Filtration of Complex Suspensions Using N anofiltration andReverse Osmosis Membranes: Foulant-Foulant and FoulantMembraneInteractions

[摘要] Membrane filtration is a promising advanced treatment method that has thetechnological capability to treat waters containing contaminants that typicallyescape traditional water treatment methods, including trace micro-pollutants aswell as high salt concentrations. The accurate prediction of nanofiltration andreverse osmosis membrane performance in industrial applications is dependentupon understanding the fouling behavior of representative feed solutions.Combining conventional crossflow filtration experiments and characterization offoulant-foulant and foulant-membrane interactions, three mechanisms involved incombined fouling of organic and inorganic colloidal foulants are identified:increased hydraulic resistance of the mixed cake layer structure, hindered foulantdiffusion due to interactions between solute concentration polarization layers, andchanges in colloid and membrane surface properties due to organic adsorption. Arange of typical organic foulants that exhibited different interactions in themembrane system were studied in combination with inorganic silica on low andhigh salt-rejecting membranes. Autopsying of the fouled membrane usingiiitransmission electron microscopy (TEM) helped identify combined fouling layerstructure. Direct organic adsorption of BSA onto inorganic colloids was shown tocause the greatest synergistic fouling through creation of an aggregated foulinglayer structure. A stratified, active salt-rejecting layer of natural organic matterminimizes cake enhanced osmotic pressure (CEOP) and reduces fouling. Thepresence of divalent ions can lead to the creation of salt concentrating layers bycausing aggregation of alginate molecules and enabling CEOP.The effect of membrane surface chemistry on adsorptive fouling by organicswas studied using self-assembled monolayers (SAMs) with different endingfunctionalities. Surfaces were characterized by hydrophobicity and surface freeenergy incorporating van der Waals and Lewis acid-base interactions. Acid-baseinteractions were dominant for all model membrane surfaces tested and totalinterfacial energies predicted natural organic matter and polysaccharide adsorption,but do not account for protein adsorption. Specific interactions, such as hydrogenbonding and electrostatic interaction between specific functionalities, playa moreimportant role than non-specific electrostatic and hydrophobic interactions inadsorption of and irreversible fouling by proteins. Therefore, surface modificationsof NF and RO membranes that minimize -COOH and -NHz as well as other chargedsites may be an effective approach to develop fouling resistant membranes.

[发布机构] Rice University

[效力级别] engineering