Humic Acid

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Miray Bekbolet - One of the best experts on this subject based on the ideXlab platform.

  • evaluation of Humic Acid photocatalytic degradation by uv vis and fluorescence spectroscopy
    Catalysis Today, 2005
    Co-Authors: Ceyda Senem Uyguner, Miray Bekbolet
    Abstract:

    Abstract Photodegradation of Humic substances causes drastic changes in the UV–vis absorption and fluorescence properties of Humic Acids. In this study it is intended to fulfill the lack of knowledge about the spectral changes of Humic Acids during photocatalytic oxidation process es and elucidate the effects observed on the molecular size distribution of Humic Acid focusing on their analysis by UV–vis and fluorescence spectroscopy. As confirmed by the spectroscopic evaluation of the molecular size distribution data, photocatalytic degradation of Humic Acid leads to the formation of lower molecular size (small fractions) and higher UV absorbing compounds. For fractions less than 10 kDa, UV 254 absorbing moieties in treated Humic Acid samples become higher than that of raw Humic Acid designating the generation of new species during photocatalysis. UV–vis spectroscopic changes were also evaluated by the parameters relating to the concomitant removal of the total organic carbon as well as by the ratios using absorption values at discrete wavelengths. Moreover, the fluorescence spectra of treated Humic Acid samples show decreasing intensity profiles with increasing photocatalytic irradiation time.

  • Evaluation of Humic Acid photocatalytic degradation by UV-vis and fluorescence spectroscopy
    Catalysis Today, 2005
    Co-Authors: Ceyda Senem Uyguner, Miray Bekbolet
    Abstract:

    Photodegradation of Humic substances causes drastic changes in the UV-vis absorption and fluorescence properties of Humic Acids. In this study it is intended to fulfill the lack of knowledge about the spectral changes of Humic Acids during photocatalytic oxidation processes and elucidate the effects observed on the molecular size distribution of Humic Acid focusing on their analysis by UV-vis and fluorescence spectroscopy. As confirmed by the spectroscopic evaluation of the molecular size distribution data, photocatalytic degradation of Humic Acid leads to the formation of lower molecular size (small fractions) and higher UV absorbing compounds. For fractions less than 10 kDa, UV254 absorbing moieties in treated Humic Acid samples become higher than that of raw Humic Acid designating the generation of new species during photocatalysis. UV-vis spectroscopic changes were also evaluated by the parameters relating to the concomitant removal of the total organic carbon as well as by the ratios using absorption values at discrete wavelengths. Moreover, the fluorescence spectra of treated Humic Acid samples show decreasing intensity profiles with increasing photocatalytic irradiation time. © 2005 Elsevier B.V. All rights reserved.

Ceyda Senem Uyguner - One of the best experts on this subject based on the ideXlab platform.

  • evaluation of Humic Acid photocatalytic degradation by uv vis and fluorescence spectroscopy
    Catalysis Today, 2005
    Co-Authors: Ceyda Senem Uyguner, Miray Bekbolet
    Abstract:

    Abstract Photodegradation of Humic substances causes drastic changes in the UV–vis absorption and fluorescence properties of Humic Acids. In this study it is intended to fulfill the lack of knowledge about the spectral changes of Humic Acids during photocatalytic oxidation process es and elucidate the effects observed on the molecular size distribution of Humic Acid focusing on their analysis by UV–vis and fluorescence spectroscopy. As confirmed by the spectroscopic evaluation of the molecular size distribution data, photocatalytic degradation of Humic Acid leads to the formation of lower molecular size (small fractions) and higher UV absorbing compounds. For fractions less than 10 kDa, UV 254 absorbing moieties in treated Humic Acid samples become higher than that of raw Humic Acid designating the generation of new species during photocatalysis. UV–vis spectroscopic changes were also evaluated by the parameters relating to the concomitant removal of the total organic carbon as well as by the ratios using absorption values at discrete wavelengths. Moreover, the fluorescence spectra of treated Humic Acid samples show decreasing intensity profiles with increasing photocatalytic irradiation time.

  • Evaluation of Humic Acid photocatalytic degradation by UV-vis and fluorescence spectroscopy
    Catalysis Today, 2005
    Co-Authors: Ceyda Senem Uyguner, Miray Bekbolet
    Abstract:

    Photodegradation of Humic substances causes drastic changes in the UV-vis absorption and fluorescence properties of Humic Acids. In this study it is intended to fulfill the lack of knowledge about the spectral changes of Humic Acids during photocatalytic oxidation processes and elucidate the effects observed on the molecular size distribution of Humic Acid focusing on their analysis by UV-vis and fluorescence spectroscopy. As confirmed by the spectroscopic evaluation of the molecular size distribution data, photocatalytic degradation of Humic Acid leads to the formation of lower molecular size (small fractions) and higher UV absorbing compounds. For fractions less than 10 kDa, UV254 absorbing moieties in treated Humic Acid samples become higher than that of raw Humic Acid designating the generation of new species during photocatalysis. UV-vis spectroscopic changes were also evaluated by the parameters relating to the concomitant removal of the total organic carbon as well as by the ratios using absorption values at discrete wavelengths. Moreover, the fluorescence spectra of treated Humic Acid samples show decreasing intensity profiles with increasing photocatalytic irradiation time. © 2005 Elsevier B.V. All rights reserved.

James O Leckie - One of the best experts on this subject based on the ideXlab platform.

  • fouling of reverse osmosis and nanofiltration membranes by Humic Acid effects of solution composition and hydrodynamic conditions
    Journal of Membrane Science, 2007
    Co-Authors: Chuyang Y Tang, Youngnam Kwon, James O Leckie
    Abstract:

    Fouling of reverse osmosis (RO) and nanofiltration (NF) membranes by Humic Acid, a recalcitrant natural organic matter (NOM), was systematically investigated. The membrane flux performance depended on both hydrodynamic conditions (flux and cross-flow velocity) and solution composition (Humic Acid concentration, pH, ionic strength, and calcium concentration), and was largely independent of virgin membrane properties. While increasing Humic Acid concentration and ionic strength, and lowering cross-flow velocity affected flux performance moderately, severe flux reduction occurred at high initial flux, low pH, and high calcium concentration. At a calcium concentration of 1 mM, all the membranes exhibited an identical stable flux, independent of their respective intrinsic membrane permeabilities. The effect of solution composition was more significant at higher fluxes. Improved salt rejection was observed as a result of Humic Acid fouling, which was likely due to Donnan exclusion by Humic material close to membrane surfaces. Greater rejection improvement was observed for membranes with rougher surfaces.

  • characterization of Humic Acid fouled reverse osmosis and nanofiltration membranes by transmission electron microscopy and streaming potential measurements
    Environmental Science & Technology, 2007
    Co-Authors: Chuyang Y Tang, Youngnam Kwon, James O Leckie
    Abstract:

    Reverse osmosis and nanofiltration membranes fouled by Humic Acid were systematically characterized by transmission electron microscopy. All fouled membranes, except those with very low initial flux, were completely covered by a layer of Humic Acid whose thickness and density were greatly affected by the feedwater composition ([H+] and [Ca2+]) and initial flux. A low-density Humic layer (about 0.1 g of purified Aldrich Humic Acid (PAHA)/cm3) was formed at low initial flux (2 m/day or less) at pH 7 without calcium. It was several times denser at a higher initial flux, pH 4.5, or 1 mM Ca2+. Corresponding to the denser foulant layers under these conditions, PAHA accumulation was greatly increased. The denser foulant layers together with the greater PAHA accumulations were responsible for the severe flux reductions. Both virgin and fouled membranes were characterized by streaming potential measurements. While considerable differences existed for virgin membranes, Humic Acid fouled membranes exhibited identica...

Menachem Elimelech - One of the best experts on this subject based on the ideXlab platform.

  • impact of Humic Acid fouling on membrane performance and transport of pharmaceutically active compounds in forward osmosis
    Water Research, 2013
    Co-Authors: Long D Nghiem, William E Price, Menachem Elimelech
    Abstract:

    Abstract The impact of Humic Acid fouling on the membrane transport of two pharmaceutically active compounds (PhACs) – namely carbamazepine and sulfamethoxazole – in forward osmosis (FO) was investigated. Deposition of Humic Acid onto the membrane surface was promoted by the complexation with calcium ions in the feed solution and the increase in ionic strength at the membrane surface due to the reverse transport of NaCl draw solute. The increase in the Humic Acid deposition on the membrane surface led to a substantial decrease in the membrane salt (NaCl) permeability coefficient but did not result in a significant decrease in the membrane pure water permeability coefficient. As the deposition of Humic Acid increased, the permeation of carbamazepine and sulfamethoxazole decreased, which correlated well with the decrease in the membrane salt (NaCl) permeability coefficient. It is hypothesized that the hydrated Humic Acid fouling layer hindered solute diffusion through the membrane pore and enhanced solute rejection by steric hindrance, but not the permeation of water molecules. The membrane water and salt (NaCl) permeability coefficients were fully restored by physical cleaning of the membrane, suggesting that Humic Acid did not penetrate into the membrane pores.

  • influence of Humic Acid on the aggregation kinetics of fullerene c60 nanoparticles in monovalent and divalent electrolyte solutions
    Journal of Colloid and Interface Science, 2007
    Co-Authors: Kai Loon Chen, Menachem Elimelech
    Abstract:

    Abstract The early stage aggregation kinetics of fullerene C60 nanoparticles were investigated in the presence of Suwannee River Humic Acid and common monovalent and divalent electrolytes through time-resolved dynamic light scattering (DLS). In the absence of Humic Acid, the aggregation behavior of the fullerene nanoparticles in the presence of NaCl, MgCl2, and CaCl2 was found to be consistent with the classic Derjaguin–Landau–Verwey–Overbeek (DLVO) theory of colloidal stability. In the presence of Humic Acid and NaCl or MgCl2 electrolytes, the adsorbed Humic Acid on the fullerene nanoparticles led to steric repulsion, which effectively stabilized the nanoparticle suspension. This behavior manifested in a dramatic drop in the rate of aggregation, an increase in the critical coagulation concentration (CCC), and an attained value of less than unity for the inverse stability ratio (or attachment efficiency) at high MgCl2 concentrations. While the increase in the nanoparticle stability was similarly observed in the presence of Humic Acid at low CaCl2 concentrations, enhanced aggregation occurred at higher CaCl2 concentrations. Measurement of scattered light intensities over time indicated significant aggregation of the Humic Acid macromolecules in solutions of high CaCl2 concentrations. Transmission electron microscopy (TEM) imaging of the fullerene aggregate structures in the presence of Humic Acid revealed that bridging of the fullerene nanoparticles and aggregates by the Humic Acid aggregates is the likely mechanism for the enhanced aggregation at high CaCl2 concentrations.

Andrew L Zydney - One of the best experts on this subject based on the ideXlab platform.

  • analysis of Humic Acid fouling during microfiltration using a pore blockage cake filtration model
    Journal of Membrane Science, 2002
    Co-Authors: Wei Yuan, Aleksandra Kocic, Andrew L Zydney
    Abstract:

    Fouling by natural organic matter, such as Humic substances, is a major factor limiting the use of microfiltration for water purification. The objective of this study was to develop a fundamental understanding of the underlying mechanisms governing Humic Acid fouling during microfiltration using a combined pore blockage–cake filtration model. Data were obtained over a range of Humic Acid concentrations, transmembrane pressures, and stirring speeds. The initial flux decline was due to pore blockage caused by the deposition of large Humic Acid aggregates on the membrane surface, with a Humic Acid deposit developing over those regions of the membrane that have first been blocked by an aggregate. The rate of cake growth approaches zero at a finite filtrate flux, similar to the critical flux concept developed for colloidal filtration. The data were in good agreement with model calculations, with the parameter values providing important insights into the mechanisms governing Humic Acid fouling during microfiltration. In addition, the basic approach provides a framework that can be used to analyze Humic Acid fouling under different conditions.

  • Humic Acid fouling during ultrafiltration
    Environmental Science & Technology, 2000
    Co-Authors: Wei Yuan, Andrew L Zydney
    Abstract:

    Recent studies have shown that natural organic matter (e.g., Humic and fulvic Acids) is a major foulant during ultrafiltration of surface water. The objective of this study was to develop a more complete understanding of the mechanisms governing Humic Acid fouling, including the effects of Humic Acid adsorption, concentration polarization, and aggregate deposition on the rate and extent of fouling. Data were obtained with Aldrich and Suwannee River Humic Acids using ultrafiltration membranes with a broad range of molecular weight cutoffs. Fouled membranes were also examined using streaming potential and contact angle measurements. The extent of flux decline was greatest for the largest molecular weight cutoff membranes due to the greater relative hydraulic resistance of the Humic Acid deposit formed on the surface of these membranes. This Humic Acid deposit reduced the apparent zeta potential and increased the membrane contact angle. Simple static adsorption and concentration polarization caused relatively little flux decline. Humic Acid aggregates had a significant effect on fouling only for the larger molecular weight cutoff membranes. The rate and extent of Humic Acid fouling increased at low pH, high ionic strength, and in the presence of calcium due to changes in intermolecular electrostatic interactions. These results provide important insights into the mechanisms of Humic Acid fouling during ultrafiltration.

  • Humic Acid fouling during microfiltration
    Journal of Membrane Science, 1999
    Co-Authors: Wei Yuan, Andrew L Zydney
    Abstract:

    Recent studies have shown that natural organic matter (e.g., Humic and fulvic Acids) is a major foulant during ultrafiltration of surface water. The objective of this study was to develop a more complete understanding of the mechanisms governing Humic Acid fouling, including the effects of Humic Acid adsorption, concentration polarization, and aggregate deposition on the rate and extent of fouling. Data were obtained with Aldrich and Suwannee River Humic Acids using ultrafiltration membranes with a broad range of molecular weight cutoffs. Fouled membranes were also examined using streaming potential and contact angle measurements. The extent of flux decline was greatest for the largest molecular weight cutoff membranes due to the greater relative hydraulic resistance of the Humic Acid deposit formed on the surface of these membranes. This Humic Acid deposit reduced the apparent zeta potential and increased the membrane contact angle. Simple static adsorption and concentration polarization caused relativel...