Selected Products for Continuous Backwash Filtration & Underdrains

Continuous Backwash Filtration & Underdrains

Continuous backwash filters utilize sand media with bed depths of 48" or 60". An airlift pump brings sand from the bottom of the filter up to a scrubber box where the residuals are separated from the sand particles, the backwash waste is rejected over a weir and the washed sand particles fall from the scrubber to the top of the filter bed. Flow in the filter is either countercurrent (most common) with the inlet flow introduced near the bottom of the filter traveling upward and the sand bed moving downward due to the action of the airlift pump. There are also co-current systems with the water flow and the sand flow moving in the same direction. Filters can be placed in series with a finer grade of sand in the second stage, this arrangement is typically used if there is a phosphorous limitation.