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 most 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.
Diatomaceous earth (D.E.) is a naturally occurring sedimentary rock with an abrasive, chalk-like feel. This light rock is white to off-white and crumbles easily into powder. Silica makes up the major role of the rock’s typical chemical composition at eighty-five percent, but it also contains sodium, magnesium, and iron. D.E. is made from the fossils of diatoms, a type of algae whose size range from five micrometers to one hundred micrometers. The diatomate composite has no odor or taste and is chemically inert, which makes the diatomaceous earth filter an attractive option for filtering drinking water as well as other consumed liquids, such as syrup or beer.
The diatomaceous earth filter was first used in WWII as a drinking water filter for the United States Army. The filter had to be lightweight to fit the needs of mobile army operations, but still able to produce clean water. The U.S. Army Engineer Research and Development Laboratories (ERDL) came up with the D.E. filter which, after the war, was used in swimming pools. The filter then came into use as a drinking water filter, especially for small municipalities.
A diatomaceous earth filter mechanically strains water of its contaminants. A D.E. cake is attached to the filter leaves and flushed through the filter system so that a thin layer of D.E. accumulates on the filter septum or grid. The septum is plastic or wire cloth pulled over a steel frame. Once the pre-coat layer of D.E. has built up on the septum, another low dose D.E. is introduced to the system. The diatomaceous earth filter then makes unwanted particulate matter part of the filter and passes clean water through its microscopic pores.
Over time, the filter causes a loss of head flow. Because the diatomaceous earth filter works by adding matter to the pre-coat layer, eventually the water is obstructed so that even clean water cannot pass through. When this happens, the filter needs to be cleaned. This is achieved by detaching the cake with high pressure spray and cleaning the filter. Used D.E. is usually disposed of and a new D.E. cake is attached to the filter leaves and flushed through to create a new pre-coat layer.
There are two types of diatomaceous earth filters: the pressure filter and the vacuum filter. Pressure filters are enclosed in pressure chambers and have a pump or a source of high pressure water at the site of inflow. Vacuum filters are open to the atmosphere and have a pump located at the effluent side of the filter. D.E. filters are attractive to many operators because they are relatively cheap to install and do not use chemicals.