ABerkefeld filter[1] is awater filter made ofdiatomaceous earth (Kieselgur). It was invented in Germany in 1891, and by 1922 was being marketed in theUnited Kingdom by the Berkefeld Filter Co.[2] Berkefeld was the name of the owner of themine inHanover,Germany, where the ceramic material was obtained.
The Berkefeld is a good bacterial water filter used inmicrobiological laboratories, in homes and out in the field.[3][4]
The filter housing consists of twocylinders 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 withdiatomaceous earth (Kieselgur) filter columns (filter candles). The water is forced through the filters bygravity,[5] and then trickles down to the lower cylinder where it is stored and tapped off as required.
Some types of filters are fitted with acarbon core to act as a deodorizingadsorbent.[6] They may also be impregnated withsilver to inhibitbacterial growth. Some types, depending on their grade of porosity, also remove certain microscopicfungi and particulate matter. The filters without silver impregnation are sterilized byautoclaving or bysteam sterilizer after a thorough cleaning.
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.[7]
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.
The filters are classified according to thediameter of the pores in the ceramic material:
The Berkefeld is a cheap, portable and efficient bacterial filter in general, though it does not removeviruses likeHepatitis A and some bacteria such asmycoplasma.[6] 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.[5] These are very durable filters, and the filter elements may be cleaned over 100 times before requiring replacement.[8] Some of the first Berkefeld filters were used during the 1892cholera epidemic inHamburg.[9]