Berkefeld filter

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A Bakerfeld filter^[1] is British water filter made up of diatomaceous earth (called "Kieselguhr"[1] taken from the name of the mine in Hanover, Germany where it was mined) used since 1891. It was named after the owner of the mine.

It is a good bacterial water filer used in Microbiological laboratories and, home water filter, and also in the field.^[2]^[3]

1 Design and mode of action
2 Types
3 Usefulness
4 References

[edit] Design and mode of action

Schematic diagram of a Bakerfeld filter

Usually these are made up of two metal or plastic cylinders sitting on top of each other. The upper one has a lid opening which, one can fill it with water. The upper cylinder communicates with the lower through a channel in the intervening guarding which sits one or more porcelain filter columns. The water, after purification trickles down to the lower chamber and gets stored. It is tapped out as and when required.

Sometimes the filters are fitted with a carbon core^[4] to act as a deodorizing adsorbent. They may also have a silver impregnation to inhibit bacterial growth. They also remove certain microscopic fungi and particulate matter depending on its grade of porosity.

These filters act as "gravity filters." Water gravitates through the porous material from the upper to the lower container while being cleaned of particulate matter that get trapped in the porcelain.^[5]

It is sterilized by autoclaving or by steam sterilizer, after thorough cleaning.

[edit] Types

Depending on the diameter of the pores of the earth, these are of the following types:

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

[edit] Usefulness

^[6] It is cheap, portable, and a good bacterial filter in general though it is not a filter for viruses like Hepatitis A and mycoplasma. Some companies claim^[7] that they filter out from between 100% of particles above 0.9 micron to 98% of particles above 0.5 micron in diameter. These are very durable filters and the filter elements may be cleaned over 100 times before their replacement becomes necessary.