Research Progress of Ozone/Peroxymonosulfate Advanced Oxidation Technology for Degrading Antibiotics in Drinking Water and Wastewater Effluent: A Review

Nowadays, antibiotics are widely used, increasing the risk of contamination of the water body and further threatening human health. The traditional water treatment process is less efficient in degrading antibiotics, and the advanced oxidation process (AOPs) is cleaner and more efficient than the traditional biochemical degradation process. The combined ozone/peroxymonosulfate (PMS) advanced oxidation process (O3/PMS) based on sulfate radical (SO4•−) and hydroxyl radical (•OH) has developed rapidly in recent years. The O3/PMS process has become one of the most effective ways to treat antibiotic wastewater. The reaction mechanism of O3/PMS was reviewed in this paper, and the research and application progress of the O3/PMS process in the degradation of antibiotics in drinking water and wastewater effluent were evaluated. The operation characteristics and current application range of the process were summarized, which has a certain reference value for further research on O3/PMS process.


Introduction
As an emerging pollutant, pharmaceuticals and personal care products (PPCPs) include various antibiotics and other common drugs [1][2][3][4].These substances enter the environment through various channels, including veterinary medicine, agricultural medicine, human medicine, and the use of cosmetics.Antibiotics are small molecular substances synthesized by secondary metabolism after organisms grow to a certain stage, and their function is to produce resistance to pathogenic microorganisms.Since the discovery of penicillin, antibiotics have been widely used to prevent or treat infectious diseases in human and animal bodies.According to the data [5,6], between 2000 and 2015, the global use of antibiotics increased by 65%.In recent years, the use of antibiotics has increased due to the prevalence of COVID-19.According to the report [7,8], antibiotics are used globally in an amount of about 200,000 tons/year, among which, China has the highest consumption and output of antibiotics in the world.Antibiotics result in toxic effects of refractory parts on aquatic organisms in the water environment, and the residual antibiotics in the water promote the formation of drug-resistant bacteria.Antibiotic microbial resistance (AMR) is carried by antibiotic resistant bacteria (ARB) and expressed by antibiotic resistant genes (ARGs).Therefore, the accumulation of antibiotics in the water body results in the production of ARB and ARGs [9,10].
Research has shown that with the rapid development of the pharmaceutical industry and animal husbandry, more and more antibiotics are being used every year as veterinary drugs and feed in many countries across the globe.Nearly 90% of antibiotics enter various water bodies through parent or metabolites and cannot be absorbed by human beings and animals [11].The detection of antibiotics in surface water body, drinking water, and sewage effluent has been reported widely, with a concentration ranging from ng/L-µg/L [12][13][14].Although there are few residues, the long-term persistence of antibiotics affects the stability and health of the environment and organisms.Therefore, an economical and effective treatment method for antibiotic wastewater becomes indispensable.
In the process of antibiotic degradation, AOPs can produce the two highly active free radicals of hydroxyl radical (•OH) and sulfate radical (SO 4 •− ) to oxidize the target pollutants [15].Both •OH and SO 4 •− have strong oxidizability, which means they can react with most organic matter and remove various antibiotic pollutants efficiently.Therefore, the process shows good prospects for application in the treatment of antibiotic wastewater and is expected to replace the traditional process.For example, O 3 /PMS oxidation, Fenton/Fenton-like oxidation, photocatalytic oxidation, electrochemical oxidation, and O 3 /H 2 O 2 oxidation are recognized as effective treatment processes for removing organic pollutants from wastewater.In recent years, perovskite-based oxides have shown high catalytic efficiency in AOPs, in which non-free radical and free radical optimization pathways may occur simultaneously.Xu X. et al. [16] reviewed the latest progress of double perovskite in various catalytic reactions such as electrocatalysis and photocatalysis.Yang L. et al. [17] uses Ruddlesden-Popper (RP) layered perovskite oxide as the material to activate PMS.The active oxygen in RP perovskite has high activity and mobility and promotes the formation of non-radical singlet oxygen.Through the adjustment and optimization of singlet oxygen, LaSrCo 0.8 Fe 0.2 O 4, which can effectively activate PMS, was found.
Table 1 listed several currently prevailing AOPs, some of which are combined to further improve the degradation efficiency.Compared with other AOPs, the O 3 /PMS process can produce SO 4 •− with higher selectivity and longer half-life.The O 3 /PMS has broad application prospects in the field of antibiotics, in the treatment of drinking water and wastewater effluent [18].Weak mineralization ability, and the running in weak alkaline environment.[19] Fenton oxidation Friendly to the environment, occupies a small space, high oxidation efficiency and strong oxidation ability.
High treatment cost, harsh operating conditions and the running in strong acid conditions. [20]

Photochemical catalytic oxidation
Green and environment-friendly lighting, little impact on water quality, low operating cost and long service life.
Needs to be combined with other technologies to achieve better results: such as UV/H 2 O 2 , and UV/PDS; ultraviolet light beam with built-in light tube harmful to human body. [21]

Electrochemical oxidation
Simple electrolysis device, convenient operation and control, the oxidization of pollutants by the anode, and the changes of the anode material to destroy different types of organic matter.
Excessive energy consumption, low reactor efficiency and high equipment cost. [ O 3 /H 2 O 2 oxidation Fast oxidation speed and high oxidation efficiency.
Complex equipment, high energy consumption, high cost and easy to produce bromate.[23] Because the O 3 /PMS process has the advantages of being green, highly efficient, and brings a strong oxidation ability, and at the same time residual antibiotics in water environments are gradually increasing, the development of the O 3 /PMS process and the degradation of antibiotics have attracted more and more attention from scholars.In this review, the reaction mechanism of the O 3 /PMS advanced oxidation process, the latest progress in treating antibiotic pollutants in water based on this process, and the countermeasures for by-products generated by the O 3 /PMS system were described in detail.Compared with other reviews, firstly, this review focused on the treatment of antibiotic pollutants, and specifically summarizes the efficiency of AOPs based on O 3 /PMS to degrade antibiotic pollutants in drinking water and wastewater effluent.Therefore, it is convenient for scholars who have just stepped into the field of AOPs to read.Secondly, most of the objects reviewed in this paper are representative antibiotic pollutants with high concentration in water.Finally, the by-products produced in the process of pollutant degradation and the corresponding inhibition methods were summarized.Therefore, this paper provided reference for further study of the O 3 /PMS process and offered both theoretical support and a scientific basis for the development of antibiotic degradation process in the water body.

Proposal of O 3 /PMS Advanced Oxidation Technology
Ozone oxidation is mainly used in the field of water and wastewater treatment, including drug source treatment in medical wastewater, post treatment of secondary sewage effluent, etc. [24][25][26].While the combined process of ozone oxidation with other oxidants/ catalysts generally exhibits a high degradation effect in treating antibiotic wastewater, the experiments showed that [27] ozone is effective in disinfection, decoloration and removal of micro-pollutants.Ozone is a strong oxidant with the main property of generating •OH in water.Ozone itself is a selective strong oxidant, the order of oxidation being as follows: alkene > amine > phenol > polycyclic aromatic hydrocarbon > alcohol > aldehyde > alkane.Ozone is likely to attack the double bonds of organic compounds, activated aromatic groups, and unprotonated amines [28].Its reaction rate is much faster than that of ozone molecules, and its reaction rate constant is 10 8 -10 10 mol −1 •s −1 [29 -31].There- fore, the degradation of micro-pollutants by O 3 is usually achieved through the co-action of molecular O 3 and •OH.However, for the refractory pollutants in water, the oxidation efficiency of O 3 alone is low, because only a small amount of •OH is produced by O 3 decomposition and the molecular O 3 is selective.
Therefore, •OH-based AOPs have attracted wide attention.The combined process of O 3 and hydrogen peroxide (H 2 O 2 ) is one of the most common advanced oxidation technologies used to degrade pollutants by •OH [32].Table 2 showed the reaction equation for the O 3 /H 2 O 2 system, see reference for detailed principles [33].
As a strong oxidant, SO 4 •− has a higher oxidation-reduction potential (E 0 = 2.5-3.1 V) and higher selectivity than •OH.In addition to this, the reaction of SO 4 •− with micropollutants is less affected by alkalinity and natural organic matter [34][35][36].SO 4 •− is formed by the activation of persulfate (PS) (that is, persulfacte (PDS) and peroxymonosulfate (PMS)).Both PMS and PDS have strong oxidizability, but when PMS and PDS are used alone to degrade organic matter, the oxidation effect is not obvious.Therefore, a certain activation mode is required to activate them to produce SO 4 •− and •OH with strong oxidizability.Activation methods mainly include ultraviolet irradiation, heating or addition of transition metals and carbon materials, etc.PS has the same peroxy bonds as H 2 O 2 , generating free radicals in the form of breaking peroxy bonds, the only difference being that they form SO 4 •− and •OH, respectively [37].Cong J. et al. [38] proposed that the O 3 -activated PMS process could enhance the degradation effect of chlorobenzoic acid (pCBA), and verify that PMS had the effect of promoting the generation of free radicals, similar to H 2 O 2 .In addition, the research of Li S. et al. [39] proved that the high chemical reactivity and low kinetic stability of PMS promoted it to react with O 3 .The molecular formulas of H 2 O 2 , PMS and PDS are shown in Figure 1.PDS exists in a symmetrical structure, and the peroxy group is stable and can hardly react with O 3 [30].Therefore, extensive research has been conducted on the use of O 3 to activate PMS, thereby simultaneously producing •OH and SO 4 •− , which can rapidly and effectively degrade a variety of micro-pollutants [33].
tion metals and carbon materials, etc.PS has the same peroxy bonds as H2O2, generating free radicals in the form of breaking peroxy bonds, the only difference being that they form SO4 •− and •OH, respectively [37].Cong J. et al. [38] proposed that the O3-activated PMS process could enhance the degradation effect of chlorobenzoic acid (pCBA), and verify that PMS had the effect of promoting the generation of free radicals, similar to H2O2.
In addition, the research of Li S. et al. [39] proved that the high chemical reactivity and low kinetic stability of PMS promoted it to react with O3.The molecular formulas of H2O2, PMS and PDS are shown in Figure 1.PDS exists in a symmetrical structure, and the peroxy group is stable and can hardly react with O3 [30].Therefore, extensive research has been conducted on the use of O3 to activate PMS, thereby simultaneously producing •OH and SO4 •− , which can rapidly and effectively degrade a variety of micro-pollutants [33].

Reaction Mechanism of O3/PMS Advanced Oxidation Technology
Researchers have proposed various methods for activating PMS to generate SO4 •− , including thermal decomposition, ultrasonic method, ultraviolet irradiation, alkali activation, laser flash method, transition metal or metal oxide catalysis, and so on [29].Table 3 shows the reaction equations for the generation of •OH and SO4 •− in the O3/PMS system, see reference for detailed principles [20,33].Figures 2 and 3 show the reaction paths of •OH and SO4 •− in the O3/PMS system and the generation mechanism of •OH promoted by PMS and SO4 •− , respectively (the serial numbers in the figures correspond to the serial numbers of reaction equations in Table 3).

Reaction Mechanism of O 3 /PMS Advanced Oxidation Technology
Researchers have proposed various methods for activating PMS to generate SO 4 •− , including thermal decomposition, ultrasonic method, ultraviolet irradiation, alkali activation, laser flash method, transition metal or metal oxide catalysis, and so on [29].Table 3 shows the reaction equations for the generation of •OH and SO 4 •− in the O 3 /PMS system, see reference for detailed principles [20,33].Figures 2 and 3 show the reaction paths of •OH and SO 4 •− in the O 3 /PMS system and the generation mechanism of •OH promoted by PMS and SO 4 •− , respectively (the serial numbers in the figures correspond to the serial numbers of reaction equations in Table 3).•− in the O 3 /PMS system.Sulfame-thoxazo (SMX), sulfamethazine (SMZ), and sulfadiazine (SDZ) are typical sulfonamide antibiotics in drinking water and wastewater effluent.Research has shown that the sulfate radical-based advanced oxidation process (SR-AOPs) can effectively degrade SMX, such as Fe 0 /PS [40], Fe(II)/PS [41], Co(II)/PMS [42].Liu Z. et al. [43] studied the degradation of SMX by adding novel catalysts CuCo2O4-GO and CuCo2O4 as heterogeneous catalysts in the O3/PMS process.Liu Z. et al. prepared CuCo2O4 and CuCo2O4-GO nanoparticles by sol-gel method and hydrothermal method, respectively, and synthesized CuCo2O4-GO with different proportions of GO (5%, 10%, 20%, and 40%).The experiment was carried out in a 1000 mL hemispherical glass bottle.The experimental conditions were as follows: the temperature was 20 ± 2 °C, the pH was 7.0, the initial     Sulfame-thoxazo (SMX), sulfamethazine (SMZ), and sulfadiazine (SDZ) are typical sulfonamide antibiotics in drinking water and wastewater effluent.Research has shown that the sulfate radical-based advanced oxidation process (SR-AOPs) can effectively degrade SMX, such as Fe 0 /PS [40], Fe(II)/PS [41], Co(II)/PMS [42].Liu Z. et al. [43] studied the degradation of SMX by adding novel catalysts CuCo2O4-GO and CuCo2O4 as heterogeneous catalysts in the O3/PMS process.Liu Z. et al. prepared CuCo2O4 and CuCo2O4-GO nanoparticles by sol-gel method and hydrothermal method, respectively, and synthesized CuCo2O4-GO with different proportions of GO (5%, 10%, 20%, and 40%).The experiment was carried out in a 1000 mL hemispherical glass bottle.The experimental conditions were as follows: the temperature was 20 ± 2 °C, the pH was 7.0, the initial  •− radicals.The results showed that Fe 2+ and Mn 2+ in groundwater played an in situ catalytic role in the system, which accelerated the yield of •OH and SO 4

Equation Reaction Rate Constant (L•mol
•− and further oxidized SMZ or natural organic matter (NOM).The particularity of the method was that Fe 2+ in the groundwater could be used to activate the PMS in situ.In the oxidation process, the NOM in the water was also degraded.In recent years, Lu H. et al. [45] studied the degradation of SDZ in water by the O 3 /PMS process and compared the experimental results with the O 3 alone and the O 3 /UV method.The experiment was carried out in a cylindrical glass reactor with a volume of 6 L. The experimental conditions were as follows: the temperature was 25 ± 0.5 • C, the initial concentration of SDZ was 10 mg/L, the concentration of O 3 was 3 mg/L, the concentration of PMS was 22.8 mg/L, the UV intensity was 0.9 mw/cm 2 , and the pH was 6.8 ± 0.1.In the O 3 /PMS system, the degradation rate of SDZ reached 95.9% at 12 min, and the degradation rate of SDZ was below the detection limit at 13 min.However, at 12 min, the degradation rates of O 3 and O 3 /UV were only 73.8% and 76.5%, respectively.The time required for O 3 /PMS to degrade SDZ was about 7 min shorter than that required by the O 3 and O 3 /UV processes.In the O 3 /PMS system, the most suitable pH range is weak alkalinity.O 3 /PMS effectively degrade SDZ and fluorescent substances dissolved in water, which showed a good prospect for practical engineering applications.
most completely degrade SMX after 25 min.Figure 4 shows that the addition of CuCo2O4 and CuCo2O4-GO promoted the degradation of SMX and greatly shortened the time for complete degradation of SMX.It is an effective way to strengthen the degradation of SMX.Du X. et al. [44] adopted a PMS/(oxidation/coagulation) coupled ceramic membrane process to remove Fe 2+ , Mn 2+ , and SMZ.The experimental conditions were as follows: the initial concentration of SMZ was 400 µg/L, the concentration of PMS was 100 µmol/L, the concentration of O2 was 0.14 mg/L, the concentration of Fe(II) was 4.2 mg/L, the concentration of Mn was 1.0 mg/L, and the initial pH was 7.3.A large number of humus substances are oxidized by the •OH radical and SO4 •− radicals.The results showed that Fe 2+ and Mn 2+ in groundwater played an in situ catalytic role in the system, which accelerated the yield of •OH and SO4 •− and further oxidized SMZ or natural organic matter (NOM).The particularity of the method was that Fe 2+ in the groundwater could be used to activate the PMS in situ.In the oxidation process, the NOM in the water was also degraded.In recent years, Lu H. et al. [45] studied the degradation of SDZ in water by the O3/PMS process and compared the experimental results with the O3 alone and the O3/UV method.The experiment was carried out in a cylindrical glass reactor with a volume of 6 L. The experimental conditions were as follows: the temperature was 25 ± 0.5 °C, the initial concentration of SDZ was 10 mg/L, the concentration of O3 was 3 mg/L, the concentration of PMS was 22.8 mg/L, the UV intensity was 0.9 mw/cm 2 , and the pH was 6.8 ± 0.1.In the O3/PMS system, the degradation rate of SDZ reached 95.9% at 12 min, and the degradation rate of SDZ was below the detection limit at 13 min.However, at 12 min, the degradation rates of O3 and O3/UV were only 73.8% and 76.5%, respectively.The time required for O3/PMS to degrade SDZ was about 7 min shorter than that required by the O3 and O3/UV processes.In the O3/PMS system, the most suitable pH range is weak alkalinity.O3/PMS could effectively degrade SDZ and fluorescent substances dissolved in water, which showed a good prospect for practical engineering applications.Ciprofloxacin (CIP) is a quinolone antibiotic considered to be a high-risk environmental pollutant [46].In recent years, Li S. et al. [47] proposed a pore confinement method based on green ball milling, in which Co-Ce nanoparticles were immobilized on a mesoporous silica support as a catalyst to promote the degradation of CIP using the O3/PMS process.The catalyst exhibited higher activity due to enhanced interfacial mediated electron transfer.The heterogeneous O3/PMS reaction was carried out in a cylindrical reactor containing 500 mL 10 ppm CIP solution.The experimental conditions were as follows: the Ciprofloxacin (CIP) is a quinolone antibiotic considered to be a high-risk environmental pollutant [46].In recent years, Li S. et al. [47] proposed a pore confinement method based on green ball milling, in which Co-Ce nanoparticles were immobilized on a mesoporous silica support as a catalyst to promote the degradation of CIP using the O 3 /PMS process.The catalyst exhibited higher activity due to enhanced interfacial mediated electron transfer.The heterogeneous O 3 /PMS reaction was carried out in a cylindrical reactor containing 500 mL 10 ppm CIP solution.The experimental conditions were as follows: the initial concentration of CIP was 10 mg/L, the concentration of PMS was 0.4 g/L, the concentration of the catalyst was 0.2 g/L, and the initial pH was 2.8.The total organic carbon removal rate of CIP was more than 70% after the treatment by the O 3 /PMS/Co-Ce-CS process for 10 min.The catalyst provides new possibilities for the treatment of organic pollutants in water environment.
The isothiazolinone bactericide is an antibiotic insecticide [48].Li A. et al. [49] studied the kinetics and mechanism of oxidative degradation of methyl-isothiazolinone (MIT) by ozone.The experiment was carried out in a reactor with a volume of 3 L.The research showed that ozone could react with MIT at a low temperature.The molar concentration of ozone should be more than four times higher than that of MIT to achieve a higher removal rate.Ozone could reduce the toxicity of MIT by converting sulfur atoms in MIT to sulfate ions.The primary ozonation products of MIT showed toxicity, but the toxicity could be minimized by the ozonation reaction for 80 min.Yang Z. et al. [50] used O 3 /PMS to degrade isothiazolinone bactericide.The batch degradation experiment was carried out in a 100 mL conical flask.The experimental conditions were as follows: phosphate buffered saline with a concentration of 5 mmol/L was used as the medium, the concentration of O 3 was 42 µmol/L, the concentration of PMS was 21 µmol/L, the initial concentration of MIT and CMIT was 1 mg/L, and the pH was 7. O 3 /PMS could degrade MIT and Chloro-methylisothiazolin (CMIT) by 91% and 81.8%, respectively, within 90 s, which were 30.6% and 62.5% higher than those of ozone oxidation alone.The experimental results showed that the total generation amount of O 3 /PMS free radicals was 24.6 times higher than O 3 alone, indicating that •OH and SO 4 •− played a major role in the oxidation of MIT and CMIT.Compared with O 3 /H 2 O 2 , it was found that the reaction rate of the deprotonation component of O 3 /PMS was higher than that of O 3 /H 2 O 2 .This shows that PMS can consume ozone molecules efficiently and improve the utilization rate of ozone.
Both cefalexin (CFX) and Amoxicillin (AM) belong to β-lactam antibiotics.Nguyen V. et al. [51] developed 2-Co 2 SnO 4 and 2-Co 2 SnO 4 @rGO nanocomposites with different compounding ratios using a sol-gel method.Then, these nanocomposites were used as heterogeneous catalysts to degrade CFX in the form of a O 3 /PMS/2-Co 2 SnO 4 @rGO system.The experiment was carried out in a cylindrical borosilicate glass reactor with a height of 450 mm and a diameter of 60 mm.The experimental conditions were as follows: the concentration of CFX was 100 mg/L, the concentration of catalyst was 0.3 g/L, the concentration of PMS was 300 mg/L, the O 3 flow rate was 15 mL/min, and the initial pH was 7. The CFX degradation efficiencies of Co 2 SnO 4 @rGO/PMS and O 3 /Co 2 SnO 4 @rGO/PMS reached 95.07% and 99.07%, respectively, at the compounding ratio of 2-Co 2 SnO 4 and 1-rGO.The synergistic effect of O 3 /Co 2 SnO 4 @rGO/PMS led to the production of more •OH and SO 4 •− , thereby increasing the degradation rate of CFX in the system.Therefore, it is feasible to adopt the nano-composite catalyst to activate PMS in combined ozone oxidation to degrade antibiotic residues in wastewater.Gholikandi G. et al. [52] degraded AM in wastewater from a sewage treatment plant using the O 3 /PMS process and compared it with O 3 /PS, O 3 /H 2 O 2 and O 3 alone processes.In this experiment, a cylindrical glass reactor with a diameter of 3 cm and a height of 40 cm was used.The experimental conditions were as follows: the temperature was 17.6 • C, the concentration of O 3 was 0.083 mmol/L, the concentration of PMS was 0.09 mmol/L, the concentration of H 2 O 2 was 1.05 mmol/L, the concentration of PS was 3 mmol/L, and the initial pH was 6.9 ± 0.1.The removal rate of AM by O 3 /PMS reached 90 ± 2% within 30 min, while that of O 3 /PS and O 3 /H 2 O 2 methods was only about 60-70%.Therefore, the removal rate of AM by O 3 /PMS was higher than that of the other three methods, and it could be used as an effective new method for sewage disinfection and removal of organic pollutants.
In recent years, biochar has exhibited great potential in environmental remediation due to low cost, large specific surface area, high porosity, and high conductivity.Biocharassisted methods have attracted more and more attention in the degradation of organic pollutants in water [53].Fang G. et al. [54] carried out research on the utilization of manganese oxide/biochar composite (Mn x O y @BC) to activate periodate (PI) to degrade oxytetracycline (OTC).The experimental conditions were as follows: the temperature was 25 • C, the concentration of PI was 0.25 mmol/L, the initial concentration of OTC was 20 mg/L, the concentration of Mn x O y @BC was 0.3 g/L, and the pH was 3.0.The degradation rate of OTC in Mn x O y @BC/PI system was almost 98%, and the TOC removal rate was 75%.Various characterization analyses also verified that the functional groups on the surface of biochar and manganese active species (Mn (II), Mn (III) and Mn (IV)) could effectively activate PI.The Mn x O y @BC system has great room for improvement and great practical application potential.Miao J. et al. [55] improved the activation efficiency of persulfate heterogeneous catalysts by loading metals on N-doped carbon materials.They studied and synthesized a Co/NC composite catalyst derived from Co 3 O 4 /PPY and used it to activate PMS to degrade benzothiazole (BTH).The catalytic degradation experiment confirmed the synergistic catalytic effect of Co, C, and N on PMS activation.The experimental conditions were as fol-lows: the concentration of Co/NC-0.4 was 0.05 g/L, the concentration of PMS was 0.4 g/L, the initial concentration of BTH was 20 ppm, and the pH was 7.21.BTH was completely degraded within 20 min at 25 • C. In addition, under the same conditions, the production rate of free radicals in the Co/NC-0.4/PMSsystem is faster than that in other systems, and the effective utilization rate of PMS is also improved.The metal leaching of Co/NC-0.4/PMSsystem is also obviously inhibited by the coating of NC layer.
The O 3 /PMS process is an effective technology for treating antibiotics in various water bodies.But the generation of by-products cannot be ignored in practical application, and appropriate measures should be taken to inhibit the generation of by-products.

Inhibition of By-Product Generation in O 3 /PMS System by Adding Carbon Materials
The O 3 /PMS process can effectively remove organic pollutants from water by utilizing •OH and SO 4 •− , and meanwhile, a large number of by-product bromate (BrO 3 − ) is formed due to the existence of Br − [56].Figure 5 showed the formation mechanism of bromate in O 3 /PMS system [33].
of biochar and manganese active species (Mn (II), Mn (III) and Mn (IV)) could effectively activate PI.The MnxOy @BC system has great room for improvement and great practical application potential.Miao J. et al. [55] improved the activation efficiency of persulfate heterogeneous catalysts by loading metals on N-doped carbon materials.They studied and synthesized a Co/NC composite catalyst derived from Co3O4/PPY and used it to activate PMS to degrade benzothiazole (BTH).The catalytic degradation experiment confirmed the synergistic catalytic effect of Co, C, and N on PMS activation.The experimental conditions were as follows: the concentration of Co/NC-0.4 was 0.05 g/L, the concentration of PMS was 0.4 g/L, the initial concentration of BTH was 20 ppm, and the pH was 7.21.BTH was completely degraded within 20 min at 25 °C.In addition, under the same conditions, the production rate of free radicals in the Co/NC-0.4/PMSsystem is faster than that in other systems, and the effective utilization rate of PMS is also improved.The metal leaching of Co/NC-0.4/PMSsystem is also obviously inhibited by the coating of NC layer.
The O3/PMS process is an effective technology for treating antibiotics in various water bodies.But the generation of by-products cannot be ignored in practical application, and appropriate measures should be taken to inhibit the generation of by-products.

Inhibition of By-Product Generation in O3/PMS System by Adding Carbon Materials
The O3/PMS process can effectively remove organic pollutants from water by utilizing •OH and SO4 •− , and meanwhile, a large number of by-product bromate (BrO3 − ) is formed due to the existence of Br − [56].Figure 5 showed the formation mechanism of bromate in O3/PMS system [33].Wen G. et al. [57] studied the formation mechanism of BrO3 − in the O3/PMS system.The first path was as follows: Br − was oxidized to Br • by SO4 •− and •OH, then Br • reacted with O3 to form BrO2•, and then BrO• was oxidized to BrO3 − by SO4 •− and •OH; another path was that O3 oxidized Br − to hypobromous acid (HOBr/OBr − ), then HOBr/OBr − reacted with O3 to form BrO2 • , and BrO2 • continued to be oxidized to BrO3 − .It could be seen that SO4 •− and •OH promoted the generation of by-products, so the O3/PMS process was more likely to produce BrO3 − than ozone oxidation alone.
Liu Z. et al. [43] proposed the addition of novel catalysts CuCo2O4-GO and CuCo2O4 as heterogeneous catalysts to the O3/PMS process for the degradation of SMX.Compared with CuCo2O4, CuCo2O4-GO not only retained the catalytic performance of CuCo2O4, but also inhibited the generation of BrO3 − in the O3/PMS system.HOBr/OBr − was a decisive intermediate in the generation of BrO3 − .The addition of CuCo2O4-GO mainly inhibited the further transformation of HOBr/OBr − to reduce HOBr/OBr − to Br − , thereby inhibiting the − could reach over 80% after the first two uses.Wen G. et al. [58] studied the addition of low-dose carbon materials to inhibit the generation of BrO 3 − in the O 3 /PMS process.The added carbon materials included powdered activated carbon (PAC), carbon nanotubes (CNT) and graphene oxide (GO).The results showed that all three of the carbon materials played the role of reducing the intermediate product (HOBr/OBr − ) in the reaction, thereby inhibiting the generation of BrO 3 − in the system.The order of inhibition ability was as follows: GO > CNT > PAC.It can be seen from Figure 6 that adding low-dose carbon material is an effective way to promote the degradation of organic pollutants and control the formation of bromate.But, the inhibition methods are far more than that, including the adoption of NH 3 , Cl 2 -NH 3 , NH 3 -Cl 2 , and other treatment methods.See references [56,59] for details.
large decrease in the generation of BrO3 − .Meanwhile, when CuCo2O4-GO was added into actual water samples, the generation of BrO3 − was significantly inhibited.In addition, after CuCo2O4-GO was recycled three times, the degradation efficiency of SMX reached 90% within 10 min, and the inhibition efficiency of CuCo2O4-GO on BrO3 − could reach over 80% after the first two uses.Wen G. et al. [58] studied the addition of low-dose carbon materials to inhibit the generation of BrO3 − in the O3/PMS process.The added carbon materials included powdered activated carbon (PAC), carbon nanotubes (CNT) and graphene oxide (GO).The results showed that all three of the carbon materials played the role of reducing the intermediate product (HOBr/OBr − ) in the reaction, thereby inhibiting the generation of BrO3 − in the system.The order of inhibition ability was as follows: GO > CNT > PAC.It can be seen from Figure 6 that adding low-dose carbon material is an effective way to promote the degradation of organic pollutants and control the formation of bromate.But, the inhibition methods are far more than that, including the adoption of NH3, Cl2-NH3, NH3-Cl2, and other treatment methods.See references [56,59] for details.

Conclusions
The O3/PMS process can simultaneously produce two highly active free radicals: •OH and SO4 •− , in which O3 reacts with H2O to generate •OH, and O3 activates PMS to produce SO4 •− .SO4 •− and •OH co-oxidize pollutants, which makes it possible to treat more complex organic pollution in water environment.SO4 •− and •OH have strong oxidizability, so the process has the advantages of rapidly degrading organic pollutants and mineralizing the same into CO2 and H2O.Meanwhile, for the research of the O3/PMS process, the generation of by-product BrO3 − should be considered.In the reaction, a low dosage of carbon material can reduce HOBr/OBr − to Br − , thereby inhibiting the generation of bromate.
This paper focuses on the treatment efficiency of O3/PMS and its composite system for different kinds of antibiotic pollutants in drinking water and wastewater effluent.The addition of a catalyst composite can generate more •OH radicals and SO4 •− radicals.The addition of carbon materials can inhibit the generation of by-products, greatly shorten the reaction time, and improve the degradation efficiency.This also can realize the efficient removal of antibiotic pollutants in the water environment.This has great implications for protecting water resources and ecosystems and reducing human health risks.

Conclusions
The O 3 /PMS process can simultaneously produce two highly active free radicals: This paper focuses on the treatment efficiency of O 3 /PMS and its composite system for different kinds of antibiotic pollutants in drinking water and wastewater effluent.The addition of a catalyst composite can generate more •OH radicals and SO 4 •− radicals.The addition of carbon materials can inhibit the generation of by-products, greatly shorten the reaction time, and improve the degradation efficiency.This also can realize the efficient removal of antibiotic pollutants in the water environment.This has great implications for protecting water resources and ecosystems and reducing human health risks.

Future Directions
The O 3 /PMS process has wide application potential in water treatment, and future directions for research include the following: Firstly, it is necessary to combine other technologies on the basis of the O 3 /PMS system, which can improve the degradation efficiency to some extent [60].Secondly, researchers should look for or independently develop economic and environmental catalyst materials.By adding a catalyst composite and optimizing reaction conditions, the process can be cleaner and more efficient, and the catalytic activity and stability of the system can be further improved [61].Thirdly, the evaluation of side reactions and toxicity of intermediate products in the process of degradation needs further study, including in the areas of degradation mechanisms and degradation pathways.It is necessary to explore more targeted treatment methods to degrade pollutants and reduce toxic by-products from the treatment of antibiotic wastewater [57].At the same time, it is important to develop a combined process with other water treatment technologies [62], and to deeply study the scale of AOPs process to protect human health and ecological environment.

Figure 3 .
Figure 3. Reaction mechanism promoting the generation of •OH in the O3/PMS system.2.3.Research Status of O3/PMS Advanced Oxidation Technology for Treatment of Antibiotics in Drinking Water and Wastewater Effluent 2.3.1.Treatment Efficacy of O3/PMS Advanced Oxidation Technology for Antibiotics in Drinking Water and Wastewater Effluent Due to the incomplete degradation of pollutants in water by traditional water treatment methods, clean and efficient advanced oxidation technology has attracted extensive attention from scholars.The O3/PMS process has more advantages in oxidation and can be used for the treatment of antibiotic pollutants in the water body.Sulfame-thoxazo (SMX), sulfamethazine (SMZ), and sulfadiazine (SDZ) are typical sulfonamide antibiotics in drinking water and wastewater effluent.Research has shown that the sulfate radical-based advanced oxidation process (SR-AOPs) can effectively degrade SMX, such as Fe 0 /PS[40], Fe(II)/PS[41], Co(II)/PMS[42].Liu Z. et al.[43] studied the degradation of SMX by adding novel catalysts CuCo2O4-GO and CuCo2O4 as heterogeneous catalysts in the O3/PMS process.Liu Z. et al. prepared CuCo2O4 and CuCo2O4-GO nanoparticles by sol-gel method and hydrothermal method, respectively, and synthesized CuCo2O4-GO with different proportions of GO (5%, 10%, 20%, and 40%).The experiment was carried out in a 1000 mL hemispherical glass bottle.The experimental conditions were as follows: the temperature was 20 ± 2 °C, the pH was 7.0, the initial

Figure 2 .
Figure 2. Reaction paths of •OH and SO 4•− in the O 3 /PMS system.

Figure 3 .
Figure 3. Reaction mechanism promoting the generation of •OH in the O3/PMS system.2.3.Research Status of O3/PMS Advanced Oxidation Technology for Treatment of Antibiotics in Drinking Water and Wastewater Effluent 2.3.1.Treatment Efficacy of O3/PMS Advanced Oxidation Technology for Antibiotics in Drinking Water and Wastewater Effluent Due to the incomplete degradation of pollutants in water by traditional water treatment methods, clean and efficient advanced oxidation technology has attracted extensive attention from scholars.The O3/PMS process has more advantages in oxidation and can be used for the treatment of antibiotic pollutants in the water body.Sulfame-thoxazo (SMX), sulfamethazine (SMZ), and sulfadiazine (SDZ) are typical sulfonamide antibiotics in drinking water and wastewater effluent.Research has shown that the sulfate radical-based advanced oxidation process (SR-AOPs) can effectively degrade SMX, such as Fe 0 /PS[40], Fe(II)/PS[41], Co(II)/PMS[42].Liu Z. et al.[43] studied the degradation of SMX by adding novel catalysts CuCo2O4-GO and CuCo2O4 as heterogeneous catalysts in the O3/PMS process.Liu Z. et al. prepared CuCo2O4 and CuCo2O4-GO nanoparticles by sol-gel method and hydrothermal method, respectively, and synthesized CuCo2O4-GO with different proportions of GO (5%, 10%, 20%, and 40%).The experiment was carried out in a 1000 mL hemispherical glass bottle.The experimental conditions were as follows: the temperature was 20 ± 2 °C, the pH was 7.0, the initial

Figure 3 .
Figure 3. Reaction mechanism promoting the generation of •OH in the O 3 /PMS system.

2. 3 .
Research Status of O 3 /PMS Advanced Oxidation Technology for Treatment of Antibiotics in Drinking Water and Wastewater Effluent 2.3.1.Treatment Efficacy of O 3 /PMS Advanced Oxidation Technology for Antibiotics in Drinking Water and Wastewater Effluent Due to the incomplete degradation of pollutants in water by traditional water treatment methods, clean and efficient advanced oxidation technology has attracted extensive attention from scholars.The O 3 /PMS process has more advantages in oxidation and can be used for the treatment of antibiotic pollutants in the water body.Sulfame-thoxazo (SMX), sulfamethazine (SMZ), and sulfadiazine (SDZ) are typical sulfonamide antibiotics in drinking water and wastewater effluent.Research has shown that the sulfate radical-based advanced oxidation process (SR-AOPs) can effectively degrade SMX, such as Fe 0 /PS [40], Fe(II)/PS [41], Co(II)/PMS [42].Liu Z. et al. [43] studied the degradation of SMX by adding novel catalysts CuCo 2 O 4 -GO and CuCo 2 O 4 as heterogeneous catalysts in the O 3 /PMS process.Liu Z. et al. prepared CuCo 2 O 4 and CuCo 2 O 4 -GO nanoparticles by sol-gel method and hydrothermal method, respectively, and synthesized CuCo 2 O 4 -GO with different proportions of GO (5%, 10%, 20%, and 40%).The experiment was carried out in a 1000 mL hemispherical glass bottle.The experimental conditions were as follows: the temperature was 20 ± 2 • C, the pH was 7.0, the initial concentration of SMX was 30 µmol/L, the concentration of PMS was 100 µmol/L, the concentration of O 3 was 1.30 mg/min, and the concentration of CuCo 2 O 4 and CuCo 2 O 4 -GO was 100 mg/L.The degradation rate of SMX reached more than 98% after 10 min in the O 3 /PMS/CuCo 2 O 4 and O 3 /PMS/CuCo 2 O 4 -GO system, while the O 3 /PMS process could almost completely degrade SMX after 25 min.Figure4shows that the addition of CuCo 2 O 4 and CuCo 2 O 4 -GO promoted the degradation of SMX and greatly shortened the time for complete degradation of SMX.It is an effective way to strengthen the degradation of SMX.Du X. et al.[44] adopted a PMS/(oxidation/coagulation) coupled ceramic membrane process to remove Fe 2+ , Mn 2+ , and SMZ.The experimental conditions were as follows: the initial concentration of SMZ was 400 µg/L, the concentration of PMS was 100 µmol/L, the concentration of O 2 was 0.14 mg/L, the concentration of Fe(II) was 4.2 mg/L, the concentration of Mn was Molecules 2024, 29, 1170 6 of 12 1.0 mg/L, and the initial pH was 7.3.A large number of humus substances are oxidized by the •OH radical and SO 4

Figure 5 .
Figure 5. Formation mechanism of bromate in O3/PMS system (the red path represents the adding of carbon materials).

Figure 5 .
Figure 5. Formation mechanism of bromate in O 3 /PMS system (the red path represents the adding of carbon materials).Wen G. et al.[57] studied the formation mechanism of BrO 3 − in the O 3 /PMS system.The first path was as follows: Br − was oxidized to Br • by SO 4•− and •OH, then Br • reacted with O 3 to form BrO2•, and then BrO• was oxidized to BrO 3 − by SO4•− and •OH; another path was that O 3 oxidized Br − to hypobromous acid (HOBr/OBr − ), then HOBr/OBr − reacted with O 3 to form BrO 2 • , and BrO 2 • continued to be oxidized to BrO 3 − .It could be seen that SO4•− and •OH promoted the generation of by-products, so the O 3 /PMS process was more likely to produce BrO 3 − than ozone oxidation alone.Liu Z. et al.[43] proposed the addition of novel catalysts CuCo 2 O 4 -GO and CuCo 2 O 4 as heterogeneous catalysts to the O 3 /PMS process for the degradation of SMX.Compared with CuCo 2 O 4 , CuCo 2 O 4 -GO not only retained the catalytic performance of CuCo 2 O 4 , but also inhibited the generation of BrO 3 − in the O 3 /PMS system.HOBr/OBr − was a decisive intermediate in the generation of BrO 3 − .The addition of CuCo 2 O 4 -GO mainly inhibited the further transformation of HOBr/OBr − to reduce HOBr/OBr − to Br − , thereby inhibiting the generation of BrO 3 − .The results showed that the optimal dosage of GO in CuCo 2 O 4 -GO was 20%.Under this ratio, CuCo 2 O 4 -GO had the highest first-order rate constant for the degradation of SMX and the lowest utilization efficiency of O 3。 This almost completely inhibited the generation of BrO 3 − , indicated that it promoted the decomposition of O 3 to produce •OH, thereby reducing the reaction of O 3 with Br − , and indirectly resulting in a large decrease in the generation of BrO 3 − .Meanwhile, when CuCo 2 O 4 -GO was added into actual water samples, the generation of BrO 3 − was significantly inhibited.In addition, after CuCo 2 O 4 -GO was recycled three times, the degradation efficiency of SMX reached 90% within 10 min, and the inhibition efficiency of CuCo 2 O 4 -GO on BrO 3 − could reach over 80% after the first two uses.Wen G. et al. [58] studied the addition of low-dose carbon materials to inhibit the generation of BrO 3 − in the O 3 /PMS process.The added carbon materials included powdered activated carbon (PAC), carbon nanotubes (CNT) and
•OH and SO 4 •− , in which O 3 reacts with H 2 O to generate •OH, and O 3 activates PMS to produce SO 4 •− .SO 4 •− and •OH co-oxidize pollutants, which makes it possible to treat more complex organic pollution in water environment.SO 4 •− and •OH have strong oxidizability, so the process has the advantages of rapidly degrading organic pollutants and mineralizing the same into CO 2 and H 2 O.Meanwhile, for the research of the O 3 /PMS process, the generation of by-product BrO 3 − should be considered.In the reaction, a low dosage of carbon material can reduce HOBr/OBr − to Br − , thereby inhibiting the generation of bromate.

Table 1 .
Comparison of mainstream advanced oxidation technologies.

Table 3 .
Reaction equation and reaction rate constant for the generation of •OH and SO4 •− in the O3/PMS system.

Table 2 .
Reaction equation for the generation of •OH in O 3 /H 2 O 2 system.

Table 3 .
Reaction equation and reaction rate constant for the generation of •OH and SO 4 4 •− in the O 3 /PMS system.