Microfiltration
Encyclopedia
Microfiltration is a membrane technical
filtration
process which removes contaminants from a fluid
(liquid & gas) by passage through a microporous membrane
. A typical microfiltration membrane pore
size range is 0.1 to 10 micrometre
s (µm). Microfiltration is fundamentally different from reverse osmosis
and nanofiltration
because those systems use pressure as a means of forcing water to go from low pressure to high pressure. Microfiltration can use a pressurized system but it does not need to include pressure.
at the University of Göttingen, Germany
, in 1927, membrane filters were first commercially produced by Sartorius GmbH a few years later. Membrane filters found immediate application in the field of microbiology
and in particular in assessment of safe drinking water
. Further development of microfilters in the mid-1970s led by the United States Food and Drug Administration requirement for non-fibre releasing filters to be used in the production of injectable solutions. Microporous membranes are used by the micro-electronics
industry as an integral part of water production. Membrane filters are widely used in biotechnology
and food
and beverage applications where sterile
product is required.
Increasingly used in drinking water treatment
, it effectively removes major pathogen
s and contaminants such as Giardia lamblia
cysts, Cryptosporidium
oocysts, and large bacteria
. For this application the filter has to be rated for 0.2 µm or less. For mineral and drinking water bottlers, the most commonly used format is pleated cartridges usually made from polyethersulfone (PES) media. This media is asymmetric with larger pores being on the outside and smaller pores being on the inside of the filter media.
Microfiltration membranes were first introduced to the municipal water treatment market in 1987 and applied primarily to waters that were relatively easy to treat. These were cold, clear source waters that were susceptible to microbial contamination. Low pressure membranes were selected to remove turbidity
spikes and pathogens without chemical conditioning. As low pressure membranes increased in acceptance and popularity, users began to apply the technology to more difficult waters which contained more solids and higher levels of dissolved organic compounds. Some of these waters required chemical pretreatment, including pre-chlorination
. These shifts in water quality
triggered change in low pressure membrane technology. New products and processes were introduced to deal with higher solids and chemical compatibility.
s, flat sheet, tubular
, spiral wound, hollow fine fiber or track etched. These filters are porous and allow water
, monovalent species (Na+, Cl-), dissolved organic matter, small colloid
s and viruses through but do not allow particles, sediment
, algae
or large bacteria through.
Microfiltration systems are designed to remove suspended solids down to 0.1 micrometres in size, in a feed solution with up to 2-3% in concentration. It is very suitable for use in place of traditional clarifiers or as a pre-filter to a water recycling/recovery reverse osmosis system.
Membrane technology
The membrane technology covers all process engineering measures for the transport of substances between two fractions with the help of permeable membranes...
filtration
Filtration
Filtration is commonly the mechanical or physical operation which is used for the separation of solids from fluids by interposing a medium through which only the fluid can pass...
process which removes contaminants from a fluid
Fluid
In physics, a fluid is a substance that continually deforms under an applied shear stress. Fluids are a subset of the phases of matter and include liquids, gases, plasmas and, to some extent, plastic solids....
(liquid & gas) by passage through a microporous membrane
Semipermeable membrane
A semipermeable membrane, also termed a selectively permeable membrane, a partially permeable membrane or a differentially permeable membrane, is a membrane that will allow certain molecules or ions to pass through it by diffusion and occasionally specialized "facilitated diffusion".The rate of...
. A typical microfiltration membrane pore
Pore
- Animal biology and microbiology :* Sweat pore, an anatomical structure of the skin of humans used for secretion of sweat* Canal pore, an anatomical structure that is part of the lateral line sense system of some aquatic organisms...
size range is 0.1 to 10 micrometre
Micrometre
A micrometer , is by definition 1×10-6 of a meter .In plain English, it means one-millionth of a meter . Its unit symbol in the International System of Units is μm...
s (µm). Microfiltration is fundamentally different from reverse osmosis
Reverse osmosis
Reverse osmosis is a membrane technical filtration method that removes many types of large molecules and ions from solutions by applying pressure to the solution when it is on one side of a selective membrane. The result is that the solute is retained on the pressurized side of the membrane and...
and nanofiltration
Nanofiltration
Nanofiltration is a relatively recent membrane filtration process used most often with low total dissolved solids water such as surface water and fresh groundwater, with the purpose of softening and removal of disinfection by-product precursors such as natural organic matter and synthetic organic...
because those systems use pressure as a means of forcing water to go from low pressure to high pressure. Microfiltration can use a pressurized system but it does not need to include pressure.
History
Developed by Professor Richard Adolf ZsigmondyRichard Adolf Zsigmondy
Richard Adolf Zsigmondy was an Austrian-Hungarian chemist and Nobel laureate for chemistry known for his research in colloids. The crater Zsigmondy on the Moon is named in his honour....
at the University of Göttingen, 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...
, in 1927, membrane filters were first commercially produced by Sartorius GmbH a few years later. Membrane filters found immediate application in the field of microbiology
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...
and in particular in assessment of safe drinking water
Drinking water
Drinking water or potable water is water pure enough to be consumed or used with low risk of immediate or long term harm. In most developed countries, the water supplied to households, commerce and industry is all of drinking water standard, even though only a very small proportion is actually...
. Further development of microfilters in the mid-1970s led by the United States Food and Drug Administration requirement for non-fibre releasing filters to be used in the production of injectable solutions. Microporous membranes are used by the micro-electronics
Electronics manufacturing
The industrial electronics manufacturing process for the electronic assemblies found in many of today's electronic devices, is a multi-step process.-Component and PCB manufacturing:...
industry as an integral part of water production. Membrane filters are widely used in biotechnology
Biotechnology
Biotechnology is a field of applied biology that involves the use of living organisms and bioprocesses in engineering, technology, medicine and other fields requiring bioproducts. Biotechnology also utilizes these products for manufacturing purpose...
and food
Food processing
Food processing is the set of methods and techniques used to transform raw ingredients into food or to transform food into other forms for consumption by humans or animals either in the home or by the food processing industry...
and beverage applications where sterile
Asepsis
Asepsis is the state of being free from disease-causing contaminants or, preventing contact with microorganisms. The term asepsis often refers to those practices used to promote or induce asepsis in an operative field in surgery or medicine to prevent infection...
product is required.
Increasingly used in drinking water treatment
Water purification
Water purification is the process of removing undesirable chemicals, materials, and biological contaminants from contaminated water. The goal is to produce water fit for a specific purpose...
, it effectively removes major pathogen
Pathogen
A pathogen gignomai "I give birth to") or infectious agent — colloquially, a germ — is a microbe or microorganism such as a virus, bacterium, prion, or fungus that causes disease in its animal or plant host...
s and contaminants such as Giardia lamblia
Giardia lamblia
Giardia lamblia is a flagellated protozoan parasite that colonizes and reproduces in the small intestine, causing giardiasis. The giardia parasite attaches to the epithelium by a ventral adhesive disc, and reproduces via binary fission...
cysts, Cryptosporidium
Cryptosporidium
Cryptosporidium is a protozoan that can cause gastro-intestinal illness with diarrhea in humans.Cryptosporidium is the organism most commonly isolated in HIV positive patients presenting with diarrhea...
oocysts, and large 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...
. For this application the filter has to be rated for 0.2 µm or less. For mineral and drinking water bottlers, the most commonly used format is pleated cartridges usually made from polyethersulfone (PES) media. This media is asymmetric with larger pores being on the outside and smaller pores being on the inside of the filter media.
Microfiltration membranes were first introduced to the municipal water treatment market in 1987 and applied primarily to waters that were relatively easy to treat. These were cold, clear source waters that were susceptible to microbial contamination. Low pressure membranes were selected to remove turbidity
Turbidity
Turbidity is the cloudiness or haziness of a fluid caused by individual particles that are generally invisible to the naked eye, similar to smoke in air. The measurement of turbidity is a key test of water quality....
spikes and pathogens without chemical conditioning. As low pressure membranes increased in acceptance and popularity, users began to apply the technology to more difficult waters which contained more solids and higher levels of dissolved organic compounds. Some of these waters required chemical pretreatment, including pre-chlorination
Chlorination
Chlorination is the process of adding the element chlorine to water as a method of water purification to make it fit for human consumption as drinking water...
. These shifts in water quality
Water quality
Water quality is the physical, chemical and biological characteristics of water. It is a measure of the condition of water relative to the requirements of one or more biotic species and or to any human need or purpose. It is most frequently used by reference to a set of standards against which...
triggered change in low pressure membrane technology. New products and processes were introduced to deal with higher solids and chemical compatibility.
Process
Microfiltration is the process of filtration with a micrometre sized filter. The filters can be in a submerged configuration or a pressure vessel configuration. They can be hollow fiberFiber
Fiber is a class of materials that are continuous filaments or are in discrete elongated pieces, similar to lengths of thread.They are very important in the biology of both plants and animals, for holding tissues together....
s, flat sheet, tubular
Tubular
Tubular may refer to:*the form of a cylinder or tube*Tubular, a television-related entertainment blog on the Houston Chronicle website*Tubular, a level in the video game Super Mario World...
, spiral wound, hollow fine fiber or track etched. These filters are porous and allow 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...
, monovalent species (Na+, Cl-), dissolved organic matter, small colloid
Colloid
A colloid is a substance microscopically dispersed evenly throughout another substance.A colloidal system consists of two separate phases: a dispersed phase and a continuous phase . A colloidal system may be solid, liquid, or gaseous.Many familiar substances are colloids, as shown in the chart below...
s and viruses through but do not allow particles, sediment
Sediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....
, algae
Algae
Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...
or large bacteria through.
Microfiltration systems are designed to remove suspended solids down to 0.1 micrometres in size, in a feed solution with up to 2-3% in concentration. It is very suitable for use in place of traditional clarifiers or as a pre-filter to a water recycling/recovery reverse osmosis system.
Syringe filters
The most advanced syringe filters to date is 0.02 micrometres used for applications including removal of mycoplasma and enhanced bacterial removal.External links
- www.siemens.com/water- Siemens Water Technologies Inc. Specialists in Microfiltration Systems
- www.kontekecology.com-Kontek Ecology Systems Inc. Specialists in wastewater treatment
- www.microfiltusa.com-Microfilt Sales and Service LLC. Specialists in Sanitary Filter Housings
- www.sartorius.com Sartorius first commercial membrane filter manufacturer and leader in filtration
- www.bioprocessresources.com Compressed and comprehensive information on membrane filtration