Use of Submerged Filters

Abstract

This article discusses the use of a submerged filter at the St. Louis County Water Company's South County Plant. Treatment basin down time required for submerged filter backwashing coincides with the off‐peak operation hours at night. Because the filter beds are not readily accessible during normal backwashing, sufficient prefiltration water treatment should be provided. The amount of floc retained, as measured by initial filter head loss, is the same following each wash, and probably is beneficial in that it prevents floc penetration of the sandbed. Filter beds are skimmed semi‐annually as a preventive maintenance procedure. Backwashing the submerged filter does not cause floc destruction. Filtering to waste after backwashing and before returning the filter to service has not been necessary. Surface washing of the filter would probably cause destruction of the floc washed out of the filter and would thus interfere with this floc settling in the purification basin. Wash water requirements for filter backwashing are in excess of the requirements for conventional filter washing; however, all of the wash water is reclaimed in the purification basin. The submerged filter, serving as the treatment basin takeoff system, has improved treatment basin velocities and sedimentation, and has resulted in a very substantial savings in plant construction costs.

Filtration—theory and Practice

“…The submerged filter at the St. Louis County Water Co., South County Plant (41), which serves as the treatment basin take-off system, has improved treatment basin velocities and sedimentation, and in general has resulted in a very substantial saving in plant construction costs.…”