Filtreler
Filtreler
Bulunan: 82 Adet 0.001 sn
Koleksiyon [20]
Tam Metin [2]
Yayın Türü [1]
Yazar [20]
Yayın Yılı [18]
Konu Başlıkları [20]
Yayıncı [19]
Yayın Dili [2]
Dergi Adı [20]
Membrane potentials for linearly varying fixed charges

Genç, Ayten

Article | 2009 | Turkish Journal of Engineering and Environmental Sciences33 ( 1 ) , pp.73 - 81

The membrane potentials for asymmetric membranes where fixed charges varied linearly with position were evaluated from the numerical solutions of Nernst-Planck flux and Donnan potential equations. The evaluated membrane potentials were compared with the results obtained from the conventional TMS theory where the fixed charge concentration in the membrane was assumed to be uniform. In the comparison, the number of fixed charges was kept constant by defining an average for the fixed charge concentration. The numerical results showed that the membrane potential increased in magnitude when the distributions of fixed charges at the membr . . .ane-solution interfaces were unequal. In addition, the deviation from TMS theory increased more as the charge difference at the interfaces increased. © TÜBİTAK Daha fazlası Daha az

Experimental studies on the effect of electrode configuration in electrofiltration

Genç, Ayten | Tosun, İbrahim

Article | 2002 | Separation Science and Technology37 ( 13 ) , pp.3053 - 3064

Results from the electrofiltration of anatase (TiO2) particles in a water suspension and using three different electrode configurations are presented. The three electrode configurations studied were spot, foil, and mesh. For the first two configurations, the electric field was perpendicular to the direction of flow while for the mesh configuration it was opposite to the direction of flow. The percent gain volume filtrate and power consumption were measured for each electrode configuration. For a given percent gain volume filtrate, it was observed that the foil electrode configuration consumes the least power.

Wild-growing Rosa heckeliana Tratt.: phenolic constituents with cytotoxic and antioxidative properties

Çoruh, Nursen | Özdoğan, Nizamettin

Article | 2017 | Turkish Journal of Biology41 ( 1 ) , pp.195 - 212

Rosa heckeliana, as one of the wild-growing species of the family Rosacea, has a wide use in the folk medicine; however, scientifically there is very little known about it. Our objective was to examine the antioxidative and antiproliferative properties of Rosa heckeliana root extract and its phenolics. The phenolic constituents, namely catechin, caffeic acid, and ellagic acid, were obtained by the methods of extraction, fractionation, and purification through column chromatography. The DPPH and ABTS radical scavenging assays and total flavonoid content analysis were employed as the current antioxidant methods over the crude extract . . .and fractionated parts. Among the extracts/fractions, the ethyl acetate fraction exhibited the highest amount of flavonoid content (4.58 ± 0.018 µg CE/ mg of extract). The ethyl acetate fraction also displayed high antioxidative properties for DPPH (EC50 value: 2.78 ± 0.01 µg/mL) and ABTS scavenging capacities (586 ± 6.64 µM trolox as TEAC value). Additionally, the antiproliferative properties of the crude extract and the ethyl acetate fraction and its isolated constituents were evaluated for two breast cancer cell lines (MCF-7 and MDA-MB-231) using the XTT method. Acetate fraction over the cells of MCF-7 and MDA-MB-231 resulted in ED50 values of 61.18 ± 0.99 µg/mL and 62.54 ± 2.01 µg/mL, respectively. The isolated phenolic constituents were twice as effective as the ethyl acetate fraction on both MCF-7 and MDA-MB-231 cells. Rosa heckeliana, as one of the wild-growing species of the family Rosacea, has a wide use in the folk medicine; however, scientifically there is very little known about it. Our objective was to examine the antioxidative and antiproliferative properties of Rosa heckeliana root extract and its phenolics. The phenolic constituents, namely catechin, caffeic acid, and ellagic acid, were obtained by the methods of extraction, fractionation, and purification through column chromatography. The DPPH and ABTS radical scavenging assays and total flavonoid content analysis were employed as the current antioxidant methods over the crude extract and fractionated parts. Among the extracts/fractions, the ethyl acetate fraction exhibited the highest amount of flavonoid content (4.58 ± 0.018 µg CE/ mg of extract). The ethyl acetate fraction also displayed high antioxidative properties for DPPH (EC50 value: 2.78 ± 0.01 µg/mL) and ABTS scavenging capacities (586 ± 6.64 µM trolox as TEAC value). Additionally, the antiproliferative properties of the crude extract and the ethyl acetate fraction and its isolated constituents were evaluated for two breast cancer cell lines (MCF-7 and MDA-MB-231) using the XTT method. Acetate fraction over the cells of MCF-7 and MDA-MB-231 resulted in ED50 values of 61.18 ± 0.99 µg/mL and 62.54 ± 2.01 µg/mL, respectively. The isolated phenolic constituents were twice as effective as the ethyl acetate fraction on both MCF-7 and MDA-MB-231 cells Daha fazlası Daha az

Separation performances of supported liquid membrane and electrodialysis processes at removal of CD(II) from dilute solutions.

Altın, Süreyya | Gemici, Betül Tuba

Article | 2017 | FRESENIUS ENVIRONMENTAL BULLETIN26 ( 11 ) , pp.6438 - 6446

In this study, the performances of supported liquid membrane (SLM) and electrodialysis (ED) processes have been compared for separation of Cd (II) ions from aqueous solution. The operating parameters for the both laboratory-scale prepared processes have been optimized. The influence of operating parameters on the process performance has been established. Then separation efficiency, initial concentration and flux values of the processes optimized have been compared. The optimum initial concentration of the SLM process (75 mg/L) is higher than the optimum initial concentration of the ED process (5 mg/L). The separation efficiency of t . . .he ED process (85%) is higher than the SLM process (58%). As a conclusion, it has been established that the both processes deliver a significant separation performance for separating Cd(II) ions, however, ED Process is more efficient than SLM process for low initial concentration. SLM process is suitable for relatively high concentration and chemical selectivity Daha fazlası Daha az

Changes in slurry concentration during the initial stages of filtration

Genç, Ayten | Tosun, İbrahim

Article | 2009 | Filtration9 ( 2 ) , pp.135 - 140

The variation in slurry concentration within the filter chamber during the startup of constant pressure filtration experiments and its effect on the cake length and filtrate volume are studied. Theoretical equations relating slurry concentration to cake length and filtrate volume are developed by using the equations of continuity together with the jump conditions at the cake-slurry interface. Comparison with experimental values indicates that the change in slurry concentration within the filter chamber, especially during the initial stages of filtration, should be taken into consideration in the evaluation of model parameters from e . . .xperimental data Daha fazlası Daha az

Effect of carrier type on coupled transport kinetics of thiocyanate ions through liquid membranes

Kobya, Mehmet | Demirbaş, Erhan | Demircioğlu, Nesli | Yıldırım, Yılmaz | Yıldız, Şevki Yalçın

Article | 2004 | Desalination160 ( 3 ) , pp.253 - 262

Coupled transport of thiocyanate ions through a liquid membrane containing quaternary ammonium chloride salts in chloroform was examined. The influences of the carrier type in the membrane phase on the coupled transport of thiocyanate ions were investigated. The kinetics of the coupled transport were analyzed in the formalism of two consecutive irreversible first-order reactions and the kinetic parameters (k1d, k2m, k2a, Rmmax, tmax, Jdmax, Jamax,) were also calculated. For the coupled transport of thiocyanate ions, quaternary ammonium chloride salts having different carbon atom numbers (Cn) used as carriers were found to increase t . . .hiocyanate ions transport efficiency with increasing carbon atom numbers. Tetradecyl trimethylammonium chloride (TDTMACl), hexadecyl trimethylammonium chloride (HDTMACl), and tetraoctyl ammonium chloride (TOACl) were found to be the most effective carrier types for transport of thiocyanate ions when Cn is greater than 16. The activation energies for maximum membrane entrance and exit fluxes were calculated as 32.45 kJ/mol and 34.75 kJ/mol, respectively. The values of the activation energy indicate that the process is controlled by species diffusion Daha fazlası Daha az

Magnetic cobalt particle–assisted solid phase extraction of tellurium prior to its determination by slotted quartz tube-flame atomic absorption spectrophotometry

Özdoğan, Nizamettin | Kapukıran, Fatih | Öztürk Er, Elif | Bakırdere, Sezgin

Article | 2019 | Environmental Monitoring and Assessment191 ( 6 ) , pp.253 - 262

The emergence of magnetic materials has opened up doors to numerous applications including their use as sorbents for preconcentration of trace elements. Magnetic materials exhibit many unique advantages in sample preparation such as easy separation from the sample, high preconcentration factor, and short operation period. In the present study, magnetic cobalt material was synthesized, characterized, and used as an effective sorbent in a solid phase extraction process. Experimental variables of the extraction process including pH and volume of buffer solution, eluent concentration and volume, mixing type and period, and sorbent amoun . . .t were optimized to achieve maximum extraction efficiency. Instrumental variables of flame atomic absorption spectrophotometry and the type of slotted quartz tube were also investigated. Under the optimum conditions, the combined method provided a wide linear range between 50 and 200 ng/mL with detection and quantification limits of 15.4 ng/mL and 51.3 ng/mL, respectively. Relative standard deviations of the proposed method were less than 5.0% and a high enrichment factor of 86.7 was obtained. The proposed method was successfully applied to soil samples for the determination of trace tellurium. © 2019, Springer Nature Switzerland AG Daha fazlası Daha az

An alternative type of photoelectro-Fenton process for the treatment of landfill leachate

Altın, Ahmet

Article | 2008 | Separation and Purification Technology61 ( 3 ) , pp.391 - 397

An alternative type of photoelectro-Fenton (PEF) process has been proposed to remove COD, color and phosphate from the landfill leachates. The process was improved by combining the different type of electro-Fenton (EF) process with UV irradiation. The efficiency of the process and settling characteristics of waste sludge produced from the process were investigated by changing some operating parameters such as initial pH, H2O2 and current. In addition, the proposed process was compared with other treatment processes such as electro-coagulation (EC), electro-Fenton and UV/H2O2 in terms of treatment efficiency. The high removal efficie . . .ncies were observed at the initial pH 3, initial H2O2 concentration, 3000 mg L-1; current, 2.5 A; and treatment time, 20 min. Removal of COD, color and phosphate under the reported conditions were 94%, 97%, 96%, respectively. The obtained results from the comparative experiments revealed that the proposed PEF process is more effective than the other treatment processes for the landfill leachate. © 2007 Elsevier B.V. All rights reserved Daha fazlası Daha az

Analysis of the electrofiltration mechanism based on multiphase filtration theory

Genç, Ayten | Tosun, İsmail

Article | 2004 | Chemical Engineering Communications191 ( 1 ) , pp.125 - 136

A mathematical model based on multiphase filtration theory is developed to describe the electrofiltration process. The model takes both electrophoretic and electroosmotic effects into account. The electrophoretic migration velocity of solid particles is predicted from the model using the filtrate volume time data obtained from electrofiltration experiments.

Accurate and Sensitive Determination Method for Procymidone and Chlorflurenol in Municipal Wastewater, Medical Wastewater and Irrigation Canal Water by GC–MS After Vortex Assisted Switchable Solvent Liquid Phase Microextraction

Kapukıran, Fatih | Fırat, Merve | Chormey, Dotse Selali | Bakırdere, Sezgin | Özdoğan, Nizamettin

Article | 2019 | Bulletin of Environmental Contamination and Toxicology102 ( 6 ) , pp.848 - 853

In this study, the detection power of a gas chromatography mass spectrometer (GC–MS) for procymidone and chlorflurenol was significantly enhanced using switchable solvent liquid phase microextraction (SS-LPME) as a preconcentration tool. This was achieved by a comprehensive optimization of significant parameters to the SS-LPME method such as switchable solvent amount, concentration and amount of sodium hydroxide, pH effect and mixing effect. The optimum experimental conditions obtained were used to determine analytical figures of merit for the analytes. The limits of detection obtained were 0.44 and 2.9 ng/mL for procymidone and chl . . .orflurenol, respectively. The optimum method was applied to water sampled from an irrigation canal and two wastewater samples. The samples were spiked at two concentrations and the percent recovery results obtained ranged between 86 and 115% for both analytes. The recovery results together with the low standard deviations recorded validated the method as accurate and precise. © 2019, Springer Science+Business Media, LLC, part of Springer Nature Daha fazlası Daha az

Characterization of natural organic matter in conventional water treatment processes and evaluation of THM formation with chlorine

Özdemir, Kadir

Article | 2014 | The Scientific World Journal2014 , pp.848 - 853

This study investigates the fractions of natural organic matter (NOM) and trihalomethane (THM) formation after chlorination in samples of raw water and the outputs from ozonation, coagulation-flocculation, and conventional filtration treatment units. All the water samples are passed through various ultrafiltration (UF) membranes. UF membranes with different molecular size ranges based on apparent molecular weight (AMW), such as 1000, 3000, 10,000, and 30,000 Daltons (Da), are commonly used. The NOM fraction with AMW < 1000 Da (1 K) is the dominant fraction within all the fractionated water samples. Its maximum percentage is 85.86% a . . .fter the filtration process and the minimum percentage is 65.01% in raw water samples. The total THM (TTHM) yield coefficients range from 22.5 to 42 g-TTHM/mg-DOC in all fractionated samples, which is related to their specific ultraviolet Absorbance (SUVA) levels. As the molecular weight of the fractions decreased, the TTHM yield coefficients increased. The NOM fractions with AMW values less than 1 K had lower SUVA values Daha fazlası Daha az

Spatial and Seasonal Variations of Disinfection Byproducts (DBPs) in Drinking Water Distribution Systems of Istanbul City, Turkey

Uyak, Vedat | Soylu, Senay | Topal, Tufan | Karapınar, Nazan | Özdemir, Kadir | Özaydın, Şahin | Avşar, Edip

Article | 2014 | Environmental Forensics15 ( 2 ) , pp.190 - 205

This study presents the seasonal and spatial variations of trihalomethanes (THMs) and haloacetic acids (HAAs) in 30 sampling points within three water distribution systems of Istanbul City, Turkey. The effects of surface water quality, seasonal variation, and species differences were examined. The occurrence of chlorinated THMs and HAAs levels was considerably lower in the system in which raw water is subjected to pre-ozonation versus pre-chlorination. Seasonal analysis of the data indicated that the median concentration of four THMs (THM4) was higher than nine HAAs (HAA9) concentrations in all three distribution systems sampling po . . .ints. For all distribution systems monitored, the highest median THM4 and HAA9 concentrations were observed in the spring and summer season, while the lowest concentrations of these disinfection byproduct (DBP) compounds were obtained in the fall and winter period. Due to the higher level of bromide in supplying waters of these two systems, moderate levels of brominated DBP species have been observed in the Kagithane and Buyukcekmece distribution systems districts. In fact, Spearman partial correlations (Spearman rank correlation coefficients [rs]) tend to be higher among analogues in terms of number and types of substituent, especially TCAA with TCM (rs 0.91), and DBAA with DBCM (rs 0.90). In contrast, the hydraulic (residence time and flow rate) and chemical mechanisms (hydrolysis, volatilization, and adsorption) affect the fate and transport of DBPs in distribution systems. Seasonal and spatial variations of DBPs presented in this study have important implications on regulatory issues and from an epidemiological point of view. © 2014 Taylor & Francis Group, LLC Daha fazlası Daha az

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