Last updated on March 05, 2007
This web outlines the technical, operating and managing aspects of home water purification systems. It describes the types of contaminants that will be removed by the different types of filter systems These systems are plumbed-in with separate faucets and are ordinarily installed under the kitchen sink or in close proximity to provide convenient use for drinking and cooking, and are called point of use systems (POU).
Reverse Osmosis (RO) Systems
For Removal Of A Large Variety Of Contaminants.
In RO systems water dissolves into and through a membrane while contaminant is rejected and concentrated waste goes to drain. There are two types of reverse osmosis membranes Thin Film Composite (TFC) and Cellulose Triacetate (CTA). TFC membranes have considerably higher contaminant rejection rate than CTA type but are prone to damage by chlorine and must be protected with a carbon prefilter. TFC are normally stored dry and CTA are stored in a biocide wetting solution and have a one year shelf life
RO systems have been found to remove arsenic, uranium, and radium, copper, lead, fluoride, antimony, barium, beryllium, cadmium, chromium, selenium, and thallium. A complete list along with further information may be found on the RO page.
Granular Activated Carbon(GAC)
For Removal of Synthetic Organic Chemicals.
GAC is most effective at removing organic contaminants. It is also effective at removing many synthetic organic compounds.The capacity to adsorb these chemical compounds varies and is dependent on their properties. GAC has the added benefit of improving taste, odor, and color. Systems performance and longevity are dependent on the amount of GAC used and quality of feed water. Carbon media is prone to microbial growth. Follow manufactures recommendations for replacement intervals. Further information may be found on the carbon page
Adsorptive Media
For Removal of Arsenic and Selenium
Adsorptive media includes activated alumina granular ferric hydroxide or other specialty iron-based media. Activated alumina is a hydrated aluminum oxide that has been heat-treated. Iron-based media is generated in a proprietary process that may consist of granules of ferric oxide or ferric hydroxide, activated alumina coated with iron, or natural minerals impregnated with a substantial quantity of ferric hydroxide.This type of treatment media is used for fluoride removal, arsenic (in an oxidized state) and selenium removal. Adsorptive media systems should be installed with sediment pre-filter to prevent fouling of the adsorptive media and should be changed per manufactures recommendations.
Ion Exchange
For Removal of Various Inorganic Chemicals Nitrate, Radium, and Uranium.
Ion Exchange (IX) can consist of anion exchange (AX) or cation exchange used in water softening (CX). IX achieves the selective removal of charged inorganic contaminants from water using an ion-specific resin. As water, containing undesired ionare exchanged with the undesired ions in the water. The resin is replaced periodically per manufacture recommendations. Further information on the cation process may be found on the softener page.
Ceramic Media
For Removal Of Cysts, Algae, And Asbestos
At the core of the ceramic filter element is Diatomaceous Earth, a fossil made up of tiny silicon shells left by trillions of microscopic,one celled algae called diatoms that have inhabited the waters of the earth for the last 150 million years. Odorless, tasteless, and chemically inert make DE ideal for filtering water for human consumption.
Ceramic Filters Are best suited to the treatment of low turbidity sources of water supply, DE filtration has shown a superior capability for the removal of pathogens. Results have shown that ceramic water filters maintain the microbiologic quality of their drinking water.
Carbon, or other media may be placed in the interior of a ceramic cylinder to assist with removing additional contaminates tastes and odors. The tight porosity of a ceramic serves as a flow restrictor ( ie pressure drop), increasing contact times, and can improve the effectiveness of the media.
Distillation
For Removal Of Lead, Copper, Sodium, Nitrates, Pesticides And Fungicides, Volatile Organic Contaminants, Unwanted Minerals, Chemicals, Organisms, And Tastes.
The processes: water is boiled and the steam enters a condenser where it is cooled and returned as distilled water. The impurities and dissolved solids that are left behind in the boiler are drained away. The distillation process is very slow (daily capacity is usually between two and five gallons). Approximately five gallons of tap water is required to produce one gallon of distilled water. Additional limitations are the effectiveness of the removal of volatile organic contaminants. Their effectiveness is dependent upon the performance of the VOC trap that are highly energy dependent.
Nanofiltration (NF)
Membrane type technology.
Nanofiltration (NF) equipment removes organic compounds and rejectsome salts and passes more water at lower pressures than RO. NF economically softens water without the pollution of regenerated systems.
Nano Alumina Microglass Fibers /NanoCeram™
Pleated filter design. A fibrous filter has been developed that has the following characteristics
• High (>99.9999%) virus and bacteria removal efficiency
• Flow capability is greater than equivalent membrane filters
• Higher capacity for particulates and less clogging pleated type filter
• Chemisorbs dissolved heavy metals by ion exchange
• Filtration of sub-micron and nano particulates including radioisotopes
Design and development is underway for a cartridge suitable for certification to the EPA Guide Standard for Drinking Water Filters.
Ultrafiltration
(UF) Membrane type technology.
Ultrafiltration (UF) is similar to RO and NF, but is defined as a cross flow process that does not reject ions. Because of the larger pore size in the membrane, UF requires a much lower differential operating pressure: 10 to 100 psig UF removes larger organics, colloids, bacteria, and pyrogens while allowing most small organics such as sucrose to permeate the porous structure.
Microfiltration(MF)
Membrane and pleated cartridge filters.
Microfiltration(MF) membranes are absolute filters typically rated the 0.1- to 3.0-micron range. Available in polymer, metal and ceramic membrane discs or pleated cartridge filters, MF is now also available in cross flow configurations. Operating differential pressures of 5 to 25 psig are typical. Cross flow MF substantially reduces the frequency of filter media replacement required compared to normal flow MF because of the continuous self-cleaning feature. Cross flow MF systems typically have a higher capital cost than MF cartridge filter systems however, operating costs are substantially lower. This type of filtration is generally not used in the home.
Ultraviolet (UV) Light:
Disinfectant.
This technology uses UV radiation to inactivate microbes. The UV spectrum is divided into four regions, defined in wavelength expressed in nm: UV (100 to 200 nm), UVC (200 to 280 nm), UV-B (280 to 315 nm), and UV-A (315 to 400 nm). For application in home purification systems, an effective and practical germicidal wavelength range is 200 to 300 nm. UV light deactivates microbes by causing a molecule composed of two identical subunits, such as thymine, which is one of the DNA base units to form within the organism’s DNA, thereby making it difficult for survival unless the organism is able to repair this damage.
