Order Degradation Rate Research Articles

Degradation of Atrazine by Flow-Through UV-Based Advanced Oxidation Processes: Roles of Light Source and Chlorine Addition

Understanding the degradation kinetics and mechanisms of trace organic contaminants (TrOCs) by UV-based advanced oxidation processes (UV-AOPs) are pivotal in realizing their efficient application in water treatment. However, the relevant knowledge in practical flow-through reactors remains a void, compared with that of commonly used batch reactors. To fill the knowledge gaps, the current work investigated the degradation of atrazine (ATZ) in flow-through UV-AOP systems with different light sources and chlorine additions. The results showed that UV/Cl2 in the reactors (with a diameter of 50 mm) was not very efficient in ATZ degradation while the pseudo-first order degradation rate constant was elevated by over 2.7 times with vacuum UV (VUV)/UV. In contrast to observations in the batch reactors, the addition of chlorine to the flow-through VUV/UV system unexpectedly decreased the rate constant by about 39%. The analysis of the relative contributions of different degradation pathways revealed that the inhibitory effect of the chlorine addition arose from the transformation of HO• to reactive chlorine species (e.g., ClO•) which had low reaction rate constants with ATZ. The baffle implementation promoted the ATZ degradation by 12–58%, mainly due to an enhanced mixing that facilitated the radical oxidation. The energy costs of the UV-AOPs in ATZ removal ranged within 0.40–1.11 kWh m−3 order−1. The findings of this work are helpful in guiding efficient VUV/UV and VUV/UV/Cl2 processes in drinking water treatment.

MoS2 Nanosheets@Metal organic framework nanocomposite for enhanced visible light degradation and reduction of hazardous organic contaminants

Present research focuses on the environmental cleanup of hazardous organic pollutants that are discharged into the natural aquatic bodies which upshots an undesirable shift in the ecological balance. Recently, aromatic nitro compounds and hazardous organic dyes have been recognized as a threat to fauna, flora and human life forms. Therefore, effective and selective eradication of these hazardous pollutants from wastewater systems is a pressing global issue for the academic community. This study aims to design a MoS2 Nanosheets (NS)@Cu-MOF (MS−HK) catalyst via a convenient hydrothermal approach for the elimination of organic and aromatic nitro contaminants from wastewater effluent. Under visible light irradiation, this photocatalyst presented 96.4% removal efficiency for Rose Bengal (RB) dye within a short duration of 30 min, with a first order degradation rate constant of 0.12223 min−1and a catalyst loading of 240 mg/L. Again, the rate constant of the room temperature reduction of 2,4,6−trinitrophenol (TNP) using NaBH4 as a reducing agent, in presence of the prepared nanocatalyst was calculated to be 2.7 × 10−3 s−1. This excellent degradation efficiency could be due to the loading of HKUST-1 with a narrow band gap semiconductor MoS2 leading to enhanced visible light absorption, effective separation and transport of photoinduced h+−e− pairs that limit their recombination. The plausible photodegradation mechanism was supported by photoluminescence and radical trapping experiments. In addition, the impact of various inorganic ions, water matrices, environmental conditions, different dye molecules and mixed dye system was explored on the RB degradation of the synthesized catalyst. Meanwhile, the as-prepared MS−HK nanocomposite displayed significant stability during the photocatalytic experiments, as evident from XRD results, until four successive cycles maintaining an outstanding degradation efficiency of >89%.

Effect of Benzophenone Type UV Filters on Photodegradation of Co-existing Sulfamethoxazole in Water

Benzophenones (BPs) frequently occur in water environments, and they are able to both screen UV light and to sensitize reactive intermediate (RI) production. However, BPs have largely been overlooked as a background water component when studying photodegradation of co-existing organic micropollutants (OMPs). Therefore, in this study, we investigated the influence of BP and its derivative oxybenzone (BP3) on the degradation of the co-existing model OMP sulfamethoxazole (SMX). A series of photodegradation experiments were conducted covering a range of BPs concentrations in μg/L levels, and the degradation of 1.00 μM of SMX was studied. The addition of BP at 0.10 μM, 0.25 μM, and 0.30 μM, and BP3 at 0.10 μM and 0.25 μM, significantly increased the first order degradation rate constant of 1.00 μM of SMX (kobs(BP)) by 36.2%, 50.0%, 7.3%, 31.5%, and 36.2% respectively, compared to that in the absence of any BPs. The maximum indirect photodegradation induced by BP and BP3 reached 33.8% and 27.7%, respectively, as a percentage of the observed SMX degradation rate at the [BPs]/[SMX] ratio of 0.25. In general, triplet excited dissolved organic matter (3SMX*, 3BP*, and 3BP3*) played the major role in the photosensitizing ability of BPs. The results further implied that the increase of SMX degradation at the molar ratio of 0.25 was possibly due to 3BP* for the mixture of SMX and BP. Overall, this study revealed the sensitizing ability of BP and BP3 on the co-existing OMP, SMX, in water for the first time. Our findings can be applied to other BP type UV filters which are similar to BP and PB3 in molecular structure.

Synthesis of carboxymethyl cellulose stabilized sulfidated nanoscale zero-valent iron (CMC-S-nZVI) for enhanced reduction of nitrobenzene

Sulfidated nanoscale zero-valent iron (S-nZVI) had been widely applied for in situ groundwater remediation, but it still suffered from aggregation, surface passivation, and low reactivity in the reaction system. Herein, sodium carboxymethyl cellulose (CMC) was used as a stabilizer, and the effects of the CMC on the physicochemical properties, reactivity, and reusability of S-nZVI on nitrobenzene (NB) degradation were investigated. The characterizations revealed that the CMC improved the degree of sulfidation and accumulated more FexSy phase on the particle surface. The NB degradation rate by Fe/CMC mass ratio of 0.25 was the highest, and its pseudo-first order degradation rate constant (0.203 min−1) was nearly 15 times higher than that of S-nZVI (0.014 min−1), mainly because CMC significantly inhibited the surface oxidation of S-nZVI, improved the hydrophobicity, and reduced the electron transfer resistance compared to S-nZVI. Meanwhile, CMC-S-nZVI exhibited superior reusability than S-nZVI on NB degradation. The product distribution indicated that almost all NB was reduced to aniline (AN) without accumulation of intermediate after reaction. Besides, the effects of initial NB concentration, initial pH, S/Fe molar ratio, and particles dosage on NB degradation by CMC-S-nZVI were also investigated systematically. These results suggested that CMC-S-nZVI provided better reactivity and reusability than S-nZVI, which can guide the optimal design of robust CMC-S-nZVI and display great potential for in situ remediation application.

Transfer of trace organic compounds in an operational soil-aquifer treatment system assessed through an intrinsic tracer test and transport modelling.

Soil Aquifer Treatment (SAT) can provide supplementary treatment of trace organic compounds (TrOCs) such as pharmaceutical and industrial compounds present in Secondary Treated Wastewater (STWW). Concern on presence of unregulated TrOCs in natural systems has raised recently as well as the interest in SAT systems for remediation. The present study quantifies, at the field scale over35 m of lateral groundwater flow, the effectiveness of the Agon-Coutainville SAT system (Manche, Normandy, France) for TrOCs removal by sorption and biodegradation through monitoring of seven TrOCs (oxazepam, carbamazepine, benzotriazole, tolyltriazole, caffein, paracetamol, ibuprofen) and major inorganic compounds as intrinsic tracers in STWW and groundwater during a 34-day STWW infiltration experiment during operational use of the SAT. Cationic exchanges and mixing between groundwater and STWW during the experiment were highlighted by major ions and geochemical simulations. Due to the low thickness of the unsaturated zone, a 1D analytical solution of the advection-dispersion equation (ADE) was applied on chloride data. Chloride was used as conservative intrinsic tracer to calibrate the horizontal flow and transport parameters such as the aquifer dispersion coefficient (D) and the average pore water velocity (ν) allowing estimation of the groundwater residence time. Transport and attenuation of the TrOCs were simulated assuming first-order degradation constant (μ) and linear retardation coefficient (R), calibrated to simulate the observed temporal changes in the breakthrough of TrOCs. Sorption was found to play a role in the transport of TrOCs, notably for oxazepam with a higher linear retardation coefficient value of 2.2, whereas no significant differences of retardation were observed for carbamazepine, tolyltriazole, benzotriazole (1.37, 1.35, 1.36 respectively). Estimated first order degradation rate constants, between 0.03d-1 for carbamazepine and 0.09d-1 for tolyltriazole, were generally high compared to the literature, possibly due to favourable redox conditions and important microbial activities within the system. This study provides evidence of the efficiency of the Agon-Coutainville SAT system for the removal of TrOCs.

Photocatalytic process augmented with micro/nano bubble aeration for enhanced degradation of synthetic dyes in wastewater

This research combines TiO2 nanopowder photocatalyst (TNP) with micro/nano bubble aeration (MNBA) to enhance the dye degradation of the photocatalytic process treating synthetic dye wastewater. The experimental synthetic dyes were indigo carmine (IC) and reactive black 5 (RB5). The dye degradation performance of the photocatalytic process without MNBA (TNP ​+ ​UVA) and with MNBA (TNP ​+ ​UVA ​+ ​MNBA) under various initial dye concentrations were evaluated. The results showed that, given the initial IC and RB5 dye concentrations of 2 ​μM, the degradation efficiency of TNP ​+ ​UVA and TNP ​+ ​UVA ​+ ​MNBA were 100%. With higher dye concentrations (4–10 ​μM), the degradation efficiency of TNP ​+ ​UVA and TNP ​+ ​UVA ​+ ​MNBA were between 84.05-98.20% and 90.64–100%. The kinetics of the photodegradation reaction of both dyes were described by the Langmuir-Hinshelwood kinetic model. The pseudo first order degradation rate constants of the photocatalytic process with MNBA were 1.44 and 1.66 times higher than those without MNBA for IC and RB5.

Fate of four Different Classes of Chemicals Under Aerobic and Anaerobic Conditions in Biological Wastewater Treatment

The removal mechanisms and extent of degradation of 28 chemicals (triclosan, fifteen polycyclic aromatic hydrocarbons, four estrogens, and eight polybrominated diphenyl ether congeners) in different biological treatment systems [activated sludge, up-flow anaerobic sludge blanket reactor (UASB) and waste stabilization pond (WSP)] was investigated to provide insights into the limits of engineered biological treatment systems. This was done through degradation experiments with inhibition and abiotic controls in static reactors under aerobic and anaerobic conditions. Estrogens showed higher first order degradation rates (0.1129 h−1) under aerobic conditions with activated sludge inocula followed by low molecular weight (LMW) PAHs (0.0171 h−1), triclosan (0.0072 h−1), middle (MMW) (0.0054 h−1) and high molecular weight PAHs (HMW) (0.0033 h−1). The same trend was observed under aerobic conditions with a facultative inoculum from a WSP, although at a much slower rate. Biodegradation was the major removal mechanism for these chemicals in the activated sludge and WSP WWTPs surveyed. Photodegradation of these chemicals was also observed and varied across the group of chemicals (estrogens (light rate = 0.4296 d−1; dark = 0.3900 d−1) degraded faster under light conditions while reverse was the case for triclosan (light rate = 0.0566 d−1; dark = 0.1752 d−1). Additionally, all the chemicals were resistant to anaerobic degradation with UASB sludge, which implies that their removal in the UASB of the surveyed WWTP was most likely via sorption onto solids. Importantly, the first order degradation rate determined in this study was used to estimate predicted effluent concentrations (PECs). The PECs showed good agreement with the measured effluent concentrations from a previous study for these treatment systems.

Hydrogen peroxide and persulfate activation using UVA-UVB radiation: Degradation of estrogenic compounds and application in sewage treatment plant waters

In the present work, the degradation of three estrogens (17β-estradiol (E2), estrone (E1) and 17α-ethinylestradiol (EE2)) was investigated under photoactivation of hydrogen peroxide and persulfate. Lab-scale irradiation experiments showed that both UVA and UVB radiations are able to photoactivate the oxidant precursors, although UVB is more efficient to generate radicals and therefore to degrade the targets. The efficiency of both oxidant precursors was investigated showing higher efficiency in the system with persulfate. The pseudo-first order degradation rate constants and the second order rate constants between the hydroxyl or the sulfate radicals and estrogens were measured. In order to evaluate the process efficiency in real treatment conditions, the degradation of the estrogens spiked into sewage treatment plant effluent was studied. Measurements of second order rate constants between the radical and the effluent organic matter by laser flash photolysis allowed to understand the involved quenching mechanisms. A Yeast Estrogen Screen (YES) assay was used to follow the decrease in estrogenic activity during the estrogen degradation. This assay permitted to ensure that the studied processes are not only able to degrade the estrogens but also to remove their estrogenic activity.

Sonochemical degradation of trimethoprim in water matrices: Effect of operating conditions, identification of transformation products and toxicity assessment.

The sonochemical degradation of trimethoprim (TMP), a widely used antibiotic, in various water matrices was investigated. The effect of several parameters, such as initial TMP concentration (0.5-3mg/L), actual power density (20-60W/L), initial solution pH (3-10), inorganic ions, humic acid and water matrix on degradation kinetics was examined. The pseudo-first order degradation rate of TMP was found to increase with increasing power density and decreasing pH, water complexity (ultrapure water>bottled water>secondary wastewater) and initial TMP concentration. TMP degradation is accompanied by the formation of several transformation products (TPs) as evidenced by LC-QToF-MS analysis. Nine such TPs were successfully identified and their time-trend profiles during degradation were followed. An in silico toxicity evaluation was performed showing that several TPs could potentially be more toxic than the parent compound towards Daphnia magna, Pimephales promelas and Pseudokirchneriella subcapitata.

Facile fabrication of g-C3N4 supported Fe3O4 nanoparticles/ZnO nanorods: A superlative visible light responsive architecture for express degradation of pantoprazole

Fe3O4/ZnO nanorods were first fabricated through a facile chemical route and then anchored on g-C3N4 sheets. X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX) spectroscopy, elemental mapping, X-ray photoelectron spectroscopy (XPS), UV–visible (UV–vis) spectrophotometry and photoluminescence (PL) techniques were carried out for the evaluation of the morphology, structure, composition, and optical properties of the nanocomposite thus constructed. Further, magnetic properties of the nanocomposite were evaluated using vibrating sample magnetometer (VSM) techniques. All tests confirmed the formation of heterostructured Fe3O4 nanoparticles/ZnO nanorods that were anchored on g-C3N4 sheets. Photoluminescence results revealed remarkable separation of photo-generated charged carriers and their delayed recombination in the ternary nanocomposite. The hybrid catalyst showed remarkable photocatalytic activity under visible light, as evident from the efficient degradation of pantoprazole, a pharmaceutical drug widely known as a recalcitrant organic water pollutant. The effect of parameters such as catalyst dose, initial concentration, pH, and contact time was studied and a detailed investigation into their corresponding kinetics was made. The photodegradation efficiency of the ternary nanocomposite could be attributed to the synergistic interactions between ZnO, Fe3O4 and g-C3N4. A degradation efficiency of 97.09% with a TOC removal of 85.45% was achieved within 90 min with a remarkable pseudo-first order degradation rate constant of 0.04330 min−1. The incorporation of Fe3O4 expectedly facilitated the ready recovery of catalyst. Furthermore, the degradation rate displayed fair consistency up to 4 cycles. The work thus offers a cost-efficient strategy for tackling organic water pollutants.

Fabrication of a novel Bi2O3 nanoparticle impregnated nitrogen vacant 2D g-C3N4 nanosheet Z scheme photocatalyst for improved degradation of methylene blue dye under LED light illumination

Herein, we report the facile fabrication of a novel visible light active photocatalyst by hydrothermally loading Bi2O3 nanoparticles on nitrogen vacant 2D g-C3N4 nanosheets. It showed excellent photocatalytic efficiency toward refractory pollutant under LED light illumination. The nitrogen vacant 2D g-C3N4 nanosheets were prepared through thermal treatment of bulk g-C3N4 under alkaline condition. A wide range of characterization techniques such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), UV–Vis diffuse reflectance spectroscopy (DRS), electron spin resonance spectroscopy (ESR), atomic force microscopy (AFM) and photoluminescence spectroscopy (PL) were employed to reveal the structural, morphological and optical properties of the nitrogen vacant material as well as of the composite. The nitrogen vacant material exhibited a significant red shift in the visible light absorption edge as compared to the bulk material. The photoluminescence spectra confirmed the enhanced electron hole separation efficiency of the nitrogen vacant g-C3N4 and the composite over the precursors. The enhanced photocatalytic activity toward methylene blue (MB) degradation could be attributed to the enhanced light absorption efficiency and the superior charge carrier separation of the nitrogen vacant material and the composite. The photocatalytic activity was assessed through the degradation of refractory MB dye under LED illumination. The composite material 2% Bi2O3/g-C3N4 displayed the highest degradation efficiency with a first order degradation rate constant of 0.040 min−1, which is 2.5 and 1.9 fold superior than the rate constants of bulk and nitrogen vacant 2D g-C3N4 nanosheet, respectively. Furthermore, based on the findings of the radical scavenging experiment, a direct Z scheme electron transfer mechanism has been proposed. This study would unlock a new direction toward further enhancing the efficiency of vacancy engineered materials.

Coupling of nanofiltration and UV, UV/TiO2 and UV/H2O2 processes for the removal of anti-cancer drugs from real secondary wastewater effluent

The detection of anti-cancer drugs in surface waters at ng/L indicates that most wastewater treatment processes currently applied are not effective enough to remove these resilient compounds from wastewater. Therefore alternative treatment processes should be tested to avoid discharges in the environment of drugs that have been linked to genotoxic effects. The innovative contribution of this study stands in coupling nanofiltration with advanced oxidation processes to treat real secondary wastewater effluents spiked with 4 widely consumed anti-cancer drugs. Direct photolysis was found to be extremely effective to degrade etoposide and paclitaxel from the secondary effluent as well as from the highly concentrated retentate produced by nanofiltration. The two drugs were not detected after 10 min of exposure that corresponds to higher than 98% removals given the method detection limits by direct injection. This is equivalent to pseudo-first order degradation rate constants higher than 0.46 min−1, which, to the best of the author's knowledge, has not yet been reported for paclitaxel in the literature. However, none of the tested oxidation processes (UV, UV/TiO2 and UV/H2O2) using the reactor setup, exposure times and concentrations of TiO2 and H2O2 tested, were able to degrade cyclophosphamide or ifosfamide effectively. Compared to literature data, this is probably related to the low amount of photons received by the treated media. Finally important aggregation of catalyst particles was observed in secondary effluent, and photocatalysis had no advantage compared to the other two processes tested.

Temperature-dependent redox zonation, nitrate removal and attenuation of organic micropollutants during bank filtration

River bank filtration (RBF) is considered to efficiently remove nitrate and trace organic micropollutants (OMP) from polluted surface waters. This is essential for maintaining good groundwater quality and providing high quality drinking water. Predicting the fate of OMP during RBF is difficult as the biogeochemical factors controlling the removal efficiency are not fully understood. To determine in-situ removal efficiency and degradation rates of nitrate and OMP indicator substances we conducted a field study in a RBF system during a period of one and a half years incorporating temporally and spatially varying redox conditions and temperature changes typically occurring in temperate climates. RBF was analyzed by means of mixing ratios between infiltrated river water and groundwater as well as average residence times of surface water towards the individual groundwater observation wells. These results were used to calculate temperature dependent first order degradation rates of redox sensitive species and several OMP. Five out of ten investigated OMP were completely removed along RBF pathways. We demonstrate that degradation rates of several OMP during bank filtration were controlled by redox conditions and temperature whereby temperature itself also had a significant influence on the extent of the most reactive oxic zone. The seasonal variations in temperature alone could explain a considerable percentage of the variance in dissolved oxygen (34%), nitrate (81%) as well as the OMPs diclofenac (44%) and sulfamethoxazole (76%). Estimated in-situ degradation rates roughly varied within one order of magnitude for temperature changes between 5 °C and 20 °C. This study highlights that temporal variability in temperature and redox zonation is a significant factor for migration and degradation of nitrate and several OMPs.

Role of pH on the photocatalytic activity of TiO2 tailored by W/T mole ratio

Tailoring of TiO2 properties by controlling W/T mole ratio (70, 140, 210 and 280) was carried out by sol–gel method using TTIP as Ti precursor and H2O as O2 precursor. The anatase phase evolution with Ti and O2 composition variations was verified, respectively, through X-ray diffraction and EDX analysis. The spherical topography of TiO2 particles was elucidated by FESEM, which was noticeably affected with W/T mole ratio. The quantitative measurement of particles’ size, shape and their distribution were directly observed at a scale approaching a bunch of atoms by HRTEM. The numerical values of crystallite size and particle size, as measured by the XRD peak broadening and TEM techniques, differ slightly. The optical study, by UV–Visible spectroscopy, registered blue shift in the absorption edge wavelength of TiO2 as well as increase in the band gap energy, with increase in W/T mole ratio. The presence of functional groups at the interface of TiO2 nanoparticles was confirmed by FTIR. Considering MB dye as a model pollutant, the characterization of photo-oxidation kinetics was also performed to assess the effect of pH and W/T mole ratio on removal efficiency of TiO2. Excellent photocatalytic performance of TiO2-70 R under UV light irradiation for 180 min was observed at a pH of 11; the corresponding photocatalytic kinetics, denoted by first order degradation rate constant (Kappa) was found to be approximately 0.00404 min−1.

Destruction of phenicol antibiotics using the UV/H2O2 process: Kinetics, byproducts, toxicity evaluation and trichloromethane formation potential

Phenicol antibiotics (PABs) degradation by UV/H2O2 is important because we need to determine the reduction in toxicity and disinfection byproducts for post-chlorine. In this study, the degradation of PABs, including florfenicol (FLO), chloramphenicol (CAP) and thiamphenicol (THA), was examined. The pseudo-first order degradation rate constants of PABs were 3 times higher in ultrapure water (UW) than that in synthetic wastewater (SW) for these conditions: [PABs]0 = 1 μM, [H2O2] = 0.1 mM, and I0 = 1.985 × 10−6 E L−1 s−1. Fulvic acid (FA) and HCO3– inhibited PABs degradation, Cl− and NO3– concentrations of up to 5 mM and 10 mM had a negligible impact. The impact of water matrix on PABs degradation was successfully predicted using pseudo-steady-state kinetic model. The degradation of PABs was triggered via hydroxylation and/or hydrogen abstraction. The treatment of PABs via UV/H2O2 could decrease their antimicrobial properties, while the byproducts of FLO and THA showed higher acute toxicity in Vibrio fischeri. In addition, two identification products (TP-276 and TP-354) of FLO had higher ecotoxicity toxicity (using ECOSAR) in fish, daphnid and green algae. The trichloromethane formation potential (TCMFP) for PABs with post-chlorination in UW and SW can be reduced after UV/H2O2 compared to UV, and is related to the corresponding decrease of dissolved organic carbon (DOC).

TOXICITY STUDIES DURING THE DEGRADATION OF PENTACHLOROPHENOL BY OZONATION IN THE PRESENCE OF MnO2/TiO2

Ozone is a strong oxidant used in the water treatment to remove organochloride compounds. Given that many processes of degradation generate chemical compounds that are more toxic than initial compounds, the development of optimized ozonation processes are required. In this study, pentachlorophenol (PCP) was used as a model of an organochlorine compound and the toxicity of its degradation products generated by both non-catalytic and catalytic ozonation processes were evaluated with a fresh-water Daphnia magna (ecotoxicity) and vegetables species Lactuca sativa and Panicum millaceum (Phytoxicity). The catalytic ozonation used MnO2/TiO2 as catalyst, which was characterized by X-ray diffraction analysis showing the presence of crystalline TiO2 phases, rutile and anatase. The specific BET surface area of MnO2/TiO2 was 43 m2/g. It was found that the use of ozone as an oxidant showed a first order degradation rate constant (kobs = 0.5 ± 0.1 min- 1). The uncatalyzed reaction showed several reaction intermediates like mono- and polychlorinated phenols, and quinones. The oxidation of these compounds led to low molecular weight organic acids. From these results, we proposed a pathway of PCP degradation using ozone. The catalyzed reaction showed a more potent effect in reducing the toxicity of the treated solution. Unlike the use of only ozone which does not decrease the toxicity. It was found that the treatment with catalytic ozonation decreases the toxicity of the solutions.

Base-catalyzed hydrolysis and speciation-dependent photolysis of two cephalosporin antibiotics, ceftiofur and cefapirin

Lately, special attention has been given to veterinary cephalosporin antibiotics due to their broad activity spectrum and significant consumption. Indeed, the determination of hydrolytic and photolytic kinetics provides a better comprehension of the undesired persistence of cephalosporins in aqueous matrices. In this work, the two widely used veterinary antibiotics ceftiofur (CEF) and cefapirin (CEPA) showed high instability under alkaline conditions, degrading in few minutes at pH > 11. In buffered solutions at neutral pH and natural temperature (T = 22 ± 1 °C), both drugs presented moderate stability (t½ = 3 d, CEPA and 1.4 d, CEF). Our study also demonstrated that CEPA and CEF speciation did not significantly influence the direct photolysis rates. Using a simulated water disinfection set-up (λ = 254 nm), all ionic species of CEF and CEPA presented fast and similar pseudo-first order degradation rates, kapp 0.0095 ± 0.0004 and 0.0092 ± 0.001 cm2 mJ-1, respectively. Furthermore, using surface water in hydrolysis experiments, CEF demonstrated significant matrix-dependent stability with a half-life (t½ = 14.7 d) tenfold higher than in buffered solutions. In contrast, CEPA presented a very similar hydrolysis rate in river water (t½ = 4.2 d) and a subtle faster photo-degradation rate in this same matrix (kapp 0.0128 ± 0.001 cm2 mJ-1), highlighting the importance of disinfection radiation for cephalosporin depletion in aqueous environments.

Suitability of various chromatographic and spectroscopic techniques for analysis and kinetic degradation study of trelagliptin

Multifaceted comparative analytical methods for trelagliptin (TRL) were investigated, applied to ZAFATEK tablets and HPLC-UV was selected for a degradation kinetic study. UPLC-MS/MS (Method I), UPLC-UV (Method II), HPLC-UV (Method III), UHPLC-UV (Method IV) and direct UV (Method V) methods were developed. Methods (I-V) showed satisfactory results using TRL concentration ranges of 50–800 ng/mL, 2.5–80 μg/mL, 5–100 μg/mL, 5–100 μg/mL and 5–50 μg/mL, respectively. Multiple Reaction Monitoring (MRM) of the transition pairs of m/z 358.176 to 134.127 for TRL and m/z 340.18 to 116.08 for alogliptin (IS) were employed utilizing positive mode Electrospray Ionization (ESI). The degradation kinetic study (Method VI) was carried out using 1 N HCl based on three different temperatures (70 °C, 80 °C and 90 °C). Through the optimized method-3, a good chromatographic separation of TRL from its major degradation product was achieved. Arrhenius plot was used in the kinetic study and the apparent 1st order degradation rate constant (K), t1/2, t90, and the activation energies were calculated for each temperature and at 25 °C. The optimized UPLC-MS/MS method is suitable for further TRL assay either in biological fluids or in the presence of impurities.

Degradation of propyl paraben by activated persulfate using iron-containing magnetic carbon xerogels: investigation of water matrix and process synergy effects.

An advanced oxidation process comprising an iron-containing magnetic carbon xerogel (CX/Fe) and persulfate was tested for the degradation of propyl paraben (PP), a contaminant of emerging concern, in various water matrices. Moreover, the effect of 20kHz ultrasound or light irradiation on process performance was evaluated. The pseudo-first order degradation rate of PP was found to increase with increasing SPS concentration (25-500mg/L) and decreasing PP concentration (1690-420μg/L) and solution pH (9-3). Furthermore, the effect of water matrix on kinetics was detrimental depending on the complexity (i.e., wastewater, river water, bottled water) and the concentration of matrix constituents (i.e., humic acid, chloride, bicarbonate). The simultaneous use of CX/Fe and ultrasound as persulfate activators resulted in a synergistic effect, with the level of synergy (between 35 and 50%) depending on the water matrix. Conversely, coupling CX/Fe with simulated solar or UVA irradiation resulted in a cumulative effect in experiments performed in ultrapure water.

Activation of sodium persulfate by magnetic carbon xerogels (CX/CoFe) for the oxidation of bisphenol A: Process variables effects, matrix effects and reaction pathways

An advanced oxidation process comprising sodium persulfate (SPS) and a novel magnetic carbon xerogel was tested for the degradation of bisphenol A (BPA), a model endocrine-disrupting compound. The catalyst, consisting of interconnected carbon microspheres with embedded iron and cobalt microparticles, was capable of activating persulfate to form sulfate and hydroxyl radicals at ambient conditions.The pseudo-first order degradation rate of BPA in ultrapure water (UPW) was found to increase with (i) increasing catalyst (25–75 mg/L) and SPS (31–250 mg/L) concentrations, (ii) decreasing BPA concentration (285–14,200 μg/L), and (iii) changing pH from alkaline to acidic values (9–3).Besides UPW, tests were conducted in drinking water, treated wastewater, groundwater and surface water; interestingly, the rate in UPW was always lower than in any other matrix containing several organic and inorganic constituents. The effect of natural organic matter (in the form of humic acids) and alcohols was detrimental to BPA degradation owing to the scavenging of radicals. Conversely, chlorides at concentrations greater than 50 mg/L had a positive effect due to the formation and subsequent participation of chlorine-containing radicals.Liquid chromatography time-of-flight mass spectrometry was employed to identify major transformation by-products (TBPs) of BPA degradation in the absence and presence of chlorides; in the latter case, several chlorinated TBPs were detected confirming the role of Cl-related radicals. Based on TBPs, main reaction pathways are proposed.