Development of carbon nanotube membranes for wastewater treatment and surface enhanced Raman scattering study of the membrane efficiency and eventual contamination caused

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Αναστασόπουλος, Ιωάννης
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Membrane Bioreactors (MBRs) are well established preferably in industrial wastewater treatment and were introduced aiming at the coupling of membrane separation properties simultaneously with a biochemical reaction. The solid-liquid separation that is conventionally carried out in gravity-based clarifier is replaced by membrane filtration in a MBR system thus combining the strength of biological treatment processes and efficiency of membrane filtration. MBRs have been implemented across a number of industrial sectors such as the food and beverage sector, chemical, pharmaceutical and cosmetics, textile industry as well as in laundries, and have seen extensive take-up of this technology. However, the commonly employed MBRs combined to nanofiltration membrane systems have a high operating efficiency with respect to cost and quality for treatment of wastewater containing high biodegradable organic compounds. The successful fusion of nanotechnology and membrane technology has been stated to lead to efficient next generation separation systems. A novel technology with regards to MBR and membrane systems for efficient wastewater treatment is proposed for the development of a new class of functional low fouling membranes showing enhanced properties such as high water flux and high rejection of organic matter with low molecular weight, by the subsequent inclusion of carbon nanotubes (CNTs) into porous polymeric membranes. The hollow CNT structure provides frictionless transport of water molecules, a feature that makes them suitable for the development of high flux separation systems. The type and quality of CNTs, the filling/host/substrate materials, the processing, and the fabrication methods used for the synthesis of CNT-membranes are the main factors influencing their performances. Different approaches concerning the fabrication of CNT-membranes were studied in the context of the present thesis. The study of the experimental parameters influencing the efficient incorporation of CNTs in the thin selective layer of the ultra-filtration membrane with pore diameters of ~40 nm in order to transform it to a nano-filtration one with pores to be defined exclusively by the hollow CNT-internal diameters, aiming at the rejection of a variety of organic pollutants of industrial wastewaters was the main target of the thesis. Additionally, the immersion precipitation phase separation method was studied and employed for the preparation of porous membranes of tailored morphological features. Mixed matrix membranes prepared by the subsequent mixing of CNTs during the preparation processes were investigated as well, while, the incorporation of vertically aligned CNTs, grown on silicon substrates, to polymer matrix was also examined for the preparation of a CNT-membrane. A basic principle of the CNT-membranes is the efficient binding of CNTs in the membranes to eliminate probable health risk associated with chances of product water getting contaminated with CNTs. Provided that health issues are important concerns to be addressed, the potent release of CNTs into water was investigated by the use of Surface Enhanced Raman Scattering (SERS) technique on the detection and quantification of multi-walled CNTs functionalized with pyridine moieties. In addition, given that extremely small amounts of substances can be detected and further quantified via SERS, the method applied on the investigation of the dye molecules Methylene blue and Remazol Brilliant Blue R, potent wastewater effluents.
Membrane bioreactor, Membranes for wastewater treatment, Carbon nanotubes (CNT), Polyether sulfone membranes, Carbon nanotube membranes, CNT infiltrated membranes, Mixed matrix CNT membranes, Phase separation, Surface enhanced Raman scattering (SERS), Sers of carbon nanotubes, Pyridine functionalized carbon nanotubes, Sers of dye molecules, Methylene blue, Remazol brilliant blue R