A Berkefeld filter [1] is a water filter made of diatomaceous earth ( Kieselguhr ). It was invented in Germany in 1891, and by 1922 was being marketed in the United Kingdom by the Berkefeld Filter Co. [2] 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. [3] [4]
The filter housing consists of two metal or plastic cylinders 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 diatomaceous earth ( Kieselguhr) filter columns (filter candles). The water is forced through the filters by gravity, [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 a carbon core to act as a deodorizing adsorbent. [6] 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 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 the diameter of the pores in the ceramic material:
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. [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.
Some of the first Berkefeld filters were used during the 1892 cholera epidemic in Hamburg. [8]
Filtration is a physical separation process that separates solid matter and fluid from a mixture using a filter medium that has a complex structure through which only the fluid can pass. Solid particles that cannot pass through the filter medium are described as oversize and the fluid that passes through is called the filtrate. Oversize particles may form a filter cake on top of the filter and may also block the filter lattice, preventing the fluid phase from crossing the filter, known as blinding. The size of the largest particles that can successfully pass through a filter is called the effective pore size of that filter. The separation of solid and fluid is imperfect; solids will be contaminated with some fluid and filtrate will contain fine particles. Filtration occurs both in nature and in engineered systems; there are biological, geological, and industrial forms.
Filter paper is a semi-permeable paper barrier placed perpendicular to a liquid or air flow. It is used to separate fine solid particles from liquids or gases.
Water purification is the process of removing undesirable chemicals, biological contaminants, suspended solids, and gases from water. The goal is to produce water that is fit for specific purposes. Most water is purified and disinfected for human consumption, but water purification may also be carried out for a variety of other purposes, including medical, pharmacological, chemical, and industrial applications. The history of water purification includes a wide variety of methods. The methods used include physical processes such as filtration, sedimentation, and distillation; biological processes such as slow sand filters or biologically active carbon; chemical processes such as flocculation and chlorination; and the use of electromagnetic radiation such as ultraviolet light.
A nephelometer or aerosol photometer is an instrument for measuring the concentration of suspended particulates in a liquid or gas colloid. A nephelometer measures suspended particulates by employing a light beam and a light detector set to one side of the source beam. Particle density is then a function of the light reflected into the detector from the particles. To some extent, how much light reflects for a given density of particles is dependent upon properties of the particles such as their shape, color, and reflectivity. Nephelometers are calibrated to a known particulate, then use environmental factors (k-factors) to compensate lighter or darker colored dusts accordingly. K-factor is determined by the user by running the nephelometer next to an air sampling pump and comparing results. There are a wide variety of research-grade nephelometers on the market as well as open source varieties.
Sterilization refers to any process that removes, kills, or deactivates all forms of life and other biological agents present in or on a specific surface, object, or fluid. Sterilization can be achieved through various means, including heat, chemicals, irradiation, high pressure, and filtration. Sterilization is distinct from disinfection, sanitization, and pasteurization, in that those methods reduce rather than eliminate all forms of life and biological agents present. After sterilization, an object is referred to as being sterile or aseptic.
A water filter removes impurities by lowering contamination of water using a fine physical barrier, a chemical process, or a biological process. Filters cleanse water to different extents, for purposes such as: providing agricultural irrigation, accessible drinking water, public and private aquariums, and the safe use of ponds and swimming pools.
Diatomaceous earth, diatomite, celite 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 mm to less than 1 μm, but typically 10 to 200 μm. Depending on the granularity, this powder can have an abrasive feel, similar to pumice powder, and has a low density as a result of its high porosity. The typical chemical composition of oven-dried diatomaceous earth is 80–90% silica, with 2–4% alumina, and 0.5–2% iron oxide.
Sand filters are used as a step in the water treatment process of water purification.
A plasmid preparation is a method of DNA extraction and purification for plasmid DNA. It is an important step in many molecular biology experiments and is essential for the successful use of plasmids in research and biotechnology. Many methods have been developed to purify plasmid DNA from bacteria. During the purification procedure, the plasmid DNA is often separated from contaminating proteins and genomic DNA.
Portable water purification devices are self-contained, easily transported units used to purify water from untreated sources for drinking purposes. Their main function is to eliminate pathogens, and often also of suspended solids and some unpalatable or toxic compounds.
A syringe filter is a single-use filter cartridge. It is attached to the end of a syringe for use. Syringe filters may have Luer lock fittings, though not universally so. The use of a needle is optional; where desired it may be fitted to the end of the syringe filter.
Ceramic water filters (CWF) are an inexpensive and effective type of water filter that rely on the small pore size of ceramic material to filter dirt, debris, and bacteria out of water. This makes them ideal for use in developing countries, and portable ceramic filters are commonly used in backpacking.
Aquarium filters are critical components of both freshwater and marine aquaria. Aquarium filters remove physical and soluble chemical waste products from aquaria, simplifying maintenance. Furthermore, aquarium filters are necessary to support life as aquaria are relatively small, closed volumes of water compared to the natural environment of most fish.
Bioaerosols are a subcategory of particles released from terrestrial and marine ecosystems into the atmosphere. They consist of both living and non-living components, such as fungi, pollen, bacteria and viruses. Common sources of bioaerosols include soil, water, and sewage.
A Chamberland filter, also known as a Pasteur–Chamberland filter, is a porcelain water filter invented by Charles Chamberland in 1884. It was developed after Henry Doulton's ceramic water filter of 1827. It is similar to the Berkefeld filter in principle.
Filtered beer refers to any ale, lager, or fermented malt beverage in which the sediment left over from the brewing process has been removed. Ancient techniques included the use of straw mats, cloth, or straws, and frequently left some sediment in the drink. Modern filtration, introduced at the end of the 19th century, uses a mechanical process that can remove all sediment, including yeast, from the beer. Such beer is known as bright beer and requires force carbonation before bottling or serving from a keg. In the United Kingdom, a beer which has been filtered in the brewery is known as "brewery-conditioned", as opposed to unfiltered cask ales.
Spa filters work continuously to keep debris and sediments from the water in a spa pool.
Membrane technology encompasses the scientific processes used in the construction and application of membranes. Membranes are used to facilitate the transport or rejection of substances between mediums, and the mechanical separation of gas and liquid streams. In the simplest case, filtration is achieved when the pores of the membrane are smaller than the diameter of the undesired substance, such as a harmful microorganism. Membrane technology is commonly used in industries such as water treatment, chemical and metal processing, pharmaceuticals, biotechnology, the food industry, as well as the removal of environmental pollutants.
Water chlorination is the process of adding chlorine or chlorine compounds such as sodium hypochlorite to water. This method is used to kill bacteria, viruses and other microbes in water. In particular, chlorination is used to prevent the spread of waterborne diseases such as cholera, dysentery, and typhoid.
Diatomaceous earth (DE) filtration is a special filtration process that removes particles from liquids as it passes through a layer of fossilized remains of microscopic water organism called diatoms. These diatoms are mined from diatomite deposits which are located along the Earth's surface as they have accumulated in sediment of open and moving bodies of water. Obtained diatomaceous earth is then purified using acid leaching or liquid-liquid extraction in order for it to be used in any form of application. The process of D.E. filtration is composed of three main stages: pre-coating, body feed, and cleaning.