Importance

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Abstract

Systems and methods for clarifying liquids, especially water, of the two stage upflow/downflow type that operate in a filtering mode, a first stage flush mode and a bistage backwash mode are improved by the use in the first, upflow stage of particulate filter media consisting of solid particles with a specific gravity of between 3.5 and 4.4 and a size between 1.5 and 4 mm. and, preferably, in the second, downflow stage particulate filter media consisting of solid particles having a specific gravity of between 1.5 and 4.0 and sizes of between 0.3 and 1.5 mm and providing for upward passage of gas bubbles through the first stage media particles without appreciable expansion thereof during at least part of each flush and backwash mode of operation.

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First Claim