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1.
The presence of disinfection byproducts (DBPs) such as trihalomethanes (THMs) and haloacetic acids (HAAs) in drinking water is of great concern due to their adverse effects on human health. Emerging regulation limiting the concentration of DBPs in drinking water has increased demands for technologies and processes which reduce the formation of DBPs in drinking water. In this study, UV-H 2O 2 based advance oxidation process (AOP) was used to treat raw surface water. Experiments were conducted using low pressure mercury vapor UV lamps in collimated beam and flow-through annular photoreactors. The effect of UV fluence (0–3500 mJ cm −2) and hydrogen peroxide concentration (0–23 mg l −1) in reducing the concentration of THMs and HAAs was examined. The UV-H 2O 2 AOP was then coupled with a downstream biological activated carbon (BAC) treatment to assess the synergetic benefits of combining the two treatments. It was observed that UV-H 2O 2 AOP was only effective at reducing DBPs at UV fluences of more than 1000 mJ cm −2and initial H 2O 2 concentrations of about or greater than 23 mg l −1. However, the combined AOP–BAC treatment showed significant reductions of 43%, 52%, and 59% relative to untreated raw water for DBPs, TOC, and UV 254, respectively. 相似文献
2.
The degradation of a common textile dye, Reactive-brilliant red X-3B, by several advanced oxidation technologies was studied in an air-saturated aqueous solution. The dye was resistant to the UV illumination (wavelength λ 320 nm), but was decolorized when one of Fe 3+, H 2O 2 and TiO 2 components was present. The decolorization rate was observed to be quite different for each system, and the relative order evaluated under comparable conditions followed the order of Fe 2+–H 2O 2–UV Fe 2+–H 2O 2 > Fe 3+–H 2O 2–UV > Fe 3+–H 2O 2 > Fe 3+–TiO 2–UV > TiO 2–UV > Fe 3+–UV > TiO 2–visible light ( λ 450 nm) > H 2O 2–UV > Fe 2+–UV. The mechanism for each process is discussed, and linked together for understanding the observed differences in reactivity. 相似文献
3.
Aqueous 4-nitrophenol solutions containing TiO 2 or Al 2O 3 nanoparticles were irradiated with electron beam. 4-nitrophenol was decomposed by the ionizing radiation process in the absence of the nanoparticles. The addition of TiO 2 or Al 2O 3 (2 g l −1) before irradiation improved the removal of 4-nitrophenol, total organic carbon (TOC) but also nitrogen (TN). To identify the origin of the loss (catalysis or simply adsorption), TiO 2 or Al 2O 3 nanoparticles were added after irradiation. Experiments show that the effect of the presence of TiO 2 or Al 2O 3 during irradiation is just due to adsorption. 相似文献
4.
Arsenic oxidation (As(III) to As(V)) and As(V) removal from water were assessed by using TiO 2 immobilized in PET (polyethylene terephthalate) bottles in the presence of natural sunlight and iron salts. The effect of many parameters was sequentially studied: TiO 2 concentration of the coating solution, Fe(II) concentration, pH, solar irradiation time; dissolved organic carbon concentration. The final conditions (TiO 2 concentration of the coating solution: 10%; Fe(II): 7.0 mg l −1; solar exposure time: 120 min) were applied to natural water samples spiked with 500 μg l −1 As(III) in order to verify the influence of natural water matrix. After treatment, As(III) and total As concentrations were lower than the limit of quantitation (2 μg l −1) of the voltammetric method used, showing a removal over 99%, and giving evidence that As(III) was effectively oxidized to As(V). The results obtained demonstrated that TiO 2 can be easily immobilized on a PET surface in order to perform As(III) oxidation in water and that this TiO 2 immobilization, combined with coprecipitation of arsenic on Fe(III) hydroxides(oxides) could be an efficient way for inorganic arsenic removal from groundwaters. 相似文献
5.
The photocatalytic inactivation (PCI) of Escherichia coli (Gram-negative) and Bacillus subtilis (Gram-positive) was performed using polyoxometalate (POM) as a homogeneous photocatalyst and compared with that of heterogeneous TiO 2 photocatalyst. Aqueous suspensions of the microorganisms (10 7–10 8 cfu ml −1) and POM (or TiO 2) were irradiated with black light lamps. The POM-PCI was faster than (or comparable to) TiO 2-PCI under the experimental conditions employed in this study. The relative efficiency of POM-PCI was species-dependent. Among three POMs (H 3PW 12O 40, H 3PMo 12O 40, and H 4SiW 12O 40) tested in this study, the inactivation of E. coli was fastest with H 4SiW 12O 40 while that of B. subtilis was the most efficient with H 3PW 12O 40. Although the biocidal action of TiO 2 photocatalyst has been commonly ascribed to the role of photogenerated reactive oxygen species such as hydroxyl radicals and superoxides, the cell death mechanism with POM seems to be different from TiO 2-PCI. While TiO 2 caused the cell membrane disruption, POM did not induce the cell lysis. When methanol was added to the POM solution, not only the PCI of E. coli was enhanced (contrary to the case of TiO 2-PCI) but also the dark inactivation was observed. This was ascribed to the in situ production of formaldehyde from the oxidation of methanol. The interesting biocidal property of POM photocatalyst might be utilized as a potential disinfectant technology. 相似文献
6.
In this study, the rates of degradation of organic compounds by several AOPs (H 2O 2/UV, Fe(III)/UV, Fe(III)/H 2O 2/UV, Fe(II)/H 2O 2 and Fe(III)/H 2O 2) have been compared. Experiments were carried out at pH ≈ 3 (perchloric acid / sodium perchlorate solutions) and with UV reactors equipped with a low-pressure mercury vapour lamp (emission at 253.7 run). The data obtained with atrazine ([Atrazine] o = 100 μg/L) showed that the rate of degradation of atrazine in very dilute aqueous solution is much more rapid with Fe(III)/UV than with H 2O 2/UV. Photo-Fenton process (Fe(III)/H 2O 2/UV) was found to be more efficient than H 2O 2/UV and Fe(II)/H 2O 2 for the mineralization of acetone ([Acetone] o = 1 mM). 相似文献
7.
The combined electrochemical oxidation-solar-light/immobilized TiO 2 film process was conducted to degrade an azo dye, Reactive Black 5 (RB5). The toxicity was also monitored by the Vibrio fischeri light inhibition test. The electrochemical oxidation rapidly decolorized RB5 (55, 110 μM) with a supporting electrolyte of 2 g l −1 NaCl at current density 277 A m −2 and pH 4. However, TOC mineralization and A 310 removal were low. Additionally, the treated solution showed high biotoxicity. RB5 at 110 μM significantly retarded the de-colorization efficiency by using the solar-light/immobilized TiO 2 film process. The combined electrochemical oxidation-solar-light/immobilized TiO 2 process effectively increased the removal of color, A 310, and TOC. The toxicity was also significantly reduced after 3 h of solar irradiation. The results indicated that the low-cost combined process is a potential technique for rapid treatment of RB5. 相似文献
8.
The photodegradation of five representative nitromusk compounds in water has been performed in a stirred batch photoreactor with a UV low-pressure immersed mercury lamp, at constant temperature and different doses of hydrogen peroxide. The rate constants have been calculated on the basis of experimental data and a postulated first-order kinetic model. The rate constants, at 298 K and a dose of 1.1746 μmol l −1 H 2O 2 ranges from 0.3567 × 10 −3 s −1 for musk tibetene, to 1.785 × 10 −3 s −1 for musk ambrette. 相似文献
9.
UV/Fenton, near-UV-visible/Fenton, dark Fenton, and H 2O 2/UV reactions have been used to treat simulated dyehouse effluents representing wastewater from the textile dyeing and rinsing process. Experiments were carried out in a lab - scale photochemical reactor using concentrations of 0.5–25 mM H 2O 2, 0.04-0.5 mM Fe 2+-ion and different dilutions of textile wastewater. To assess the extent of mineralization, decolourization kinetics and the effect of different fight sources on treatment efficiency, DOC, optical density at 254 nm and 600 nm wavelength and residual H 2O 2 concentrations were measured during the course of the advanced oxidation reactions. Comparative evaluation of the obtained results revealed that the decolourization rate increased with applied H 2O 2 and Fe 2+-ion dose as well as the strength of the synthetic textile wastewater. The best results were obtained by the near - UV/visible/Fenton process with a decolourization rate constant of 1.57 min −1, a UV 254nm reduction of 97% and a DOC removal of 41% at relatively low doses of the H 2O 2 oxidant and Fe 2+-ion catalyst within 60 min treatment time. 相似文献
10.
A new Aeromonas bioassay is described to assess the potential harmful effects of the glyphosate-based herbicide, Roundup ®, in the Albufera lake, a protected area near Valencia. Viability markers as membrane integrity, culturability and β-galactosidase production of Aeromonas caviae were studied to determine the influence of the herbicide in the bacterial cells. Data from the multifactor analysis of variance test showed no significant differences ( P > 0.05) between A. caviae counts of viability markers at the studied concentrations (0, 50 and 100 mg l −1 of glyphosate). The effects of Roundup® on microbial biota present in the lake were assessed by measuring the number of indigenous mesophilic Aeromonas in presence of different amounts of the herbicide at 0, 50 and 100 mg l−1 of glyphosate. In samples containing 50 and 100 mg l−1 of glyphosate a significant (P < 0.05) increase in Aeromonas spp. counts and accompanying flora was observed. The acute toxicity of Roundup® and of Roundup® diluted with Albufera lake water to Microtox® luminescent bacterium (Vibrio fischeri) also was determined. The EC50 values obtained were 36.4 mg l−1 and 64.0 mg l−1 of glyphosate respectively. The acidity (pH 4.5) of the herbicide formulation was the responsible of the observed toxicity. 相似文献
11.
Wetland loss along the Louisiana Gulf coast and excessive nitrate loading into the Gulf of Mexico are interrelated environmental problems. Nitrate removal by soil denitrification activity was studied in a ponded freshwater marsh receiving diverted Mississippi River water for the purpose of reversing or slowing wetland loss. Labeled 15N-nitrate was applied at 3.8 g N m −2 into four replicate study plots after removing above ground vegetation. Nitrogen gas (N 2) and nitrous oxide (N 2O) emissions from the plots were determined by isotope ratio mass spectrometry (IRMS). Nitrous oxide emissions were also compared with the results determined by gas chromatograph (GC). Results showed that it took 2 weeks to remove the added nitrate with N 2O emission occurring over a period of 4 d. The apparent denitrification dynamics were assumed to follow the Michaelis–Menten equation. The maximum denitrification rate and Km value were determined as 12.6 mg N m −2 h −1, and 6.5 mg N l −1, respectively. Therefore the maximum capacity for nitrate removal by the marsh soil would be equivalent to 110 g N m −2 yr −1, with more than 30% of nitrogen gas evolved as N 2O. For typical nitrate concentrations in Mississippi River water of about 1 mg N l −1, nitrate would be removed at a rate of 14.7 g N m −2 yr −1 with N 2O emission about 1.5%. A denitrification dynamic model showed that the efficiency of nitrate removal would largely depend on the water discharge rate into the ponded wetland. Higher discharge rate will result in less retention time for the water in the marsh where nitrate is denitrified. 相似文献
12.
Phenol is degraded by biological treatment, however mineralization requires long time. To decrease the time and operational cost necessary for the mineralization of phenol, an optimum operation condition of the combined biological–photocatalytical treatment was investigated. The mineralization of phenol (50 mg l −1) was conducted in a flow-type biomembrane tank combined with a batch-type TiO 2-suspended photocatalytic reactor. Phenol was degraded biologically to the concentration of 6.8 mg l −1, an effective concentration for further photocatalytic treatment. After the biological treatment, the biotreated phenol was treated photocatalytically to complete the mineralization of phenol. The combined treatment shortened the mineralization time compared to the biological treatment and electric cost compared to the photocatalytic treatment only. The combined treatment may be suitable for a short-time mineralization of phenol in wastewater. 相似文献
13.
Glucose oxidase is a well-known enzyme that catalyzes the oxidation of β-d-glucose to produce gluconic acid and hydrogen peroxide. Fenton reaction is a powerful oxidation technology used for the oxidation of groundwater pollutants. For the application of Fenton reaction in groundwater remediation, successful operation of Fenton reaction near neutral pH, and on-site generation of both H 2O 2 and chelate will be beneficial. The focus of this experimental study was to couple the glucose oxidation reaction with chelate-based Fenton reaction. The idea was to use the hydrogen peroxide and chelate gluconic acid generated during glucose oxidation for the dechlorination of 2,4,6-trichlorophenol (TCP) by Fenton reaction. The oxidation of glucose was achieved using the enzyme in free and immobilized forms. The rate of production of hydrogen peroxide was determined for each system, and was used to estimate the time required for complete consumption of glucose during the process, thus avoiding any traces of glucose in the Fenton reaction. In the case of free enzyme reaction, separation of the enzyme was achieved using an ultrafiltration membrane before initiating the Fenton reaction. The oxidation of TCP by Fenton reaction was performed at varying ratios of gluconic acid/Fe, and its effect on the decomposition of TCP and H 2O 2 was studied. TCP degradation was studied both in terms of parent compound degradation and free chloride generation. 相似文献
14.
Wastewater samples from an anaerobic reactor were extracted with hexane and derivatized with diazomethane (method 1) and with acetic anidride (method 2). Gas chromatography with electron-capture detection (ECD) was employed for separating the parent compound and intermediates trichlorophenols (TCP) and dichlorophenols (DCP) which originated from the penta chlorophenol (PCP) degradation process. The relations between concentrations of PCP, TCP and DCP areas were linear in the range of concentrations of 0.2 to 8 mg/L and 0.025 mg/L to 5 mg/L for methods 1 and 2, respectively. The repeatability of the extraction methods was satisfactory, with variation coefficients lower than 11%. For method 1, at the fortification level of 0.2 mg/L, recovery of PCP, TCP, and DCP was 112%, 74% and 45%, respectively. For method 2, the corresponding recovery values at the fortification level of 0.1 mg/L were 91%, 93% and 103%, respectively. Storage of the frozen samples did not alter their PCP determination properties. The chromatographic methods adapted for chlorophenol determination in wastewater were suitable with relatively simple manipulation techniques. The obtained results were reproducible and allowed identification of intermediates formed during the PCP degradation process. 相似文献
15.
Wastewater samples from an anaerobic reactor were extracted with hexane and derivatized with diazomethane (method 1) and with acetic anidride (method 2). Gas chromatography with electron-capture detection (ECD) was employed for separating the parent compound and intermediates trichlorophenols (TCP) and dichlorophenols (DCP) which originated from the penta chlorophenol (PCP) degradation process. The relations between concentrations of PCP, TCP and DCP areas were linear in the range of concentrations of 0.2 to 8 mg/L and 0.025 mg/L to 5 mg/L for methods 1 and 2, respectively. The repeatability of the extraction methods was satisfactory, with variation coefficients lower than 11%. For method 1, at the fortification level of 0.2 mg/L, recovery of PCP, TCP, and DCP was 112%, 74% and 45%, respectively. For method 2, the corresponding recovery values at the fortification level of 0.1 mg/L were 91%, 93% and 103%, respectively. Storage of the frozen samples did not alter their PCP determination properties. The chromatographic methods adapted for chlorophenol determination in wastewater were suitable with relatively simple manipulation techniques. The obtained results were reproducible and allowed identification of intermediates formed during the PCP degradation process. 相似文献
16.
Fe-doped TiO 2 was prepared by the calcination of Fe xTiS 2 ( x = 0, 0.002, 0.005, 0.008, 0.01) and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and UV–visible diffuse reflectance spectra. All the Fe-doped TiO 2 were composed of an anatase crystal form and showed red shifts to a longer wavelength. The activity of the Fe-doped TiO 2 for the degradation of phenol was investigated by varying the iron content during UV (365 nm) and visible light (405 nm and 436 nm) irradiation. The degradation rate depended on the Fe content and the Fe-doped TiO 2 was responsive to the visible light as well as the elevated activity toward UV light. The molar ratio of 0.005 was the optimum for both the UV and visible light irradiations. The result was discussed on the basis of the balance of the excited electron–hole trap by the doped Fe 3+ and their charge recombination on the doped Fe 3+ level. The Fe-doped TiO 2 ( x = 0.005) was more active than P25 TiO 2 under solar light irradiation. The suspended Fe-doped TiO 2 spontaneously precipitated once the stirring of the reaction mixture was terminated. 相似文献
17.
Natural humic water was treated with ultraviolet (UV) light and UV + hydrogen peroxide (UV/H 2O 2. The effects on the dissolved organic carbon content (DOC), the UV-absorbance at 254 nm (UV-abs.), the molecular size distribution, pH, and mutagenic activity were monitored, and the identity and concentrations of the most abundant gas chromatographable organic degradation products were determined. The DOC content and the UV-abs. of the water decreased substantially during treatment with UV/H2O2. The decreases were dependent on the time of irradiation (UV dose) as well as on the H2O2 dose applied. The humus macromolecules were degraded to smaller fragments during irradiation. At higher UV doses, however, part of the dissolved organic matter (DOM) was found to precipitate, probably as a result of polymerization. Oxalic acid, acetic acid, malonic acid, and n-butanoic acid were the most abundant degradation products detected. These acids were found to account for up to 20% and 80% of the DOM in UV- and UV/H2O2-treated waters, respectively. No mutagenic activity was generated by the UV irradiation or the UV/H2O2 treatment. It is further concluded that the substantial mutagenic activity formed during chlorination of humic waters cannot be decreased by using UV irradiation as a pretreatment step. 相似文献
18.
Lanthanum-doped anatase TiO 2 thin films on glass prepared via a sol–gel process have been shown to have much higher photocatalytic activity for the degradation of gaseous benzene than pure anatase TiO 2 thin film. The photodecomposition of benzene on both types of TiO 2 films follows the first-order kinetics while the CO 2 and CO formation followed the zero-order kinetics. GC/MS identification of the intermediates produced during the photodegradation of benzene revealed that doping lanthanum into TiO 2 thin film favors a cleavage of benzene ring. An optimal lanthanum amount with respect to photocatalytic activity was about 2.5 wt% (La 2O 3/TiO 2). 相似文献
19.
We report the effects of 1,2- and 1,4-dichlorobenzene (1,2-DCB and 1,4-DCB) on the aquatic macrophyte Ceratophyllum demersum. We evaluated the response of the antioxidant system through the assay of glutathione reductase (GR), guaiacol peroxidase (POD) and glutathione peroxidase (GPx). Additionally, the effect of DCBs on the detoxication system by measuring the activity of glutathione- S-transferase (GST) was evaluated. C. demersum showed elevated GST activities when exposed to 10 and 20 mg l−1 1,2-DCB, and at 10 mg l−1 for 1,4-DCB. These results show that glutathione conjugation take place at relatively high concentrations of both isomers. Significantly increased activities of POD were also detected in C. demersum exposed to concentrations above 5 mg l−1 of the corresponding isomer. The GR activity was enhanced in plants exposed to 1,2-DCB (5 mg l−1) and 1,4-DCB (10 mg l−1). GPx was also significantly increased in exposures to the corresponding isomer, each at a concentration of 10 mg l−1. However, plants exposed to low doses of 1,4-DCB (1 mg l−1) showed significantly decreased activities of both enzymes GR and GPx. Consequently, it is clear that the exposure of the aquatic macrophyte C. demersum to DCBs is able to cause an activation of the antioxidant system, showing an isomer specific pattern, which suggests that the defence system of this plant is playing an important role in scavenging ROS, helping to protect the organism against adverse oxidative effects generated by the prooxidant action of the tested xenobiotics. Furthermore, increased GST activities give indirect evidence on the conjugation of either DCBs or the corresponding metabolites during phase II of detoxication, which supports the elimination process of toxic metabolites from cells of C. demersum. 相似文献
20.
The sequential UV-biological degradation of a mixture of 4-chlorophenol (CP), 2,4-dichlorophenol (DCP), 2,4,6-trichlorophenol (TCP), and pentachlorophenol (PCP) was first tested with each pollutant supplied at an initial concentration of 50 mg l(-1). Under these conditions, the chlorophenols were photodegraded in the following order of removal rate: PCP>TCP>DCP>CP with only CP and DCP remaining after 40 h of irradiation. The remaining CP (41 mg l(-1)) and DCP (13 mg l(-1)) were then completely removed by biological treatment with an activated sludge mixed culture. Biodegradation did not occur in similar tests conducted with a non-irradiated mixture due to the high microbial toxicity of the solution. UV treatment lead to a significant reduction of the phytotoxicity to Lipedium sativum but no further reduction of phytotoxicity was observed after biological treatment. Evidence was found that the pollutants were partially photodegraded into toxic and non-biodegradable products. When the pollutants were tested individually (initial concentration of 50 mg l(-1)), PCP, TCP, DCP, 4-CP were photodegraded according to first order kinetic model (r2>99) with half-lives of 2.2, 3.3, 5.7, and 54 h, respectively. The photoproducts were subsequently biodegraded. This study illustrates the potential of UV as pre-treatment for biological treatment in order to remove toxicity and enhance the biodegradability of organic contaminants. However, it also shows that UV treatment must be carefully optimized to avoid the formation of toxic and/or recalcitrant photoproducts and results from studies conducted on single contaminants cannot be extrapolated to mixtures. 相似文献
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