Characterization and performance of polymeric reverse osmosis and nanofiltration membranes

Investigation of reverse osmosis (RO) and nanofiltration (NF) membrane surface characteristics is crucial for understanding the interactions of water and dissolved and colloidal species with membranes. Streaming potential measurements have been effectively used to determine the zeta potential of a membrane surface and to investigate the effect of solution chemical composition on membrane surface charge. Contact angle measurements have been used to evaluate the hydrophobicity/hydrophilicity of a membrane surface. Atomic force microscopy (AFM) measurements have given topographic images and information on the roughness of a membrane surface. Together, these methods of surface analysis have been used to characterize the surface properties and to explain the performance (i.e., water flux, solute rejection, fouling behavior) of several "new generation" water treatment membranes.; Zeta potential measurements revealed that in the presence of an indifferent electrolyte, all of the membranes had a positive zeta potential in the low pH range, passed through an isoelectric point between pH 3 and 5, and had a negative zeta potential in the mid to high pH range. Humic substances and surfactants were found to readily adsorb to the membrane surface and markedly influence the membrane surface charge.; AFM images used to investigate the colloidal fouling behavior of cellulose acetate and thin-film composite polyamide RO membranes showed that thin-film composite membranes exhibit large-scale surface roughness while cellulose acetate membranes are relatively smooth. The greater surface roughness of the aromatic polyamide composite membrane was found to be responsible for the higher colloidal fouling rate of these membranes. Addition of an anionic surfactant to the colloid suspension resulted in a slight decrease in the fouling rate of both membranes due to increased electrostatic repulsion between the membrane and colloids.; Additional AFM images revealed that thin-film composite NF membranes are less rough than thin-film composite RO membranes. Contact angle measurements on cellulose acetate and thin-film composite (RO and NF) membranes showed all of the membranes to have low contact angles ({dollar}<{dollar}30{dollar}spcirc{dollar}). The contact angles were found to not be systematically affected by the presence of humic acid and surfactant. Graphs of zeta potential versus pH in conjunction with graphs of performance versus pH illustrated that dissociation of membrane functional groups accounts for most changes in membrane flux and rejection.