In order to ensure the safety of our drinking water, water filtration systems offer protection from various bacteria and other harmful products that may exist within our water supply. While some filter designs are more suitable for the removal of certain pathogens compared to others, it is essential to understand which porous materials are most appropriate for your home.
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Preventing Diseases in the Home
According to the United States Centers for Disease Control and Prevention (CDC), water filters with a pore size of 1 micron or less can remove microbes with a diameter of 1 micron or greater.
Within the micron filter category are two types of filters known as “absolute 1 micron” filters and “nominal 1 micron” filters1. The absolute 1 micron filter has been shown to remove Cryptosporidium, a microscopic parasite known to cause diarrheal disease upon ingestion, more consistently than a nominal filter.
Similarly, filters that have the words “reverse osmosis” on the label are able to protect against Cryptosproidium or Giardia, a similar microscopic parasite known to cause diarrheal illnesses1.
Carbon Water Filtration
Filters labeled with either “NSF 53” or “NSF 58” have a confirmed absolute pore size of 1 micron or smaller. The most common technology with this standard of filtration for both NSF 53 and NSF 58 filters is carbon filtration. The two types of carbon water filtration systems include carbon block or carbon granular activated filters, and these filters can be configured with other systems for enhanced filtration.
Carbon block successfully removes gaseous and low weight molecules such as chlorine, herbicides, pesticides, and certain volatile organic compounds2. As water moves through the micro pores within the carbon block filter, organics within the water adhere to, or “hang on”, to the carbon through molecular bonds.
Activated carbon filtration systems are often made from a variety of carbon based materials such as coal, petroleum, nutshells, and fruit pits2. Within this category of activated carbon filtration systems exist granular activated carbon.
Granular activated carbon is formed following the treatment of charcoal in high temperatures and steam in the absence of oxygen, in order to produce extremely porous granules with a high surface area. One pound of granular activated carbon has a total surface area of about 125 acres, providing each filter the ability to handle large amounts of water before needing to be replaced2.
Combining Carbon Filtration with Reverse Osmosis
Carbon filtration can also be combined with reverse osmosis to enhance the filtration capability against lighter, low molecular weight volatile organics such as trihalomethanes (THM’s), trichloroethylene (TCE), chlorine, and relating byproducts.
Reverse osmosis membranes, often referred to as thin-film composite membranes, are typically composed of three crucial layers for filtration. A thin polyamide layer less than 200 nm thick is deposited on top of a polyethersulfone or polysulfone porous layer of about 50 microns thickness, which is placed on top of a non-woven fabric support sheet3.
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This three-layer system, particularly the polyamide top layer, allows for the high rejection of undesirable compounds present in water, and is relatively impermeable to typically filterable molecules. For example, volatile organic compounds are often too small to be removed by the traditional straining methods, therefore removal by a carbon filter with reverse osmosis is the most effective2.
Alternative Filtration Materials
While carbon filtration systems are often regarded as the most sensitive ways to filter and purify water, other porous materials that can be used include fiber and plastic. Essentra Porous Technologies’ Nylon Melt Blown Filter Cartridge is a fibrous material that provides optimized dirt-holding capacity, with increased flexibility and durability4.
The fiber material within this nylon filter is particularly useful in the filtration of hydrocarbons, special and organic chemicals, paints, inks, solvents, and other unwanted compounds. Produced from polyethylene polymers, Essentra also offer porous plastic tubes for water purification purposes.
References and Further Reading
- A Guide to Water Filters
- Carbon Filtration
- Thin-film Composite Membrane
- Water & Industrial Filtration