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Removal of Ciprofloxacin from Wastewater by Ultrasound/Electric Field/Sodium Persulfate (US/E/PS)

Processes 2022, 10(1), 124; https://doi.org/10.3390/pr10010124

by Xiao Ma^1,2,* and Zhenjun Wang^3,*

Reviewer 1: Anonymous

Reviewer 2: Anonymous

Reviewer 3: Anonymous

Processes 2022, 10(1), 124; https://doi.org/10.3390/pr10010124

Submission received: 26 October 2021 / Revised: 23 December 2021 / Accepted: 23 December 2021 / Published: 7 January 2022

Round 1

Reviewer 1 Report

The manuscript ID processes-1445586 entitled "Removal of ciprofloxacin form wastewater by ultrasound/electric field/sodium persulfate (US/E/PS)" is interesting and valuable scientific material. It fully corresponds to the Processes journal profile. In my opinion, it may be published after adding the following remarks:

A graphical abstract would be very useful and would allow the reader to understand the idea the research being carried out.
Remove “CIP” from keywords and replace with full name Ciprofloxacin.
Chapter 2 Experimental methods needs to be thoroughly improved. The authors must define the criteria for distinguishing the experimental variants, describe the experimental stand in detail, characterize the laboratory equipment used, provide the exact data of the producers, precisely present the analytical methods, describe the method of chromatographic analysis, the origin of the antibiotics used, etc.
The methodology must be like a "recipe for a cake" each researcher after reading it must be able to repeat the research presented in the manuscript. Experimental methods needs to be thoroughly improved. It is necessary.
Separation of sub-chapters should be considered, eg Concept of research, Materials, Experimental stand, Analytical methods, Statistical methods.
How many repetitions were there carried out research and analytical determinations?
The drawback of the manuscript is the lack of a reliable statistical analysis of the obtained research results. Without such an analysis, the conclusions drawn are unreliable.
The chapter Experimental methods should present what statistical tests were used to determine the significance of differences between the analyzed variables, and what level of probability or significance was used.

Author Response

Ref.No: processes-1445586

Submission Title: Removal of ciprofloxacin form wastewater by ultra-sound/electric field/sodium persulfate (US/E/PS)

Dear Editor,

On behalf of my co-authors, we appreciate editor and reviewers very much for their positive and constructive comments and suggestions on our manuscript entitled “Removal of ciprofloxacin form wastewater by ultra-sound/electric field/sodium persulfate (US/E/PS)”. (Ref.No: processes-1445586). We have studied the comments carefully and have tried our best to revise our manuscript according to the comments. The changes in the manuscript have been highlighted in yellow background in “Highlight revised manuscript” for your evaluation. The main corrections in the manuscript and the responses to the comments are shown in point-to-point as follows. For better understanding we have copied reviewer’s remark and marked it with R, while our answers are marked with A. We will much appreciate it if you could agree with us. Please contact me if it is not appropriate. Thank you very much.

Comments:

Reviewer 1

R-1: A graphical abstract would be very useful and would allow the reader to understand the idea the research being carried out.

A-1: First thanks for your constructive suggestion and comment. A graphical abstract is added as follows.

Graphical abstract

R-2: Remove “CIP” from keywords and replace with full name Ciprofloxacin.

A-2: First thanks for your warm and kind reminder. We have removed “CIP” from keywords and replaced by full name Ciprofloxacin.

R-3: Chapter 2 Experimental methods needs to be thoroughly improved. The authors must define the criteria for distinguishing the experimental variants, describe the experimental stand in detail, characterize the laboratory equipment used, provide the exact data of the producers, precisely present the analytical methods, describe the method of chromatographic analysis, the origin of the antibiotics used, etc.

And R-4: The methodology must be like a "recipe for a cake" each researcher after reading it must be able to repeat the research presented in the manuscript. Experimental methods needs to be thoroughly improved. It is necessary.

And R-5: Separation of sub-chapters should be considered, eg Concept of research, Materials, Experimental stand, Analytical methods, Statistical methods.

A-3, A-4 and A-5: First thanks for your warm and kind reminder. Following your suggestion, the experimental methods, the methodology and separation of sub-chapters have been thoroughly improved as follows.

Experimental materials

2.1.The main experimental instruments and equipment are as follows:

High-Performance Liquid Chromatograph, LC-15C, Shimadzu Company, Japan; Electronic Analytical Balance, FA2204B, Shanghai Jingke Tianmei Scientific Instrument Co., Ltd.; Low-Temperature Constant Temperature Trough, THD-1015, Ningbo Tianheng Instrument Factory; Ultrasonic Cell Grinder, JYP2-IIN, Ningbo Scientz Biotechnology Co., Ltd.; DC Power Supply, GPR-6030D, Guwei Electronics (Shanghai) Co., Ltd.; Platinum electrode, 1 cm × 1 cm, Xuzhou Zhenghao Electronic Technology Co., Ltd.; CNC Ultrasonic Cleaner, KQ5200DB, Kunshan Ultrasonic Instrument Co., Ltd.; Ultraviolet-visible Spectrophotometer, UV-3100, Shanghai Mapada Instrument Co., Ltd.; Electric Blast Dryer, DHG9075A, Shanghai Yiheng Scientific Instrument Co., Ltd.; Digital Display pH Meter, PHS-3C, Shanghai Yidian Scientific Instruments Co., Ltd.; Temperature-controlled magnetic stirrer, XMTD-702, Jintan Medical Instrument Factory; Circulating water type multi-purpose vacuum pump, SHZ-D (III), Wuhan Keer Instrument and Equipment Co., Ltd.; UPHW-II-90T, Chengdu Ultra Pure Technology Co., Ltd.; Two-dimensional Liquid Chromatography-Ion Trap Mass Spectrometry, 1100LC/MSD Trap, Agilent Company, USA.

2.2. Major chemical reagents and pharmaceuticals

Ciprofloxacin, C₁₇H₁₈FN₃O₃, Purity > 98.0%, Shanghai Aladdin Biochemical Technology Co., Ltd.; Norfloxacin, C₁₆H₁₈FN₃O₃, 98%, Shanghai Aladdin Biochemical Technology Co., Ltd.; Acetonitrile, C₂H₃NHPLC, Sino Pharma Group Chemical Reagent Co., Ltd.; Methanol, CH₃OHHHPLC, Sino Pharma Group Chemical Reagent Co., Ltd.; Methanol, CH₃OHA. R, Sino Pharma Group Chemical Reagent Co., Ltd.; Tert-Butanol, C₄H₁₀OA. R, Sinopharm Chemical Reagent Co., Ltd.; Sodium hydroxide, NaOHA.R., Sino Pharma Group Chemical Reagent Co., Ltd.; Sulfuric acid, H₂SO₄A. R, Sino Pharma Group Chemical Reagent Co., Ltd.; Hydrochloric acid, HClA.R., Sino Pharma Group Chemical Reagent Co., Ltd.; Sodium persulfate, Na₂S₂O₈A. R, Sino Pharma Group Chemical Reagent Co., Ltd.

2.3. Experimental methods

A double-layer glass jacket beaker with a volume of 250 mL and an inner diameter of about 6.5 cm was used as the reaction vessel, and the reaction solution was 200mL. The pH value of the solution was adjusted by 1.0 mol/L NaOH and H₂SO₄ solution for coarse adjustment and 0.1 mol/L NaOH and H₂SO₄ solution for fine adjustment. After the reaction solution is prepared, the ultrasonic horn (located in the center of the reaction vessel, insert the liquid level, 3 cm from that bottom of the reactor) and a DC power supply electrode are used. The liquid level for the electrode is inserted at a symmetrical position on both sides of the horn, within 3 cm away from that bottom of the reactor and 3 cm away from the positive and negative electrode. The react equipment for US/E/PS is sealed with PVC membrane to prevent volatilization loss in the reaction process of the reaction solution. The circulation pump from the low-temperature constant temperature tank is used for the temperature control. When the temperature of the reaction system reaches the experimental set temperature, DC voltage and ultrasonic power are conducted to carry out the reaction. The experimental device is shown in Figure 1. The reaction time was set at 2 hours, and the sampling time was set to 0 min, 15 min, 30 min, 45 min, 60 min, 90 min, and 120 min respectively. 2 mL of ciprofloxacin (0.03 mmol/L) was sampled in the experiment, an appropriate amount of free radical inhibitor (MeOH and TBA) was added. After filtration by 0.45 m filter membrane, the characteristic peak area was determined by high-performance liquid chromatography, and the concentration was determined by high-performance liquid chromatography. Finally, the samples under the parameters with good removal effect were analyzed by high-Performance Liquid Chromatograph, LC-15C, Shimadzu Company, Japan; Electronic Analytical Balance, FA2204B, Shanghai Jingke Tianmei Scientific Instrument Co., Ltd with a XBridge-C18 (4.6 mm×150 mm, 5μm) reversed-phase column. And the possible intermediates and degradation paths of the antibiotics were speculated the ultrasound-enhanced electro-activated persulfate system. The experimental conditions are set at pH of 5.0-11.0, initial molar concentration of ciprofloxacin is 0.03 mmol/L, initial molar concentration of PS is 1.5-30 mmol/L, ultrasonic power of 0-200 W, electrode potential is 0- 9 V, temperature of 25-55 °C and ultrasonic frequency of 20 kHz.

The samples were treated at standard atmospheric pressure and under light protection. The concentration of ciprofloxacin in the reaction solution was analyzed by HPLC at intervals of 30 min.

Figure 1. Experimental device 1-ultrasonic cell pulverize, 2-ultrasonic horn, 3-DC power supply, 4-platinum sheet electrode, 5-low temperature and constant temperature distiller's grains, 6-jacket beaker reactor.

2.4.Solution preparation and measurement method

① Solution preparation and storage method

The preparation and storage of 0.62 mmol/L (200 mg/L) ciprofloxacin stock solution. ciprofloxacin 0.2000 g is accurately weighed, and appropriate amount of deionized water is added, and appropriate amount of hydrochloric acid is dropped to aid dissolution. Avoid light and stir with a magnetic stirrer for 8 hours, transfer to a 1000 mL volumetric flask and fix the volume with deionized water.

Preparation of 100 mmol/L sodium persulfate solution: weigh 11.9050 g of sodium persulfate accurately, dissolve in an appropriate amount of deionized water and transfer to a 500 mL volumetric flask to fix the volume. The shelf life of sodium persulfate solution is about one week, and the expiration date of the agent should be ensured when it is used.

② Analytical method

An LC-15C high performance liquid chromatograph with an XBridge-C18 (4.6 mm×150 mm, 5μm) reversed-phase column is used. The liquid chromatographic test conditions for ciprofloxacin are as follows: The injection volume is 20 μL, the column temperature is 30 ℃, and the flow rate is 0.6 mL/min; The mobile phase is acetonitrile: 0.1% acetic acid = 20:80 (v/v); The detection wavelength is 278 nm, and the retention time of ciprofloxacin is 4.4 min under the liquid chromatographic conditions.

③ Index calculation formula

(1) Removal rate

The removal rate of ciprofloxacin is calculated according to Equation (1):

(1)

where C₀ and C is the concentration of ciprofloxacin (mg/L) at the 0 and t moments, respectively.

(2) First order reaction rate constant

For the reaction conforming to first-order reaction kinetics, the reaction rate constant can be expressed by Equation (2):

(2)

By integrating it, the formula (3) is obtained:

(3)

where, C₀ is the initial substrate concentration, mmol/L; C_t is the substrate concentration at time t, mmol/L; t is reaction time, min; K is the rate constant, min^-1

R-6: How many repetitions were there carried out research and analytical determinations?

A-6: First thanks for your warm and kind reminder. Each experiment was carried out three times, and the average was taken as the final experimental result, which was reliable.

R-7: The drawback of the manuscript is the lack of a reliable statistical analysis of the obtained research results. Without such an analysis, the conclusions drawn are unreliable.

A-7: First thanks for your warm and kind reminder. Each experiment was carried out three times, and the average was taken as the final experimental result, which was reliable.

R-8: The chapter Experimental methods should present what statistical tests were used to determine the significance of differences between the analyzed variables, and what level of probability or significance was used.

A-8: First thanks for your constructive suggestion and comment. In this study, It is so important to know the effect of the single factor on the experimental system, and know the potential applications and performance of US/E/PS. What we did was the single factor experiment and did not carry out the orthogonal experiment research. We only discussed the influence of the single factor on the experimental system, and explored the law and mechanism of the influence of the single factor on the degradation experiment. This is the research purpose of this paper. We will carry out orthogonal experiments in the follow-up research. And your suggestion will be a new research topic, thanks for your help.

We know that you are a great and famous scientist in this filed. Followed with your suggestions and comments, I have learned a lot. However, I must admit that my explanation may be not good, I hope you can support us. Thanks for your constructive suggestion and comment again.

We all appreciated for your hard work and effort for our manuscript. You patiently guide me how to advise the manuscript, and which lets me impressive and moving. Thank you very much. At last, you should take care of your health during this time of COVID - 19 viruses outbreak, and has a happy life and work.

With warm regards,

Sincerely,

Dr. Xiao Ma

[email protected] (Xiao Ma)

Author Response File: Author Response.pdf

Reviewer 2 Report

The paper deals with the elimination of ciprofloxacin with advanced oxidation processes involving ultrasounds, electric field and persulfate. The topic is interesting but authors have to revise deeply the manuscript before its publication. The following comments have to be taken into account:

Line 9. Abstract “in large quantities” This is not true. Perhaps authors mean that concentration has increased in the last years, but large quantities can be misunderstood.
Line 45. CIP is repeated
Introduction section. It is too general. Which concentrations have been found in wastewaters? Data of CIP removal efficiencies in the wastewater treatment plants have to be added. Is ciprofloxacin not removed either by adsorption onto the microbial flocs or by degradation? More data have to be included. Have other authors studied these techniques? Which were the main results? There is no data in the introduction.
Line 89. 2 mL CIP (at which concentration?)
Line 90. Which was the free-radical inhibitor?
Line 94. Give more details (reference of the equipment, column…)
The experimental conditions have to be moved to the experimental methods section. A table where the experiments carried out and their conditions can be quickly observed has to be added in this section. Frequency of US is not indicated.
Captions of the Figures (for example Figure 4) have to include the conditions (PS concentration….)
In results section, authors have to compare the removal efficiencies they obtained with those of other authors.
Results are not very promising. Temperature modifications are not possible in municipal wastewater (it will never be viable). pH variations are also expensive. Are authors sure that it could be applied at industrial level? Some general comments have to be included in the conclusions and discussion has to be deeper.

Author Response

Ref.No: processes-1445586

Submission Title: Removal of ciprofloxacin form wastewater by ultra-sound/electric field/sodium persulfate (US/E/PS)

Dear Editor,

Comments:

Reviewer 2

R-1: Line 9. Abstract “in large quantities” This is not true. Perhaps authors mean that concentration has increased in the last years, but large quantities can be misunderstood.

A-1: First thanks for your warm and kind reminder. We have used “and its concentration has increased in the last years” in the Abstract.

R-2: Line 45. CIP is repeated

A-2: First thanks for your warm and kind reminder. We have deleted it.

R-3: Introduction section. It is too general. Which concentrations have been found in wastewaters? Data of CIP removal efficiencies in the wastewater treatment plants have to be added. Is ciprofloxacin not removed either by adsorption onto the microbial flocs or by degradation? More data have to be included. Have other authors studied these techniques? Which were the main results? There is no data in the introduction.

A-3: First thanks for your constructive suggestion and comment. The CIP wastewater concentration is almost low near at micrograms and nanograms per liter, but the concentration of CIP wastewater in factories is even at the milligram-per-liter level. It is added in the introduction. The chemical structure of CIP antibiotics is very stable and is not easy to be absorbed and degraded by microorganisms.

CIP has strong chemical interference and toxicity to microorganisms, which is not conducive to its microbial adsorption. Therefore, activated carbon, chitosan synthesis or other MOFs materials are often used for CIP adsorption. However, the adsorption method can not completely degrade CIP and make it innocuously. Therefore, advanced oxidation methods are needed to degrade and remove it. It is added in the introduction.

Compared with those of other authors, the removal efficiencies of CIP is not so higher and excellent by US/E/PS, the CIP removal efficiency is near 40%. However, the CIP concentration is 0.03 mmol/L (about 10 mg/L) which is higher than those with 1-20 μg/L or even with low concentration. In real industrial CIP waste water, the concentration of CIP may be higher than 10 mg/L, so US/E/PS are more practical and useful. In addition, the US/E/PS is environmentally friendly with little secondary pollutants, low energy consumption, and simple operation. Thus, it has huge potential for application and improvement. In addition, it is found that, if the CIP concentration is 10μg/L, the CIP removal efficiency can reached 100% in US/E/PS. So, the US/E/PS is more useful and effective for CIP degradation and removal. Thanks for your constructive suggestion and comment again.

R-4: Line 89. 2 mL CIP (at which concentration?)

A-4: First thanks for your warm and kind reminder. We have add it, and now it is that “2 mL CIP (0.03 mmol/L)”.

R-5: Line 90. Which was the free-radical inhibitor?

A-5: First thanks for your warm and kind reminder. The free radical inhibitor (Methanol and Tert-Butanol) is added.

R-6: Line 94. Give more details (reference of the equipment, column…)

A-6: First thanks for your warm and kind reminder. The details of liquid chromatography-mass spectrometry (LC-MS) were added, and now it is that “high-Performance Liquid Chromatograph, LC-15C, Shimadzu Company, Japan; Electronic Analytical Balance, FA2204B, Shanghai Jingke Tianmei Scientific Instrument Co., Ltd with a COSMOSIL 3C18-MS-II column (5 μm particle size, 4.6 × 150 mm, Nacalai Tesque, Inc., Japan) with a XBridge-C18 (4.6 mm×150 mm, 5μm) reversed-phase column”.

R-7: The experimental conditions have to be moved to the experimental methods section. A table where the experiments carried out and their conditions can be quickly observed has to be added in this section. Frequency of US is not indicated.

A-7: First thanks for your warm and kind reminder. The experimental conditions have been moved to the experimental methods section. The experiments carried out and their conditions are added in the section 2.3 (Experimental methods). It is that “The experimental conditions are set at pH of 5.0-11.0, initial molar concentration of ciprofloxacin is 0.03 mmol/L, initial molar concentration of PS is 1.5-30 mmol/L, ultrasonic power of 0-200 W, electrode potential is 0- 9 V, temperature of 25-55 °C and ultrasonic frequency of 20 kHz.” The frequency of US is 20 kHz.

R-8: Captions of the Figures (for example Figure 4) have to include the conditions (PS concentration….)

A-8: First thanks for your warm and kind reminder. The experimental conditions are added in the section 3.2 (Effect of ultrasonic power on CIP removal efficiency) and it is that “the experimental conditions are set as follows: ciprofloxacin initial molar concentration is 0.03 mmol/L, PS initial molar concentration is 1.5 mmol/L, the initial pH value is 5.0, the electrode potential is 4 V, the reaction temperature is 35°C, ultrasonic power is adjusted to 0 W, 50 W, 100 W and 200 W. After reaction for 120 min, the removal of ciprofloxacin is observed (Figure 4)”.

R-9: In results section, authors have to compare the removal efficiencies they obtained with those of other authors.

A-9: First thanks for your constructive suggestion and comment. Compared with those of other authors, the removal efficiencies of CIP is not so higher and excellent, the CIP removal efficiency is near 40%. However, the CIP concentration is 0.03 mmol/L (about 10 mg/L) which is higher than those with 1-20 μg/L or even with lower concentration. In real industrial CIP waste water, the concentration of CIP may be higher than 10 mg/L, so US/E/PS are more practical and useful. In addition, the US/E/PS is environmentally friendly with little secondary pollutants, low energy consumption, and simple operation. Thus, it has huge potential for application and improvement. In addition, it is found that, if the CIP concentration is 10μg/L, the CIP removal efficiency can reached 100% in US/E/PS. So, the US/E/PS is more useful and effective for CIP degradation and removal. Thanks for your constructive suggestion and comment again.

R-10: Results are not very promising. Temperature modifications are not possible in municipal wastewater (it will never be viable). pH variations are also expensive. Are authors sure that it could be applied at industrial level? Some general comments have to be included in the conclusions and discussion has to be deeper.

A-10: First thanks for your constructive suggestion and comment. We know that this method should be researched deeply and it will have the chance for the future application. We admit that there really has the challenge for temperature modifications, pH variations and others, but this is really a new method (US/E/PS), and it has the huge space for improvement and enhancement. US/E/PS can work with other advanced oxidation technology (such as Fenton method, Ozone oxidation, Photocatalysis, Dielectric electrochemistry and so on) to improve its performance. Following your suggestion, the conclusions and discussion is to be deeper. And now it is shown as follows.

Conclusion

In this paper, the removal of ciprofloxacin from water by US/E/PS system was investigated. The conclusions are as follows:

(1) The reaction of ciprofloxacin by US/E/PS system is consistent with quasi-primary reaction kinetics with a reaction rate constant of 0.0046 min^-1, which is about 2.7 times that of peroxynitrite oxidation alone (0.0017 min^-1). The combination of ultrasonic oxidation, electro-oxidation and persulfate oxidation has a strong synergistic effect with a synergistic coefficient S=2.10. Ultrasonic oxidation, electro-oxidation all can active the PS to persistently generate SO₄^•⁻ and ·OH to remove and degrade CIP efficiently.

(2) Ultrasound can effectively increase the removal rate of ciprofloxacin. Excessive ultrasound power leads to excessive growth of cavitation bubbles, which affects the reaction and deteriorates the removal effect. The removal rates at 50 W, 100 W and 200 W are 13.2%, 37.4% and 36.9%, respectively.

(3) It is helpful to remove ciprofloxacin by electrifying the reaction system, but the electrode potential increases excessively, the current efficiency decreases, and the removal effect of ciprofloxacin shows a downward trend. The removal rates of ciprofloxacin were 29.3%, 37.4%, 33.5%, and 30.5% respectively when the electrode potentials were 0 V, 4 V, 6 V, and 9 V.

(4) The apparent activation energy of ciprofloxacin is 54.00 kJ/mol, and the removal efficiency of ciprofloxacin increases obviously with the increase of reaction temperature, and the removal rate at 55 ℃ is more than 3 times that at 25 ℃.

(5) The removal efficiency of ciprofloxacin increases with the increase of the initial molar concentration ratio of persulfate to ciprofloxacin. The ratio of PS to ciprofloxacin increases 100 times from 5: 1 to 500: 1, and the removal efficiency of ciprofloxacin correspondingly increases from 23.1% to 64.0%, which increases nearly 3 times. The quasi-stage reaction rate constant increased from 0.0019 min^-1 to 0.0099 min^-1, a 5.2-fold acceleration.

(6) The pH of the solution has multiple effects on the removal of ciprofloxacin in the reaction system, such as the morphology of substrate, the type, and activity of free radicals, etc. The removal rate is the highest when pH = 11.0. The removal rates of ciprofloxacin were 37.4%, 39.1%, and 42.3% respectively after 2 hours of reaction at initial pH=5. 0, 7.0 and 11.0.

(7) The sulfate radicals and hydroxyl radicals were present in US/E/PS system for the removal of ciprofloxacin from water, and the sulfate radicals were dominant. So, strategies and methods to increase the number of sulfate radical are beneficial to better degradation and removal of CIP.

(8) The piperazine ring in the structure of ciprofloxacin is easy to cleave, the piperazine ring (P.1) is attacked by SO₄^•⁻ and ·OH, and the ring-opening of piperazine ring to make C₂H₂O generation. SO₄^•⁻ and ·OH is likely to completely dealkylate the piperazine ring after further action, and the product (P.3) are generated. The product (P.2) comes from hydroxylation of the aromatic ring, and the substitution reaction may take place at two positions. Free radicals of SO₄^•⁻ and ·OH are the most direct driving force for CIP decomposition, degradation and removal.

In a word, the results indicate that the ultrasound-enhanced electro-activated persulfate system is of great potential application value in removal of organic pollution and environmental purification.

With warm regards,

Sincerely,

Dr. Xiao Ma

[email protected] (Xiao Ma)

Author Response File: Author Response.pdf

Reviewer 3 Report

The manuscript is very interesting from the research topic perspective, because the presence of emerging pollutants in the aquatic environment is becoming an progressively pressing topic and the need to remove them from the environment is an increasingly intense concern of researchers in the field.

In addition to the novelty elements it presents, the manuscript also has a series of drawbacks that require the major intervention of the authors to correct them. First of all, it should be noted that the manuscript contains a series of expressions, correct from the point of view of the English language, but often unsuitable for this scientific context. Therefore, I recommend the authors to consider the benefits that the paper would have if it were corrected by a native English, but with knowledge in the field of manuscript topics.

Below are some comments on the content of the manuscript, which the authors are invited to take into account. Besides the authors should carefully analyze, again, the content of the manuscript and make some adjustments.

R45- it is not clear why the acronym CIP appears two times and what is its signification here

R55-59: the authors highlights the advantages of advanced oxidation process (AOP), which is a positive thing. However, it would be very opportune to include also the disadvantages, since this process raises some drawbacks, as well!

R61: the expression “has been perplexing” is a bit inappropriate here. Please find another one, maybe “has been provoked”.

R62-64: Please rephrase the sentence, since it is not clear what should mean: “research at home and abroad”, “advanced oxidation technology has been favored by workers”

R68: the acronym CIP was not made explicit in the paper body at its first appearance. This has to be done, regardless of whether the acronym has been defined in the Abstract (see also comments for R45).

A discussion is missing in the Introduction on why ciprofloxacin is a micropollutant, what effects it induces in the aquatic environment, human health etc. and in what concentrations it can be found in water resources and in wastewater, which need treatment. It must also be justified why no other, conventional type of treatment is applied in the authors’ research presented in the manuscript, and what are the advantages of this AOP process (and others) over other processes which have been used to remove and mineralize ciprofloxacin, some of which include Fenton, electro-Fenton and electrochemical oxidation.

You should also briefly describe the newer category of advanced oxidation processes (AOPs) based on the production of radical sulfate and why you have used ultrasound as an energy source instead of other sources that you should mention. Also, a brief description of how other researchers have used this oxidation technique and with what results might be useful to readers.

R78-87: The phrase needs to be divided into several sentences, because it is too long and difficult to understand its full meaning.

The results and discussion section states that samples were taken during certain time intervals during the degradation process of ciprofloxacin. It would have been very relevant and a progress compared to other research in the literature if the formation of degradation intermediates had been discussed and possibly highlighted, as well as their identification and characterization, especially from toxicity point of view.

R155: what should mean “the desirable CIP removal performance is observed” and what this term “desirable” refers to.

Section 4.3: should be: “Effect of electrode potential on … what?”

Similar comments for sections 4.4, 4.6, 4.7

R260: what should mean “OTC initial molar concentration”? OTC (perhaps oxytocin) is an acronym which does not appear in the manuscript body and it is unclear the presence of oxytocin here.

Author Response

Ref.No: processes-1445586

Submission Title: Removal of ciprofloxacin form wastewater by ultra-sound/electric field/sodium persulfate (US/E/PS)

Dear Editor,

Comments:

Reviewer 3

R-1: R45- it is not clear why the acronym CIP appears two times and what is its signification here

A-1: First thanks for your warm and kind reminder. Just one CIP is left, and we have made a change. Thanks.

R-2: R55-59: the authors highlights the advantages of advanced oxidation process (AOP), which is a positive thing. However, it would be very opportune to include also the disadvantages, since this process raises some drawbacks, as well!

A-2: First thanks for your constructive suggestion and comment. We add that “However, it must be noted that advanced oxidation methods have limitations. Advanced oxidation process requires some pretreatment conditions (for example, coagulation precipitation, turbidity removal, pH control, pollutant concentration control, temperature control, etc.) to meet the conditions of advanced oxidation operation before it can realize these above advantages. Sometimes it is even necessary to use other water treatment methods to achieve better performance and efficiency.” for the disadvantages of AOP.

R-3: R61: the expression “has been perplexing” is a bit inappropriate here. Please find another one, maybe “has been provoked”.

A-3: First thanks for your warm and kind reminder. Following your suggestions, the “has been provoked” is used to replace “has been perplexing”. Thanks.

R-4: R62-64: Please rephrase the sentence, since it is not clear what should mean: “research at home and abroad”, “advanced oxidation technology has been favored by workers”

A-4: First thanks for your warm and kind reminder. And now it becomes that “advanced oxidation technology has been noticed and concerned by workers in the field of water treatment research in the world”.

R-5: R68: the acronym CIP was not made explicit in the paper body at its first appearance. This has to be done, regardless of whether the acronym has been defined in the Abstract (see also comments for R45).

A-5: First thanks for your warm and kind reminder. We have add the full name of CIP at its first appearance at R68 and R45.

R-6: A discussion is missing in the Introduction on why ciprofloxacin is a micropollutant, what effects it induces in the aquatic environment, human health etc. and in what concentrations it can be found in water resources and in wastewater, which need treatment. It must also be justified why no other, conventional type of treatment is applied in the authors’ research presented in the manuscript, and what are the advantages of this AOP process (and others) over other processes which have been used to remove and mineralize ciprofloxacin, some of which include Fenton, electro-Fenton and electrochemical oxidation.

A-6-1: First thanks for your warm and kind reminder. We have added that “It is reported that about more than 5340 t CIP was used in China in 2020, which is the second highest used antibiotic among all fluoroquinolones. The large use of CIP causes some pathogenic bacteria to develop drug resistance, which will threaten human health if they survive in the environment for a long time. In addition, CIP can promote the generation of resistance genes (ARGs), and the spread and diffusion of resistance genes may accelerate the mass reproduction of resistant bacteria and form a potential threat to microbial community structure, thus posing a secondary threat to human health and ecological environment security.” So, CIP wastewater is needed to treat by high efficient methods.

R-6-2:For the reason why no other, conventional type of treatment is applied in the authors’ research presented in the manuscript, and what are the advantages of this AOP process (and others) over other processes which have been used to remove and mineralize ciprofloxacin, some of which include Fenton, electro-Fenton and electrochemical oxidation.

And

R-6-3: You should also briefly describe the newer category of advanced oxidation processes (AOPs) based on the production of radical sulfate and why you have used ultrasound as an energy source instead of other sources that you should mention. Also, a brief description of how other researchers have used this oxidation technique and with what results might be useful to readers.

A-6-2 and 6-3: First thanks for your constructive suggestion and comment. Because we know that Fenton, electro-Fenton and electrochemical oxidation can be used to remove the CIP wastewater and maybe have good performance. However, we should continue to develop and explore new methods for high efficient CIP wastewater treatment and purification. For the ultra-sound/electric field/sodium persulfate (US/E/PS), it is really a new method, and we should pay more attention to it and do enough research for it. Although it is challenging and difficult, and even not effective, we still need to keep faith and efforts to try and improve this technology. I hope you can understand and support us. Thanks.

Following your suggestion, we have add the description of US and the other related messages in the revised manuscript, it is shown as follows.

Ultrasonic oxidation technology is a special application of ultrasonic chemical technology in purifying pollutants (especially difficult to degrade pollutants). Using ultrasonic wave (US) to accelerate reaction or open up a new reaction channel, improve the yield of chemical reaction or obtain new chemical reactants, is a new frontier science. Its application research has attracted wide attention all over the world. Besides, the advanced oxidation method based on sulfate free radical (SO₄^•⁻) is considered to be an effective organic wastewater treatment technology with high standard redox potential. As a strong oxidant, sodium persulfate (PS) can theoretically degrade most organic pollutants and has great utilization potential. Using US and electric field-assisted activating PS technology has the evident advantages as follows. On the one hand, US and electric field have a strong mechanical effect, which can enhance the mass transfer to speed up the oxidation reaction for a good pollution degradation and removal effect. On the other hand, cavitation effect from US and electric field also activate PMS to generate SO₄^•⁻, which is used for enhanced treatment of organic pollutants. So, it is proposed combine US, electric field and PMS to treat CIP wastewater with high efficiency.

R-7: R78-87: The phrase needs to be divided into several sentences, because it is too long and difficult to understand its full meaning.

A-7: First thanks for your warm and kind reminder. The phrase is divided into several sentences, and now it is shown as follows.

After the reaction solution is prepared, the ultrasonic horn (located in the center of the reaction vessel, insert the liquid level, 3 cm from that bottom of the reactor) and a DC power supply electrode are used. The liquid level for the electrode is inserted at a symmetrical position on both sides of the horn, within 3 cm away from that bottom of the reactor and 3 cm away from the positive and negative electrode. The react equipment for US/E/PS is sealed with PVC membrane to prevent volatilization loss in the reaction process of the reaction solution. The circulation pump from the low-temperature constant temperature tank is used for the temperature control. When the temperature of the reaction system reaches the experimental set temperature, DC voltage and ultrasonic power are conducted to carry out the reaction.

R-8: The results and discussion section states that samples were taken during certain time intervals during the degradation process of ciprofloxacin. It would have been very relevant and a progress compared to other research in the literature if the formation of degradation intermediates had been discussed and possibly highlighted, as well as their identification and characterization, especially from toxicity point of view.

A-8: First thanks for your constructive suggestion and comment. Following your suggestion, the added part in the section 4 (Mechanism analysis) is displayed as follows.

It can be seen that US/E/PS can not only degrade and remove CBZ rapidly, but also produce intermediate products with relatively weak toxicity, which has little inhibitory effect on microbial growth. The original chemical structure of CIP is thoroughly destroyed to generate with low molecular weight and low toxicity. Therefore, US/E/PS can effectively degrade organic pollutants, is a safe and environmental protection technology, has broad market application prospects.

R-9: R155: what should mean “the desirable CIP removal performance is observed” and what this term “desirable” refers to.

A-9: First thanks for your warm and kind reminder. And now it becomes that “When the ultrasonic power at 100W, the ciprofloxacin removal efficiency is relatively good with low energy and economic consumption, compared with that of 200W”.

R-10: Section 4.3: should be: “Effect of electrode potential on … what?”

Similar comments for sections 4.4, 4.6, 4.7

A-10: First thanks for your warm and kind reminder. It should be Effect of electrode potential on CIP removal efficiency, which is similar with other sections. We have added it.

R-11: R260: what should mean “OTC initial molar concentration”? OTC (perhaps oxytocin) is an acronym which does not appear in the manuscript body and it is unclear the presence of oxytocin here.

A-11: First thanks for your warm and kind reminder. It should be “ciprofloxacin initial molar concentration is 0.03 mmol/L”, we have made a change. Thanks.

With warm regards,

Sincerely,

Dr. Xiao Ma

[email protected] (Xiao Ma)

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

In my opinion manuscript can be publish in present form.

Author Response

Thanks for your positve comments for acceptance.

Reviewer 2 Report

Once the manuscript has been revised, I recommend it for publication.

Author Response

Thanks for your positve comments for acceptance.

Reviewer 3 Report

After major revision:

Paragraph R49-R63 does not include any source of information and it is not clear where the author got the information included here. In fact, all the revised paragraphs according to the peer-reviewers' recommendations do not have any citation of the information sources. I understand that it is difficult to re-number the citations and the list of references according to the Vancouver citation style, but it is not accepted to provide concrete data or ideas without specifying the source. It was also recommended to include information on the concentration levels of ciprofloxacin in the water, as evidenced by scientific work in the field (even in tabular form), but we did not find this information in the manuscript. As the additions are now made, they seem to be improvisations. The information on ciprofloxacin use in China is interesting, but its impact on water quality is not discussed, in terms of concentrations.

R49-51 - the sentence must be reformulated, in a correct English language so as not to generate confusions

R52-54 - it is not clear what "chitosan synthesis" refers to in the existing context in the text

R56: "it is added in the introduction". What is added to the introduction?

R56: "It is reported that ..": Where is reported and by whom? Please cite all sources you have used for all new information included during the revision.

R82: please rephrase: ".... before it can realize these above advantages".

R89-103: the revised text does not include any citation of information sources, and it does not appear that the authors are specialized in the field of ultrasounds

Also, I maintain the recommendation made to the authors to consider the benefits that the paper would have if it would be corrected by a native English, but with knowledge in the field of manuscript topics.

The manuscript contains many inaccuracies about English, some sentences need to be reconsidered to avoid confusion.

Author Response

Ref.No: processes-1445586

Submission Title: Removal of ciprofloxacin form wastewater by ultra-sound/electric field/sodium persulfate (US/E/PS)

Dear Editor,

Comments:

Reviewer 3

R-1: Paragraph R49-R63 does not include any source of information and it is not clear where the author got the information included here. In fact, all the revised paragraphs according to the peer-reviewers' recommendations do not have any citation of the information sources. I understand that it is difficult to re-number the citations and the list of references according to the Vancouver citation style, but it is not accepted to provide concrete data or ideas without specifying the source. It was also recommended to include information on the concentration levels of ciprofloxacin in the water, as evidenced by scientific work in the field (even in tabular form), but we did not find this information in the manuscript. As the additions are now made, they seem to be improvisations. The information on ciprofloxacin use in China is interesting, but its impact on water quality is not discussed, in terms of concentrations.

A-1: First thanks for your warm and kind reminder. The related references, CIP concentration and its impact on water quality are added as follows.

It is reported in China sewage treatment engineering network that about more than 5340 t CIP was used in China in in 2013 and it became higher at now, which is the second highest used antibiotic among all fluoroquinolones[16]. The large use of CIP causes some pathogenic bacteria to develop drug resistance, which will threaten human health if they survive in the environment for a long time. CIP can promote the generation of resistance genes (ARGs), and the spread and diffusion of resistance genes may accelerate the mass reproduction of resistant bacteria and form a potential threat to microbial community structure, thus posing a secondary threat to human health and ecological environment security [17,18]. In addition, CIP has an enrichment effect in the human body, which can interfere with normal hormone secretion, cause mental disorders and destroy the normal metabolism of the human body. CIP also interferes with the human digestive system and can lead to gastric cancer [19,20]. So, CIP wastewater is needed to treat by high efficient methods.

[15] Nannapaneni, R.; Story, R.; Wiggins, K.C.; Johnson, M.G. Concurrent quantitation of total Campylobacter and total ciprofloxacin-resistant Campylobacter loads in rinses from retail raw chicken carcasses from 2001 to 2003 by direct plating at 42°C. Appl. Environ. Microbiol. 71 (2005) 4510-4515.

[16] Wang, C.; Gao, S.; Zhu, J.; Xia, X.; Wang, M.; Xiong, Y. Enhanced activation of peroxydisulfate by strontium modified BiFeO3perovskite for ciprofloxacin degradation. J. Environ. Sci. (China).99 (2021) 249-259.

[17] Giri, A.S.; Golder, A.K. Ciprofloxacin degradation in photo-Fenton and photo-catalytic processes: Degradation mechanisms and iron chelation. J. Environ. Sci. (China).80 (2019) 82-92.

[18] Cai, Y.; He, J. Degradation of ciprofloxacin by the Mn cycle system (MnCS): Construction, characterization and bacterial analysis. Environ. Res. 195 (2021)110860.

[19] Carabineiro, S.A.C.; Thavorn-Amornsri, T.; Pereira, M.F.R.; Figueiredo, J.L. Adsorption of ciprofloxacin on surface-modified carbon materials. Water Res. 45 (2011) 4583-4591.

[20] Carabineiro, S.A.C.; Thavorn-Amornsri, T.; Pereira, M.F.R.; Serp, P.; Figueiredo, J.L. Comparison between activated carbon, carbon xerogel and carbon nanotubes for the adsorption of the antibiotic ciprofloxacin. Catal. Today 186 (2012) 29-34.

R49-51-the sentence must be reformulated, in a correct English language so as not to generate confusions.

A-2: First thanks for your warm and kind reminder. The sentence has be reformulated, and now it is as follows.

CIP shoes strong chemical interference and has toxicity to microorganisms, and CIP is difficult to be adsorbed and utilized by microbial.

R52-54 - it is not clear what "chitosan synthesis" refers to in the existing context in the text.

A-3: First thanks for your warm and kind reminder. It should be “chitosan synthesized adsorbent” in the revised manuscript.

R56: "it is added in the introduction". What is added to the introduction?

A-4: First thanks for your warm and kind reminder. The sentence that "it is added in the introduction" is unnecessary and redundant, so it is deleted in the revised manuscript.

R56: "It is reported that ..": Where is reported and by whom? Please cite all sources you have used for all new information included during the revision.

A-5: First thanks for your warm and kind reminder. It is reported in China sewage treatment engineering network that about more than 5340 t CIP was used in China in 2013 and it became higher at now. We searched these related information in China sewage treatment engineering network.

R82: please rephrase: ".... before it can realize these above advantages".

A-6: First thanks for your warm and kind reminder. The sentence has be rephrased, and now it is as follows.

Advanced oxidation process requires some pretreatment conditions to meet its operations. These pretreatment conditions include coagulation precipitation, turbidity removal, pH control, pollutant concentration control, temperature and so on.

R89-103: the revised text does not include any citation of information sources, and it does not appear that the authors are specialized in the field of ultrasounds

A-7: First thanks for your warm and kind reminder. We have added the US related references as follows.

[30] Pirsaheb, M.; Moradi, N. Sonochemical degradation of pesticides in aqueous solution: Investigation on the influence of operating parameters and degradation pathway-a systematic review. RSC Adv. 10 (2020) 7396-7423.

[31] Wang, J.; Wang, Z.; Vieira, C.L.Z.; Wolfson, J.M.; Pingtian, G.; Huang, S. Review on the treatment of organic pollu-tants in water by ultrasonic technology. Ultrason. Sonochem. 55 (2019) 273-278.

[32] Yang, Y.; Zhang, Q.; Peng, C.; Wu, B.; Xu, J.; Ma, F.; Gu, Q. Sustained-Release of Sodium Persulfate Composite and Degradation of 2, 4-Dinitrotoluene. Res. Environ. Sci. 03(2020) 26.

[33] Kuppa, R.; Moholkar, V.S. Physical features of ultrasound-enhanced heterogeneous permanganate oxidation. Ultra-son. Sonochem. 2010, doi:10.1016/j.ultsonch.2009.05.011.

[34] Qiao, J.; Guo, Y.; Dong, H.; Guan, X.; Zhou, G.; Sun, Y. Activated peroxydisulfate by sulfidated zero-valent iron for enhanced organic micropollutants removal from water. Chem. Eng. J. 396(2020)125301.

The manuscript contains many inaccuracies about English, some sentences need to be reconsidered to avoid confusion.

A-8: First thanks for your warm and kind reminder. We have got a hand from a native English teacher with this field of manuscript topics to polish and revised our language.

With warm regards,

Sincerely,

Dr. Xiao Ma

[email protected] (Xiao Ma)

Author Response File: Author Response.doc

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