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Starch-clay based composites for water purification by filtration

AutorUndabeytia López, Tomás ; Nir, Shlomo ; Laiz Trobajo, L. ; Morillo González, Esmeralda ; Gardi, Ido; Lozano, V.
Fecha de publicación17-jul-2017
EditorSociedad Española de Arcillas
CitaciónXVI International Clay Conference ICC 2017 Granada (Spain) July 17-21, 2017
ResumenSignificant concerns have been raised due to increasing pollution of surface and ground waters. In the vast majority of water treatment plants, depth filtration is incorporated through the use of non-compressible filters made of granular activated carbon (GAC), but the efficiency of GAC for removal of pathogens is very poor. In addition, the removal of small organic polar molecules is not usually satisfactory. Therefore, there is a growing interest in the development of composites that improve the performance of GAC or even can be an alternative to its use. The current research describes the synthesis, characterization and potential use of clay-polymer composites for their use in water purification by filtration. The advantages of these clay-polymer composites are that they can be easily scaled for production at industrial levels; and they were formed by inexpensive materials, a day mineral (bentonite), and cationic starches which are widely used as additives in paper-making, textile and cosmetic industry. These starches are derivatized by the introduction of the cationic functional moiety 2-hydroxypropyltrimethylammonium. The interactions of three polymers with different degree of substitution with the surface of a commercial bentonite were examined. Sorption of the polymers and analysis of the surface charge of the complexes formed showed that charge neutralization at the external surface was observed at loadings lower than the CEC of this day. The lower values for the point of zero charge than the CEC of the clay can be explained by the high screening of the clay surface by non-charged segments of the polycation after sorption. The loading of polymer on the clay was highest for the polymer with the lowest charge density adopting a loop-and-train conformation on the clay surface, whereas a planar conformation was elucidated for the other two higher charged polymers. Several polymer-clay complexes were synthesized and tested for the inactivation and killing of the enteroindicator Escherichia coli as a function of the polymer loading and surface charges. The critical parameters affecting the bactericidal activity were the surface potential and the concentration of cationic monomers in excess over that needed for neutralization of the clay surface. The clay-polymer composite with higher bactericidal activity was also tested for the removal of the emerging contaminants diclofenac and sulfamethoxazole. This study showed that the introduction of functional moieties that are capable to create a network of H-bonds with the pollutants promoted their sorption in addition to electrostatic interactions. Filtration experiments showed a better performance of the columns including clay-polymer composites over that of GAC for the removal of E. coli, diclofenac and sulfamethoxazole. The performance of fillers based on the composites under different constructive and operational parameters, such as the flow rate, and concentration of bacteria, or pharmaceuticals added, was investigated and modeled. The success in the modeling of these filtration processes by using an adsorption-convection model enabled predictions under different operational conditions, and economic projections based on the estimated capacity. Since regeneration of the filters was achieved by the use of dilute and inexpensive HCI or NaOCI solutions, implication is that the effective capacity of the filters is larger than that preliminary determined and consequently the price for successive water treatments will be significantly reduced.
URIhttp://hdl.handle.net/10261/161393
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