Unstratified filtration medium

摘要

According to research conducted for the city of Sioux Falls, S.D., the Sioux Falls Water Reclamation Plant could replace dual-media filters in its final clarifiers with depth filtration using anthracite coal unstratified media filters and still maintain acceptable effluent quality. An unstratified filter is backwashed at a velocity lower than that required to fluidize the media. The backwash water is generally accompanied by air scour to help shake filtered solids from the media. By using unstratified filters with a large effective size, as well as air and water backwash, the plant could maximize filter run lengths and still meet effluent requirements. A larger effective media size (sieve opening through which 10% of the media pass), generally translates into higher filtration rates and longer run times between backwashing periods.