Çevre Bilimleri Enstitüsü

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Browsing Çevre Bilimleri Enstitüsü by Subject "Adsorption."

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    Biogeneration of activated carbon in the treatment of phenolic compounds
    (Thesis (Ph.D.)-Bogazici University. Institute of Environmental Sciences, 2006., 2006.) Aktaş, Özgür.; Çeçen, Ferhan.
    This study aimed to clarify the effect of adsorbability, desorbability, biodegradability and activated carbon type on the extent of bioregeneration in the treatment of phenolic compounds in activated sludge systems combined with activated carbon. Bioregenerabilities of activated carbons preloaded with phenol, 2-chlorophenol and 2-nitrophenol were studied. For this purpose, four different activated carbon types; thermally activated and chemically activated powdered carbons (PAC), and their granular countertypes (GAC) with similar physical characteristics were used. Thermally activated carbons were better adsorbers for phenolic compounds than chemically activated ones. However, apparently higher adsorption irreversibility was calculated in the case of thermally activated carbons. The results suggested that, rather than the physical form, carbon activation type and chemical surface characteristics played a more important role on adsorbability of phenolic compounds and its reversibility. Also, adsorption and its reversibility were highly dependent on the type of the target compound. Bioregeneration of chemically activated carbons was also higher than thermally activated ones. This showed that bioregeneration was controlled by the reversibility of adsorption. The results suggested that carbon activation type was of crucial importance for bioregeneration. PAC and GAC countertypes showed comparable bioregeneration efficiencies indicating that carbon size was not an effective factor. Oxidative polymerization of phenol and 2-chlorophenol was a plausible explanation for lesser bioregeneration of thermally activated carbons. However, bioregeneration efficiencies of thermally activated carbons were much higher than their total desorbabilities. This indicated the presence of exoenzymatic bioregeneration. Bi-solute experiments showed that competition for adsorption sites greatly determined the extent of adsorption reversibility and bioregeneration. Cometabolic biodegradation of 2-chlorophenol and 2-nitrophenol in the presence of phenol resulted in efficient bioregenerability of activated carbons, when they were loaded with non-growth substances together with a growth substrate.
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    Evaluation of natural organic matter-metal oxide adsorption isotherms under influential structural concepts
    (Thesis (Ph.D.)-Bogazici University. Institute of Environmental Sciences, 2006., 2006.) Süphandağ, Şerif Altan.; Bekbölet, Miray.
    The adsorption of molecules onto a surface is a necessary prerequisite to any surface mediated chemical process. Therefore, the mechanism of binding of humic acids to TiO2 surface has to be addressed in order to improve the understanding of photocatalytic degradation. From the fundamental point of view, natural organic matter (NOM) for water scientists can be perceived as very complex entities both in terms of chemistry and comprehension. Especially the fulvic (FA) and humic acids (HA), the soluble portions of NOM, are often considered as oligomeric and polymeric materials. In literature, there are ongoing discussions regarding the high molecular mass is due to aggregation of small units, as in micelles, or due to covalently bound units, as in polymers. The essence of this thesis is to evaluate the adsorption under the light of these two debatable approaches and bring reasonable interpretations of the observed isotherm patterns through the use of proposed structures. In this dissertation the isotherms of humic acid (HA) on titanium dioxide are analyzed at acidic, neutral, and basic pH. Combined effects of pH and increasing ionic strength were evaluated in order to asses the effect of changing solution matrix on the molecular structure of humic acid.|Keywords: humic acid, titanium dioxide, adsorption, natural organic matter, metal oxides
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    Photocatalytic oxidation of humic acid in heterogeneous aqueous systems: a comparative investigation between montmorillonite and kaolinite
    (Thesis (Ph.D.)-Bogazici University. Institute of Environmental Sciences, 2013., 2013.) Şen, Sibel.; Bekbölet, Miray.
    Humic acids representing the major fraction of the naturally occurring humic substances are composed of highly functionalized carbon rich polydisperse organic fractions. Clay minerals which are responsible for the transport of inorganic and organic contaminants constitute the main component of the suspended inorganic material in natural waters. The understanding of interactions between humic substances and clay minerals is an important task for the achievement of an effective water treatment performance. The aim of this research was to investigate the influence of montmorillonite and kaolinite as representative clay minerals on the TiO2 photocatalytic degradation of humic acid as the model compound of natural organic matter. The interactions prevailing between humic acid, montmorillonite, kaolinite and TiO2 surface were assessed prior to the application of photocatalysis in order to evaluate the adsorptive and photolytic behavior of humic acids. Adsorption of humic acid onto sole TiO2 and TiO2 in the presence of clay minerals either montmorillonite or kaolinite were assessed by batch adsorption experiments. The changes attained in humic acid were described by UV-vis spectroscopic parameters i.e. color forming moieties (Color436) and UV absorbing centers (UV365, UV280 and UV254), and dissolved organic carbon (DOC) contents. Photocatalytic oxidation of humic acid in the presence of clay particles i.e. montmorillonite or kaolinite was also followed by using specific UV-vis parameters (SUVA365, SUVA280, SUVA254 and SCoA) calculated by respective absorbance measurements (E) through conversion to mass of carbon. Fractional UV-vis parameters (E254/E365; E254/E436; E280/E365; E280/E436, and E365/E436) that signify the removal of color forming groups in relation to the removal of UV absorbing centers revealing further information on the different oxidation pathways through photocatalysis. No noteworthy variation could be detected for fractional UV-vis parameters under photocatalytic conditions for sole humic acid as well as for humic acid in the presence of either montmorillonite or kaolinite. However, a significant correlative interaction was attained between the specific UV-vis and fractional UV-vis parameter (E254/E436) (r2 > 0.80). Therefore, it could be concluded that E365/E436 parameter could be effectively used as a discriminative indicator parameter for the type of clay minerals. Application of the pseudo first order kinetic model revealed both enhancement and retardation effect with respect to the applied montmorillonite and kaolinite doses. Upon non-selective oxidation, a slight rate enhancement could be indicated for Color436, UV365, UV280 and UV254 of HA in the presence of either montmorillonite or kaolinite. However, the presence of clay particles did not significantly change the DOC degradation rate of HA. The effect of ionic strength (Ca2+ loading from 5x10-4 M to 5x10-3 M) was also assessed for the photocatalytic degradation of sole HA and HA in the presence of either montmorillonite or kaolinite. The overall effect of montmorillonite and kaolinite on the photocatalytic degradation of humic acid was also evaluated in terms of molecular size distribution profiles (0.45 μm filtered fraction, 100 kDa fraction, 30 kDa fraction and 3 kDa fraction) described by the specified and DOC normalized specific UV-vis parameters. Besides the effective removal of higher molecular size fractions (100 kDa and 30 kDa fractions), transformation to lower molecular size fractions (< 3kDa) was more pronounced for sole humic acid rather than humic acid in the presence of clay minerals. Scanning electron microscopic (SEM) images accompanying with energy dispersive X-ray analysis were also examined for the elucidation of the surface morphologies of the binary and ternary systems composed of humic acid, TiO2 and montmorillonite or kaolinite both prior to and following photocatalysis. Excitation emission matrix (EEM) fluorescence spectral features were also evaluated for the elucidation of the photocatalytic degradation of sole humic acid and humic acid in the presence of clay minerals either as montmorillonite or kaolinite. The role of Ca2+ ions was also visualized through EEM under the specified conditions. EEM features reflected the irradiation time dependent transformation of the humic like fluorophores to fulvic like fluorophores in accordance with the photocatalytic removal of humic acid. Adsorption of humic acid onto sole TiO2 and TiO2 in the presence of either montmorillonite or kaolinite with Ca2+ were evaluated by the application of batch adsorption experiments. Adsorption properties of humic acid onto sole TiO2 and TiO2 in the presence of clay minerals either as montmorillonite or kaolinite were evaluated in terms of the specified UV-vis parameters as well as DOC. Adsorption isotherms were evaluated in terms of the adsortion isotherm types (Types S, L, and C). Adsorption data of the indicated humic parameters were further modeled by Freundlich and Langmuir adsorption isotherm model. It could be concluded that, the presence of clay particles i.e. montmorillonite and kaolinite would not significantly alter the photocatalytic degradation efficiency of humic acid. This result signifies that photocatalysis could be an alternative treatment option for the successful removal of natural organic matter in water treatement systems. As shown by the results attained through the application of the UV-vis and fluorescence spectroscopic techniques, the chemical composition of the resultant organic matter would be the indicative parameter for the assessment of the drinking water quality. Since chlorination and/or ozonation is widely applied as the final disinfection step, from public health point of view, it is highly recommended that further research should be directed to the evaluation of the possible side effects related to the formation of the disinfection by-products.
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    Sorption of tetracycline antibiotics on natural and modified zeolite
    (Thesis (M.S.)-Bogazici University. Institute of Environmental Sciences, 2007., 2007.) Şalcıoğlu, Aslı Şükriye.; Balcıoğlu, Işıl.
    Antibiotics found in different compartments of environment are classified as emerging pollutants. Animal farming and aquaculture facilities are two potential sources for antibiotic pollution in the environment. In this study, the adsorption of widely used antibiotic, oxytetracycline (OTC) onto sodium (Na) and hexadecyltrimethylammonium (HDTMA) modified zeolite was investigated. The adsorption isotherm data were fitted to the Freundlich model. HDTMA-modified zeolite exhibited stronger pH dependence and 90 per cent antibiotic removal was achieved at pH 8 with 30 mg/L OTC. The adsorption capacity of Na-zeolite did not change significantly in the pH range of 2-10 and it exhibited a maximum OTC adsorption of 88 per cent at pH 6.5. The effect of various ions on the adsorption of OTC onto zeolite was also investigated. While the presence of calcium, magnesium, phosphate, chloride, and sulfate ions decreased the sorption of OTC onto Na and HDTMA-modified zeolite, bicarbonate ion promoted the adsorption of OTC on HDTMA-modified zeolite. NH4+ and OTC simultaneously removed from water by Na-zeolite. The obtained results show that both types of zeolites can be considered as a potential adsorbent for tetracycline antibiotics.|Keywords : Adsorption, zeolites, Oxytetracycline hydrochloride (OTC), UV spectroscopy, hexadecyltrimethylammonium (HDTMA)