In order to remove or reduce contaminants in your water that are dissolved in the water, you need filters that can do adsorption, absorption or ion exchange.
These filters come as either throw away cartridge type filters or as a media in larger back washable media type filters.
Generally, activated carbon is used in many cases. Activated carbon can attract and absorb many things in your water, including taste and odors, chlorine, organics, and color causing chemicals like tannins.
Ion exchange takes a dissolved ion (negatively or positively charged particle) dissolved in your water, and replaces it with another ion. You know these devices as softeners, and replace calcium and magnesium (the dissolved ions that cause hardness) with sodium.
A Brita water pitcher is a good example of a filter that does absorption, adsorption and ion exchange. It contains activated carbon to reduce chlorine, tastes and odors in the water and ion exchange beads to soften the water.
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What I call particle size filters are filters that have a set ‘pore’ size so that particle matter of a certain size and above cannot penetrate the filter. These filters can be both surface area filters made of a material that has set pore sizes, or a depth type filter that has a solid media that will only allow particles of a certain size to pass through.
These filters generally come in replaceable cartridges made of paper like material, cellulose fibers or glass fibers for surface area filters or cotton/wound string/composite materials for depth types.
Surface area filters are usually pleated to gain more surface area to a smaller space so they can filter more and last longer. These filters are used as a polishing filter to take out smaller particles as the particle sizes are better controlled with these filters. These filters cannot take large dirt loads.
Depth type filters generally can handle a lower volume of water but can handle a much higher load, making them ideal pre-filters for the surface area type filters.
Usually these cartridge particle size filters cannot be cleaned. Some special units, usually membrane filters constructed of a plastic, rubber or composite sheet (usually pleated or constructed like small straws) can be cleaned by backwash. These units are more expensive, and most home owners opt for throw away cartridges.
Reverse osmosis membranes use the molecular structure of the membrane, rather than have holes of known sizes be perforated. This means that not only can these filters take out suspended particles, they take out just about everything leaving pure water behind. These filters are easily contaminated and fouled so need extensive pre-filtration.
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Tortuous path filters, or as they are called, sand filters, media filters, or multimedia filters, are filters that are a hollow vessel filled with a media of some sort. Typically this media is a crushed rock, sand, various grades of gravel, depending on the make up. More exotic materials can also be added to these filters that provide higher level filtration with adsorption or absorption, but that will be covered in another post.
These filters are known as depth filters, because they provide filtration throughout the whole media bed. If there is 15″ of media, then the water will be filtered through the whole 15″ of media. The filters can be gravity fed, or pressure fed. Usually water is fed at the top and comes out near the bottom of the filter. Water flow is reversed to clean the filter in what’s known as a ‘backwash’.
This filter can:
- Filter high volumes of water and high flow rates of water
- Self clean using a ‘backwash’ cycle
- Remove dirt, turbidity, and suspended solids to a low level
- Excellent pre-filter for dirty waters such as lake water or river water
- Remove organics, color, dissolved ions if specialized media is used
This filter cannot:
- Disinfect water
- reduce/remove pathogens such as bacteria, protozoa, or virus’s (unless coupled with certain pre-treatments usually used in large scale water treatment)
- Be fit into small spaces
These filters are generally only used by cottage owners who need a high quantity of water and have dirty waters such as from a river or a lake.
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