Ph.D. Theses
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Browsing Ph.D. Theses by Author "Bekbölet, Miray."
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Item Oxidation of aqueous humic substances by ozonation(Thesis (Ph.D) - Bogazici University. Institute of Environmental Sciences, 2002., 2002.) Kerç, Aslıhan.; Bekbölet, Miray.Chemical oxidation techniques have been used in water treatment for the removal of natural organic matter, which produce halogenated organic compounds upon chlorination. Although being a powerful oxidant, ozone is known to be ineffective for oxidizing recalcitrant organics. Accumulation of carboxylic acids upon ozonation makes the complete mineralization impossible or unfeasible. Therefore, in this study ozonation was combined with photocatalytic oxidation using TiO2 for humic acid degradation. First part of this study covers the ozonation kinetics in humic acid solutions. An empirical model was proposed for defining humic acid degradation with ozonation. The proceeding sections cover the combination of ozonation with photocatalytic oxidation in a sequential system in which ozonation was applied as a pretreatment stage. Langmuir-Hinshelwood model as well as first order degradation kinetics model was studied for defining the photocatalytic oxidation of humic acids. Pretreatment by ozonation resulted in increased first order degradation rates during photocatalysis. Adsorption characteristics of humic acids on the catalyst surface were also evaluated. UV absorbance and color were the parameters used to monitor humic acid degradation. The changes in the molecular size distributions were determined in oxidized humic acid samples using ultrafiltration. Trihalomethane formation potential (THMFP) was measured to demonstrate the oxidation efficiencies.Item 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.Item Removal of organics in reverse osmosis concentrate by advanced treatment(Thesis (Ph.D.) - Bogazici University. Institute of Environmental Sciences, 2020., 2020.) Birben, Nazmiye Cemre.; Bekbölet, Miray.Due to its effective and reliable purification performance, reverse osmosis technology is one of the practical and affordable ways to produce high quality recycled water. However, a major drawback of reverse osmosis is the production of concentrate usually accounting for 15-20% of the input stream containing high levels of organic pollutants some of which could be toxic and bio-accumulative. Possessing a threat to the environment, reverse osmosis concentrate (ROC) must be treated to reduce or even eliminate the negative impact associated with the presence of organic pollutants. The main objective of this research was to investigate the applicability of homogeneous and heterogeneous advanced oxidation processes on municipal wastewater derived reverse osmosis concentrate treatment. For this purpose, reverse osmosis concentrate samples in the absence and presence of emerging contaminants were synthetically prepared with respect to physicochemical characteristics reported in the literature. Sulfamethoxazole and Carbamazepine were selected as target emerging contaminants owing to their common presence in wastewater sources. UVC/H2O2 and Fenton processes were selected as homogeneous advanced oxidation processes whereas solar photocatalysis by using commercially available photocatalysts as well as synthesized ones was considered as heterogeneous advanced oxidation process. Assessment of selected processes for their effectiveness on the removal of complex organic matter was presented in comparison to the sole photolytic oxidation conditions. Since molecular size distribution profiles of organic compounds in ROC plays an important role in order to assess the removal of different pollutants with respect to different molecular size fractions ROC samples were exposed to molecular size fractionation prior to and following photolytic and photocatalytic degradation processes. Expected potential risk was investigated through toxicity assessment prior to and following photodegradation and photocatalytic degradation processes. Organic fraction of reverse osmosis concentrate samples were monitored mainly by UV-vis and advanced fluorescence spectroscopic techniques in combination with PARAFAC modeling as well as organic carbon content.Item Soil metal interactions and investigation of extractive metal removal pathways(Thesis (Ph.D.) - Bogazici University. Institute of Environmental Sciences, 2001., 2001.) Özkaraova, Emre Burcu.; Bekbölet, Miray.The aim of this work was to interprete the interaction of zinc with soils varying in composition and investigate methods for the removal of zinc from soil. The adsorption behaviour of zinc was evaluated with isotherms, kinetic studies and sequential fractionation. The findings derived from isotherms were in consistence with the results of sequential extraction experiments, suggesting the presence of more than two sites participating in the adsorption of zinc. Thus, it was presented that high affinity sites with high binding energies like iron and manganese oxides and carbonates were occupied at lower zinc concentrations, and low affinity sites with low binding energies like exchangeable sites at higher zinc concentrations. The removal of zinc with naturally occurring humic and fulvic acids was found to be low. The reason of this could not be explained by the number of functional groups involved in the extractions. The adsorption of humic and fulvic acid was proposed as the mechanism hindering the removal of zinc. The removal of zinc with synthetic chelating agents such as EDT A and DTPA increased with increasing EDT A and DTP A concentrations, revealing efficiencies over 100 %. These observations were well explained with the stoichiometric molar ratios and the pH dependent speciation of EDT A and DTP A. Sequentia.l extraction experiments helped to understand from which soil fraction zinc was taken by humic acid, EDT A and DTP A. Thus, humic acid preferred to remove zinc adsorbed by the exchangeable sites of soils, whereas EDT A and DTP A took the zinc associated with carbonates and iron and manganese oxides.Item Toxicity-oriented control of advanced oxidation processes a case study on phenol derivatives(Thesis (Ph.D.)-Bogazici University. Institute of Environmental Sciences, 2013., 2013.) Karcı, Akın.; Bekbölet, Miray.; Arslan, İdil.Advanced oxidation processes are expected to be carefully operated and monitored based on their ecotoxicological impact because the partial oxidation of organic contaminants may result in the formation of intermediates more toxic than parent compounds. Toxicity tests in combination with the transformation product analyses could be an important tool for the control of advanced oxidation processes. Considering the commercial importance as well as toxicological properties of chlorophenol and nonylphenol polyethoxylate group phenolic compounds, degradation and detoxification of 2,4-dichlorophenol (2,4-DCP) and nonylphenol decaethoxylate (NP-10) in distilled water and synthetically prepared freshwater were investigated by applying the H2O2/UV-C, Fenton and photo-Fenton advanced oxidation processes that are well-known for their effectiveness in removing many organic pollutants from waste streams. Although not an advanced oxidation process, UV-C photolysis was also included in the study due to the fact that it is becoming an attractive technology in water treatment facilities due to several advantages. The marine photobacteria Vibrio fischeri were employed as the test organism to assess changes in acute inhibitory effect during the studied treatment processes, whereas the umu-test using Salmonella typhimurium TA1535/pSK1002 strain was selected as the genotoxicity assay. Toxicity results were complemented by transformation product analyses performed by means of high performance liquid chromatography, gas chromatography-mass spectrometry, liquid chromatography-mass spectrometry, colorimetry and ion chromatography in order to gain a deeper insight into acute toxicity and genotoxicity patterns during application of the studied treatment processes. The H2O2/UV-C and photo-Fenton processes ensured complete 2,4-DCP removal and near-complete mineralization as well as effective abatement of UV280/254 absorbances. Hydroquinone, chlorohydroquinone, maleic and formic acids and aldehydes were identified as the common transformation products of the studied treatment processes. The most rapid decrease in the acute inhibitory effect was achieved by the H2O2/UV-C and photo-Fenton processes, however a re-increase in toxic effect was evidenced in the former advanced oxidation process when extending the treatment time beyond 30 min. The acute inhibitory effect ultimately measured in synthetic freshwater was higher than that recorded in distilled water for UV-C photolysis and lower for the H2O2/UV-C and Fenton processes, whereas the photo-Fenton process was not significantly affected by the inorganic constituents of synthetic freshwater based on acute toxicity test results. During application of the studied treatment processes in distilled water no significant genotoxic effect was observed with and without metabolic activation. Complete NP-10 degradation that is very fast accompanied with high total organic carbon removal efficiencies were achieved by the H2O2/UV-C and photo-Fenton processes, whereas the Fenton’s reagent provided only poor NP-10 abatement and insignificant mineralization. Aliphatic carboxylic acids including formic, acetic and oxalic acids, aldehydes and polyethylene glycols containing 2-8 ethoxy units were all identified as the degradation products of NP-10 by the studied treatment processes. The photo-Fenton process appeared to be toxicologically safer both in distilled water and synthetic freshwater based on the acute toxicity tests since the inhibitory effect did not increase relative to the original NP-10 solution after treatment. The genotoxic effects obtained in distilled water both with and without metabolic activation followed the order; Fenton > H2O2/UV-C > photo-Fenton > UV-C. Formation of weakly to moderately genotoxic transformation products was evidenced in the presence and absence of metabolic activation when the H2O2/UV-C process was applied to synthetically prepared freshwater. The genotoxic effect levels were typically lower during photo-Fenton treatment of synthetic freshwater contaminated with NP-10 as compared to those achieved with the H2O2/UV-C process both in the presence and absence of metabolic activation.