Investigation on Mechanism of Tetracycline Removal from Wastewater by Sinusoidal Alternating Electro-Fenton Technique

Round 1

Reviewer 1 Report

This paper describes a very interesting study on the removal of the antibiotic tetracycline (TC) from wastewater by a novel technique, sinusoidal alternating electro-Fenton (SAEF).

The main operational parameters were optimized (pH, conductivity, current density, and hydrogen peroxide dosage. Sludges produced by this treatment have been characterised using different instrumental techniques (SEM, FT-IR, XRD, XPS), and UV-Vis has been used to confirm the degradation of TC over time and LC-MS/MS to identify some of the degradation products (only at a certain reaction time).

The work seems to be new and to have been properly carried out. The manuscript is generally well written and organized.

Given the novelty of the study I recommend publication after minor revision.

 

Specific comments:

I recommend replacing LC-MSMS by LC-MS/MS

Line 25                 c[H₂O₂] = 1.17 cm.dm^-3                 c[30%H₂O₂] =1.17 cm.dm^-3

Lines 87 and 88                The dimensions of the steel plates are repeated.

Lines 108-109                   “All samples should be filtered by 0.45 μm microporous membrane before determination. After filtration and vacuum drying, the flocculant samples were obtained.”

Please clarify this experimental part. Does the filtration by 0.45 μm microporous membrane applies only to LC-MS/MS determination? Or it also applies to the sludge samples?

I suggest replacing “flocculant” by sludges throughout the text.

 

Line 123              “…TC simulated wastewater raw liquid.”

This simulated TC wastewater is a TC solution 100 mg/L prepared in ultrapure water?

 

Lines 135 – 138                The injection volume is usually in the µL range, not mL. There are other operational parameters associated to the LC-MS/MS that are not presented. Please complete or include a reference.

Line 213                             0.50 mg.dm^-3                    0.50 cm³.dm^-3

Line 224                             3.2 Comparison and application effect analysis

Please rephrase

Line 230                             aerobic pollutants?

Lines 376 – 386                Regarding the LC-MS/MS analysis is there any support in the literature to the degradation products identified at time = 5 min? Why was this time chosen?

Reference [27] seems not to be cited in the text.

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

Comments and suggestions:

1. Abstract: “ The results showed that the removal rates of TC and chemical oxygen demand (COD) could reach up to 94.87%, and 82.42% respectively, but electric energy consumption (EEC) is only 1.383 kWhm−3 and the amount of produced sludge (Ws) is also 0.1833 kgm−3 by SAEF under the optimum conditions of initial pH = 3.0, conductivity (κ) = 1075 μScm−1, current density (j) =0.694 mAcm−2, initial c(TC) = 100 mgdm−3 , c[H2O2] = 1.17 cm3dm−3, frequency (f) = 50 Hz, t = 120 min”, rewrite the sentence, it’s too large..

 

2. “Therefore, how to efficiently remove TC from wastewater is a research hotspot in the field of water treatment..”--- I suggest the author, to discuss a paragraph related water pollution due to various contamination. The author may use the below related references to support this.

Environmental research 2019, 170, 389-397

Desalination and Water Treatment 57 (46), 2016, 21863-21869

Separation Science and Technology 55 (10), 2020, 1766-1775

Journal of Hazardous Materials 400, 2020, 123247

Materials 5 (12), 2012 2874-2902

3. “Biotechnology is limited by the growth process of microorganisms, and there is a risk of releasing resistant bacteria and resistant genes into the environment; physical-chemical treatment technology contains advanced oxidation, coagulation, membrane separation and adsorption”--There are plenty of recent literature on water treatment techniques, which need to be discussed in the introduction section.

Journal of Cleaner Production 241, 2019, 118263

Nanomaterials 9 (5), 2019, 776

Microporous and Mesoporous Materials 261, 2018, 198-206

Environmental research 2019, 170, 389-397

 

4. “The mechanism of SAEF treating TC wastewater was studied by SEM, FT-IR, XRD, XPS, UV-vis and LC-MSMS”—define LC-MSMS using the below references. Also correct LC-MSMS as LC-MS/MS.--Journal of King Saud University-Science 32 (4), 2020, 2414-2418; Journal of separation science 43 (11), 2020, 2079-2087.
5. “……silver sulfate powder, mercury sulfate powder, ascorbic acid, potassium persulfate, as analytical grade, were purchased from Changsha Pengjin reagent distributor and Sinopharm Group.—Provide the details of the supplier for each chemical including city and country.
6. “….electronic balance (BSA224S, sartorius Co., LTD); vacuum drying oven (DZF-6020AB, Beijing Zhongxing Weiye Co., LTD); filtration device (RZK-B01, Beijing Yiyang Runze Co., LTD)”-- Provide the details of the manufacturer for each instruments including city and country.
7. “Before the experiment, the iron plate was polished with sandpaper, and then the surface rust was removed by washing with 10% dilute hydrochloric acid.” What kind of sand paper was used? Explain the reason of using HCL.
8. “As alkaline conditions were more likely to convert iron ions into precipitation, thus inhibiting the generation of ·OH and limiting the oxidation reaction.” ---need citation, . Journal of environmental management 219, 2018, 285-293.
9. “The absorption peaks at 3346 cm1 and 3364 cm1 were caused by O-H stretching vibration in H-O-H, and the peak at 1645 cm1 and 1650 cm1 might be caused by the skeleton vibration of benzene ring or H-O-H bending vibration” -; Journal of Molecular Liquids 317, 2020, 113916
10. The English quality very poor. All the typos and grammar need to check thoroughly in the manuscript. E.g., “All samples should be filtered by 0.45 μm microporous membrane before de- termination”---avoid using future tense. “All samples were filtered by 0.45 μm microporous membrane before determination”.

Also, the fig. quality needs to be improved.

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

Article entitled Investigation on mechanism of tetracycline removal from wastewater by sinusoidal alternating electro-Fenton technique written by Yihui Zhou, Bonian Hu, Xiaojie Zhuang, Jingxian Qiu, Tao Xu, Muping Zeng, Xi He, Gang Yu and submitted to Sustainability journal deals with an important issue of effective antibiotics removal from wastewater.

The idea of article is interesting.

As English is not my native language, I am not able to assess language correctness. However, while reading, I found some statements missing, confusing or unclear. Below I enclose the list of my comments.

In the introduction there should be a literature review regarding the TC content observed in the environment, and especially in wastewater.

How many electrodes were there and how far apart were they placed. How many electrodes were used? I would like ask for a more detailed description of the experimental setup.

I propose to split Fig 1 into two separate figures. While the right panel seems to be in place in Chapter 2.1, the left panel probably should be when describing the results and the discussion.

Lines 87-88, dimensions – repetition.

The presence of chlorides, iron (II) and hydrogen peroxide affects the correctness of the COD determination. How did the Authors remove the influence of the disturbing factors?

How did the EC process affect the temperature? Has it been inspected/measured?

How much energy was used during the process?

What were TC doses?

Why only water solution of TC was used? Why the Authors did not collect real environmental sample, at least just to confirm findings?

Did the pH change during the process?

For which process conditions the data from Fig. 2, 3, 4, 5 were obtained?

Fig 2 shows that the pH =3 is optimal and allows to remove c.a 90% TC in 5 min. The other parameters are practically irrelevant. Meanwhile, it can be expected that salinity, current density and others should have an influence on the process. Comment is needed. The following figures show that extending the process time increases the efficiency minimally. Why shorter process times, e.g. 1 min, were not tested?

Doses are not given in mL/L (or cm³/dm³). What was hydrogen peroxide concentration and solution density?

Fig 6. The shape of the red curve (COD) shows errors during determination.

Fig 7. How DEC and SACC were performed?

What is the point of extending the process to 120 minutes, since it is known that already 5 minutes is very effective? What is the point of this in terms of energy consumption or installation size?

The article is very sloppy. The research cannot be recreated based on the description in the manuscript. The specific conditions under which the experiments were conducted are not given. So, it is impossible to verify the correctness. The article is full of data, but it is not known where they came from.

While the research idea was interesting, the research was minimal. It is not known how much TC was used, the parameters of the experiments in which the results were obtained are unknown etc.

As it stands, the manuscript does not meet the requirements for scientific articles. The methodology and description of the results are to be completely rewritten. Numerous additional experiments should be performed, e.g. the influence of TC dose on the effectiveness of the process. On the basis of my comments and my general impression, I suggest to reject the article in its current form. However, the concept is interesting. I may be possible that a revised and significantly supplemented new version of the manuscript may be resubmitted.

Author Response

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Author Response File: Author Response.pdf

Reviewer 4 Report

This article reported the tetracycline removal from wastewater by sinusoidal alternating electro-Fenton technique. Although the topic is interesting, however, revisions are needed before considering this paper for publication.

Below are specific comments. 

1. Cleary state the novelty of this work in comparison to other papers published on similar topic.
2. All the abbreviations must be defined first, and full form must be used before using the abbreviated form.
3. It is recommended to mention the explement conditions, preferably in the caption of figures.
4. In my opinion, characterization analysis should be section 3.1.
5. The authors need to provide a more detailed inside on the removal mechanism. It is better to provide a schematic of mechanism.
6. It is always better to mention TC concentration when reporting the removal %.
7. The authors need to explain the potential reasons of varying the preference under various experimental conditions.
8. The following references are suggested to be included.

• https://doi.org/10.1016/j.scitotenv.2021.151955
• https://doi.org/10.1016/j.chemosphere.2021.133196

 

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

This is my second review of this article. Second version is far better than the previous one. The Authors answered all of my questions. Suggested corrections have been applied. I suggest to accept this article in its present form.

Reviewer 4 Report

The revised version of the manuscript can be considered for publication.