Çevre Bilimleri

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Browsing Çevre Bilimleri by Subject "Ammonium compounds -- Environmental aspects."

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    Biotransformation of benzalkonium chlorides by immobilized cells of Pseudomonas Sp. Biomigi
    (Thesis (M.S.)-Bogazici University. Institute of Environmental Sciences, 2015., 2015.) Sakarya, Fahri Koray.; Tezel, Ulaş.
    Mass use of quaternary ammonium compounds (QACs) caused these chemicals to become an environmental concern. Little or no elimination of QACs in wastewater treatment plants necessitates a removal policy for these chemicals within treatment system before discharge. In this study, an advanced treatment system after biological treatment is proposed for efficient removal of benzalkonium chlorides (BACs), the most common type of QACs in consumer products. Cultures of Pseudomonas sp. BIOMIG1BDMA which can convert BACs into dimethylbenzylamine (BDMA) were immobilized into Ca-alginate beads. Beads were optimized with respect to CaCl2 concentration and diameter for the best BAC biotransformation efficiency at a cell density of 107 CFU/mL. Optimal beads were 3 mm beads produced by using 0.15 M CaCl2. Number of cells in these beads was found to be 4.6±1.4x106 CFU/bead. BAC degradation kinetics of these beads were analyzed for C12BDMA and C14BDMA. The cell specific utilization rate constant was estimated to be 0.46 μM-BACs/hr. Continuous flow packed bed reactors were prepared using alginate beads as packing material and operated at 4.7, 2.3, and 1.2 hrs empty bed contact times corresponding to 1.3 hrs, 0.8 hrs, and 0.3 hrs mean residence times. 85±5% removal efficiency was obtained with the setup of 0.3 hrs mean residence time at 20 μM BACs. The same flow rate gave 102±11% removal efficiency for 2 μM BAC concentration, and 95±5% removal efficiency for actual wastewater.
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    Modeling evolution and dissemination of resistance under temporally changing antimicrobial concentration
    (Thesis (M.S.) - Bogazici University. Institute of Environmental Sciences, 2018., 2018.) Kubilay, Dilara Selin.; Tezel, Ulaş.
    Quaternary ammonium compounds (QACs) are one of the most extensively used cationic biocides in human and animal health care facilities. Along with their many advantages as an antimicrobial agent, one of their biggest disadvantage is that QACs may facilitate development of antimicrobial resistance in bacteria which also promote antibiotic resistance at sub-inhibitory concentrations. Since QACs are biodegradable biocides, their concentrations may decrease substantially after they are applied to surfaces in hospitals. Thus, biodegradation creates environments with QACs at sub-inhibitory concentrations which are hotspots for evolution of QAC resistance. The objective of this study was to elucidate the role of biodegradation on the development of resistance to benzalkonium chlorides (BACs), one of the most extensively used group of QACs, by a BAC susceptible microorganism when a BAC degrader is present. Pseudomonas sp. BIOMIG 1 and a strain of E. coli were used as BAC degrader and BAC susceptible model organisms, respectively, in the experiments. E. coli growth was observed above the minimum inhibitory concentrations of BAC when BIOMIG 1 was present in the medium. Furthermore, E. coli's BAC resistance increased when this co-culture system was operated in a continuous reactor. Additionally, a model that simulates the dynamics of interactions in such a microbial community was developed, calibrated and verified successfully with the experimental data. Outcomes of this study may be useful to further explore processes involved in the evolution and dissemination of antimicrobial resistance in microbial communities in human health related environments.