The Experts below are selected from a list of 159 Experts worldwide ranked by ideXlab platform
Beate I Escher - One of the best experts on this subject based on the ideXlab platform.
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liposome water and octanol water partitioning of alcohol ethoxylates
Environmental Toxicology and Chemistry, 1999Co-Authors: Markus T Muuller, Alexander J. B. Zehnder, Beate I EscherAbstract:Liposome—water partitioning coefficients, (Klipws), were determined for eight pure alcohol ethoxylates using equilibrium dialysis and ultracentrifugation. Both methods yielded statistically indistinguishable results. The experimentally determined log Klipws were compared with log Kow values estimated with the fragment method using different literature sources for the fragment constants. Fragments of log Klipw were calculated for the ethoxy group (EO) and the -CH2- units from the experimentally determined data. An additional -CH2- unit causes an average increase of log Klipw by 0.45, and an additional EO causes an average decrease of log Klipw by −0.12. With these fragments, the quality of log Klipw estimations can be improved significantly as compared to simple linear regression of log Klipw versus log Kow. The Klipw values calculated according to the new fragment method for pure compounds and for commercial mixtures are shown to be adequate descriptors for quantitative structure—activity relationships of bioaccumulation, toxicity, and sorption to Natural Organic Material.
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Liposome—water and octanol—water partitioning of alcohol ethoxylates
Environmental Toxicology and Chemistry, 1999Co-Authors: Markus T Muuller, Alexander J. B. Zehnder, Beate I EscherAbstract:Liposome—water partitioning coefficients, (Klipws), were determined for eight pure alcohol ethoxylates using equilibrium dialysis and ultracentrifugation. Both methods yielded statistically indistinguishable results. The experimentally determined log Klipws were compared with log Kow values estimated with the fragment method using different literature sources for the fragment constants. Fragments of log Klipw were calculated for the ethoxy group (EO) and the -CH2- units from the experimentally determined data. An additional -CH2- unit causes an average increase of log Klipw by 0.45, and an additional EO causes an average decrease of log Klipw by −0.12. With these fragments, the quality of log Klipw estimations can be improved significantly as compared to simple linear regression of log Klipw versus log Kow. The Klipw values calculated according to the new fragment method for pure compounds and for commercial mixtures are shown to be adequate descriptors for quantitative structure—activity relationships of bioaccumulation, toxicity, and sorption to Natural Organic Material.
Markus T Muuller - One of the best experts on this subject based on the ideXlab platform.
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liposome water and octanol water partitioning of alcohol ethoxylates
Environmental Toxicology and Chemistry, 1999Co-Authors: Markus T Muuller, Alexander J. B. Zehnder, Beate I EscherAbstract:Liposome—water partitioning coefficients, (Klipws), were determined for eight pure alcohol ethoxylates using equilibrium dialysis and ultracentrifugation. Both methods yielded statistically indistinguishable results. The experimentally determined log Klipws were compared with log Kow values estimated with the fragment method using different literature sources for the fragment constants. Fragments of log Klipw were calculated for the ethoxy group (EO) and the -CH2- units from the experimentally determined data. An additional -CH2- unit causes an average increase of log Klipw by 0.45, and an additional EO causes an average decrease of log Klipw by −0.12. With these fragments, the quality of log Klipw estimations can be improved significantly as compared to simple linear regression of log Klipw versus log Kow. The Klipw values calculated according to the new fragment method for pure compounds and for commercial mixtures are shown to be adequate descriptors for quantitative structure—activity relationships of bioaccumulation, toxicity, and sorption to Natural Organic Material.
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Liposome—water and octanol—water partitioning of alcohol ethoxylates
Environmental Toxicology and Chemistry, 1999Co-Authors: Markus T Muuller, Alexander J. B. Zehnder, Beate I EscherAbstract:Liposome—water partitioning coefficients, (Klipws), were determined for eight pure alcohol ethoxylates using equilibrium dialysis and ultracentrifugation. Both methods yielded statistically indistinguishable results. The experimentally determined log Klipws were compared with log Kow values estimated with the fragment method using different literature sources for the fragment constants. Fragments of log Klipw were calculated for the ethoxy group (EO) and the -CH2- units from the experimentally determined data. An additional -CH2- unit causes an average increase of log Klipw by 0.45, and an additional EO causes an average decrease of log Klipw by −0.12. With these fragments, the quality of log Klipw estimations can be improved significantly as compared to simple linear regression of log Klipw versus log Kow. The Klipw values calculated according to the new fragment method for pure compounds and for commercial mixtures are shown to be adequate descriptors for quantitative structure—activity relationships of bioaccumulation, toxicity, and sorption to Natural Organic Material.
Philip C Singer - One of the best experts on this subject based on the ideXlab platform.
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a pilot scale evaluation of magnetic ion exchange treatment for removal of Natural Organic Material and inOrganic anions
Water Research, 2006Co-Authors: Treavor H Boyer, Philip C SingerAbstract:The objective of this research was to evaluate a magnetic ion exchange process (MIEX) for the removal of Natural Organic Material (NOM) and bromide on a continuous-flow pilot-scale basis under different operating conditions and raw water characteristics. The most important operating variable was the effective resin dose (ERD), which is the product of the steady-state resin concentration in the contactor and the regeneration ratio. The raw water employed in this study had a moderate concentration of ultraviolet (UV)-absorbing substances and dissolved Organic carbon (DOC), and a low turbidity, alkalinity, and concentration of competing anionic species. Experiments were conducted using the ambient raw water and raw water spiked with bromide, chloride, and sulfate. Substantial removal of UV-absorbing substances and DOC was achieved at ERDs as low as 0.16mL/L. Moderate bromide removal was achieved, depending on the ERD. Increasing the sulfate concentration resulted in decreased removal of UV-absorbing substances, DOC, and bromide. Consistent results were observed between the continuous-flow pilot plant tests and batch equilibrium studies.
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inhibition of calcite precipitation by Natural Organic Material kinetics mechanism and thermodynamics
Environmental Science & Technology, 2005Co-Authors: Yipin Lin, Philip C Singer, George R AikenAbstract:The inhibition of calcite precipitation by Natural Organic Material (NOM) in solutions seeded with calcite was investigated using a pH-stat system. Experiments were carried out using three NOMs with different physical/chemical properties. For each of the Materials, inhibition was found to be more effective at lower carbonate/calcium ratios and lower pH values. The reduction in the precipitation rate could be explained by a Langmuir adsorption model using a conditional equilibrium constant. By identification of the type of site on the NOM molecules that is involved in the adsorption reaction, the "conditional" equilibrium constants obtained at different solution compositions converged to a single "nonconditional" value. The thermodynamic data determined at 25 degrees C and 1 atm suggest that the interaction between NOM molecules and the calcite surface is chemisorptive in nature and that adsorption is an endothermic reaction driven by the entropy change. The greatest degree of inhibition was observed for the NOM with the highest molecular weight and aromatic carbon content. For a given type of NOM, the degree of inhibition of calcite precipitation was dictated bythe balance between the enthalpy change and the entropy change of the adsorption reaction.
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coagulation of Natural Organic Material effects on speciation of halogenated disinfection by products
Water Science & Technology: Water Supply, 2004Co-Authors: Philip C Singer, L LiangAbstract:A recent paper by Liang and Singer showed that haloacetic acid (HAA) precursors were removed by coagulation to a greater degree than trihalomethane (THM) precursors. Furthermore, they showed that coagulation generally removed more trihaloacetic acid precursors than THM precursors but removed dihaloacetic acid precursors and THM precursors to a similar degree. The objectives of this current study were to compare the findings by Liang and Singer to those of three other investigations conducted in the senior author's laboratory to demonstrate the extent to which coagulation removes THM and HAA precursors, and to contrast the removal of dihaloacetic acid and trihaloacetic precursors by coagulation. These other studies were conducted on seventeen other waters from across the US.
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humic substances as precursors for potentially harmful disinfection by products
Water Science and Technology, 1999Co-Authors: Philip C SingerAbstract:During the chlorination of drinking water, chlorine reacts with Natural Organic Material to produce disinfection by-products, such as trihalomethanes and haloacetic acids, which are believed to be harmful to human health. The formation of these by-products is related to the aromatic carbon content of the water, for which specific ultraviolet absorbance serves as a useful surrogate. Because humic substances in water tend to have a higher aromatic carbon content and a higher specific ultraviolet absorbance than non-humic substances, they produce greater levels of disinfection by-products.
Alexander J. B. Zehnder - One of the best experts on this subject based on the ideXlab platform.
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liposome water and octanol water partitioning of alcohol ethoxylates
Environmental Toxicology and Chemistry, 1999Co-Authors: Markus T Muuller, Alexander J. B. Zehnder, Beate I EscherAbstract:Liposome—water partitioning coefficients, (Klipws), were determined for eight pure alcohol ethoxylates using equilibrium dialysis and ultracentrifugation. Both methods yielded statistically indistinguishable results. The experimentally determined log Klipws were compared with log Kow values estimated with the fragment method using different literature sources for the fragment constants. Fragments of log Klipw were calculated for the ethoxy group (EO) and the -CH2- units from the experimentally determined data. An additional -CH2- unit causes an average increase of log Klipw by 0.45, and an additional EO causes an average decrease of log Klipw by −0.12. With these fragments, the quality of log Klipw estimations can be improved significantly as compared to simple linear regression of log Klipw versus log Kow. The Klipw values calculated according to the new fragment method for pure compounds and for commercial mixtures are shown to be adequate descriptors for quantitative structure—activity relationships of bioaccumulation, toxicity, and sorption to Natural Organic Material.
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Liposome—water and octanol—water partitioning of alcohol ethoxylates
Environmental Toxicology and Chemistry, 1999Co-Authors: Markus T Muuller, Alexander J. B. Zehnder, Beate I EscherAbstract:Liposome—water partitioning coefficients, (Klipws), were determined for eight pure alcohol ethoxylates using equilibrium dialysis and ultracentrifugation. Both methods yielded statistically indistinguishable results. The experimentally determined log Klipws were compared with log Kow values estimated with the fragment method using different literature sources for the fragment constants. Fragments of log Klipw were calculated for the ethoxy group (EO) and the -CH2- units from the experimentally determined data. An additional -CH2- unit causes an average increase of log Klipw by 0.45, and an additional EO causes an average decrease of log Klipw by −0.12. With these fragments, the quality of log Klipw estimations can be improved significantly as compared to simple linear regression of log Klipw versus log Kow. The Klipw values calculated according to the new fragment method for pure compounds and for commercial mixtures are shown to be adequate descriptors for quantitative structure—activity relationships of bioaccumulation, toxicity, and sorption to Natural Organic Material.
Treavor H Boyer - One of the best experts on this subject based on the ideXlab platform.
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removal of Natural Organic Material by a magnetic ion exchange resin
Water Science & Technology: Water Supply, 2008Co-Authors: Treavor H Boyer, Phil C SingerAbstract:The aim of this research was to elucidate the interactions among dissolved Organic carbon (DOC), inOrganic anions and a magnetic ion exchange (MIEX) resin. Model waters containing well characterised Natural Organic matter (NOM) extracts in addition to DOC-free model waters containing sulphate and bicarbonate were used in all experiments. The NOM extracts used in this work included two reference fulvic acids supplied by the International Humic Substances Society (IHSS): Suwannee River Fulvic Acid (SRFA) and Pony Lake Fulvic Acid (PLFA). These reference fulvic acids possess unique chemical characteristics that are representative of their distinct end-member environments. The charge density of the NOM extracts, obtained by potentiometric titration, was used to perform charge balance analyses for ion exchange reactions involving DOC, sulphate, bicarbonate and chloride. For SRFA, the results clearly show the stoichiometric exchange of DOC and bicarbonate for chloride. This work provides an improved understanding of the interactions between NOM, MIEX resin and the background solution matrix, and should result in more effective applications of ion exchange treatment for the removal of DOC during drinking water treatment.
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a pilot scale evaluation of magnetic ion exchange treatment for removal of Natural Organic Material and inOrganic anions
Water Research, 2006Co-Authors: Treavor H Boyer, Philip C SingerAbstract:The objective of this research was to evaluate a magnetic ion exchange process (MIEX) for the removal of Natural Organic Material (NOM) and bromide on a continuous-flow pilot-scale basis under different operating conditions and raw water characteristics. The most important operating variable was the effective resin dose (ERD), which is the product of the steady-state resin concentration in the contactor and the regeneration ratio. The raw water employed in this study had a moderate concentration of ultraviolet (UV)-absorbing substances and dissolved Organic carbon (DOC), and a low turbidity, alkalinity, and concentration of competing anionic species. Experiments were conducted using the ambient raw water and raw water spiked with bromide, chloride, and sulfate. Substantial removal of UV-absorbing substances and DOC was achieved at ERDs as low as 0.16mL/L. Moderate bromide removal was achieved, depending on the ERD. Increasing the sulfate concentration resulted in decreased removal of UV-absorbing substances, DOC, and bromide. Consistent results were observed between the continuous-flow pilot plant tests and batch equilibrium studies.
