DESIGN OF MICELLAR-ENHANCED ULTRAFILTERS

A systematic calculational procedure is developed for the design of mi cellar-enhanced ultrafilters to treat aqueous streams contaminated wit h organic pollutants. Flat plate, spiral wound, hollow fiber, and tubu lar modules are evaluated for performance (reduction in organic concen tration and volume reduction of the retentate) and cost (capital and o perating). Membranes having a 5000 molecular weight cutoff (MWCO), whi ch reject all micelles, and 50 000 MWCO membranes, which do not, are u sed as examples. The surfactant considered is hexadecyl(=cetyl)pyridin ium chloride (CPC), and the organic pollutants are chlorobenzene, tric hloroethylene, tetrachloroet-hylene, and toluene. The goal is to desig n an ultrafiltration system to reduce the concentration of a pollutant from its saturation value in water to the Environmental Protection Ag ency pretreatment standard for municipal sewage. A combined osmotic-pr essure and fouling-resistance model quantifies the ultrafiltration per meate flux. Also important are the molar solubilization ratios of the respective organics in aqueous CPC solutions, the osmotic pressure of the surfactant as a function of concentration, and the intrinsic rejec tion behavior of the membranes for surfactant monomers and micelles. A n equilibrium-staged configuration operating countercurrently is propo sed for the ultrafiltration system. For treatment of 7.6 m(3) per day [2000 gal/day] of wastewater saturated with chlorobenzene, the optimal design consists of a 3 equilibrium stage system using 18 tubular 50 0 00 MWCO modules in the first stage operating at 207 kPa [30 psig], 2 s piral wound 50 000 MWCO modules in the second stage operating at 207 k Pa [30 psig], and 2 spiral wound 5000 MWCO modules operating at 1034 k Pa [150 psig] in the final stage. The optimum volume concentration rat io is 6; the surfactant concentrate leaves the ultrafilter at 17 kg/m( 3), and the crossflow velocity is 2 m/s in each stage. This design eli minates the need for prefiltration of the total feed and minimizes cap ital and operating costs.