OTHER TYPES OF WATER FILTERS
Adsorption Filters (also called Activated Carbon Filters) use materials that have the ability to attract and hold on to the contaminants. The attraction is due the opposite electrical charges of the contaminant and the filter material. The filter material must present a huge surface area relative to its weight. This design is exemplified by activated carbon water filter systems in the form of granular activated carbon (GAC) or solid block carbon.
Activated carbon is made from carbon-based materials, the most common of which is coconut shell. The raw material is subjected to a high temperature process under carefully controlled conditions in order to create a matrix of billions of microscopic pores, and a huge amount of activated surface area. The pores trap microscopic particles and large organic molecules, while the activated surface areas attract and hold (adsorb) organic and inorganic molecules, including chlorine which is a common chemical resulting from the chlorination of municipal or city water supplies.
Activated carbon filters are widely used in home water treatment because of their ability to improve water by removing disagreeable tastes and odors, including objectionable chlorine. Activated carbon effectively removes many chemicals (especially pesticides) and gases, including microorganisms in some cases. Generally however, activated carbon filters do not affect total dissolved solids, hardness, or heavy metals.
Carbon Filters, with their long life and high capacity, are usually used in combination with other treatment processes. The placement of carbon in relation to other components is an important consideration in the design of a water purification system.
Chemical Filters use chemicals to react and retain the contaminants in water. The water softener is a very good example of a chemical filter. It is packed with a solid resin matrix with an open fishnet-like structure called the ion exchanger. It removes the Calcium and Magnesium ions in the hard water by exchanging them with Sodium ions in the resin. In effect, the hardness is captured and attached into the resin bed while the sodium from resin is released into the water during the exchange process. When the exchange resin becomes almost all changed to Calcium and Magnesium compounds and its ability to produce softened water is exhausted, it is backwashed to cleanse and regrade the bed and regenerated with solution of common salt to restore to its sodium state. Regeneration removes the Calcium and Magnesium in the form of soluble chlorides.
Water softeners remove the “hardness” but not other contaminants and microorganisms. They are an important component of a total water purification system when used in combination with Reverse Osmosis, mechanical filters and activated carbon filters.
It has a high upfront cost, and although it can be regenerated, it is expensive over the long term.
Ultraviolet (UV) Radiation is an effective sterilizer. It is used as a component in a water conditioning system to kill bacteria and other microorganisms. It is usually placed in the final stage where it maximizes its contribution to the elimination of harmful microbiological contaminants.
Ultra Violet sterilizer is not however effective against particles, colloids, ions, organics and inorganics.
Types of Water Filters By Location of Application
Whole House Filters are placed in the main water line entering the house. Usually, WHF are particulate type of filters that are designed to eliminate sediments and rust particles. They can serve as pre-filters for other downstream filters if needed.
Under Sink Filters are installed usually as multiple cartridges under the sink. They may be plumbed in such a way as to enable selection of water lines to be filtered with the desired type of water filters and to which faucet for particular usage. They are out-of view but relatively more expensive. For example, bath water may need to be clear and free from odor, taste, hardness, and bacteria.
Faucet-mounted Filters attach directly to the faucet, thus are basically a point-of-use type, requiring no complicated plumbing. They may be types specific to the kind of contaminants intended to be removed. They are small and easy to install, but highly visible.
Countertop or Canister Filters are essentially countertop units with combination of filters to remove certain contaminants. They however require provision for connection to water outlets.