key: cord-0018572-mbxnk5ja
authors: Luo, Yiting; Su, Rongkui; Yao, Haisong; Zhang, Aoshan; Xiang, Siyuan; Huang, Lei
title: Degradation of trimethoprim by sulfate radical-based advanced oxidation processes: kinetics, mechanisms, and effects of natural water matrices
date: 2021-07-01
journal: Environ Sci Pollut Res Int
DOI: 10.1007/s11356-021-15146-0
sha: b73879a727b0459c6e52c97e3e9065adca1c0ed8
doc_id: 18572
cord_uid: mbxnk5ja

In this study, we investigated the removal efficiency of a broad-spectrum antimicrobial agent trimethoprim (TMP) in a UV-activated persulfate system (UV/PS). The pseudo-first-order reaction kinetic model based on the steady-state hypothesis was used to explain TMP degradation behavior in UV-activated persulfate system. Due to the low quantum yield and molar absorptivity of TMP at 254 nm, the direct photolysis of TMP was slower. Since the free radicals generated by adding H(2)O(2) or PS to the system can react with TMP, the degradation rate was significantly accelerated, and[Formula: see text] played a dominant role in the UV/PS system. [Formula: see text] and [Formula: see text] were determined by the pseudo-first-order reaction kinetic model to be 6.02×10(9) and 3.88×10(9) M(−1)s(−1), respectively. The values were consistent with competitive kinetic measurements. The pseudo-first-order reaction kinetics model can predict and explain the effect of PS concentration, natural organic matter, and chloride ion on the TMP degradation in the UV/PS system. The observed pseudo first-order rate constants for TMP degradation (k(obs)) increased with the persulfate concentration, but it significantly decreased in the presence of NOM and chloride. [Formula: see text] has no effect on the degradation of TMP, while [Formula: see text] promotes the degradation and [Formula: see text] inhibits the degradation. The common transition metal ion (such as Cu(2+), Zn(2+), and Co(2+)) in industrial wastewater has a synergistic effect on the TMP degradation in the UV/PS system, but excessive metal ions will lead to a decrease of the degradation rate.

Trimethoprim (TMP), a broad-spectrum antibacterial, has been widely used for its high effective and unique antibacterial properties. TMP can enter the environmental water through the pharmaceutical wastewater generated during industrial production processes and the domestic sewage formed during daily use. TMP concentrations up to 605 μg/L has been detected in the Pearl River basin of China (Bu et al. 2013) . Residues and accumulation of TMP in the surface water and groundwater can have a major impact on the ecological environment. The priority control of 39 commonly used medicines and personal care products was studied by considering three factors: consumption, removal efficiency, and potential ecological risk, and it was found that TMP priority control ranks among the top in China (Sui et al. 2012 ). However, the study of Adams et al. (2002) showed that conventional water treatment processes (aluminum salt or iron salt coagulation process) cannot effectively remove TMP in surface water and deionized water. Zhao et al. (2019) used the activated sludge (AS) process to treat high-concentration antibiotic wastewater and found that the adsorption of trimethoprim was negligible, and no biodegradation occurred during the AS process.

This study aims to establish an efficient UV/PS technology to degrade EOCs in wastewater. TMP is used as the target compound. Under the steady-state assumption, the pseudofirst-order reaction kinetic model is used to study the degradation mechanism of TMP in a UV/PS system. Competitive kinetics technique and kinetics model were used to determine k TMP;SO •− 4 . The effects of persulfate concentration and matrix components (natural organic matters, inorganic anions) were evaluated by the kinetics model and experiment. Then, the effects of transition metal ions (Cu 2+ , Zn 2+ , Co 2+ ) in industrial wastewater on the photodegradation kinetics of TMP were further evaluated.

Materials TMP (99.0%), 4-chlorobenzoic acid (pCBA, 99.0%), sodium dihydrogen phosphate (99.0%), disodium phosphate (99.0%), sodium persulfate (99.0%), fulvic acid (technical), and t-butanol (99.7%) were obtained from Sigma Aldrich. Copper sulfate (guaranteed reagent, GR), cobalt sulfate (GR), zinc sulfate (GR), sodium chloride (GR), sodium sulfate (analytical grade), sulfuric acid (GR), and hydrogen peroxide (30% by weight) were obtained from Sinopharm Chemical Reagent. Deionized (DI) water was obtained from a Molresearc 1010A molecular water system.

In the kinetics tests, the initial concentrations of the target compound TMP and probe compound pCBA are both set at 10 uM. Phosphate buffer system (NaH 2 PO 4 /Na 2 HPO 4 , 10mM) was used to stabilize solution pH at 7.55. The value of pH did not change during the experiments. The detailed experimental design, operation process, data collection, and result analysis had been described in our previous articles (Su et al. 2018; Yang et al. 2017 ).

According to the measurement method we previously reported, the average light intensity per volume (I 0 ) and effective optical path length (b) were determined to be 7.496 × 10 −6 Einstein L −1 s −1 and 0.935 cm, respectively (Beltran et al. 1995; Parker 1953; Yang et al. 2017) .

A USB 2000+, Ocean Optics fiber optic spectrometer was used to measure the emission spectrum and light intensity of low-pressure mercury lamp. Shimadzu UV-1800 spectrometer was used to determine the absorption spectra of TMP and pCBA (Fig. 1) . A Mettler Toledo S220 pH meter was used to measure the solution pH.

The concentration of TMP and pCBA was performed using an ultra-performance liquid chromatography (Waters ACQUITY H-Class) with a BEH C18 column (1.7 μm, 2.1 mm × 50 mm, Waters). The detailed method is shown in Table 1 .

Degradation of TMP in UV, UV/H 2 O 2 , and UV/PS systems Linear regression analysis of the TMP degradation process showed that it followed the pseudo-first-order reaction kinetics. As shown in Fig. 2 , under the reaction conditions of UV intensity 7.496×10 −6 Einstein L − 1 s − 1, pH = 7.55, and [TMP] 0 = 10 μM, the initial direct photolytic degradation rate of TMP in only the UV system was 0.038 μM min − 1. Without UV irradiation, the dark reaction experiments showed that TMP had no degradation. The same results were observed in the presence of H 2 O 2 or PS. Therefore, the degradation of TMP under UV radiation was mainly attributed to the direct photolysis of TMP. As shown in Fig. 1 , at the wavelength ranging from 250 to 260 nm, TMP has a relative trough in the absorption of light. Therefore, the direct photolysis of TMP under 254 nm ultraviolet mercury lamp irradiation is slower.

The molar absorption coefficient (ε) and quantum yield (φ) are two important factors that affect the kinetics of target compound direct photolysis (Pereira et al. 2007 ). The molar absorption coefficient is a measure of the absorb light ability of a target compound at a specific wavelength (λ). ε can be calculated as Eq. 1.

A is the absorbance of 10 μM TMP solutions. The TMP solution pH is adjusted to 7.55 by phosphate buffer solution. l is the path length of quartz cuvette. In this study, a 1 cm path length quartz cuvette was used to measure the TMP solution absorbance. Figure 1 illustrates the decadic molar extinction coefficient for TMP with reference to Hg lamp emission spectra. At the wavelength of 254 nm, the ε values of TMP were 3078.56 M −1 cm −1 , which is consistent with the reported value of 2942 M −1 cm −1 (Baeza and Knappe 2011). ε TMP was lower than the reported value of carbamazepine (6070 M −1 cm −1 ) and sulfamethoxazole (16580 M −1 cm −1 ), while it was higher than that of ibuprofen (256 M −1 cm −1 ) and bisphenol (750 M −1 cm −1 ) (Baeza and Knappe 2011; Pereira et al. 2007; Yuan et al. 2009 ).

The quantum yield described the ratio of the total numbers of molecules of the compound destroyed to the total numbers of photons absorbed by the system. The quantum yield of TMP can be calculated as follows (Pereira et al. 2007) :

where φ TMP is the quantum yield of TMP at 254 nm (mol Einstein −1 ), r uv (M s −1 ) is the direct photolytic degradation rate at an initial concentration of 10 μM. I 0 is the incident UV intensity, ε TMP is the molar extinction coefficient of TMP at wavelength 254 nm, and b is the reactor light path. φ TMP was calculated to be 1.29×10 −3 mol Einstein −1 , which was close to the reported value of 1.18×10 −3 M −1 cm −1 (Baeza and Knappe 2011) . Different Pharmaceutical and Personal Care Products (PPCPs) have different molecular structures, which can result in different quantum yield values (Yuan et al. 2009 ). The value of φ TMP was relatively low compared to the values of other PPCPs (ibuprofen, 0.192 M −1 cm −1 and sulfamethoxazole, 0.0215 M −1 cm −1 ) (Yang et al. 2016; Yuan et al. 2009 ).

Due to the relatively low molar absorptivity and extremely low quantum yield, the direct photolysis degradation rate of TMP was slow. As shown in Fig. 2 , the degradation kinetics of TMP was significantly enhanced by adding 100 μM H 2 O 2 / PS compared to direct photolysis. The initial degradation rate in the UV/H 2 O 2 and UV/PS systems was 1.657 μM min −1 and 2.581 μM min −1 , respectively. These results indicated that the degradation of TMP in the UV/H 2 O 2 or UV/PS systems included direct photolysis and radical degradation, but radical degradation played a major role (more than 95%). The enhanced degradation of TMP with the addition of H 2 O 2 or PS was due to the fact that TMP degradation mainly contributed to • OH/SO •− 4 radical-mediated oxidation. The results were consistent with the results reported by Kwon et al. (2015) , and they also demonstrated that • OH/SO •− 4 played a major role in the degradation of ibuprofen by UV/H 2 O 2 or UV/PS. Therefore, the degradation rate constants of TMP largely depended on the formation of • OH/SO •− 4 in the UV system. The competitive kinetics method was used to determine the second-order rate constants of TMP with SO •− 4 (k SO •− 4 ;TMP ), and pCBA ( k SO •− 4 ;pCBA = 3.60×10 8 M −1 s −1 ) was chosen as a reference compound in this study (Kwon et al. 2015) . The 1 mM t-butanol was added to suppress any contribution of • OH in oxidizing TMP. The competitive kinetics method had been described in detail in our previous study (Yang et al. 2017) . Figure 3 shows that an average reaction rate constant ratio between TMP and pCBA with SO •− 4 was 10.58. The k SO •− 4 ;TMP values were determined to be 3.81×10 9 M −1 s −1 . It was lower than the reported value of 7.71×10 9 M −1 s −1 (Zhang et al. 2015) . pH values determine the morphology of TMP in the system. The possible reason was that our pH conditions (pH = 7.55) are different from those of Zhang (pH = 6).

The steady-state approximation for the kinetic description of radicals was also used to estimate the k SO •− 4 ;IBU (Luo et al. 2016a; Yang et al. 2017) . The model was developed based on the hypothesis that the degradation of the target compound depended primarily on radicals (i.e., SO •− 4 and • OH) generated from the irradiation of PS. SO •− 4 was produced from activation of S 2 O 2− 8 by UV and • OH was simultaneously formed from the reaction of SO •− 4 with H 2 O or OH − . The reactions in the UV/PS system and these second-order rate constants are presented in Table 2 

The average of r 0 SO •− 4 and k app was 4.623×10 −8 M s −1 and 4.301×10 −3 s −1 , respectively. The value of α was 8.78×10− 3 (unitless), and β was 9.00×10 3 s −1 as calculated. k HO • ;TMP was 

k 2 = 6.5 × 10 7 (Neta et al. 1977) 3

.5 × 10 9 (Klaning et al. 1991 ) (Buxton et al. 1988) In the presence of pCBA and t-butanol 16 SO •− 4 þ t−butanol→products k 13 = 4.0× 10 5 (Neta et al. 1977) 17

• OH þ t−butanol→products k 14 = 6.0 × 10 8 (Buxton et al. 1988 The pseudo first-order reaction kinetics model can be used to study and simulate the effects of other factors on TMP degradation. In this study, we used the pseudo first-order reaction kinetics model to predict and explain the effects of PS concentration and matrix components on TMP degradation by UV/PS process. Then the contributions of • OH and SO •− 4 to TMP degradation (i.e., k cal, UV , k cal, • OH and k cal;SO •− 4 ) under various experimental conditions were calculated by Eqs. 8, 9, and 10, respectively.

The total contribution of • OH and SO •− 4 to TMP degradation (k cal ) can be expressed by Eq. 11.

The degradation rates of TMP were affected by the PS concentration in the UV/PS system. As shown in Fig. 4 , the observed pseudo first-order rate constants (in the unit of s −1 ) for TMP degradation (k obs ) increased from 4.95×10 −3 s −1 to 25.12×10 −3 s −1 when PS concentration increases from 100 μM to 500 μM. This result could be accurately predicted by the kinetic model (the calculated result, k cal ). The contributions of direct UV, • OH, and SO •− 4 to TMP degradation were also calculated. As the dose of PS increased, the contribution rate of direct photolysis was significantly reduced due to the competition of PS for UV, and there was no significant change in the contribution rate of • OH. However, the results showed that SO •− 4 was the main reactive species in the UV/PS system at pH 7.55, with a contribution to TMP degradation (k cal;SO •− 4 ) always greater than 97%. This result was also consistent with the previous study of Luo et al. (2016a) who found that the contribution of SO •− 4 was increased from 82.6 to 92.5% with the increase of PS concentration from 100 to 500 μM in the degradation of 2,4,6-trichloroanisole. However, Xie et al. (2015) found that the contribution of • OH was about 3.5 times and 2.0 times higher than SO •− 4 for 2-methylisoborneol and geosmin degradation, respectively. This discrepancy might be ascribed to the secondary reaction rate constant of radicals with the target compound and the concentration of free radicals in the system. The k •OH /k SO •− 4 of 2,4,6-trichloroanisole and TMP were 1.37 and 1.55, which is smaller than the value of 2methylisoborneol and geosmin (10.24 and 7.50, respectively). On the other hand, SO •− 4 Â Ã SS was expected to be about two orders of magnitude higher than [HO • ] SS based on Eqs. 4 and 5, which was consistent with Luo's study (Luo et al. 2016a 

NOM is a mixture of macromolecular organic compounds prevalent in the natural environment, widely distributed in soil, lake, river, and ocean. The impact of NOM on the degradation of organic contaminants has received more and more attention. Fulvic acid (FA) is a mixture of non-homogeneous compounds that can be dissolved in a base but cannot be dissolved in acid (Fu et al. 2006) . Since FA was the main component of NOM, the effect of NOM in the UV/PS processes was examined by adding different concentrations of FA (0~2.88 mgC L −1 ) in this study. Figure 5 shows that k obs decreased from 11.36×10 −3 s −1 to 7.07×10 −3 s −1 with FA concentrations increasing from 0 to 2.88 mgC L− 1 . The experimental data was basically consistent with the modeling results (k cal ). Two factors could be responsible for the inhibitory effect of FA on TMP degradation. First, FA would exert an inner filter effect for the photolysis of persulfate, and A can be modified to

) (ε FA = 0.10 L mgC −1 cm −1 measured in this work). Second, FA acted as a radical scavenger as described by Eqs. 20 and 21 in Table 2 . The kinetic model was used to estimate the relative contributions of the inner filter effect and radical scavenger in decreasing k obs values. If the inner filter effect of FA was not accounted for k, then ε FA was equal to zero. As we can see from the experimental data (black dots) by assuming ε FA = 0. If FA did not have a radical scavenging effect (i.e., k 17 and k 18 values in Table 2 were equal to zero), k cal (blue line) greatly deviated from the experimental data (black dots) in Fig. 5 . These results indicated that the radical scavenger effect of FA played a more significant role than the inner filter effect in decreasing TMP degradation rates. At the same time, the model calculation results showed that as the concentration of fulvic acid increased, the contribution rate of direct photolysis and SO •− 4 to TMP degradation did not change significantly, and the contribution rate of • OH dropped significantly. The possible reason was that k FA, • OH (3.0×10 8 M −1 C s −1 ) was larger than k FA;SO •− 4 (2.35×10 7 M −1 C s −1 ) (Weishaar et al. 2003; Xie et al. 2015) .

Inorganic anions present in environmental water (e.g., SO 2− 4 ; NO − 3 , Cl − , and HCO − 3 ) also have a greater effect on the degradation of TMP by UV/PS. In this study, the effect of inorganic ions on the degradation kinetics of SO •− 4 was studied by adding anion concentrations close to those in the environment in deionized water (SO 2− 4 and NO − 3 concentration of 0.5 mM, Cl − and HCO − 3 the concentration is 1 mM). The results (Fig. 6) show that SO 2− 4 has little effect on the degradation of TMP, while HCO − 3 will promote the degradation of TMP (11.5%). The main reason why HCO − 3 promotes the TMP degradation in the UV/PS system is that HCO − 3 can react with SO •− 4 to produce CO •− 3 (1.59 V NHE), which has certain oxidation ability. The oxidation potential of CO •− 3 was 1.59 V vs NHE (Giannakis et al. 2021) . The secondary free radicals CO •− 3 can continue to react with TMP (Lian et al. 2017; Luo et al. 2016b; Zuo et al. 1999) . NO − 3 and Cl − will inhibit the degradation of TMP, and the inhibition rates are 32.1% and 20.4%, respectively. NO − 3 can produce • OH, NO •− 3 , and NO •− 2 under a series of complex reactions under UV and sunlight (Dong and Rosario-Ortiz 2012; Ji et al. 2012; Keen et al. 2012; Vione et al. 2006; Xiao et al. 2014) . The oxidation potentials of NO •− 3 and NO •− 2 were 2.3-2.5 V and 1.03 V, respectively (Giannakis et al. 2021 (Lian et al. 2017; Yang et al. 2014; Yang et al. 2016 ). On the other hand, the generated secondary free radicals can continue to oxidatively degrade TMP. Cl • and Cl •− 2 have strong oxidation ability. The oxidation potentials of Cl • and Cl •− 2 were 2.47 V and 2.0 V, respectively (Beitz et al. 1998) . Cl • is also a selective oxidant, which can react with electron-rich components through electron transfer, hydrogen extraction, and addition (Beitz et al. 1998) . Therefore, the contribution of secondary free radicals (Cl • , ClOH •− , and Cl •− 2 ) and the inhibition of Cl − comprehensive determine the effect on TMP degradation.

The effect of Cl − on TMP degradation was studied using concentrations ranging from 0 to 5 mM. As shown in Fig. 7 , for the effect of Cl − , k obs slightly decreased from 11.36×10 −3 s −1 in the absence of Cl − to 5.73×10 −3 s −1 in the presence of 5 mM Cl − . The negative effect of Cl − in the system might result from the fact that significant amounts of SO •− 4 react with Cl − forming chloride-derived radicals. For instance, the influence of Cl − depended on its fast rate constants with both • OH and SO •− 4 (Eqs. 22 and 23 in Table 2 ). Usually, the fast Table 2 ).

Since most of those rate constants of reactive chlorine radicals with TMP are relatively unknown, it is difficult to accurately predict how Cl − affected TMP degradation in the UV/PS process by the steady-state kinetic model. Thus, in this study, only Cl − was considered the scavenger of • OH and SO •− 4 for calculating the k cal values. As shown in Fig. 6 , k cal was significantly smaller than the experimental data (red line), which contradicts the observation that Cl − had a minor inhibitory effect on TMP degradation. Still, those secondary radicals might play a role in the degradation of TMP in UV/PS process, since Cl • and Cl •− 2 were strong oxidants with oxidation potentials of 2.47 V and 2.0 V, respectively (Beitz et al. 1998) . Cl • is a selective oxidant that reacts with electron-rich moieties through one-electron oxidation, H-abstraction, and addition to unsaturated bonds (Grebel et al. 2010) . Previous studies had shown conflicting results of Cl − in the UV/S 2 O 2− 8 process, depending on the target compound. Yuan et al. (2011) reported that a dual effect of chloride (i.e., inhibitory and accelerating effect) on azo dye (Acid Orange 7) degradation in an emerging cobalt/peroxymonosulfate (Co/ PMS) advanced oxidation process. Ghauch et al. (2017) showed that the k value of chloramphenicol increased first and then decreased with the concentration increase of chloride anion in UV/ PS system. The reaction between • OH/SO •− 4 and Cl − produces secondary chlorine radical species, but the influence of Cl − was compound dependent, either promoting target compound removal (Criquet and Leitner 2009; , or inhibiting the degradation (Liang et al. 2006; Shah et al. 2013 ).

Transition metal ions (M n+ ) were very common in industrial wastewater, and some research results showed that the presence of M n+ had a very important effect on the degradation of organic matter by UV-activated persulfate system. As shown in Fig. 8 , as the concentration of transition metal ions (Cu 2+ , Zn 2+ , Co 2+ ) in the UV/PS system increased from 0 to 100 μM, k exp increased from 1.96×10 −3 to 2.44×10 −3 , 3.11×10 −3 , 2.62×10 −3 s −1 , respectively. The results showed that the presence of transition metal ions can significantly promote the degradation of TMP. Take Co 2+ for example, The main reason was that transition metal ions can activate PS to produce more SO •− 4 , such as Eq. (12) (Liu et al. 2012; Nfodzo and Choi 2011) .

At the same time, the generated M (n + 1)+ is not stable, and M (n + 1)+ oxidative degradation of TMP may be another main reason for the significant increase in k exp (Liang et al. 2013) .

However, as the concentration of transition metal ions (Cu 2+ , Zn 2+ , Co 2+ ) in the system continued to increase from 100 to 400 μM, k exp did not continue to increase but gradually decreased. The main reason was that excess transition metal ions can be combined with SO •− 4 to continue the reaction and consume free radicals (Eq. 24) (Furman et al. 2010; Nfodzo and Choi 2011) , and excessive transition metal ions can also form hydrated ions with water (such as [Zn(H 2 O) 6 ] 2+ ) as UV contenders affected TMP and S 2 O 2− 8 absorption of UV.

Transition metal ions showed a good synergistic effect in the UV/PS system. Only a very small amount of transition metal ions can significantly accelerate the degradation of organic pollutants, which provided a meaningful exploration for 

The lower molar absorption coefficient and quantum yield limited the direct photolysis of TMP. After adding H 2 O 2 or PS to the reaction system, the degradation effect of TMP was significantly enhanced, among which free radicals played a major role. k HO • ;TMP and k SO •− 4 ;TMP showed good agreement with previously reported values, which was measured by competitive kinetics method and steady-state assumption model. Steady-state approximation and kinetic model were also developed in order to predict and simulate the destruction of TMP by a variety of water matrices in UV-activated persulfate system. k obs of TMP degradation decreased in the presence of FA and Cl − , but k obs was increased with the concentration of PS. Transition metal ions had a good synergistic effect in UV/ PS degradation of TMP. However, excessive transition metal ions could reduce the TMP degradation due to the trapping effect of free radicals and the competition of formed hydrated ions against UV. The reported k HO • ;TMP and k SO •− 4 ;TMP values and effect of matrix components are more beneficial to predict and explain TMP degradation mechanism and select more efficient radical-based advanced oxidation processes in engineered water.

Author contribution All authors contributed to the study conception and design. Material preparation, data collection, and analysis were performed by Yiting Luo, Rongkui Su, Haisong Yao, Aoshan Zhang, Siyuan Xiang, and Lei Huang. The first draft of the manuscript was written by Yiting Luo and Rongkui Su, and all authors commented on the previous versions of the manuscript. All authors read and approved the final manuscript.

Removal of antibiotics from surface and distilled water in conventional water treatment processes

Activation of persulfate by irradiated magnetite: implications for the degradation of phenol under heterogeneous photo-fenton-like conditions

Transformation kinetics of biochemically active compounds in low-pressure UV photolysis and UV/H 2 O 2 advanced oxidation processes

Investigations of reactions of selected azaarenes with radicals in water. 2. chlorine and bromine radicals

Oxidation of polynuclear aromatic hydrocarbons in water. 2. UV radiation and ozonation in the presence of UV radiation

Textile wastewater treatment by peroxydisulfate/Fe(II)/UV: operating cost evaluation and phytotoxicity studies

Pharmaceuticals and personal care products in the aquatic environment in China: a review

Critical review of rate constants for reactions of hydrated electrons, hydrogen atoms and hydroxyl radicals (·OH/·O − ) in aqueous solution

Degradation of acetic acid with sulfate radical generated by persulfate ions photolysis

Reactivity and role of SO 5

•− radical in aqueous medium chain oxidation of sulfite to sulfate and atmospheric sulfuric acid generation

Photochemical formation of hydroxyl radical from effluent organic matter

Bromate formation from bromide oxidation by the UV/persulfate process

Sulfate radical-based degradation of polychlorinated biphenyls: effects of chloride ion and reaction kinetics

A new submerged membrane photocatalysis reactor (SMPR) for fulvic acid removal using a nanostructured photocatalyst

Mechanism of base activation of persulfate

Contribution of persulfate in UV-254nm activated systems for complete degradation of chloramphenicol antibiotic in water

A review of the recent advances on the treatment of industrial wastewaters by sulfate radicalbased advanced oxidation processes (SR-AOPs)

Effect of halide ions and carbonates on organic contaminant degradation by hydroxyl radical-based advanced oxidation processes in saline waters

Chlorate formation mechanism in the presence of sulfate radical, chloride, bromide and natural organic matter

Degradation of contaminants of emerging concern by UV/H 2 O 2 for water reuse: kinetics, mechanisms, and cytotoxicity analysis

Some simple, highly reactive, inorganic chlorine derivatives in aqueous solution. Their formation using pulses of radiation and their role in the mechanism of the fricke dosimeter

Nitrateinduced photodegradation of atenolol in aqueous solution: kinetics, toxicity and degradation pathways

Degradation of trimethoprim by thermo-activated persulfate oxidation: reaction kinetics and transformation mechanisms

Photodegradation of sulfasalazine and its human metabolites in water by UV and UV/peroxydisulfate processes

The role of effluent nitrate in trace organic chemical oxidation during UV disinfection

Laser flash photolysis of HCIO, CIO − , HBrO, and BrO − in aqueous solution. Reactions of Cl − and Br − atoms

Laser flash photolysis and pulse radiolysis of aqueous solutions of the fluoroxysulfate ion, SO 4 F

Comparative evaluation of ibuprofen removal by UV/H 2 O 2 and UV/S 2 O 8 2− processes for wastewater treatment

Kinetic study of hydroxyl and sulfate radical-mediated oxidation of pharmaceuticals in wastewater effluents

Influences of carbonate and chloride ions on persulfate oxidation of trichloroethylene at 20°C

Oxidative degradation of p-chloroaniline by copper oxidate activated persulfate

Treatment of organosilicon wastewater by UV-based advanced oxidation processes: performance comparison and fluorescence parallel factor analysis

Oxidative degradation of propachlor by ferrous and copper ion activated persulfate

Oxidation of the odorous compound 2,4,6-trichloroanisole by UV activated persulfate: kinetics, products, and pathways

Oxidation of the odorous compound 2,4,6-trichloroanisole by UV activated persulfate: kinetics, products, and pathways

Degradation of chlorotriazine pesticides by sulfate radicals and the influence of organic matter

A laser photolysis study of the reaction of SO 4 − with

Cl − and the subsequent decay of Cl 2 − in aqueous solution

Ranitidine abatement in chemically activated persulfate systems: assessment of industrial iron waste for sustainable applications

Rate constants and mechanism of reaction of sulfate radical anion with aromatic compounds

Triclosan decomposition by sulfate radicals: effects of oxidant and metal doses

UV/Chlorine process for dye degradation in aqueous solution: mechanism, affecting factors and toxicity evaluation for textile wastewater

A new sensitive chemical actinometer. I. Some trials with potassium ferrioxalate

UV degradation kinetics and modeling of pharmaceutical compounds in laboratory grade and surface water via direct and indirect photolysis at 254 nm

Degradation of refractory organic compounds from dinitrodiazophenol containing industrial wastewater through UV/ H2O2 and UV/PS processes

Efficient removal of endosulfan from aqueous solution by UV-C/peroxides: a comparative study

Comparison of the degradation of molecular and ionic ibuprofen in a UV/H 2 O 2 system

Identification of priority pharmaceuticals in the water environment of China

Rate constants for the reaction of hydroxyl and sulfate radicals with organophosphorus esters (OPEs) determined by competition method

Sources and sinks of hydroxyl radicals upon irradiation of natural water samples

Comparative study on the pretreatment of algae-laden water by UV/ persulfate, UV/chlorine, and UV/H 2 O 2 : variation of characteristics and alleviation of ultrafiltration membrane fouling

Kinetics and mechanism of ultrasonic activation of persulfate: an in situ EPR spin trapping study

Evaluation of specific ultraviolet absorbance as an indicator of the chemical composition and reactivity of dissolved organic carbon

Photodegradation of iodinated trihalomethanes in aqueous solution by UV 254 irradiation

Removal of 2-MIB and geosmin using UV/persulfate: contributions of hydroxyl and sulfate radicals

Comparison of halide impacts on the efficiency of contaminant degradation by sulfate and hydroxyl radical-based advanced oxidation processes (AOPs)

Effect of matrix components on UV/H 2 O 2 and UV/S 2 O 8 2− advanced oxidation processes for trace organic degradation in reverse osmosis brines from municipal wastewater reuse facilities

Comparison of the reactivity of ibuprofen with sulfate and hydroxyl radicals: an experimental and theoretical study

Free radical reactions involving Cl • , Cl 2 •− , and SO 4

•− in the 248 nm photolysis of aqueous solutions containing S 2 O 8 2− and Cl

Degradation of selected pharmaceuticals in aqueous solution with UV and UV/H 2 O 2

Effects of chloride ion on degradation of Acid Orange 7 by sulfate radical-based advanced oxidation process: implications for formation of chlorinated aromatic compounds

Degradation of pharmaceuticals and metabolite in synthetic human urine by UV, UV/H 2 O 2 , and UV/PDS

Unravelling molecular transformation of dissolved effluent organic matter in UV/H 2 O 2 , UV/persulfate, and UV/chlorine processes based on FT-ICR-MS analysis

Deciphering of microbial community and antibiotic resistance genes in activated sludge reactors under high selective pressure of different antibiotics

Reinvestigation of the acid-base equilibrium of the (bi) carbonate radical and pH dependence of its reactivity with inorganic reactants

Publisher's note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations

Data availability Not applicable.

Ethical approval Not applicable.Consent to participate Not applicable.

Competing interest The authors declare no competing interests.