Sand filter

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Sand filter

Sand filters are used for water purification

Water purification

This article discusses large scale, municipal water purification. For portable/emergency water purification, see Portable water purification.Water purification is the process of removing undesirable chemical and biological contaminants from raw water....
. There are three main types;

rapid (gravity) sand filters
Rapid sand filter

The rapid sand filter or rapid gravity filter is a type of filter used in water purification and is commonly used in municipal water treatment facilities....
upflow sand filters
slow sand filter
Slow sand filter

Slow sand filters are used in water purification for treating raw water to produce a potable product. They are typically 1 to 2 metres deep, can be rectangular or cylindrical in cross section and are used primarily to treat surface water....
s

All three methods are used extensively in the water industry throughout the world. The first two require the use of flocculant chemicals to work effectively whilst slow sand filters can produce very high quality water free from pathogens, taste and odour without the need for chemical aids.

Passing flocculated

Flocculation

Flocculation is a process where a solute comes out of solution in the form of floc or flakes. The action differs from Precipitation in that the solute coming out of solution does so at a concentration generally below its solubility limit in the liquid....
water through a rapid gravity sand filter strains out the floc

Floc

Floc can refer to either:* FLOC is the abbreviation for the Farm Labor Organizing Committee, a labor unionor* Floc is flake of precipitate that comes out of solution during the process of flocculation...
and the particles trapped within it reducing numbers of bacteria

Bacteria

The Bacteria are a large group of unicellular microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals....
and removing most of the solids.

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Encyclopedia

Sand filters are used for water purification

Water purification

rapid (gravity) sand filters
Rapid sand filter

The rapid sand filter or rapid gravity filter is a type of filter used in water purification and is commonly used in municipal water treatment facilities....
upflow sand filters
slow sand filter
Slow sand filter

Slow sand filters are used in water purification for treating raw water to produce a potable product. They are typically 1 to 2 metres deep, can be rectangular or cylindrical in cross section and are used primarily to treat surface water....
s

Flocculation

Floc

Bacteria

Sand

Sand is a naturally occurring granular material composed of finely divided rock and mineral particles.As the term is used by geologists, sand particles range in diameter from 0.0625 to 2 millimeters....
of varying grades. Where taste and odour may be a problem (organoleptic impacts), the sand filter may include a layer of activated carbon

Activated carbon

Activated carbon, also called activated charcoal or activated coal, is a form of carbon that has been processed to make it extremely porous and thus to have a very large surface area available for adsorption or chemical reactions....
to remove such taste and odour.

Sand filters become clogged with floc after a period in use and they are then backwashed or pressure washed to remove the floc. This backwash water is run into settling tanks so that the floc can settle out and it is then disposed of as waste material. The supernatant water is then run back into the treatment process or disposed off as a waste-water stream. In some countries the sludge may be used as a soil conditioner

Soil conditioner

A soil conditioner, also called a soil amendment, is a material added to soil to improve plant growth and health. The type of conditioner added depends on the current soil composition, climate, and the type of plant....
. Inadequate filter maintenance has been the cause of occasional drinking water contamination.

Sand filters are occasionally used in the treatment of sewage

Sewage

Sewage is the mainly liquid waste containing some solids produced by humans which typically consists of washing water, feces, urine, laundry waste and other material which goes down Plumbing fixture from households and industry....
as a final polishing stage (see Sewage treatment

Sewage treatment

Sewage treatment, or domestic wastewater treatment, is the process of removing contaminants from wastewater and household sewage, both runoff and domestic....
). In these filters the sand traps residual suspended material and bacteria and provides a physical matrix for bacterial decomposition of nitrogenous material, including ammonia

Ammonia

Ammonia is a chemical compound with the chemical formula nitrogenhydrogen. It is normally encountered as a gas with a characteristic pungent odor....
and nitrates, into nitrogen

Nitrogen

Nitrogen is a chemical element that has the symbol N and atomic number 7 and atomic mass 14.00674?. Elemental nitrogen is a colorless, odorless, tasteless and mostly inert diatomic gas at standard conditions, constituting 78% by volume of Earth's atmosphere....
gas.

Sand filter

See also