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1.
Synthetic musks have been reported in wastewaters at concentrations as high as tens of micrograms per litre. The two most significant polycyclic musk fragrance compounds are 1,3,4,6,7,8-hexahydro-4,6,6,7,8,8-hexamethylcyclopenta(g)-2-benzopyran (HHCB, trade name galaxolide®) and 7-acetyl-1,1,3,4,4,6-hexamethyltetrahydronaphthalene (AHTN, trade name tonalide®). We report the result of several irradiation and advanced oxidation processes carried out on samples of the effluent of a wastewater treatment plant located in Alcalá de Henares, Madrid. Wastewater samples were pre-ozonated and spiked with 500 ng/L of tonalide or galaxolide in order to obtain final concentrations in the same order as the raw effluent. The treatments assayed were ozonation with and without the addition of hydrogen peroxide (O3, O3/H2O2), ultraviolet (254 nm low pressure mercury lamp) and xenon-arc visible light irradiation alone and in combination with ozone (UV, O3/UV, Xe, O3/Xe) and visible light photocatalytic oxidation using a Ce-doped titanium dioxide photocatalyst performed under continuous oxygen or ozone gas bubbling (O2/Xe/Ce-TiO2, O3/Xe/Ce-TiO2). In all cases, samples taken at different contact times up to 15 min were analyzed. An analytical method based on stir bar sorptive extraction (SBSE), followed by comprehensive two-dimensional gas chromatography (SBSE-GC × GC-TOF-MS), was used for the automatic searching and evaluation of the synthetic musks and other nonpolar or semipolar contaminants in the wastewater samples. In all cases tonalide was more easily removed than galaxolide. The best results for the latter (more than 75% removal after 5 min on stream) were obtained from ozonation (O3) and visible light photocatalytic ozonation (O3/Xe/Ce-TiO2). A significant removal of both pollutants (∼60% after 15 min) was also obtained during visible light photocatalysis (O2/Xe/Ce-TiO2). UV radiation was able to deplete tonalide (+90%) after 15 min but only reduced the concentration of galaxolide to about half of its initial concentration. The toxicity of treated samples decreased for O3/UV and O3/Ce-TiO2, but increased during irradiation processes UV, Xe and Xe/Ce-TiO2. Ozone treatments tend to decrease toxicity up to a certain dosage, from which point the presence of toxic transformation products has adverse effects on aquatic microorganisms.  相似文献   

2.
The photocatalytic degradation of two phenolic compounds, p-coumaric acid and caffeic acid, was performed with a suspended mixture of TiO2 and powdered activated carbon (PAC) (at pH = 3.4 and 8). Adsorption, direct photolysis and photocatalytic degradation were studied under different pH and UV light sources (sunlight vs. 365 nm UV lamps). The potential for reusing this catalyst mixture in sequential photocatalytic runs was examined as well. Quantum yields for the direct photolysis of caffeic acid under solar and artificial 365 nm light were calculated (for the first time) as 0.005 and 0.011, respectively.A higher removal rate of contaminants by either adsorption or photocatalysis was obtained at a low pH (pH 4). Furthermore, the addition of PAC increased the removal efficiency of the phenolic compounds. Fast removal of the pollutants from the solution over three sequential runs was achieved only when both TiO2 and PAC were present. This suggests that at medium phenolic concentrations, the presence of PAC as a co-sorbent reduces surface poisoning of the TiO2 catalyst and hence improves photocatalysis degradation of phenolic pollutants.The adsorption equilibrium of caffeic acid or p-coumaric acid on TiO2, PAC and the combined mixture of TiO2 and PAC follows the Langmuir isotherm model. Experiments with PAC TiO2 mixture and olive mill wastewater (anaerobically treated and diluted by a factor of 10) showed higher removal of polyphenols than of chemical oxygen demand (COD). 87% removal of total polyphenols, compared to 58% of COD, was achieved after 24 h of exposure to 365 nm irradiation (7.6 W/m2) in the presence of a suspended mixture of TiO2 and PAC, indicating “self-selectivity” of polyphenols.  相似文献   

3.
The coupling of membrane separation and photocatalytic oxidation has been studied for the removal of pharmaceutical pollutants. The retention properties of two different membranes (nanofiltration and reverse osmosis) were assessed. Comparable selectivity on the separation of pharmaceuticals were observed for both membranes, obtaining a permeate stream with concentrations of each pharmaceutical below 0.5 mg L1 and a rejected flux highly concentrated (in the range of 16–25 mg L1 and 18–32 mg L1 of each pharmaceutical for NF-90 and BW-30 membranes, respectively), when an initial stream of six pharmaceuticals was feeding to the membrane system (10 mg L1 of each pharmaceutical). The abatement of concentrated pharmaceuticals of the rejected stream was evaluated by means of heterogeneous photocatalytic oxidation using TiO2 and Fe2O3/SBA-15 in presence of hydrogen peroxide as photo-Fenton system. Both photocatalytic treatments showed remarkable removals of pharmaceutical compounds, achieving values between 80 and 100%. The nicotine was the most refractory pollutant of all the studied pharmaceuticals. Photo-Fenton treatment seems to be more effective than TiO2 photocatalysis, as high mineralization degree and increased nicotine removal were attested. This work can be considered an interesting approach of coupling membrane separation and heterogeneous photocatalytic technologies for the successful abatement of pharmaceutical compounds in effluents of wastewater treatment plants.  相似文献   

4.
Parshetti GK  Doong RA 《Water research》2011,45(14):4198-4210
The coupled removal of priority pollutants by nanocomposite materials has recently been receiving much attention. In this study, trichloroethylene (TCE) and 2,4-dichlorophenol (DCP) in aqueous solutions were simultaneously removed by Fe/TiO2 nanocomposites under anoxic conditions in the presence of nickel ions and UV light at 365 nm. Both TCE and DCP were effectively dechlorinated by Fe/TiO2 nanocomposites, and the pseudo-first-order rate constants (kobs) for TCE and DCP dechlorination were (1.39 ± 0.05)×10−2 and (1.08 ± 0.05)×10−2 h−1, respectively, which were higher than that by nanoscale zerovalent iron alone. In addition, the kobs for DCP dechlorination was enhanced by a factor of 77 when Fe/TiO2 was illuminated with UV light for 2 h. Hydrodechlorination was found to be the major reaction pathway for TCE dechlorination, while DCP could undergo reductive dechlorination or react with hydroxyl radicals to produce 1,4-benzoquinone and phenol. TCE was a stronger electron acceptor than DCP, which could inhibit the dechlorination efficiency and rate of DCP during simultaneous removal processes. The addition of nickel ions significantly enhanced the simultaneous photodechlorination efficiency of TCE and DCP under the illumination of UV light. The kobs values for DCP and TCE photodechlorination by Fe/TiO2 in the presence of 20-100 μM Ni(II) were 30.4-136 and 13.2-192 times greater, respectively, when compared with those in the dark. Electron spin resonance analysis showed that the photo-generated electron-hole pairs could be effectively separated through Ni ions cycling, leading to the improvement of electron transfer efficiency of TCE and DCP by Fe/TiO2.  相似文献   

5.
Degradation kinetics and mineralization of an urban wastewater treatment plant effluent contaminated with a mixture of pharmaceutical compounds composed of amoxicillin (10 mg L−1), carbamazepine (5 mg L−1) and diclofenac (2.5 mg L−1) by TiO2 photocatalysis were investigated. The photocatalytic effect was investigated using both spiked distilled water and actual wastewater solutions. The process efficiency was evaluated through UV absorbance and TOC measurements. A set of bioassays (Daphnia magna, Pseudokirchneriella subcapitata and Lepidium sativum) was performed to evaluate the potential toxicity of the oxidation intermediates. A pseudo-first order kinetic model was found to fit well the experimental data. The mineralization rate (TOC) of the wastewater contaminated with the pharmaceuticals was found to be really slow (t1/2 = 86.6 min) compared to that of the same pharmaceuticals spiked in distilled water (t1/2 = 46.5 min). The results from the toxicity tests of single pharmaceuticals, their mixture and the wastewater matrix spiked with the pharmaceuticals displayed a general accordance between the responses of the freshwater aquatic species (P. subscapitata > D. magna). In general the photocatalytic treatment did not completely reduce the toxicity under the investigated conditions (maximum catalyst loading and irradiation time 0.8 g TiO2 L−1 and 120 min respectively).  相似文献   

6.
In this article, the rational design of a physically coated TiO2-WO3 nanocube-polyaniline photocatalytic membrane (hierarchical) reactor for the efficient reduction of chromium (VI) under visible light is discussed. The incorporation of TiO2-WO3 in the polyaniline (PANI) membrane provides excellent hydrophilicity and high photo-corrosion resistance and facilitates the rapid permeation of water with a flux rate of 12 L/m2 h and higher Cr (VI) reduction. The exposure of bare PANI membranes in Cr (VI) solution leads to over-oxidation of PANI membrane and eventually leads to the destruction of the membrane. The hierarchical photocatalytic coating improves the lifetime of the membrane by blocking it from deprotonation. The photocatalytic membrane could offer 79.30% Cr (VI) reduction under visible light irradiation in a photocatalytic membrane reactor. After several reduction cycles, the membrane showed good self-cleaning ability. The present work suggests that TiO2-WO3 nanocube-coated PANI hierarchical membrane is a promising approach for the reduction and removal of Cr (VI) from wastewater.  相似文献   

7.
The kinetics of photodegradation of the pesticide metaldehyde by UV/H2O2 and UV/TiO2 in laboratory grade water and a natural surface water were studied. Experiments were carried out in a bench scale collimated beam device using UVC radiation. Metaldehyde was efficiently degraded by both processes in laboratory grade water at identical rates of degradation (0.0070 and 0.0067 cm2 mJ−1 for UV/TiO2 and UV/H2O2 respectively) when optimised doses were used. The ratio between oxidant and metaldehyde was significantly higher for H2O2 due to its low photon absorption efficiency at 254 nm. However, the presence of background organic compounds in natural water severely affected the rate of degradation, and whilst the pseudo first-order rate constant of degradation by UV/H2O2 was slowed down (0.0020 cm2 mJ−1), the degradation was completely inhibited for the UV/TiO2 process (k′ = 0.00007 cm2 mJ−1) due to the blockage of active sites on TiO2 surface by the background organic material.  相似文献   

8.
While the photocatalytic degradation of various volatile organic compounds in conjunction with UV light has been widely reported, visible-light-induced photocatalytic degradation of low-levels of the pollutants MTBE and TCE, which have been linked to potential adverse health effects, is rarely reported. The present study examined whether visible-light-activated S- or N-doped TiO2 photocatalytic technology can be used to control indoor concentrations of MTBE and TCE. This study consists of the characterization of the doped TiO2 powders, as well as an investigation of their photocatalytic activities. In regards to both powders, a shift of the absorbance spectrum towards the visible light region was observed. An activity test suggested that these photocatalysts exhibited reasonably high degradation efficiencies towards MTBE and TCE under visible light irradiation. The degradation efficiencies of MTBE and TCE by S- and N-doped photocatalysts exceeded 75 and 80%, respectively, at input concentrations (IC) of 0.1 ppm. Degradation efficiency was dependent on both IC and relative humidity. TCE could enhance the degradation efficiency of MTBE even under visible-light irradiation. The estimated mineralization efficiencies (MEs) were comparable to those of previous studies conducted with UV/TiO2 systems. Similar to the relative degradation efficiencies, the ME of TCE was higher in comparison to that of MTBE. The CO production measured during the photocatalytic processes represented a negligible addition to indoor CO levels. These results suggest that visible-light-activated S- and N-doped TiO2 photocatalysts may prove a useful tool in the effort to improve indoor air quality.  相似文献   

9.
This article examines the oxidative disposal of Prozac® (also known as Fluoxetine, FXT) through several oxidative processes with and without UV irradiation: for example, TiO2 alone, O3 alone, and the hybrid methods comprised of O3 + H2O2 (PEROXONE process), TiO2 + O3 and TiO2 + O3 + H2O2 at the laboratory scale. Results show a strong pH dependence of the adsorption of FXT on TiO2 and the crucial role of adsorption in the whole degradation process. Photolysis of FXT is remarkable only under alkaline pH. The heterogeneous photoassisted process removes 0.11 mM FXT (initial concentration) within ca. 60 min with a concomitant 50% mineralization at pH 11 (TiO2 loading, 0.050 g L−1). The presence of H2O2 enhances the mineralization further to >70%. UV/ozonation leads to the elimination of FXT to a greater extent than does UV/TiO2: i.e., 100% elimination of FXT is achieved by UV/O3 in the first 10 min of reaction and almost 97% mineralization is attained under UV irradiation in the presence of H2O2. The hybrid configuration UV + TiO2 + O3 + H2O2 enhances removal of dissolved organic carbon (DOC) in ca. 30 min leaving, however, an important inorganic carbon (IC) content. In all cases, the presence of H2O2 improves the elimination of DOC, but not without a detrimental effect on the biodegradability of FXT owing to the low organic carbon content in the final treated effluent, together with significant levels of inorganic byproducts remaining. The photoassisted TiO2/O3 hybrid method may prove to be an efficient combination to enhance wastewater treatment of recalcitrant drug pollutants in aquatic environments.  相似文献   

10.
The use of membrane processes for wastewater treatment and reuse is rapidly expanding. Organic, inorganic, and biological constituents are effectively removed by reverse osmosis (RO) membrane processes, but concentrate in membrane retentates Disposal of membrane concentrates is a growing concern. Applying advanced oxidation processes (AOPs) to RO retentate is logical because extensive treatment and energy inputs were expended to concentrate the organics, and it is cheaper to treat smaller flowstreams. AOPs (e.g., UV irradiation in the presence of titanium dioxide; UV/TiO2) can remove a high percentage of organic matter from RO retentates. The combination of AOPs and a simple biological system (e.g., sand filter) can remove higher levels of organic matter at lower UV dosages because AOPs produce biologically degradable material (e.g., organic acids) that have low hydroxyl radical rate constants, meaning that their oxidation, rather than that of the primary organic matter in the RO retentate, dictates the required UV energy inputs. At the highest applied UV dose (10 kWh m3), the dissolved organic carbon (DOC) in the RO retentate decreased from ∼40 to 8 mg L1, of which approximately 6 mg L1 were readily biologically degradable. Therefore, after combined UV treatment and biodegradation, the final DOC concentration was 2 mg L1, representing a 91% removal. These results suggest that UV/TiO2 plus biodegradation of RO retentates is feasible and would significantly reduce the organic pollutant loading into the environment from wastewater reuse facilities.  相似文献   

11.
Qiu R  Zhang D  Diao Z  Huang X  He C  Morel JL  Xiong Y 《Water research》2012,46(7):2299-2306
In this study, both Cr(VI) reduction and phenol oxidation induced by polymer-sensitized TiO2 were investigated under visible light. Study of the reaction mechanism indicated that poly(fluorene-co-thiophene) (PFT) acted as a semiconductor and was by itself able to reduce Cr(VI) under visible light irradiation. When coupled with TiO2, PFT served not only as the electron donor for Cr(VI) reduction, but also as a sensitizer. Upon irradiation by visible light, electrons in the sensitizing PFT polymer are excited and are transferred to the conduction band of TiO2. PFT-catalyzed reduction of Cr(VI) was significantly promoted by the presence of phenol, and synergism between Cr(VI) reduction and phenol degradation was demonstrated both by analysis of the FT-IR spectrum of PFT/TiO2 and by measuring the effect of repeated use of PFT/TiO2 on its photocatalytic efficiency. The results provide a cost-effective method to remove organic and inorganic pollutants simultaneously in the complex wastewater.  相似文献   

12.
Photoreactivation of microorganisms following UV disinfection can represent a disadvantage to using UV technology for wastewater treatment since recovery may, in some cases, reach several logs. Thus, decreasing photoreactivation can lead to considerable savings in capital and operating costs. Objectives of this study were to determine pre- and post-UV irradiation conditions which could decrease fecal coliform (FC) photoreactivation in wastewater effluents. Results indicated that delaying exposure to photoreactivating light for 3 h suppressed photoreactivation after relatively low UV doses of 10 and 20 mJ/cm2. Moreover, at least 440 lux (0.065 mW/cm2) of visible light was needed to initiate photoreactivation. Additionally, photoreactivation decreased significantly when samples were exposed to visible light simultaneously or prior to UV irradiation. This was more significantly observed for winter samples, where photoreactivation decreased by nearly 50%. Finally, summer FC populations were more sensitive to inactivation and less able to photoreactivate than winter populations. The effect of visible light on photoreactivation levels may be explained by several photo-mechanisms of FC photolyase, such as photodecomposition of the MTHF co-factor and reduction of FAD.  相似文献   

13.
A study was performed to determine the effect of pH, alkalinity, natural organic matter (NOM) and dissolved oxygen in the performance of nitrogen and fluorine doped TiO2 (NF-TiO2) for the degradation of hepatotoxin microcystin-LR (MC-LR) in synthetic and natural water under visible light irradiation. The initial degradation rate of MC-LR was fastest under acidic conditions (3.50 ± 0.02 × 10−3 μM min−1 at pH 3.0) and decreased to 2.29 ± 0.07 × 10−3 and 0.54 ± 0.02 × 10−3 μM min−1 at pH 5.7 and 7.1, respectively. Attractive forces between the opposite charged MC-LR and NF-TiO2 are likely responsible for the enhancement in the photocatalytic decomposition of MC-LR resulting from increased interfacial adsorption. For carbonate buffered solutions, the photocatalytic activity of NF-TiO2 was reduced when increasing the carbonate concentration up to 150 mg CaCO3 L−1. The scavenging of radical species by the bicarbonate ion at pH 7.1 is discussed. In the presence of NOM, the degradation rates decreased as pH and initial concentration of the NOM increased. The inhibition was higher with fulvic acid than humic acid under alkaline conditions. Oxygenated solution yields higher NF-TiO2 photocatalytic degradation of MC-LR compared to nitrogen sparged solution at pH 5.7. The involvement of specific reactive oxygen species implicated in the photodegradation is proposed. Finally, no significant degradation is observed with various natural waters spiked with MC-LR under visible light (λ > 420 nm) but high removal was achieved with simulated solar light. This study provides a better understanding of the interactions and photocatalytic processes initiated by NF-TiO2 under visible and solar light. The results indicate solar photocatalytic oxidation is a promising technology for the treatment of water contaminated with cyanotoxins.  相似文献   

14.
The appearance and the persistence of pharmaceutical products in the aquatic environment urgently call for the development of an innovative and practical water treatment technology. This study deals with the development of nanostructured nitrogen-doped TiO2 photoanodes and their subsequent use for chlortetracycline (CTC) photoelectrocatalytic oxidation under visible light. The N-doped TiO2 photoanodes with different nitrogen contents were prepared by means of a radiofrequency magnetron sputtering (RF-MS) process, with the objective to tune shift their optical absorption from the UV towards the visible. The N-doped TiO2 consist of nanostructured anatase phase with average TiO2 nanocrystallite size of 29 nm. The nitrogen doping is clearly shown to produce the desired red shift of the absorption onset of the TiO2 coatings (from ∼380 nm to ∼550 nm). Likewise, the N-doped TiO2 are found to be highly photo-electroactive not only under the UV light but most interestingly under the visible light as well. Using the optimal N-doped photoanodes, 99.6% of CTC (100 μg/L) was successfully degraded after 180 min of treatment time with a current intensity of 0.6 A. Under these conditions, a relatively high mineralization of CTC (92.5% ± 0.26% of TOC removal and 90.3% ± 1.1% of TN removal) was achieved.  相似文献   

15.
During membrane treatment of secondary effluent from wastewater treatment plants, a reverse osmosis concentrate (ROC) containing trace organic contaminants is generated. As the latter are of concern, effective and economic treatment methods are required. Here, we investigated electrochemical oxidation of ROC using Ti/Ru0.7Ir0.3O2 electrodes, focussing on the removal of dissolved organic carbon (DOC), specific ultra-violet absorbance at 254 nm (SUVA254), and 28 pharmaceuticals and pesticides frequently encountered in secondary treated effluents. The experiments were conducted in a continuously fed reactor at current densities (J) ranging from 1 to 250 A m−2 anode, and a batch reactor at J = 250 A m−2. Higher mineralization efficiency was observed during batch oxidation (e.g. 25.1 ± 2.7% DOC removal vs 0% removal in the continuous reactor after applying specific electrical charge, Q = 437.0 A h m−3 ROC), indicating that DOC removal is depending on indirect oxidation by electrogenerated oxidants that accumulate in the bulk liquid. An initial increase and subsequent slow decrease in SUVA254 during batch mode suggests the introduction of auxochrome substituents (e.g. -Cl, NH2Cl, -Br, and -OH) into the aromatic compounds. Contrarily, in the continuous reactor ring-cleaving oxidation products were generated, and SUVA254 removal correlated with applied charge. Furthermore, 20 of the target pharmaceuticals and pesticides completely disappeared in both the continuous and batch experiments when applying J ≥ 150 A m−2 (i.e. Q ≥ 461.5 A h m−3) and 437.0 A h m−3 (J = 250 A m−2), respectively. Compounds that were more persistent during continuous oxidation were characterized by the presence of electrophilic groups on the aromatic ring (e.g. triclopyr) or by the absence of stronger nucleophilic substituents (e.g. ibuprofen). These pollutants were oxidized when applying higher specific electrical charge in batch mode (i.e. 1.45 kA h m−3 ROC). However, baseline toxicity as determined by Vibrio fischeri bioluminescence inhibition tests (Microtox) was increasing with higher applied charge during batch and continuous oxidation, indicating the formation of toxic oxidation products, possibly chlorinated and brominated organic compounds.  相似文献   

16.
A comparative study on the photocatalytic activities of four different catalysts, P-25 TiO2, TiO2 nanofibers, tin-doped TiO2 nanofibers under UV light irradiation at 350 nm, and coumarin (C-343) coated TiO2 nanofibers at 436 nm light emitting diodes (LED) is reported. Catalysts performance has been compared based on their reflectance spectrum and activity. A common water contaminant 4-chlorophenol was used as a substrate to compare the activity of the different catalysts under both direct and dye sensitized conditions. Results indicated that amongst the four different catalysts the activity of P-25 was the highest. However the activity of C-343 coated TiO2 nanofibers in the LED (436 nm) based reactor was competitive. Identification of reaction intermediates implied that the reaction pathways under UV (band gap) and visible (dye sensitized) irradiation were different. Nonetheless, ring opening took place in all reactions with both maleic and dihydroxymaleic have been identified as intermediates. The study indicates that ordered arrays of TiO2 irradiated by panels of arrays of low cost high intensity LEDs might be used for the design of reactors. The near monochromaticity, long life, and operation under direct currents are advantages of using LEDs.  相似文献   

17.
Nontuberculous mycobacteria are resistant to conventional water treatment; indeed, they have been recovered from a wide variety of environmental sources. Here, we applied the photoelectrocatalytic technique using a Ti/TiO2–Ag photoanode to inactivate mycobacteria. For a mycobacteria population of 5 × 108 CFU mL−1, we achieved 99.9 and 99.8% inactivation of Mycobacterium kansasii and Mycobacterium avium with rate constant of 6.2 × 10−3 and 4.2 × 10−3 min−1, respectively, after 240 min. We compared the proposed method with the photolytic and photocatalytic methods. Using a mycobacteria population of 7.5 × 104 CFU mL−1, the proposed Ti/TiO2–Ag photoanode elicited total mycobacteria inactivation within 3 min of treatment; the presence of Ag nanoparticles in the electrode provided 1.5 larger degradation rate constant as compared with the Ti/TiO2 anode (1.75 × 10−2 for M. kansassi and 1.98 × 10−2 for M. avium). We monitored the degradation of the metabolites released during cellular lysis by TOC removal, sugar release, chromatography, and mass spectrometry measurements; photoelectrocatalysis and Ti/TiO2–Ag photoanodes furnished the best results.  相似文献   

18.
Yap PS  Lim TT 《Water research》2012,46(9):3054-3064
This study demonstrated a green technique to regenerate spent powdered activated carbon (AC) using solar photocatalysis. The AC was impregnated with a photocatalyst photoexcitable under visible-light irradiation to yield a solar regenerable composite, namely nitrogen-doped titanium dioxide (N-TiO2/AC). This composite exhibited bifunctional adsorptive-photocatalytic characteristics. Contaminants of emerging environmental concern, i.e. bisphenol-A (BPA), sulfamethazine (SMZ) and clofibric acid (CFA) which exhibited varying affinities for AC were chosen as target pollutants. The adsorption of BPA and SMZ by the N-TiO2/AC was significantly higher than that of CFA. The performance of solar photocatalytic regeneration (SPR) of the spent N-TiO2/AC composite generally increased with light intensity, N-TiO2 loading and temperature. The regeneration efficiency (RE) for CFA-loaded spent composite was the highest compared to the other pollutant-loaded spent composites, achieving 77% within 8 h of solar irradiation (765 W m−2). The rate-limiting process was pollutant desorption from the interior AC sorption sites. A kinetic model was developed to predict the transient concentration of the sorbate remaining in the spent composite during SPR. Comparison studies using solvent extraction technique indicated a different order of RE for the three pollutants, attributable to their varying solubilities in the aqueous and organic solvents.  相似文献   

19.
Wang P  Lim TT 《Water research》2012,46(6):1825-1837
The hybrid membrane photoreactor (MPR) combining a photoreactor irradiated with visible-light-emitting diode (vis-LED) and a cross-flow microfiltration (MF) membrane module was investigated in both closed-loop and continuous flow-through modes for the simultaneous degradation of penicillin G (PG) and separation of visible-light responsive TiO2 particles, namely C-sensitized-N-doped TiO2 (T300) and C-N-S tridoped TiO2 (T0.05-450). The turbidity of permeate water was <0.2 NTU for both T300 and T0.05-450 suspensions in the MPR system operated at different transmembrane pressures (TMPs) and cross-flow velocities (CFVs), indicating effective separation of TiO2 particles by the MF membrane. The operations at a higher TMP or lower CFV were more prone to induce TiO2 deposition on the membrane surface without backwashing, which resulted in the membrane fouling, the loss of TiO2 from the photoreactor and the decrease of PG photocatalytic degradation efficiency. 75% and 84% of PG were degraded in the closed-loop MPR without backwashing operated at 10 kPa and 0.15 m s−1 after 4 h of vis-LED irradiation using 1.0 g L−1 of T300 and T0.05-450, respectively. With backwashing of the membrane, the PG photocatalytic degradation efficiencies in the closed-loop MPR could be significantly enhanced to achieve 93% and 95% using 1.0 g L−1 of T300 and T0.05-450, respectively, which were almost comparable to those achieved in the batch photoreactor. Due to its shorter hydraulic residence time in the photoreactor, the PG degradation efficiency in the continuous flow-through MPR with backwashing was lower than that achieved in the closed-loop MPR.  相似文献   

20.
Liu K  Roddick FA  Fan L 《Water research》2012,46(10):3229-3239
While reverse osmosis (RO) technology is playing an increasingly important role in the reclamation of municipal wastewater, safe disposal of the resulting RO concentrate (ROC), which can have high levels of effluent organic pollutants, remains a challenge to the water industry. The potential of UVC/H2O2 treatment for degrading the organic pollutants and increasing their biodegradability has been demonstrated in several studies, and in this work the impact of the water quality variables pH, salinity and initial organic concentration on the UVC/H2O2 (3 mM) treatment of a municipal ROC was investigated. The reduction in chemical oxygen demand and dissolved organic carbon was markedly faster and greater under acidic conditions, and the treatment performance was apparently not affected by salinity as increasing the ROC salinity 4-fold had only minimal impact on organics reduction. The biodegradability of the ROC (as indicated by biodegradable dissolved organic carbon (BDOC) level) was at least doubled after 2 h UVC/H2O2 treatment under various reaction conditions. However, the production of biodegradable intermediates was limited after 30 min treatment, which was associated with the depletion of the conjugated compounds. Overall, more than 80% of the DOC was removed after 2 h UVC/3 mM H2O2 treatment followed by biological treatment (BDOC test) for the ROC at pH 4-8.5 and electrical conductivity up to 11.16 mS/cm. However, shorter UV irradiation time gave markedly higher energy efficiency (e.g., EE/O 50 kWh/m3 at 30 min (63% DOC removal) cf. 112 kWh/m3 at 2 h). No toxicity was detected for the treated ROC using Microtox® tests. Although the trihalomethane formation potential increased after the UVC/H2O2 treatment, it was reduced to below that of the raw ROC after the biological treatment.  相似文献   

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