The efficiency of the ultraviolet (UV)/chlorine process strongly depends on UV wavelength because chlorine photolysis and its subsequent radical formation are highly wavelength-dependent. This study ...compared the degradation of humic acid (HA) during the UV/chlorine process by low pressure mercury lamp (LPUV, 254 nm) and ultraviolet light-emitting diode (UV-LED, 275 and 310 nm). The results indicated that HA degradation followed the pseudo-first-order kinetics, and the fluence-based degradation rate constants (kobs) were significantly affected by UV wavelength and solution pH. HA degradation decreased greatly with increasing solution pH during the UV/chlorine process at 254 nm, while the opposite trend was observed at 275 and 310 nm. In the meantime, kobs decreased in the order of 275 nm > 254 nm > 310 nm at pH > 7.0. The changes of chlorine molar absorption coefficients at different UV wavelengths resulted in the variation of chlorine photodecay rates (kobs, chlorine), and the synergistic effects of kobs, chlorine and chlorine quantum yields (Φchlorine) affected HA reduction. The formation of disinfection by-products (DBPs) during the UV/chlorine process was also evaluated. A significant suppression on DBP formation and DBP-associated calculated theoretical cytotoxicity were observed at 275 nm high UV fluence and alkaline pHs. These findings in this study demonstrate that UV wavelength at 275 nm is more suitable for HA degradation by the UV/chlorine advanced oxidation process in practical applications.
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•HA degradation rate constants were significantly affected by UV wavelength in the UV/chlorine process.•The UV/chlorine process was more efficient at 275 nm than 254 and 310 nm at alkaline conditions.•Effective mitigation of DBPs and toxicity was achieved at 275 nm at high UV fluence.•DBP-associated cytotoxicity decreased in the order of 254 > 310 > 275 nm at high UV fluence in the presence of Br−.
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•The degradation of SMP in water was accomplished by UV-activated persulfate.•The second-order rate constants of SMP with SO4– and OH were derived.•Degradation pathways based on ...transformation products analysis were proposed.•Impacts of UV/PS treatment on DBP formation during post-chlorination were evaluated.
The kinetics and mechanisms of the degradation of sulfamethoxypyridazine (SMP) by an ultraviolet-activated persulfate (UV/PS) advanced oxidation process (AOP) and the formation of disinfection byproducts (DBPs) during subsequent chlorination were investigated in this study. The UV/PS process can significantly remove SMP through pseudo-first-order reaction kinetics. In a competitive kinetic experiment, the second-order rate constant of SMP with sulfate radical was determined to be 2.73 × 1010 M−1 s−1, while that with hydroxyl radical was 2.22 × 1010 M−1 s−1. Six major transformation products in SMP degradation were recognized by LC/MS/MS analysis. It was assumed that the degradation pathway of SMP involves the hydroxylation of the aromatic ring, cleavage of the sulfonamide bond, oxidation of the aniline moiety and elimination of SO2. The impacts of persulfate dose, pH, anions (HCO3–, SO42−, and Br−) and humic acid (HA) concentration on SMP degradation efficiency and DBP formation during subsequent chlorination were also examined. SMP degradation was accelerated with increasing persulfate dose, HCO3– and Br- concentration as well as decreasing pH and HA concentration. However, the amount of chloroform (CF) formed was reduced under a higher persulfate dosage and lower pH. In contrast, the amount of dichloroacetonitrile (DCAN) formed was enhanced under a higher persulfate dose and lower pH. Adding HA also increased the formation of both CF and DCAN. While, both HCO3– and SO42– had little effects on the formation of CF and DCAN. The presence of Br– had no significant effects on the bromine incorporation factors (BIFs) of trihalomethanes (THMs) and dihaloacetonitriles (DHANs). Raw water experiments showed that the UV/PS process could destroy SMP in natural water as well as control the formation of DBPs.
Oxidative stress is a key contributor to the pathogenesis of stroke-reperfusion injury. Neuroinflammatory peptides released after ischemic stroke mediate reperfusion injury. Previous studies, ...including ours, have shown that lipocalin-2 (LCN2) is secreted in response to cerebral ischemia to promote reperfusion injury. Genetic deletion of LCN2 significantly reduces brain injury after stroke, suggesting that LCN2 is a mediator of reperfusion injury and a potential therapeutic target. Immunotherapy has the potential to harness neuroinflammatory responses and provides neuroprotection against stroke. Here we report that LCN2 was induced on the inner surface of cerebral endothelial cells, neutrophils, and astrocytes that gatekeep the blood-brain barrier (BBB) after stroke. LCN2 monoclonal antibody (mAb) specifically targeted LCN2 in vitro and in vivo, attenuating the induction of LCN2 and pro-inflammatory mediators (iNOS, IL-6, CCL2, and CCL9) after stroke. Administration of LCN2 mAb at 4 h after stroke significantly reduced neurological deficits, cerebral infarction, edema, BBB leakage, and infiltration of neutrophils. The binding epitope of LCN2 mAb was mapped to the β3 and β4 strands, which are responsible for maintaining the integrity of LCN2 cup-shaped structure. These data indicate that LCN2 can be pharmacologically targeted using a specific mAb to reduce reperfusion injury after stroke.
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•UV/chlorination can significantly accelerate the degradation of CHI3.•The rate constant of OH and CHI3 was determined as 7.7×109M−1s−1.•Solution pH has remarkable influence on the ...degradation rate of CHI3 during UV/chlorination.•Bicarbonate and NOM can reduce the degradation rate of CHI3 during UV/chlorination.•IO3− contributed 13.7% of the total iodine species after CHI3 degradation during UV/chlorination.
Iodoform (CHI3) is an emerging disinfection by-product (DBP) that may be formed during pre-oxidation or disinfection processes in drinking water treatment. Degradation kinetics, modeling and mechanism of CHI3 by combined UV/chlorine advanced oxidation processes (AOPs) were studied in this manuscript. CHI3 was effectively removed by UV/chlorine process with the reactions followed pseudo-first order kinetics. The contributions of direct UV photolysis as well as indirect photolysis (hydroxyl radicals (OH) to CHI3 degradation during UV/chlorination under different experimental factors were investigated and determined as 20.3% and 79.7% at pH 5 to 97.1% and 2.9% at pH 9, respectively. Chlorine dosage and CHI3 concentration had slight effects on the contributions of different degradation pathways. NOM and bicarbonate have negative effects on CHI3 degradation. The degradation model of CHI3 during UV/chlorine processes was established, and the satisfactory match of the model calculation results and the experimental data were found. The reaction rate constant between CHI3 and UV light as well as CHI3 and OH were determined as 3.43×10−3s−1 and 7.7×109M−1s−1, respectively. On the basis of the iodine species (such as IO3−, HOI, I2 and I3−) mass balance analysis, the degradation pathways of CHI3 were proposed and IO3− contributed 13.7% of the total liberated iodine species during UV/chlorination. These results demonstrated that UV/chlorination process is a promising AOP technology for the treatment of water containing CHI3.
Haloacetamides (HAcAms) are an emerging class of nitrogenous disinfection byproducts (N-DBPs). However, there is a limited understanding about the precursors of HAcAms. In this study, we screened the ...precursors of dichloroacetamide (DCAcAm), the most commonly identified HAcAm in chlorinated or chloraminated drinking water. DCAcAm formation potential (FP) of raw water samples collected in different months from a reservoir in China was determined during chlorination, and the highest DCAcAm FP typically occurred in the summer samples. Dissolved organic matter (DOM) in a representative summer raw water sample was separated into six fractions by a series of resin elutions. Among them, hydrophilic acid (HiA) DOM showed the maximum DCAcAm FP, followed by hydrophilic bases (HiB) and, to a much lower extent, hydrophobic acids (HoA). Fluorescence excitation−emission matrix (EEM) spectra revealed that a mass of protein-like substances in the HiA fraction, made up of amino acids (AAs), were the likely DCAcAm precursors. Finally, we investigated the DCAcAm yields of 20 AAs during chlorination. Among them, seven AAs (aspartic acid, histidine, tyrosine, tryptophan, glutamine, asparagine, phenylalanine) could form DCAcAm during chlorination, with the corresponding DCAcAm yields of 0.231, 0.189, 0.153, 0.104, 0.078, 0.058, and 0.050 mmol/mol AA.
Surface water are frequently subjected to problems of algal blooms and release of algae organic matter (AOM) from the algae cells, which cause many water quality issues. This study investigated the ...formation of organic chloramines and nitrogenous disinfection by-products (N-DBPs) during chlor(am)ination and UV/chlor(am)ination of AOM in drinking water. AOM caused higher organic chloramine formation than humic acid and fulvic acid during chlor(am)ination. The formation of organic chloramines increased first and then decreased with the increase of free chlorine dosage, but kept increasing with the increase of NH2Cl dosage. During AOM chlorination, the formation of organic chloramines kept decreasing as the reaction time went by, and the maximum organic chloramine proportion (79.1%) in total chlorine occurred at 8 h. However, during AOM chloramination, the formation of organic chloramines increased first, decreased in the following and then increased again as the reaction time went by, and the maximum organic chloramine proportion (22.1%) in total chlorine occurred at 24 h. UV irradiation pretreatment did not effectively influence organic chloramine formation during AOM chlor(am)ination, but accelerated the degradation of organic chloramines during chloramination. Besides, UV pretreatment enhanced the formation of N-DBPs during the subsequent chlor(am)ination of AOM, especially dichloroacetonitrile.
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•AOM made a great contribution to organic chloramine formation in chlor(am)ination.•Free chlorine produced organic chloramines more easily but less stably than NH2Cl.•UV had no influence on organic chloramine formation during AOM chlor(am)ination.•UV enhanced N-DBP formation from organic chloramines during AOM chlor(am)ination.
Ultraviolet light-emitting diodes (UV-LEDs) are promising alternatives to conventional low-pressure UV (LPUV) lamps, mainly because they contain no toxic mercury and have a potential for less energy ...consumption and longer lifetime. In this study, UV sources including UV-LEDs (265, 275 and 285 nm) and LPUV (254 nm) were compared in UV/chlorine degradation of an organic contaminant, ronidazole (RNZ). UV-LED/chlorine performed better than LPUV/chlorine at neutral and alkaline pH values for RNZ degradation considering the fluence-based rate constant. However, the wall plug efficiencies of UV-LEDs are relatively low at present and must reach about 20–25% to achieve the same electrical energy per order as the LPUV in UV/chlorine degradation of RNZ at pH 7.5 and 9. Neither the contribution of radical (HO· or Cl·) nor the quantum yield of chlorine could explain the different RNZ degradation rate by UV/chlorine at different wavelengths and pH values, while the chlorine photolysis rate should be the key factor for these phenomena. The effects of common co-existing substances in real water (chloride, bicarbonate and natural organic matter) on UV/chlorine degradation of RNZ were similar at different UV wavelengths. Opposite to other oxidants or reductants, the molar absorption coefficient of chlorine increases when the UV wavelength increases from 254 to 285 nm at neutral and alkaline pH, which makes UV-LED/chlorine one of the best choices for UV-LED-based advanced oxidation/reduction processes.
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•UV-LED/chlorine performed better than LPUV/chlorine at neutral and alkaline pH.•Ronidazole degradation rate was highly dependent on UV wavelength by UV/chlorine.•Chlorine photolysis rate was the key factor for enhancement by UV-LED/chlorine.•Radicals or quantum yield of chlorine was not the key factor for the enhancement.•UV-LED/chlorine has advantage over other UV-LED-based AOPs.
Photochemical degradation of fluoroquinolone ciprofloxacin (CIP) in water by UV and UV/H
2
O
2
were investigated. The degradation rate of CIP was affected by pH, H
2
O
2
dosage, as well as the ...presence of other inorganic components. The optimized pH value and H
2
O
2
concentration were 7.0 and 5 mM. Carbonate and nitrate both impeded CIP degradation. According to liquid chromatography–tandem mass spectrometry analysis, four and 16 products were identified in UV and UV/H
2
O
2
system, respectively. Proposed degradation pathways suggest that reactions including the piperazinyl substituent, quinolone moiety, and cyclopropyl group lead to the photochemical degradation of CIP. Toxicity of products assessed by
Vibrio qinghaiensis
demonstrated that UV/H
2
O
2
process was more capable on controlling the toxicity of intermediates in CIP degradation than UV process.
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•Ultrasonic degradation of BPA was confirmed by the Langmuir-Hinshelwood model.•Both OH and RNSs accounted for BPA degradation during ultrasonic irradiation.•Ultrasonic pretreatment ...significantly enhanced TCNM formation during subsequent chlorination.•Nitrogen in TCNM from chlorination of treated BPA solution derived from N2 in air.•Effect of influencing factors on BPA degradation and its DBP formation were evaluated.
Ultrasonic irradiation has been widely adopted to remove emerging contaminants (ECs) in water, while little attention has been given to the impact of ultrasonic pretreatment on the downstream formation of disinfection byproducts (DBPs). In this study, bisphenol A (BPA), a typical EC that is frequently detected in water, was selected as a model contaminant to investigate the influence of ultrasonic pretreatment on DBP formation during the chlorination process. The ultrasonic degradation behaviors of BPA fit the heterogeneous Langmuir-Hinshelwood (L-H) model well, indicating that BPA undergoes decomposition by free radical reactions predominantly at the water-bubble interface. Interestingly, compared to direct chlorination, the ultrasonic pretreatment obviously enhanced trichloronitromethane (TCNM) formation from subsequent chlorination. The LC/MS/MS technique was applied to analyze the transformation products of BPA. In addition to hydroxyl radicals (OH) dominating hydroxylation of the aromatic ring and cleavage of the CC bond, an ultrasonic-induced nitration mechanism was also involved in BPA degradation, and the formed nitration products may be responsible for TCNM formation during subsequent chlorination. Factors affecting the ultrasonic degradation rate of BPA as well as DBP formation were also investigated. Generally, dissolved O2, higher ultrasonic frequency and higher power favored BPA degradation, whereas the presence of HCO3− and HA hindered BPA degradation, and Cl− showed a minor influence. TCNM formation was largely diminished by sparging with O2 or N2 alone. Higher ultrasonic frequency and power enhanced the TCM and TCNM formation. The presence of HA promoted THM formation, while HCO3− inhibited TCNM formation. Therefore, once ultrasonic treatment is adopted as an alternative water treatment, its impact on subsequent DBP formation requires further study.
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