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Diatomaceous earth is comprised of the fossilized remains of small, aquatic organisms known as diatoms. The fossilized skeletons are made of a natural compound known as silica. Over millennia, diatoms accrued in the sediment of various bodies of water. Today, silica deposits are extracted from these areas.
There are two fundamental kinds of diatomaceous earth: food grade, which is acceptable for consumption, and filter grade, which is toxic but has numerous industrial uses. Authorized for usage by the EPA, USDA and FDA, food grade diatomaceous earth has 0.5 to 2% crystalline silica and is primarily used as an insecticide and an anti-caking agent in the food production industry. Filter grade, or non-food grade, diatomaceous earth can include an excess of 60% crystalline silica. It is toxic to humans but has numerous industrial uses, including use in water filtration and as an ingredient in dynamite.
Silica is very common in nature and comprises 26% of the earth's crust by weight. While silica is fairly easy to locate, diatomaceous earth is a concentrated source of silica, which makes it distinctive. Commercially accessible diatomaceous earth is said to include 80 to 90% silica, many other trace minerals and small quantities of iron oxide.
Diatomaceous earth in commercial products
Products containing diatomaceous earth are most frequently in the form of dust. Other formulations consist of wettable powders and pressurized liquids. At present, there are more than 100 items registered for indoor and outdoor use. Its most common use is as a non-toxic insecticide. Diatomaceous earth insecticides are commonly used against bed bugs, crickets, cockroaches, fleas, spiders, ticks and other pests.
Diatomaceous earth does not have to be consumed by insects to be effective. It causes them to dehydrate and die by soaking up the oils and fats from the insect's exoskeleton. Its sharp edges are coarse, accelerating the process. It is effective as a pesticide provided that it is kept dry and undisturbed.
There are also many non-pesticide products that include diatomaceous earth., such as cosmetics, toothpastes, foods, medicines, rubbers, paints and filters. The FDA lists diatomaceous earth as "Generally Recognized as Safe.”
Diatomaceous earth in filtration
Diatomaceous earth is also used in a common filtration method, in which it is applied to precoat a mesh display screen (known as a septum) ahead of each filtration. Diatomaceous earth filters normally have lesser costs and require less overhead than other standard filters. They are easy to use and effective for the elimination of cysts, algae and asbestos fibres. The use of diatomaceous earth filters is more labour intensive than with standard filters and diatomaceous earth filters are not appropriate for taking care of large changes in influent water quality.
Diatomaceous earth filters are the best option to treat waters with small bacterial counts and low turbidities. Coagulant and filter aid can be necessary to enhance filtrate quality. Effluent water quality of diatomaceous earth filtration is determined by influent water quality and the quality of diatomaceous earth being used.
Diatomaceous earth filtration can be defined as a three-step sequence. First, a filter cake or precoat of approximately 1/8-in. is laid down on the septum. Second, a small quantity of diatomaceous earth is fed to preserve the porosity of the precoat as filtration begins. Straining occurs mostly inside the filter cake that has established on the septum. Third, when maximum headloss is attained the filter cake is taken from the septa through backwash. Thus, diatomaceous earth filter media is purged and wasted at the conclusion of each filter run.
There are three primary kinds of diatomaceous earth filters: vacuum, pressure and horizontal plate filters. All three types are based on the same practice of pre-coating the septum. The changes in equipment are the location of the filter pump and the disposal processes of spent diatomaceous earth.
Vacuum filters are set up in a way that makes them capable of handling a large quantity of surface area for such a relatively small unit. Pressure filters are typically used for smaller installations. Horizontal plate filtration is a kind of pressure filtration normally used in compact applications where removal of wash water is an issue.