Levofloxacin ozonation in water: rate determining process parameters and reaction pathway elucidation

Computational Insights for Interactions between nsP2 and nsP3 of CHIKV and Hormones through DFT Computations and Molecular Dynamics Simulations

The non-structural protein (nsP2 & nsP3) of the Chikungunya virus (CHIKV) is responsible for the transmission of viral infection. The main role of non-structural proteins are involved in the transcription process at an early stage of the infection. In this work, authors have studied the impact of nsP2 and nsP3 of CHIKV on hormones present in the human body using a computational approach. The ten hormones of chemical properties such as 4-Androsterone-2,17-dione, aldosterone, androsterone, corticosterone, cortisol, cortisone, estradiol, estrone, progesterone and testosterone were taken as a potency. From the molecular docking, the binding energy of the complexes is estimated, and cortisone was found to be the highest negative binding energy (-6.57 kcal/mol) with the nsP2 and corticosterone with the nsP3 (-6.47 kcal/mol). This is based on the interactions between hormones and nsP2/nsP3, which are types of noncovalent intermolecular interactions categorized into three types: electrostatic interactions, van der Waals (vdW) interactions, and hydrogen-bonding (H-bonding) interactions. To validate the docking results, additional molecular dynamics simulations and MM-GBSA methods were performed. The change in enthalpy, entropy, and free energy were calculated using MM-GBSA methods. The nsP2 and nsP3 of CHIKV interact strongly with the cortisone and corticosterone with free energy changes of -20.55 & -36.08 kcal/mol, respectively. Methods: The crystal structures of 3TKR and 3GPO proteins of nsP2 and nsP3 were extracted from the RCSB Protein Data Bank. Initially, unnecessary atoms like extra cations or anions and missing explicit hydrogen atoms were removed and added from the native domain of nsP2 and nsP3. The alignment of coordinated in the native domain was performed using Chimera and Notepad++ tools. The molecular docking of protein and ligand was performed usingAutoDock tool; it is essential for the prediction of the orientation of the ligand into the cavity of the target protein based on binding affinity. Based on thermodynamic parameters, MD Simulations were employed to calculate the change in binding free energies of various complexes followed by a change in enthalpy and entropy with time. According to MD production, the CPPTAJ and PTRAJ programs were used to analyse the trajectories, such as dynamic stability (RMSD), residual fluctuation (RMSF), compatibility, and hydrogen bonds of the newly formed complexes. After that, the Density Functional Theory (DFT) were used to calculate the electronic properties of selected molecules by Gaussian 16 on applying the B3LYP method with the 6-311G (d, p) basis set.

A photocatalysis-self-Fenton system based on NCDs@ZnIn2S4 composites at neutral pH and low amount of Fe2+ for the effective degradation of antibiotics

Photocatalysis-self-Fenton combining photocatalytic production of H2O2 with Fenton reaction has been a hotspot, but the pH limitation and iron sludge production problems remain unsolved. Herein, we proposed a self-fenton system based on N-doped carbon dots modified ZnIn2S4 (NCDs@ZnIn2S4) composites that exhibits effective degradation of antibiotics under neutral pH using low amounts of Fe2+. The decoration of ZnIn2S4 with NCDs significantly increased the surface area, visible light absorption, charge transfer ability and oxygen adsorption ability. NCDs@ZnIn2S4 composites exhibited a high H2O2 production rate (1528 μM g-1•h-1) under visible light, which was 1.9 and 5.3 times higher than ZnIn2S4 and NCDs, respectively. Meanwhile, the Fe2+/NCDs@ZnIn2S4 system with a low concentration of Fe2+(1 mg/L) could remove over 95% levofloxacin and oxytetracycline within 30 min. Interestingly, the highest degradation efficiency occurred under neutral pH. Quenching experiments and analytical measurements indicated that the high catalytic performance under pH = 7 with low amounts of Fe2+ stemmed from the higher amount of inner-generate H2O2 under neutral pH and easy regeneration of Fe2+ by photoinduced electrons for high •OH yields. Additionally, the Fe2+/NCDs@ZnIn2S4 system exhibited high degradation performance under different water matrix and ultrahigh degradation efficiency towards levofloxacin under real sunlight irradiation. The work shows the prospects of photocatalysis-self-Fenton systems for overcoming the pH limitation and the difficulty of iron sludge separation in the purification of effluents.

Predicting ciprofloxacin and levofloxacin decomposition utilizing ozone micro-nano bubbles through the central composite design method

Antibiotics have several negative effects on aquatic ecosystems and are difficult to degrade using traditional water/wastewater treatment methods. As a result, new treatment techniques must be employed to eliminate these contaminants from aquatic environments. Research on the relationship between the decomposing process of antibiotics and different factors by new technologies is scarce. This research focuses on the capability of ozone micro-nano bubbles (OzMNBs) to eliminate the antibiotics ciprofloxacin (CIPR) and levofloxacin (LEVO) in aqueous solutions. We studied the CIPR and LEVO decomposition to different variables through the central composite design method. The main variables included pH, ozonation time, and initial antibiotic concentration. The correlation coefficients of the quadratic model obtained by using the software, Design Expert version 13.0.1. Analysis of variances proved the significance of models and main factors. Verification tests also confirmed that the final optimum conditions of the antibiotics decomposition were: pH 9, ozonation for 40 min and, initial antibiotic concentration of 5 mg/L. In optimum conditions, removal rate of about 97% and 100% was obtained for CIPR and LEVO, respectively. The order of influence of various factors on CIPR and LEVO decomposition were obtained and the interactions between the main factors were also investigated. At the last stage of the research, the efficiency of OzMNBs in the removal of total organic carbon and mineralization of the solutions containing CIPR and LEVO under optimum conditions was examined.

Unveiling the oxidation mechanism of persistent organic contaminants via visible light-induced dye-sensitized reaction by red mud suspension with peroxymonosulfate

A dye-sensitized photocatalysis system was developed for degrading persistent organic contaminants using solid waste (i.e., red mud, RM) and peroxymonosulfate (PMS) under visible light. Complete degradation of acid orange 7 (AO7) was achieved in RM suspension with PMS, where the co-existence of amorphous FeO(OH)/α-Fe2O3 was the key factor for PMS activation. The experimental results obtained from photochemical and electrochemical observations confirmed the enhanced PMS activation due to the Fe-OH phase in RM. DFT calculations verified the acceleration of PMS activation due to the high adsorption energy of PMS on FeO(OH) and low energy barrier for generating reactive radicals. Compared to the control experiment without AO7 showing almost no degradation of other organic contaminants (phenol, bisphenol A, 4-chlorophenol, 4-nitrophenol, and benzoic acid), photo-sensitized AO7* enhanced electron transfer in the FeIII/FeII cycle, dramatically enhancing the degradation of organic contaminants via radical (•OH, SO4•-, and O2•-) and non-radical (dye*+ and 1O2) pathways. Therefore, the novel finding of this study can provide new insights for unique PMS activation by heterogeneous Fe(III) containing solid wastes and highlight the importance of sensitized dye on the interaction of PMS with Fe charge carrier for the photo-oxidation of organic contaminants under visible light.

Peroxymonosulfate activation by Fe-Mn Co-doped biochar for carbamazepine degradation

Antibiotics in aquatic environments present a serious threat to the ecological environment and human health. Activation of carbon-catalyzed persulfate is a prospective approach for oxidizing antibiotics. There is a pressing need for inexpensive carbon catalysts of high quality. In this study, biochar (BC) modified by Fe, Mn and Fe@Mn was employed to activate peroxymonosulfate (PMS) to degrade carbamazepine (CBZ) in water. The surface of Fe@Mn BC had a dense, stalactite-like morphology comprising a square chassis that was elliptical. The catalyst Fe@Mn-BC possessed the optimal degradation effect (99%) on CBZ at 100 min. Electron paramagnetic resonance spectroscopy and the quenching spectrum suggested that ˙O2- and 1O2 contributed to CBZ degradation.

Degradation of Levofloxacin by a green zero-valent iron-loaded carbon composite activating peroxydisulfate system: Reactivity, products and mechanism

In this study, a green zero-valent iron-loaded carbon composite (ZVI-SCG) was synthesized using coffee grounds and FeCl3 solution through two-steps method, and the synthesized ZVI-SCG was used in the activation of peroxydisulfate (PDS) to degrade Levofloxacin (LEX). Results revealed that ZVI-SCG exhibited a great potential for LEX removal by adsorption and catalytic degradation in the ZVI-SCG/PDS system, and 99% of LEX was removed in the ZVI-SCG/PDS system within 60 min. ZVI-SCG/PDS system showed a high reactivity toward LEX degradation under realistic environmental conditions. Also, the ZVI-SCG/PDS system could effectively degrade several quinolone antibiotics including gatifloxacin, ciprofloxacin and LEX in single and simultaneous removal modes. A potential reaction mechanism of LEX degradation by ZVI-SCG/PDS system was proposed, SO4•-, HO•, O2•- and 1O2 involved in radical and non-radical pathways took part in catalytic degradation of LEX by ZVI-SCG/PDS system, but HO• might be the main reactive species for LEX degradation. The possible degradation pathway of LEX was also proposed based on the identified ten intermediate products, LEX degradation was successfully achieved through decarboxylation, opening ring and hydroxylation processes. The potential toxicity of LEX and its oxidation products decreased significantly after treatment. This study provides a promising strategy of water treatment for the antibiotics-containing wastewater.

Plasmonic-driven charge separation through combining Ag nanoparticles (Ag NPs) to form a double Z-scheme heterostructure in WO3/BiOCl/g-C3N4 for the photocatalytic degradation of antibiotics

Integrating a heterojunction system with the impact of surface plasmon resonance (SPR) is an executable and innovative tactic for photocatalyst amelioration. Ag nanoparticle (Ag NP)-modified WO3/BiOCl/g-C3N4 (WB-CN) was favorably fabricated through in situ photo deposition assembly to form double heterojunctions (A-WBCN). The degradation performance of A-WBCN is better than that of pure g-C3N4 (CN) and WO3/BiOCl (WB), it can degrade more than 90% of OFLX within 20 minutes, due to Ag NPs performing as a bridge for electron mediators, apart from the implications of SPR in A-WBCN. The results of UV diffuse reflectance spectroscopy indicate that loading with Ag NPs can expand the light absorption range of WB-CN to near-infrared. The photoluminescence spectra and transient photocurrent spectra indicate that Ag NP loading significantly improves the separation efficiency of photogenerated carriers. Density functional theory (DFT) simulation results show that the introduction of Ag NPs can change the direction of carrier movement, resulting in bending of the energy bands of WB and CN, improving the redox ability of A-WBCN, and improving its photocatalytic efficiency. In addition, the intermediate products of OFLX was determined by HPLC-MS analysis. The spin electron resonance (ESR) results indicate that ˙O2- and ˙OH are the main active species in photocatalytic degradation. This work furnishes a fresh idea for upgrading photocatalytic performance and advancing electron transfer.

Design and synthesis of high performance magnetically separable exfoliated g-C3N4/γ-Fe2O3/ZnO yolk-shell nanoparticles: a novel and eco-friendly photocatalyst toward removal of organic pollutants from water

Herein, a new visible-light active exfoliated g-C3N4/γ-Fe2O3/ZnO yolk-shell nanoparticles (NPs) was synthesized as a magnetically separable photocatalyst. For an in-depth understanding of the magnetic photocatalyst's structural, morphological, and optical properties, the products were extensively characterized with FT-IR, XRD, TEM, HRTEM, FESEM, EDS, EDS-mapping, VSM, DRS, EIS, and photocurrent. The photocatalyst was then utilized to degrade Levofloxacin (LEVO) and Indigo Carmine (IC) by visible light at room temperature. The exfoliated g-C3N4/γ-Fe2O3/ZnO yolk-shell NPs photocatalyst revealed 80% and 95.6% degradation efficiency for Levofloxacin and Indigo Carmine within 25 and 15 min, respectively. In addition, the optimal factors such as concentration, loading of photocatalyst, and pH were also assessed. Levofloxacin degradation mechanistic studies showed that electrons and holes significantly contribute to the photocatalytic process of photocatalyst degradation. In addition, after 5 times regeneration, exfoliated g-C3N4/γ-Fe2O3/ZnO yolk-shell NPs remained as an excellent magnetic photocatalyst for the eco-friendly degradation of Levofloxacin and Indigo Carmine (76% and 90%), respectively. The superior photocatalytic performance of exfoliated g-C3N4/γ-Fe2O3/ZnO yolk-shell nanoparticles (NPs) was mostly ascribed to the synergistic advantages of stronger visible light response, larger specific surface area, and the more effective separation and transfer of photogenerated charge carriers. Based on these results, the highly effective magnetic photocatalyst achieved better results than numerous studied catalysts in the literature. The degradation of Levofloxacin and Indigo Carmine under environmentally friendly conditions can be achieved using exfoliated g-C3N4/γ-Fe2O3/ZnO yolk-shell NPs (V) as an efficient and green photocatalyst. The magnetic photocatalyst was characterized by spectroscopic and microscopic methods, revealing a spherical shape and particle size of 23 nm. Additionally, the magnetic photocatalyst could be separated from the reaction mixture by a magnet without significantly reducing its catalytic activity.

Integrated adsorption and photocatalytic degradation based removal of ciprofloxacin and sulfamethoxazole antibiotics using Fc@rGO-ZnO nanocomposite in aqueous systems

Ferrocene functionalized rGO-ZnO nanocomposite was synthesized via the facile hydrothermal method. ZnO was reduced over the 3-dimensional rGO framework (3D-Fc@rGO) using Camellia sinensis extract. The Fc@rGO-ZnO nanocomposite was employed for pharmaceutical degradation (sulfamethoxazole (SMX) and ciprofloxacin (CIP)) in an aqueous solution under UV C light. The physicochemical properties of the as-prepared photocatalyst were characterized using FTIR, XRD, FESEM, EDS mapping, HR-TEM, XPS, and DR-UV Vis. The as-synthesized Fc@rGO-ZnO photocatalyst performed remarkably against pristine ZnO, with a fivefold increase in removal efficiency. This superior activity was attributed to its improved light harvesting, charge carrier interface, and enhanced charge separation. Additionally, the photocatalyst obeyed the Lagergen model for pseudo-first-order kinetics. Congruously, the integrated approach of Fc@rGO and ZnO as oxidizing agents was proficient in removing >95% of antibiotics (CIP and SMX) within 180 min. Furthermore, the heterostructure configuration developed between Fc@rGO and ZnO helps in charge migration and generation of abundant •OH and •O₂^- radicals for photodegradation activities. The toxicity assessment of the treated solutions showed improved cell viability in the algal strains of Scenedesmus and Chlorella sp. Moreover, this novel approach for the synthesis of a photoactive nanocomposite is found to be low-cost and reusable for three cycles. The nanocomposite is environmentally sustainable paving the way for practical applications in the treatment of different classes of antibiotics.

Further transformation of the primary ozonation products of tramadol- and venlafaxine N-oxide: Mechanistic and structural considerations

Ozonation has been used to effectively remove micropollutants from the secondary effluent in several wastewater treatment plants. It is known that ozonation transforms tertiary amine compounds into their respective N-oxides, however in an earlier study a mass balance could not be closed at elevated ozone concentrations, leading to the assumption that more ozonation products are possible. This study was conducted to elucidate which (hitherto unknown) ozonation products can be formed from venlafaxine and tramadol when ozonating wastewater. Ozonation experiments were performed with tramadol and venlafaxine N-oxide in two different set-ups. Both tramadol- and venlafaxine N-oxide degraded during ozonation in pure (deionized) water in both semi-continuous and batch mode ozonation set-ups. 13 and 17 new transformation products were detected from tramadol- and venlafaxine N-oxide respectively, using high resolution mass spectrometry with ESI(+) ionization. Empirical chemical formulas were proposed based on the determination of the exact masses and interpretation of the product ion spectra. These transformation products result from the addition of one to three oxygen atoms and removal of C, -CH₂, C₂H₂, C₃H₆, etc., from the parent molecule, respectively. Quenching experiments suggested that most of the transformation products originated from the direct reaction with ozone (eight for tramadol N-oxide and ten for venlafaxine N-oxide), whereas fewer products originated from the reaction with OH radicals (three for tramadol N-oxide and three for venlafaxine N-oxide). Reaction mechanisms and chemical structures of products are proposed, based on the available active sites and past literature on ozone reaction mechanisms. The experimental results are compared to theory and literature on ozone reactive sites and ozone reaction mechanisms. All in all this shows that there can be multiple ozonation products, and ozonation pathways can be complex, even if initially only one ozonation product is formed.

Comparison of sunlight-AOPs for levofloxacin removal: kinetics, transformation products, and toxicity assay on Escherichia coli and Micrococcus flavus

Levofloxacin (LFX) is a widely used antibiotic medication. Persistent traces of LFX in water and wastewater may induce bacterial resistance. Photon-driven advanced oxidation processes (AOPs) can assist in attaining complete abatement of LFX for environmental protection. This work benchmarks different solar AOPs based on hydroxyl radical (OH^•) and sulphate radical (SO₄^•-) chemistry. Other oxidant precursors, as radical sources, were used to selectively control the generation of either hydroxyl radical (i.e., H₂O₂), sulphate radical (i.e., peroxydisulphate (PDS)), or a controlled mixture ratio of both OH^•/SO₄^•- (i.e., peroxymonosulphate (PMS)). The influence of pH on degradation performance was evaluated using unbuffered and buffered solutions. Simulated irradiation/PMS process exhibited a strong pH-dependence attaining partial degradation of ca. 56% at pH 5 up to complete degradation at pH 7. Despite the similitudes on the abatement of target pollutant LFX in pristine solutions, only simulated irradiation/PDS treatment achieved effective abatement of LFX in wastewater samples given the higher selectivity of SO₄^•-. Toxicity tests were conducted with Escherichia coli (LMG2092) and Micrococcus flavus (DSM1790), demonstrating successful inhibition of the antibiotic character of polluted waters, which would contribute to preventing the development of resistant bacterial strains. Finally, a degradative pathway was suggested from the by-products and intermediates identified by LC-MS. Results demonstrate that the degradation of specific functional groups (i.e., piperazine ring) is associated with the loss of antibacterial character of the molecule.

High efficiency of osmotically stable laccase for biotransformation and micro-detoxification of levofloxacin in the urea-containing solution: Catalytic performance and mechanism

Laccase-catalyzed oxidation was applied in the biotransformation of levofloxacin (a potentially environmental antibiotic contamination); however, the enzyme may denature in urea-containing wastewater and lead to the formation of an inactive form followed by decreasing the yield of the bio-removal. In this study, the osmolytes-stabilized laccase was used to eliminate levofloxacin in the urea-containing solution. Sorbitol and proline 100 mM appeared to be the two most efficient laccase protectants against the urea-induced denaturation. In a 1-M urea solution, the maximum velocity (V_max) of laccase was estimated to be 39.1 μmol min^-1 mg^-1. This value was improved to 101.7 and 51.8 μmol min^-1 mg^-1 in the presence of sorbitol and proline, respectively. In optimal conditions for the elimination of levofloxacin, sorbitol- and proline-treated laccase led to 82.9 % and 76.2 % bio-removal of the applied fluoroquinolone in 1 M urea solution, respectively. Biotransformation products of the parent antibiotic were spectroscopically analyzed that assigned to different reaction pathways including demethylation, defluorination, decarboxylation, deamination, and hydroxylation. A micro-toxicity study concerning the growth of some Gram⁺ and Gram^- bacteria exhibited decreasing in inhibition of laccase-treated levofloxacin after a 10-h incubation at 37 °C.

Effectiveness of Advanced Oxidation Processes in Wastewater Treatment: State of the Art

In recent years, many scientific studies have focused their efforts on quantifying the different types of pollutants that are not removed in wastewater treatment plants. Compounds of emerging concern (CECs) have been detected in different natural environments. The presence of these compounds in wastewater is not new, but they may have consequences in the future. These compounds reach the natural environment through various routes, such as wastewater. This review focuses on the study of tertiary treatment with advanced oxidation processes (AOPs) for the degradation of CECs. The main objective of the different existing AOPs applied to the treatment of wastewater is the degradation of pollutants that are not eliminated by means of traditional wastewater treatment.

Synthesis of nano-FeS2 and its application as an effective activator of ozone and peroxydisulfate in the electrochemical process for ofloxacin degradation: A comparative study

In this work, nanopyrite particles (NP) were synthesized by ball mill method and used as a novel source of Fe²⁺ in the electro-activation of ozone and peroxydisulfate (PDS) for ofloxacin (OFX) removal. Fourier transform infrared spectroscopy, X-ray powder diffraction, field emission scanning electron microscopy and energy-dispersive X-ray spectroscopy analyzes were performed to characterize the as-made NP. Optimal values of operating parameters in NP/PDS and NP/O₃ processes were obtained. The OFX (10 mgL^-1) removal efficiency and molar ratio of OFX: oxidant in NP/PDS and NP/O₃processes were 92%, 0.1:11 and 89%, 0.1:9, respectively. Although the synergistic effect was observed in both systems, it was more significant in the NP/PDS. The results of free radical tracing showed that HO^•and SO₄^•- had the more contribution in NP/O₃ and NP/PDS systems for OFX degradation, respectively. In this way, the OFX removal mechanism was the effective release of Fe²⁺ from the NP in the electro-activation of O₃ and PDS. Moreover, the effect of electrocoagulation process on OFX removal was negligible. The as-made NP overcame the disadvantages of iron electrode corrosion and iron sludge production in the Fe-based classical electro-activation processes. Overall, the performance of the synthesized NP in the OFX oxidation was very successful in terms of sustainability, Fe²⁺distribution, removal efficiency, energy consumption and PDS or O₃ activation.

Electron beam irradiation of typical sulfonamide antibiotics in the aquatic environment: Kinetics, removal mechanisms, degradation products and toxicity assessment

Due to their widespread use and harmful effects on aquatic environment, sulfonamide antibiotics (SAs) have become an emerging pollutant of great concern around the world. In this study, we investigated the degradation process and mechanism of sulfamerazine (SMR), sulfadiazine (SDZ), and sulfapyridine (SPD) by electron-beam irradiation (EBI). The results showed that the three SAs were well suited to the pseudo-first-order reaction kinetics, and they could be almost completely removed with high efficiency (5 kGy). Among the environmental factors, pH (3.0) and O₂ atmosphere can further enhance the removal of the sulfonamides (SAs), while NO₂^- has the most pronounced degrading inhibitory effects among the many ions, these results illustrate that hydroxyl radicals play a dominant role. Compared with SMR and SDZ, the degree of mineralization of lower molecular weight SPD is obvious (45%). LC-MS and DFT calculations indicate that the concentrations of degradation products of the three SAs show a tendency to increase and then decrease, demonstrating that EBI can achieve efficient removal and further mineralization of SAs. Meanwhile, the results of the common product 4-Aminophenol produced during the degradation process further indicate that HO is the predominant reactive oxygen species (ROS). In addition, acute toxicity experiments with luminescent bacteria and predictions of ECOSAR procedures proved the toxic effects greatly decreased after the degradation. This study provides new ideas for achieving efficient and profound removal of emerging pollutants from the aquatic environment.

Evaluation of residual antimicrobial activity and acute toxicity during the degradation of gatifloxacin by ozonation

The concerns regarding the occurrence of pharmaceuticals in wastewater treatment plants have increased in the last decades. Gatifloxacin (GAT), the fourth generation of fluoroquinolones, has been widely used to treat both Gram-positive and Gram-negative bacteria and has a limited metabolization. The present study aimed to evaluate ozonation as a technique to degrade GAT. An exchange A UHPLC-MS/MS by an UHPLC-MS/MS method was used to quantify the residual of GAT and to assess its degradation products. The removal efficiency was higher under alkaline conditions (pH = 10), reaching up to 99% of GAT after 4 min. It was also observed that the first ozone attack on the GAT molecule was through the carboxylic group. In contrast, under acid conditions (pH = 3), the ozone attack was first to the piperazinyl ring. The antimicrobial activity was evaluated using Escherichia coli and Bacillus subtilis as test organisms, and it was observed that the residual activity reduced most under alkaline conditions. In contrast, the best condition to remove the residual toxicity evaluated for the marine bacteria V. fischeri was the acidic one. Due to this, ozonation seemed to be an exciting process to remove GAT in aqueous media.

Water-soluble manganese porphyrins as good catalysts for cipro- and levofloxacin degradation: Solvent effect, degradation products and DFT insights

Synthetic manganese porphyrins (MnPs), in the presence of oxidants, were employed for the degradation of fluoroquinolone antibiotics. Ciprofloxacin (CIP) and levofloxacin (LEV) degradation by iodosylbenzene, iodobenzene diacetate, H₂O₂ and meta-chloroperbenzoic acid using water-soluble MnP catalysts yielded thirteen and nine products, respectively, seven of which have been proposed for the first time. The MnP catalysts have demonstrated the ability to degrade these antibiotics to a high degree (up to 100% degradation). The structures of the degradation products were proposed based on mass spectrometry analysis, and density functional theory calculations could confirm how the substituent moieties attached to the basic chemical structure of the fluoroquinolones influence the degradation reactions. CIP has been shown to be a more reactive substrate towards the porphyrinic catalysts tested because of its three-membered ring. However, the catalysts could almost completely degrade LEV, highlighting the ability of these porphyrins to act as catalysts to degrade environmental pollutants.

Fe2+ and UV Catalytically Enhanced Ozonation of Selected Environmentally Persistent Antibiotics

The aim of the study was to determine oxidation potential of selected persistent, environmentally relevant antibiotics (Amoxicillin, Levofloxacin, and their mixture with Vancomycin) to reduce their environmental emissions. Ozonation (O3) and indirect ozonation at pH 9.5 (O3/pH9.5) were catalytically enhanced by addition of Fe2+ (O3/Fe2+) and photocatalytic ozonation in combination with Fe2+ and UV-A black light (O3/Fe2+/UV) at two temperatures using total organic carbon (TOC) and chemical oxygen demand (COD) to identify formation of by-products. Oxidative degradation followed pseudo-first order consecutive reactions. Initial phase of oxidation was more intensive than mineralisation at 21 and 40 °C: up to 57.3% and 69.2%, respectively. After 120 min mineralization at 21 °C was up to 64.9% while at 40 °C it was up to 84.6%. Oxidation reached up to 86.6% and 93.4% at 21 °C and 40 °C, respectively. The most efficient processes were indirect ozonation at pH 9.5 (O3/pH9.5) (up to 93.4%) and photocatalytic enhanced ozonation with Fe2+ and UV-A black light (O3/Fe2+/UV) (up to 89.8%). The lowest efficiency was determined in experiments with direct ozonation (up to 75.5%). Amoxicillin was the only one completely mineralised. Study confirmed that ozonation with addition of Fe2+ and UV radiation has the potential to improve efficiency of the antibiotic-removal processes. Further experiments varying amounts of Fe2+ and other experimental conditions should be accomplished to set up more general methodological approach for reduction of antibiotics emissions.

Ozone dose dependent formation and removal of ozonation products of pharmaceuticals in pilot and full-scale municipal wastewater treatment plants

The removal of micropollutants from municipal wastewater is challenged by the number of compounds with diverse physico-chemical properties. Ozonation is increasingly used to remove micropollutants from wastewater. However, ozonation does not necessarily result in complete mineralization of the organic micropollutants but rather transforms them into new compounds which could be persistent or have adverse environmental effects. To explore ozone dose dependency of the formation and successive removal of ozonation products, two pilot-scale and one full-scale ozonation plants were operated subsequent to a conventional activated sludge treatment. The results from these trials indicated that the concentrations of several N-oxides, such as Erythromycin N-oxide, Venlafaxine N-oxide and Tramadol N-oxide, increased up to an ozone dose of 0.56-0.61 mg O₃/mg DOC while they decreased at elevated doses of 0.7-1.0 mg O₃/mg DOC. Similar results were also obtained for two transformation products of Diclofenac (Diclofenac 2,5-quinone imine and 1-(2,6-dichlorophenyl)indolin-2,3-dione) and one transformation product of Carbamazepine (1-(2-benzoic acid)-(1H,3H)-quinazoline-2,4-dione), where the highest concentrations appeared around 0.27-0.31 mg O₃/mg DOC. The formation maximum of a given compound occurred at a specific ozone dose that is characteristic for each compound, but seemed to be independent of the wastewater used for the experiments at the two pilots and the full-scale plant.

Ultrathin Ag2WO4-coated P-doped g-C3N4 nanosheets with remarkable photocatalytic performance for indomethacin degradation

As a metal-free photocatalyst, the photocatalytic activity of graphitic carbon nitride (g-C₃N₄) remains restricted due to an insufficient visible-light absorption capacity, the rapid recombination of photoinduced carriers, and low surface area. Consequently, P-doped g-C₃N₄ (PCN) was successfully prepared via a single -step thermal polymerization technique using phytic acid biomass and urea, which exhibited remarkable photocatalytic activity for the degradation of indometacin (IDM). The IDM degradation rate was 7.1 times greater than that of pristine g-C₃N₄ (CN). Furthermore, Ag₂WO₄ was loaded onto the surface of the PCN, which formed a Z-scheme heterostructure that promoted the separation of photogenerated carriers. According to analyses of the chemical binding states of PCN, P atoms replaced carbon atoms in the CN framework. According to electron localization function analysis, the low ELF values of P-N facilitated the transfer of photoelectrons. The results of active species scavenging experiments confirmed that superoxide radicals were the primary active species in the photocatalytic degradation system. Finally, the photocatalytic degradation pathways of IDM were predicted through the identification of by-products and IDM reaction sites.

Effect of ultrasound irradiation combined with ozone pretreatment on the anaerobic digestion for the biosludge exposed to trace-level levofloxacin: Degradation, microbial community and ARGs analysis

Anaerobic digestion, the principal method of stabilizing biosolids in wastewater treatment plants (WWTPs), can efficiently and largely attenuate the antibiotic resistances in biosludge. This study aims to investigate the effect of oxidative pretreatment with ultrasound irradiation combined with ozone (US/O₃) on the mesophilic and thermophilic anaerobic digestion (MAD and TAD) for the biosludge bearing trace fluoroquinolones contaminants-levofloxacin (LEVO) which was widely used in recent years. During the oxidation, the trace-level LEVO was almost completely degraded. The methanogenic activity in US/O₃ pretreated TAD dosed 0.1 mg/L LEVO was much higher than those in single MAD and TAD, therefore leading to a remarkable increase in biogas production. The identification of levofloxacin intermediates during chemical degradation was analyzed using LCMS technique and the reaction pathway based on them was proposed. Hydroxyl radicals provided by US/O₃ contributed to oxidative ring opening of LEVO as well as degradation of other biomacromolecules in the biosludge. Besides, the quinoline resistance genes-qnrA and qnrS declined significantly by 1-2 orders of magnitude in US/O₃-pretreated TAD, indicating that the active radicals produced by US/O₃ oxidized and degraded LEVO and therefore inactivated the antibiotic resistant bacteria or genes in the biosolids. Meanwhile, the composition and structure of the microbial community altered and the diversity and richness of total bacterial and potential human pathogens decreased, the pattern of which was correlated with LEVO-resistant genes. Among the well-known AD-related phylum including Bacteroidetes, Firmicutes, Methanobacteria as well as Thermotogae which has been previously detected in TAD and performed organic hydrolysis and degradation, the potential LEVO-resistant bacteria were probably affiliated to Actinobacteria, Bacteroidetes, Proteobacteria, Thermotogae. This study revealed the contribution of US/O₃ pretreatment to the anaerobic digestion in terms of ARGs reduction for trace-LEVO- exposed biosludge and could provide useful guidance for controlling the dissemination of ARB and ARGs in sewage sludge.

Environmental Conversion Path Inference of New Designed Fluoroquinolones and Their Potential Environmental Risk

Fluoroquinolone (FQ) derivatives with environmental friendliness regarding photodegradation, bioconcentration, and genotoxicity were selected from our previous works so that their transformation pathways of biological metabolism, photodegradation, microbial degradation, and chlorination disinfection could be studied. The pathways of these molecules and their derivatives were simulated to investigate the genotoxicity of their transformation products. The results showed that the genotoxicity of the biological metabolites, photodegradation products, and microbial degradation products of the maternal FQ derivatives partially increased, whereas the disinfection by-products exhibited lower genotoxicity than their precursors. Some designed FQ molecular derivatives still had potential environmental risks in biological metabolism, photodegradation, and microbial degradation. This study demonstrated that it is necessary to take into account the potential environmental risks of the transformed products of the modified FQs molecules during biometabolism, photodegradation, microbial degradation, and chlorination processes when designing novel FQ molecules. In future studies, assessing the potential environmental risks during various artificial or natural processes can be applied to screen environmentally friendly novel FQ molecules to avoid and or reduce their threat to environmental and human health.

Advanced Oxidation Processes for the Removal of Antibiotics from Water. An Overview

In this work, the application of advanced oxidation processes (AOPs) for the removal of antibiotics from water has been reviewed. The present concern about water has been exposed, and the main problems derived from the presence of emerging pollutants have been analyzed. Photolysis processes, ozone-based AOPs including ozonation, O3/UV, O3/H2O2, and O3/H2O2/UV, hydrogen peroxide-based methods (i.e., H2O2/UV, Fenton, Fenton-like, hetero-Fenton, and photo-Fenton), heterogeneous photocatalysis (TiO2/UV and TiO2/H2O2/UV systems), and sonochemical and electrooxidative AOPs have been reviewed. The main challenges and prospects of AOPs, as well as some recommendations for the improvement of AOPs aimed at the removal of antibiotics from wastewaters, are pointed out.

The degradation of levofloxacin in infusions exposed to daylight with an identification of a degradation product with HPLC-MS

In this paper the decomposition product of levofloxacin was identified. Levofloxacin was dissolved in 0.9% NaCl, 5% glucose, and Ringer's solution. The solutions were divided into two batches: the first one was exposed to daylight and the second one was protected from it. The solutions were stored at the room temperature. The qualitative analysis of the degradation product was performed using MS and TOF detectors. The quantitative assay was done by a validated HPLC method. Visual inspection and pH assessment were done. Levofloxacin protected from daylight remained stable in 0.9% NaCl, 5% dextrose, and Ringer's solution. A slight decomposition of the analyte was observed in the solutions exposed to daylight with the fastest decomposition rate in Ringer's solution as compared with 0.9% NaCl and 5% dextrose solutions. The degradation product of levofloxacin detected with MS was levofloxacin N-oxide. Levofloxacin solutions should be protected from direct daylight to maintain drug stability. Levofloxacin N-oxide is formed regardless of the solvent used.

Construction of 2D heterojunction system with enhanced photocatalytic performance: Plasmonic Bi and reduced graphene oxide co-modified Bi5O7I with high-speed charge transfer channels

The efficient electron-hole charge pair separation, ultra-fast electron migration and excellent light harvest capacity are essential for semiconductor photocatalyst with superior photocatalytic performance. In this study, we constructed layered 2D/2D heterojunction composite of Bi@Bi₅O₇I/rGO (BiBGOI) through a facile surface charge mediated self-assembly strategy. The unique 2D/2D heterostructure with face to face contact can increase the contact area and generate a large amount of charge transfer nanochannels in the interfacial heterojunction, resulting in the enhancement of photocatalytic activity. Addition of semimetal Bi can enhance light absorption, and the local electromagnetic field dominated by SPR effect is favorable for photoinduced charge pair separation. The novel composite showed superior photocatalytic performance for decomposing levofloxacin (LVFX), which was attributed to the unique 2D/2D structure and SPR effect. The enhanced mineralization ability of the novel composite was ascribed to the strong oxidization ability of photoinduced holes, further evaluating high charge pair separation efficiency. In addition, the strong adsorption capacity of rGO for LVFX molecules can enable active radicals transfer into the surface to decompose it. This work will shed light on constructing 2D/2D heterojunction system assisted with SPR effect for the practical application in removal of organic pollutants.

Assessment of reaction intermediates of gamma radiation-induced degradation of ofloxacin in aqueous solution

Gamma radiolytic degradation of an antibiotic, ofloxacin (OFX) was investigated under different experimental conditions. The parameters such as initial OFX concentration, solution pH, absorbed dose and the concentrations of inorganic (CO₃^2-) and organic (t-BuOH) additives were optimized to achieve the efficient degradation of OFX. The degradation dose constant values of OFX were calculated as 2.364, 1.159, 0.776 and 0.618 kGy^-1 for the initial OFX concentrations of 0.05, 0.1, 0.15 and 0.2 mM with their corresponding (G (-OFX)) values of 0.481, 0.684, 1.755 and 1.971, respectively. Degradation rate of OFX was significantly increased with increase in the absorbed dose and decrease in the initial OFX concentration under acidic condition when compared to neutral or alkaline condition. Reaction of OFX in the presence of CO₃^2- and t-BuOH showed that the degradation was primarily caused by the reaction of OFX with radiolytically generated reactive hydroxyl radicals. Mineralization extent of OFX was determined in terms of percentage reduction in total organic carbon (TOC) and results revealed that the addition of H₂O₂ enhanced the mineralization of OFX from 29% to 36.1% with H₂O₂ dose of 0.5 mM at an absorbed dose of 3.0 kGy. Based on the LC-QTOF-MS analysis, gamma radiolytic degradation intermediates/products of OFX were identified and the possible degradation pathways of OFX were proposed. Cytotoxicity study of the irradiated OFX solutions showed that gamma radiation has potential to detoxify OFX.

Abatement of the antibiotic levofloxacin in a solar photoelectro-Fenton flow plant: Modeling the dissolved organic carbon concentration-time relationship

The degradation of solutions of the antibiotic levofloxacin (LVN) in sulfate medium at pH 3.0 has been investigated at pre-pilot scale by solar photoelectro-Fenton (SPEF) process. The flow plant included an FM01-LC filter-press cell equipped with a Ti|Pt anode and a three-dimensional-like air-diffusion cathode, connected to a compound parabolic collector as photoreactor and a continuous stirred tank under recirculation batch mode. The effect of volumetric flow rate on H₂O₂ electrogeneration from O₂ reduction was assessed. Then, the influence of initial LVN concentration and Fe²⁺ concentration as catalyst on dissolved organic carbon (DOC) removal was thoroughly investigated. LVN was gradually mineralized by SPEF process, with faster DOC abatement at 0.50 mM Fe²⁺, yielding 100% after 360 min at applied cathodic potential of -0.30 V|SHE. The high mineralization current efficiency (MCE) and low specific energy consumption (EC_DOC) revealed the extraordinary role of homogeneous hydroxyl radicals and natural UV light, which allowed the degradation of the antibiotic and its by-products with MCE values greater than 100%. Five cyclic by-products, N,N-diethylformamide and three short-chain linear carboxylic acids were detected by GC-MS and HPLC analyses. A parametric model to simulate the DOC decay versus electrolysis time was implemented for the SPEF pre-pilot flow plant, showing good agreement with experimental data.

Ozonation of norfloxacin and levofloxacin in water: Specific reaction rate constants and defluorination reaction

The degradation kinetics and mechanism of two typical fluoroquinolones (FQs), norfloxacin (NF) and levofloxacin (LOF), by ozone in water were investigated. Semi-continuous mode and competition kinetics mode experiments were conducted to determine the reaction rate constants of target FQs with ozone and OH, separately. Results indicate that both NF and LOF were highly reactive toward ozone, and the reactivity was strongly impacted by the solution pH. The specific reaction rate constants of the diprotonated, monoprotonated and deprotonated species were determined to be 7.20 × 10², 8.59 × 10³, 4.54 × 10⁵ M^-1 s^-1 respectively for NF and 1.30 × 10³, 1.40 × 10⁴, 1.33 × 10⁶ M^-1 s^-1 respectively for LOF. The reaction rate constants of target FQs toward OH were measured to be (4.81-7.41) × 10⁹ M^-1 s^-1 in the pH range of 6.3-8.3. Furthermore, NF was selected as a model compound to clarify the degradation pathways, with a particular focus on the defluorination reaction. The significant release of F^- ions and the formation of three F-free organic byproducts indicated that defluorination was a prevalent pathway in ozonation of FQs, while six F-containing organic byproducts indicated that ozone also attacked the piperazinyl and quinolone moieties. Escherichia coli growth inhibition tests revealed that ozonation could effectively eliminate the antibacterial activity of target FQ solutions, and the residual antibacterial activity had a negative linear correlation with the released F^- concentration.

Studies on the formation of formaldehyde during 2-ethylhexyl 4-(dimethylamino)benzoate demethylation in the presence of reactive oxygen and chlorine species

In order to protect the skin from UV radiation, personal care products (PCPS) often contain chemical UV-filters. These compounds can enter the environment causing serious consequences on the water ecosystems. The aim of this study was to examine, the effect of different factors, such as UV light, the presence of NaOCl and H2O2 on the formaldehyde formation during popular UV filter, 2-ethylhexyl 4-(dimethylamino)benzoate (ODPABA) demethylation. The concentration of formaldehyde was determined by VIS spectrophotometry after derivatization. The reaction mixtures were qualitatively analyzed using GC/MS chromatography. The highest concentration of formaldehyde was observed in the case of ODPABA/H2O2/UV reaction mixture. In order to describe two types of demethylation mechanisms, namely, radical and ionic, the experimental results were enriched with Fukui function analysis and thermodynamic calculations. In the case of non-irradiated system containing ODPABA and NaOCl, demethylation reaction probably proceeds via ionic mechanism. As it was established, amino nitrogen atom in the ODPABA molecule is the most susceptible site for the HOCl electrophilic attack, which is the first step of ionic demethylation mechanism. In the case of irradiated mixtures, the reaction is probably radical in nature. The results of thermodynamic calculations showed that abstraction of the hydrogen from N(CH3)2 group is more probable than from 2-ethylhexyl moiety, which indicates higher susceptibility of N(CH3)2 to the oxidation.

Antimicrobial activity and acute toxicity of ozonated lomefloxacin solution

Lomefloxacin (LOM) is a synthetic antimicrobial from the fluoroquinolone family (FQ) used as a veterinary and human drug. Once in the environment, LOM may pose a risk to aquatic and terrestrial microorganisms due to its antimicrobial activity. This study evaluated the effect of ozonation of LOM (500 μg L^-1), the residual antimicrobial activity against Escherichia coli and acute toxicity against Vibrio fischeri. In addition, degradation products were investigated by UHPLC-MS/MS and proposed. Ozonation was carried out varying the applied ozone dose from 0 to 54.0 mg L^-1 O₃ and pH values of 3, 7, and 11. Ozonation was most efficient at pH 11 and led to 92.8% abatement of LOM in a 9-min reaction time (54.0 mg L^-1 O₃ applied ozone dose). Ozonation at pH 3 was able to degrade 80.4% of LOM. At pH 7, 74.3% of LOM was degraded. Although the LOM concentration and the antimicrobial activity of the solution dropped as ozone dose increased (antimicrobial activity reduction of 95% at pH 11), toxicity to V. fischeri increased for pH 7 and 11 (i.e., 65% at pH 7 and 75% at pH 11). The reduction in antimicrobial activity may be related to the oxidation of piperazinyl and the quinolone moiety. The formation of intermediates depended on the oxidant (hydroxyl radicals or/and molecular O₃) that acted the most in the process.

Co-modified MCM-41 as an effective adsorbent for levofloxacin removal from aqueous solution: optimization of process parameters, isotherm, and thermodynamic studies

Antibiotics are emerging contaminants due to their potential risks to human health and ecosystems. Poor biodegradability makes it necessary to develop effective physical-chemical methods to eliminate these contaminants from water. The cobalt-modified MCM-41 was prepared by a one-pot hydrothermal method and characterized by SAXRD, N₂ adsorption-desorption, SEM, UV-Vis DR, and FTIR spectroscopy. The results revealed that the prepared 3% Co-MCM-41 possessed mesoporous structure with BET surface areas at around 898.5 m²g^-1. The adsorption performance of 3% Co-MCM-41 toward levofloxacin (LVF) was investigated by batch experiments. The adsorption of LVF on 3% Co-MCM-41 was very fast and reached equilibrium within 2 h. The adsorption kinetics followed the pseudo-second-order kinetic model with the second-order rate constants in the range of 0.00198-0.00391 g mg^-1 min^-1. The adsorption isotherms could be well represented by the Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) isotherm equations. Nevertheless, D-R isotherm provided the best fit based on the coefficient of determination and average relative error values. The mean free energy of adsorption (E) calculated from D-R model was about 11 kJ mol^-1, indicating that the adsorption was mainly governed by a chemisorption process. Moreover, the adsorption capacity was investigated as a function of pH, adsorbent dosage, LVF concentration, and temperature with help of respond surface methodology (RSM). A quadratic model was established, and an optimal condition was obtained as follows: pH 8.5, adsorbent dosage of 1 g L^-1, initial LVF concentration of 119.8 mg L^-1, and temperature of 31.6 °C. Under the optimal condition, the adsorption capacity of 3% Co-MCM-41 to LVF could reach about 108.1 mg g^-1. The solution pH, adsorbent dosage, LVF concentration, and a combination of adsorbent dose and LVF concentration were significant factors affecting the adsorption process. The adsorption thermodynamic functions were also determined. The negative ΔH ⁰ (-33.50 kJ mol^-1) and ΔS ⁰ (-43.57 J mol^-1 K^-1) suggested that the adsorption was an exothermic process accompanied by decreasing disorder. This study may indicate that 3% Co-MCM-41 is a promising adsorbent for removing emerging pollutants of LVF from water.

Assessment of N-Oxide Formation during Wastewater Ozonation

Worldwide, ozonation of secondary wastewater effluents is increasingly considered in order to decrease the load of organic contaminants before environmental discharge. However, despite the constantly growing knowledge of ozonation over the past few years, the characterization of transformation products (TPs) is still a major concern, particularly because such TPs might remain biologically active. It has been shown for selected tertiary amine pharmaceuticals that they react with ozone and form the corresponding N-oxides. This study therefore applies liquid chromatography-high resolution mass spectrometry (LC-HRMS) to assess the overall N-oxide formation during the pilot-scale ozonation of a secondary wastewater effluent from a major city in Germany. Sample analysis by LC-HRMS revealed the occurrence of 1,229 compounds, among which 853 were precursors attenuated by ozone and 165 were TPs. Further examination of precursors and TPs using Kendrick mass and Kendrick mass defect analysis revealed 34 pairs of precursors and products corresponding to a mono-oxygenation. Among these, 27 pairs (16% of all TPs) were consistent with N-oxides since the TP had a higher retention time than the precursor, a characteristic of these compounds. Using high resolution tandem mass spectrometry, 10 of these N-oxides could be identified and were shown to be stable during a subsequent filtration step.

Genotoxicity of quinolone antibiotics in chlorination disinfection treatment: formation and QSAR simulation

Lots of unexpected disinfection by-products were formed during the chlorination disinfection of contaminated water bodies, leading to a potential threat to human health and ecological safety. In this study, SOS/umu assay was used to trace the genotoxicity variation of 20 quinolone compounds during the chlorination disinfection. Furthermore, two- and three-dimensional quantitative structure-activity relationship models were developed based on the electronic and hydrophobic properties of the quinolones, which were used to quantify the impact of the different structural features of the compounds on their genotoxicity variation. The results revealed that quinolones bearing hydrophilic substituents with less H-bond donors and negative charge at the 1-position of the quinolone ring exhibited a positive correlation with genotoxicity elevation. More notably, the chlorination of quinolones in both ultrapure water and secondary effluent matrices provided comparable levels of genotoxicity, indicating that our research could potentially be used to evaluate the environmental risk of quinolone antibiotics in chlorination disinfection treatment.

Simultaneous degradation of ofloxacin and recovery of Cu(II) by photoelectrocatalysis with highly ordered TiO2 nanotubes

A photoelectrocatalytic system for removal of ofloxacin and Cu(2+) complex was developed. In such a photoelectrocatalytic system, highly ordered titanium dioxide nanotubes served as a highly active photoanode for photoelectrocatalytic degradation of ofloxacin; and titanium plate was used as the cathode, on which Cu(2+) ions were electrodeposited. Compared with other treatment methods including photocatalysis, electrochemistry and direct photolysis, photoelectrocatalytic technique exhibited the highest removal efficiency for either ofloxacin or Cu(2+). To obtain the optimum photoelectrocatalytic operation conditions, some influencing factors such as current, pH and supporting electrolyte concentration were investigated systematically. The mutual influence analysis indicated that the photoelectrocatalytic removal efficiency of ofloxacin was first promoted by Cu(2+) but was then suppressed with prolonging the treatment time; whereas the removal of Cu(2+) was always promoted by ofloxacin over the whole photoelectrocatalytic treatment process. Furthermore, the photoelectrocatalytic removal of ofloxacin -Cu(2+) was studied by differential pulse voltammetry and high-performance liquid chromatography-mass spectrometry. The results indicated that although Cu(2+) influenced the removal rate of ofloxacin, it did not change the degradation mechanism of ofloxacin. The formation of an electroactive intermediate product during the photoelectrocatalytic process was clearly observed by voltammetric analysis. Based on intermediate products identified by high-performance liquid chromatography-mass spectrometry, a possible photoelectrocatalytic removal mechanism for ofloxacin -Cu(2+) was proposed.

Partial degradation of levofloxacin for biodegradability improvement by electro-Fenton process using an activated carbon fiber felt cathode

Solutions of 500 mL 200 mg L(-1) fluoroquinolone antibiotic levofloxacin (LEVO) have been degraded by anodic oxidation (AO), AO with electrogenerated H2O2 (AO-H2O2) and electro-Fenton (EF) processes using an activated carbon fiber (ACF) felt cathode from the point view of not only LEVO disappearance and mineralization, but also biodegradability enhancement. The LEVO decay by EF process followed a pseudo-first-order reaction with an apparent rate constant of 2.37×10(-2)min(-1), which is much higher than that of AO or AO-H2O2 processes. The LEVO mineralization also evidences the order EF>AO-H2O2>AO. The biodegradability (BOD5/COD) increased from 0 initially to 0.24, 0.09, and 0.03 for EF, AO-H2O2 and AO processes after 360 min treatment, respectively. Effects of several parameters such as current density, initial pH and Fe(2+) concentration on the EF degradation have also been examined. Three carboxylic acids including oxalic, formic and acetic acid were detected, as well as the released inorganic ions NH4(+), NO3(-) and F(-). At last, an ultra-performance liquid chromatography coupled with time-of-flight mass spectrometry was used to identify about eight aromatic intermediates formed in 60 min of EF treatment, and a plausible mineralization pathway for LEVO by EF treatment was proposed.

Fast removal of the antibiotic flumequine from aqueous solution by ozonation: Influencing factors, reaction pathways, and toxicity evaluation

As one of the first generation of fluoroquinolone antibiotics, flumequine (FLU) has been detected ubiquitously in surface waters and municipal wastewaters. In light of FLU's possible adverse effects on aquatic species, the removal of this antibiotic has received worldwide attention. In this study, the kinetics, transformation products, mechanisms and toxicity variations of the ozonation process for FLU were systematically determined. The possible effects of solution pH, addition of inorganic ions, dissolved organic matter, and tert-butyl-alcohol (a radical scavenger), as well as the type of water matrices on FLU removal by ozonation, were studied from the perspective of the degradation kinetics. The data obtained suggested that ozone can be used as an effective oxidant for the fast removal of FLU from natural waters. Using liquid chromatography-mass spectrometry, a total of thirteen transformation products of FLU during ozonation were identified, and their specific reaction mechanisms were also proposed. The degradation pathways involving the hydroxylation, decarboxylation and defluorination were tentatively proposed. Meanwhile, the generation of three low-molecular-weight carboxylic acids was also observed. In addition, the potential toxicity of the transformation mixtures of FLU by ozone was evaluated. Overall, this paper can be a unique contribution to the systematic elucidation of the ozonation process of this antibiotic in water.

Formation of chlorinated breakdown products during degradation of sunscreen agent, 2-ethylhexyl-4-methoxycinnamate in the presence of sodium hypochlorite

In this study, a new degradation path of sunscreen active ingredient, 2-ethylhexyl-4-methoxycinnamate (EHMC) and 4-methoxycinnamic acid (MCA) in the presence of sodium hypochlorite (NaOCl), was discussed. The reaction products were detected using gas chromatography-mass spectrometry (GC-MS). Since HOCl treatment leads to more polar products than EHMC, application of polar extracting agents, dichloromethane and ethyl acetate/n-hexane mixture, gave better results in terms of chlorinated breakdown products identification than n-hexane. Reaction of EHMC with HOCl lead to the formation of C=C bridge cleavage products such as 2-ethylhexyl chloroacetate, 1-chloro-4-methoxybenzene, 1,3-dichloro-2-methoxybenzene, and 3-chloro-4-methoxybenzaldehyde. High reactivity of C=C bond attached to benzene ring is also characteristic for MCA, since it can be converted in the presence of HOCl to 2,4-dichlorophenole, 2,6-dichloro-1,4-benzoquinone, 1,3-dichloro-2-methoxybenzene, 1,2,4-trichloro-3-methoxybenzene, 2,4,6-trichlorophenole, and 3,5-dichloro-2-hydroxyacetophenone. Surprisingly, in case of EHMC/HOCl/UV, much less breakdown products were formed compared to non-UV radiation treatment. In order to describe the nature of EHMC and MCA degradation, local reactivity analysis based on the density functional theory (DFT) was performed. Fukui function values showed that electrophilic attack of HOCl to the C=C bridge in EHMC and MCA is highly favorable (even more preferable than phenyl ring chlorination). This suggests that HOCl electrophilic addition is probably the initial step of EHMC degradation.

Mineralization of the antibiotic levofloxacin in aqueous medium by electro-Fenton process: kinetics and intermediate products analysis

The present study investigates the feasibility of using electro-Fenton (EF) process for the oxidative degradation of antibiotic levofloxacin (LEV). The EF experiments have been performed in an electrochemical cell using a carbon-felt cathode. The effect of applied current in the range 60-500 mA and catalyst concentration in the range 0.05-0.5 mM on the kinetics of oxidative degradation and mineralization efficiency have been investigated. Degradation of LEV by hydroxyl radicals was found to follow pseudo-first-order reaction kinetics. The absolute rate constant for oxidative degradation of LEV by hydroxyl radical has been determined by a competition kinetics method and found to be (2.48 ± 0.18) × 10(9) M(-1) s(-1). An optimum current value of 400 mA and a catalyst (Fe(2+)) concentration of 0.1 mM were observed to be optimal for an effective degradation of LEV under our operating conditions. Mineralization of aqueous solution of LEV was performed by the chemical oxygen demand analysis and an almost mineralization degree (>91%) was reached at the end of 6 h of electrolysis. A number of intermediate products have been identified using high performance liquid chromatography and liquid chrmatography-mass spectrometry analyses. Based on these identified reaction intermediates, a plausible reaction pathway has been suggested for the mineralization process. The formation and evolution of [Formula: see text] and [Formula: see text] ions released to the medium during the process were also discussed.

One-step solvothermal synthesis of magnetic Fe3O4-graphite composite for Fenton-like degradation of levofloxacin

A novel Fe3O4-graphite composite was prepared, characterized, and investigated as a heterogeneous Fenton-like catalyst for the degradation of levofloxacin (LEV) in an aqueous solution. The results revealed that the Fe3O4-graphite composite exhibited excellent properties for the degradation and mineralization of LEV, achieving a nearly complete degradation of 50 mg L(-1) LEV in 15 min and 48% of total organic carbon removal in 60 min under optimal conditions. A large electronic conjugation structure exists in graphite, which may lead to the fast production of •OH radical species because of the easy reduction of Fe(III) to Fe(II). In addition, we observed that the graphite can degrade LEV in the presence of H2O2. Therefore, the synergistic results of the graphite structure and Fe3O4 magnetic nanoparticles (MNPs) may contribute to the high catalytic activity of the Fe3O4-graphite composite. Compared with pure Fe3O4 MNPs, lesser iron leaching of the Fe3O4-graphite composite was observed during the degradation of LEV. The degradation efficiency of LEV remained approximately 80% at the fifth recycling run, which indicates that the Fe3O4-graphite composite has potential applications in water treatment for removing organic pollutants.