Filter Backwashing by Ejector

Abstract

The effectiveness of backwashing a filter has a significant impact on the performance of the subsequent filter run. Since the primary mechanism of cleaning the filter media is due to the hydraulic shearing action of the backwashing water, a new ejector-backwashing system, taking advantage of hydrodynamic shear created within the mixing zone of an ejector, was developed and evaluated in both pilot and full-scale plants. The mechanism involved in backwashing a filter bed consists of two sequential steps: (1)Hydrodynamic shear dislodges solid flocs from the surface of the medium within an ejector's mixing zone; and (2)dislodged solid flocs are carried upward and ultimately removed from the filter. A significant saving in the backwashing water can be realized by using raw water during the beginning period of backwashing and clean water only during the polishing period. In addition, energy requirement for backwashing is less than that used in most conventional backwashing techniques.