transformation products.
Kanakaraju et al. (2018) reviewed the significant findings of 50 selected publications using various AOP for the degradation of pharmaceuticals. Only three of them evaluated the potential ecotoxicity of the treated effluents.
Kanakaraju D, Glass BD, Oelgemöller M. Advanced oxidation process-mediated removal of pharmaceuticals from water: A review. Journal of Environmental Management. 2018;219:189-207.
- As the results are not much. I suggest adding the cost-effectiveness of the system comparing to the others.
We disagree with the present request because it is out of scope from the present paper. There are several literature review papers investigating in deep such aspect starting from 10.1016/j.ultsonch.2009.09.005.
- The language still needs improvement by a native speaker.
The Reviewer as for the first request looke at an old version of the paper also. English was carefully reviewed by a mother tongue.
