Oxidative degradation of atenolol by heat-activated persulfate: Kinetics, degradation pathways and distribution of transformation intermediates

Highly stable carbon-coated nZVI composite Fe0@RF-C for efficient degradation of emerging contaminants

Nanoscale zerovalent iron (nZVI) has garnered significant attention as an efficient advanced oxidation activator, but its practical application is hindered by aggregation and oxidation. Coating nZVI with carbon can effectively addresses these issues. A simple and scalable production method for carbon-coated nZVI composite is highly desirable. The anti-oxidation and catalytic performance of carbon-coated nZVI composite merit in-depth research. In this study, a highly stable carbon-coated core-shell nZVI composite (Fe0@RF-C) was successfully prepared using a simple method combining phenolic resin embedding and carbothermal reduction. Fe0@RF-C was employed as a heterogeneous persulfate (PS) activator for degrading 2,4-dihydroxybenzophenone (BP-1), an emerging contaminant. Compared to commercial nZVI, Fe0@RF-C exhibited superior PS activation performance and oxidation resistance. Nearly 95% of BP-1 was removed within 10 min in the Fe0@RF-C/PS system. The carbon layer promotes the enrichment of BP-1 and accelerates its degradation through singlet oxygen oxidation and direct electron transfer processes. This study provides a straightforward approach for designing highly stable carbon-coated nZVI composite and elucidates the enhanced catalytic performance mechanism by carbon layers.

Matching periodate peak absorbance by far UVC at 222 nm promotes the degradation of micropollutants and energy efficiency

Periodate (PI)-based advanced oxidation processes have gained increasing interest. This study for the first time elevates the light-activation capacity of PI by using far UVC at 222 nm (UV222/PI) without extra chemical inputs. The effectiveness and the underlying mechanisms of UV222/PI for the remediation of micropollutants were studied by selecting atenolol (ATL) as a representative. PI possessed a high molar absorption coefficient of 9480-6120 M-1 cm-1 at 222 nm in the pH range of 5.0-9.0, and it was rapidly decomposed by UV222 with first-order rate constants of 0.0055 to 0.002 s-1. ATL and the six other organic compounds were effectively degraded by the UV222/PI process under different conditions with the fluence-based rate constants generally two to hundred times higher than by UVA photolysis. Hydroxyl radical and ozone were confirmed as the major contributors to ATL degradation, while direct photolysis also played a role at higher pH or lower PI dosages. Degradation pathways of ATL were proposed including hydroxylation, demethylation, and oxidation. The high energy efficiency of the UV222/PI process was also confirmed. This study provides a cost-effective and convenient approach to enhance PI light-response activity for the treatment of micropollutants.

Preparation of chitosan-iron oxide modified sludge-based biochar for effective removal of tetracycline from water: performance and mechanism

The release of antibiotics has attracted wide attention due to their abuse and discharge. How to remove these emerging contaminants is an urgent need to be solved. In the present study, sludge-based biochar combining chitosan and iron oxide was prepared via municipal sewage sludge. The novel biochar modified with chitosan and iron oxide exhibited satisfying performance in eliminating antibiotics from water. The application of modified biochar combined with activated persulfate (PS) showed a remarkable removal efficiency of 96.98% for tetracycline (TC). Analysis of the surface characteristics of the modified biochar showed the presence of structural defects, dispersed iron oxides, abundant functional groups, a porous structure, and a relatively stable crystal structure. These characteristics attributed significant importance to facilitating the degradation of TC. A series of experimental conditions including preparation temperature (600-900 ℃), reaction temperature (15-45 ℃), contaminant concentration (30-180 mg/L), adsorbent usage (0.1-1 g/L), pH (2-10), and persulfate addition concentration (1-5 mmol) were conducted. The results revealed that the highest removal efficiency was achieved at 96.98% under the conditions of TC concentration at 30 mg/L, reaction temperature at 35 ℃, pH of 4, adsorbent addition amount of 0.6 g/L, and PS concentration of 2 mmol, respectively. Three degradation pathways and seven intermediate products of TC were proposed. Therefore, our study provides a promising approach for developing effective removal of antibiotic pollutants.

Insights into degradation of pharmaceutical pollutant atenolol via electrochemical advanced oxidation processes with modified Ti4O7 electrode: Efficiency, stability and mechanism

A novel active Ce-doped Ti₄O₇ (Ti/Ti₄O₇-Ce) electrode was prepared and evaluated for improvement of the refractory pollutants degradation efficiency in Electrochemical advanced oxidation processes (EAOPs). The results showed that the addition of Ce in Ti/Ti₄O₇ electrode leading to great impact on •OH generation rate and electrode stability compared to pristine Ti/Ti₄O₇ electrode. Ti/Ti₄O₇-Ce electrode presented efficient oxidation capacity for pharmaceutical pollutant atenolol (ATL) in EAOPs, which could be attributed to the improvement of indirect oxidation mediated by electro-generated •OH, as the amount of •OH production was 16.5% higher than that in Ti/Ti₄O₇ within 120 min. The operational conditions greatly influenced the ATL degradation. The degradation efficiency of ATL increased as the current density, the degradation efficiency reached 100% under pH 4, but it just removed 81% of ATL under pH 10 after 120 min treatment. Results also suggested that the inhibiting effect from the ATL degradation was mostly associated with the decreased oxidation capacity induced by water hardness and natural organic matter (NOM). It displayed a satisfactory durability after 40 cycles of experimental detections in this research. The results of study suggested that Ti/Ti₄O₇-Ce was a promising electrode for the efficient degradation of PPCPs-polluted wastewater and provided constructive suggestion for the refractory pollutants of EAOPs.

Relationship between photolysis mechanism and photo-enhanced toxicity to Vibrio Fischeri for neonicotinoids with cyano-amidine and nitroguanidine structures

Neonicotinoids are widely used pesticides that contaminate aquatic environments. Although these chemicals can be photolyzed under sunlight radiation, it is unclear for the relationship between photolysis mechanism and toxicity change in aquatic organisms. This study aims to determine the photo-enhanced toxicity of four neonicotinoids with different main structures (acetamiprid, and thiacloprid for cyano-amidine structure, imidacloprid and imidaclothiz for nitroguanidine). To Achieve the goal, photolysis kinetics, effect of dissolved organic matter (DOM) and reactive oxygen species (ROSs) scavengers on photolysis rates, photoproducts, and photo-enhanced toxicity to Vibrio fischeri were investigated for four neonicotinoids. The results showed direct photolysis plays a key role in the photo-degradation of imidacloprid and imidaclothiz (photolysis rate constants are 7.85 × 10^-3 and 6.48 × 10^-3 min^-1, respectively), while the photosensitization process of acetamiprid and thiacloprid was dominated by ·OH reactions and transformation (photolysis rate constants are 1.16 × 10^-4 and 1.21 × 10^-4 min^-1, respectively). All four neonicotinoid insecticides exerted photo-enhanced toxicity to Vibrio fischeri, indicating photolytic product(s) posed greater toxicity than their parent compounds. The addition of DOM and ROS scavengers influenced photo-chemical transformation rates of parent compounds and their intermediates, leading to diverse effects on photolysis rates and photo-enhanced toxicity for the four insecticides as a result of different photo-chemical transformation processes. Based upon the detection of chemical structures of intermediates and Gaussian calculations, we observed different photo-enhanced toxicity mechanisms for the four neonicotinoid insecticides. Molecular docking was used to analyze the toxicity mechanism of parent compounds and photolytic products. A theoretical model was subsequently employed to describe the variability of toxicity response to each of the four neonicotinoids.

Degradation of Bisphonel AF (BPAF) by zero-valent iron activated persulfate: Kinetics, mechanisms, theoretical calculations, and effect of co-existing chloride

The removal of Bisphonel AF (BPAF) by zero-valent iron activated persulfate (Fe⁰/PS) system was systematically evaluated in this work. 30.0 μM BPAF was removed by 94.4% in 60 min of treatment under optimal conditions of pH = 3.0 and [PS] = [Fe⁰] = 3.0 mM. Cl^- significantly accelerated the removal of BPAF, resulting from accelerated Fe²⁺ release and reactive chlorine species (RCS) formation. Liquid chromatography-time-of-flight-mass spectrometry identified thirteen degradation products, and bond breaking, coupling reactions, hydroxylation and sulfate addition were considered as the major transformation pathways. When Cl^- was present, six new chlorinated byproducts were also generated. Based on density functional theory (DFT) calculations, the occurrence of radical addition reactions was verified and the preferential reaction channels were determined. Significantly BPAF degradation products were less toxic, according to toxicity assessment by the ECOSAR program. Moreover, a high removal efficiency of BPAF (>90%) was also obtained in the three actual water matrixes. The present work demonstrates the feasibility of Fe⁰/PS system for treating BPAF, which could also provide new insights into the influence of coexisting Cl^- on the environmental fate of organic pollutants in sulfate radicals based advanced oxidation processes.

Fate of typical organic halogen compounds in the coexistence of endogenic chlorine atoms and exogenic X. CHEMOSPHERE 2022;309:136761. [PMID: 36220428 DOI: 10.1016/j.chemosphere.2022.136761]

The transformation of halogenated organics in advanced oxidation processes (AOPs) has been extensively investigated. However, we currently know little about the fate of halogenated pollutants in the presence of exogenic halides (Cl^- or Br^-). Herein, the degradability, mineralization rate, and accumulation capacity of adsorbable organic halogen (AOX) for chlorophenols (2-chlorophenol (2-CP), 3-chlorophenol (3-CP), 4-chlorophenol (4-CP), and 2,4,6-trichlorophenol (TCP)) were compared in the Fe²⁺/persulfate (PS) process with the addition of exogenic halides. Results indicate that exogenic X^- can lead to a decrease in chlorophenols degradation and mineralization rate, undesirable accumulation of AOX, and generation of halogenated by-products which are more toxic than precursor chlorophenols. Results of kinetics modeling show that Cl₂^•- plays more important role than SO₄^•- with an addition of Cl^-, while SO₄^•-, Br₂^•-, and Br₂ are responsible for the effect of Br^-. As well, the effect of endogenic chlorine atoms on chlorophenols reveals that the degradability and AOX formation potential of 3-CP are highest while that of TCP are the lowest. This study demonstrates the significant influence of endogenic chlorine atoms and exogenic X^- on the fate of typical organic halogen compounds. Consequently, the X^- level and position/number of halogen atoms should be considered simultaneously when treating organohalogen compounds.

Heat-activated persulfate for the degradation of micropollutants in water: A comprehensive review and future perspectives

This work is a critical review of the most important studies that have dealt with heat-activated persulfate to degrade persistent micropollutants in the last six years. The effect of the different operating parameters is discussed, wherein in all cases, the efficiency was favored at higher temperatures and oxidant concentrations. Particular emphasis was given to the effect of the aqueous matrix. Since heat activation is a homogeneous process based on the production of free radicals, in most of the studies presented, the removal of pollutants decreases as the complexity of the aqueous matrix increases except in cases where secondary oxidative species are produced that are selective with specific pollutants. It has also been observed that the change in toxicity usually follows the removal of the parent compound despite the formation of several by-products. Nowadays, combining different processes for the simultaneous activation of persulfate seems to be gaining ground. A hybrid process is an interesting strategy to reduce costs and increase efficiency, especially in real wastewater. In this light, the most interesting studies of hybrid systems for the destruction of micropollutants in recent years based on thermally activated persulfate are also summarized. Finally, some steps are proposed for future research towards the industrial application, including the study of chemical mixtures, the integrated toxicity assessment, the examination of simultaneous disinfection and decomposition of pollutants into real wastewater, the estimation of the required costs, and energy the combination of processes and their coupling with renewable sources, and the design of pilot plants and the scale-up of the hybrid processes.

A comprehensive review on persulfate activation treatment of wastewater

With increasingly serious environmental pollution and the production of various wastewater, water pollutants have posed a serious threat to human health and the ecological environment. The advanced oxidation process (AOP), represented by the persulfate (PS) oxidation process, has attracted increasing attention because of its economic, practical, safety and stability characteristics, opening up new ideas in the fields of wastewater treatment and environmental protection. However, PS does not easily react with organic pollutants and usually needs to be activated to produce oxidizing active substances such as sulfate radicals (SO₄^-) and hydroxyl radicals (OH) to degrade them. This paper summarizes the research progress of PS activation methods in the field of wastewater treatment, such as physical activation (e.g., thermal, ultrasonic, hydrodynamic cavitation, electromagnetic radiation activation and discharge plasma), chemical activation (e.g., alkaline, electrochemistry and catalyst) and the combination of the different methods, putting forward the advantages, disadvantages and influencing factors of various activation methods, discussing the possible activation mechanisms, and pointing out future development directions.

Sensitivity Analysis with the Monte Carlo Method and Prediction of Atenolol Removal Using Modified Multiwalled Carbon Nanotubes Based on the Response Surface Method: Isotherm and Kinetics Studies

Atenolol (ATN) is a β-blocker drug extensively used to treat arrhythmias and high blood pressure. Because the human body cannot metabolize it completely, this drug has been commonly found in many environmental matrices. In the present study, the response surface method (RSM) was used for adsorption prediction of ATN on modified multiwalled carbon nanotubes (M-MWCNTs) by NaOCl and ultrasonic. The sensitivity analysis was done by the Monte Carlo method. Sensitivity analysis was performed to determine the effective parameter by the Monte Carlo simulator. Statistical analysis of variance (ANOVA) was performed by using the nonlinear second-order model of RSM. The influential parameters including contact time (min), adsorbent dosage (g/L), pH, and the initial concentration (mg/L) of ATN were investigated, and optimal conditions were determined. Kinetic of ATN adsorption on M-MWCNTs was evaluated using pseudo-first, pseudo-second-order, and intraparticle diffusion models. Equilibrium isotherms for this system were analyzed by the ISOFIT software. As per our result, optimum conditions in the adsorption experiments were pH 7, 60 min of contact time, 0.5 mg/L ATN initial concentration, and 150 mg/L adsorbent dose. In terms of ATN removal efficiency, coefficients of R2 and adjusted R2 were 0.999 and 0.998, respectively. Sensitivity analysis also showed that contact time has the greatest effect on increasing the removal of ATN. Pseudo-first-order (R2 value of 0.99) was the best kinetic model for the adsorption of ATN, and for isotherm, BET (AICC value of 3.27) was the best model that fit the experimental data. According to the obtained results from sensitive analysis, time was the most important parameter, and after that, the adsorbent dose and pH affect positively on ATN removal efficiency. It can be concluded that the modified multiwalled carbon nanotubes can be applied as one of the best adsorbents to remove ATN from the aqueous solution.

Degradation of methyl orange by pyrite activated persulfate oxidation: mechanism, pathway and influences of water substrates

Degradation mechanism of methyl orange (MO), a typical azo dye, with pyrite (FeS₂) activated persulfate (PS) was explored. The results showed that when the initial concentration of MO was 0.1 mM, FeS₂ was 1.6 g/L and PS was 1.0 mM, the removal rate of MO could reach 92.9% in 150 min, and the removal rate of total organic carbon could reach 14.1%. In addition, both pH ≤ 2 and pH ≥ 10 could have an inhibitory effect in the FeS₂/PS system. Furthermore, Cl^- and low concentrations of HCO^-₃ had little effect on the degradation of MO with FeS₂/PS. However, H₂PO^-₄ and high concentrations of HCO^-₃ could inhibit the degradation of MO in the system. Besides, MO in river water and tap water were not degraded in FeS₂/PS system, but acidification (pH = 4) would greatly promote the degradation. In addition, the removal rate of MO with FeS₂/PS could still reach about 90% after five cycles of FeS₂. Furthermore, the intermediates and possible degradation pathways were speculated by LC-MS, and the degradation mechanism of MO by FeS₂/PS was that the cycle of Fe(III)/Fe(II) could continuously activate persulfate to produce SO₄^•-. The results could provide technical support for azo dye degradation in the FeS₂/PS system.

Amlodipine removal via peroxymonosulfate activated by carbon nanotubes/cobalt oxide (CNTs/Co3O4) in water

Amlodipine (AML) is an effective drug that has been widely used for hypertension and angina. However, AML is frequently detected in aqueous environments, posing potential risks to human and ecological health. In this study, the degradation of AML via peroxymonosulfate (PMS) activated by CNTs/Co₃O₄ was investigated. CNTs/Co₃O₄ was prepared via a facile method, and multiple characterizations suggested that Co₃O₄ were uniformly dispersed on the surface of MWCNTs-COOH. Experimental results indicated that complete removal of 10 μM AML was achieved within 30 min by using 2 mg/L CNTs/Co₃O₄ and 4 μM PMS at 25 °C in PBS buffered solution (pH 7.0). The observed pseudo-first-order rate constant was calculated to be 0.1369 min^-1. Interestingly, the presence of 100 mM Cl^- resulted in a slight enhancement of AML removal rate from 0.0528 to 0.0642 min^-1. The addition of 100 mM HCO₃^-, 5 mg/L Pony Lake fulvic acid (PLFA), or Suwannee River humic acid (SRHA) retarded AML degradation by 15.5, 0.7, and 1.6 times, respectively. As per the quenching experiments, SO₄^⦁- rather than ⦁OH were verified to be the dominant reactive oxygen species (ROS). Additionally, ten major intermediates were identified using TOF-LC-MS and three associated reaction pathways including ether bond broken, H-abstraction, and hydroxylation were proposed. We outlook these findings to advance the feasibility of organic contaminants removal via CNTs/Co₃O₄ + PMS systems that have extremely low-level PMS.

Effective degradation of 2,4-dihydroxybenzophenone by zero-valent iron powder (Fe0)-activated persulfate in aqueous solution: Kinetic study, product identification and theoretical calculations

2,4-Dihydroxybenzophenone (BP-1), a typically known derivative of the benzophenone-type UV filter, has been frequently detected in aqueous environments and poses a potential risk to human health and the entire ecosystem. In this study, an effective advanced oxidation technique using zero-valent iron powder (Fe⁰)-activated persulfate (PS) was used for the degradation of BP-1. The effects of several experimental parameters, including Fe⁰ dosages, PS dosages, pH, and common natural water constituents, were systematically investigated. The BP-1 degradation efficiency was enhanced by increasing the Fe⁰ and PS dosages and decreasing the solution pH. The presence of different concentrations of humic acid (HA) could inhibit BP-1 removal, while the addition of various cations and anions had different effects on the degradation. Moreover, the degradation of BP-1 in five water matrices was also compared, and the removal rates followed the order of ultrapure water > tap water > secondary clarifier effluent > river water > synthetic water. Thirteen oxidation products were identified by liquid chromatography-time-of-flight-mass spectrometry (LC-TOF-MS) analysis, and five possible degradation pathways were proposed. The addition reactions initiated by HO and SO₄^-, as well as single-electron coupling reactions and ring-closing reactions, were further supported by density functional theory (DFT) calculations. Assessment of toxicity of intermediates of the oxidation of BP-1 suggested decreased toxicity from the parent contaminant. The present work illustrates that BP-1 could be efficiently degraded in the Fe⁰/PS system, which may provide new insights into the removal of benzophenones in water and wastewater.

Synergistic mechanism and degradation kinetics for atenolol elimination via integrated UV/ozone/peroxymonosulfate process

The present research systematically investigates the atenolol (ATL) degradation in integrated UV/Ozone (O₃)/peroxymonosulfate (PMS) process focusing on the synergistic mechanism, reaction kinetics, pollutant degradation pathway and antibacterial activity. The results manifested that the integrated UV/O₃/PMS process showed the noteworthy superiority to ATL degradation compared with UV/PMS, UV/O₃ and O₃/PMS systems. Simultaneously, the impacts of operating parameters like PMS dosage, initial ATL concentration, solution pH and water matrix were comprehensively explored. The ATL elimination efficiency increased linearly with PMS dose and significantly enhanced in alkaline conditions. The ^•OH and SO₄^•- were the primary reactive radicals for ATL oxidation in UV/O₃/PMS system based on the radical scavenging experiments and electron paramagnetic resonance characterization. Besides, a simplified kinetic model on the basis of the dominant reactions and the steady-state assumption was established to foretell the relative contributions of reactive oxidants for ATL elimination in UV/O₃/PMS process. Main transformation products were determined via UPLC-QTOF-MS to infer the possible degradation pathways of ATL. Furthermore, the UV/O₃/PMS process could distinctly mitigate the antibacterial activity of ATL and its intermediates to E. coli and B. subtilis. Our findings may have critical implications for the development of novel oxidation processes for recalcitrant contaminants mitigation in water purification.

Degradation of aniline by ferrous ions activated persulfate: Impacts, mechanisms, and by-products

Wastewater contains a large number of anions and organics which can scavenge reactive radicals and limit the application of sulfate radical-based advanced oxidation processes (SR-AOPs) in practical engineering. Here, we studied the removal rate and mechanism of aniline by SR-AOPs in different influencing factors, such as sodium persulfate dosage, ferrous ions dosage, solution pH, Cl^-, HCO₃^-, NO₃^-, and other organic matter. By recognizing and analyzing free radicals, we concluded that SO₄^•- plays a major role in aniline degradation. The aniline removal rate increased with the initial concentrations of persulfate and ferrous ions, but aniline degradation was inhibited by excessive dosage. The aniline removal rate by ferrous-ions-catalyzed persulfate was higher under acidic conditions and could be improved under alkaline conditions if no ferrous ions were added. The addition of bicarbonate ions inhibited aniline removal, and the addition of nitrate ions barely caused the effect. While the addition of chloride ions promoted aniline degradation, which was confirmed that HClO generated from the reacting of Cl^- and persulfate played a key role. However, TOC indicated that aniline was not completely mineralized in the process. Further analysis of the products from GC-MS demonstrated that chloride-ion additions produced some harmful halogenated by-products. Our results can act as a basis for developing processes for the aniline degradation in wastewater.

The defluorination of perfluorooctanoic acid by different vacuum ultraviolet systems in the solution

Perfluorooctanoic acid (PFOA) is one kind of persistent organic pollutants that is often detected in water. In recent years, the effective degradation technologies of PFOA have attracted widespread attentions. Thus, in this study, the defluorination efficiency of PFOA in different systems (i.e., ultraviolet (UV), vacuum ultraviolet (VUV), vacuum ultraviolet/persulfate (VUV/PS) and vacuum ultraviolet/residual chlorine (VUV/RC)) was evaluated. Moreover, the different impact factors (i.e., the initial concentrations of persulfate and PFOA, temperature, anions, and initial pH values) on PFOA degradation by VUV/PS system were investigated. The results showed that VUV system was more effective than UV system for PFOA defluorination. VUV system combined with persulfate would further enhance the defluorination efficiency while residual chlorine would decrease it. In VUV/PS system, the defluorination efficiency of PFOA was the best as the molar ratio of PFOA and persulfate at 1:60. Moreover, higher temperature, lower initial PFOA concentration, and acid condition were favorable for the defluorination of PFOA. Under the different influence factors, the defluorination efficiency of PFOA fitted well to the first-order reaction kinetic model. When the temperature was range from 20°C to 40°C, the value of activation energy was 8.73 kJ/mol. Besides, the inhibition effect of three kinds of anions on PFOA defluorination followed the order: NO 3 -  > Cl^-  >  CO 3 2 - . PRACTITIONER POINTS: The defluorination efficiency of perfluorooctanoic acid (PFOA) in water by different VUV systems was compared. VUV system is more effective than UV system for PFOA defluorination. Persulfate will enhance the defluorination efficiency by VUV system. Hypochlorite will decrease the defluorination efficiency by VUV system.

Preparation of porous silicate supported micro-nano zero-valent iron from copper slag and used as persulfate activator for removing organic contaminants

Porous silicate supported micro-nano zero-valent iron (PSi@ZVI) was prepared from copper slag (CS) through carbothermal reduction technology, and used as a persulfate (PS) activator for removing organic contaminants. Results showed that the properties of the activator were greatly affected by the preparation conditions. Calcination for 20 min at 1100 °C with 20% anthracite was considered the optimum preparation condition for degradation of orange G (OG). The removal rate of OG was improved by increasing the dosages of PSi@ZVI or PS and raising the reaction temperature. Moreover, PSi@ZVI exhibited excellent PS activator ability in a wide range of initial pH, good degradation capability for eosin Y, methyl orange, acid fuchsine, and methylene blue. The reusability and safety of PSi@ZVI were verified. Electron paramagnetic resonance and radical quenching tests indicated that sulfate radical (SO₄^-) was the main active species in the PSi@ZVI/PS system. The X-ray diffraction results indicated that a high calcination temperature (1100 °C) was beneficial to the reduction of iron-bearing minerals to ZVI. Scanning electron microscopy and energy-dispersive spectroscopy results revealed that the formation of porous structure of PSi@ZVI and the generation of nano to micro-sized ZVI particles on the surface of the silicate holes. The X-ray photoelectron spectra showed that ZVI was first convert into Fe(II), which mainly activated PS and generated Fe(III) in the PSi@ZVI/PS system. Furthermore, the intermediates of OG were detected using gas chromatography-mass spectrometry, and the possible degradation pathway of OG was proposed. This study provides a novel approach for reuse of CS as a heterogeneous activator to effectively activate PS.

Determination methods for steady-state concentrations of HO• and SO4•- in electrochemical advanced oxidation processes

Competitive kinetics and scavenging assay are commonly used for radical quantification. However, the accuracy of the two methods has been challenged in electrochemical advanced oxidation processes (EAOPs) since the strong reactivity of electrode against organic indicators may disrupt the quantitative relationship between indicator consumption and radical concentration. The present study focused on screening suitable indicators and developing suitable methods for determining the steady-state concentrations of SO₄^•- and HO^• ([SO₄^•-]_ss and [HO^•]_ss) in several EAOPs for water treatment based on competitive kinetics and scavenging assay. The applicability of the modified methods and available indicators were investigated through experimental and kinetic analysis. In anode alone process, the competitive kinetics was more appropriate than scavenging assay and benzoic acid (BA) met the basic requirement of being a competitor to determine the [HO^•]_ss. In cathode alone process, BA was more resistant to interfering factors than other competitors (ibuprofen, atrazine and nitrobenzene) and its reaction rate involved only the radical oxidation even when the reaction conditions varied over a wide range. Therefore, the [HO^•]_ss could be obtained by the competitive kinetic equation of BA when HO^• existed alone. When HO^• coexisted with SO₄^•-, a two-step method combining scavenging assay and competitive kinetics was proposed to measure [SO₄^•-]_ss and [HO^•]_ss, in which tert-butyl alcohol and BA were added as scavenger and competitor, respectively. Furthermore, the reliability of each approach was verified by the experimental results and kinetic analysis.

Cu2+ activated persulfate for sulfamethazine degradation

Sulfonamide antibiotics (SAs) are widely used in veterinary medicine but are poorly metabolized in biological systems; thus, they can cause a selective pressure to promote the proliferation of antibiotic resistant pathogens and threaten human health. Persulfate (PS)-based advanced oxidation processes (AOPs) have been applied for SA degradation, but using transition metal ions as PS activators is relatively limited. In this study, sulfamethazine (SMZ) was used as a model SA to evaluate the performance of a Cu²⁺ -activated PS system. Cu²⁺-PS exhibited better SMZ removal than other metal ions, and 25 mg/L SMZ can be degraded in the presence of 0.2 mM Cu²⁺ and 2.5 g L^-1 PS within 120 min. Various anions inhibited SMZ degradation to different degrees except HCO₃^-. Among the cations, Fe³⁺ significantly inhibited SMZ removal, while Ni²⁺ increased the removal rate. High concentrations of humic acid and protein also increased the degradation rate of SMZ. Radical and singlet oxygen quenching experiments, together with the results of electron spin-resonance spectroscopy (ESR), showed that the main active species generated from Cu²⁺-PS are SO₄·^- and ·OH. The degradation pathway of SMZ was identified through HPLC-HRMS. Direct SO₄·^- and ·OH oxidation products of SMZ were not found, suggesting that the complex formed between Cu²⁺ and SMZ may affect the fate of SMZ. On the other hand, the efficiency and selectivity of Cu²⁺-PS against different SAs were confirmed. Overall, this study provides a facile and effective method for SMZ and other SA removal.

Efficient removal of triclosan via peroxymonosulfate activated by a ppb level dosage of Co(II) in water: Reaction kinetics, mechanisms and detoxification

Triclosan (TCS), an extensively used broad-spectrum antimicrobial agent, has raised significant environmental concerns regarding its widespread occurrence in waters. In this study, the removal of TCS in aqueous solution via peroxymonosulfate (PMS) activated by an extremely low-level Co²⁺ (0.02 μM) was systematically investigated. During preliminary test, TCS (10 μM) was totally degraded in 30 min by using 0.1 μM Co²⁺ and 40 μM PMS at pH 7.0 with a degradation rate constant of 0.1219 min^-1. A first-order apparent degradation rate of TCS was found with respect to the PMS concentrations. At extremely low dosage of Co²⁺ (0.02 μM), the presence of NO₃^-, HCO₃^-, PLFA, and SRHA within test concentrations significantly inhibited TCS removal, while a dual effect of Cl^- on the degradation rate of TCS was observed. The quenching experiments verified that SO₄^- was the dominant reactive oxygen species (ROS) rather than OH. Six major intermediates were identified using TOF-LC-MS, based on which we proposed three associated reaction pathways including hydroxylation, ether bond breakage, and dechlorination. Toxicity predictions by ECOSAR software exhibited aquatic toxicity reduction of TCS after Co²⁺/PMS treatment. We outlook these findings to advance the feasibility of organic contaminants removal via Co²⁺/PMS system with Co²⁺ at extremely low levels.

Enhanced catalytic degradation of tetracycline antibiotic by persulfate activated with modified sludge bio-hydrochar

In this research, a one-pot prepared modified sludge bio-hydrochar (IBHC) was prepared to activate persulfate (PS) for the degradation of tetracycline (TC) antibiotic. The obtained IBHC bearing defect structure, dispersed iron and large amounts of surface organic functional groups, acts as an outstanding modified biomass carbonaceous material for catalyzing PS to improve the removal efficiency of TC as high as 99.72%. The IBHC + PS system can remove TC effectively with a relative low IBHC dosage (0.2 g·L^-1), limited PS consumption (5 mmol·L^-1) and wide pH values (2-10). In addition, the degradation of TC still keep in 94.70% after 5 rounds reuse proving that IBHC possesses excellent stability and practicability. During the activation, both and ^•OH were generated and the contribution of each component on the TC degradation in IBHC + PS system was explored. Furthermore, the degradation pathways of TC were proposed based on the results of LC-MS.

Advanced landfill leachate biochemical effluent treatment using Fe-Mn/AC activates O3/Na2S2O8 process: process optimization, wastewater quality analysis, and activator characterization

A novel catalyst of Fe-Mn/AC was prepared and used as a heterogeneous catalyst to activate O₃/Na₂S₂O₈ for landfill leachate biochemical effluent treatment. The experimental results indicated that the highest COD (84%) and color (98%) removal was obtained at Fe-Mn/AC dosage 1.2 g/L, O₃ concentration 1.2 g/L, Na₂S₂O₈ dosage 6 g/L, initial pH 10, and reaction time 100 min. Three-dimensional and excitation emission matrix (3D-EEM) fluorescence spectrometry, Fourier transform infrared spectroscopy (FTIR), and gas chromatography mass spectrometry (GC/MS) of wastewater samples before and after treatment demonstrated that the leachate biochemical effluent contained a large amount of humic and fulvic acid organic compounds. After treatment with this coupling system, both the pollution level of dissolved organic matter (DOM) and the fluorescence intensity declined. The micro morphology of Fe-Mn/AC was characterized using scanning X-ray diffraction patterns (XRD), electron microscope spectra (SEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) spectroscopy. It can be concluded that the microscopic morphology of the catalyst is porous. The main active components are amorphous MnO₂ and multivalent iron oxides. Furthermore, the Fe-Mn/AC catalyst showed great reusability; the removal efficiency of COD was only reduced from 84% to 79% at the fourth reaction. Moreover, the COD removal efficiency could recover to 81% after catalyst regeneration.

Photolysis and photo-induced toxicity of pyraclostrobin to Vibrio fischeri: Pathway and toxic mechanism

Pyraclostrobin is a fungicide used widely across the world. However, its photolysis pathway and toxic mechanism is unclear. In this study, photolysis and photo-induced toxicity of pyraclostrobin to Vibrio fischeri were determined. The results showed that direct photolysis dominated the degradation of pyraclostrobin. Gas Chromatography-Mass spectrometry and quantum chemical calculation revealed that the pyraclostrobin was firstly photo-degraded into Methyl N-phenyl-carbamate and 1-(4-chlorophenyl)-3-hydroxy-1H-pyrzole, synthetic intermediates of pyraclostrobin, then into aniline, benzoquinone and acids. Toxicity assay showed that bioluminescent inhibition rate to V. fischeri fluctuated with radiation/illumination time and the toxicity curve can be classified into three phases (Phase I: 0-10 min, incline; Phase II: 10-60 min, decline; Phase III: 60-120 min, incline). The up-and-down curve indicates the change of parent compound during the photolysis. Simulation of molecular docking showed that the CDOCKER interaction energy of pyraclostrobin (-44.71) lower than other intermediate products (>-30.00), indicating that the parent compound is more toxic than its intermediates. An increased toxicity observed in the toxicity curve was attributed to the generation of benzoquinone with log1/EC₅₀ of 6.73, which can greatly change structure of target luciferase in Vibrio fischeri. In addition, the addition of radical scavengers can inhibit the bioluminescence of the tested solutions, indicating the involvement of radicals in the transformation of intermediates. This paper reveals that one of photochemical transformation products of pyraclostrobin can cause more toxic than its parent compound to bacteria. Environmental risk assessment should consider not only the parent compound, but also its metabolites.

Electrocoagulants Characteristics and Application of Electrocoagulation for Micropollutant Removal and Transformation Mechanism

Predominantly, the removal of dissolved contaminates via the Fe electrocoagulation (EC) process depends on the electrocoagulants stability, specific area, porosity, dissolution rate, and phase transformation kinetics. The present investigation elucidates the role of applied currents and electrolyte counteranions on the crystalline phase and surface topography of electrocoagulants generated from Fe EC. Moreover, the dissolved contaminant micropollutant removal efficiency was also evaluated by electrochemically produced coagulants. This study confirms that mixed-phase iron (oxyhydr) oxide nanostructures were consistently produced from Fe EC with predominant formation of the goethite phase. The applied current controls the morphology of the coagulants, with flake-like morphology observed with currents at and below 100 mA and spherical morphology observed with currents above 100 mA. The counteranions in the electrolyte also impacted the morphology with spherical, nanosheet, and nanorod morphologies produced by Cl^- or SO₄^2-, CO₃^2-, and HCO₃^- counteranions, respectively. BET analysis revealed the formation of electrocoagulants with micro-, meso-, and macropores. Surface area was markedly reduced from 142.85 to 41.96 m² g^-1 by incident coagulation resulting from increased anodic dissolution. Applicability of the electrocoagulant was examined by different micropollutants (acetaminophen (AC), antipyrine (AT), and atenolol (AT)). Results suggest that >90% and >80% TOC reduction were achieved with Na₂CO₃ and NaHCO₃ as electrolyte media. The lower TOC reduction was rationalized by the identified intermediate products, and possible micropollutant degradation pathways were proposed based on LC-MS/MS analysis.

The efficient degradation of organic pollutants in an aqueous environment under visible light irradiation by persulfate catalytically activated with kaolin-Fe2O3

Characterizations and properties of catalysts.

Study of the atenolol degradation using a Nb/BDD electrode in a filter-press reactor

The present paper deals with the atenolol (ATL) degradation by advanced anodic oxidation using a boron-doped diamond anode supported on niobium (Nb/BDD). Cyclic voltammetry performed on this electrode revealed that it presents a high quality (diamond-sp³/sp²-carbon ratio), high potential for OER and that ATL can be oxidized directly and/or indirectly by the electrogenerated oxidants, such as hydroxyl radicals, persulfate ions and sulfate radicals. Electrolysis experiments demonstrated that ATL degradation and mineralization follow a mixed (first and zero) order kinetics depending on the applied current density. At high applied current densities, the amount of OH radicals is very high and the overall reaction is limited by the transport of ATL (pseudo first-order kinetics) whereas for low applied current densities, the rate of OH radicals generation at the anode is slower than the rate of arrival of ATL molecules (pseudo-zero order kinetics). Estimated values of k_zero and k_first based on the assumption of pseudo-zero or pseudo-first order kinetics were carried oud as a function of the supporting electrolyte concentration, indicating that both parameters increased with its concentration due the higher production of sulfate reactive species that play an important role in degradation. Finally, MCE increased with the decrease of current density, due to the lower amount of OH present in solution, since this species could be rapidly wasted in parasitic reactions; and the increase of sulfate concentration due to the more efficient production of persulfate.

Transformation of atenolol by a laccase-mediator system: Efficiencies, effect of water constituents, and transformation pathways

In this study, we investigated the transformation of atenolol (ATL) by the naturally occurring laccase from Trametes versicolor in aqueous solution. Removal efficiency of ATL via laccase-catalyzed reaction in the presence of various laccase mediators was examined, and found that only the mediator 2, 2, 6, 6-tetramethyl-1-piperidinyloxy (TEMPO) was able to greatly promote ATL transformation. The influences of TEMPO concentration, laccase dosage, as well as solution pH and temperature on ATL transformation efficiency were tested. As TEMPO concentrations was increased from 0 to 2000 μM, ATL transformation efficiency first increased and then decreased, and the optimal TEMPO concentration was determined as 500 μM. ATL transformation efficiency was gradually increased with increasing laccase dosage. ATL transformation was highly pH-dependent with an optimum pH of 7.0, and it was almost constant over a temperature range of 25-50 °C. Humic acid inhibited ATL transformation through competition reaction with laccase. The presence of anions HCO₃^- and CO₃^2- reduced ATL transformation due to both anions enhanced solution pHs, while Cl^-, SO₄^2-, and NO₃^- at 10 mM showed no obvious influence. The main transformation products were identified, and the potential transformation pathways were proposed. After enzymatic treatment, the toxicity of ATL and TEMPO mixtures was greatly reduced. The results of this study might present an alternative clean strategy for the remediation of ATL contaminated water matrix.

Data for persulfate activation by UV light to degrade theophylline in a water effluent

The aim of this study was to degrade theophylline (TP) drug in a pharmaceutical effluent solution utilizing persulfate (PS). A simulated and a real effluent solution were used, with different conditions tested to optimize the degradation process. HPLC analyses and a modified-HPLC method were used to track concentrations of TP and PS respectively in the treatment process. Experiments were done in triplicates and treated data is presented as graphs. A detailed analyses of this study can be found in the article “Degradation of theophylline in a UV₂₅₄/PS system: matrix effect and application to a factory effluent” [1] published in Chemical Engineering Journal.

Enhanced Cu(II)-mediated fenton-like oxidation of antimicrobials in bicarbonate aqueous solution: Kinetics, mechanism and toxicity evaluation

Increasing attention has been attracted in developing new technologies to remove chlorofene (CF) and dichlorofene (DCF), which were active agents in antimicrobials for general cleaning and disinfecting. This study investigated the significant influences of bicarbonate (HCO₃^-) on the degradation of CF and DCF in the Cu(II)-mediated Fenton-like system Cu²⁺/H₂O₂. Our results indicate that HCO₃^- may play a dual role to act 1) as a ligand to stabilize Cu(II), forming soluble [Cu^II(HCO₃^-)(S)]⁺ species to catalyze H₂O₂ producing hydroxyl radical (OH) and superoxide ion (O₂^-) and 2) as a OH scavenger. Furthermore, the reaction kinetics, mechanisms, and intermediates of CF and DCF were assessed. The apparent rate constants of CF and DCF were enhanced by a factor of 8.5 and 5.5, respectively, in the presence of HCO₃^- at the optimized concentration of 4 mM. Based on the intermediate identification and frontier electron densities (FEDs) calculations, the associated reaction pathways were tentatively proposed, including C-C scission, single or multiple hydroxylation, and coupling reaction. In addition, significant reduction in the aquatic toxicity of CF and DCF was observed after treatment with Cu²⁺/H₂O₂-HCO₃^- system, evaluated by Ecological Structure Activity Relationships (ECOSAR) program. These findings provide new insights into Cu(II)-mediated reactions to better understand the environmental fate of organic contaminants in carbonate-rich waters.

BiOCl facilitated photocatalytic degradation of atenolol from water: Reaction kinetics, pathways and products

Atenolol (ATL), a kind of largely used beta-blockers, has been widely detected in the aquatic environment, which could cause adverse impact on human beings. In this study, bismuth oxychloride (BiOCl) photocatalyst was synthesized and applied to remove ATL in the aqueous system under simulated natural light. Emphasis was laid on the reaction kinetics and the impact of natural organic matter (NOM) (0-20 mg/L). Possible transformation pathways were systematically investigated based on identification of reaction products via liquid chromatography-mass spectrometry (LC-MS). As a consequence, BiOCl presents highly photocatalytic efficiency yielding up to nearly 100% ATL conversion after 60 min of interaction, together with fairly high photostability evidenced by considerably efficient removal of ATL after 10 catalytic cycles. Four kinds of possible products are detected using LC-MS in the process of reaction, indicating possible transformation ways of ATL photocatalysis. NOM has an inhibiting impact on the removal of ATL and influences the products distribution. This study provides an emerging nanocatalyst for ATL photodegradation and could eventually lead to development of novel methods to control pharmaceutical contamination in water.

Chemically and thermally activated persulfate for theophylline degradation and application to pharmaceutical factory effluent

Degradation of PPCPs by AOPs has gained major interest in the past decade. In this work, theophylline (TP) oxidation was studied in thermally (TAP) and chemically (CAP) activated persulfate systems, separately and in combination (TCAP). For [TP]₀ = 10 mg L⁻¹, (i) TAP resulted in 60% TP degradation at [PS]₀ = 5 mM and T = 60 °C after 60 min of reaction and (ii) CAP showed slight degradation at room temperature; however, (iii) TCAP resulted in complete TP degradation for [PS]₀ = [Fe²⁺]₀ = 2 mM at T = 60 °C following a pseudo-first order reaction rate with calculated k_obs = 5.6 (±0.4) × 10⁻² min⁻¹. In the TCAP system, the [PS]₀ : [Fe²⁺]₀ ratio of 1 : 1 presented the best results. A positive correlation was obtained between the TP degradation rate and increasing temperature and [PS]₀, and a negative correlation was obtained with increasing pH. Both chloride and humic acid inhibited the degradation process, while nitrates enhanced it. TP dissolved in spring, sea and waste water simulating real effluents showed lower degradation rates than in DI water. Waste water caused the highest inhibition (k_obs = 2.6 (±0.6) × 10⁻⁴ min⁻¹). Finally, the TCAP system was tested on a real factory effluent highly charged with TP, e.g. [TP]₀ = 160 mg L⁻¹, with successful degradation under the conditions of 60 °C and [PS]₀ = [Fe²⁺]₀ = 50 mM.

Chemically activated persulfate in heated medium showed synergistic effect toward full degradation of theophylline in industrial factory effluents. This makes such AOP a well-adapted technology to treat highly concentrated hazardous pharmaceuticals.

Kinetic and mechanistic investigations of the degradation of propranolol in heat activated persulfate process

This study investigated the heat activated persulfate (heat/PS) process in the degradation of propranolol from water. Various factors (e.g., temperature, persulfate dose, initial pH and natural water constituent) on PRO degradation kinetics have been investigated. The results showed that the PRO degradation followed a pseudo-first-order kinetics pattern. As temperature rises, the pseudo-first-order rate constant (k obs) was improved significantly, and the k obs determined at 40-70 °C satisfied the Arrhenius equation, yielding an activation energy of 99.0 kJ mol-1. The radical scavenging experiments and the EPR tests revealed that both SO4˙- and ·OH participated in degrading PRO, with SO4˙- playing a dominant role. Higher PS concentration and neutral pH favored PRO degradation. The impact of Cl- and HCO3 - were concentration-dependent. A lower concentration of Cl- and HCO3 - could accelerate PRO degradation, while the presence of HA showed inhibitory effects. Seven degradation products were recognized through LC/MS/MS analysis. Cleavage of ether bond, hydroxylation, and ring-opening of naphthol moiety are involved in the PRO's degradation pathway. Finally, the formation of disinfection byproducts (DBPs) before and after pre-treated by heat/PS was also evaluated. Compared with direct chlorination of PRO, the heat/PS pre-oxidation greatly impacted the DBPs formation. The higher PRO removal efficiency in natural water indicated the heat/PS process might be capable of treating PRO-containing water samples, however, its impacts on the downstream effect on DBPs formation should be also considered.