Sand Filter - an overview | ScienceDirect Topics
26.3.3.1 Continuous Sand Filter. Continuous sand filters (see Fig. 26.6) are gravity-driven depth filters with countercurrent flows of filter sand and dirty fluid.Dirty fluid is introduced into the bottom of the structure, and clean fluid is collected at the top. An airlift pump carries dirty sand from the bottom of the structure to a pneumatic sand washer at the top.