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1.
J Hazard Mater ; 392: 122349, 2020 Feb 18.
Artigo em Inglês | MEDLINE | ID: mdl-32109798

RESUMO

In this work, the influence of oxygen-containing surface groups of activated carbon electrodes on the charge efficiency of electro-assisted adsorption of As(V) was investigated. It was distinguished between activated carbons modified through acidic (oxidation) and thermal (reduction) treatments, starting with a granular pristine commercial activated carbon of bituminous origin. The textural characterization of the three materials showed that the treatments did not produce significant changes in the surface area and in the distribution of pores. The three carbon samples were used to fabricate packed electrodes with stainless-steel mesh as electric current collector. This work report that the application of anodic potentials (1.01 and 1.41 V vs. NHE) increased the adsorption capacity and rate of arsenate uptake in solutions containing only this contaminant (2.5 mg L-1) at pH 7. The oxidized carbon electrode presented the lowest capacitance and adsorption capacity during electroadsorption (0.33 mg g-1), compared to pristine material (1.77 mg g-1). On the other hand, the reduced electrode displayed the highest adsorption capacity of arsenate (3.14 mg g-1) when applying a potential of 1.01 V. The results were correlated with the potential of zero charge values. In addition, for this material, the rate of kinetics increased 26.7 % compared to experiments without applied potential.

2.
Chemosphere ; 239: 124823, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31726520

RESUMO

Several studies have demonstrated that gypsum (CaSO4·2H2O) and calcite (CaCO3) can be important hosts of arsenic in contaminated hydrogeological systems. However, the extent to which microbial reducing processes contribute to the dissolution and transformation of carbonate and sulfate minerals and, thereby, to arsenic mobilization is poorly understood. These processes are likely to have a strong impact on arsenic mobility in iron-poor environments and in reducing aquifers where iron oxyhydroxides become unstable. Anoxic batch bioassays with arsenate (As(V)) coprecipitated with calcite, gypsum, or ferrihydrite (Fe(OH)3) were conducted in the presence of sulfate or molybdate to examine the impact of bioprocesses (i.e. As(V), sulfate, and Fe(III)-reduction) on arsenic dissolution, speciation, and eventual remineralization. Microbial reduction of As(V)-bearing calcite caused an important dissolution of arsenite, As(III), which remained in solution up to the end of the experiment (30 days). The reduction of As(V) from gypsum-As(V) also led to the release of As(III), which was subsequently remineralized, possibly as arsenic sulfides. The presence of sulfate triggered arsenic dissolution in the bioassays with ferrihydrite-As(V). This study showed that although gypsum and calcite have a lower capacity to bind arsenic, compared to iron oxides, they can play a critical role in the biogeochemical cycle of arsenic in natural calcareous and gypsiferous systems depleted of iron since they can be a source of electron acceptors for reducing bioprocesses.


Assuntos
Arsênico/química , Bactérias/metabolismo , Carbonato de Cálcio/química , Sulfato de Cálcio/química , Compostos Férricos/química , Arseniatos/química , Arsenicais/química , Arsenitos/química , Carbonatos/química , Água Subterrânea/química , Ferro/química , Molibdênio/química , Oxirredução , Solubilidade , Sulfatos/química , Sulfetos/química
4.
Artigo em Inglês | MEDLINE | ID: mdl-31758363

RESUMO

It is well known that activated sludge treatment systems generate a lot of surplus sludge having environmental and economic impacts. Although several approaches have been proposed for the treatment/reuse of the excess of sludge, there are few studies focused on decreasing the biomass yield without affecting the metabolic activity. This work reports the effect of low magnitude electrical fields (0.07 to 0.2 V/cm) on the growth yield of a pure strain of Pseudomonas denitrificans (used as model microorganism). Cell potentials between 0.2 and 0.57 V were measured during 24 h to the aerobic culture; biomass production and substrate consumption were evaluated at regular intervals. Results indicated that the substrate (lactate) consumption efficiency increased with the applied potential, up to 100%, while the yield diminished 31% (0.34 g biomass/g lactate consumed) at 0.7 V vs. NHE. Bioenergetics showed that the fraction of electron equivalents toward biomass synthesis decreased from 0.68 (when no potential was applied) to 0.47 at 0.57 V, pointing out the redirection of the energy flow toward maintenance to cope with the stress caused by the imposed voltage. Therefore, the electrical stimulus could be used as control of biomass growth in aerobic wastewater treatment lines.

5.
Water Sci Technol ; 77(9-10): 2311-2319, 2018 May.
Artigo em Inglês | MEDLINE | ID: mdl-29757183

RESUMO

In this work, polyvinylidene fluoride (PVDF)/polyaniline (PANI) heterogeneous anion-exchange membranes filled with pore-forming agents polyvinylpyrrolidone (PVP) and lithium chloride were prepared by the solution-casting technique using the solvent 1-methyl-2-pyrrolidone (NMP) and a two-step phase inversion procedure. Key properties of the as-prepared membranes, such as hydrophilicity, water content, ion exchange capacity, fixed ion concentration, conductivity and transport number were examined and compared between membranes in different conditions. The pore-forming hydrophilic additives PVP and lithium chloride to the casting solution appeared to improve the ion-exchange membranes (IEMs) by increasing the conductivity, transport number and hydrophilicity. The effects of increasing membrane drying time on the porosity of the as-prepared membranes were found to lower membrane porosity by reducing membrane water content. However, pore-forming agents were found to be able to stabilise membrane transport number with different drying times. As-prepared PVDF/PANI anion-exchange membrane with pore-forming agent is demonstrated to be a more efficient candidate for water purification (e.g. desalination) and other industrial applications.


Assuntos
Compostos de Anilina/química , Cloreto de Lítio/química , Membranas Artificiais , Polivinil/química , Povidona/química , Purificação da Água/métodos , Interações Hidrofóbicas e Hidrofílicas , Troca Iônica , Porosidade , Eliminação de Resíduos Líquidos/métodos , Água , Poluentes Químicos da Água
6.
J Hazard Mater ; 339: 114-121, 2017 Oct 05.
Artigo em Inglês | MEDLINE | ID: mdl-28633082

RESUMO

High arsenic concentrations have been detected in alluvial aquifers of arid and semi-arid zones in Mexico. This work describes the potential of microbial arsenate reduction of the indigenous community present in sediments from an arsenic contaminated aquifer. Microcosms assays were conducted to evaluate arsenate and sulfate-reducing activities of the native microbiota. Two different sediments were used as inoculum in the assays amended with lactate (10mM) as electron donor and with sulfate and arsenate (10mM each) as electron acceptors. Sediments were distinguished by their concentration of total arsenic 238.3±4.1mg/kg or 2263.1±167.7mg/kg, which may be considered as highly contaminated sediments with arsenic. Microbial communities present in both sediments were able to carry out arsenate reduction, accomplished within 4days, with the corresponding formation of arsenite; sulfate reduction took place as well. Both reducing activities occurred without previous acclimation period or enrichment, even at potential inhibitory concentrations of arsenate as high as 750mg/L (10mM). The formation of a yellowish colloidal precipitate was evident when both reducing processes occurred in the microcosm, which contributed to remove between 52 and 90.9% of As(III) from the liquid phase by bioprecipitation of arsenic as arsenic sulfide.


Assuntos
Arsênico/metabolismo , Sedimentos Geológicos/microbiologia , Microbiota , Poluentes Químicos da Água/metabolismo , Acetatos/metabolismo , Biodegradação Ambiental , Lactatos/metabolismo , Oxirredução , Sulfatos/metabolismo , Sulfetos/metabolismo
7.
Bioresour Technol ; 207: 39-45, 2016 May.
Artigo em Inglês | MEDLINE | ID: mdl-26868154

RESUMO

Metal-humic acid complexes were synthesized and immobilized by a granulation process in anaerobic sludge for their application as solid-phase redox mediators (RM) in the biotransformation of iopromide. Characterization of Ca- and Fe-humic acid complexes revealed electron accepting capacities of 0.472 and 0.556milli-equivalentsg(-1), respectively. Once immobilized, metal-humic acid complexes significantly increased the biotransformation of iopromide in upflow anaerobic sludge blanket (UASB) reactors. Control UASB reactor (without humic material) achieved 31.6% of iopromide removal, while 80% was removed in UASB reactors supplied with each metal-humic acid complex. Further analyses indicated multiple transformation reactions taking place in iopromide including deiodination, N-dealkylation, decarboxylation and deacetylation. This is the first successful application of immobilized RM, which does not require a supporting material to maintain the solid-phase RM in long term operation of bioreactors. The proposed redox catalyst could be suitable for enhancing the redox conversion of different recalcitrant pollutants present in industrial effluents.


Assuntos
Reatores Biológicos/microbiologia , Complexos de Coordenação/química , Substâncias Húmicas/análise , Iohexol/análogos & derivados , Esgotos/microbiologia , Anaerobiose , Análise da Demanda Biológica de Oxigênio , Biotransformação , Eletroquímica , Elétrons , Meio Ambiente , Iohexol/metabolismo , Oxirredução
8.
Phys Chem Chem Phys ; 11(30): 6505-13, 2009 Aug 14.
Artigo em Inglês | MEDLINE | ID: mdl-19809683

RESUMO

The electrochemical oxidation of the chemically prepared polymer poly[2-(3-thienyl)ethyl acetate] (PTEtAc), its partially hydrolyzed derivative PTEtAcOH and the fully hydrolyzed compound poly[2-(3-thienyl)ethanol] (PTEtOH) was studied by in situ electron spin resonance (ESR)/UV-Vis-NIR spectroelectrochemistry. The spectroelectrochemical response of these films on ITO substrates was analyzed with respect to the influence of the functionalized alkyl side chain on polymer doping. The simultaneous use of both electron spin resonance and UV-Vis-NIR spectroscopy allows the analysis of the nature, extent and stability of the charge carriers electrogenerated during p-doping. It was found that PTEtAc has a higher capacity for charged species due to the flexibility of the longer side chains making the redox states more stable at different doping levels. At low doping levels the charged states are dominated by polaronic species while at high doping levels bipolarons and diamagnetic polaron pairs are formed. The presence of the OH groups in the polymer side chains of the hydrolyzed derivatives favors hydrogen bonds. These interactions by hydrogen bonding fix the conjugated chains thus making a charge-discharge reaction more difficult. At high doping levels the hydrolyzed polymers favor the formation of polaron pairs.

9.
J Phys Chem B ; 113(8): 2310-6, 2009 Feb 26.
Artigo em Inglês | MEDLINE | ID: mdl-19191716

RESUMO

A combined spectroelectrochemical study by ESR/UV-vis-NIR as well as FTIR spectroscopy on the influence of the copolymer composition on the stabilization of charges upon electrochemical p-doping is presented. As compared to the parent homopolymers 3-hexylthiophene (3-HeTh) and 3-methylthiophene (3-MeTh) which seems to be irregular, FTIR studies of the copolymer of both monomers (copMeHeTh) point to a regioregular structure. The in situ ESR and UV-vis-NIR spectroelectrochemistry at higher doping levels of the polymeric materials proves bipolarons and polaron pairs as stable charged states in poly(3-hexylthiophene) as well as the copolymer copMeHeTh. During the p-doping of poly(3-methylthiophene) bipolarons are the dominating species at higher doping levels. It is demonstrated that only the simultaneous use of both the ESR and the UV-vis-NIR spectroscopy enables the differentiation of polarons (paramagnetic) and polaron pairs (diamagnetic) in a conducting polymer.

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