AWWA ACE90037

A laser-based particle size analyzer was used to characterize the raw, settled, and filtered water particulate size distributions in a conventional water treatment plant. Particle size distribution trends were characterized and a pilot plant was used to characterize particle size distributions in the direct filtration mode of operation. The authors formulated a conceptual filtration model that incorporates particle attachment and detachment as well as wormhole flow in the filter bed. The proposed equation incorporates terms for particle attachment and detachment in a form compatible with trajectory theories that have been developed from fundamental considerations. The conclusion that the particle size distribution in the effluent from dual-media filters using alum coagulation is controlled by the detachment of deposits from the filter bed raises the possibility of the passage of destabilized particles through a well-operated filter. These particles could interfere with disinfection.