Çevre Bilimleri

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Browsing Çevre Bilimleri 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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    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)