Date of Award
Doctor of Philosophy (PhD)
Civil, Construction, and Environmental Engineering
Reverse osmosis (RO) and nanofiltration (NF) membranes are widely used for water treatment applications. They are charged porous materials, in which size exclusion and charge exclusion work together to dictate solute transport. In this study, membrane porosity was primarily determined by pore size. Thicker, more porous membranes with smaller pores had higher NaCl removal and less permeate water flux. Higher porosity membranes have greater inner pore surface area available to support a greater number of functional groups, thereby rejecting ion flux and increasing ion removal. The Donnan steric pore model (DSPM) was used to determine that the contribution of diffusion and electromigration to the total counter-ion flux declined with increasing porosity, while the contribution of convection flux increased. Co-ion flux was dominated by diffusion flux. RO and NF do not remove disinfection by-products (DBPs) well because DBPs are small and neutral. Here, polysulfone (PS) membranes were loaded with powdered activated carbon (PAC) to target improved removal of the DBPs. The PAC membrane made by 90% PAC (D50 size 16.5 to 27.5 µm) and 10% PS provided the highest observed DBPs (chloroform) adsorption capacity (2.85 mg g-1 per layer). The adsorption capacity improved to 5.51 mg g-1 per layer by using six layers of overlapping membranes. The pristine membrane offered 2~6 log reduction of E. coli using up to 6 layers of overlapping membranes. Membrane flux could be increased more than 100% by polishing the top to minimize the impact of the dense PS layer on flux. Using thermal regeneration at 250 °C provided effective regeneration of the PAC membrane, where one cycle of thermal regeneration successfully recovered 94% adsorption capacity. However, after the fourth thermal regeneration cycle, the regeneration efficiency dropped to 83% and the mechanical strength of the membrane decreased, likely due to thermal degradation of the PS. Thus, the number of regeneration cycles should be limited to no more than 6 hours of total regeneration time. Compared with thermal regeneration, regeneration using dimethyl formamide (DMF) solvent only recovered 48% to 66% of the adsorption capacity in four regeneration cycles.