Degradation of tetracycline in aqueous medium by electrochemical method

Using green nanocomposite containing eggshell in the electroperoxone process in a baffled reactor to remove the emerging tetracycline pollutant

This study examined the eradication of Tetracycline hydrochloride (TCH) antibiotic, an emerging pollutant, by utilizing eggshell membrane activated carbon (EMAC) and magnetite (Fe3O4) nanocomposite in conjunction with the electroperoxone process employing the One Factor at a Time method (OFAT) in a baffled reactor. The nanocomposite was synthesized through the hydrothermal method using an autoclave, and its properties were assessed via XRD, FTIR, FESEM, EDAX Mapping, BET, and VSM analyses. The findings revealed that under optimal conditions (including a pollutant concentration of 300 mg/L, a natural pH of 6.2, an ozone consumption rate of 0.28 g/h, a nanocomposite concentration of 0.2 g/L, a flow intensity of 0.5 A, a wastewater recirculation flow rate of 8 L/h, and a 0.1 M Na2SO4 electrolyte concentration), 95.9%, 76.4%, and 53.4% of pollutants, COD, and TOC were respectively eliminated after 90 min. Additionally, the reusability of the nanocomposite was evaluated over five usage periods, during which the process efficiency decreased from 95.9% to 83.1%. In short, this study proved that EMAC/Fe3O4 nanocomposites are promising electroperoxone catalysts due to their low cost, excellent stability and reusability, environmental compatibility, and superior catalytic activity for TCH antibiotics removal.

Facile introduction of coordinative Fe into oxygen-enriched graphite carbon nitride for efficient photo-Fenton degradation of tetracycline

Tetracycline (TC) antibiotics have been widely used over the past decades, and their massive discharge led to serious water pollution. Photo-Fenton process has gained ever-increasing attention for its excellent oxidizing ability and friendly solar energy utilization ability in TC polluted water treatment. This work introduced coordinative Fe into oxygen-enriched graphite carbon nitride (OCN) to form FeOCN composites for efficient photo-Fenton process. Hemin was chosen as the source to provide the source of coordinative Fe-Nx groups. The degradation efficiency of TC reached 82.1 % within 40 min of irradiation, and remained 76.9 % after five runs of reaction. The degradation intermediates of TC were detected and the possible degradation pathways were gained. It was found that h+, OH, and O2- played major roles in TC degradation. Notably, the photo-Fenton performance of FeOCN was stable in highly saline water or strong acid/base environment (pH 3.0-9.0). Besides, H2O2 can be generated in-situ in this photo-Fenton process, which is favorable for practical application. It can be anticipated that the coordinative FeOCN composites will promote the application of photo-Fenton oxidation process in TC polluted water treatment.

Construction of multifunctional NH2-UiO-66 metal organic framework: sensing and photocatalytic degradation of ketorolac tromethamine and tetracycline in aqueous medium

Existence of pharmaceutical residues in water has endangered environmental pollution worldwide, which makes it ineludible to develop prospective bifunctional materials which not only possess excellent fluorescence behaviour to monitor pharmaceuticals but also exhibit simultaneous photocatalytic removal efficiency. Strengthened by functionalized metal organic framework (MOF) materials, we present here an amine functionalized zirconium-based MOF NH₂-UiO-66 which has been successfully synthesized using solvothermal approach. The as prepared MOF was subjected to numerous structural, morphological and compositional characterizations. Interestingly, featured by the excellent fluorescent intensity of MOF modulated by LMCT effect, NH₂-UiO-66 was screened to detect pharmaceutical compounds with KTC and TC in aqueous solution. The prepared functionalized MOF showcased excellent sensing platform with magnificent response range (0‒3 µM), lower limit of detection (160 nM; KTC and 140 nM; TC), excellent selectivity and influential anti-interference capability. More importantly, the practical utility of the proposed sensor was further explored for the determination of pharmaceutical drugs in real water samples with suitable recoveries. Simultaneously, the synthesized MOF also exhibited high photocatalytic efficiency towards the removal of KTC and TC under solar light irradiation. The degradation efficiency for KTC and TC was found to be 68.3% and 71.8% within 60 and 280 min of solar light, respectively. Moreover, excellent recyclability was demonstrated by the current synthesized system over five cycles. Overall, this study presents a feasible route for the utilization of functionalized MOFs as potential dual functional materials towards the simultaneous detection and degradation of specific pharmaceuticals from aqueous medium.

Electro-oxidation of Ni (II)-citrate complexes at BDD electrode and simultaneous recovery of metallic nickel by electrodeposition

The simultaneous electro-oxidation of Ni (II)-citrate and electrodeposition recovery of nickel metal were attempted in a combined electro-oxidation-electrodeposition reactor with a boron-doped diamond (BDD) anode and a polished titanium cathode. Effects of initial nickel citrate concentration, current density, initial pH, electrode spacing, electrolyte type, and initial electrolyte dosage on electrochemical performance were examined. The efficiencies of Ni (II)-citrate removal and nickel metal recovery were determined to be 100% and over 72%, respectively, under the optimized conditions (10 mA/cm², pH 4.09, 80 mmol/L Na₂SO₄, initial Ni (II)-citrate concentration of 75 mg/L, electrode spacing of 1 cm, and 180 min of electrolysis). Energy consumption increased with increased current density, and the energy consumption was 0.032 kWh/L at a current density of 10 mA/cm² (pH 6.58). The deposits at the cathode were characterized by scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). These characterization results indicated that the purity of metallic nickel in cathodic deposition was over 95%. The electrochemical system exhibited a prospective approach to oxidize metal complexes and recover metallic nickel.

A High Flux Electrochemical Filtration System Based on Electrospun Carbon Nanofiber Membrane for Efficient Tetracycline Degradation

In this work, an electrochemical filter using an electrospun carbon nanofiber membrane (ECNFM) anode fabricated by electrospinning, stabilization and carbonization was developed for the removal of antibiotic tetracycline (TC). ECNFM with 2.5 wt% terephthalic acid (PTA) carbonized at 1000 °C (ECNFM-2.5%-1000) exhibited higher tensile stress (0.75 MPa) and porosity (92.8%), more graphitic structures and lower electron transfer resistance (23.52 Ω). Under the optimal condition of applied voltage 2.0 V, pH 6.1, 0.1 mol L−1 Na2SO4, initial TC concentration 10 ppm and membrane flux 425 LMH, the TC removal efficiency of the electrochemical filter of ECNFM-2.5%-1000 reached 99.8%, and no obvious performance loss was observed after 8 h of continuous operation. The pseudo-first-order reaction rate constant in flow-through mode was 2.28 min−1, which was 10.53 times higher than that in batch mode. Meanwhile, the energy demand for 90% TC removal was only 0.017 kWh m−3. TC could be converted to intermediates with lower developmental toxicity and mutagenicity via the loss of functional groups (-CONH2, -CH3, -OH, -N(CH3)2) and ring opening reaction, which was mainly achieved by direct anodic oxidation. This study highlights the potential of ECNFM-based electrochemical filtration for efficient and economical drinking water purification.

Efficiency of an up-flow Anaerobic Sludge Blanket reactor coupled with an electrochemical system to remove chloramphenicol in swine wastewater

The application and design of treatment systems in wastewater are necessary due to antibiotics' potential toxicity and resistant genes on residual effluent. This work evaluated a coupled bio-electrochemical system to reduce chloramphenicol (CAP) and chemical oxygen demand (COD) on swine wastewater (SWW). SWW characterization found CAP of <10 μg/L and 17,434 mg/L of COD. The coupled system consisted of preliminary use of an Up-flow Anaerobic Sludge Blanket Reactor (UASB) followed by electrooxidation (EO). The UASB reactor (primary stage) was operated for three months at an organic load of 8.76 kg of COD/m³d and 50 mg CAP/L as initial concentration. In EO, we carried out a 2² (time operation and intensity) factorial design with a central composite design; we tried two Ti cathodes and one anode of Ti/PbO₂. Optimal conditions obtained in the EO process were 240 min of operation time and 1.51 A of current intensity. It was possible to eliminate 44% of COD and 64.2% of CAP in the preliminary stage. On bio-electrochemicals, total COD and CAP removal were 82.35 and >99.99%, respectively. This coupled system can be applied to eliminate antibiotics and other organic pollutants in agricultural, industrial, municipal, and other wastewaters.

Effect of Pleurotus ostreatus and Trametes versicolor on triclosan biodegradation and activity of laccase and manganese peroxidase enzymes

INTRODUCTION

Triclosan (TCS) is an extensively used antibacterial agent which has been frequently detected in different environmental compartments. Because of TCS inhibition effect on vast majority of bacterial species, it is important to explore fungal species and their involved enzymes in TCS biodegradation. The aim of this study was to compare the potential of two white rot fungi Pleurotus ostreatus and Trametes versicolor for TCS biodegradation through the whole cell culture of fungi in an aqueous culture medium. Additionally, the changes in ligninolytic enzyme activities and possible correlations and contributions of degradative enzymes during TCS biodegradation process were monitored.

MATERIAL AND METHODS

This study was carried out using a factorial experiment with a completely randomized design in three replications. factorial design in The experimental factors included: two white rot fungi Pleurotus ostreatus and Trametes versicolor and uninoculated controls which were subjected to five levels of TCS concentrations (0, 5, 10, 20, 30 and 50 μg mL-1) to assess ligninolytic enzymatic activity during biodegradation of TCS. Samples were harvested periodically at three time intervals (4, 7 and 10 days). An AB SCIEX 3200 QTRAP LC-MS/MS system was used in order to analyze the biodegradation of TCS in liquid medium.

RESULTS

Results suggested that the two white rot fungi responded differently when exposed to the different concentrations of TCS. In general, P. ostreatus exhibited more potential and ligninolytic enzymatic activity compared to T. versicolor. LC-MS/MS analyses also showed that P. ostreatus degraded TCS with higher efficiency compared to T. versicolor. In addition, almost all P. ostreatus biodegradation activity was completed within the first day of sampling. Contrasting, less efficient degradation was observed by T. versicolor, reaching around 88% of TCS biodegradation at concentration of 20 μg mL-1after 10 days. At higher TCS concentrations (≥30 μg mL-1), the growth of T. versicolor severely inhibited and led to a drop in enzymatic activity and biodegradation. Furthermore, laccase and manganese peroxidase (MnP) were determined as more involved enzymes which significantly correlated to TCS biodegradation by T. versicolor and P. ostreatus, respectively.

CONCLUSION

P. ostreatus might be considered as efficient fungus in biodegradation of high amount of TCS in environmental matrices. The results of the present study might provide insights for future investigations on potential of fungi for applications in bioaugmentation-based strategies to remove TCS from wastewater and activated sludge.

Photo-electrocatalytic degradation of cyclic volatile methyl siloxane by ZnO-coated aluminum anode: Optimal parameters, kinetics, and reaction pathways

Cyclic volatile methylsiloxanes (cVMSs) are widely used in industrial processes and consumer products, which have been reported to be potentially toxic to human health due to their persistence and bioaccumulation. In this study, a novel photo-catalytic zinc oxide (ZnO)-coated aluminum (ZnO@Al) anode was prepared by a facile hydrothermal epitaxial process for the purpose of degrading cVMSs in practical wastewater. Morphological data and compositional analysis showed a compact coating layer that had the characteristic peaks of ZnO. To optimize the degradation process, central composite design combined with response surface methodology was applied to acquire the optimum parameters of cVMSs removal, and results indicated the cVMSs removal efficiency was approximately 63.3% at the conditions of current density = 17.3 mA/cm², initial pH of electrolyte = 7.8, plate distance = 18 mm, UV intensity = 90 W, and reaction time = 80 min. Furthermore, the photo-electrocatalytic degradation of cVMSs obeys the pseudo-first order kinetic reaction, and the anode exhibited high durability as the attenuation of cVMSs removal efficiency was <6% after four times reuse. It was also observed that with the application period of the anode was extended, the electroflocculation reaction gradually occurred. The FT-IR of the generated flocs and the total ion gas chromatograms mass spectrometer analysis unraveled the methyl groups in Si-CH₃ could be easily attacked by hydroxyl radicals to form the intermediates of monohydroxy substituted products (m/z = 298, 372, and 446) and eventually short-chain carboxylic acids, alkyl radical and silicate. The effective removal of cVMSs by photo-electrocatalytic process using ZnO@Al anode provide significant implication in treatment of practical wastewater.

Rapid decontamination of tetracycline hydrolysis product using electrochemical CNT filter: Mechanism, impacting factors and pathways

In this study, electrooxidation of the tetracycline hydrolysis products was investigated using a carbon nanotube (CNT) electrochemical filter and 4-epianhydrochlortetracycline (EACTC) as a model compound. Electrochemical filtration of 10 μmol L^-1 EACTC at a voltage of 2.5 V and a flow rate of 1.5 mL min^-1 (hydraulic residence time <3 s) provided an oxidation flux of 1251 ± 28 μmol h^-1 m^-2. Replacement of the Ti cathode with a CNT filter cathode increased the EACTC oxidative flux by 1.3 fold at a voltage of 2.5 V. The electrochemical filtration process is effective for the degradation of EACTC and the reduction of the antimicrobial activity based on liquid chromatography time-of-flight mass spectrometry (LC-TOF-MS) analysis and luminescent bacteria test. The high oxidation flux within 300 min (1212-1263 μmol h^-1 m^-2) and affordable cost (0.25 kWh m^-3) at a voltage of 2.5 V show the potential application of the electrochemical filtration system as a promising unit for EACTC degradation. These findings provided new insights into the rational design principles of novel continuous-flow filtration system aimed to efficiently remove hydrolysis products of the antibiotic tetracycline.

Electrokinetic remediation of antibiotic-polluted soil with different concentrations of tetracyclines

This study investigated the efficacy of electrokinetic remediation of soils polluted with different concentrations of tetracyclines (TCs). Three widely used TCs (oxytetracycline, chlortetracycline, and tetracycline) were selected, and concentrations of 0, 5, 10, 20, and 50 mg/kg (C0, C5, C10, C20, C50) were selected for comparison. Antibiotic-polluted soils with no electric field served as controls. The average removal rates of TCs in different treatments ranged from 25 to 48% after 7-day remediation. The contributing ratios of electrokinetics to TCs removal varied from 22 to 84%. The concentrations of NH₄⁺ increased in soils and electrolytes, which indicated the decomposition of TCs in the electric field. The highest removal amount of TCs was obtained in the C50 treatment, due to efficient reactions of TCs with oxidative radicals generated during the electrolysis. The fluctuant range of pH in the electrolytes was decreased with increasing concentration of TCs, while the soil pH was increased. The removal rate of antibiotic-resistant bacteria (ARB) in the C5 treatment was significantly higher than that in other treatments. The abundance of antibiotic resistance genes (ARGs) increased with the concentrations of TCs in soils. It might result from the induction of increasing selective pressure of antibiotics. Significant removal of ARGs occurred in the C50 treatment (38-60%). In terms of controlling ARB and ARGs, which were more resistant, the electrokinetic technology showed advantageous effects. Above all, electrokinetic technology provides an effective remediation method, especially for TC-polluted soil with a concentration of 20-50 mg/kg.

Anti-corrosion porous RuO2/NbC anodes for the electrochemical oxidation of phenol

Efficient anode materials with porous structures have drawn increasing attention due to their high specific surface area, which can compensate for the slow reaction rate of electrochemical oxidation. However, the use of these materials is often limited due to their poor corrosion resistance. Herein, we report a facile scale-up method, by carbothermal reduction, for the preparation of porous niobium carbide to be used as an anode for the electrochemical oxidation of phenol in water. No niobium ions were detected when the anodes were under aggressive attack by sulfuric acid and under electrochemical corrosion tests with a current density less than 20.98 mA cm⁻². The porous niobium carbide was further modified by applying a ruthenium oxide coating to improve its catalytic activity. The removal rates of phenol and chemical oxygen demand by the RuO₂/NbC anode reached 1.87 × 10⁻² mg min⁻¹ cm⁻² and 6.33 × 10⁻² mg min⁻¹ cm⁻², respectively. The average current efficiency was 85.2%. Thus, an anti-corrosion, highly catalytically active and energy-efficient porous RuO₂/NbC anode for the degradation of aqueous phenol in wastewater was successfully prepared.

Efficient anode materials with porous structures have drawn increasing attention due to their high specific surface area, which can compensate for the slow reaction rate of electrochemical oxidation.

Synthesis and characterization of a novel CNT-FeNi3/DFNS/Cu(ii) magnetic nanocomposite for the photocatalytic degradation of tetracycline in wastewater

Herein, Cu(ii) complexes were anchored within the nanospaces of a magnetic fibrous silicate with a high surface area and easily accessible active sites via a facile approach, leading to the successful synthesis of a novel potent nanocatalyst (FeNi₃/DFNS/Cu). Furthermore, FeNi₃/DFNS/Cu was supported on carbon nanotubes (CNTs) via an usual nozzle electrospinning method (CNT-FeNi₃/DFNS/Cu). In addition, its performance as a photocatalyst for the degradation of tetracycline was tested in a batch reactor. Tetracycline is an antibiotic that is commonly utilized in veterinary medicine and in the treatment of human infections, but is hazardous to aquatic environments. However, the usual processes for the removal of tetracycline are not efficient. The eco-friendly attributes of this catalytic system include high catalytic activity and ease of recovery from the reaction mixture using an external magnet, and it can be reused several times without significant loss in its performance. Also, protocols such as hot filtration, and mercury poisoning provided complete insight into the nature of this heterogeneous catalyst.

Herein, Cu(ii) complexes were anchored within the nanospaces of a magnetic fibrous silicate with a high surface area and easily accessible active sites via a facile approach, leading to the successful synthesis of a novel potent nanocatalyst (FeNi₃/DFNS/Cu).

Evaluating tetracycline degradation pathway and intermediate toxicity during the electrochemical oxidation over a Ti/Ti4O7 anode

Tetracycline (TC) is one of the most widely used antibiotics with significant impacts on human health and thus it needs appropriate approaches for its removal. In the present study, we evaluated the performance and complete pathway of the TC electrochemical oxidation on a Ti/Ti₄O₇ anode prepared by plasma spraying. Morphological data and composition analysis indicated a compact coating layer on the anode, which had the characteristic peaks of Ti₄O₇ as active constituent. The TC electrochemical oxidation on the Ti/Ti₄O₇ anode followed a pseudo-first-order kinetics, and the TC removal efficiency reached 95.8% in 40 min. The influential factors on TC decay kinetics included current density, anode-cathode distance and initial TC concentration. This anode also had high durability and the TC removal efficiency was maintained over 95% after five times reuse. For the first time, we unraveled the complete pathway of the TC electrochemical oxidation using high-performance liquid chromatograph (HPLC) and gas chromatograph (GC) coupled with mass spectrometer (MS). ·OH radicals produced from electrochemical oxidation attack the double bond, phenolic group and amine group of TC, forming a primary intermediate (m/z = 461), secondary intermediates (m/z = 432, 477 and 509) and tertiary intermediates (m/z = 480, 448 and 525). The latter were further oxidized to the key downstream intermediate (m/z = 496), followed by further downstream intermediates (m/z = 451, 412, 396, 367, 351, 298 and 253) and eventually short-chain carboxylic acids. We also evaluated the toxicity change during the electrochemical oxidation process with bioluminescent bacteria. The bioluminescence inhibition ratio peaked at 10 min (55.41%), likely owing to the high toxicity of intermediates with m/z = 461, 432 and 477 as obtained from quantitative structure activity relationship (QSAR) analysis. The bioluminescence inhibition ratio eventually decreased to 16.78% in 40 min due to further transformation of TC and intermediates. By comprehensively analyzing the influential factors and complete degradation pathway of TC electrochemical oxidation on the Ti/Ti₄O₇ anode, our research provides deeper insights into the risk assessment of intermediates and their toxicity, assigning new perspectives for practical electrochemical oxidation to effectively eliminate the amount and toxicity of TC and other antibiotics in wastewater.

Electrochemical treatment of 2, 4-dichlorophenol using a nanostructured 3D-porous Ti/Sb-SnO2-Gr anode: Reaction kinetics, mechanism, and continuous operation

2, 4-dichlorophenol (2, 4-DCP) is considered to be a highly toxic, mutagenic, and possibly carcinogenic pollutant. This study is focused on the electrochemical oxidation of 2, 4-DCP on nanostructured 3D-porous Ti/Sb-SnO₂-Gr anodes, with the aim of presenting a comprehensive elucidation of mineralization process through the investigation of influential kinetics, the reactivity of hydroxyl radical's and analysis of intermediates. High efficiency was achieved at pH of 3 using Na₂SO₄ electrolytes at a current density of 30 mA cm^-2. Under the optimized conditions, a maximum removal of 2, 4-DCP of up to 99.9% was reached, whereas a TOC removal of 81% was recorded with the lowest EC_TOC (0.49 kW h g^-1) within 40 min of electrolysis. To explore the stability of the 3D-Ti/Sb-SnO₂-Gr electrodes, a continuous electrochemical operation was established, and the consistent mineralization results indicated the effectiveness of the 3D-Ti/Sb-SnO₂-Gr system concerning its durability and practical utilization. EPR studies demonstrated the abundant generation of OH radicals on 3D-Ti/Sb-SnO₂-Gr, resulting in fast recalcitrant pollutant incineration. From dechlorination and the reactivity of the OH radicals, several intermediates including six cyclic byproducts and three aliphatic carboxylic acids were detected, and two possible degradation pathways were proposed that justify the complete mineralization of 2, 4-DCP.

Electrochemical degradation of the antihypertensive losartan in aqueous medium by electro-oxidation with boron-doped diamond electrode

In this work the electrochemical oxidation of losartan, an emerging pharmaceutical pollutant, was studied. Electrochemical oxidation was carried out in batch mode, in an open and undivided cell of 100cm(3) using a boron-doped diamond (BDD)/stainless steel system. With Cl(-) medium 56% of mineralization was registered, while with the trials containing SO4(2-) as supporting electrolyte a higher mineralization yield of 67% was reached, even obtaining a total removal of losartan potassium at 80mAcm(-2) and 180min of reaction time at pH 7.0. Higher losartan potassium concentrations enhanced the mineralization degree and the efficiency of the electrochemical oxidation process. During the mineralization up to 4 aromatic intermediates were identified by ultra high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS). Moreover, short-linear carboxylic acids, like oxalic, succinic and oxamic were detected and quantified by ion-exclusion HPLC. Finally, the ability of the electrochemical oxidation process to mineralize dissolved commercial tablets containing losartan was achieved, obtaining TOC removal up to 71% under optimized conditions (10mAcm(-2), 0.05M Na2SO4, pH 7.0 and 25°C and 360min of electrolysis).

Ti/β-PbO2 versus Ti/Pt/β-PbO2: Influence of the platinum interlayer on the electrodegradation of tetracyclines

The behaviors of the electrodes Ti/PbO2 and Ti/Pt/PbO2 as anodes in the electro-oxidation of two antibiotics-tetracycline and oxytetracycline-were evaluated at different applied current densities, to evaluate the influence of the Pt interlayer. In the preparation of the electrodes, the electrodeposited β-PbO2 phase was homogeneous; no Ti or Pt peaks were detected in the diffractograms. The β-PbO2 surface presented significant roughness when deposited over the Pt interlayer, which also conferred significant conductivity to the material. In the electro-oxidation assays, the COD, TOC and absorbance removals increased with the current density due to an increase in the concentration of hydroxyl radicals, for both electrode materials and antibiotics tested. Slightly better results were obtained with Ti/PbO2. The primary differences observed in the antibiotics concentration decay consisted of zero-order kinetics at the Ti/Pt/PbO2 anode and first-order kinetics at the Ti/PbO2 anode with a higher oxytetracycline concentration decay than the tetracycline concentration decay. A greater amount of total nitrogen was eliminated with the Ti/PbO2 electrode. At the Ti/Pt/PbO2 anode, the organic nitrogen primarily transformed into NH4(+) and the total nitrogen remained unchanged. The specific energy consumption with the Ti/Pt/PbO2 anode was significantly lower than the specific energy consumption with the Ti/PbO2 anode due to the higher electrical conductivity of the Ti/Pt/PbO2 anode. Both anode materials were also utilized in the electro-oxidation of a leachate sample collected at sanitary landfill and spiked with tetracycline, and the complete elimination of the antibiotic molecule was observed.

Heterogeneous activation of hydrogen peroxide using γ-Al2O3 supported bimetallic Fe, Mn for the degradation of reactive black 5

A Fe–Mn/γ-Al₂O₃ catalyst was prepared via a wet impregnation method and used for the degradation of reactive black 5 (RB5) as an activator of hydrogen peroxide (H₂O₂).

Degradation of tetracycline at a boron-doped diamond anode: influence of initial pH, applied current intensity and electrolyte

The anodic oxidation of tetracycline was performed in an up-flow reactor, operating in batch mode with recirculation, using as anode a boron-doped diamond electrode. The influence on the degradation rate of solution initial pH (2 to 12), applied current intensity (25 to 300 A m(-2)) and type of electrolyte (sodium sulphate or sodium chloride) were investigated. For the assays run at equal current density, with sodium sulphate as electrolyte, the solution's initial pH of 2 presented the highest absorbance and chemical oxygen demand removals. Regarding the influence of current density, for equal charge passed, the organic load removal rate decreased with the increase in applied current. When sodium sulphate was used as an electrolyte, high-performance liquid chromatography (HPLC) results have shown an almost complete removal of tetracycline after a 2-h assay. HPLC results have also shown the presence of oxamic acid as one of the intermediates of tetracycline anodic oxidation. The complete removal of tetracycline was much faster in the presence of chloride ions that promoted the complete degradation of this antibiotic in 30 min. However, in the presence of chloride ions, the tetracycline mineralization is slower, as observed by the lower organic carbon removal rate when compared to that of the tetracycline degradation in the presence of sulphate.

Activated sludge systems removal efficiency of veterinary pharmaceuticals from slaughterhouse wastewater

The knowledge on the efficiency of wastewater treatment plants (WWTPs) from animal food production industry for the removal of both hormones and antibiotics of veterinary application is still very limited. These compounds have already been reported in different environmental compartments at levels that could have potential impacts on the ecosystems. This work aimed to evaluate the role of activated sludge in the removal of commonly used veterinary drugs, enrofloxacin (ENR), tetracycline (TET), and ceftiofur, from wastewater during a conventional treatment process. For that, a series of laboratory-controlled experiments using activated sludge were carried out in batch reactors. Sludge reactors with 100 μg/L initial drug charge presented removal rates of 68 % for ENR and 77 % for TET from the aqueous phase. Results indicated that sorption to sludge and to the wastewater organic matter was responsible for a significant percentage of drugs removal. Nevertheless, these removal rates still result in considerable concentrations in the aqueous phase that will pass through the WWTP to the receiving environment. Measuring only the dissolved fraction of pharmaceuticals in the WWTP effluents may underestimate the loading and risks to the aquatic environment.

Pharmaceuticals as emerging contaminants and their removal from water. A review

The main objective of this study was to conduct an exhaustive review of the literature on the presence of pharmaceutical-derived compounds in water and on their removal. The most representative pharmaceutical families found in water were described and related water pollution issues were analyzed. The performances of different water treatment systems in the removal of pharmaceuticals were also summarized. The water treatment technologies were those based on conventional systems (chlorine, chlorine dioxide, wastewater treatment plants), adsorption/bioadsorption on activated carbon (from lotus stalks, olive-waste cake, coal, wood, plastic waste, cork powder waste, peach stones, coconut shell, rice husk), and advanced oxidation processes by means of ozonation (O₃, O₃/H₂O₂, O₃/activated carbon, O₃/biological treatment), photooxidation (UV, UV/H₂O₂, UV/K₂S₂O₈, UV/TiO₂, UV/H₂O₂/TiO₂, UV/TiO₂/activated carbon, photo-Fenton), radiolysis (e-Beam, ⁶⁰Co, ¹³⁷Cs. Additives used: H₂O₂, SO₃²⁻, HCO₃⁻, CH₃₋OH, CO₃²⁻, or NO₃⁻), and electrochemical processes (Electrooxidation without and with active chlorine generation). The effect of these treatments on pharmaceutical compounds and the advantages and disadvantages of different methodologies used were described. The most important parameters of the above water treatment systems (experimental conditions, removal yield, pharmaceutical compound mineralization, TOC removal, toxicity evolution) were indicated. The key publications on pharmaceutical removal from water were summarized.

Selective degradation of tetracycline antibiotics present in raw milk by electrochemical method

The dairy industry disposes of a large volume of waste milk with antibiotic residues, which is a great cause of much concern in soil and water environments. In this study, the electrochemical oxidation of tetracycline antibiotics (TCs) in cow's milk was investigated. Milk contains a high concentration of organic matter, and the concentrations of TCs residues are extremely low. The effects of anode materials and electrolytes on the degradation of oxytetracycline (OTC) were investigated. A higher degradation rate for the OTC was attained using the inactive anode or a NaCl electrolyte. It was found that a physically adsorbed oxidant on the surface of the anode and indirect oxidation using electrogenerated hypochlorite could enhance the degradation of OTC in raw milk. The organic components in milk samples affected the removal rate of the OTC. The removal rate constants for the OTC in raw milk were 2.8-7.7 times higher than the chemical oxygen demand values. It was found that electrochemical oxidation could decompose low concentrations of TCs in high concentrations of organic matter solutions selectively. The results indicate that electrochemical oxidation is an effective method for the treatment of TCs in waste milk.

Electro-Fenton treatment of mature landfill leachate in a continuous flow reactor

The treatment of mature landfill leachate by EF-Fere (also called Fered-Fenton) method was carried out in a continuous stirred tank reactor (CSTR) using Ti/RuO(2)-IrO(2)-SnO(2)-TiO(2) mesh anodes and Ti mesh cathodes. The effects of important parameters, including initial pH, inter-electrode gap, H(2)O(2) to Fe(2+) molar ratio, H(2)O(2) dosage and hydraulic retention time, on COD removal were investigated. The results showed that the complete mixing condition was fulfilled in the electrochemical reactor employed in this study and COD removal followed a modified pseudo-first order kinetic model. The COD removal efficiency increased with the decrease of H(2)O(2) to Fe(2+) molar ratio and hydraulic retention time. There existed an optimal inter-electrode gap or H(2)O(2) dosage so that the highest COD removal was achieved. Nearly the same COD removal was obtained at initial pH 3 and 5, but the steady state was quickly achieved at initial pH 3. The organic pollutants in the leachate were analyzed through a gas chromatography coupled with mass spectrometry (GC-MS) system. About 73 organics were detected in the leachate, and 52 of which were completely removed after EF-Fere process.

Application of response surface methodology to the removal of the antibiotic tetracycline by electrochemical process using carbon-felt cathode and DSA (Ti/RuO2-IrO2) anode

The removal of antibiotic tetracycline (TC) from water by electrochemical advanced oxidation process (EAOP) was performed using a carbon-felt cathode and a DSA (Ti/RuO(2)-IrO(2)) anode. The influence of applied current, initial pH and initial TC concentration on TC removal efficiency was investigated. Response surface methodology (RSM) based on Box-Behnken statistical experiment design (BBD) was applied to analyze the experimental variables. The positive and negative effects of variables and the interaction between variables on TC removal efficiency were determined. The applied current showed positive effect, while the initial pH value and initial tetracycline concentration gave negative effect on TC removal. The interaction between applied current and initial pH value was significant, while the interactions of initial TC concentration with applied current or initial pH were not pronounced. The results of adequacy check confirmed that the proposed models were accurate and reliable to analyze the variables of EAOP. The reaction intermediates were identified by high-performance liquid chromatography-mass spectrometry (LC-MS) technique and a plausible degradation pathway for tetracycline degradation was proposed. The acute toxicity experiments illustrated that the Daphnia magna immobilization rate reached the maximum after 240 min of electrolysis and then decreased with the progress of the reaction.

Behaviour of multi-component mixtures of tetracyclines when degraded by photoelectrocatalytic and electrocatalytic technologies

The main objective of this work was to study and contrast the degradation behaviour of multi-component mixtures of tetracyclines (TCs) during processes of the photoelectrocatalysis (PEC) and electrocatalysis (EC). During these two processes, we investigated the degradation efficiency of TCs under different influence factors and their reaction mechanisms and degradation kinetics, and the degradation difference ofTC, oxytetracycline (OTC) and chlortetracycline (CTC). The results indicate that applied bias potentials, pH and reaction atmosphere greatly influenced the degradation of TCs. Under different pH conditions, the degradation efficiency of TC and OTC changed little, but that of CTC varied greatly. This difference may stem from the halogen group (-Cl) that CTC carries. Under given conditions, PEC generated greater photocurrent, and the degradation efficiency during the PEC process was higher by about 10% at 180 min. The manners in which HO* radicals were generated during the PEC and EC processes were also compared. TCs degradation in the two processes accorded well with the first-order reaction kinetics equation at lower bias potentials, whereas at a higher bias potential of2 V, both reactions deviated from the equation, and their fitting curves were closer to parabolic.

Remediation of water pollution caused by pharmaceutical residues based on electrochemical separation and degradation technologies: a review

In the last years, the decontamination and disinfection of waters by means of direct or integrated electrochemical processes are being considered as a very appealing alternative due to the significant improvement of the electrode materials and the coupling with low-cost renewable energy sources. Many electrochemical technologies are currently available for the remediation of waters contaminated by refractory organic pollutants such as pharmaceutical micropollutants, whose presence in the environment has become a matter of major concern. Recent reviews have focused on the removal of pharmaceutical residues upon the application of other important methods like ozonation and advanced oxidation processes. Here, we present an overview on the electrochemical methods devised for the treatment of pharmaceutical residues from both, synthetic solutions and real pharmaceutical wastewaters. Electrochemical separation technologies such as membrane technologies, electrocoagulation and internal micro-electrolysis, which only isolate the pollutants from water, are firstly introduced. The fundamentals and experimental set-ups involved in technologies that allow the degradation of pharmaceuticals, like anodic oxidation, electro-oxidation with active chlorine, electro-Fenton, photoelectro-Fenton and photoelectrocatalysis among others, are further discussed. Progress on the promising solar photoelectro-Fenton process devised and further developed in our laboratory is especially highlighted and documented. The abatement of total organic carbon or reduction of chemical oxygen demand from contaminated waters allows the comparison between the different methods and materials. The routes for the degradation of the some pharmaceuticals are also presented.

Degradation of tetracycline in aqueous media by ozonation in an internal loop-lift reactor

The degradation of tetracycline by ozone was investigated in this paper. In the laboratory scale experiments, the effect of major parameters, including pH, gas flow rate, gaseous ozone concentration, hydrogen peroxide concentration and hydroxyl radical scavenger (tert-butyl alcohol) on the degradation of tetracycline was studied. A pseudo-first order kinetic model was used to simulate the experimental results. The results indicated that the tetracycline degradation rate increased with pH, gaseous ozone concentration and gas flow rate. The addition of hydrogen peroxide or hydroxyl radical scavenger had little effect on tetracycline removal, indicating that the direct oxidation of tetracycline by ozone was dominant process and the radical contribution to the tetracycline oxidation could be neglected. The main intermediates were separated and identified as well as the simple degradation pathway of tetracycline was proposed. The COD removal reached to 35% after 90 min reaction. The acute toxicity experiments illustrated that the Daphnia magna mortality reached the maximum after 25 min ozonation and then decreased to zero after 90 min ozonation.

Evaluation of electro-oxidation of biologically treated landfill leachate using response surface methodology

Box-Behnken statistical experiment design and response surface methodology were used to investigate electrochemical oxidation of mature landfill leachate pretreated by sequencing batch reactor (SBR). Titanium coated with ruthenium dioxide (RuO(2)) and iridium dioxide (IrO(2)) was used as the anode in this study. The variables included current density, inter-electrode gap and reaction time. Response factors were ammonia nitrogen removal efficiency and COD removal efficiency. The response surface methodology models were derived based on the results. The predicted values calculated with the model equations were very close to the experimental values and the models were highly significant. The organic components before and after electrochemical oxidation were determined by GC-MS.