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1.
J Hazard Mater ; 424(Pt B): 127472, 2021 Oct 09.
Artigo em Inglês | MEDLINE | ID: mdl-34655881

RESUMO

As(III) removal from groundwaters is challenging because of its neutral charge and low surface affinity under circumneutral pH conditions. In this work, we investigate the influence of Ca2+ and Mg2+ on the removal of As(III) by a redox active polyvinylferrocene (PVF) functionalized electrode in a modified double potential step chronoamperometry (DPSC) setup. In the absence of divalent cations, nearly 90% As(III) removal is achieved over ten continuous cycles by single-pass DPSC, even in the presence of competing anions, however the presence of divalent cations at concentrations ≥ 1.25 mM significantly inhibits As(III) removal. The divalent cations enhance arsenic removal in the first (removal) step but suppress electrode regeneration in the 2nd step. Our results suggest that Ca2+/Mg2+ either acts as a bridge between the electrode surface and As anions or the sorption of Ca2+/Mg2+ increases the positive charge on the electrode surface thereby facilitating As(V) sorption. We show that effective electrode regeneration can be achieved using an NaOH wash however the overall complexity of the process increases. Overall, we conclude that the influence of divalent cations on As removal by electro-sorption processes needs to be taken into consideration for application of this technology for real groundwater treatment.

2.
J Am Chem Soc ; 143(37): 15400-15412, 2021 Sep 22.
Artigo em Inglês | MEDLINE | ID: mdl-34491045

RESUMO

Aqueous solutions of the iron(III) complex of N,N,N'-tris(2-pyridylmethyl)ethylenediamine-N'-acetate (tpena) react with hypochlorite (ClO-) to produce the reactive high-valent [FeIV(O)(tpena)]+. Under catalytic conditions, in bicarbonate-buffered media (pH 8) with a set ionic strength (10 mM NaCl), kinetic analysis shows that two equivalents of [FeIV(O)(tpena)]+ per one ClO- are produced, with benign chloride ions the only byproduct. An unprecedented supramolecular activation of ClO- by {(HCO3)⊂[(tpena)FeIII(µ-O)FeIII(Htpena)]}2+ is proposed. This mode of activation has great advantage for use in the catalytic oxidation of C-H bonds in water since: (i) the catalyst scaffold is protected from oxidative degradation and (ii) undesirable radical side reactions which produce toxic chlorinated compounds are circumvented by this novel coactivation of water and ClO-. The unique activation mechanism by the Fe-tpena system makes possible the destruction of organic contaminants as an add-on technology to water disinfection by chlorination, demonstrated here through (i) the catalytic oxidation of micropollutant metaldehyde, and (ii) mineralization of the model substrate formate. The resting-state speciation at pH 3, 5, 7, and 9, as well as the catalytically active iron speciation are characterized with Mössbauer and EPR spectroscopy and supported by DFT calculations. Our study provides fundamentally new insights into the design and activation mode of iron-based catalysts relevant to applications in water remediation.

3.
Water Res ; 204: 117646, 2021 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-34543974

RESUMO

Membrane capacitive deionization (MCDI) is an emerging electric field-driven technology for brackish water desalination involving the removal of charged ions from saline source waters. While the desalination performance of MCDI under different operational modes has been widely investigated, most studies have concentrated on different charging conditions without considering discharging conditions. In this study, we investigate the effects of different discharging conditions on the desalination performance of MCDI electrode. Our study demonstrates that low-current discharge (1.0 mA/cm2) can increase salt removal by 20% and decrease volumetric energy consumption by 40% by improving electrode regeneration and increasing energy recovery, respectively, while high-current discharge (3.0 mA/cm2) can improve productivity by 70% at the expense of electrode regeneration and energy recovery. Whether discharging electrodes at the low current or high current is optimal depends on a trade-off between productivity and energy consumption. We also reveal that stopped flow discharge (85%) can achieve higher water recovery than continuous flow discharge (35-59%). However, stopped flow discharge caused a 20-30% decrease in concentration reduction and a 25-50% increase in molar energy consumption, possibly due to the higher ion concentration in the macropores at the end of discharging step. These results reveal that an optimal discharging operation should be obtained from achieving a balance among productivity, water recovery and energy consumption by varying discharging current and flow rate.


Assuntos
Eletricidade , Purificação da Água , Adsorção , Eletrodos , Membranas , Águas Salinas , Cloreto de Sódio
4.
Environ Sci Technol ; 55(19): 13274-13285, 2021 10 05.
Artigo em Inglês | MEDLINE | ID: mdl-34525801

RESUMO

In this study, copper aluminum layered hydroxides (Cu-Al LDHs) and copper oxide (CuO) were utilized as catalysts for heterogeneous catalytic ozonation (HCO). Target compounds oxalate and formate were used with removal by adsorption and oxidation quantified to elucidate the role of the catalyst in contaminant removal. Oxidation of oxalate mostly occurred on the catalyst surface via interaction of surface oxalate complexes with surface-located oxidants. In contrast, the oxidation of formate occurred in the bulk solution as well as on the surface of the catalyst. Measurement of O3 decay kinetics coupled with fluorescence microscopy image analysis corresponding to 7-hydroxycoumarin formation indicates that while surface hydroxyl groups in Cu-Al LDHs facilitate slow decay of O3 resulting in the formation of hydroxyl radicals on the surface, CuO rapidly transforms O3 into surface-located hydroxyl radicals and/or other oxidants. Futile consumption of surface-located oxidants via interaction with the catalyst surface was minimal for Cu-Al-LDHs; however, it becomes significant in the presence of higher CuO dosages. A mechanistic kinetic model has been developed which adequately describes the experimental results obtained and can be used to optimize the process conditions for the application of HCO.

5.
Environ Sci Technol ; 55(19): 13317-13325, 2021 10 05.
Artigo em Inglês | MEDLINE | ID: mdl-34544235

RESUMO

Iron oxychloride (FeOCl) has been reported to be a highly efficient heterogeneous Fenton catalyst over a wide pH range. In order to determine the true catalytic performance of FeOCl, we simultaneously quantified the adsorptive and oxidative removal of formate, oxalate, and rhodamine-B (RhB) and the formation of RhB oxidation products at both pH 4.0 and 7.0. FeOCl was found to be a poor Fenton catalyst at either pH, as gauged by the oxidation of formate, oxalate, and rhodamine B and the decomposition of H2O2, in comparison with ferrihydrite (Fhy), one of the most common Fe-containing Fenton catalysts. The adsorption of target contaminants to FeOCl and homogeneous Fenton processes, induced by dissolved iron, resulted in overevaluation of the catalytic performance of FeOCl, especially for (i) the use of strongly adsorbing target compounds, without consideration of the role of adsorption in their removal and (ii) exceedingly high concentrations of H2O2 to remove trace quantities of target contaminants. Overall, this study highlights that the systematic quantification of H2O2 decomposition, target compound adsorption, and oxidation as well as the concentrations of oxidized products formed are prerequisites for unequivocal elucidation of the catalytic nature and reaction mechanism of solid Fenton catalysts.

6.
Water Res ; 203: 117498, 2021 Sep 15.
Artigo em Inglês | MEDLINE | ID: mdl-34371229

RESUMO

A novel design for a flow-electrode capacitive deionization (FCDI) system consisting of tubular electrodes in a shell and tube heat exchanger configuration is proposed. Each electrode consists of a metallic mesh current collector along the inner circumference of a tubular ion-exchange membrane. This tubular FCDI design is suitable for scale-up as it consists of easily manufactured components which can be assembled in an array. An apparatus with 4 tubular electrodes with a large effective area (202.3 cm2) was constructed and shown to provide a high net salt (NaCl) removal rate (0.15 mg s-1 at 1.2 V applied voltage and ∼2000 mg L-1 influent total dissolved solids concentration). A computational fluid dynamics (CFD) model incorporating ion migration and transport mechanisms was developed to simulate the ion concentration and electrical potential profiles in the water channel. The results of CFD modelling highlighted the need to maximize regions of both high potential gradient and high hydraulic flow in order to achieve optimal salt removal. In brief, this study presents a new design approach for FCDI scale-up and provides a computational tool for optimization of this design and future innovative FCDI designs.


Assuntos
Purificação da Água , Adsorção , Eletricidade , Eletrodos , Troca Iônica , Cloreto de Sódio
7.
Water Res ; 203: 117547, 2021 Sep 15.
Artigo em Inglês | MEDLINE | ID: mdl-34412015

RESUMO

In flow anode systems, surface-bound hydroxyl radicals (*OH) are generated at the solid-liquid interface of suspended particulate charge carriers at potentials well below that required for oxygen evolution as a result of water splitting. While these surface-bound radicals are powerful indiscriminant oxidants that often lead to complete mineralization of organic pollutants, the more selective process of direct electron transfer (DET) may also occur at the particle electrode interfaces and play a critical role in the degradation of some contaminants. In this study, we investigated DET processes in a flow anode system in which carbon black was utilized as the flow anode material and Pt, Ti, IrRu and IrTa meshes were used as the current collectors. The results indicate that the use of a carbon black flow anode enhanced the DET rate by 20 times at 1.0 V vs Ag/AgCl compared to the control experiment with no carbon black particles present. Low solution conductivity had a more obvious negative effect on the DET process (compared to *OH mediated oxidation) due to the high potential drop and inhibition of mass transfer processes at the solid-liquid interfaces of the anode particles. The DET rates were dependent on the particular anode current collector used (i.e., Ti, IrRu, IrTa or Pt mesh) with differences in rates ascribed to the electron transfer resistance of the current collectors in the flow anode system. Detailed investigation of the degradation of phenol in a flow anode system revealed that this widely studied contaminant could be degraded with an energy consumption of 3.08 kWh m-3, a value substantially lower than that required with other techniques. Results of this study provide a better understanding of the DET mechanism at the solid-solid and solid-liquid interfaces with these insights expected to benefit the design of flow anode materials and current collectors and lead to the improvement in performance of flow anode systems.


Assuntos
Fenol , Poluentes Químicos da Água , Eletrodos , Elétrons , Oxirredução , Fenóis , Poluentes Químicos da Água/análise
8.
Environ Sci Technol ; 55(15): 10695-10703, 2021 08 03.
Artigo em Inglês | MEDLINE | ID: mdl-34132087

RESUMO

The contamination of water resources by nitrate is a major problem. Herein, we report a mechanically flexible 2D-MXene (Ti3C2Tx) membrane with multilayered nanofluidic channels for a selective electrochemical reduction of nitrate to nitrogen gas (N2). At a low applied potential of -0.8 V (vs Ag/AgCl), the MXene electrochemical membrane was found to exhibit high selectivity for NO3- reduction to N2 (82.8%) due to a relatively low desorption energy barrier for the release of adsorbed N2 (*N2) compared to that for the adsorbed NH3 (*NH3) based on density functional theory (DFT) calculations. Long-term use of the MXene membrane for treating 10 mg-NO3-N L-1 in water was found to have a high faradic efficiency of 72.6% for NO3- reduction to N2 at a very low electrical cost of 0.28 kWh m-3. Results of theoretical calculations and experimental results showed that defects on the MXene nanosheet surfaces played an important role in achieving high activity, primarily at the low-coordinated Ti sites. Water flowing through the MXene nanosheets facilitated the mass transfer of nitrate onto the low-coordinated Ti sites with this enhancement of particular importance under cathodic polarization of the MXene membrane. This study provides insight into the tailoring of nanoengineered materials for practical application in water treatment and environmental remediation.


Assuntos
Nitratos , Purificação da Água , Eletrodos , Óxidos de Nitrogênio , Titânio
9.
Environ Sci Technol ; 55(13): 8793-8805, 2021 07 06.
Artigo em Inglês | MEDLINE | ID: mdl-34110792

RESUMO

Results of investigations into factors influencing contaminant mobility in a replica trench located adjacent to a legacy radioactive waste site are presented in this study. The trench was filled with nonhazardous iron- and organic matter (OM)-rich components, as well as three contaminant analogues strontium, cesium, and neodymium to examine contaminant behavior. Imposed redox/water-level oscillations, where oxygen-laden rainwater was added to the anoxic trench, resulted in marked biogeochemical changes including the removal of aqueous Fe(II) and circulation of dissolved carbon, along with shifts to microbial communities involved in cycling iron (Gallionella, Sideroxydans) and methane generation (Methylomonas, Methylococcaceae). Contaminant mobility depended upon element speciation and rainfall event intensity. Strontium remained mobile, being readily translocated under hydrological perturbations. Strong ion-exchange reactions and structural incorporation into double-layer clay minerals were likely responsible for greater retention of Cs, which, along with Sr, was unaffected by redox oscillations. Neodymium was initially immobilized within the anoxic trenches, due to either secondary mineral (phosphate) precipitation or via the chemisorption of organic- and carbonate-Nd complexes onto variably charged solid phases. Oxic rainwater intrusions altered Nd mobility via competing effects. Oxidation of Fe(II) led to partial retention of Nd within highly sorbing Fe(III)/OM phases, whereas pH decreases associated with rainwater influxes resulted in a release of adsorbed Nd to solution with both pH and OM presumed to be the key factors controlling Nd attenuation. Collectively, the behavior of simulated contaminants within this replica trench provided unique insights into trench water biogeochemistry and contaminant cycling in a redox oscillatory environment.


Assuntos
Resíduos Radioativos , Compostos Férricos , Ferro , Minerais , Oxirredução , Resíduos Radioativos/análise
10.
Chem Rev ; 121(13): 8161-8233, 2021 Jul 14.
Artigo em Inglês | MEDLINE | ID: mdl-34143612

RESUMO

Iron (Fe) is the fourth most abundant element in the earth's crust and plays important roles in both biological and chemical processes. The redox reactivity of various Fe(II) forms has gained increasing attention over recent decades in the areas of (bio) geochemistry, environmental chemistry and engineering, and material sciences. The goal of this paper is to review these recent advances and the current state of knowledge of Fe(II) redox chemistry in the environment. Specifically, this comprehensive review focuses on the redox reactivity of four types of Fe(II) species including aqueous Fe(II), Fe(II) complexed with ligands, minerals bearing structural Fe(II), and sorbed Fe(II) on mineral oxide surfaces. The formation pathways, factors governing the reactivity, insights into potential mechanisms, reactivity comparison, and characterization techniques are discussed with reference to the most recent breakthroughs in this field where possible. We also cover the roles of these Fe(II) species in environmental applications of zerovalent iron, microbial processes, biogeochemical cycling of carbon and nutrients, and their abiotic oxidation related processes in natural and engineered systems.

11.
Environ Sci Technol ; 2021 May 27.
Artigo em Inglês | MEDLINE | ID: mdl-34042428

RESUMO

The heterogeneous Fenton process has been widely applied though some aspects of this process are still poorly understood. In this study, we simultaneously quantify the adsorption and decomposition of formate and H2O2 at pH 4.0 in the presence of freshly formed ferrihydrite and provide new insights into the ferrihydrite-induced heterogeneous Fenton mechanism with the aid of kinetic and reactive-transport modeling. Our results show that the decomposition of H2O2 and formate is controlled by surface-initiated reactions. Adsorbed formate occupies the surface sites otherwise available for reaction with H2O2 and therefore hampers the surface Fenton reactions despite the negligible accumulation of H2O2 on the surface. The minimal impact of methanol (an effective HO• scavenger) on formate oxidation as well as the poor oxidation of fully adsorbed oxalate compared with the ready oxidation of partially adsorbed formate demonstrates that oxidation mainly occurs in the solid-liquid boundary layer, rather than in bulk or on the surface. This is suggested to be due to the diffusion of surface-generated HO•, rather than surface Fe(II), to the boundary layer with the results of kinetic and reactive-transport modeling supporting this conclusion. The new findings are critical to our understanding of the removal behavior of more complex organic target species and to the design of more effective heterogeneous Fenton technologies.

12.
Water Res ; 200: 117259, 2021 Jul 15.
Artigo em Inglês | MEDLINE | ID: mdl-34058481

RESUMO

Electrochemical advanced oxidation processes (EAOPs) have emerged as a promising water treatment alternative but major breakthroughs are still needed in order for EAOPs to be competitive with traditional treatment technologies in terms of energy cost. Most existing studies have been conducted at high potentials to generate the powerful hydroxyl radical oxidant (aqueous •OH). While adsorbed hydroxyl radicals (OH*) may form at a much lower energy cost, their possible utilization is limited due to the poor mass transfer of this highly reactive species on solid electrodes. In this report, we describe a novel flow anode system using 4-16 µm Magnéli phase titanium suboxide particles as the anode material which enables the generation of a high steady state •OH concentration (5.4 × 10-12 mol m-2) at only 1.5 V (vs SHE) in a dilute electrolyte (5 mM KH2PO4). The energy cost of removal per order of selected water contaminants (tetracycline and orange II in this study) using the flow anode is 1.5--6.7 Wh m-3, which is 1 - 4 orders of magnitude lower than that of existing techniques. The anode material used demonstrates great stability with the configuration readily scaled up. The results of this study provide new insight into a high efficiency, low cost water treatment technology for organic contaminant degradation.


Assuntos
Poluentes Químicos da Água , Purificação da Água , Eletrodos , Radical Hidroxila , Oxirredução , Água
13.
Environ Sci Technol ; 55(8): 4243-4267, 2021 04 20.
Artigo em Inglês | MEDLINE | ID: mdl-33724803

RESUMO

With the increasing severity of global water scarcity, a myriad of scientific activities is directed toward advancing brackish water desalination and wastewater remediation technologies. Flow-electrode capacitive deionization (FCDI), a newly developed electrochemically driven ion removal approach combining ion-exchange membranes and flowable particle electrodes, has been actively explored over the past seven years, driven by the possibility of energy-efficient, sustainable, and fully continuous production of high-quality fresh water, as well as flexible management of the particle electrodes and concentrate stream. Here, we provide a comprehensive overview of current advances of this interesting technology with particular attention given to FCDI principles, designs (including cell architecture and electrode and separator options), operational modes (including approaches to management of the flowable electrodes), characterizations and modeling, and environmental applications (including water desalination, resource recovery, and contaminant abatement). Furthermore, we introduce the definitions and performance metrics that should be used so that fair assessments and comparisons can be made between different systems and separation conditions. We then highlight the most pressing challenges (i.e., operation and capital cost, scale-up, and commercialization) in the full-scale application of this technology. We conclude this state-of-the-art review by considering the overall outlook of the technology and discussing areas requiring particular attention in the future.


Assuntos
Purificação da Água , Adsorção , Eletrodos , Troca Iônica , Cloreto de Sódio
14.
Water Res ; 194: 116939, 2021 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-33640752

RESUMO

It is critical to both effectively remove and recover phosphate (P) from wastewater given the wide-ranging environmental (i.e., preventing eutrophication and restoring water quality) and economic (i.e., overcoming P resource scarcity) benefits. More recently, considerable academic effort has been devoted towards harvesting P as vivianite, which can be used as a potential slow-release fertilizer and possible reagent for the manufacture of lithium iron phosphate (LiFePO4), the precursor in fabricating Li-ion secondary batteries. In this study, we propose an innovative P recovery process, in which P is first preconcentrated via a flow-electrode capacitive deionization (FCDI) device followed by immobilization as vivianite crystals in a fluidized bed crystallization (FBC) column. The effects of different operational parameters on FCDI P preconcentration performance and energy consumption are investigated. Results show that 63% of P can be removed and concentrated in the flow-electrode chamber with a reasonable energy requirement under optimal operating conditions. The FBC system resulted in immobilization of ~80% of P as triangular or quadrangular pellets, which were verified to be high-purity vivianite crystals by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) and extended X-ray absorption fine structure (EXAFS) spectroscopy. This study provides a pathway for efficient recovery of P as a value-added product (i.e., vivianite) from P-rich wastewaters.


Assuntos
Purificação da Água , Cristalização , Eletrodos , Compostos Ferrosos , Fosfatos
15.
Environ Sci Technol ; 55(1): 655-664, 2021 01 05.
Artigo em Inglês | MEDLINE | ID: mdl-33103901

RESUMO

Heavy metals in industrial wastewaters are typically present as stable metal-organic complexes with their cost-effective treatment remaining a significant challenge. Herein, a self-enhanced decomplexation scenario is developed using an electrochemical membrane filtration (EMF) system for efficient decomplexation and Cu recovery. Using Cu-EDTA as a model pollutant, the EMF system achieved 81.5% decomplexation of the Cu-EDTA complex and 72.4% recovery of Cu at a cell voltage of 3 V. The •OH produced at the anode first attacked Cu-EDTA to produce intermediate Cu-organic complexes that reacted catalytically with the H2O2 generated from the reduction of dissolved oxygen at the cathode to initiate chainlike self-enhanced decomplexation in the EMF system. The decomplexed Cu products were further reduced or precipitated at the cathodic membrane surface thereby achieving efficient Cu recovery. By scavenging H2O2 (excluding self-enhanced decomplexation), the rate of decomplexation decreased from 8.8 × 10-1 to 4.1 × 10-1 h-1, confirming the important role of self-enhanced decomplexation in this system. The energy efficiency of this system is 93.5 g kWh-1 for Cu-EDTA decomplexation and 15.0 g kWh-1 for Cu recovery, which is much higher than that reported in the previous literature (i.e., 7.5 g kWh-1 for decomplexation and 1.2 g kWh-1 for recovery). Our results highlight the potential of using EMF for the cost-effective treatment of industrial wastewaters containing heavy metals.


Assuntos
Peróxido de Hidrogênio , Águas Residuárias , Cobre , Ácido Edético , Oxirredução
16.
Water Res ; 189: 116653, 2021 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-33232816

RESUMO

The recovery of phosphorus (P) from wastewaters is a worthy goal considering the potential environmental and economic benefits. Flow-electrode capacitive deionization (FCDI), which employs flowable carbon electrodes instead of the static electrodes used in conventional CDI, has been demonstrated to be a promising P recovery technology. FCDI outperforms CDI and other competitive technologies in a number of aspects including (i) large salt adsorption capacity and (ii) extremely high water recovery rate. In this study, magnetic (Fe3O4 impregnated) activated carbon particles were prepared and applied as FCDI electrodes. The magnetic carbon electrodes were found to have a strong affinity towards P, facilitating the selective adsorption of P to the magnetic particles through a ligand exhange mechanism. Continuous operation of the FCDI system could be achieved with only three minutes required to separate the electrode particles from the brine stream on application of an external magnetic field. A P-rich stream was produced on regeneration of the exhausted magnetic electrodes using alkali solution. We envision that the use of magnetic carbon enhanced flow-electrodes will pave the way for efficient operation of FCDI as well as the preferential recovery of P.


Assuntos
Fosfatos , Purificação da Água , Adsorção , Eletrodos , Compostos Férricos , Fenômenos Magnéticos
17.
ACS Chem Neurosci ; 11(21): 3646-3657, 2020 11 04.
Artigo em Inglês | MEDLINE | ID: mdl-33143428

RESUMO

The occurrence and progression of Parkinson's disease (PD) has been associated with the observation of elevated iron concentrations in the substantia nigra pars compacta (SNpc). While the reasons for the impact of elevated iron concentrations remain unclear, one hypothesis is that the presence of labile iron induces the oxidation of dopamine (DA) to toxic quinones such as aminochrome (DAC) and reactive oxygen species (ROS). As such, one of the proposed therapeutic strategies has been the use of iron chelators such as deferiprone (DFP) (which is recognized to have limitations related to its rapid degradation in the liver) to reduce the concentration of labile iron. In this study, a detailed investigation regarding the novel iron chelator, CN128, was conducted and a kinetic model developed to elucidate the fundamental behavior of this chelator. The results in this work reveal that CN128 is effective in alleviating the toxicity induced by iron and DA to neurons when DA is present at moderate concentrations. When all the iron is chelated by CN128, the formation of DAC and the oxidation of DA can be reduced to levels identical to that in the absence of iron. The production of H2O2 is lower than that generated via the autoxidation of the same amount of DA. However, when severe leakage of DA occurs, the application of CN128 is insufficient to alleviate the associated toxicity. This is attibuted to the less important role of iron in the production of toxic intermediates at high concentrations of DA. CN128 is superior to DFP with regard to the reduction in formation of DAC and elevation in DA concentration. In summary, the results of this study suggest that prodromal application of the chelator CN128 could be effective in preventing the onset and slowing the early stage development of PD symptoms associated with oxidants and toxic intermediates resulting from the iron-mediated oxidation of the neurotransmitter dopamine with CN128 likely to be superior to DFP in view of its greater in vivo availability and less problematic side effects.


Assuntos
Dopamina , Doença de Parkinson , Humanos , Peróxido de Hidrogênio , Quelantes de Ferro/farmacologia , Oxirredução , Doença de Parkinson/tratamento farmacológico
19.
Environ Sci Technol ; 54(19): 12081-12091, 2020 10 06.
Artigo em Inglês | MEDLINE | ID: mdl-32924448

RESUMO

In this work, we investigate selective sorption of arsenic from simulated groundwaters at pH 8 by a redox-active polyvinylferrocene (PVF)-functionalized electrode using a modified double potential step chronoamperometry (DPSC) method. Our results show that effective and sustainable As(III) removal can be achieved at 0 V once the electrode is activated via anodic polarization. During activation, ferrocene (Fc) in PVF is oxidized to the ferrocenium ion (Fc+) with the latter facilitating As(III) sorption and subsequent oxidation as well as As(V) sorption. The high affinity of Fc+ to As and weak attraction to competing anions at 0 V ensure high selectivity of As over Cl-, SO42-, and NO3- at concentrations typical of groundwaters. Following the removal process, efficient regeneration of the electrode is achieved at -1.2 V wherein Fc+ is reduced to Fc thereby facilitating As desorption from the electrode surface. Our results further show that O2 and associated generation of hydrogen peroxide during the regeneration step drive the oxidation of Fc to Fc+, thereby maintaining the constant generation of Fc+ required to achieve As(III) removal in subsequent cycles. Our results show that 91.8 ± 0.6% of As(III) could be selectively removed from simulated groundwater over 10 cycles at an ultralow energy consumption of 0.12 kWh m-3.


Assuntos
Arsênio , Água Subterrânea , Poluentes Químicos da Água , Purificação da Água , Arsênio/análise , Eletrodos , Compostos Ferrosos , Oxirredução , Oxigênio , Polivinil , Poluentes Químicos da Água/análise
20.
Environ Sci Technol ; 54(19): 12539-12549, 2020 10 06.
Artigo em Inglês | MEDLINE | ID: mdl-32897064

RESUMO

The formation of vivianite (Fe3(PO4)2·8H2O) in iron (Fe)-dosed wastewater treatment facilities has the potential to develop into an economically feasible method of phosphorus (P) recovery. In this work, a long-term steady FeIII-dosed University of Cape Town process-membrane bioreactor (UCT-MBR) system was investigated to evaluate the role of Fe transformations in immobilizing P via vivianite crystallization. The highest fraction of FeII, to total Fe (Fetot), was observed in the anaerobic chamber, revealing that a redox condition suitable for FeIII reduction was established by improving operational and configurational conditions. The supersaturation index for vivianite in the anaerobic chamber varied but averaged ∼4, which is within the metastable zone and appropriate for its crystallization. Vivianite accounted for over 50% of the Fetot in the anaerobic chamber, and its oxidation as it passed through the aerobic chambers was slow, even in the presence of high dissolved oxygen concentrations at circumneutral pH. This study has shown that the high stability and growth of vivianite crystals in oxygenated activated sludge can allow for the subsequent separation of vivianite as a P recovery product.


Assuntos
Ferro , Fósforo , Compostos Ferrosos , Fosfatos , Esgotos , Eliminação de Resíduos Líquidos
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