Degradation of climbazole by UV/chlorine process: Kinetics, transformation pathway and toxicity evaluation

Pivotal role of intracellular oxidation by HOCl in simultaneously removing antibiotic resistance genes and enhancing dewaterability during conditioning of sewage sludge using Fe2+/Ca(ClO)2

Pre-acidification has been shown to be crucial in attenuating antibiotic resistance genes (ARGs) during the conditioning of sewage sludge. However, it is of great significance to develop alternative conditioning approaches that can effectively eliminate sludge-borne ARGs without relying on pre-acidification. This is due to the high investment costs and operational complexities associated with sludge pre-acidification. In this study, the effects of Fe2+/Ca(ClO)2 conditioning treatment on the enhancement of sludge dewaterability and the removal of ARGs were compared with other conditioning technologies. The dose effect and the associated mechanisms were also investigated. The findings revealed that Fe2+/Ca(ClO)2 conditioning treatment had the highest potential, even surpassing Fenton treatment with pre-acidification, in terms of eliminating the total ARGs. Moreover, the effectiveness of the treatment was found to be dose-dependent. This study also identified that the •OH radical reacted with extracellular polymeric substance (EPS) and extracellular ARGs, and the HOCl, the production of which was positively correlated with the dose of Fe2+/Ca(ClO)2, could infiltrate the EPS layer and diffuse into the cell of sludge flocs, inducing the oxidation of intracellular ARGs. Furthermore, this study observed a significant decrease in the predicted hosts of ARGs and MGEs in sludge conditioned with Fe2+/Ca(ClO)2, accompanied by a significant downregulation of metabolic pathways associated with ARG propagation, thereby contributing to the attenuation of sludge-borne ARGs. Based on these findings, it can be concluded that Fe2+/Ca(ClO)2 conditioning treatment holds great potential for the removal of sludge-borne ARGs while also enhancing sludge dewaterability, which mainly relies on the intracellular oxidation by HOCl.

Kinetics and mechanism of triclocarban degradation by the chlorination process: Theoretical calculation and experimental verification

Triclocarban (TCC) is an antimicrobial agent commonly used in many household and personal care products, and has been found persistent in the aquatic environment. Here we elucidate the kinetics and mechanism of TCC degradation during chlorination process by density functional theory (DFT) calculation and experimental verification. Results showed that hypochlorous acid (HOCl)/hypochlorite (OCl-) reacted with TCC via Cl-substitution, OH-substitution and C-N bond cleavage pathways. The reactivity of OCl- (2.80 × 10-7 M-1 s-1) with TCC was extremely low and HOCl (1.96 M-1 s-1) played the dominant role in TCC chlorination process. The N site of TCC was the most reactive site for chlorination. The second-order rate constants, which are determined using density functional theory (DFT) (kTCC-chlorineC, 1.96 M-1 s-1), can be separated into reaction rate constants related to the reactions of HOCl and OCl- with different isomers of TCC (TCC2 and TCC6). The obtained kTCC-chlorineC was consistent with the experimental determined second-order rate constant (kTCC-chlorineE, 3.70 M-1 s-1) in chlorination process. Eight transformation products (TP348, TP382, TP127, TP161, TP195, TP330, TP204, and TP296) were experimentally detected for chlorination of TCC, which could also be predicted by DFT calculation. Explicit water molecules participated in the chlorination reaction by transmitting the proton and connecting with TCC, HOCl/OCl- and other H2O molecules, and obviously reduced the energy barrier of chlorination.

Guidance document on the impact of water treatment processes on residues of active substances or their metabolites in water abstracted for the production of drinking water

This guidance document provides a tiered framework for risk assessors and facilitates risk managers in making decisions concerning the approval of active substances (AS) that are chemicals in plant protection products (PPPs) and biocidal products, and authorisation of the products. Based on the approaches presented in this document, a conclusion can be drawn on the impact of water treatment processes on residues of the AS or its metabolites in surface water and/or groundwater abstracted for the production of drinking water, i.e. the formation of transformation products (TPs). This guidance enables the identification of actual public health concerns from exposure to harmful compounds generated during the processing of water for the production of drinking water, and it focuses on water treatment methods commonly used in the European Union (EU). The tiered framework determines whether residues from PPP use or residues from biocidal product use can be present in water at water abstraction locations. Approaches, including experimental methods, are described that can be used to assess whether harmful TPs may form during water treatment and, if so, how to assess the impact of exposure to these water treatment TPs (tTPs) and other residues including environmental TPs (eTPs) on human and domesticated animal health through the consumption of TPs via drinking water. The types of studies or information that would be required are described while avoiding vertebrate testing as much as possible. The framework integrates the use of weight-of-evidence and, when possible alternative (new approach) methods to avoid as far as possible the need for additional testing.

Toxicological aspect of water treated by chlorine-based advanced oxidation processes: A review

As well established in the literature, residual toxicity is an important parameter for evaluating the sanitary and environmental safety of water treatment processes, and this parameter becomes even more crucial when chlorine-based processes are applied for water treatment. Eliminating initial toxicity or preventing its increase after water treatment remains a huge challenge mainly due to the formation of highly toxic disinfection by-products (DBPs) that stem from the degradation of organic contaminants or the interaction of the chlorine-based oxidants with different matrix components. In this review, we present a comprehensive discussion regarding the toxicological aspects of water treated using chlorine-based advanced oxidation processes (AOPs) and the recent findings related to the factors influencing toxicity, and provide directions for future research in the area. The review begins by shedding light on the advances made in the application of free chlorine AOPs and the findings from studies conducted using electrochemical technologies based on free chlorine generation. We then delve into the insights and contributions brought to the fore regarding the application of NH₂Cl- and ClO₂-based treatment processes. Finally, we broaden our discussion by evaluating the toxicological assays and predictive models employed in the study of residual toxicity and provide an overview of the findings reported to date on this subject matter, while giving useful insights and directions for future research on the topic.

Does climbazole instigate a threat in the environment as persistent, mobile and toxic compound? Unveiling the occurrence and potential ecological risks of its phototransformation products in the water cycle

Persistent, mobile, and toxic chemicals (PMT), such as the antimycotic climbazole-(CBZ), proliferate in water cycle and imperil drinking water quality, sparking off research about their environmental fate. Unlike the parent compound, its transformation products-(TPs) are scarcely investigated, much less as PMTs. To this end, phototransformation of CBZ was investigated. A novel suspect-screening workflow was developed and optimized by cross-comparing the results of the identified photo-TPs against literature data to create an enhanced HRMS-database for environmental investigations of CBZ/TPs in the water cycle. In total, 24 TPs were identified, 14 of which are reported for the first time. Isomerism, dechlorination, hydroxylation, and cleavage of the ether or C-N bond are suggested as the main transformation routes. A screening of CBZ/TPs was conducted in wastewater, leachates, surface, and groundwater, revealing a maximum concentration of 464.8 ng/L in groundwater. In silico and in vitro methods were used for toxicity assessment, indicating toxicity for CBZ and some TPs. Seemingly, CBZ is rightly considered as PMT, and a higher potential to occur in surface or groundwater than non-PM chemicals appears. Likewise, the occurrence of TPs due to PMT properties or emission patterns was evaluated.

Reactive Blue 19 dye removal by UV-LED/chlorine advanced oxidation process

In recent years, advanced oxidation processes (AOPs) have indicated the greatest potential in the removal of stable organic compounds, including dyes. In this study, the ultraviolet light-emitting diodes (UV-LEDs) combined with chlorine was evaluated to remove Reactive Blue 19 (RB19) dye from aqueous solution. The effect of key experimental parameters including pH, initial chlorine concentration, initial dye concentration, and reaction time on the performance of UV-LED irradiation, UV-LED/chlorine, and the chlorination method for the removal of RB19 was studied in this research. Results showed that, more than 99% of RB19 was removed after 30 min of reaction time under optimized conditions (pH = 5, [chlorine] = 300 μM, and [RB19] = 20 mg L^-1) with apparent kinetic rate constant (k_app) of 17.1 × 10^-2 min^-1 in UV-LED/chlorine process. However, for the chlorination method, removal efficiency was 64.7% (k_app = 3.41 × 10^-2 min^-1) with an apparent kinetic rate constant of 0.0341 min^-1. Results also showed that UV-LED irradiation is not effective at all in removing RB19. The scavenging assay showed that OH^• radicals (67.23%) had the highest contribution in RB19 removal in UV-LED/chlorine process while Cl^• (17.82%) and [Formula: see text] (8.56%) had a minor role in the degradation of the dye. The RB19 degradation kinetics analysis revealed that the processes of UV-LED/chlorine and chlorination degradation followed the pseudo-first-order kinetic model. In this study, the impact of chloride, nitrate, bicarbonate, carbonate, sulfate, and sulfite anions on the performance of the process was investigated. It indicated that sulfite anion has the most negative impact on the RB19 removal process. By evaluating the synergistic effect between UV-LED lamp and chlorine, a synergy index of 5.0 was obtained for the UV-LED/chlorine process. The results presented that the UV-LED/chlorine process has a better performance than each of them alone and has the necessary efficiency for RB19 removal. Measuring COD reported its removal efficiency of 98% during the UV-LED/chlorine process under optimized conditions. Experiments continued with textile factory wastewater and indicated 30.9% of its COD removed after treatment when 1.0 μM chlorine was used.

CeO2 modified carbon nanotube electrified membrane for the removal of antibiotics

Electrified carbon nanotube membranes (ECM) are used as electroactive porous materials for the degradation of micropollutants. It integrated design of both electrochemical processes and filtration functions. In this study, CeO₂ modified carbon nanotube electrified membrane (CeO₂@CNT membrane) was prepared and activate NaClO towards degradation of antibiotics. As CeO₂ with face-centered cubic (Fcc) fluorite structure was loaded onto the CNT sidewalls, the CeO₂@CNT membrane showed a higher over potential and a smaller equivalent polarization resistance compared to ECM. More reactive oxygen species (ROS) and reactive chlorine species (RCS) were generated by CeO₂@CNT membrane due to faster electron transfer at the solid-liquid interface. Thus, the removal efficiencies of DCF, SMX, CIP, TC and CBZ were more than 91.2%, 91.3%, 94.4%, 99.3% and 89.4% by the CeO₂@CNT membrane with NaClO, respetively. And the apparent reaction rate constant (k) of the CeO₂@CNT membrane was 2.9 times of that of ECM. The selective capping experiments and density functional theory (DFT) calculation showed that the oxygen vacancies of CeO₂ contributed to the generation of ‧OH, and the generation of ClO‧ and ‧O₂^- would mainly occur on Lewis acid sites of CeO₂. In addition, the CeO₂@CNT membrane showed a reasonable stability to treat actual water samples and reduced disinfection byproducts (DBPs) formation, suggesting that it can potentially be combined with the conventional chlorine disinfection to degrade antibiotics in water.

Kinetic study on methylene blue removal from aqueous solution using UV/chlorine process and its combination with other advanced oxidation processes

This study investigated the kinetic degradation of methylene blue (MB) by a UV/chlorine process and its combination with other advanced oxidation processes. The ∙OH and reactive chlorine species (RCS: Cl∙, ClO∙, etc.) were the primary reactive species, which accounted for 56.7% and 37.6% of MB degradation at pH 7, respectively. The second-order rate constant of Cl∙ towards MB was calculated to be 2.8 × 10⁹ M^-1 s^-1. When the pH increased from 3 to 7, k_MB by ∙OH increased from 0.15 to 0.21 min^-1 before being reduced to 0.11 min^-1 at pH 11. k_MB by RCS continuously reduced from 0.16 to 0.13 min^-1 when the pH was increased to 11. Humic acid (HA), Br^-, and Cl^- inhibited the degradation with k_MB in the order: k_MB (in HA) < k_MB (in Br^-) < k_MB (in Cl^-). HCO₃^- increased k_MB from 0.37 to 0.48 min^-1. The experimental and modeling methods fit well, indicating the effectiveness of using Kintecus® in predicting concentrations of free radicals in complex water matrices. TOC removal was achieved at 60% after 30 min in a control process and it was strongly inhibited by the presence of HA, with 22% removal achieved at 5 mg_c L^-1 HA. UV/chlorine/electrochemical oxidation (UV/chlorine/EO) significantly improves k_MB from 0.37 to 0.94 min^-1 at a high current (240 mA), while UV/chlorine/H₂O₂ decreased k_MB at a low concentration of 0.01 mM H₂O₂ (k_MB decreased by 6.1%). The results indicate that the energy cost for UV irradiation was the main cost in MB treatment in both UV/chlorine and UV/persulfate (UV/PS) processes, accounting for 91% and 84%, respectively.

Rate constants of chlorine atom reactions with organic molecules in aqueous solutions, an overview

Rate constants of chlorine atom (Cl^•) reactions (k_Cl•) determined using a large variation of experimental methods, including transient measurements, steady-state and computation techniques, were collected from the literature and were discussed together with the reaction mechanisms. The k_Cl• values are generally in the 10⁸-10⁹ mol^-1 dm³ s^-1 range when the basic reaction between the Cl^• and the target molecule is H-atom abstraction. When Cl^• addition to double bonds dominates the interaction, the k_Cl• values are in the 1 × 10⁹-2 × 10¹⁰ mol^-1 dm³ s^-1 range. In the k_Cl• = 1 × 10¹⁰-4 × 10¹⁰ mol^-1 dm³ s^-1 range, single-electron-transfer reactions may also contribute to the mechanism. The Cl^• reactions with organic molecules in many respects are similar to those of ^•OH, albeit Cl^• seems to be less selective as ^•OH. However, there is an important difference, as opposed to Cl^• in the case of ^•OH single-electron-transfer reactions have minor importance. The uncertainty of Cl^• rate constant determinations is much higher than those of ^•OH. Since Cl^• reactions play very important role in the emerging UV/chlorine water purification technology, some standardization of the rate constant measuring techniques and more k_Cl• measurements are recommended.

Suspect, non-target and target screening of pharmaceuticals and personal care products (PPCPs) in a drinking water system

Drinking water quality and safety are very important in protecting human health. Chemical contaminants in drinking water system have become an increasing concern. Our knowledge about what chemicals are present in drinking water is still limited. Here we screened chemicals of emerging concern in a conventional drinking water system based on suspect, non-target screening and target analysis, and assessed their variations in different seasons and different treatment units. Overall, 720 chemicals were identified with HRMS databases from the suspect and non-target screening and 48 chemicals in five categories were further confirmed with the high confidence level, with predominance of pharmaceuticals and personal care products (PPCPs) and pesticides. Four compounds are newly found in aquatic environment with no literature or chemical occurrence data record. Temporal variations and variable removals were observed for these chemicals in the system. Target analysis of 110 PPCPs showed detection of 21, 19 and 22 compounds in the drinking water treatment plant with a concentration range of 0.11-844 ng/L in the three seasons, but only 8, 9 and 15 compounds detected in tap water (0.16-32.5 ng/L). The variations of the detected chemicals were less obvious in tap water, with most having concentrations below 2 ng/L. The results indicated efficient removal for most PPCPs in the drinking water system. The findings from this study demonstrated the strong capability of combined non-target screening and target analysis in identifying and assessing various organic chemicals in drinking water system.

High efficiency electrochemical disinfection of Pseudomons putida using electrode of orange peel biochar with endogenous metals

The electrochemical disinfection efficiency of Pseudomons putida was studied using ruthenium iridium coated titanium (RICT) electrode as anode and carbonized orange peel biochar (OPB) or graphite as the cathode. The results indicated that RICT/OPB system induced 6.5 and 7.0 log of P. putia inactivation after 60 s at 2 V and 45 s at 10 V, respectively. RICT/OPB system showed better efficiency than RICT/graphite system. The energy consumption of OPB cathode (17.5 Wh m^-3 per log) was significantly lower than that of graphite cathode (23.09 Wh m^-3 per log). Both anode and cathode played great roles on the disinfection. The anode absorbed electric energy to generate electrical hole, which can oxidize chloride ions to chlorine free radicals. The continuous porous structure of OPB can provide more adsorption sites and reduce electrolyte transport resistance, resulting in more Cl· production. Moreover, P. putia was much easier adsorbed to the anode surface in the RICT/OPB system because of the stronger electrostatic repulsion between cells and OPB cathode. As a result, P. putia was more easily inactivated by the Cl· produced on the anode. Besides chlorine active species, superoxide radical (O₂·﹣) produced on surface of cathode may also result in P. putia inactivation. The endogenous CuO in OPB can induce persistent free radicals (PFRs) production during pyrosis process. O₂·﹣ can be produced by O₂ activation through the function of Cu₂O/CuO and PFRs existed in OPB cathode. The more superoxide radical production led to the better disinfection effect than the graphite cathode. As a consequence, OPB electrode showed high efficiency electrochemical disinfection of P. putida.

Azole fungicides: (Bio)degradation, transformation products and toxicity elucidation

The increasing consumption of azole antifungal agents leads to their uncontrolled release into the environment. Therefore, it is crucial to remove their residues from natural ecosystems. This study aimed to examine the biological and chemical degradation of four typical azole fungicides: fluconazole (Fc), clotrimazole (Cl), climbazole (Cb), and epoxiconazole (Ep). The biodegradation was investigated using activated sludge and two novel Gram-negative bacterial strains. The chemical degradation experiments aimed to assess the efficiency of fungicides removal through UV treatment, the Fenton reaction, and a combination of these methods. Transformation products of Cb, Ep, and Cl photocatalytic removal were identified by mass spectrometry. In addition, the AlamarBlue® Assay and the MTT Assay allowed careful evaluation of the toxicity of azole derivatives and their transformation products towards newly isolated strains, Stenotrophomonas maltophilia AsPCl2.3 and Pseudomonas monteilii LB2. Among all azole fungicides, Cb was the most susceptible to biological removal while Fc, Ep, and Cl were basically resistant to biodegradation. Cl and Ep showed a significant biosorption on the activated sludge. Under optimized photolysis conditions, the removal efficiency of Cl, Cb, and Ep was significantly higher than that of biodegradation. The Fenton reaction supported by the UV-irradiation offered the best results of fungicides elimination. After 1 min of the experiment, Cl was almost completely removed while Cb and Ep removal rates reached an average of 60%. The proposed main degradation route of azole fungicides during UV-irradiation includes halogen atoms substitution by hydroxyl moieties. The final degradation product was imidazole or triazole. Azole fungicides and their transformation products differently affected the metabolic activity of Gram-negative bacteria. Cl and Cb intermediates showed lower toxicity than parent compounds. The findings help better understand the environmental impact of azole fungicides, their degradation, and toxicity. They also stress the need for reducing their uncontrolled release to the environment.

Biodegradation of typical azole fungicides in activated sludge under aerobic conditions

Widespread use of azole fungicides and low removal efficiency in wastewater treatment plants (WWTPs) have led to the elevated concentration of azole fungicides in receiving environment. However, there was limited research about the removal mechanism of azole fungicides in the biological treatment of WWTPs. Imidazole fungicide climbazole and triazole fungicide fluconazole were selected to investigate the biodegradation mechanism of azole fungicides in activated sludge under aerobic conditions. Climbazole was found to be adsorbed to solid sludge and resulted in quick biodegradation. The degradation of climbazole in the aerobic activated sludge system was fitted well by the first-order kinetic model with a half-life of 5.3 days, while fluconazole tended to stay in liquid and had only about 30% of loss within 77 days incubation. Ten biotransformation products of climbazole were identified by high resolution mass spectrometry using suspect and non-target screening method. But no biodegradation products of fluconazole were identified due to its limited removal. The possible biodegradation pathways for climbazole were proposed based on the products identification and pathway prediction system, and involves oxidative dehalogenation, side chain oxidation and azole ring loss. The findings from this study suggest that it should be a concern for the persistence of fluconazole in the environment.

Efficient Degradation of Organoarsenic by UV/Chlorine Treatment: Kinetics, Mechanism, Enhanced Arsenic Removal, and Cytotoxicity

Roxarsone (ROX) has been widely used as an organoarsenic additive in animal feeding operations and poses a risk to the environment. Here, we first report the efficient degradation of ROX by UV/chlorine, where the kinetics, removal of total arsenic (As), and cytotoxicity were investigated. The kinetics study presented that reactive chlorine species (RCS) and HO^• were the dominant species to react with ROX. Furthermore, the degradation rate of ROX can reach the maximum value at pH 7.5 due to the formation of more RCS. The degradation of ROX was affected by the amount of chlorine, pH, and water matrix. Through product analysis and Gauss theoretical calculation, two possible ROX degradation pathways were proposed. The free radicals attacked the As-C bond of ROX and resulted in releasing arsenate (As(V)). It was the reason that for an enhancement of the removal of total As by ferrous appeared after UV/chlorine, and over 98% of the total As was removed. In addition, cytotoxicity studies indicated that the cytotoxicity significantly enhanced during the degradation of ROX by UV/chlorine. However, by combination of UV/chlorine and adsorption, cytotoxicity can be greatly eliminated, probably due to the removal of As(V) and chlorinated products. These results further demonstrated that UV/chlorine treatment could be an effective method for the control of the potential environmental risks posed by organoarsenic.

Characterization of UV and chlorine contributions to transformation of 2,3,4-trihydroxybenzophenone under combined UV-chlorine treatment

Combined UV-chlorine treatment is a promising disinfection technology providing synergistic effects on bacteria-killing. The interaction between UV and chlorine would affect pollutants removal and disinfection by-products formation, while little is known about how UV and chlorine respectively contribute to pollutants transformation under combined UV-chlorine treatment. In this study, UV filter 2,3,4-trihydroxybenzophenone (2,3,4-THBP) was selected as a model compound to investigate the transformation characteristics and acute toxicity variation under combined UV-chlorine treatment. Especially, separative UV and chlorination treatments were conducted to illustrate their respective contribution in combined UV-chlorine treatment. It was found that the optimal removal percentage of 2,3,4-THBP under combined UV-chlorine treatment was 85.3% within 5 min and kept stable until 3 h at 3-equivalent (equiv.) of free available chlorine (FAC) and 1 mW/cm² of irradiation intensity. Correspondingly, acute toxicity of reaction mixture at 3 h increased twice as high as that of 2,3,4-THBP itself. Four transformation products were tentatively identified, and their formation possibly involved the reactions of chlorine substitution, oxidation, hydroxylation, and hydrolysis. FAC initiated the preliminary transformation of 2,3,4-THBP, and the synergistic effects of UV and chlorine promoted the further transformation of intermediates from chlorination treatment. Most important was that, 2,3,4-THBP could form some toxic products in the real ambient water matrix under solar irradiation, and acute toxicity of reaction mixture was 1.84 times higher than that of 2,3,4-THBP. This study would provide a better understanding on the transformation characteristics of pollutants under combined UV-chlorine treatment, and provide a reference for optimizing disinfection treatment.

Transformation of diazepam in water during UV/chlorine and simulated sunlight/chlorine advanced oxidation processes

Psychoactive drug diazepam is one of benzodiazepines widely used in human medicine. It has been found to be relatively resistant to chlorination and photolysis. Here we investigated the transformation mechanism of diazepam in aqueous solution through UV/chlorine and simulated sunlight/chlorine treatments. The results showed that the UV/chlorine and sunlight/chlorine processes significantly increased the degradation of diazepam in water. These observed degradations can be elucidated by in-situ generation of reactive species including hydroxyl radical (HO), reactive chlorine species (RCS) and ozone (O₃) during photolysis of chlorine. In the UV/chlorine treatment, the degradation efficiency of diazepam for HO, chlorine, UV and RCS reaction at 90 min was calculated to be 62.1%, 3.8%, 11.9% and 12.3%, respectively. In the simulated sunlight/chlorine treatment, the calculated degradation of 53.1%, 8.1% and 11.2% was attributed to HO, chlorine and RCS reaction, with negligible loss by O₃ reaction and sunlight irradiation. In the UV/chlorine and sunlight/chlorine treatments, a total of 70 transformation products was detected using a high-resolution TripleTOF mass system. Six transformation pathways have been tentatively proposed for the diazepam, which includes hydroxylation, chlorination, hydrolyzation, N-demethylation, loss of phenyl group, benzodiazepine ring rearrangement and contraction. Most of the obtained transformation products were less toxic to aquatic organisms including fish, daphnia and green algae than diazepam itself according to the toxicity prediction tool, and did not cause significant changes in toxicity to luminescent bacteria.

Energy-efficient erythromycin degradation using UV-LED (275 nm)/chlorine process: Radical contribution, transformation products, and toxicity evaluation

In this study, we investigated the degradation mechanism of erythromycin (ERY) during UV-LED/chlorine treatment using a 275-nm ultraviolet light-emitting diode (UV-LED). This wavelength is known to generate fewer disinfection byproducts (DBPs), and to have higher energy and photon yield efficiency compared to low pressure mercury (LP-UV) lamp which emits 254 nm of UV radiation. The degradation of ERY during the UV-LED/chlorine reaction followed pseudo-first-order kinetics. While Cl• and ClO• radicals along with other secondary radicals played key roles in the degradation of ERY at alkaline pH conditions, •OH radical was the main contributor at acidic pH conditions. Using ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-QToF-MS), we tentatively identified six byproducts. Trace amounts of DBPs, such as chloroform (CHCl₃) and chlorate (ClO₃^-) ions, were also detected at less than 0.3 mg/L. There was no residual antibiotic effect at the end of the UV-LED/chlorine reaction due to the complete degradation of important moieties, such as macrolide, in ERY. Toxicity decreased by 20% after 20 min during the UV-LED/chlorine process of ERY (1.0 mg/L) degradation. Finally, we confirmed the inactivation of ARB and ARG during the UV-LED/chlorine process.

Antibiotics in wastewater from multiple sources and surface water of the Yangtze River in Chongqing in China

Antibiotic contamination attracts growing concerns because of their deleterious effects on the ecosystem and human health. In this study, 43 antibiotics in wastewater from a variety of sources and water of the Yangtze River in Chongqing City in western China were measured. Thirty compounds were detected, and their concentrations were highest in leachates from the municipal solid waste treatment facilities (landfills and incineration plants) with total concentrations of 3584-57,106 ng/L. The total concentrations in influents of municipal and industrial wastewater treatment plants (WWTPs) were comparable (401-7994 ng/L versus 640-8945 ng/L). The concentrations in raw sewage from swine farms (with a total of 10,219-39,195 ng/L) and poultry farms (1419-36,027 ng/L) were noticeably higher than those from other farms (54.0-5516 ng/L). Fluoroquinolones were the dominant antibiotics contributing over 50% in all the sources, and sulfonamides and imidazole fungicides contributed 3.2-34%, whereas tetracyclines and macrolides had minor contributions. The overall antibiotic removal rates were highest in solid waste treatment facilities (88% on average), comparable between municipal and industrial WWTPs (61%), and lowest in animal farms (39%). The mass loads to the investigated municipal WWTPs via influent wastewater ranged from 7.80 to 1531 kg/year (53.2-2482 μg/day per capital). The influent mass loads to the industrial WWTPs and farms were 3.7-50 kg/year and 0.9-5437 g/year, respectively. We estimated that the mass inventories of antibiotics from these sources to the environment via effluent discharges were approximately 2044 kg for municipal WWTPs, 61 kg for industrial WWTPs, and 34 kg for animal farms in the whole city. Antibiotic concentrations in the Yangtze River water were substantially low (< 492 ng/L, with a mean of 57.8 ng/L) suggesting dissipation during the movement.

Enhanced ozonation of antibiotics using magnetic Mg(OH)2 nanoparticles made through magnesium recovery from discarded bischofite

Techniques for reutilization of the discarded bischofite are limited while efficient recovery of the Mg(OH)₂ nanoparticles from water during the synthesis and reuse processes is a challenge. In this study, the Fe₃O₄@Mg(OH)₂ core-shell magnetic nanoparticles were firstly prepared from discarded bischofite and used as catalyst for improving the ozonation of metronidazole (MNZ). The removal rate constant of MNZ increased by 694.7% using Fe₃O₄@Mg(OH)₂. Compared with the Mg(OH)₂ control, the MNZ removal rate constant of Fe₃O₄@Mg(OH)₂ treatment was almost tripled. The persistent high catalytic activity of the Fe₃O₄@Mg(OH)₂ catalyst was observed since the MNZ removal rate constant decreased by just 13.2% in the third reuse run. The Fe₃O₄@Mg(OH)₂ primarily enhanced ozone decomposition through producing hydroxyl radicals. The MNZ removal rate constant increased from 0.075 min^-1 to 0.643 min^-1 as catalyst dose increased from 0 to 0.6 g L^-1 while it decreased by 96.0% when its initial concentration increased from 10 to 200 mg L^-1. The maximum removal rate constant was observed at 25 °C when temperature increased from 15 °C to 35 °C. The Cl^-, HCO₃^-, SO₄^2-, Ca²⁺, Mg²⁺ ions could jeopardize MNZ degradation. The antibacterial activity of MNZ was eliminated after catalytic ozonation while the mineralization efficiency was almost doubled. The nitro group reduction and the cleavage of hydroxyethyl bond were two main transformation pathways of MNZ. These findings suggest that Fe₃O₄@Mg(OH)₂ nanoparticle made from discarded bischofite is the promising catalyst for the ozonation of antibiotics in the terms of water purification practice and reutilization of the bischofite.

Degradation of six typical pesticides in water by VUV/UV/chlorine process: Evaluation of the synergistic effect

Vacuum ultraviolet/ultraviolet/chlorine (VUV/UV/chlorine) is considered a novel advanced oxidation process (AOP), but little is known about its kinetics for pollutant degradation in water treatment. This study investigated the degradation of six typical pesticides, namely dimethoate (DMT), atrazine (ATZ), prometon (PMT), propoxur (PPX), bromacil (BRM) and propachlor (PPC), by VUV/UV/chlorine. The results show that all pesticides were rapidly degraded by VUV/UV/chlorine with a high removal efficiency of over 95% after 60 s. The pesticide degradation fitted well with pseudo-first-order reaction kinetics and a significant synergistic effect was observed during the VUV/UV/chlorine process. The synergistic factor (F_V/U/Cl) for DMT, ATZ, PMT, PPX, BRM and PPC were determined to be 1.75, 1.70, 2.06, 1.57, 2.84 and 1.61, respectively, indicating a synergistic improvement of 57%-184% for all pesticides. As hydroxyl radical (HO^•) transformed into reactive chlorine species (RCSs), the contribution ratio of RCSs for the pesticide degradation was much higher than that of HO^• in the VUV/UV/chlorine process, thus causing the synergistic effect. Solution pH ranging from 5.0 to 10.0 had various influence on the pesticide degradation by VUV/UV/chlorine. As initial concentration of free chlorine increased from 0 to 0.25 mM, the apparent rate constants of the pesticides kept on increasing while the F_V/U/Cl first increased and reached the highest value, and decreased afterwards. The formation of nitrite was significantly inhibited during the degradation of all pesticides by VUV/UV/chlorine. It suggests that VUV/UV/chlorine is a promising AOP for the pesticide degradation in water treatment.

A chloride-radical-mediated electrochemical filtration system for rapid and effective transformation of ammonia to nitrogen

Water contamination from ammonia has recently became a global concern. Herein, a chloride-radical-mediated electrochemical filtration system has been developed towards effective and rapid conversion of ammonia to nitrogen (N₂). This continuous-flow system consists of a nanoscale tin oxide modified carbon nanotube (SnO₂-CNT) anode and a Pd-Cu co-modified Ni foam (Pd-Cu/NF) cathode. The SnO₂-CNT anode enables the Cl^- oxidation to a chloride radical (Cl) at a proper anode potential (e.g., 2.5 V vs. Ag/AgCl) without severe self-oxidation. The macro-porous Pd-Cu/NF cathode further reduces anodic by-products (e.g., NO₃^- and NO₂^-) to N₂. EPR and scavenging tests indicate that Cl was the dominant radical specie responsible for ammonia conversion. Anode potentials, chloride concentration, flow rate and solution pH were identified as key parameters affecting the overall conversion performance. The proposed continuous-flow system showed enhanced conversion kinetics as compared to the conventional batch reactor due to the convectively enhanced mass transport. This study provides new insight for the rational design of advanced continuous-flow systems towards ammonia decontamination from water bodies.