Ph.D. Theses
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Browsing Ph.D. Theses by Author "Çeçen, Ferhan."
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Item Application of biological activated carbon (BAC) in drinking water treatment(Thesis (Ph.D.)-Bogazici University. Institute of Environmental Sciences, 2008., 2008.) Yapsaklı, Kozet.; Çeçen, Ferhan.Biological filtration represents an important process step for the production of high quality drinking water. Bacteria attached to the filter media as biofilm use biodegradable organic matter (BOM) present in the filter influent as a source of carbon and energy. The decrease of BOM levels through biofiltration is important with respect to the prevention of bacterial growth and related problems in the distribution system. The research presented in this thesis examined the applicability of biological activated carbon filtration using the water from the Ömerli Reservoir. The experimental results showed that, the choice of filter material is crucial in BAC systems. The ability of GAC to better adsorb and retain organic compounds increases their chance of being biodegraded by bacteria. Biological activity extended the service life of GAC columns. Thermally activated carbons adsorbed NOM better than chemically activated carbon. Likewise, this better adsorption resulted in higher biodegradation. DOC biodegradation was high and was related to the low specific ultraviolet absorption (SUVA) values in raw water. In the case of low SUVA values, ozonation may not be necessary to increase biodegradability of water. High nitrification efficiencies were observed in BAC columns filled with chemically and steam activated carbons. In-situ and membrane hybridization results indicated that Nitrosomonas species were the dominant ammonia oxidizing bacteria and Nitrospira-related species were the prevailing nitrite oxidizing bacteria. The results suggest that the real-time PCR analysis, the amoA/16S rRNA ratio, is an alternative method to understand nitrifying bacterial population and activity in BAC columns.|Keywords: Biological Activated Carbon (BAC), Granular Activated Carbon (GAC), Ozonation, Biodegradation, Drinking WaterItem Cometabolic degration of trichloroethylene (TCE) and 1,2-dichloroethane (1,2-DCA) in nitrification systems(Thesis (Ph.D.)-Bogazici University. Institute of Environmental Sciences, 2005., 2005.) Kocamemi, Bilge Alpaslan.; Çeçen, Ferhan.Public concern for the environment has taken on a new prominence with wastemanagement becoming a priority. As a consequence, new and environmental friendlymethods for pollutant degradation are vastly investigated. Advanced Oxidation Processes, involving ozonolysis, photolysis, electron beams and ultrasonic irradiation have beenidentified as viable alternatives to such research. In recent years, chemistry with ultrasoundwaves has become a method of interest among other Advanced Oxidation Processes,owing to the extreme conditions generated during acoustic cavitation. These extremes are such that water molecules are fragmented into radical species, such as the hydroxyl radical,which is the most powerful chemical oxidant ever known.The dissertation presented herein is about the investigation of advanced oxidationtechniques particularly, ultrasound for the remediation of water contaminated with bacterial and organic constituents. The method of study involved the application of threeultrasonic frequencies under various ambient conditions on infected water samples andsynthetic effluents containing phenol and phenolic derivatives. Reactor effluents weremonitored for assessing the reduction in bacterial density and phenolic concentration. The results were evaluated with the aim of optimizing process parameters anddetermining the reaction kinetics. Moreover, the study with phenol covered comparison ofultrasonic decay with that of ozonolysis and assessing impacts of combined ultrasound,ozone and UV applications. It was found that the efficiency of bacterial decay under 20 kHz ultrasonicirradiation could be enhanced by the addition of solid catalysts such as activated carbon,metallic zinc, ceramic beads. The reaction kinetics was found to represent that of chemicaldisinfection with chlorine. The degradation of phenol was found to proceed with maximum efficiency under300 kHz irradiation at acidic pH and ultrasound rendered detoxification of water samplesvalong with phenol degradation, although mineralization was not effective. Combination ofultrasound with ozone and UV irradiation was found to induce synergistic effects as a consequence of the enhancement in the mass transfer rate of ozone and photolysis ofultrasound-induced hydrogen peroxide to generate excess hydroxyl radicals.Item Effect of heavy metal speciation on nitrification inhibition(Thesis (Ph.D.)-Bogazici University. Institute of Environmental Sciences, 2007., 2007.) Semerci, Neslihan Yazıcı.; Çeçen, Ferhan.Industrial effluents and high-strength wastewaters such as landfill leachates may contain significant amounts of heavy metals. The presence of heavy metals causes toxicity in biological treatment systems. The toxic and inhibitory characteristics of heavy metals depend on several factors such as exposure time, type of buffer, pH, type and concentration of ligands and acclimation. Therefore, a quite high variation is seen in the reported inhibitory range for metals. Surprisingly, very little information exists on the importance of heavy metal speciation in nitrification inhibition studies. Furthermore, the behaviour of heavy metals under prolonged exposure times, acclimation, adaptation, shifts and changes in bacterial community have not been examined yet. The aim of this study was to investigate the influence of Cd and Zn speciation on nitrification inhibition in batch systems enriched in terms of nitrifiers and to investigate the response of nitrifying biomass to prolonged Cd exposure in a continuous-flow system. These experiments showed that the measurement methodologies applied in assessing heavy metal inhibition should be carefully selected since physical and chemical speciation highly affects inhibition. The activity of nitrifying bacteria in continuous-flow systems could change as a result of shifts in microbial community. It also showed the necessity of incorporation of molecular tools into heavy metal inhibition studies.|Keywords: Nitrification, heavy metals, inhibition, biosorption, activated sludge