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1.
J Environ Sci (China) ; 85: 129-137, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31471019

RESUMO

Benzotriazole UV stabilizers (BT-UVs) have attracted concerns due to their ubiquitous occurrence in the aquatic environment, and their bioaccumulative and toxic properties. However, little is known about their aquatic environmental degradation behavior. In this study, photodegradation of a representative of BT-UVs, 2-(2-hydroxy-5-methylphenyl)benzotriazole (UV-P), was investigated under simulated sunlight irradiation. Results show that UV-P photodegrades slower under neutral conditions (neutral form) than under acidic or alkaline conditions (cationic and anionic forms). Indirect photodegradation is a dominant elimination pathway of UV-P in coastal seawaters. Dissolved organic matter (DOM) from seawaters accelerate the photodegradation rates mainly through excited triplet DOM (3DOM⁎), and the roles of singlet oxygen and hydroxyl radical are negligible in the matrixes. DOM from seawaters impacted by mariculture exhibits higher steady-state concentration of 3DOM⁎ ([3DOM⁎]) relative to those from pristine seawaters, leading to higher photosensitizing effects on the photodegradation. Halide ions inhibit the DOM-sensitized photodegradation of UV-P by decreasing [3DOM⁎]. Photodegradation half-lives of UV-P are estimated to range from 24.38 to 49.66 hr in field water bodies of the Yellow River estuary. These results are of importance for assessing environmental fate and risk UV-P in coastal water bodies.


Assuntos
Protetores Solares/química , Triazóis/química , Poluentes Químicos da Água/química , Fotólise , Água do Mar
2.
J Environ Sci (China) ; 85: 147-155, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31471021

RESUMO

Polymer hydrogel-based materials have been shown to act as novel Fenton catalysts for water treatment, but the rational design of hydrogel-based catalysts with good stability has been a great challenge. To increase the stability and activity of polymer-based Fenton catalysts, uniform urchin-like α-Fe2O3 was grown in situ in a PVA carrier matrix here. PVA molecules promoted the growth of urchin-like α-Fe2O3, and then the PVA hydrogel acted as a barrier and carrier to reduce agglomeration. Through coordination by hydroxyl groups, PVA had good combination with Fe ions and α-Fe2O3. The formation of Fe-O-C bonds between iron oxides and polymers was reported for the first time, enhancing the material stability during catalysis. Under higher PVA concentrations, the resulting composite hydrogel could generate more ˙OH due to the increase in the number of active sites because of the hairy urchin-like structure. In tetracycline degradation through a heterogeneous Fenton reaction, the resulting material had good catalytic activity from pH 2 to pH 10 with low iron leaching, good reusability and remained at a level of nearly 90% after five consecutive cycles. Density functional theory calculations were used to further prove the mechanism of structural change of the iron oxides. The HOMO and LUMO energies of the iron oxides changed from 5.428 and 4.899 eV to 5.926 and 5.310 eV, indicating that the presence of PVA could influence the charge of the iron atom. The results provide new insights into the preparation of polymer hydrogel-based heterogeneous Fenton catalysts with enhanced stability for water treatment.


Assuntos
Hidrogéis/química , Poluentes Químicos da Água/química , Purificação da Água/métodos , Compostos Férricos , Peróxido de Hidrogênio/química , Polímeros
3.
J Environ Sci (China) ; 85: 56-65, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31471031

RESUMO

In this study, greatly enhanced Mn(II) adsorption was achieved by as-synthesized diethylenetriaminepentaacetate acid intercalated Mg/Al layered double hydroxides (LDHs-DTPA). The adsorption capacity of LDHs-DTPA was 83.5 mg/g, which is much higher than that of LDHs-EDTA (44.4 mg/g), LDHs-Oxalate (21.6 mg/g) and LDHs (28.8 mg/g). The adsorption data of aqueous Mn(II) using LDHs-DTPA could be well described by the pseudo-second order kinetics and Langmuir isotherm model. Thermodynamics study results also showed that the adsorption process of Mn(II) by LDHs-DTPA was exothermic as indicated by the negative ΔH value. Furthermore, based on the structural, morphological and thermostable features, as well as FT-IR and XPS characterizations of LDHs-DTPA and the pristine LDHs, the adsorption mechanism of Mn(II) was proposed. The carboxyl groups of DTPA were proposed to be the main binding sites for Mn(II), and the hydroxyl groups of LDHs also played a minor role in the adsorption process. Among the three common regeneration reagents, 0.1 mol/L Na2CO3 was the best for reusing LDHs-DTPA in Mn(II) adsorption. Besides, the Mn(II) adsorption performance could be hindered in the presence of typical inorganic ions, especially cations. Further specific modifications of LDHs-DTPA are suggested to get more selective adsorption of Mn(II) in practical applications.


Assuntos
Manganês/química , Ácido Pentético/química , Poluentes Químicos da Água/química , Hidróxidos , Modelos Químicos
4.
Ying Yong Sheng Tai Xue Bao ; 30(9): 3215-3223, 2019 Sep.
Artigo em Chinês | MEDLINE | ID: mdl-31529897

RESUMO

The modified fly ash (MFA) was prepared through roasting the mixture of fly ash and NaOH/Ca(OH)2 at 250 ℃ for 1.5 h. The physicochemical properties of MFA were analyzed by scanning electron microscope (SEM), energy dispersive spectrometer (EDS), X-ray diffraction (XRD), surface area analyze (BET), and Fourier transform infrared spectroscopy (FTIR) techniques. Results from BET analysis showed that the BET of MFA was enlarged by 20.6 times compared with FA. Results from SEM analysis showed that the glass phase was dissolved, with a rough surface and porous structure. Results from FTIR analysis demonstrated that -OH played an important role in Cd2+ adsorption. Results from the static adsorption experiment revealed that the removal efficiency of Cd2+ reached 97.3% when 0.2 g MFA was applied while the concentration of Cd2+ was 100 mg·L-1, the solution pH was 7.0, the adsorption temperature was 25 ℃ and the adsorption time was 90 min. In addition, the coexisting cations (K+, Na+, Mg2+, and Ca2+) might inhibit Cd2+ adsorption. Among all the cations, Ca2+ showed a most significant inhibitory effect on the removal of Cd2+. Langmuir isotherm and the pseudo-second-order kinetic models could well describe the adsorption behavior of Cd2+ on MFA, with the maximum adsorption capacity of 55.77 mg·g-1. Meanwhile, thermodynamic studies showed that Cd2+ adsorption onto MFA was spontaneous and endothermic process. MFA had better adsorption capacity than FA and had certain application pro-spects in wastewater treatment.


Assuntos
Cádmio/química , Eliminação de Resíduos Líquidos/métodos , Águas Residuárias , Poluentes Químicos da Água/química , Adsorção , Cinza de Carvão , Concentração de Íons de Hidrogênio , Cinética , Espectroscopia de Infravermelho com Transformada de Fourier
5.
Water Sci Technol ; 80(2): 300-307, 2019 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-31537766

RESUMO

The aim of this work is to study the performances of isomeric α-, ß-, and γ-FeOOH (goethite, akaganéite and lepidocrocite, including five samples named as Gth1 and Gth2, Aka1 and Aka2, and Lep, respectively) for removing hexavalent chromium (Cr(VI)) from aqueous solutions. The adsorption mechanisms were explored by kinetic and isothermal experiments. Adsorption efficiencies under the different pH values, anions, and the levels of adsorbate and adsorbent were also measured. Results showed that the Cr(VI) adsorption by isomeric FeOOH could be best described by pseudo-second-order kinetic model. The processes of Cr(VI) isothermal adsorption could be greatly fitted by the Langmuir and Freundlich equations with the high correlation coefficients of R2 (>0.92). Also, there were the optimum pH values of 3.0-8.0 for FeOOH to adsorb Cr(VI), and their adsorption capacities were tightly related with the active sites of adsorbents. Cr(VI) adsorptions by these adsorbents were easily influenced by H2PO4-, and then SO42-, while there were little effects by Cl-, CO32- and NO3-. These obtained results could provide a potentially theoretical evidence for isomeric FeOOH materials applied in the engineering treatment of the polluted chromate-rich waters.


Assuntos
Cromo/química , Poluentes Químicos da Água/química , Purificação da Água/métodos , Adsorção , Cromo/análise , Concentração de Íons de Hidrogênio , Cinética , Poluentes Químicos da Água/análise
6.
Water Sci Technol ; 80(2): 308-316, 2019 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-31537767

RESUMO

In this study, a novel composite of modified diatomite supported nanoscale zero-valent iron (mD-NZVI) was synthesized and characterized. The effects of four factors (mD-NZVI dose, temperature, contact time and initial pH) on the removal of Cr(VI) by mD-NZVI were studied by experimental work and analyzed by response surface methodology (RSM). A second-order polynomial equation fitted by Box-Behnken design was used as a statistical model and proved to be precise in describing the significance of four factors. The analysis results show that the effects of four factors on the removal efficiency of Cr(VI) were significant (F value is 19.83), initial pH was found to be the key factor. In addition, the effect of initial pH was further studied and the maximum removal efficiency of 89.34% was obtained at pH of 3, the decrease in removal efficiency with the increase in pH is a synergistic effect of Cr(VI) species, surface charge of mD-NZVI and OH- amount at different pH.


Assuntos
Cromo/química , Poluentes Químicos da Água/química , Purificação da Água/métodos , Cromo/análise , Terra de Diatomáceas , Concentração de Íons de Hidrogênio , Poluentes Químicos da Água/análise
7.
Water Sci Technol ; 80(2): 329-338, 2019 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-31537769

RESUMO

In this study, biochar was prepared from Alternanthera philoxeroides (AP) under O2-limited condition at 350 °C (LB) and 650 °C (HB) and treated with aging by HNO3/H2SO4 oxidation. Structural changes of the biochar after aging treatment and the treatment's effect on Pb(II) absorption were explored. The results showed that oxygen-containing functional groups, aromatic structure and surface area of the biochar increased after the aging treatment. However, the integrity of the tubular structure was broken into fragments. The adsorption process of Pb(II) was in accordance with the pseudo-second-order kinetic model and fitted by the Langmuir model. With the increase of pH, the adsorption capacities of Pb(II) increased gradually, and the adsorption effect was best at pH 5. The aged HB presented a decrease of the carboxyl group, which caused less adsorption capacity of Pb(II) than that of aged LB. The maximum adsorption capacities of Pb(II) on fresh biochar at 350 °C and 650 °C were 279.85 and 286.07 mg·g-1 and on aged biochar were 242.57 and 159.82 mg·g-1, respectively. The adsorption capacity of HB for Pb(II) was higher than that of LB, and the adsorption capacity of aged biochar for Pb(II) decreased obviously, which might be attributable to changes in physicochemical properties of biochar after the aging treatment.


Assuntos
Carvão Vegetal/química , Chumbo/química , Poluentes Químicos da Água/química , Adsorção , Cinética , Chumbo/análise , Poluentes Químicos da Água/análise
8.
Water Sci Technol ; 80(2): 365-376, 2019 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-31537773

RESUMO

At different calcination conditions, titanium-based manganese oxides (MnOx) electrodes were fabricated by spraying method without adhesive. The MnOx/Ti electrodes were applied in electrochemical oxidation of wastewater treatment for the first time. The surface morphologies of electrodes were tested by scanning electron microscopy. The formation of different manganese oxidation states on electrodes was confirmed by X-ray diffraction and X-ray photoelectron spectroscopy. The electrochemical properties of the electrodes have been performed by means of cyclic voltammetry and electrochemical impedance spectroscopy. The characterizations revealed that the MnOx/Ti-350(20) electrode, prepared at calcination temperature of 350 °C for 20 min, exhibited fewer cracks on the electrode surface, larger electrochemically effective surface area and lower charge transfer resistance than electrodes prepared at other calcination conditions. Moreover, Acid Red B was used as target pollutant to test the electrode activity via monitoring the concentration changes by UV spectrophotometer. The results showed that the MnOx/Ti-350(20) electrode presented the best performance on decolorization of Acid Red B with the lowest cell potential during the process of electrochemical oxidation, and the chemical oxygen demand (COD) conversion was 50.7%. Furthermore, the changes of Acid Red B during the electrochemical oxidation process were proposed by the UV-vis spectra.


Assuntos
Compostos Azo/química , Técnicas Eletroquímicas , Eletrodos , Naftalenossulfonatos/química , Poluentes Químicos da Água/química , Oxirredução , Titânio
9.
Ecotoxicol Environ Saf ; 182: 109443, 2019 Oct 30.
Artigo em Inglês | MEDLINE | ID: mdl-31398782

RESUMO

The continuous presence of toxic elements in the aquatic environments around mine tailings occurs due to bioleaching or chemical extraction promoted by the mining operations. Biogenic passivation treatment of tailings dams can be a new environment-friendly technique to inhibit the solubility of heavy metals. In spite of current bioleaching researches, we tried to minimize the mobility of the trace elements in the laboratory scale through the formation of a passivation layer in the presence of a mixed culture of Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans. The X-ray diffraction (XRD) and scanning electron microscope (SEM) represented the jarosite generation as an inhibitory layer on the mineral surfaces of the tested materials. More detailed observations on electron probe micro-analyzer (EPMA) showed the co-precipitation of metals with the passivation layer. Thereby, the passivation layer demonstrates potential in elements immobilization which, in turn, can be optimized in the natural systems. Our working hypothesis was to exploit and optimize the formation of the passivation layer to maximize the immobilization of heavy metals (e.g., Cu, Cr). The optimization process of bioleaching experiments using indigenous bacteria caused a reduced solubility for Cu (from around 20% to 4.5%) and Cr (from around 30% to 10.6%) and the formation of 6.5 gr passivation layer. The analyses finally represented the high efficiency of the passivation technique to minimize metals bioleaching in comparison to earlier studies.


Assuntos
Metais Pesados/química , Mineração , Sulfetos/química , Poluentes Químicos da Água/química , Acidithiobacillus , Acidithiobacillus thiooxidans , Bactérias , Biodegradação Ambiental , Compostos Férricos , Metais Pesados/análise , Minerais , Solubilidade , Sulfatos , Sulfetos/análise , Poluentes Químicos da Água/análise
10.
Water Sci Technol ; 79(12): 2357-2365, 2019 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-31411590

RESUMO

In this work, quinone-modified metal-organic framework MIL-101(Fe)(Q-MIL-101(Fe)), as a novel heterogeneous Fenton-like catalyst, was synthesized for the activation of persulfate (PS) to remove bisphenol A (BPA). The synthetic Q-MIL-101(Fe) was characterized via X-ray diffraction, scanning electron microscope, Fourier transform infrared, electrochemical impedance spectroscopy, cyclic voltammetry and X-ray photoelectron spectroscopy. As compared to the pure MIL-101(Fe), Q-MIL-101(Fe) displayed better catalytic activity and reusability. The results manifested that the Q-MIL-101(Fe) kept quinone units, which successfully promoted the redox cycling of Fe3+/Fe2+ and enhanced the removal efficiency. In addition, the reaction factors of Q-MIL-101(Fe) were studied (e.g. pH, catalyst dosage, PS concentration and temperature), showing that the optimum conditions were [catalyst] = 0.2 g/L, [BPA] = 60 mg/L, [PS] = 4 mmol/L, pH = 6.79, temperature = 25 °C. On the basis of these findings, the probable mechanism on the heterogeneous activation of PS by Q-MIL-101(Fe) was proposed.


Assuntos
Complexos de Coordenação , Estruturas Metalorgânicas , Poluentes Químicos da Água/química , Quinonas
11.
Water Sci Technol ; 79(12): 2387-2394, 2019 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-31411593

RESUMO

The frequent detection of antibiotics in water bodies gives rise to concerns about their removal technology. In this study, the degradation kinetics and mechanisms of norfloxacin (NOR), a typical fluoroquinolone pharmaceutical, by the UV/peroxydisulfate (PDS) was investigated. NOR could be degraded effectively using this process, and the degradation rate increased with the increasing dosage of PDS but decreased with the increasing concentration of NOR. In real water, the degradation of NOR was slower than that in ultrapure water, which indicated that laboratory results cannot be directly used to predict the natural fate of antibiotics. Further experiments suggested that the degradation of NOR was the most fast under neutral condition, the existence of HA or FA inhibited the degradation of NOR, and the presence of inorganic ions (NO3-, Cl-, CO32- and HCO3-) had no significant effect on degradation of NOR. Total organic carbon (TOC) removal rate (40%) indicated NOR was not completely mineralized, and six transformation products were identified, and possible degradation pathways of NOR had been proposed. It can be prospected that UV/PDS technology could be used for advanced treatment of wastewater containing fluoroquinolones.


Assuntos
Norfloxacino/química , Poluentes Químicos da Água/química , Purificação da Água/métodos , Peróxido de Hidrogênio , Cinética , Oxirredução , Raios Ultravioleta
12.
Sci Total Environ ; 689: 1044-1053, 2019 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-31466145

RESUMO

In this work, the feasibility and performance of zero valent iron (ZVI) coupled anaerobic microorganisms in nitrogen removal under low organic carbon condition were investigated, through the comparison of mono-ZVI system and mono-cell system. Coupled system showed the highest total nitrogen (TN) removal efficiency of 67.85% with the addition of 15 g L-1 iron shavings at pH 7.0, which was higher than 29.62% in the mono-ZVI system and 43.86% in the mono-cell system. Besides, the activities of nitrate reductase (NAR), nitrite reductase (NIR), nitric oxide reductase (NOR) and nitrous oxide reductase (N2OR) were significantly improved at ZVI dosage of 15 g L-1 and pH 7.0, which contributed to the higher TN removal efficiency in coupled system. The extent of sludge granulation was greater in the coupled system than mono-cell system, which benefited to the high operational performance and stability of coupled system. The promoted generation of extracellular polymeric substances (EPS) and formation of iron oxides in the coupled system also took advantages on nitrogen removal through adsorption. In addition, ZVI could largely enrich the functional species related to nitrogen removal in the system at phyla and genera level, which could be reasoned for the enhanced nitrogen removal efficiency. In conclusion, this study will improve the understandings of nitrogen removal in the coupled system and be useful to ensure the application of ZVI-supported biological process in the remediation of farmland drainage.


Assuntos
Fazendas , Eliminação de Resíduos Líquidos/métodos , Adsorção , Reatores Biológicos , Carbono , Desnitrificação , Compostos Férricos , Ferro/química , Nitratos/química , Nitrogênio , Oxirredução , Esgotos/química , Poluentes Químicos da Água/química
13.
Top Curr Chem (Cham) ; 377(5): 22, 2019 Aug 23.
Artigo em Inglês | MEDLINE | ID: mdl-31444578

RESUMO

A methodology for photocatalytic reactor modeling applied to advanced oxidation processes for chemical pollution abatement is presented herein. Three distinct reactor configurations typically employed in the field of air and water purification-wall reactors, slurry reactors, and fixed-bed reactors-are considered to illustrate the suggested approach. Initially, different mechanistically derived kinetic expressions to represent the photocatalytic rate of pollutant degradation are reviewed, indicating the main assumptions made by the authors in the published contributions. These kinetic expressions are needed to solve the mass balances of the reactant species in the photocatalytic reactors. As is well known, at least one of the steps of the reaction mechanism requires evaluation of the rate of electron-hole generation, which depends on the photon absorption rate: a volumetric property for reactions with the catalyst particles in aqueous suspension or a surface property for systems with a fixed catalyst deposited on an inert support. Subsequently, the different techniques for evaluating the optical properties of slurry and immobilized systems, and the numerical methods applied to calculate the photon absorption rate, are described. The experimental and theoretical results of pollutant degradation in each reactor type are then presented and analyzed. Finally, the definition, calculation, and relevance of different efficiency parameters are briefly reviewed. Using these illustrative examples, we emphasize the need for a systematic and rigorous approach for photocatalytic reactor modeling in order to overcome the inherent drawbacks of photocatalysis and to improve the overall efficiency of the process.


Assuntos
Luz , Modelos Teóricos , Poluentes Químicos da Água/química , Catálise , Ácido Clofíbrico/química , Cinética , Oxirredução , Fótons , Titânio/química
14.
Water Sci Technol ; 80(1): 25-36, 2019 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-31461419

RESUMO

The ozonation efficiency for removal of recalcitrant organic pollutants in alkaline wastewater is always low because of the presence of some hydroxyl radical scavengers. To solve this problem, the O3/Ca(OH)2 system was put forward, and p-nitrophenol (PNP) was chosen to explore the mechanism of this system. The effects of key operational parameters were studied respectively; the Ca(OH)2 dosage 3 g/L, ozone inlet flow rate 3.5 L/min, ozone concentration 65 mg/L, reactor pressure 0.25 MPa, and temperature 25 °C were obtained as the optimal operating conditions. After 60 min treatment, the organic matter mineralized completely, which was higher than the sum of the ozonation-alone process (55.63%) and the Ca(OH)2 process (3.53%). It suggests that the calcium hydroxide in the O3/Ca(OH)2 process possessed a paramount role in the removal of PNP. The liquid samples and the precipitated substances were analyzed by gas chromatography mass spectrometry, X-ray diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy; it was demonstrated that Ca(OH)2 could accelerate the generation of hydroxyl radical and simultaneously in situ separate partial intermediate products and CO32- ions through some precipitation reactions.


Assuntos
Microbolhas , Nitrofenóis/química , Ozônio , Poluentes Químicos da Água/química , Radical Hidroxila , Eliminação de Resíduos Líquidos
15.
Water Sci Technol ; 80(1): 86-97, 2019 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-31461425

RESUMO

The present study investigated the preparation of nitric acid modified powder activated carbon (MPAC) and its adsorption of trace amounts of Ni(II) from aqueous solution. Results showed that raw powder activated carbon modified with 15% nitric acid (MPAC-15%) had the most developed pore structure and the highest adsorption efficiency for Ni(II) in aqueous solution. For MPAC-15%, the pore width was dominated by micropores with pore width about 1 nm and the total amount of chemical functional groups of MPAC-15% was 0.6630 mmol/g. Ni(II) adsorption tests indicated that the highest adsorption efficiency of MPAC-15% was 98%. The adsorption saturation time of MPAC-15% was about 120 min and the pH-dependent adsorption test showed that neutral conditions (6.5 < pH < 7.5) were suitable for Ni(II) adsorption. The adsorption kinetic analysis revealed that the pseudo-second order adsorption model fitted the adsorption process significantly. Thus, Ni(II) adsorption by MPAC-15% was dominated not only by physical adsorption via highly developed micropores but also by chemical adsorption between Ni(II) and surface functional groups. Adsorption isotherm analysis illustrated the Langmuir model was favorable for the adsorption of Ni(II), with R2 = 0.9874.


Assuntos
Níquel/química , Ácido Nítrico/química , Poluentes Químicos da Água/química , Adsorção , Carvão Vegetal , Concentração de Íons de Hidrogênio , Cinética , Purificação da Água
16.
Water Sci Technol ; 80(1): 126-133, 2019 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-31461429

RESUMO

This work is dedicated to the removal of free cyanide from aqueous solution through oxidation with hydrogen peroxide H2O2 catalyzed by copper oxide nanoparticles. Effects of initial molar ratio [H2O2]0/[CN-]0, catalyst dose, temperature, pH and the catalyst stability on cyanide removal have been investigated. The use of copper oxide has improved the reaction rate showing catalytic activity. The cyanide removal efficiency was increased from 60% to 94% by increasing in the dose of catalyst from 0.5 g/L to 5.0 g/L. Increasing the temperature from 20 °C to 35 °C promotes cyanide removal and the four successive times re-use of catalyst shows good stability. Kinetics of cyanide removal was found to be of pseudo-first-order with respect to cyanide. The rate constants have been determined.


Assuntos
Cobre/química , Cianetos/química , Poluentes Químicos da Água/química , Purificação da Água/métodos , Catálise , Peróxido de Hidrogênio/química , Oxirredução
17.
Water Sci Technol ; 80(1): 134-143, 2019 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-31461430

RESUMO

The aim of this article was to clarify which type of dye chromophores could be decolorized efficiently with the use of laccase enzyme. For this purpose, enzymatic degradation of different type of dye classes (4 reactive, 2 acid and 1 basic dye) having various chromophore groups was investigated by using commercial laccase from Cerrena unicolor. It was observed that the chromophore structure of dye is very important on enzymatic color removal efficiency. According to the experimental results, it was found that color removal efficiencies (20 mg/L initial dye) were 98.7% for RB220 (0.1 g/L enzyme after 6 h), 95.1% for RB19 (0.1 g/L enzyme after 48 h), 90.8% for AR42 (0.1 g/L enzyme after 48 h) while they were 60.9% for AR114 (0.25 g/L enzyme), 58.6% for RB21 (0.5 g/L enzyme), 39.7% for RR239 (0.25 g/L enzyme) even after seven days. As a result, it can be said that the highest decolorization rate was achieved for the reactive dye having formazan copper complex (RB220) chromophore. On the other hand, the enzymatic degradation of basic dye (BB9) was found to be rather difficult compared to the acid and reactive dyes used in this study and the maximum color removal was 42.8% after seven days.


Assuntos
Corantes/análise , Lacase/química , Poluentes Químicos da Água/análise , Purificação da Água/métodos , Cor , Corantes/química , Cobre , Poluentes Químicos da Água/química
18.
Water Sci Technol ; 80(1): 164-172, 2019 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-31461433

RESUMO

The purpose of this study was to investigate the effect of Cu(II) on the adsorption performance and mechanism of tetracycline (TC) adsorption by natural zeolite (NZ) in aqueous solution. Low levels of Cu(II) (<0.01 mmol/L) enhanced the extent of TC adsorption from ∼0.4 mg/g (in the absence of Cu(II)) to ∼0.5 mg/g (with 0.01 mmol/L Cu(II)), resulting in 99% removal of the total TC content. The TC adsorption gradually decreased with increase in the initial pH, but the coexistence of Cu(II) lowered the extent of decrease. The adsorption process was better simulated by the pseudo-second-order kinetics model, but the isotherm model that was more fitting changed from the Langmuir to the Freundlich model as Cu(II) increased, indicating the coexistence of Cu(II) and TC altered the adsorption mechanisms. However, the residual TC in solution increased from 0 to ∼6 mg/L as the concentration of Cu(II) increased from 0 to 1 mmol/L, suggesting a competition between TC and Cu(II) for the adsorption sites in NZ. Fourier transform infrared spectroscopy analysis showed that the functional groups on the surface of NZ changed after the adsorption of TC, suggesting that complex reactions had occurred on the surface of the adsorbent.


Assuntos
Cobre/química , Tetraciclina/química , Poluentes Químicos da Água/química , Adsorção , Concentração de Íons de Hidrogênio , Cinética , Espectroscopia de Infravermelho com Transformada de Fourier , Eliminação de Resíduos Líquidos , Zeolitas/química
19.
Sci Total Environ ; 685: 847-855, 2019 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-31390714

RESUMO

A low-cost and well-separated approach is introduced for adsorption pollutants in water. Chemical modified lignin is prepared with diethylenetriamine to enhance the reaction activities, then used to prepare lignin derivate magnetic hydrogel microspheres (LDMHMs) via blending with Fe3O4. The LDMHMs are successful prepared by the determination of FT-IR data, and the morphology shown from SEM imagine indicates the LDMHMs are in nanosized. The prepared LDMHMs are used as adsorbents for organic dyes, such as methylene blue (MB), methyl orange (MO) and malachite green (MG), the plateaus data are 43 mg/g, 39 mg/g and 155 mg/g, respectively. For inorganic pollutions, such as Pb2+, Hg2+ and Ni2+, the plateaus data are 33 mg/g, 55 mg/g and 23 mg/g, respectively. The adsorption data of unmodified lignin are 2.6 mg/g (Pb2+), 3.3 mg/g (Hg2+), 2.1 mg/g (Ni2+), 8 mg/g (MB), 10 mg/g (MG) and 2 mg/g (MO) in the same condition. The adsorbents are recycled by magnetic separation, regenerating from acid condition and reused for multiple cycles. The regeneration ratios are all above 90%, indicating a highly reusability and further reducing the cost of the treatment.


Assuntos
Corantes/química , Hidrogéis/química , Lignina/química , Microesferas , Poluentes Químicos da Água/química , Purificação da Água/métodos
20.
Sci Total Environ ; 691: 417-429, 2019 Nov 15.
Artigo em Inglês | MEDLINE | ID: mdl-31323587

RESUMO

The pharmaceutical compounds sulfamethoxazole (SMX), propranolol (PRO) and carbamazepine (CBZ) are biorecalcitrant and frequently detected in waters causing negative impacts on human health and aquatic organisms. Electrochemical oxidation appears as an effective option for the removal of recalcitrant compounds and its enhancement is an important issue for the removal of emerging compounds in water. The contribution of this research lies in the comprehensive analysis of the oxygenated electro chemical oxidation of CBZ, SMX and PRO using Nb/BDD mesh anode. The effect of treatment time, current, pH and oxygen injection on the SMX, PRO and CBZ degradation was assessed using Na2SO4 as electrolyte, process optimization was performed, by-products were identified, kinetic and toxicity tests were carried out using different electrolytes. Finally, the process effectiveness was tested using real secondary effluent spiked with the mixture of the pharmaceutical compounds and the acute toxicity was determined. The obtained results indicated that the oxygenated electrochemical oxidation allows effective simultaneous SMX, PRO and CBZ degradation, which showed a significant dependence of treatment time, current and oxygen injection in Na2SO4 electrolyte. At 90 min of electrolysis the parent compounds were detected as well as eight by-products. At 150 min of treatment, further to the already determined by-products and the parent compounds, appeared phenol and p-benzoquinone. Based on the identified compounds, degradation pathways were explained as a result of two main mechanisms: transformation (hydroxylation, deamination, desulfunation) and bond rupture. The kinetic study indicated an increase of the first-order kinetic constant in the oxygenated electrochemical oxidation process using Na2SO4 and NaBr as electrolyte, nevertheless the constant decreased in the presence of NaCl. In the assays with secondary effluent spiked with SMX, PRO and CBZ, the oxygenation did not enhance the performance of the process, however; pharmaceuticals were degraded with a higher removal rates compared with the ones determined in the Na2SO4 synthetic solutions assays; the oxygenation enhanced the TOC and COD removal. The acute toxicity of spiked secondary effluent was reduced from the first few minutes of the electrochemical oxidation process.


Assuntos
Técnicas Eletroquímicas , Preparações Farmacêuticas/análise , Poluentes Químicos da Água/análise , Purificação da Água/métodos , Cinética , Oxirredução , Preparações Farmacêuticas/química , Poluentes Químicos da Água/química
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