A Berkefeld filter is a water filter made of diatomaceous earth

Diatomaceous earth

Diatomaceous earth also known as diatomite or kieselgur/kieselguhr, is a naturally occurring, soft, siliceous sedimentary rock that is easily crumbled into a fine white to off-white powder. It has a particle size ranging from less than 1 micrometre to more than 1 millimetre, but typically 10 to...

 or Kieselguhr. It was invented in Germany in 1891, and by 1922 was being marketed in the United Kingdom

United Kingdom

The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

 by the Berkefeld Filter Co. Berkefeld was the name of owner of the mine

Mining

Mining is the extraction of valuable minerals or other geological materials from the earth, from an ore body, vein or seam. The term also includes the removal of soil. Materials recovered by mining include base metals, precious metals, iron, uranium, coal, diamonds, limestone, oil shale, rock...

 in Hanover

Hanover

Hanover or Hannover, on the river Leine, is the capital of the federal state of Lower Saxony , Germany and was once by personal union the family seat of the Hanoverian Kings of Great Britain, under their title as the dukes of Brunswick-Lüneburg...

, Germany

Germany

Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...

 where the ceramic material was obtained.

The Berkefeld is a good bacterial water filter

Filter (water)

A water filter removes impurities from water by means of a fine physical barrier, a chemical process or a biological process. Filters cleanse water to various extents for irrigation, drinking water, aquariums, and swimming pools.-Methods of filtration:...

 used in microbiological

Microbiology

Microbiology is the study of microorganisms, which are defined as any microscopic organism that comprises either a single cell , cell clusters or no cell at all . This includes eukaryotes, such as fungi and protists, and prokaryotes...

 laboratories, in homes and out in the field.

Design and mode of action

The filter housing consists of two metal

Metal

A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...

 or plastic

Plastic

A plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...

 cylinders

Cylinder (geometry)

A cylinder is one of the most basic curvilinear geometric shapes, the surface formed by the points at a fixed distance from a given line segment, the axis of the cylinder. The solid enclosed by this surface and by two planes perpendicular to the axis is also called a cylinder...

 sitting one on top of the other. The upper one has a lid and can be filled with impure water

Water

Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

. In the bottom of the upper cylinder are one or more holes fitted with porcelain

Porcelain

Porcelain is a ceramic material made by heating raw materials, generally including clay in the form of kaolin, in a kiln to temperatures between and...

 filter columns. The water is forced through the filters by gravity, and then trickles down to the lower cylinder where it is stored and tapped off as required.

Some types of filter are fitted with a carbon

Carbon

Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

 core to act as a deodorizing adsorbent. They may also be impregnated with silver

Silver

Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...

 to inhibit bacteria

Bacteria

Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

l growth. Some types, depending on their grade of porosity, also remove certain microscopic fungi and particulate matter.

The filters without silver impregnation are sterilized by autoclaving

Autoclave

An autoclave is an instrument used to sterilize equipment and supplies by subjecting them to high pressure saturated steam at 121 °C for around 15–20 minutes depending on the size of the load and the contents. It was invented by Charles Chamberland in 1879, although a precursor known as the...

 or by steam sterilizer after thorough cleaning.

Types

The filters are classified according to the diameter

Diameter

In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints are on the circle. The diameters are the longest chords of the circle...

 of the pores in the ceramic material:

• V (Viel) - Coarsest pores
• N (Normal) - Intermediate sized pores
• W (Wenig) - Finest pores

Usefulness

The Berkefeld is a cheap, portable and efficient bacterial filter in general, though it does not remove virus

Virus

A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...

es like Hepatitis A

Hepatitis A

Hepatitis A is an acute infectious disease of the liver caused by the hepatitis A virus , an RNA virus, usually spread the fecal-oral route; transmitted person-to-person by ingestion of contaminated food or water or through direct contact with an infectious person...

 and mycoplasma

Mycoplasma

Mycoplasma refers to a genus of bacteria that lack a cell wall. Without a cell wall, they are unaffected by many common antibiotics such as penicillin or other beta-lactam antibiotics that target cell wall synthesis. They can be parasitic or saprotrophic. Several species are pathogenic in humans,...

. Some companies claim that they filter out from between 100% of particles above 0.9 micrometre to 98% of particles above 0.5 micrometre in diameter. These are very durable filters and the filter elements may be cleaned over 100 times before requiring replacement.