Total Organic Carbon Removal Research Articles

Degradation of amoxicillin applying photo-Fenton and acid hydrolysis processes with toxicity evaluation via antimicrobial susceptibility tests

ABSTARCT The antibiotic amoxicillin (AMX) is a semisynthetic aminopenicillin, classified as an β-lactam antibiotic. This work aims to evaluate the AMX degradation (190 mg L–1), in aqueous medium, applying photo-Fenton ([TOC]0 = 100 mgC L−1; FH2O2 = 3.27 mmol min−1; [Fe2+] = 0.27 mmol L−1; pH = 3.0; T = 40°C) and acid hydrolysis processes. Along the experiments, samples were withdrawn and analyzed by a total organic carbon (TOC) analyzer and a liquid chromatography system coupled to diode array (HPLC-DAD) and mass spectrometry (HPLC-MS) detectors. The hydrolysis process proved to be less efficient, because AMX removals greater than 80% were observed only after 24 hours of reaction (pH 2). Conversely, the photo-Fenton process removed completely AMX in just 20 minutes, reaching 85% of TOC removal in 2 hours. Finally, the AMX aqueous solutions treated by the studied processes was also evaluated in respect of its toxicity to some microorganisms, applying two antimicrobial susceptibility tests: disk-diffusion and broth microdilution methods. It was observed that the AMX aqueous solutions, pretreated by the photo-Fenton process, for just 7.5 min of reaction time, did not inhibit the microorganisms growth. The obtained results show that the photo-Fenton process was able to degrade AMX, in a relatively short time, and that the generated degradation products did not inhibit the microorganisms growth, when compared to acid hydrolysis process. Thus, it was verified the potential application of the photo-Fenton system as a pretreatment step to conventional biological oxidation processes for the treatment of industrial wastewaters.

Improved mineralization and total nitrogen reduction by combination of electro-reduction and electro-oxidation for nitrophenol removal

In this work, p-Nitrophenol (p-NP) was electro-chemically removed by using a prepared Co3O4/Ti cathode and a BDD anode to achieve the simultaneous reduction of total organic carbon (TOC), total nitrogen (TN) and toxicity. The prepared Co3O4/Ti cathode showed higher electro-activity than the Ti cathode towards p-NP reduction with the removal rate higher than 90.6% but without mineralization. The electro-oxidation removed 84.3% of TOC but none of TN. To develop an optimized process for mineralization and TN removal during p-NP electrolysis, the combination of electro-oxidation and electro-reduction were evaluated by using a dual-chamber cell and a single-chamber cell, respectively. As a result of the re-oxidation and re-reduction in the single-chamber cell, the typically used mode of the simultaneous redox, showed a lower removal of TOC and TN than the combination processes as well as an increased toxicity. The TN removal for both combined modes (21.0%–32.9%) was all higher than that of the mode of reduction because the produced inorganic nitrogen such as ammonia and nitrate could be partially oxidized or reduced to nitrogen gas. The results suggested that the combination process could significantly improve the mineralization and TN reduction for p-NP removal, accompanied with 60.3% decrease of acute toxicity for the reduction after oxidation mode.

α-(Fe, Cu)OOH/RGO nanocomposites for heterogeneous photo-Fenton-like degradation of ciprofloxacin under visible light irradiation.

Ciprofloxacin (CIP) is a third-generation fluoroquinolones (FQs) antibiotic, and the occurrence of CIP in the water environment has raised growing concerns owning to its environmental toxicity. In this paper, a novel α-(Fe, Cu)OOH/RGO nanocomposite was synthesized via a one-step reflux method for CIP degradation through a photo-Fenton-like process. When the RGO content was 1 wt%, CIP degradation ratio by the α-(Fe, Cu)OOH/RGO nanocomposite reached 100% under visible light irradiation within 120 min, and total organic carbon (TOC) removal ratio reached 60% within 180 min. The result of molecular fluorescence spectra highlighted that the loading of RGO on the α-(Fe, Cu)OOH significantly increased the content of hydroxyl radicals (·OH) in the heterogeneous photo-Fenton-like system and simultaneously inhibited the recombination of photogenerated electron and hole, which played critical roles in the enhancement of CIP degradation. In addition, 11 main intermediates were identified as the degradation products of CIP in the α-(Fe, Cu)OOH/RGO/H2O2/visible light reaction systems using liquid chromatograph-mass spectrometer (LC-MS) analyses. The results demonstrated that three degradation pathways for CIP removal by α-(Fe, Cu)OOH/RGO nanocomposite occurred, including (i) oxidation on the piperazine ring and dealkylation, (ii) defluorination and decarboxylation, and (iii) hydroxylation on the quinolone ring. This work would provide a novel insight of CIP degradation pathways in photo-Fenton-like processes.

Characterization and Evaluation of Natural Bearing and Iron-Enriched Montmorillonitic Clay as Catalysts for Wet Oxidation of Dye-Containing Wastewaters

Natural bearing (raw and calcined at 500 °C) and iron-enriched (impregnation and pillaring) montmorillonitic clay samples were prepared. The obtained samples were characterized (X-ray diffraction, Fourier Transformed Infrared Spectroscopy, Scanning Electron Microscopy, and Energy Dispersive X-ray Spectroscopy) and evaluated as catalysts in catalytic wet oxidation of Brilliant Green and Crystal Violet. Experiments were conducted in the same conditions (0.5 g catalysts, 300 mL air/min or 0.5 mL H2O2, 25 mL of dye solution, 25 °C, initial solution pH = 6.0, for 3 h) in thermostated batch reaction tubes. Process evolution was followed using UV-Vis spectrometry (200–1100 cm−1) and total organic carbon. Dye removal efficiencies (decolorization) between 98 and 99% were determined, while total organic carbon removal efficiencies were calculated to be in the 53–98% range. Iron leakage investigation showed that iron is lost in higher amounts for the catalysts prepared using the impregnation method by comparison with the pillared sample.

Degradation of diclofenac aqueous solutions in a 3D electrolytic reactor using carbon-based materials as pseudo third electrodes in fluidized bed, anodic and cathodic configurations

In this study, the degradation of diclofenac (DCF) in a 3D electrochemical reactor was evaluated. Several parameters were studied including the reactor configuration: fluidized bed (FB), anodic packed bed (APB) and cathodic packed bed (CPB); and the type of pseudo third electrode material: granular activated carbon (GAC) and granular expanded graphite (GEG). The configuration that showed the highest total organic carbon (TOC) removal was the APB, with values up to 85%. In addition, when the substrate saturation of the pseudo third electrode was 20% in the APB, the energy consumption was 2.5 times lower than the conventional 2D reactor. This efficient conversion was the result of improved contacting and reaction between hydroxyl (HO•) and sulfate (SO4•-) radicals electro-generated on the anode surface and DCF adsorbed on the particulate carbon. While the degradation efficiency with the 3D CPB reactor was higher than the FB configuration, it was less effective than the 3D APB reactor because of H2O2 production in the cathode, which decomposed to generate HO•, but only slowly and not sufficiently to oxidize DCF to a significant extent. Furthermore, it was also found that when two 3D APB reactors were connected in series a more significant TOC decrease (98%) and lower energy consumption (4 times) could be achieved than in a single 2D reactor configuration. This result demonstrated that the 3D electrochemical process can be cheaper and faster. All these results highlight the 3D anodic electro-oxidation process as a potential technology to efficiently treat recalcitrant contaminants of emerging concern.

Degradation of carbamazepine by high-voltage direct current gas-liquid plasma with the addition of H2O2 and Fe2.

Carbamazepine (CBZ) is a typical psychotropic pharmaceutical which is one of the most commonly detected persistent pharmaceuticals in the environment. The degradation of CBZ in the aqueous solution was studied by a direct current (DC) gas-liquid phase discharge plasma combined with different catalysts (H2O2 or Fe2+) in this study. The concentrations of reactive species (H2O2, O3, and NO3-) and •OH radical yield in the liquid were measured during the discharge process. The various parameters that affect the degradation of CBZ, such as discharge powers, initial concentrations, initial pH values, and addition of catalysts, were investigated. The energy efficiency was 25.2mg·kW-1·h-1 at 35.7W, and the discharge power at 35.7W was selected to achieve the optimal balance on the degradation effect and energy efficiency. Both acidic and alkaline solution conditions were conducive to promoting the degradation of CBZ. Both H2O2 and Fe2+ at low concentration (10-100mg/L of Fe2+, 0.05-2.0mmol/L of H2O2) were observed contributing to the improvement of the CBZ degradation rate, while the promotional effect of CBZ degradation was weakened even inhibition would occur at high concentrations (100-200mg/L of Fe2+, 2.0-5.0mmol/L of H2O2). The degradation rate of CBZ was up to 99.1%, and the total organic carbon (TOC) removal efficiency of CBZ was up to 67.1% in the plasma/Fe2+ (100mg/L) system at 48min, which suggested that high degradation rate and mineralization efficiency on CBZ could be achieved by employing Fe2+ as a catalyst. Based on the intermediate products identified by Ultra Performance Liquid Chromatography Tandem Mass Spectrometry (UPLC-MS), the possible degradation pathways were proposed. Finally, the growth inhibition assay with Escherichia coli (E. coli) showed that the toxicity of plasma/Fe2+-treated CBZ solution decreased and a relatively low solution toxicity could be achieved. Thus, the plasma/catalyst could be an effective technology for the degradation of pharmaceuticals in aqueous solutions.

Schwertmannite catalyze persulfate to remove oxytetracycline from wastewater under solar light or UV-254

Oxytetracycline (OTC) pollution has become an important environmental issue. It is an obvious innovation in the field of OTC degradation to comprehensively explore the effect of Schwertmannite (Sch) catalyzed persulfate to degrade OTC under different light conditions, and apply the optimized parameters to remove OTC from actual aquaculture wastewater. Therefore, the effect of sodium persulfate (PS) on the removal of OTC catalyzed by Sch under solar light and UV-254 irradiation was investigated in this study, and the optimized parameters were applied to the OTC removal from actual aquaculture wastewater. The results showed that when 0.8 g/L Sch was added and the concentration of PS was 350 μmol/L, the removal rate of OTC (40 μmol/L) was 89.8% and 92.3% after 3 h and 6 h reactions in dark conditions, respectively. Furthermore, light significantly enhanced the removal efficiency of OTC. The removal rates of OTC in the Sch + PS + OTC system were 96.8% and 99.1% after 3 h and 6 h reactions under UV-254 irradiation, respectively. In addition, it was shown that light accelerated the removal of total organic carbon (TOC); the TOC removal rates after 3 h and 6 h under UV-254 in the Sch + PS + OTC system were 49.8% and 69.7%, respectively. In actual aquaculture wastewater, the removal rates of OTC after 6 h in the Sch + PS + OTC + UV-254 system were 21.7%, 22.7%, 46.1%, 55.1%, 74.1%, 94.5%, and 98.3%, respectively, when the COD concentrations in wastewater were 10,000 mg/L, 5000 mg/L, 2000 mg/L, 1000 mg/L, 500 mg/L, 200 mg/L, and 100 mg/L. The recovery rate of Sch after the reaction in actual aquaculture wastewater was 70.0–99.8%, and the pH after treatment remained neutral. These findings provide theoretical support for the treatment of OTC-containing wastewater via the advanced oxidation technology catalyzed by Sch.

The promotion of Ag3PO4 photocatalysis on methylene blue removal and electricity generation in microbial fuel cell

The photocatalysis promoted microbial fuel cell (photo-MFC) system is designed to improve the degradation efficiency of recalcitrant organic pollutants in wastewater. In order to avoid the damage of UV light and reactive oxygen species to microorganisms, narrow bandgap Ag3PO4 photocatalyst is chosen and separated with TiN bioanode in anode chamber of MFC. Under visible light irradiation, the synergistic effect between photodegradation and biodegradation yielded a decolorization efficiency of 95.8% MB and a maximum power density of 2.90 W m−2 for 10 mg L−1 MB co-substrate with sodium acetate. The chemical oxygen demand (COD) and total organic carbon (TOC) removal efficiencies of co-substrate in the photo-MFC system are 83.21% and 72.47%, much higher than that of photocatalysis alone (8.67% for COD and 9.65% for TOC). All of the degradation efficiency, power density and mineralization capacity of the photo-MFC system are higher than that of single MFC or photocatalysis. Microbial community analysis shows that Pseudomonas (73.75%) and Geobacter (19.62%) are the main genera of the bioanode in the photo-MFC system. The abundance of Pseudomonas is increased by photocatalysis. This photo-MFC coupled system has great potential application in wastewater treatment and energy recovery.

Removal of diethyltoluamide, paracetamol, caffeine and triclosan from natural water by photo-Fenton process using powdered zero-valent iron

The removal of four pharmaceuticals and personal care products (PPCPs), namely diethyltoluamide (DEET), paracetamol (PAR), caffeine (CAF) and triclosan (TCS) (at a spiked concentration of 25 μg/L), from natural water using the photo (UVC)-Fenton (powdered zero-valent iron, pZVI) process was investigated. The results show that a molar ratio of H2O2/pZVI of 2.0, pZVI concentration of 22.4 mg/L and pH of 3.0 maximised the removal of the target compounds at 71.1%, 100%, 64.2% and 87.1%, for DEET, PAR, CAF and TCS, respectively, after 30 min in Fenton (pZVI) process. When this process was coupled with UVC radiation, 29.6%, 80.3%, 3.1% and 88.4% of DEET, PAR, CAF and TCS, respectively, were removed within the first minute, and 99.0%, 100%, 99.5% and 100%, respectively, were removed after 30 min. The pseudo first-order kinetic model best fitted the degradation data of DEET, PAR and CAF (1–20 min); and because 80% of TCS and PAR degraded within the first minutes, it is suggested to explore the kinetics during the initial period. Characterisations of pZVI after the photo-Fenton (pZVI) process indicated the corrosion of the surface of iron powder and the presence of iron oxides and iron hydroxides. Lower removals of nitrate (35–50%), phosphate (<35%) and total organic carbon (TOC, <18%) were observed, which may be attributed to the small H2O2/pZVI dosage used. Results of this investigation show that the photo-Fenton (pZVI) process has potential for efficient and cost-effective removal of PPCPs.

Optimization of Fenton Oxidation Process for Degradation of 1-Butyl-3 Methyl Imidazolium Chloride (BMIMCL) Using Response Surface Methodology

The degradation of 1-butyl 3-methyl imidazolium chloride (BMIMCl) ionic liquid (IL) by Fenton oxidation has been studied. The optimization of operating parameters for maximum degradation of BMIMCl has been carried out using the Central Composite Design (CCD) of Response Surface Methodology (RSM). The three independent input parameters selected were the dosage of Hydrogen Peroxide (H2O2), the dosage of iron (Fe2+), and the pH of the output or response selected was Total Organic Carbon (TOC) removal efficiency. Experiments were carried out according to the experimental design provided by CCD. For TOC Degradation, the model’s R2 and R2adj correlation coefficients between experimental and model-predicted values were 0.9769 and 0.9561, respectively. This indicates a satisfactory correlation of experimental results with model-predicted values. The optimum values of operating parameters for maximum degradation were found to be H2O2=307 mM (X1), Fe2+=1.1 mM (X2), and (pH)=3.3 (X3), for a reaction time of 120 min. For these operating parameters, the experimental result for TOC removal efficiency was found to be 72.89% as compared to the model-predicted value of 73.67%. These results indicate that the values were closely correlated with each other and thus the model was validated satisfactorily. Overall, the results indicate that the BMIMCl ionic liquid can be effectively degraded by the Fenton oxidation process.

Recovery of nickel from electroless nickel plating wastewater based on the synergy of electrocatalytic oxidation and electrodeposition technology.

Nickel exists primarily as a stable complex in electroless nickel plating wastewater, and the Ni recovery from it cannot be achieved solely through electrodeposition. As the electrocatalytic oxidation has excellent oxidation potential to break down the complex, an efficient and stable electrochemical system using the synergy of electrocatalytic oxidation and electrochemical deposition technology was developed for the recovery of nickel from electroless nickel plating wastewater. In the present study, the effects of initial pH, current density, and initial nickel ion concentration on the treatment performance of the electrochemical system was investigated. The highest Ni recovery (94.84%) and total organic carbon removal (63.94%) were achieved at a current density of 83.3mA/cm2 , initial pH of 3.0, and initial Ni concentration of 0.01 M. At the same time, the recovered nickel product was confirmed by scanning electron microscopy, energy dispersive X-ray, X-ray powder diffraction, and X-ray photoelectron spectroscopy. Furthermore, the electrochemical system displayed good stability and economic benefits, thereby suggesting its excellent application potential for the treatment of electroless nickel plating wastewater. PRACTITIONER POINTS: An efficient and stable electrochemical system was developed for the recovery of nickel from electroless nickel plating wastewater. In an acidic medium, the nickel recovery rate and TOC removal ratio were 94.84% and 63.94%, respectively. The system displayed good stability, thereby suggesting its excellent application potential for the treatment of nickel plating wastewater.

Promising Low-Cost Adsorbent from Waste Green Tea Leaves for Phenol Removal in Aqueous Solution.

Phenol is the most common organic pollutant in many industrial wastewaters that may pose a health risk to humans due to its widespread application as industrial ingredients and additives. In this study, waste green tea leaves (WGTLs) were modified through chemical activation/carbonization and used as an adsorbent in the presence of ultrasound (cavitation) to eliminate phenol in the aqueous solution. Different treatments, such as cavitation, adsorption, and sono-adsorption were investigated to remove the phenol. The scanning electron microscope (SEM) morphology of the adsorbent revealed that the structure of WGTLs was porous before phenol was adsorbed. A Fourier Transform Infrared (FTIR) analysis showed an open chain of carboxylic acids after the sono-adsorption process. The results revealed that the sono-adsorption process is more efficient with enhanced removal percentages than individual processes. A maximum phenol removal of 92% was obtained using the sono-adsorption process under an optimal set of operating parameters, such as pH 3.5, 25 mg L−1 phenol concentration, 800 mg L−1 adsorbent dosage, 60 min time interval, 30 ± 2 °C temperature, and 80 W cavitation power. Removal of chemical oxygen demand (COD) and total organic carbon (TOC) reached 85% and 53%. The Freundlich isotherm model with a larger correlation coefficient (R2, 0.972) was better fitted for nonlinear regression than the Langmuir model, and the sono-adsorption process confirmed the pseudo-second-order reaction kinetics. The findings indicated that WGTLs in the presence of a cavitation effect prove to be a promising candidate for reducing phenol from the aqueous environment.

Oxidative Degradation of Pharmaceutical Waste, Theophylline, from Natural Environment

The elimination of organic contaminants from natural resources is extremely important to ensure their (re-)usability. In this report, the degradation of a model pharmaceutical compound, theophylline, is compared between natural and laboratory-controlled environments. While the concentration of H2O2 variably affected the degradation efficiency (approximately from 8 to 20 min for complete degradation) in the photo-irradiation experiments, the inorganic compounds (NaNO3, KH2PO4 and ZnSO4) present in the medium seemed to affect the degradation by scavenging hydroxyl radicals (•OH). The end-product studies using high-resolution mass spectrometry (HRMS) ruled out the involvement of secondary radicals in the degradation mechanism. The quantitative calculation with the help of authentic standards pointed out the predominant role of hydroxylation pathways, especially in the initial stages. Although a noticeable decline in the degradation efficiency was observed in river water samples (complete degradation after 25 min with an approximately 20% total organic carbon (TOC) removal), appreciable TOC removal (70%) was eventually achieved after prolonged irradiation (1 h) and in the presence of additional H2O2 (5 times), revealing the potential of our technique. The results furnished in this report could be considered as a preliminary step for the construction of •OH-based wastewater treatment methodologies for the remediation of toxic pollutants from the real environment.

Tuning of Sm3+ and Er3+-doped TiO2 nanofibers for enhancement of the photocatalytic performance: Optimization of the photodegradation conditions

Titanium dioxide (TiO2)-based nanofibers doped with samarium (Sm3+) and erbium (Er3+) at doping levels tuned in the range of 0.05–1.0% were prepared by the electrospinning-calcination method. The produced materials were well characterized by X-ray diffraction, SEM, EDX, and UV–vis diffuse reflectance spectroscopy. These one-dimensional nanostructures showed a crystalline structure with values of fiber diameters values between 60 and 100 nm. The best catalyst sample of this study was formulated as TiO2:Sm (0.1%) and sintered at 600 °C. And, it was employed to intensify the photocatalytic process under visible-light irradiation. Likewise, the chemometric approach was applied to optimize the process. The results revealed that the rate constant for the photo-degradation of a cationic organic pollutant was significantly improved (k = 3.496 × 10−1 min−1). In terms of the reaction half-life, the intensification and optimization of the process led to a decrease in the half-life of the reaction from 68 to 2 min. And, these are outstanding findings for the photo-degradation process under visible-light irradiation. In addition, the total organic carbon (TOC) removal efficiencies were found to be 69.95% and 72.30% for the mineralization of MB and CIP, respectively, after a 360 min reaction time, which are significant results. Moreover, this material demonstrated remarkable photocatalytic activity for the degradation of ciprofloxacin (CIP) with a 99.6% removal efficiency and a rate constant of 4.292 × 10−1 min−1. Finally, the stability and reusability of this catalyst were demonstrated during five repetitive cycles of the CIP photodegradation.

Performance of Ti/RuO2-IrO2 electrodes and comparison with BDD electrodes in the treatment of textile wastewater by electro-oxidation process

Electrochemical oxidation (EO) technology, which may directly reduce refractory contaminants into simple inorganic molecules like H2O and CO2, is an efficient approach for treating high-concentration wastewater. Boron doped diamond (BDD) electrodes has been extensively researched and used to degrade organic contaminants from real textile wastewater. In this study, two-dimensionally stable anodes, Ti/RuO2-IrO2, were produced and compared with BDD electrodes for the treatment of textile wastewater. This study focuses on the optimization of the produced electrode under different pH and current densities. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis revealed that the oxide coating on the Ti plate’s surface was effectively produced. The EO process parameters were optimized using central composite design (CCD) under response surface methodology (RSM), with total organic carbon (TOC), chemical oxygen demand (COD), and color removals as responses and pH, current density, and reaction time as control variables. The analysis of variance (ANOVA) revealed good coefficients of determination (R2) values of.0.90, indicating that the second-order regression model matched the experimental data satisfactorily. In optimized conditions, pH 4 was shown to have the maximum effectiveness for both electrodes. The best treatment efficiency was obtained by applying an 800 A/m2 current for 5 h, taking into account the time component in the different current values employed. BDD had a color, TOC, and COD removal of 93%, 75%, and 48%, respectively, whereas Ti/RuO2-IrO2 had a color, TOC, and COD removal of 88%, 62%, and 41%, respectively. In addition, the toxicity of water treated with the BDD electrode was found to be lower, whereas the toxicity of water treated with the Ti/RuO2-IrO2 electrode was found to be higher.

Facile hydrothermal synthesis of co-glycerate as an efficient peroxymonosulfate activator for rhodamine B degradation

Sulfate radical based advanced oxidation processes (SR-AOPs) are regarded as a promising technology to degrade organic pollutants in water. Here, hydrothermally synthesized Co-glycerate (Co-G) microspheres are proposed as an efficient heterogeneous catalyst to activate peroxymonosulfate (PMS) for degradation of refractory organic pollutant rhodamine B (RhB) in aqueous solution. The presence of Co-G microspheres enhanced the degradation rate significantly with a short full degradation time (8 min) and a total organic carbon (TOC) removal exceeding 41% (10 min), thus implying the excellent catalytic performance of Co-G microspheres for PMS activation. Furthermore, the effects of PMS and catalyst concentration, initial pH value and co-existing ions on RhB degradation were investigated. Radical quenching and EPR tests identify that active species including SO4-·, HO·, O2-· and 1O2 are involved in the degradation process. Additionally, a possible reaction mechanism of PMS activation by Co-G microspheres for RhB degradation was suggested. This study can provide a new insight for design of cobalt-based heterogeneous catalysts as activators to activation PMS for pollutants degradation.

Improved the in-situ remediation effect of benthic microbial electrochemical system by optimizing the anode structure.

Six 60-L benthic microbial electrochemical systems (BMESs) were built for the bioremediation of river sediment. Carbon mesh anodes with honeycomb-structure supports were compared with horizontal anodes, and the system was tested using different cover depths and anode densities. The pollutant removal, electricity generation, and electrochemistry of the six BMES with different anodes was examined using the Ashi River (Harbin, China) as a case study. Total organic carbon and total nitrogen removal from sediments in BMES with Honeycomb-structure anodes were 20-30% and 20-33% higher for the other reactors. The maximum power densities of 43.2 mW m-2 was obtained in BMES. The maximum power densities in BMES with honeycomb-structure anodes were 10-40% higher than that of BMESs with horizontal anode reactors.

(V)UV degradation of the antibiotic tetracycline: Kinetics, transformation products and pathway

Tetracycline (TETR) is an antibiotic drug that is widely used in both human and veterinary medicine. It is frequently detected in activated sludge, wastewater effluent, river and lake water or sediment, usually in the pg/L – µg/L concentration range, but sometimes above the mg/L level. Conventional wastewater treatment plants have low removal efficiency for a large number of small organic molecules including TETR. Their efficiency can be increased by applying e.g., an advanced oxidation method for the post-treatment of the wastewater effluent. One possibility is the use of (V)UV lamps for simultaneous disinfection and micropollutant removal. In this paper, the degradation of TETR by UV (λ = 254 nm) and (V)UV (λ = 185 nm and 254 nm) light was studied, focusing on kinetics, mineralization, transformation products and degradation pathways. The effect of dissolved oxygen during irradiation was also examined. As expected, the degradation rate of TETR drastically increased in (V)UV irradiation compared to the conventional UV light. The degradation rates increased by 9% and 16% in UV and (V)UV experiments in the presence of dissolved oxygen possibly due to the generation of additional oxidative radical species. Total organic carbon removal was generally 15%, high TOC removal could only be achieved with greatly increased photon flux in (V)UV photooxidation. In total, eleven aromatic transformation products (TPs) were identified during the irradiation experiments. Three TPs (TP 418, TP 398 and TP 383) were described for the first time. The main degradation pathways include loss of water, CO, methyl or dimethylamine groups. Based on the kinetic profiles, (V)UV irradiation could effectively degrade all aromatic transformation products.

Iron (II) phthalocyanine loaded tourmaline efficiently activates PMS to degrade pharmaceutical contaminants under solar light

ABSTRACT Iron (II) phthalocyanine (FePc) is loaded on the surface of the tourmaline (TM) by the reflow method to obtain FePc/TM. This research effectively prevents the π-π stacking of FePc, increased the effective utilization rate of PMS activation under solar light, and further improved the catalytic performance of the catalytic system. The catalytic oxidation efficiency of FePc/TM on carbamazepine (CBZ) and sulfadiazine (SD) can reach 99% under solar light for 15 and 5 min, the total organic carbon (TOC) removal rate can reach 58% and 69% under solar light for 120 min. After 6 cycles, the CBZ removal rate remained above 95%. In addition, the FePc/TM catalytic system has an excellent removal rate for other pharmaceuticals. The results of spin-trapped electron paramagnetic resonance and classical quenching experiments show that FePc/TM can effectively activate PMS to generate active species under solar light, including superoxide radical (•O2 −), singlet oxygen (1O2), hydroxyl radicals(•OH), and sulphate radicals (SO4•−). The intermediates of CBZ were identified by Ultra-high performance liquid chromatography and high resolution mass spectrometry, and the degradation pathway was proposed. As the reaction progresses, all CBZ and intermediates are reduced and converted into small acids, or mineralized to H2O, CO2. This work provides an alternative method for the design of efficient activation of PMS activation catalysts under solar light to eliminate residual pharmaceuticals in actual water bodies.

Comparative Experimental and Computational Studies of Hydroxyl and Sulfate Radical-Mediated Degradation of Simple and Complex Organic Substrates.

Persulfate (PS)-based advanced oxidation processes (AOPs) have been promoted as alternatives to H2O2-based AOPs. To gauge the potential of this technology, the PS/Fe(II) and Fenton (H2O2/Fe(II)) processes were comparatively evaluated using formate as a simple target compound and nanofiltration concentrate from a municipal wastewater treatment plant as a complex suite of contaminants with the aid of kinetic modeling. In terms of the short-term rate and extent of mineralization of formate and the nanofiltration concentrate, PS/Fe(II) is less effective due to slow Fe(II)/Fe(III) cycling attributable to the scavenging of superoxide by PS. However, in the concentrate treatment, PS/Fe(II) provided a sustained removal of total organic carbon (TOC), with ∼81% removed after 7 days with SO4•- consistently produced via homolysis of the long-life PS. In comparison, H2O2/Fe(II) exhibited limited TOC removal over ∼57% after 10 h due to the futile consumption of H2O2 by HO•. PS/Fe(II) also offers better performance at transforming humic-like moieties to more biodegradable compounds as a result of chlorine radicals formed by the reaction of SO4•- with the matrix constituents present in the concentrate. The application of PS/Fe(II) is, however, subject to the limitations of slow oxidation of organic contaminants, release of sulfate, and formation of chlorinated byproducts.