What is a diatomaceous earth filter? (with photos)

Diatomaceous earth filters are often used in swimming pools.

A diatomaceous earth filter is a filter, usually for swimming pools or drinking water, made of diatomaceous earth. The filter is the most common and efficient filter on the market. It can remove algae, cysts and asbestos from water and is approved by the Environmental Protection Agency (EPA) as a method of filtering drinking water. It is not as effective, however, at removing color and other dissolved constituents.

Drinking water can be filtered with diatomaceous earth.

Diatomaceous earth (DE) is a naturally occurring sedimentary rock with a chalk-like abrasive feel. This clear rock is white to off-white and easily crumbles into powder. Silica forms the main role of the typical chemical composition of the rock at eighty-five percent, but it also contains sodium, magnesium and iron. DE is made from fossils of diatoms, a type of algae whose size ranges from five to one hundred micrometers. Diatomaceous composite has no odor or taste and is chemically inert, which makes the diatomaceous earth filter an attractive option for filtering drinking water and other consumed liquids such as syrup or beer.

The diatomaceous earth filter was first used in World War II as a drinking water filter for the United States Army. The filter needed to be lightweight to meet the needs of Army mobile operations, yet still capable of producing clean water. The US Army Engineer Research and Development Laboratories (ERDL) created the DE filter which, after the war, was used in swimming pools. The filter started to be used as a drinking water filter, mainly in small towns.

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A diatomaceous earth filter mechanically removes water of its contaminants. A DE cake is attached to the filter sheets and released through the filter system so that a thin layer of DE accumulates in the septum or filter grid. The septum is plastic or metallic fabric pulled over a steel frame. After the DE precoat layer builds up in the septum, another low dose of DE is introduced into the system. The diatomaceous earth filter then turns unwanted particles into part of the filter and passes clean water through its microscopic pores.

Over time, the filter causes loss of charge flow. As the diatomaceous earth filter works by adding matter to the pre-coat layer, eventually the water is clogged so that not even clean water can pass through. When this happens, the filter needs to be cleaned. This is accomplished by detaching the cake with high pressure spray and cleaning the filter. Used DE is usually discarded and a new cake of DE is attached to the filter sheets and washed to create a new precoat layer.

There are two types of diatomaceous earth filters: the pressure filter and the vacuum filter. Pressure filters are placed in pressure chambers and have a pump or high pressure water source at the inlet location. Vacuum filters are open to the atmosphere and have a pump located on the effluent side of the filter. DE filters are attractive to many operators because they are relatively inexpensive to install and use no chemicals.

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