A Berkefeld filter is a water filter made of

diatomaceous earth Diatomaceous earth (), diatomite (), or kieselgur/kieselguhr is a naturally occurring, soft, siliceous sedimentary rock that can be crumbled into a fine white to off-white powder. It has a particle size ranging from more than 3 μm to le ...

('' Kieselguhr''). It was invented in Germany in 1891, and by 1922 was being marketed in the United Kingdom by the Berkefeld Filter Co. Berkefeld was the name of the owner of the mine in Hanover, Germany, where the ceramic material was obtained. The Berkefeld is a good bacterial water filter used in microbiological laboratories, in homes and out in the field.

Design and mode of action

The filter housing consists of two metal or plastic

cylinders A cylinder (from ) has traditionally been a three-dimensional solid, one of the most basic of curvilinear geometric shapes. In elementary geometry, it is considered a prism with a circle as its base. A cylinder may also be defined as an infini ...

sitting one on top of the other. The upper one has a lid and can be filled with impure water. In the bottom of the upper cylinder are one or more holes fitted with

('' Kieselguhr)'' filter columns (filter candles). The water is forced through the filters by gravity,SafeTrek Survival Foods - Dried and Dehydrated One-Year and Four-Year Packages
and then trickles down to the lower cylinder where it is stored and tapped off as required. Some types of filters are fitted with a carbon core to act as a deodorizing adsorbent.FAQ from British Berkefeld on New Millennium Concepts
/ref> They may also be impregnated with silver to inhibit bacterial 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 or by

steam sterilizer An autoclave is a machine used to carry out industrial and scientific processes requiring elevated temperature and pressure in relation to ambient pressure and/or temperature. Autoclaves are used before surgical procedures to perform sterilizat ...

after a thorough cleaning.

Berkey Filters

New Millenium Concepts (NMC) Ltd. received a license to distribute British Berkefeld filters in North America. However, they developed their own purification element in 2003, called the "Black Berkey," which is used in "Berkey" water filters. NMC's Black Berkey purification elements employ a mix of six different filtration media, whereas the British Berkefeld water filter's purification elements were composed primarily of diatomaceous earth.

Rainfresh Ceramic Filters

In the mid 1990s Envirogard Products Limited in Canada developed its own proprietary version of the Berkefeld ceramic filter that would be marketed under the brand Rainfresh. These ceramic filters also utilize diatomaceous earth, but also include a unique blend of other materials that result in a 0.3-micron absolute filter that provides >7-log reduction of pathogenic bacteria.

Types

The filters are classified according to the diameter 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 viruses like Hepatitis A and some bacteria such as

mycoplasma ''Mycoplasma'' is a genus of bacteria that, like the other members of the class ''Mollicutes'', lack a cell wall around their cell membranes. Peptidoglycan (murein) is absent. This characteristic makes them naturally resistant to antibiotics ...

. 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. Some of the first Berkefeld filters were used during the 1892

cholera Cholera is an infection of the small intestine by some strains of the bacterium ''Vibrio cholerae''. Symptoms may range from none, to mild, to severe. The classic symptom is large amounts of watery diarrhea that lasts a few days. Vomiting and ...

epidemic in Hamburg.

References

{{reflist

External links

Woder Water Filter
Microbiology equipment Water filters