Water filtration process and apparatus having upflow filter with buoyant filter media and downflow filter with nonbuoyant filter media

摘要

High rate filtration system includes an upflow filter vessel containing a bed of buoyant media followed by a downflow filter vessel containing a bed of nonbuoyant media. The upflow filter vessel is unobstructed by cross-sectional, media-confining screens. A horizontal trough structure collects filter effluent and makes it possible to clean the bed by diffusing air into the liquid below the bed so that average fluid density in the bed is reduced. The reduction in fluid density results in expansion of the bed as media particles descend by gravity.