RIPENING IN DEPTH FILTRATION - EFFECT OF PARTICLE-SIZE ON REMOVAL AND HEAD LOSS

Suspensions were filtered in laboratory-scale deep-bed experiments; detailed measurement of particle size distribution at different depths and times and continuous monitoring of pressure at different depths during ripening were performed. Ripening is the improvement in removal efficiency that occurs as previously retained particles begin to serve as additional collectors for suspended particles. Monodisperse, bimodal, and trimodal suspensions of spherical latex particles were filtered under well-controlled physical and chemical conditions. Preferential removal of certain particle sizes was evident throughout ripening, even within the narrow distributions of the monodisperse suspensions. Ripening of the bed significantly affected the relative removal efficiency of particles of different size and surface characteristics; in some cases a decrease in observed initial removal efficiencies was noted. Floc formation and breakoff within the bed changed the particle size distribution of the suspension with time and depth and affected subsequent removal and head loss. The development of head loss in the bed was strongly correlated with the surface area of captured particles. © 1990, American Chemical Society. All rights reserved.