In this work, the photolysis of enrofloxacin (ENR), pefloxacin (PEF), and sulfaquinoxaline (SQX) in aqueous solution by UV combined with H2O2 or ferrous ions (Fe(II)), as well as Fenton (Fe(II)/H2O2) ...processes, was investigated. In addition, the toxicity of the final reaction solution after UV/H2O2/Fe(II) treatment toward zebrafish embryos was determined. The degradation of the test compounds followed pseudo-first-order reaction kinetics. The optimum concentrations of H2O2 for ENR, PEF and SQX removal under UV/H2O2 treatment were 20, 20 and 5 mM, respectively. The optimum concentrations of Fe(II) for ENR, PEF and SQX removal in the UV/Fe(II) system were 0.25, 10, and 1 mM, respectively. For the UV/H2O2/Fe(II) system, pH = 3 is the best initial pH for the degradation of ENR, PEF and SQX with the degradation efficiencies at 100%, 79.1% and 100% after 180 min, respectively. Considering the degradation rate and electrical energy per order of the test compounds, the UV/H2O2/Fe(II) process was better than the UV/H2O2 and UV/Fe(II) processes because of the greater OH generation. Based on major transformation products of ENR, PEF, and SQX detected during UV/H2O2/Fe(II) treatment, the probable degradation pathway of each compound is proposed. The fluorine atom of ENR and PEF was transformed into fluorine ion, and the sulfur atom was transformed into SO2/SO42−. The nitrogen atom was mainly transformed into NH3/NH4+. Formic acid, acetic acid, oxalic acid, and fumaric acid were identified in the irradiated solutions and all the test compounds and their intermediates can be finally mineralized. In addition, after the UV/H2O2/Fe(II) process, the acute toxicity of the final reaction solutions on zebrafish embryos was lower than that of the initial solution without any treatment. In summary, UV/H2O2/Fe(II) is a safe and efficient technology for antibiotic degradation.
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•ENR, PEF and SQX can be finally mineralized under UV/H2O2/Fe(II)•OH played a vital role for the UV/H2O2/Fe(II) degradation of pollutants.•The degradation pathways for ENR, PEF and SQX were proposed under UV/H2O2/Fe(II).•The acute toxicity on zebrafish embryos decreased after UV/H2O2/Fe(II) treatment.
The accumulation of ultraviolet (UV)‐absorbing compounds (flavonoids and related phenylpropanoids) and the resultant decrease in epidermal UV transmittance (TUV) are primary protective mechanisms ...employed by plants against potentially damaging solar UV radiation and are critical components of the overall acclimation response of plants to changing solar UV environments. Whether plants can adjust this UV sunscreen protection in response to rapid changes in UV, as occurs on a diurnal basis, is largely unexplored. Here, we use a combination of approaches to demonstrate that plants can modulate their UV‐screening properties within minutes to hours, and these changes are driven, in part, by UV radiation. For the cultivated species Abelmoschus esculentus, large (30–50%) and reversible changes in TUV occurred on a diurnal basis, and these adjustments were associated with changes in the concentrations of whole‐leaf UV‐absorbing compounds and several quercetin glycosides. Similar results were found for two other species (Vicia faba and Solanum lycopersicum), but no such changes were detected in Zea mays. These findings reveal a much more dynamic UV‐protection mechanism than previously recognized, raise important questions concerning the costs and benefits of UV‐protection strategies in plants and have practical implications for employing UV to enhance crop vigor and quality in controlled environments.
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•Advanced oxidation of municipal wastewater by UV/H2O2, UV/PDS and UV/Chlorine.•Oxidation performance followed the order of UV/Chlorine > UV/H2O2 ≈ UV/PDS.•UV absorbance (UVA), total ...fluorescence (TF) revealed highest R2 values with TOrCs.
UV-based advanced oxidation processes (AOPs) have been widely explored to remove organic contaminants from water streams. In this lab-scale study, the removal of 17 trace organic chemicals (TOrCs) by UV/H2O2, UV/PDS and UV/Chlorine was investigated at equimolar radical promoter concentrations in municipal wastewater. Direct comparison of the UV-AOPs was conducted with eight TOrCs being resistant to direct oxidation by H2O2, PDS and chlorine and revealed a general oxidation performance following the order of UV/Chlorine > UV/H2O2 ≈ UV/PDS while UV/PDS and UV/Chlorine exhibited higher compound selectivity than UV/H2O2. However, although oxidation performance of UV/Chlorine is outstanding in comparison of the three UV-AOPs, it has to be noted that oxidation by-product (OBP) formation potential might be substantially higher during both UV/PDS and UV/Chlorine compared to UV/H2O2 which was not investigated in this study. Evaluating potential optical surrogates to predict trace organic chemical (TOrCs) removal in UV-AOPs, nine parameters were selected representing chromophore and fluorophore features of DOM including components derived by parallel factor analysis (PARAFAC) of excitation-emission matrices. UV absorbance (UVA), total fluorescence (TF) and the selected fluorescence peak P_IV revealed highest linear correlation coefficients and were therefore identified as surrogates representing underlying mechanistic reactions of each UV-AOP. As none of the surrogates directly reacted with UV irradiation, slopes of surrogate-indicator correlations for photo-susceptible TOrCs decreased towards higher oxidant dosages. Correlations for these compounds should therefore only be determined for a limited range of oxidant dosage.
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•The degradation behaviors and differences of chiral pollutants (OFLO and LEV) were firstly identified.•UV/PS process was much more effective than the UV/H2O2 process for antibiotic ...degradation.•The second-order rate constants of SO4•−/•OH with OFLO and LEV were derived, respectively.•The acute toxicity of OFLO and LEV and their intermediate products was evaluated by TTC dehydrogenase activity assay.•Economic comparison of AOPs was based on energy and oxidant consumption.
Chiral quinolone antibiotics, as racemate and in enantiomerically form, have been attracted extensive attention due to their same molecular structure and different pharmacological properties and toxicity in environment. The present study focused on the difference of degradation efficiency and pathway of chiral antibiotics by different AOPs technology. The degradation behaviors and differences of chiral pollutants were firstly identified. Among them, UV/PS process exhibited the best performance for the elimination of chiral pollutants removal and reduction of total organic carbon (TOC). The degradation of ofloxacin and levofloxacin revealed pronounced pH dependence in UV/H2O2 and UV/PS processes, where the impact on Levofloxacin (LEV) was greater than that on Ofloxacin (OFLO). Only a slight variation of TOC was observed to be less than 50%, where the removal efficiencies were all above 96%. SO4•− generated in UV/PS process yields a greater mineralization of antibiotics than •OH in UV/H2O2 process. Cl−, NO3− and NOM had inhibitory effects on OFLO and LEV degradation in both processes, while SO42− showed positive effect on UV/PS degradation. Meanwhile, chairal antibiotics removal was dominated by •OH with the second-order rate constants of 3.97 × 109 and 2.48 × 109 M−1s−1 in UV/H2O2 process, while SO4•− played the key role in UV/PS system with second-order rate constants of 2.19 × 1010 and 2.66 × 1010 M−1s−1, respectively. The results of acute toxicity assay shown that OFLO exhibited higher acute toxicity than LEV, while TTC dehydrogenase activity of intermediate products of OFLO was lower than LEV. This study demonstrated that AOPs (especially UV/PS) were efficient for removing fluoroquinolone antibiotics, which can be considered as a clean and green method for the treatment of antibiotics-containing industrial wastewater.
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•The H2O2 and Fe(II) addition can enhance TCs mineralization under UV.•Environmental-level water constituents promoted TCs attenuation under UV.•UV light, ·OH, DOM*, H2O2, and Fe(II) ...complexation can attenuate TCs.•A tentative degradation pathway of TCs under UV-based treatment was proposed.•The evaluation for toxicity of treated solutions to zebrafish embryos was conducted.
The pollution of tetracyclines (TCs) in waters has caused public concern and scientific interest. This study investigates the effect of low-level hydrogen peroxide (H2O2) and ferrous ion (Fe(II) concentrations on the UV treatment of four TCs: oxytetracycline (OTC), tetracycline (TC), chlorotetracycline (CTC), and doxycycline (DXC). The optimum addition of Fe(II) (0.05 mM) and H2O2 (0.5 mM) promoted the attenuation and mineralization of test TCs, and a higher pH was conducive to their attenuation. Environmental-level water constituents (CO32−, HCO3−, NO3−, SO42−, NH4+, fulvic acid (FA), and humic acid (HA)) promoted test TCs attenuation under UV treatment, but inhibited their attenuation under H2O2/UV and Fe(II)/UV treatments (with the exception of HCO3− and FA). The attenuation of test TCs was attributed to UV and DOM* under UV treatment, UV, DOM*, H2O2, and ·OH under H2O2/UV treatment, and UV, DOM*, Fe-complexation, and ·OH under Fe(II)/UV treatment. A tentative degradation pathway of test TCs was proposed based on the detected intermediates and the degradation mechanisms. Additionally, an evaluation of the toxicity of treated solutions to zebrafish embryos showed that, solutions treated by only Fe(II) or H2O2 caused great toxicity, and Fe(II) or H2O2 combining with UV treatment could decrease the toxicity but required a longer irradiation time (>4h). Overall, our findings provide a scientific assessment of UV-based methods to remove antibiotics from aquatic systems.
The instability and rapid consumption of H2O2 limit the application of UV/H2O2 in water treatment. Recently, calcium peroxide (CaO2) has been demonstrated as an effective source of H2O2. However, the ...performance and mechanism of UV/CaO2 are still unknown. Herein, UV/CaO2 and UV/H2O2 were compared for degradation of aniline. The removal efficiency of aniline by UV/CaO2 was slightly lower than that by UV/H2O2, which could be attributed to the light scavenger by CaO2 suspended particles. HO‧ was identified to participate in aniline degradation in both UV/CaO2 and UV/H2O2, while O2-· was only involved in UV/CaO2. The efficiency of aniline degradation in UV/CaO2 was affected by the released H2O2 in the system. The release and decomposition rate of H2O2 in UV/CaO2 system were influenced by the CaO2 dosage and reaction pH, but slightly related with water matrix. Excessive CaO2 would scavenge aniline degradation through the released H2O2 to react with HO‧. Acidic condition would enhance the concentration of H2O2 in UV/CaO2 and promote the degradation of aniline. Cl– showed slight and almost no effect on aniline degradation in UV/CaO2 and UV/H2O2 systems, respectively, while HCO3– scavenged aniline degradation in UV/CaO2. NO3– inhibited aniline degradation in both UV/CaO2 and UV/H2O2. Compared to UV/H2O2, UV/CaO2 shows the similar efficiency on organics removal but conquers the limitations in UV/H2O2, which is a promising alternative choice in water treatment.
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•Aniline removal by UV/CaO2 was slightly lower than that by UV/H2O2.•Aniline degradation was affected by the released H2O2 in UV/CaO2.•Acidic pH enhanced H2O2 concentration and aniline degradation.•HO‧ and O2-‧ were involved in the degradation process.
In this study, ultraviolet based advanced oxidation processes (UV-AOPs) including UV/persulfate (UV/PS), UV/chlorine, and UV/H2O2 were employed to alleviate ultrafiltration membrane fouling during ...the treatment of algae-laden water. The results show that UV/PS pretreatment exhibited the best performance on fouling control, followed by the UV/H2O2 pretreatment. The fouling mitigation performance improved with the increase of oxidant dose. However, UV/chlorine pretreatment aggravated membrane fouling, and the irreversible fouling resistance increased by five times compared with that of raw water. The dissolved organic carbon (DOC) in the algae-laden solution was reduced after UV/PS pretreatment, while either UV/chlorine or UV/H2O2 pretreatment had little influence on the DOC of feed water. UV/PS and UV/H2O2 pretreatments were effective in the degradation of fluorescent compounds, thus reducing the deposition of organic matter on the membrane surface. Additionally, the decreased concentration of hydrophobic organics, algal cells, and debris in feed water after UV/PS pretreatment was also contributed to the fouling alleviation. The aggravated irreversible fouling after UV/chlorine pretreatment was probably ascribed to the increased accumulation of hydrophobic fractions in the membrane pores. Modeling result indicates that membrane fouling during the filtration of raw algae-laden water was dominated by intermediate blocking and cake filtration mechanisms. Both UV/PS and UV/H2O2 pretreatments transformed the combined fouling mechanism into standard blocking, while UV/chlorine pretreatment aggravated the pore blocking in the initial filtration period.
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•UV/PS pretreatment effectively mitigated fouling caused by algae-laden water.•UV/H2O2 pretreatment reduced fouling at high H2O2 dose.•UV/chlorine pretreatment significantly aggravated irreversible fouling.•Intrinsic mechanisms of membrane fouling after UV-AOPs pretreatment were proposed.
Quantification of Cr(VI) in an aqueous solution is conducted by direct UV–visible spectrophotometry based on the yellow coloring of the chromate ion. Measurements show that absorption follows the ...Beer–Lambert law over a wide range of concentrations. At pH below the pKa of 6.4 (HCrO4−/CrO4−2), the absorption maximum lies at 350 nm wavelength and the linear range spans from 0.5 to 100 mg Cr(VI)/L; above the pKa (pH 6.4), the absorption maximum is 373 nm and linearity occurs in the range of 0.5–25 mg/L. The wide range of validity of the Beer–Lambert law is advantageous for the measurement of concentrated samples. The standard method of analysis of aqueous Cr(VI) is by colorimetry with the 1,5-diphenylcarbazide (DPC)–Cr(VI) complex. This method, although very sensitive, bears a narrow range of linearity from 0 to 0.8 mg Cr(VI)/L. It is shown that when analyzing Cr(VI) solutions with concentrations in the range of 30–500 mg/L, the DPC method gives inaccurate results and relative standard deviations of 20–50%. This is due to high dilution factors. On the contrary, the direct method performs with high accuracy. Relative standard deviation is only 0.5% at 500 mg Cr(VI)/L. The direct method is fast, reliable, and nondestructive for the sample. The direct method is recommended for the quantification of Cr(VI) at concentrations greater than 1 mg/L.
Le dosage du Cr(VI) en solution aqueuse est effectué par spectrométrie UV–visible directe, grâce à la couleur jaune de l'ion chromate. Les mesures montrent que la loi de Beer–Lambert est respectée sur un large intervalle de concentrations. A pH inférieur à 6,4 (pKa HCrO4−/CrO4−2), l'absorption maximale se situe à la longueur d'onde 350 nm et la game linéaire d’étalonnage s’étend de 0,5 à 100 mg Cr(VI)/L; au dessus du pKa, l'absorption maximale se situe à 373 nm, la game de linéarité couvre l'intervalle 0,5–25 mg/L. Au contraire, la méthode standard d'analyse du Cr(VI) en solution, méthode colorimétrique au 1,5 diphénylcarbazide (DPC), présente une fenêtre de mesure très étroite, de 0 à 0,8 mg Cr(VI)/L. On montre que la méthode DPC appliquée à des échantillons de concentrations 30–500 mg/L, donne des résultats avec une incertitude importante et des écarts types de 20–50% autour de la moyenne. Les fortes déviations sont attribuées aux forts facteurs de dilution nécessaires. Pour la même game de concentrations, la méthode directe donne des résultats avec une très faible incertitude. Pour un échantillon de 500 mg Cr(VI)/L, l’écart type est de seulement 0,5%. La méthode directe est rapide, fiable, et elle permet de préserver l’échantillon. La méthode directe est conseillée pour le dosage du Cr(VI) à concentrations supérieures à 1 mg/L.
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•The pH affected the destruction of OTC by UV-C only and UV-C/H2O2 AOP.•Second-order rate constant of OTC with HO increased with increasing pH.•The presence of carbonate/bicarbonate ...enhanced the removal of OTC by UV/H2O2.•The effective role of CO3− for the degradation of OTC was confirmed.•Second-order rate constant of OTC with CO3− was estimated to be 2.9×108M−1s−1.
In this study, the influence of pH on the degradation of oxytetracycline (OTC) by UV-C only and UV-C/H2O2 advanced oxidation process (AOP) was investigated. The effect of carbonate and bicarbonate on the photochemical transformation of OTC in UV/H2O2 system was also evaluated. It was found that, by UV irradiation alone, the degradation of OTC was significantly improved with increasing pH; while in UV/H2O2 system, the observed UV fluence based pseudo first-order rate constant of OTC was found to be the highest at pH 5.5 and comparable at neutral and basic pH conditions. The conversion of OTC by UV/H2O2 was not inhibited in the presence of carbonate or bicarbonate. Instead, a slight promotion was observed at high concentrations of carbonate or bicarbonate. The presence of carbonate radical in UV/H2O2/Na2CO3 and UV/H2O2/NaHCO3 systems was demonstrated by adding three different alcohols, i.e., tert-butanol (t-BuOH), methanol (MeOH), and isopropanol (i-PrOH) that barely react with carbonate radical, and by adding 4-chlorophenol (4-CP) which has a high second-order rate constant with carbonate radical. The second-order rate constant of OTC with carbonate radical was subsequently determined. The results indicate that carbonate radical can play an important role on the degradation of organic compounds such as OTC in UV/H2O2 system in the presence of carbonate or bicarbonate that is commonly found in natural environment.
Sunlight is one of the main environmental resources that keeps all the organisms alive on earth. The ultraviolet (UV) radiation from the sun is essential for vitamin D synthesis in the human body, ...which is crucial for bone and muscle health. In addition, sun exposure also helps to reduce the risk of some cardiovascular diseases and cancers. However, excessive UV exposure can lead to adverse effects, including some eye diseases, premature aging, sunburn and skin cancers. The solar UV irradiance itself depends on many environmental factors. In fact, the UV index reported in weather forecasts is an estimation under cloudless conditions. Personal UV exposure also depends on one’s outdoor activities and habits. Furthermore, the UV intake depends on the skin sensitivity. Therefore, there is a need for research into monitoring the optimal daily UV exposure for health benefits, without developing potential health risks. To facilitate the monitoring of solar UV intensity and cumulative dose, a variety of UV sensors have been developed in the past few decades and many are commercially available. Examples of sensors being marketed are: portable UV dosimeter, wearable UV radiometer, personal UV monitor, and handheld Solarmeter®. Some of the UV sensors can be worn as personal health monitors, which promote solar exposure protection. The paper provides a comprehensive review of the wearable and portable UV sensors for monitoring personal UV exposure, including a discussion of their unique advantages and limitations. Proposals are also presented for possible future research into reliable and practical UV sensors for personal UV exposure monitoring.
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