Impact of Inorganic Anions on the Photodegradation of Herbicide Residues in Water by UV/Persulfate-Based Advanced Oxidation

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The main content of the work is the impact of inorganic Anions on the photodegradation of herbicide residues (Isoproturon/Terbuthylazine) in water by UV/persulphate-based advanced oxidation. However, the work only focus on the technical study, and lack of enough innovation. Moreover, there are some issues need to be solved to improve the manuscript.

(1) The “Introduccion” should be changed to “Introduction”.

(2) The introduction of water pollution is too much, more discussion should focus on the impact of inorganic anions on the degradation of pollutants in water.

(3) The abstract and conclusion of this manuscript is too verbose, which should be summarized in a concise way.

(4) This work focus on the impact of inorganic anions on the photodegradation of herbicide residues in water by UV/persulphate-based advanced oxidation, however, only the activity difference was discussed in this work, why different inorganic anions can affect the photodegradation efficiency of herbicide residues? The degradation mechanism of herbicide residues with different inorganic anions is the same or not? The author should pay more attention on this point.

Comments on the Quality of English Language

The quality of english language need to be improved.

Author Response

First of all, thanks for your kind and useful comments

The main content of the work is the impact of inorganic Anions on the photodegradation of herbicide residues (Isoproturon/Terbuthylazine) in water by UV/persulphate-based advanced oxidation. However, the work only focus on the technical study, and lack of enough innovation. Moreover, there are some issues need to be solved to improve the manuscript.

(1) The “Introduccion” should be changed to “Introduction”.

- I am sorry, it was a mistake. In the revised version it has been changed.

(2) The introduction of water pollution is too much, more discussion should focus on the impact of inorganic anions on the degradation of pollutants in water.

- The introduction has been shortened and new comments on the effects of inorganic anions have been added.

(3) The abstract and conclusion of this manuscript is too verbose, which should be summarized in a concise way.

- According to you, abstract and conclusions have been summarized in a more concise way.

(4) This work focus on the impact of inorganic anions on the photodegradation of herbicide residues in water by UV/persulphate-based advanced oxidation, however, only the activity difference was discussed in this work, why different inorganic anions can affect the photodegradation efficiency of herbicide residues? The degradation mechanism of herbicide residues with different inorganic anions is the same or not? The author should pay more attention on this point.

- The effect of inorganic anions and their mechanism (scavenging effect) is included in the results and discussion. The degradation mechanism of herbicides involves the same intermediates in all cases, although their content and appearance time is different.

 

 

Reviewer 2 Report

Comments and Suggestions for Authors

The paper contains interesting results that require a more focused discussion; at least the following should be consider for improvement:

- In the beginning of Introduction there is an extensive discussion on issues that are not directly related with the paper's topic and this should be much shortened and focused also on heterogeneous photocatalysis involving TiO2 that is not even mentioned hereby.

- It is recommended to write the Materials and Methods section accurately and similar for all reagents as e.g. " purity greater than 95%" is not an enough accurate formulation. Moreover, the "Terbuthylazine" pesticide should be nominated in Table 1 according to its chemical formula, as "Tertbuthylazine". Similarly the irradiance value used during the experiments should not be given as " approximately 10 mW cm-2" but as the interval between the minimum and the maximum irradiance values that were recorded during the experiments, expressed in W/m2.

- the pH values reported for the experiments in Table 1 are covering a rather extensive domain and this should be explained why or why was not a clear pH adopted for all the experiments.

- The description of the experimental set up should clearly mention the material used for the batch cylindrical photoreactor (e.g. regular glass or quartz)

- The detection wavelengths for the two pesticides degraded should be justified. Why were these wavelengths selected?

- The statement related to eq. (8) as "where Rr is the removal rate" cannot be true as the Rr represents an efficiency not a rate and the acronym should be correctly selected. Please take care in the Discussions section and use the appropriate wording.

The statements in the Results and Discussions section should focus on WHY? not on WHAT? in the current form, these are focused on the results as such not on why were these results recorded.

The kinetic plots used for evaluating the values in Table 3 should be inserted to outline the fit and to replace Table 3.

The discussions on the "nitrate (λ = 303 nm) and nitrite (λ = 355 nm)" the "show some adsorption" should be better formulated as at these wave lengths not "light" can be absorbed but part of the UV radiation.

The discussion on the results in Table 5 is not fully clearly formulated as it ignores the values in column 8 and give not any explanation on the higher values that are not clearly discussed in the above paragraph(s).

The discussions related to the results in Fig. 5 should be more clearly reformulated focusing on the curves presented in Fig. 5 and not on the tests inserted much above.

The proposed degradation pathways for the two herbicides are outlining that these pathways are not removing the by-products and their toxicity is not discussed, thus the aim of the proposed treatment is seems not to be fully achieved. These results require a more clear discussion, focusing not on the resulted (by)products but on their toxicity and the possibility of reusing the treated water.

The Conclusions section should be reconsidered focusing on the results presented in the paper and not on general statements already included in Introduction.

The excessive use of unusual acronyms make the paper difficult to follow. Moreover there are non-explained acronyms as e.g. CE in Table 2 or EC in Table 6 (for which the measure unit is the same) and this cannot be accepted.

Comments on the Quality of English Language

English language should be carefully improved and the appropriate terms should be selected in the paper, as above outlined.

Author Response

First of all, thanks for your kind and useful comments

The paper contains interesting results that require a more focused discussion; at least the following should be consider for improvement:

- In the beginning of Introduction there is an extensive discussion on issues that are not directly related with the paper's topic and this should be much shortened and focused also on heterogeneous photocatalysis involving TiO2 that is not even mentioned hereby.

- The introduction has been shortened and the mechanism involving TiO₂ has been included.

- It is recommended to write the Materials and Methods section accurately and similar for all reagents as e.g. " purity greater than 95%" is not an enough accurate formulation.

- The sentence has been modified.

Moreover, the "Terbuthylazine" pesticide should be nominated in Table 1 according to its chemical formula, as "Tertbuthylazine". Similarly the irradiance value used during the experiments should not be given as " approximately 10 mW cm-2" but as the interval between the minimum and the maximum irradiance values that were recorded during the experiments, expressed in W/m2.

- To avoid confusions, we write the compound as terbuthylazine, which is how it normally appears in scientific literature. The irradiance value was constant during the experiments.

- the pH values reported for the experiments in Table 1 are covering a rather extensive domain and this should be explained why or why was not a clear pH adopted for all the experiments.

- The initial pH of the water was 6.7 in all cases. However, the pH varied when PS and salts were added.

- The description of the experimental set up should clearly mention the material used for the batch cylindrical photoreactor (e.g. regular glass or quartz)

- jacketed borosilicate glass has been included.

- The detection wavelengths for the two pesticides degraded should be justified. Why were these wavelengths selected?.

- This is because the absorption is at its maximum at these wavelengths.

- The statement related to eq. (8) as "where Rr is the removal rate" cannot be true as the Rr represents an efficiency not a rate and the acronym should be correctly selected. Please take care in the Discussions section and use the appropriate wording.

- Rr has been changed by Re in the text.

The statements in the Results and Discussions section should focus on WHY? not on WHAT? in the current form, these are focused on the results as such not on why were these results recorded.

- In a similar way, the effect of the wavelength on the efficiency of the PS and the difference between the PS and TiO2 is also justified.

The kinetic plots used for evaluating the values in Table 3 should be inserted to outline the fit and to replace Table 3.

- Figure 2 has been modified and the old Table 3 has been removed.

The discussions on the "nitrate (λ = 303 nm) and nitrite (λ = 355 nm)" the "show some adsorption" should be better formulated as at these wave lengths not "light" can be absorbed but part of the UV radiation.

- The sentence has been rewritten

The discussion on the results in Table 5 is not fully clearly formulated as it ignores the values in column 8 and give not any explanation on the higher values that are not clearly discussed in the above paragraph(s).

• New comments have been included in the revised version. See you the above comment about pH values.

The discussions related to the results in Fig. 5 should be more clearly reformulated focusing on the curves presented in Fig. 5 and not on the tests inserted much above.

- Comments related to Figure 5 are now reformulated focusing on the curves.

The proposed degradation pathways for the two herbicides are outlining that these pathways are not removing the by-products and their toxicity is not discussed, thus the aim of the proposed treatment is seems not to be fully achieved. These results require a more clear discussion, focusing not on the resulted (by)products but on their toxicity and the possibility of reusing the treated water.

Three transformation products of ISP, 1-(4-Isopropylphenyl)-3-methylurea (ISP-1), 1-(4-isopropylphenyl)urea (ISP-2) and 4-isopropylaniline (ISP-3) were identified during experiment 10, although their concentrations were below their LOQs (< 2 µg L^-1) at the end of the photoperiod (120 min). The maximum concentration peak was found after 30 min from the start, reaching levels between 4 and 8 µg L^-1.

In the case of TBZ, the photooxidation of the parent compound was accompanied by the appearance of desethyl-terbuthylazine (TBZ-1), deisopropyl-atrazine (TBZ-2) and terbuthylazine-2-hydroxy (TBZ-3), whose residual levels after 120 min were in the range of 1.2, 0.6 and 0.5 µg L^-1, respectively..

- Therefore, no metabolites of ISP were found after 120 min, whereas for TBZ, the levels of intermediates found at the end of the experiments were very low.

- New comments about their toxicity are now included.

The Conclusions section should be reconsidered focusing on the results presented in the paper and not on general statements already included in Introduction.

- The conclusions section has been shortened and rewritten

The excessive use of unusual acronyms make the paper difficult to follow. Moreover there are non-explained acronyms as e.g. CE in Table 2 or EC in Table 6 (for which the measure unit is the same) and this cannot be accepted.

- CE is a mistake. The correct acronym is EC (electrical conductivity).

 

Reviewer 3 Report

Comments and Suggestions for Authors

 The data and outcomes are well supported by detailed analysis and the article is well structured and written in a clear style and presentation. useful supportive references are critically integrated within the discussion. 

Author Response

Thanks for your kind comments.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have address the issue raised by the reviewer, and the manuscript is now acceptable for publication.

Comments on the Quality of English Language

Moderate editing of English language required

Author Response

Thanks for your kind comment.

Reviewer 2 Report

Comments and Suggestions for Authors

1) Please be careful when formulating your sentences as e.g.:

a) "the reuse of the WWTP" is not correctly formulated as the result coming from WWTP is reused...

b) "solid material (semiconductor or photocatalyst)" is not correct as it is a "semiconductor photocatalyst".

Moreover, please insert the reference(s) you used when writing eqs. (1)...(8)

c) Please reformulate "To compare the effectiveness of the two herbicides on degradation" as "To compare the effectiveness of the two herbicides in degradation"

d) what is "SO4="? a similar question for "CO3="?

e) please reformulate "result in fouling on the membrane surface" as "result in fouling the membrane surface"

2) there is an excessive use of acronyms that make the text difficult to follow. Please use the chemical formula of the radical anions in the text.

3) Please use "alkaline" instead of "basic" conditions/pH/etc. all over the manuscript

4) Please use "degradation efficiency" instead of "efficiency of degradation" all over the paper

5) Eq. (19) is not correctly written; actually there are written two equation there; these should separate using ";". Moreover, the discussion on these eq. is not coherent as it mentions ln(C0/C) instead of ln([H]0/[H]t)...

6) Eq. (25) does not respect the charge conservation law.

7) The Y-axis in Fig. 4 should give a more accurate information on which "relative concentration" is the discussion about.

8) It is not clear on which pollutant system are the results in Fig. 5 as the legend of this figure does not specify. Moreover, the discussion is too general as "nondegradable organic intermediates" does not give any explanation on the different results reported over the manuscript for both pollutants.

9) It is not clear the structure of this manuscript: why is Section 3. Materials and methods not inserted immediately after 1. Introduction, to be able to discuss the results knowing the important experimental aspects? this should be improved!

Comments on the Quality of English Language

see above comments...

Author Response

1) Please be careful when formulating your sentences as e.g.:

1. a) "the reuse of the WWTP" is not correctly formulated as the result coming from WWTP is reused...

- It has been modified

1. b) "solid material (semiconductor or photocatalyst)" is not correct as it is a "semiconductor photocatalyst".

- It has been modified

Moreover, please insert the reference(s) you used when writing eqs. (1)...(8)

- The reference has been included

1. c) Please reformulate "To compare the effectiveness of the two herbicides on degradation" as "To compare the effectiveness of the two herbicides in degradation"

- It has been changed

1. d) what is "SO4="? a similar question for "CO3="?

- They are sulfate and carbonate anions

1. e) please reformulate "result in fouling on the membrane surface" as "result in fouling the membrane surface"

- The sentence has been reformulated

2) there is an excessive use of acronyms that make the text difficult to follow. Please use the chemical formula of the radical anions in the text.

- All acronyms used are specified in Introduction. Later, chemical formula is used

3) Please use "alkaline" instead of "basic" conditions/pH/etc. all over the manuscript

- Basic has been changed by alkaline according to your suggestion

4) Please use "degradation efficiency" instead of "efficiency of degradation" all over the paper

- It has been changed

5) Eq. (19) is not correctly written; actually there are written two equation there; these should separate using ";". Moreover, the discussion on these eq. is not coherent as it mentions ln(C0/C) instead of ln([H]0/[H]t)...

- Now, there is only one equation. In addition, C₀ and C have been changed by H₀ and H_t

6) Eq. (25) does not respect the charge conservation law.

- Eq. 25 has been modified

7) The Y-axis in Fig. 4 should give a more accurate information on which "relative concentration" is the discussion about.

- Relative concentration specifies concentration (presence) of carbonate species as function of pH solution as previously specified.

8) It is not clear on which pollutant system are the results in Fig. 5 as the legend of this figure does not specify. Moreover, the discussion is too general as "nondegradable organic intermediates" does not give any explanation on the different results reported over the manuscript for both pollutants.

- DOC measures dissolved organic carbon in solution and it is a parameter relative to mineralization. Legend indicates the experiment: with and without addition of salts (SO₄⁼, Cl_- and HCO₃^-). Nondegradable organic intermediates refers to possible unknow reaction intermediates according to DOC values

9) It is not clear the structure of this manuscript: why is Section 3. Materials and methods not inserted immediately after 1. Introduction, to be able to discuss the results knowing the important experimental aspects? this should be improved!

- Initially, Materials and Methods was inserted after Introduction. However, as indicated by the editor, this section must be included after Results and Discussion according to the author guidelines of the journal.