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1.
Environ Sci Technol ; 53(24): 14430-14440, 2019 Dec 17.
Artigo em Inglês | MEDLINE | ID: mdl-31738527

RESUMO

The aging effects of sodium hydroxide (NaOH) on ion-exchange membranes were systematically studied, including the membrane properties, desalination performance, and fouling behaviors. After aging in NaOH solution, there were minor changes in the cation-exchange membrane (CEM) properties; however, functional groups (i.e., quaternary amines) on the anion-exchange membranes (AEMs) were converted into benzylic alcohol, alkene, and tertiary amines, respectively, by nucleophilic substitution, Hofmann elimination, and ylide formation. These degradations rendered decreased ion-exchange capacity (IEC), increased electrical resistance, lost hydrophilicity, and weakened mechanical strength. Moreover, severe deteriorations of desalination performance were observed due to the little ion-exchange ability of the degraded AEMs. The desalination rates were restored after cultivating the aged AEMs in acid solution, mainly because the tertiary amines transformed from the hydroxide form (OH-form) to the ionic chlorine form (Cl-form). The restored desalination rates indicated that the main degradation products were tertiary amines. In addition, the antifouling performance decreased in the order of aged OH-form > aged Cl-form > original AEMs due to the reduction of foulant-membrane intermolecular interactions after aging in NaOH solution. The results contribute to establishing a more comprehensive understanding of the effects of alkaline cleaning on IEMs and provide new insights into cleaning-process optimization and membrane modification.

2.
Water Environ Res ; 2019 Oct 25.
Artigo em Inglês | MEDLINE | ID: mdl-31650659

RESUMO

A p-type TiO2 with Ti vacancies (D-TiO2 ) was synthesized by a facile solvothermal treatment, and Ag/TiO2 with different Ag loading amount was prepared through a photo-reduction deposition method. The samples were characterized through scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The adsorption and photocatalytic characteristics of tetrabromobisphenol A (TBBPA) on D-TiO2 and Ag/TiO2 were investigated. The adsorption of TBBPA on Ag/TiO2 was significantly enhanced and was five times greater than that of pure TiO2 . The increase in pH significantly inhibited the adsorption of TBBPA. The 2%-Ag/TiO2 nearly completely degraded TBBPA in 10 min under UV-Vis light (λ > 360 nm), and the apparent reaction rate constant (kapp ) reached 0.63 min-1 . The significantly enhanced UV-Vis light catalytic properties of the Ag/TiO2 in comparison with that of TiO2 were attributed to the increased adsorption capacity and electron transfer ability of the Ag/TiO2 . Free radical trap experiments results showed that holes and superoxide radicals play a major role in the catalytic degradation of TBBPA by Ag/TiO2 . Moreover, the Ag/TiO2 catalyst exhibits high stability during TBBPA degradation even after three cycles. PRACTITIONER POINTS: Ti-defected TiO2 and Ag/TiO2 were synthesized using a solvothermal and photo-reduction deposition, respectively. Ag/TiO2 exhibited outstanding adsorption and photocatalytic activity for TBBPA removal under UV-Vis light. Holes and superoxide radicals play a major role in the photocatalytic degradation of TBBPA.

3.
ACS Appl Mater Interfaces ; 11(43): 40923-40931, 2019 Oct 30.
Artigo em Inglês | MEDLINE | ID: mdl-31588719

RESUMO

Perovskite quantum dots (PQDs) are among the most important luminescent semiconducting materials; however, they are unstable. Exposure to light, heat, and air can lead to irreversible degradation, which results in fluorescence quenching. Therefore, defects in PQDs significantly limit their practical application. Herein, we describe a simple method to enhance the photostability of CsPbBr3/nCdS QDs, which involves doping their shells with aluminum. The temperature-dependent photoluminescence (PL) of colloidal CsPbBr3/nCdS/Al2O3 QDs is investigated, and the thermal quenching of PL, blue shift of the optical band gap, and PL line width broadening are observed in each QD sample. Al2O3 layers on the CsPbBr3/nCdS QDs can effectively prevent photodegradation. Nonlinear, temperature-dependent exciton-phonon coupling and lattice dilation leads to radiative and nonradiative relaxation processes at temperatures ranging from 10 to 300 K; moreover, changes in the band gap and PL spectral line broadening are observed.

4.
Water Res ; 162: 427-436, 2019 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-31301472

RESUMO

Certain amino acids (AAs) can form odorous aldehydes, nitriles and N-chloroaldimines during chlorination. Ultraviolet (UV) photolysis, ultraviolet/persulfate (UV/PS) and ultraviolet/hydrogen peroxide (UV/H2O2) treatments have been reported to decrease trace organic contaminants in drinking water. In this study, 20 common AAs in East Taihu (ET) Lake (the main drinking water source for the surrounding cities) were determined during one year (four seasons). The impacts of UV photolysis alone and two UV-advanced oxidation process (AOP) pre-treatments on the formation of aldehydes, nitriles and N-chloroaldimines during post-chlorination of water containing three of the most detected AAs (i.e. valine (Val), leucine (Leu) and isoleucine (Ile)) in ET Lake were investigated. Results showed that the two UV-AOPs significantly decreased the odorous by-product formation from AAs compared with UV photolysis alone. The formation of N-chloroaldimines was more easily controlled than that of aldehyde and nitrile. Furthermore, UV/H2O2 was more effective than UV/PS at pH = 5 and 7. At pH = 9, the two UV-AOPs had similar effects and did not perform very well. In addition, the UV-AOPs controlled the formation of odorous by-products effectively at Cl/AA (molar ratio of chlorine to amino acid) ratios of 2.4 and 3.0 but increased their formation at Cl/AA ratios of 0.8 and 1.2. Experiments in real water showed that UV/H2O2 was more suitable for controlling the off-flavor problem caused by chlorination of AAs in ET Lake.


Assuntos
Poluentes Químicos da Água , Purificação da Água , Aminoácidos , Halogenação , Peróxido de Hidrogênio , Lagos , Oxirredução , Raios Ultravioleta
5.
Water Res ; 162: 180-189, 2019 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-31272043

RESUMO

2-Methylisoborneol (2-MIB) is one of the most common taste and odor (T&O) compounds in waterbodies and causes complaints from drinking water consumers. This is a case study of two water treatment plants taking the raw water from Lake Tai, the third largest lake in China. The relationships between the 2-MIB concentration and algae density, light change and nutrients of the raw water for the most recent four years were comprehensively investigated. The yearly variation pattern of the 2-MIB concentration in the raw water is closely related to the algae cell density. Both values reached peaks in July or August with concentrations as high as ∼500 ng/L and ∼1000 × 104 count/L, respectively. For the diurnal 2-MIB variation, the concentrations increase from 5 to 6 am, reach a peak value at ∼12 p.m., and then gradually decrease and achieve the lowest value at night. These results further confirm that 2-MIB is highly related to algae cell activity (e.g., photosynthesis). In addition, 2-MIB exists both inside and outside algae cells (i.e., intracellular and extracellular or bound and dissolved 2-MIB, respectively), and the percentage of the extracellular/dissolved portion was as high as 60% during the study period. Conventional water treatment processes (usually referrings to coagulation sedimentation and sand filtration, CSF) in WTPs have extremely unstable 2-MIB removal efficiencies (from -20% to >95%), which is mainly related to the existing forms of 2-MIB. The intracellular/bound portion can be effectively removed by CSF, especially sand filtration, while advanced water treatment processes are required to remove the dissolved 2-MIB. An ozone-activated carbon process is recommended, and the 2-MIB removal rate can reach 100%. This research has great theoretical and engineering value for treating water containing T&O compounds.


Assuntos
Poluentes Químicos da Água , Purificação da Água , China , Filtração , Lagos , Odorantes , Água
6.
J Colloid Interface Sci ; 544: 303-311, 2019 May 15.
Artigo em Inglês | MEDLINE | ID: mdl-30861435

RESUMO

In this study, the kinetic and isothermal behaviors of anion polyacrylamide (APAM) on a polytetrafluoroethylene (PTFE) microfiltration membrane were investigated to better understand the adsorption mechanism. A series of adsorption experiments were conducted to determine the effects of the initial APAM concentration, contact time, solution pH and temperature on the adsorption performance. The results showed that the three isotherm models (Langmuir equation, Freundlich equation and Temkin equation) favorably fit the adsorption process with R2 values of 0.98957, 0.90721 and 0.96321, respectively. The adsorption rate of APAM onto the PTFE membrane increased with increasing temperature, and the adsorption reaction reached equilibrium at 20 h. The values of thermodynamic adsorption parameters (ΔrGmθ, ΔrHmθ, and ΔrSmθ) suggested that the adsorption process was not spontaneous but endothermic. In addition, high temperatures favored adsorption, and the adsorption can be categorized as physisorption. Specifically, the main physisorption force was hydrogen bonding. The adsorption process consisted of two phases: rapid adsorption and stable adsorption. The three kinetic equations provided a good fit according to the R2 values and were applicable in the following order: pseudo-first-order > pseudo-second-order > Elovich.

7.
Water Res ; 150: 310-320, 2019 03 01.
Artigo em Inglês | MEDLINE | ID: mdl-30530125

RESUMO

The photocatalytic decomposition of bromate (BrO3-), a possible human carcinogen, has attracted much attention because of its high efficiency and easier combination with ultraviolet (UV) disinfection in water treatment plants. In this study, the Fe(II)Ti(IV) layered double hydroxides (LDHs) have been made through a facile hydrothermal method and used as an alternative photocatalyst for reduction of BrO3-. LDHs prepared at a Fe/Ti molar ratio of ∼0.5 and pH 7.0, denoted as FeTi-0.5 (pH 7.0), exhibited the highest BrO3- removal efficiency (removal rate constant = 0.067 ±â€¯0.002 min-1) compared to commercial TiO2 and the LDHs prepared at different pHs or different Fe/Ti ratios. The presence of alcohols in water enhanced the photocatalytic reduction of BrO3- due to the greater abundance of electrons caused by alcohols effectively reacting with holes. The neutral pH also favors the degradation of BrO3-. However, the presence of nitrate and nitrite can inhibit the degradation process, due to their reactions with hydrated electrons (eaq-) and hydrogen atom radicals (H∙). Cyclic degradation runs and magnetic separation techniques demonstrated the superior reusability of the FeTi-0.5 (pH 7.0) LDH for BrO3- removal. The removal rate of BrO3- under UV was higher than that without UV, indicating that the decomposition proceeded primarily via a photo-reductive mechanism induced by eaq- and H∙ and thus degradation pathways are proposed. Moreover, when tested in tap water, greater than 90% of BrO3- was removed after 60 min reaction in UV/FeTi-0.5 (pH 7.0) LDH systems in the presence of 5‰ (v/v) methanol. This demonstrates the high potential for such systems for removing BrO3- from disinfected drinking water. This work may shed lights on the design of effective photocatalysts for the enhanced degradation of BrO3- in water plants and the influence of constituents in raw water on the treatment.


Assuntos
Nanopartículas , Poluentes Químicos da Água , Bromatos , Hidróxidos , Raios Ultravioleta
9.
Water Res ; 149: 588-595, 2019 02 01.
Artigo em Inglês | MEDLINE | ID: mdl-30522051

RESUMO

Membrane fouling, especially inorganic fouling due to salt crystal formation and deposition on the membrane surface, is still a major technical issue in membrane distillation (MD) applications. In this study, microbubble aeration (MBA) was included in a laboratory-scale vacuum membrane distillation (VMD) rig and its effect on a desalination process was examined. Without MBA, serious membrane scaling occurred during desalination of simulated high-salinity sea water (100 g.L-1 salt concentration), which resulted in a dramatic reduction of permeate flux to essentially zero after 120 min. Scanning electron microscopy showed that a layer of large cuboid salt crystals uniformly covered the membrane surface. However, membrane scaling was mitigated with the introduction of MBA, resulting in the improved VMD desalination performance, which was positively correlated with pump pressure in the microbubble (MB) generator. Results showed that the effective processing time of the VMD desalination processing cycle was respectively prolonged to 150, 180, and more than 300 and 360 min (cf. 120 min without MBA) when the pump pressure was respectively at 0.1, 0.2, 0.3 and 0.4 MPa, leading to the increase of cumulative water production. Further studies found that larger numbers of MBs of smaller size were produced at higher pump pressure, which are more beneficial for increasing water vapor production and alleviating salt precipitation. The difference in zeta potential between the MBs in distilled water (about -30 mV) and that in SW100 solution (about -2 mV) demonstrated that MBA not only effectively mitigated the negative effect of concentration polarization by enhancing the surface shear rate at the membrane surface, but also reduced salt precipitation probably due to the MBs attracting counterions to the gas-water interface. Finally, energy consumption analysis of the modified VMD desalination process revealed that MBA, while itself only adding about 3% to the total energy consumption at varied pump pressures, was able to improve the specific energy consumption, especially at higher pump pressures. Together, these results demonstrate that MBA is an effective way of improving the performance of VMD desalination of water.


Assuntos
Destilação , Purificação da Água , Membranas Artificiais , Microbolhas , Vácuo , Água
10.
Water Res ; 147: 422-428, 2018 12 15.
Artigo em Inglês | MEDLINE | ID: mdl-30342337

RESUMO

The organic pollutants produced by cyanobacteria cells, such as off-flavor compounds (e.g. 2-methylisoborneol, 2-MIB) and hazardous toxins (e.g. microcystins), are commonly detected in water sources. Although studies have shown that oxidation using potassium permanganate (KMnO4), chlorine and ozone helps to remove cyanobacteria cells, the potential effects of these oxidants on cell viability and the release of off-flavor substances have scarcely been explored. This study investigated the impacts of three widely used oxidants on Pseudanabaena sp. (a common species of 2-MIB producing cyanobacteria) inactivation, and on the release and degradation of intracellular 2-MIB. Experiments using KMnO4 showed that both the cell viability and 2-MIB release fit to a two-stage second-order kinetic model with a threshold of KMnO4 exposure (ct). No significant variations in the cell viability and 2-MIB release occurred until the exposure reached ct because KMnO4 was primarily consumed by the dissolved and cell-bound organic matters before it damaged the cell. However, chlorine permeates the cell membrane more easily, causing rapid algae inactivation and the subsequent cell lysis and 2-MIB release. Unlike permanganate and chlorine, which are unable to degrade the released 2-MIB because of their insufficient oxidation potentials, ozone is capable to inactivate the cell and degrade 2-MIB as well. When the initial O3 concentration is above a certain level (1.0 mg ·L-1 in this study), the released 2-MIB can be substantially oxidized. Therefore, the choice of a suitable oxidant and a proper dose is highly important in the control of off-flavor compounds during the treatment of algae-containing raw water.


Assuntos
Ozônio , Purificação da Água , Cloro , Cinética , Compostos de Manganês , Oxirredução , Óxidos , Permanganato de Potássio
11.
Appl Opt ; 57(19): 5380-5384, 2018 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-30117830

RESUMO

A series of erbium-doped fluoro-bromozirconate glasses modified by various concentrations of Br- was prepared using the melt-quenching method. The mid-infrared fluorescence intensity (2.7 µm) was improved by increasing the content of Br-. The differential scanning calorimetry, x-ray diffraction, Fourier-transform infrared spectra, Raman spectra, and mid-infrared luminescence spectra were measured. The decreased phonon density shows that the structural changes due to inserting Br- can enhance the mid-infrared luminescent intensity. From the Judd-Ofelt analysis, it was found that the intensity of Ω2 was enhanced with the introduction of Br- and shows greater asymmetry and stronger covalency. Using the Fuchtbauer-Ladenburg theory and McCumber theory, the emission cross section (2.9×10-20 cm2) and absorption cross section (1.68×10-20 cm2) at 2.7 µm were determined. Hence, erbium-doped fluoro-bromozirconate glass is a potential material for application in the mid-infrared region.

12.
Sci Total Environ ; 642: 988-998, 2018 Nov 15.
Artigo em Inglês | MEDLINE | ID: mdl-29929150

RESUMO

Alkali/surfactant/polymer (ASP) flooding wastewater is highly caustic, and membrane fouling is the main obstacle during ASP ultrafiltration (UF) treatment. To maintain favorable filtration performance, polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF) membranes were implemented here, and their antifouling properties and mechanisms were investigated based on the threshold flux theory. Compared with the PVDF membranes, the PTFE membranes exhibited superior antifouling properties with lower reductions in flux and smaller hydraulic resistance, and they presented a nearly identical pseudo-stable fouling rate at a later time point. In the fouling layers of the PTFE and PVDF membranes, anion polyacrylamide (APAM) was observed along with divalent/trivalent metal ions. The thermodynamic and molecular mechanisms of membrane fouling by APAM were elucidated using the Extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory and atomic force microscopy (AFM), respectively. The calculated total interfacial free energy (mJ/m2) of adhesion between the APAM and PTFE membranes was positive, and the value between the APAM and PVDF membranes was negative. Furthermore, the values and interaction distances of the measured intermolecular rupture and approaching forces were larger for APAM-PTFE than for APAM-PVDF. For the PTFE membranes, the positive free energies and smaller intermolecular interaction resulted in weaker APAM-PTFE adhesion and adsorption and therefore the lower levels of flux decline and the later achievement of the pseudo-stable fouling rate. Additionally, the total flux recoveries observed after physical cleaning reached 0.78-0.80 and 0.32-0.39 for the PTFE and PVDF membranes, respectively, which showed that the PTFE membranes can be cleaned easily. The PTFE membranes have considerable potential for extensive application in UF treatments for ASP wastewater. These results should promote understanding the essence of the threshold flux and the fouling control of UF membranes.

13.
Water Sci Technol ; 77(1-2): 229-238, 2018 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-29339622

RESUMO

A fundamental understanding of fouling mechanisms is critical to improving filtration operations. The performance of four parallel membrane bioreactors (MBRs) with different sludge retention times (SRTs) was monitored during long-term constant flowrate filtration. The characteristics of the membrane and transmembrane pressure (TMP) profiles obtained were studied to demonstrate fouling mechanisms. Both classical blocking models and their combined models were evaluated. The intermediate model provided very good agreement with all the TMP data. However, the combined cake-intermediate and intermediate-standard models were more effective in the description of the experimental data. Contributions analysis indicated that the cake, intermediate and standard blocking models were the dominant fouling mechanisms. Scanning electron microscopy and energy dispersive X-ray (SEM-EDX) imaging showed that cake blocking by organic matter and standard blocking by inorganic matter made the main contributions to membrane fouling. The combined cake-intermediate and intermediate-standard models may be applicable to systems where these two models are consistent with the experimentally observed fouling mechanisms in an MBR.


Assuntos
Incrustação Biológica/prevenção & controle , Reatores Biológicos/microbiologia , Membranas Artificiais , Modelos Teóricos , Purificação da Água/métodos , Filtração/métodos , Hidrodinâmica , Microscopia Eletrônica de Varredura , Pressão , Esgotos/microbiologia
14.
Chemosphere ; 179: 290-297, 2017 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-28371712

RESUMO

Carbonyl compounds can occur alpha-hydrogens or beta-diketones substitution reactions with disinfectants contributed to halogenated by-products formation. The objective of this research was to study the occurrence and fate of carbonyl compounds as ozonation by-products at two full-scale drinking water treatment plants (DWTPs) using different disinfectants for one year. The quality of the raw water used in both plants was varied according to the season. The higher carbonyl compounds concentrations were found in raw water in spring. Up to 15 (as the sum of both DWTPs) of the 24 carbonyl compounds selected for this work were found after disinfection. The dominant carbonyl compounds were formaldehyde, glyoxal, methyl-glyoxal, fumaric, benzoic, protocatechuic and 3-hydroxybenzoic acid at both DWTPs. In the following steps in each treatment plant, the concentration patterns of these carbonyl compounds differed depending on the type of disinfectant applied. Benzaldehyde was the only aromatic aldehyde detected after oxidation with ozone in spring. As compared with DWTP 1, five new carbonyl compounds were formed (crotonaldehyde, benzaldehyde, formic, oxalic and malonic acid) disinfection by ozone, and the levels of the carbonyl compounds increased. In addition, pre-ozonation (PO) and main ozonation (OZ) increased the levels of carbonyl compounds, however coagulation/flocculation (CF), sand filtration (SF) and granular activated carbon filtration (GAC) decreased the levels of carbonyl compounds.


Assuntos
Desinfetantes/análise , Desinfecção , Água Potável/normas , Estações do Ano , Poluentes Químicos da Água/análise , Purificação da Água , Carvão Vegetal , Filtração/métodos , Floculação , Halogenação , Hidroxibenzoatos , Compostos Orgânicos/química , Ozônio
15.
J Hazard Mater ; 324(Pt B): 230-240, 2017 Feb 15.
Artigo em Inglês | MEDLINE | ID: mdl-28340995

RESUMO

Bromate (BrO3-) is a possible human carcinogen regulated at a strict standard of 10µg/L in drinking water. Various techniques to eliminate BrO3- usually fall into three main categories: reducing bromide (Br-) prior to formation of BrO3-, minimizing BrO3- formation during the ozonation process, and removing BrO3- from post-ozonation waters. However, the first two approaches exhibit low degradation efficiency and high treatment cost. The third workaround has obvious advantages, such as high reduction efficiency, more stable performance and easier combination with UV disinfection, and has therefore been widely implemented in water treatment. Recently, advanced reduction processes (ARPs), the photocatalysis of BrO3-, have attracted much attention due to improved performance. To increase the feasibility of photocatalytic systems, the focus of this work concerns new technological developments, followed by a summary of reducing agents, activation methods, operational parameters, and applications. The reaction mechanisms of two typical processes involving UV/sulfite homogeneous photocatalysis and UV/titanium dioxide heterogeneous photocatalysis are further summarized. The future research needs for ARPs to reach full-scale potential in drinking water treatment are suggested accordingly.


Assuntos
Bromatos/química , Poluentes Químicos da Água/química , Bromatos/efeitos da radiação , Catálise , Água Potável/química , Oxirredução , Fotólise , Substâncias Redutoras/química , Poluentes Químicos da Água/efeitos da radiação , Purificação da Água/métodos
16.
Environ Sci Pollut Res Int ; 24(7): 6472-6480, 2017 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-28074362

RESUMO

Ozonation of fulvic acid (FA) can result in diverse intermediate oxidation by-products, significantly affecting disinfection by-product (DBP) formation following chlorination. The objective of this study was to provide insight into ozone reaction intermediates and reveal the possible formation pathway of DBPs from ozonation of FA due to the formation of intermediate oxidation by-products. Aldehydes, aromatic acids, short-chain acids, chloroform, and dichloroacetic acid were detected at various ozone dosage additions. Aromatic acids were studied by using solid-phase extraction-ultra high-performance liquid chromatography (SPE-UPLC). This new analytical approach enables the extraction and analysis of highly polar carboxylic acids that are difficult to measure using conventional methods. The results showed that formaldehyde, acetaldehyde, glyoxal, methyl-glyoxal, fumaric, malonic protocatechuic, 3-hydroxybenzoic, and benzoic acid were predominant oxidation by-products. The yields of the four aldehydes increased steadily with ozone dosage. When ozone dosage was 2∼2.5 mg/l, the amount of carboxylic acids was largest, and the total amount of the carboxylic acids was about 5∼10 times higher than that of the aldehydes. Besides, hydroxybenzoic acids are the major precursor, although they have low content in ozone reaction solution, they have a great contribution to the DBP formation. This study provides a new perspective on ozonation natural organic matter, which contributes to understand the other sources of DBPs and thus broadens the knowledge of drinking water treatment.


Assuntos
Benzopiranos/química , Cloro/química , Desinfecção/métodos , Ozônio/química , Poluentes Químicos da Água/análise , Purificação da Água/métodos , Ácidos Carboxílicos/análise , Oxirredução
17.
Water Res ; 111: 288-296, 2017 03 15.
Artigo em Inglês | MEDLINE | ID: mdl-28104516

RESUMO

Bromate (BrO3-) is a possible human carcinogen regulated worldwide at a strict standard of 10 µg/L in drinking water. Removal of BrO3- by advanced reduction processes (ARPs) has attracted much attention due to its high reduction efficiency and easier combination with ultraviolet (UV) disinfection. In this study, we employed a UV/sulfite process to degrade BrO3- and studied the effects of UV lamp, sulfur(IV) concentration, and pH on effectiveness of the system in degrading BrO3-. Low-pressure UV lamps (UV-L) instead of medium-pressure UV lamps (UV-M) were selected because of the high ultraviolet-C (UV-C) efficiency of UV-L. The increased sulfur(IV) concentration is proportionally correlated with enhanced degradation kinetics. BrO3- reduction was improved by increasing pH when pH is within 6.0-9.0, and principal component analysis demonstrated that pH is the most influential factor over sulfur(IV) concentration and type of UV lamp. Degradation mechanisms at different pH levels were subsequently investigated. Results showed that the reduction reactions are induced by hydrated electron (eaq-) at pH > 9.0, by H at pH 4.0, and by both eaq- and H at pH 7.0. Effective quantum efficiency for the formation of eaq- and H in the photocatalytic systems was determined to be 0.109 ± 0.001 and 0.034 ± 0.001 mol E-1, respectively. Furthermore, mass balance calculation of bromine and sulfur at pH 7 showed that bromide, sulfate and possibly dithionate ions were the major products, and a degradation pathway was proposed accordingly. Moreover, UV/sulfite processes could reduce the initial bromate concentration of 0.1 mM by 82% and 95% in the presence and absence of O2 in tap water respectively, and 99% in the absence of O2 in deionized water within 20 min at pH 9.0 and 2.0 mM sulfur (IV).


Assuntos
Bromatos , Enxofre , Concentração de Íons de Hidrogênio , Sulfitos , Raios Ultravioleta , Poluentes Químicos da Água , Purificação da Água
18.
Front Microbiol ; 8: 2465, 2017.
Artigo em Inglês | MEDLINE | ID: mdl-29312177

RESUMO

Bacteria play an important role in water purification in drinking water treatment systems. On one hand, bacteria present in the untreated water may help in its purification through biodegradation of the contaminants. On the other hand, some bacteria may be human pathogens and pose a threat to consumers. The present study investigated bacterial communities using Illumina MiSeq sequencing of 16S rRNA genes and their functions were predicted using PICRUSt in a treatment system, including the biofilms on sand filters and biological activated carbon (BAC) filters, in 4 months. In addition, quantitative analyses of specific bacterial populations were performed by real-time quantitative polymerase chain reaction (qPCR). The bacterial community composition of post-ozonation effluent, BAC effluent and disinfected water varied with sampling time. However, the bacterial community structures at other treatment steps were relatively stable, despite great variations of source water quality, resulting in stable treatment performance. Illumina MiSeq sequencing illustrated that Proteobacteria was dominant bacterial phylum. Chlorine disinfection significantly influenced the microbial community structure, while other treatment processes were synergetic. Bacterial communities in water and biofilms were distinct, and distinctions of bacterial communities also existed between different biofilms. By contrast, the functional composition of biofilms on different filters were similar. Some functional genes related to pollutant degradation were found widely distributed throughout the treatment processes. The distributions of Mycobacterium spp. and Legionella spp. in water and biofilms were revealed by real-time quantitative polymerase chain reaction (qPCR). Most bacteria, including potential pathogens, could be effectively removed by chlorine disinfection. However, some bacteria presented great resistance to chlorine. qPCRs showed that Mycobacterium spp. could not be effectively removed by chlorine. These resistant bacteria and, especially potential pathogens should receive more attention. Redundancy analysis (RDA) showed that turbidity, ammonia nitrogen and total organic carbon (TOC) exerted significant effects on community profiles. Overall, this study provides insight into variations of microbial communities in the treatment processes and aids the optimization of drinking water treatment plant design and operation for public health.

19.
Sci Total Environ ; 569-570: 1608-1617, 2016 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-27325014

RESUMO

Tetrabromobisphenol A (TBBPA), a high use brominated flame retardant (BFR), raising concerns of widespread pollution and harm to human and ecological health. BFR manufacturing, TBBPA-based product manufacturing, e-waste recycling, and wastewater treatment plants have been identified as the main emission point sources. This paper discusses the occurrence, distribution, and fate of TBBPA from source to the environment. After release to the environment, TBBPA may undergo adsorption, photolysis, and biological degradation. Exposure of humans and biota is also discussed along with the role of treatment and regulations in reducing release of TBBPA to the environment and exposure risks. In general this review found stronger enforcement of existing legislation, and investment in treatment of e-waste plastics and wastewater from emission point sources could be effective methods in reducing release and exposure of TBBPA in the environment.


Assuntos
Monitoramento Ambiental , Poluentes Ambientais/análise , Poluição Ambiental/prevenção & controle , Retardadores de Chama/análise , Bifenil Polibromatos/análise , Risco
20.
Biodegradation ; 27(2-3): 95-106, 2016 06.
Artigo em Inglês | MEDLINE | ID: mdl-26931341

RESUMO

Given the increasing discoveries related to the eco-toxicity of titanium dioxide (TiO2) nanoparticles (NPs) in different ecosystems and with respect to public health, it is important to understand their potential effects in drinking water treatment (DWT). The effects of TiO2 NPs on ammonia reduction, ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) in biological activated carbon (BAC) filters for drinking water were investigated in static and dynamic states. In the static state, both the nitrification potential and AOB were significantly inhibited by 100 µg L(-1) TiO2 NPs after 12 h (p < 0.05), and the threshold decreased to 10 µg L(-1) with prolonged exposure (36 h, p < 0.05). However, AOA were not considerably affected in any of the tested conditions (p > 0.05). In the dynamic state, different amounts of TiO2 NP pulses were injected into three pilot-scale BAC filters. The decay of TiO2 NPs in the BAC filters was very slow. Both titanium quantification and scanning electron microscope analysis confirmed the retention of TiO2 NPs in the BAC filters after 134 days of operation. Furthermore, the TiO2 NP pulses considerably reduced the performance of ammonia reduction. This study identified the retention of TiO2 NPs in BAC filters and the negative effect on the ammonia reduction, suggesting a potential threat to DWT by TiO2 NPs.


Assuntos
Amônia/metabolismo , Água Potável/análise , Nanopartículas/análise , Titânio/análise , Purificação da Água/métodos , Archaea/metabolismo , Biodegradação Ambiental , Carvão Vegetal , Filtração
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