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

Comparison of UV/H2O2, UV/PMS, and UV/PDS in Destruction of Different Reactivity Compounds and Formation of Bromate and Chlorate

In this study, we compared the decontamination kinetics of various target compounds and the oxidation by-products (bromate and chlorate) of PMS, PDS, and H₂O₂ under UV irradiation (UV/PMS, UV/PDS, UV/H₂O₂). Probes of different reactivity with hydroxyl and sulfate radicals, such as benzoic acid (BA), nitrobenzene (NB), and trichloromethane (TCM), were selected to compare the decontamination efficiency of the three oxidation systems. Experiments were performed under acidic, neutral, and alkaline pH conditions to obtain a full-scale comparison of UV/peroxides. Furthermore, the decontamination efficiency was also compared in the presence of common radical scavengers in water bodies [bicarbonate, carbonate, and natural organic matter (NOM)]. Finally, the formation of oxidation by-products, bromate, and chlorate, was also monitored in comparison in pure water and tap water. Results showed that UV/H₂O₂ showed higher decontamination efficiency than UV/PDS and UV/PMS for BA degradation while UV/H₂O₂ and UV/PMS showed better decontamination performance than UV/PDS for NB degradation under acidic and neutral conditions. UV/PMS was the most efficient among the three processes for BA and NB degradation under alkaline conditions, while UV/PDS was the most efficient for TCM degradation under all pH conditions. In pure water, both bromate and chlorate were formed in UV/PDS, small amounts of bromate and rare chlorate were observed in UV/PMS, and no detectable bromate and chlorate were formed in UV/H₂O_2. In tap water, no bromate and chlorate were detectable for all three systems.

In-situ debromination mechanism based on self-activation and catalysis of Ca(OH)2 during pyrolysis of waste printed circuit boards

Completely and deeply removed bromide from waste printed circuit boards (WPCBs) is necessary due to their toxicity and carcinogenicity. To achieve this purpose, calcium hydroxide (Ca(OH)₂) as a debromination agent was added during pyrolysis process of WPCBs. The results showed that hydrogen bromide (HBr), 4-bromophenol, 2-bromophenol and 2,4-dibromophenol were the main bromide species in pyrolysis products. The Ca(OH)₂ plays a significant role for removing HBr and organic bromide, but not affects products yield. Optimal removal efficiency for 4-bromophenol, 2-bromophenol and 2,4-dibromophenol reached 87.5 %, 74.6 % and 54.5 %, respectively. And debromination efficiency was related to the steric hindrance caused by bromide atoms. The Ca(OH)₂ can be activated by captured HBr and its thermal decomposition. And the newly-generated calcium bromide and calcium oxide significantly facilitate debromination due to their high surface energy and reactivity. The debromination mechanism was clarified by experiments coupled with computational chemistry: the coordination of bromide and calcium to form [Ph-Br···Ca²⁺] or [Ph-Br···Ca_atom]. Then, electrons were delivered form bromide atom to Ca²⁺ or Ca_atom, which resulted in the stretch and weaken the C-Br bond. Hence, the C-Br bond was more easily to break. This work can provide support for designing novel and efficient debromination agents applied for high-temperature system.

UV-Catalyzed Persulfate Oxidation of an Anthraquinone Based Dye

Wastewater from the textile industry has a substantial impact on water quality. Synthetic dyes used in the textile production process are often discharged into water bodies as residues. Highly colored wastewater causes various of problems for the aquatic environment such as: reducing light penetration, inhibiting photosynthesis and being toxic to certain organisms. Since most dyes are resistant to biodegradation and are not completely removed by conventional methods (adsorption, coagulation-flocculation, activated sludge, membrane filtration) they persist in the environment. Advanced oxidation processes (AOPs) based on hydrogen peroxide (H2O2) have been proven to decolorize only some of the dyes from wastewater by photocatalysis. In this article, we compared two very different photocatalytic systems (UV/peroxydisulfate and UV/H2O2). Photocatalyzed activation of peroxydisulfate (PDS) generated sulfate radicals (SO4•−), which reacted with the selected anthraquinone dye of concern, Acid Blue 129 (AB129). Various conditions, such as pH and concentration of PDS were applied, in order to obtain an effective decolorization effect, which was significantly better than in the case of hydroxyl radicals. The kinetics of the reaction followed a pseudo-first order model. The main reaction pathway was also proposed based on quantum chemical analysis. Moreover, the toxicity of the solution after treatment was evaluated using Daphnia magna and Lemna minor, and was found to be significantly lower compared to the toxicity of the initial dye.

Elucidating sulfate radical-mediated disinfection profiles and mechanisms of Escherichia coli and Enterococcus faecalis in municipal wastewater

Practical applications of disinfection technologies for engineered waters require an in‒depth understanding of disinfection profiles and mechanisms of pathogenic bacteria in a complex matrix. This study investigated the inactivation of E. coli and E. faecalis by SO₄^•-, an emerging advanced disinfectant, in ultrapure water (UPW) and wastewater effluent (WE). Based on the bacterial inactivation kinetics in UPW in a zerovalent iron/peroxydisulfate system, the second order rate constants (k) for SO₄^•- reacting with E. coli and E. faecalis were measured to be (1.39 ± 0.1) × 10⁹ M^-1 s^-1 and (6.71 ± 0.1) × 10⁹ M^-1 s^-1, respectively. The morphological images of both bacteria by the scanning electron microscope indicated that SO₄^•- initiates oxidative reactions on the wall/membranes, causing their irreversible damage, ultimately affecting membrane permeability and physiological functions. To profile the inactivation kinetics of two strains of bacteria in WE matrix, a mechanistic process‒based model with the obtained k values was developed. Sensitivity and uncertainty analyses indicated that the key parameters for the model predictions were the concentrations of halide ions (i.e., Br^- and Cl^-) in WE and their k values reacting with SO₄^•- accounting for >80% of uncertainty or variance expected in predicted bacterial inactivation. This model allows precise estimation of required disinfectant dose even in complex water matrices, shedding lights on the extension of application of SO₄^•-‒based technology in wastewater treatments.

Experimental and theoretical insights into kinetics and mechanisms of hydroxyl and sulfate radicals-mediated degradation of sulfamethoxazole: Similarities and differences

Hydroxyl radical (^•OH)- and sulfate radical ()-based advanced oxidation technologies (AOTs) have been proven an effective method to remove antibiotics in wastewater treatment plants (WWTPs). This study aims to gain insights into kinetics and mechanisms of neutral sulfamethoxazole (SMX) degradation, a representative antibiotic, by ^•OH and using an experimental and theoretical approach. First, the second-order rate constants (k) of SMX with ^•OH and were determined to be (7.27 ± 0.43) × 10⁹ and (2.98 ± 0.32) × 10⁹ M^-1 s^-1 in UV/H₂O₂ and UV/persulfate (UV/PS) systems, respectively. The following theoretical calculations at the M06-2X level of theory revealed that addition of radicals to the benzene ring is the most favorable first-step reaction for both ^•OH and , but that exhibits higher energy barriers and selectivity than ^•OH due to steric hindrance. We further analyzed subsequent reactions and, interestingly, our findings closely corroborated HOMO/LUMO distributions of SMX to the oxidation pathways. Finally, the estimation of energy consumption for UV alone, ^•OH-, and -mediated oxidation processes was compared. These comparative results, for the first time, provide insights into the similarities and differences of degradation of SMX by ^•OH/ at the molecular level and can help improve antibiotics removal using radical based AOTs in WWTPs.

An experimental and theoretical study on the degradation of clonidine by hydroxyl and sulfate radicals

Emerging contaminants such as pharmaceuticals that cannot be completely removed by traditional biological treatments are ubiquitously present in water bodies with detected concentrations ranging from ng L^-1 to mg L^-1. Advanced oxidation technologies (AOTs) are promising, efficient, and environmentally friendly for the removal of these pharmaceuticals. In this study, we investigated the degradation kinetics of a model pharmaceutical, clonidine (CLD), via hydroxyl radical (OH) in UV/H₂O₂ and sulfate radical (SO₄^•-) in UV/peroxydisulfate (PS) systems for the first time. The second-order rate constants (k) of protonated cationic CLD with OH and SO₄^•- were measured to be (2.15 ± 0.07) × 10⁹ M^-1 s^-1 and (1.12 ± 0.03) × 10⁹ M^-1 s^-1, respectively. We also calculated the pK_a value of CLD and thermodynamic behaviors for reactions of CLD/HCLD⁺ with OH and SO₄^•- at M05-2X/6-311++G**//M05-2X/6-31+G** level with SMD solvation model. The pK_a value was calculated to be 8.14, confirming the literature value. H atom abstraction pathway was the most favorable pathway for both OH and SO₄^•-, while single electron transfer pathway was thermodynamically feasible only for SO₄^•- for CLD but not for HCLD⁺. In addition, the reactivities of both tautomeric forms of CLD (i.e., amino and imino CLD) with both radicals were also investigated. This study contributed to a better understanding on the degradation mechanisms of CLD and proposed the possibilities of the elimination of pharmaceuticals by applying AOTs during wastewater treatment processes.

Experimental and theoretical insight into hydroxyl and sulfate radicals-mediated degradation of carbamazepine

Carbamazepine (CBZ), a widely detected pharmaceutical in wastewaters, cannot currently be treated by conventional activated sludge technologies, as it is highly resistant to biodegradation. In this study, the degradation kinetics and reaction mechanisms of CBZ by hydroxyl radical (OH) and sulfate radical ()-based advanced oxidation processes (AOPs) were investigated with a combined experimental/theoretical approach. We first measured the UV absorption spectrum of CBZ and compared it to the theoretical spectrum. The agreement of two spectra reveals an extended π-conjugation system on CBZ molecular structure. The second-order rate constants of OH and with CBZ, measured by competition kinetics method, were (4.63 ± 0.01) × 10⁹ M^-1 s^-1 and (8.27 ± 0.01) × 10⁸ M^-1 s^-1, respectively at pH 3. The energetics of the initial steps of CBZ reaction with OH and were also calculated by density functional theory (DFT) at SMD/M05-2X/6-311++G**//M05-2X/6-31 + G**level. Our results reveal that radical addition is the dominant pathway for both OH and . Further, compared to the positive ΔG_R⁰ value for the single electron transfer (SET) reaction pathway between CBZ and OH, the ΔG_R⁰ value for SET reaction between CBZ and is negative, showing that this reaction route is thermodynamically favorable. Our results demonstrated the remarkable advantages of AOPs for the removal of refractory organic contaminants during wastewater treatment processes. The elucidation of the pathways for the reaction of OH and with CBZ are beneficial to predict byproducts formation and assess associated ecotoxicity, providing an evaluation mean for the feasibility of AOPs application.

Comparison of the oxidation of halogenated phenols in UV/PDS and UV/H2O2 advanced oxidation processes

UV/peroxydisulfate (PDS) and UV/hydrogen peroxide (H₂O₂) can effectively degrade halophenols (HPs, e.g., 2,4-bromophenol and 2,4,6-trichlorophenol); meanwhile, information about the discrepancies in the related degradation kinetics and mechanisms of these two processes is limited. To gain this knowledge, the degradation of two typical HPs (i.e., bromophenols and chlorophenols) in UV/PDS and UV/H₂O₂ processes were investigated and compared. The results showed that the degradation rates of HPs with different substitution positions in the UV/PDS process were in the order of para-substituted HPs (i.e., 4-BP and 4-CP) > ortho-substituted HPs (i.e., 2-BP and 2-CP) > meta-substituted HPs (i.e., 3-BP and 3-CP), while in the UV/H₂O₂ process, these rates were in the order of para-substituted HPs > meta-substituted HPs > ortho-substituted HPs. These discrepancies were ascribed to the different reaction activities of SO₄˙⁻ and HO˙ with HPs, which were calculated based on the competition method. Further density functional theory (DFT) calculations suggested that SO₄˙⁻ reacts more readily with HPs via electron transfer than HO˙. In the presence of water matrices (such as Cl⁻, HCO₃⁻ and natural organic matter (NOM)), the degradation of 2-BP in both UV/PDS and UV/H₂O₂ treatment processes was inhibited due to the scavenging of free radicals by these background substances. The degradation products and pathways further confirmed that SO₄˙⁻ is a strong one-electron oxidant that reacts with HPs mainly via electron transfer, while HO˙ reacts with HPs via electron transfer and hydroxyl addition.

The oxidation of halogenated phenols with different substitution positions in UV/PDS and UV/H₂O₂ processes was compared.

Sulfate radical-based oxidation of an alcohol ethoxylate (Brij30®) by the PS/UV-C process

In this study, sulfate radical-based oxidation of an alcohol ethoxylate (AE) was explored by the persulfate (PS)/UV-C process. Poly(oxyethylene)(4)laurylether, commercially known as Brij30^®, was used as a model AE. PS/UV-C oxidation of aqueous Brij30^® (8-20 mg/L) was performed at initial PS concentrations varying between 0.50 and 6.50 mM and at initial pH values of 3.0 and 6.0. Results indicated that an increase in both initial PS and Brij30^® concentrations did not have a significant effect on Brij30^® removal efficiency and that Brij30^® abatements of more than 90% could be achieved after 60 min of treatment time. Total organic carbon (TOC) removals were significantly improved with increasing initial PS concentrations for both initial pH values. On the other hand, an increase in initial Brij30^® concentration had a negative effect on mineralization. By employing the competitive kinetic method, the second-order reaction rate coefficient of Brij30^® with the sulfate radical (SO₄ ^•-) was determined as 1.62 × 10⁹ ± 3.5 × 10⁷ M^-1s^-1. The second-order reaction rate constant of TOC, originating from Brij30^® and reaction intermediates, was found to be 9.09 × 10⁵ ± 2.91 × 10⁵ M^-1s^-1 and 1.13 × 10⁶ ± 0.46 × 10⁶ M^-1s^-1 for pH values of 6.0 and 3.0, respectively. Toxicity of PS/UV-C treated aqueous Brij30^® solutions towards Vibrio fischeri was also investigated to determine the possible toxic behavior of oxidation products.

Efficient degradation of pharmaceutical micropollutants in water and wastewater by FeIII-NTA-catalyzed neutral photo-Fenton process

Ferric-nitrilotriacetate complex (Fe^III-NTA) has been adopted to catalyze the photo-Fenton degradation of emerging pharmaceutical micropollutants in water and wastewater at neutral pH. The generation of hydroxyl radicals (HO) in UVA/Fe^III-NTA/H₂O₂ was identified by using electron spin resonance (ESR) trapping technique. The effects of critical parameters (e.g., NTA:Fe^III molar ratio, Fe^III-NTA and H₂O₂ dosages) on the steady-state HO concentrations were studied in terms of the degradation of carbamazepine (CBZ, as a model compound) in Milli-Q water. In addition, the degradation of pharmaceuticals mixtures (including CBZ, crotamiton (CRMT) and ibuprofen (IBP)) in wastewater effluents from a biological aerated filter (BAF) by UVA/Fe^III-NTA/H₂O₂ was studied in continuous-flow mode. The results showed that the efficacies of Fe^III-NTA in catalyzing photo-Fenton degradation of pharmaceuticals in wastewater effluents were comparable to those obtained by Fe^III-ethylenediamine-N,N'-disuccinic acid (Fe^III-EDDS), and far exceeded other Fe^III-L complex (e.g., citric acid, malonic acid, oxalic acid and tartaric acid). More than 92% degradation efficiencies of CBZ, CRMT and IBP were obtained in continuous-flow mode under the given conditions of 0.178 mM Fe^III-NTA (1:1), 4.54 mM H₂O₂, UVA intensity 4.05 mW cm^-2, hydraulic retention time (HRT) 2 h, influent pH 7.6 (±0.2) and temperature 20 °C. The results presented herein suggest that Fe^III-NTA-catalyzed neutral photo-Fenton reaction can be an alternative tertiary process for the treatment of pharmaceutical micropollutants in secondary wastewater effluents.

Experimental and theoretical investigation on photodegradation mechanisms of naproxen and its photoproducts

The photochemical degradation of the pharmaceuticals and personal care products (PPCPs) has attracted increasing attention. In this study, a deep inspection of the photolysis mechanisms of naproxen and its photoproducts has been performed by employing experimental and theoretical methods. Contributions of different reactive oxygen species (ROS, such as OH, ¹O₂, and O₂^-) in the photolysis reaction also have been clarified. Based on the detected intermediates and DFT calculations, several photodegradation pathways of naproxen and its photoproducts have been proved. Furthermore, the deprotonated form of naproxen has been confirmed to be more reactive than the protonated one, and the lowest triplet state of naproxen is the reactive state. The decarboxylation mechanism of naproxen has been fully discussed. Meanwhile, the free energy barriers of OH-induced photolysis reactions (ΔG^‡_eff(1a) = 7.6 kcal mol^-1, ΔG^‡_eff(4a) = 7.0 kcal mol^-1) are much lower than the free energy barriers induced by O₂^- and ¹O₂. It proves that OH is the most favourable one among the three ROS. The similar inhabition rates and free energy barriers of reactions induced by O₂^- and ¹O₂, respectively, have demonstrated that O₂^- and ¹O₂ equally contribute to the degradation. Additionally, the computational results are coincident with the observed experimental findings. Hence, this work has verified a part of naproxen photodegradation mechanism under UV irradiation and brought about a rational way to investigate contributions of different ROS in the complex photochemical system of PPCPs.

Intensification of UV-C tertiary treatment: Disinfection and removal of micropollutants by sulfate radical based Advanced Oxidation Processes

This study explores the enhancement of UV-C tertiary treatment by sulfate radical based Advanced Oxidation Processes (SR-AOPs), including photolytic activation of peroxymonosulfate (PMS) and persulfate (PS) and their photocatalytic activation using Fe(II). Their efficiency was assessed both for the inactivation of microorganisms and the removal or micropollutants (MPs) in real wastewater treatment plant effluents. Under the studied experimental range (UV-C dose 5.7-57 J/L; UV-C contact time 3 to 28 s), the photolysis of PMS and PS (0.01 mM) increased up to 25% the bacterial removal regarding to UV-C system. The photolytic activation of PMS led to the total inactivation of bacteria (≈ 5.70 log) with the highest UV-C dose (57 J/L). However, these conditions were insufficient to remove the MPs, being required oxidant's dosages of 5 mM to remove above 90% of carbamazepine, diclofenac, atenolol and triclosan. The best efficiencies were achieved by the combination of PMS or PS with Fe(II), leading to the total removal of the MPs using a low UV-C dosage (19 J/L), UV-C contact time (9 s) and reagent's dosages (0.5 mM). Finally, high mineralization was reached (>50%) with photocatalytic activation of PMS and PS even with low reagent's dosages.

Reclamation of agro-wastewater polluted with pesticide residues using sunlight activated persulfate for agricultural reuse

The removal of 17 pesticides (pymetrozine, flonicamid, imidacloprid, acetamiprid, cymoxanil, thiachloprid, spinosad, chlorantraniliprole, triadimenol, tebuconazole, fluopyram, difenoconazole, cyflufenamid, hexythiazox, spiromesifen, folpet and acrinathrin) found in agro-wastewater from washing of containers and phytosanitary treatments equipment, has been carried out using sodium persulfate (Na₂S₂O₈) at pilot plant scale under natural sunlight. Persulfate is a strong oxidant, inexpensive and environmentally appropriate. However, this oxidant is slow in kinetics under ordinary conditions. Na₂S₂O₈ can be activated by ultraviolet light, generating SO₄^- radicals, which are also a very strong oxidizing species (E₀ = 2.6 V). Previously, preliminary experiments were carried out at laboratory scale using a photoreactor to optimize the Na₂S₂O₈ (300 mg L^-1) concentration on the rate constants of the found pesticides. The residual levels of the studied pesticides in agro-wastewater (900 L) were in the range 0.02-1.17 mg L^-1 for acrinathrin and fluopyram, respectively. After treatment, nearly complete degradation (>97%) of the parent molecules was achieved although 13% of initial DOC was measured. No significant differences (p < 0.05) were found when comparing grown broccoli using reclaimed and unreclaimed water.

Rate constants of sulfate radical anion reactions with organic molecules: A review

The rate constants of sulfate radical anion reaction (k_SO4-) with about 230 organic molecules of environmental interest are tabulated and discussed, together with both the methods of rate constant determinations and the reaction mechanisms. k_SO4-'s were collected from the original publications. The highest values in the ∼10⁹ M^-1 s^-1 range are published for aromatic molecules. There is a tendency that electron donating substituents increase and electron withdrawing substituents decrease these values. There are just a few compounds with rate constants established using different techniques in different laboratories. k_SO4-'s determined in different laboratories by the direct techniques, pulse radiolysis or laser flash photolysis, in most cases agree reasonably. The values determined by competitive experimental techniques, by complex kinetics calculations, or by modelling show a large scatter. Some of these techniques seem to be questionable for k_SO4- determination. The sulfate radical anion reacts with ketone and amine moieties of molecules by electron transfer. The same mechanism is also suggested for the reaction with aromatic rings. However, in a few cases addition to the double bond and sulfate anion elimination reactions were distinguished. A typical reaction with the aliphatic parts of the molecule is H-abstraction.

The application of aged refuse in nitrification biofilter: Process performance and characterization

High adsorption capacity, good biocompatibility and low cost are highly demanded for biofilter used in ammonium-rich wastewater treatment. In this study, we used SEM, BET, XRD and 16S rRNA to document the evidence for good performance in adsorption and biodegradation in aged refuse. Parallel experiment between raw and inert refuse showed ammonium adsorption occurred at the initial week, with the highest ammonium removal efficiency of 90.36%, but saturated during the subsequent long-term operation. Meanwhile, over 6months' operation of an aged refuse biofilter was conducted to confirm that nitrification was the main pathway of ammonium conversion. The maximum nitrogen loading rate could reach up to as high as 1.28kg/m³/d, with ammonium removal efficiency at 99%. Further, high nitrifier biodiversity were detected with 'Nitrosomonas' and 'Nitrospira' in domination in the refuse. However, Nitrospira would outcompete Nitrosomonas under the oxygen limiting condition and resulted in the failure of partial nitrification. The physicochemical and biological analysis show that biodegradation is the main ammonium conversion pathway, which is the critical finding of this work. This investigation would help to accelerate the application of the aged refuse process in ammonium-rich wastewater treatment.

Quick start-up and stable operation of a one-stage deammonification reactor with a low quantity of AOB and ANAMMOX biomass

In this study, a quick start-up of one-stage deammonification in an immobilized aerobic ammonium oxidizing bacteria (AOB) and anoxic ammonium oxidizing (ANAMMOX) bacteria up-flow reactor (IAAR) was successfully achieved. With the aid of gel layers, AOB and ANAMMOX bacteria had excellent spatial distribution, theoretically meeting dissolved oxygen requirements for the simultaneous processes of aerobic and anaerobic ammonium oxidizing. The results indicated that an IAAR containing 0.4 g-VSS L^-1 immobilized biomass achieved a nitrogen removal rate (NRR) of 0.53 kg-N m^-3 d^-1 after only 10 days of operation and subsequently reached a maximum nitrogen removal rate (NRR_max) of 3.73 kg-N m^-3 d^-1. The micro-profiles of DO and pH were measured using microelectrodes to help understand the stratification of the microbial processes inside the gel layers. The distribution of AOB and ANAMMOX bacteria within the gel layers was verified using fluorescence in situ hybridization (FISH) analysis. The community distribution in the FISH three-dimensional images closely corresponded to the micro-profiles of DO concentration and pH, enabling rapid adaptation and stable operation of the reactor seeded with a quite low quantity of biomass.

Kinetics and modeling of artificial sweeteners degradation in wastewater by the UV/persulfate process

The frequent detection of artificial sweeteners (ASs) in wastewater and surface water gives rise to concerns about their removal, Acesulfame (ACE) and sucralose (SUC) are two ASs that are difficult to remove. The ultraviolet/persulfate (UV/PS) advanced oxidation technology (AOT) is being considered as an effective process for the degradation of micropollutants in wastewater. However, the study of the degradation of ASs in real wastewater by the UV/PS is minimal. This study investigated the kinetics and modeling of ACE and SUC degradation in wastewater by the UV/PS process. Both ACE and SUC could be degraded effectively using this process. The degradation of ACE was mainly attributed to UV photolysis (51%), HO^∙ (26%) and SO₄^∙- (16%), while that of SUC was mainly attributed to HO^∙ (68%) and SO₄^∙- (27%). The second-order rate constants of ASs with SO₄^∙- were significantly lower than that with HO^∙. Three major transformation products (TPs) of ACE and four major TPs of SUC were identified. Additionally, the effects and mechanisms of the water matrices, such as HCO₃^-, Cl^-, NO₃^- and natural organic matter (NOM), on ASs degradation were investigated through response surface methodology (RSM). NOM and Cl^- significantly inhibited the degradation of ACE in the UV/PS system, whereas NOM and HCO₃^- played a main inhibition role on the degradation of SUC. A water matrices parameter model for predicting ASs degradation in real wastewater was established by RSM for the first time, and the removal of ACE and SUC was well predicted by the model.

Assessment of full-scale tertiary wastewater treatment by UV-C based-AOPs: Removal or persistence of antibiotics and antibiotic resistance genes?

This research reports for the first time the full-scale application of different homogeneous Advanced Oxidation Processes (AOPs) (H₂O₂/UV-C, PMS/UV-C and PMS/Fe(II)/UV-C) for the removal of antibiotics (ABs) and antibiotic resistance genes (ARGs) from wastewater effluent at Estiviel wastewater treatment plant (WWTP) (Toledo, Spain). AOPs based on the photolytic decomposition of H₂O₂ and peroxymonosulfate tested at low dosages (0.05-0.5 mM) and with very low UV-C contact time (4-18 s) demonstrated to be more efficient than UV-C radiation alone on the removal of the analyzed ABs. PMS (0.5 mM) combined with UV-C (7 s contact time) was the most efficient treatment in terms of AB removal: 7 out of 10 ABs detected in the wastewater were removed more efficiently than using the other oxidants. In terms of ARGs removal efficiency, UV-C alone seemed the most efficient treatment, although H₂O₂/UV-C, PMS/UV-C and PMS/Fe(II)/UV-C were supposed to generate higher concentrations of free radicals. The results show that treatments with the highest removal of ABs and ARGs did not coincide, which could be attributed to the competition between DNA and oxidants in the absorption of UV photons, reducing the direct photolysis of the DNA. Whereas the photolytic ABs removal is improved by the generation of hydroxyl and sulfate radicals, the opposite behavior occurs in the case of ARGs. These results suggest that a compromise between ABs and ARGs removal must be achieved in order to optimize wastewater treatment processes.

Characterizing the removal routes of seven pharmaceuticals in the activated sludge process

The removal routes of pharmaceuticals especially biodegradation routes in the activated sludge process are still unclear. Some studies indicated pharmaceuticals were mainly removed via nitrification process (autotrophic biodegradation), while others suggested pharmaceuticals were mainly removed via COD degradation process (heterotrophic biodegradation). These unclear problems limited the improvements of pharmaceuticals removal. In this study, in order to elucidate three biodegradation routes (nitrification, COD degradation, or both nitrification and COD degradation), autotrophic and heterotrophic reactors were individually developed to separate nitrification and COD degradation form the activated sludge process (mix-trophic process including nitrification and COD degradation). Furthermore, the pharmaceuticals removal routes of adsorption, hydrolysis, and oxidation were also studied. Among six degradable pharmaceuticals, heterotrophic biodegradation and adsorption were the major removal routes. Two sulfonamides of five antibiotics were predominantly removed by COD degradation process, while nitrification and adsorption had no contributions. Adsorption, hydrolysis, nitrification, and COD degradation were the main elimination routes of cefalexin. COD degradation and adsorption were the dominant removal routes of norfloxacin. Tetracycline was mainly removed by the adsorption route, and hydrolysis and oxidation also played a role. For two drugs, ibuprofen was removed mainly via nitrification and COD degradation, and no adsorption occurred. Diclofenac could not be removed at all and was persistent in the aerobic conditions. Kinetic studies showed that biodegradation of the two sulfonamides, cefalexin, norfloxacin, and ibuprofen followed first-order kinetics rather than zero-order or second-order kinetics.

Mechanistic Study on the Role of Soluble Microbial Products in Sulfate Radical-Mediated Degradation of Pharmaceuticals

The role of soluble microbial products (SMP), the most important component of effluent organic matter from municipal wastewater treatment plants, in sulfate radical (SO₄^•-)-based advanced oxidation technologies (AOTs) remains substantially unclear. In this study, we first utilized a suite of macro- and microanalytical techniques to characterize the SMP from a membrane bioreactor for its fundamental molecular, spectroscopic, and reactivity properties. The degradation kinetics of three representative pharmaceuticals (i.e., naproxen, gemfibrozil, and sulfadiazine) in the presence of SMP was significantly reduced as compared to in its absence. Possible mechanisms for the interference by SMP in degrading these target compounds (TCs) were investigated. The low percentage of bound TCs to SMP ruled out the cage effect. The measurement of steady-state ¹O₂ concentration indicated that formation of ¹O₂ upon UV irradiation on SMP was not primarily responsible for the degradation of TCs. However, the comparative and quenching results reveal that SMP absorbs UV light acting as an inner filter toward the TCs, and meanwhile scavenges SO₄^•- with a high second-order rate constant of 2.48 × 10⁸ M_C^-1 s^-1.

Pharmaceuticals and pesticides in secondary effluent wastewater: Identification and enhanced removal by acid-activated ferrate(VI)

The emergence of resistance to antibacterial drugs and pesticides in water is unprecedented. This may have adverse consequences to human health and ecological systems. This paper first sought the identification of a wide range of pharmaceuticals and pesticides in two secondary effluent wastewaters (SEW) of different quality characteristics, followed by their removal by ferrate(VI) (Fe(VI), FeO₄^2-). Screening for 22 pharmaceuticals and 32 pesticides, revealed that 11 pharmaceuticals and 3 pesticides in SEW of plant A, and 14 pharmaceuticals and 5 pesticides in SEW of plant B were present at concentrations higher than the liquid chromatography mass spectrometry method quantitation limit. The concentrations of pharmaceuticals and pesticides ranged from 0.15 ng/L-413.03 ng/L. Investigation of the removal of these pharmaceuticals and pesticides by Fe(VI) showed that some had recalcitrant activity towards their oxidation. Acid-activated Fe(VI) resulted in enhanced oxidation (12.6%-56.2% degradation efficiency) of 6 and 7 pharmaceuticals in SEW of plant A and plant B, respectively, at a shorter time than Fe(VI) without activation (i.e. 3-5 min versus 15-30 min). The degradation of 1 and 3 pesticides in SEW of plant A and plant B respectively, has also been enhanced by activating Fe(VI) (13.8%-86.2% degradation efficiency). Results on testing of organic matter characterization of treated SEW with and without acid-activated Fe(VI) treatment are also presented. Acid-activated Fe(VI) treatment has potential in enhancing the removal of micropollutants in real wastewater.

Fe(VI)-Mediated Single-Electron Coupling Processes for the Removal of Chlorophene: A Combined Experimental and Computational Study

Potassium ferrate [Fe(VI)] is a promising oxidant widely used in water treatment for the elimination of organic pollutants. In this work, the reaction kinetics, products, and mechanisms of the antimicrobial agent chlorophene (CP) undergoing Fe(VI) oxidation in aqueous solutions were investigated. CP is very readily degraded by Fe(VI), with the apparent second-order rate constant, k, being 423.2 M^-1 s^-1 at pH 8.0. A total of 22 oxidation products were identified using liquid chromatography-quadrupole time-of-flight-mass spectrometry , and their structures were further elucidated using tandem mass spectrometry. According to the extracted peak areas in mass spectra, the main reaction products were the coupling products (dimers, trimers, and tetramers) that formed via single-electron coupling. Theoretical calculations demonstrated that hydrogen abstraction should easily occur at the hydroxyl group to produce reactive CP· radicals for subsequent polymerization. Cleavage of the C-C bridge bond, electrophilic substitution, hydroxylation, ring opening, and decarboxylation were also observed during the Fe(VI) oxidation process. In addition, the degradation of CP by Fe(VI) was also effective in real waters, which provides a basis for potential applications.

Aromatic organoarsenic compounds (AOCs) occurrence and remediation methods

Many researchers at home and abroad have made a body of researches and have gained great achievements on the environmental occurrence, fate, and toxicity of inorganic arsenic. But there is less research on the use of aromatic organoarsenic compounds (AOCs), which are common feed additives for livestock in the poultry industry. In this review, we outline the current state of knowledge acquired on the occurrence and remediation of AOCs, respectively. We also identify knowledge gaps and research needs, including the elucidation of the environmental fate of AOCs, metabolic pathway, the impact of metabolic modification on toxicity, and advanced analytical or repaired methods that allows for monitoring, identification or removal of the degradation products.

Micropollutants removal by full-scale UV-C/sulfate radical based Advanced Oxidation Processes

The high chemical stability and the low biodegradability of a vast number of micropollutants (MPs) impede their correct treatment in urban wastewater treatment plants. In most cases, the chemical oxidation is the only way to abate them. Advanced Oxidation Processes (AOPs) have been experimentally proved as efficient in the removal of different micropollutants at lab-scale. However, there is not enough information about their application at full-scale. This manuscript reports the application of three different AOPs based on the addition of homogeneous oxidants [hydrogen peroxide, peroxymonosulfate (PMS) and persulfate anions (PS)], in the UV-C tertiary treatment of Estiviel wastewater treatment plant (Toledo, Spain) previously designed and installed in the facility for disinfection. AOPs based on the photolytic decomposition of oxidants have been demonstrated as more efficient than UV-C radiation alone on the removal of 25 different MPs using low dosages (0.05-0.5 mM) and very low UV-C contact time (4-18 s). Photolysis of PMS and H₂O₂ reached similar average MPs removal in all the range of oxidant dosages, obtaining the highest efficiency with 0.5 mM and 18 s of contact time (48 and 55% respectively). Nevertheless, PMS/UV-C reached slightly higher removal than H₂O₂/UV-C at low dosages. So, these treatments are selective to degrade the target compounds, obtaining different removal efficiencies for each compound regarding the oxidizing agent, dosages and UV-C contact time. In all the cases, H₂O₂/UV-C is more efficient than PMS/UV-C, comparing the ratio cost:efficiency (€/m³·order). Even H₂O₂/UV-C treatments are more efficient than UV-C alone. Thus, the addition of 0.5 mM of H₂O₂ compensates the increased of UV-C contact time and therefore the increase of electrical consumption, that it should be need to increase the removal of MPs by UV-C treatments alone.

Kinetic and mechanistic aspects of hydroxyl radical‒mediated degradation of naproxen and reaction intermediates

Hydroxyl radical (^•OH) based advanced oxidation technologies (AOTs) are effective for removing non‒steroidal anti-inflammatory drugs (NSAIDs) during water treatment. In this study, we systematically investigated the degradation kinetics of naproxen (NAP), a representative NSAID, with a combination of experimental and theoretical approaches. The second-order rate constant (k) of ^•OH oxidation of NAP was measured to be (4.32 ± 0.04) × 10⁹ M^-1 s^-1, which was in a reasonable agreement with transition state theory calculated k value (1.08 × 10⁹ M^-1 s^-1) at SMD/M05-2X/6-311++G**//M05-2X/6-31+G** level of theory. The calculated result revealed that the dominant reaction intermediate is 2‒(5‒hydroxy‒6‒methoxynaphthalen‒2‒yl)propanoic acid (HMNPA) formed via radical adduct formation pathway, in which ^•OH addition onto the ortho site of the methoxy-substituted benzene ring is the most favorable pathway for the NAP oxidation. We further investigated the subsequent ^•OH oxidation of HMNPA via a kinetic modelling technique. The k value of the reaction of HMNPA and ^•OH was determined to be 2.22 × 10⁹ M^-1 s^-1, exhibiting a similar reactivity to the parent NAP. This is the first study on the kinetic and mechanistic aspects of NAP and its reaction intermediates. The current results are valuable in future study evaluating and extending the application of ^•OH based AOTs to degrade NAP and other NSAIDs of concern in water treatment plants.

Reduced Graphene Oxide Decorated Na3V2(PO4)3 Microspheres as Cathode Material With Advanced Sodium Storage Performance

Reduced graphene oxide (rGO) sheet decorated Na₃V₂(PO₄)₃ (NVP) microspheres were successfully synthesized by spray-drying method. The NVP microspheres were embedded by rGO sheets, and the surface of the particles were coated by rGO sheets and amorphous carbon. Thus, the carbon conductive network consisted of rGO sheets and amorphous carbon generated in the cathode material. NVP microspheres decorated with different content of rGO (about 0, 4, 8, and 12 wt%) were investigated in this study. The electrochemical performance of NVP exhibited a significant enhancement after rGO introduction. The electrode containing about 8 wt% rGO (NVP/G8) showed the best rate and cycle performance. NVP/G8 electrode exhibited the discharge capacity of 64.0 mAh g⁻¹ at 70°C, and achieved high capacity retention of 95.5% after cycling at 10°C for 100 cycles. The polarization of the electrode was inhibited by the introduction of rGO sheets. Meanwhile, compared with the pristine NVP electrode, NVP/G8 electrode exhibited small resistance and high diffusion coefficient of sodium ions.

Quantitative structure-activity relationship for the partition coefficient of hydrophobic compounds between silicone oil and air

The silicon oil-air partition coefficients (K_SiO/A) of hydrophobic compounds are vital parameters for applying silicone oil as non-aqueous-phase liquid in partitioning bioreactors. Due to the limited number of K_SiO/A values determined by experiment for hydrophobic compounds, there is an urgent need to model the K_SiO/A values for unknown chemicals. In the present study, we developed a universal quantitative structure-activity relationship (QSAR) model using a sequential approach with macro-constitutional and micromolecular descriptors for silicone oil-air partition coefficients (K_SiO/A) of hydrophobic compounds with large structural variance. The geometry optimization and vibrational frequencies of each chemical were calculated using the hybrid density functional theory at the B3LYP/6-311G** level. Several quantum chemical parameters that reflect various intermolecular interactions as well as hydrophobicity were selected to develop QSAR model. The result indicates that a regression model derived from logK_SiO/A, the number of non-hydrogen atoms (#nonHatoms) and energy gap of E_LUMO and E_HOMO (E_LUMO-E_HOMO) could explain the partitioning mechanism of hydrophobic compounds between silicone oil and air. The correlation coefficient R² of the model is 0.922, and the internal and external validation coefficient, Q²_LOO and Q²_ext , are 0.91 and 0.89 respectively, implying that the model has satisfactory goodness-of-fit, robustness, and predictive ability and thus provides a robust predictive tool to estimate the logK_SiO/A values for chemicals in application domain. The applicability domain of the model was visualized by the Williams plot.

Degradation of 2,4-dichlorophenol by activating persulfate and peroxomonosulfate using micron or nanoscale zero-valent copper

The ability of persulfate (PS) and peroxymonosulfate (PMS) activated by micron or nanoscale zero-valent copper (ZVC or nZVC) to degrade 2,4-dichlorophenol (2,4-DCP) was quantified under various conditions. Mechanism investigation revealed that PS and PMS accelerated the corrosion of ZVC or nZVC to release Cu⁺ under acidic conditions. The in-situ generated Cu⁺ further decomposed PS or PMS to produce SO₄^- and OH, which then dramatically degraded 2,4-DCP. The k_obs for 2,4-DCP removal followed pseudo-first-order kinetics, k_obs of ZVC/PMS and nZVC/PMS systems were 10∼30 times greater than these in ZVC/PS and nZVC/PS systems. The nZVC/PMS system was most effective to remove 2,4-DCP which even did better than the nZVI/PMS system, with rate constant values ranging from 0.041 to 1.855min^-1. At higher pH ZVC is ineffective, but nZVC can activate PS and PMS to significantly degrade 2,4-DCP at pH up to 7.3. The 2,4-DCP degradation pathway was found to involve dechloridation, dehydrogenation, hydroxylation, ring open and mineralization. 56.7% and 45.3% of TOC removals were respectively obtained in the ZVC/PMS and nZVC/PMS systems within 120min. This study helps to comprehend the application of zero-valent metals in reactive radicals-based oxidation processes and the reactivity of Cu⁺ as an activator of PS and PMS.

UV direct photolysis of sulfamethoxazole and ibuprofen: An experimental and modelling study

Photodegradation characteristics of pharmaceuticals and personal care products (PPCPs) during UV irradiation are of practical and scientific importance in selecting operational parameters during water treatment processes. In this study, the molar extinction coefficient (ε), quantum yield (φ), and degradation kinetics of neutral/anionic forms of sulfamethoxazole (SMX) and ibuprofen (IBU) were compared by varying solution pH. The degradation kinetics of the target compounds were observed to reversely correlate to the energy gap between highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) values of the target compounds. Then, a kinetic model for predicting the direct photolytic rates at different solution pH was established based on ε and φ of neutral/anionic species. The root mean squared errors for the modeled values suggest that the model exhibits good predictive power. Finally, in order to evaluate the electrical energy consumption during the UV direct photolysis process, the electrical energy per order (EE/O) was assessed. The experimental and modelling results are important to elucidate the mechanism of degradation of target PPCPs under UV irradiation and allow for the selection of optimal conditions in water treatment processes.

CNT-Decorated Na3V2(PO4)3 Microspheres as a High-Rate and Cycle-Stable Cathode Material for Sodium Ion Batteries

A novel cathode material, carbon nanotube (CNT)-decorated Na₃V₂(PO₄)₃ (NVP) microspheres, was designed and synthesized via spray-drying and carbothermal reduction methods. The microspheres were covered and embedded by CNTs, the surfaces of which were also covered by amorphous carbon layers. Thus, a carbon network composed of CNTs and amorphous carbon layers formed in the materials. The polarization of a 10 wt % CNT-decorated NVP (NVP/C10) electrode was much less compared with that of the electrode with pristine NVP without CNTs. The capacity of the NVP/C10 electrode only decreased from 103.2 to 76.2 mAh g^-1 when the current rates increased from 0.2 to 60 C. Even when cycled at a rate of 20 C, the initial discharge capacity of the NVP/C10 electrode was as high as 91.2 mAh g^-1, and the discharge capacity was 76.9 mAh g^-1 after 150 cycles. The charge-transfer resistance and ohmic resistance became smaller because of CNT decorating. Meanwhile, the addition of CNTs can tune the size of the NVP particles and increase the contact area between NVP and the electrolyte. Consequently, the resulted NVP had a larger sodium ion diffusion coefficient than that of the pristine NVP.

Temperature Effects on Rheological Properties of Fresh Thickened Copper Tailings that Contain Cement

Cemented paste backfill (CPB) is an economic and environmental friendly technique applied in underground mining for supporting surrounding rock and replacing the pillar. However, little is known about the temperature effects on CPB in mines having a large temperature fluctuation. The main purpose of this research was to investigate the effect of temperature change on the rheological properties (e.g., shear stress and apparent viscosity) of CPB with copper mine tailings. Specifically, a series of rheological tests were conducted on 6 CPB samples using a Brookfield R/S+ Rheometer under various temperatures (2°C, 10°C, 20°C, 30°C, 40°C, and 60°C). Our results showed that both shear stress and apparent viscosity of these tailing samples increased with temperature rising from 2 to 60°C. Likewise, temperature has a significant impact on the Bingham yield stress of thickened tailings. The yield stress decreased from 122 Pa (2°C) to 112 Pa (20°C) and then increased to 152 Pa (60°C). Moreover, the pipeline transport pressure drop of CPB at various temperatures was calculated, illustrating an obvious effect on the paste pipeline transport. Compared with 20°C, the pressure drop under 2°C and 60°C increased by 11% and 22%, respectively. The results of this study indicate that the temperature plays an essential role in determining rheological properties of CPB and its engineering application in mines particularly with naturally fluctuating temperatures.

Mechanistic insight into degradation of endocrine disrupting chemical by hydroxyl radical: An experimental and theoretical approach

Advanced oxidation processes (AOPs) based on formation of free radicals at ambient temperature and pressure are effective for treating endocrine disrupting chemicals (EDCs) in waters. In this study, we systematically investigated the degradation kinetics of bisphenol A (BPA), a representative EDC by hydroxyl radical (OH) with a combination of experimental and theoretical approaches. The second-order rate constant (k) of BPA with OH was experimentally determined to be 7.2 ± 0.34 × 10⁹ M^-1 s^-1 at pH 7.55. We also calculated the thermodynamic and kinetic behaviors for the bimolecular reactions by density functional theory (DFT) using the M05-2X method with 6-311++G** basis set and solvation model based on density (SMD). The results revealed that H-abstraction on the phenol group is the most favorable pathway for OH. The theoretical k value corrected by the Collins-Kimball approach was determined to be 1.03 × 10¹⁰ M^-1 s^-1, which is in reasonable agreement with the experimental observation. These results are of fundamental and practical importance in understanding the chemical interactions between OH and BPA, and aid further AOPs design in treating EDCs during wastewater treatment processes.