Diatomaceous Earth (DE) filtration and related equipment are alternatives to filter elements that can be used to handle higher flow rates. In fact, some suppliers offer disposable cartridges already coated with DE. DE is a granular material composed of the skeletal remains of diatoms. Before it can be used as a filter medium, it must be deposited in a dense layer on a porous substrate, forming a filter cake. If the filter cake is not uniform diatomite , the filter may be partially shorted. The substrate is a cloth-like material, usually polypropylene, in the form of a long tube or double-sided flat plate (leaf). This material, often called a sleeve, is removable because it can be cleaned or replaced periodically. This cloth has no structural strength and must be supported by a core structure. There are basically two types of DE units. One is called a gravity device, where the supply side is at atmospheric pressure. This type is powered by a partial vacuum on the discharge side. Another type is a pressure DE unit driven by a pump on the supply side. Both types require a preparation cycle to build up the DE layer on the porous substrate by adding DE to the supply side in a closed loop. Once in run mode, filtration runs can often be extended considerably by continuously adding small amounts of DE to unfiltered water. Filter operation varies widely and depends on conditions, but is usually designed to run typically around 24 hours. Once dirty, the DE filter is backflushed and builds a new filter cake to complete the cleaning cycle. The pressure required for backflushing is very low since the filter cake is held on the substrate only by operating pressure or partial vacuum. The performance of DE filters depends on the properties of the DE material used, equipment, operating conditions, and maintenance procedures (Spotte, 1979). DE equipment is expensive to own and operate, sometimes requiring extensive repair and labor.