Solids contact clarifiers represent an entirely different approach to high-rate clarification. They consist of a basin similar to that used for a conventional clarifier, but with a sludge recycle system to promote development of a dense sludge blanket that captures floc. These units are all similar in design in that they combine solids contact mixing, flocculation, solids-water-separation, and continuous removal of sludge in a single package-type basin. The recirculation rate of water and solids in solids contact units is critical to the units’ effective operation. Too high a recirculation rate will cause the sludge blanket to lift and create increased loading to the filters.