Microfiltration

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 micrometres (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.^[1]

History

Developed by Professor Richard Adolf Zsigmondy 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 pathogens 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.

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 fibers, flat sheet, tubular, spiral wound, hollow fine fiber or track etched.^[1] These filters are porous and allow water, monovalent species (Na+, Cl-), dissolved organic matter, small colloids and viruses through but do not allow particles, sediment, algae or large bacteria through.^[1]

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

Main article: Syringe filter

The most advanced syringe filters to date is 0.02 micrometres used for applications including removal of mycoplasma and enhanced bacterial removal.

Notes and references

1. ^ ^{a b c} [Crittenden, John; Trussell, Rhodes; Hand, David; Howe, Kerry and Tchobanoglous, George. Water Treatment Principles and Design, Edition 2. John Wiley and Sons. New Jersey. 2005.]

See also

• Syringe filter

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