Diatomaceous earth filters are made up of multiple leaf filter screens mounted on a shaft in a horizontal cylindrical tank. Flow is from both sides of each leaf into collector channels leading to the center of the shaft. DE is formed into a filter cake by precoating it on the leaves. In order to keep the cake permeable, it is fed continuously fed through the body.
When pressure drop across the cake gets too high, typically between 40-50 psi, backwash is initiated. Backwash may also be initiated when the cake becomes too thick to seal off the space between the leaves.
Backwash is accomplished by stopping filtration, draining the tank and removing the filter cake off both sides of the leaves as they are rotated.
This style of filter is the most capable of producing the cleanest water under ideal operation and is a very highly automated process. However, the process is also the most complex. Because the DE can leech through the system a cartridge filter is necessary down stream.
- Abbreviated as DE