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Granular Activated Carbon (GAC)

Time:2017/4/28 13:47:18

 In this type of filter, water flows through a bed of loose activated carbon granules which trap some particulate matter and remove some chlorine, organic contaminants, and undesirable tastes and odors.


The advantages of GAC filters:

· Simple GAC filters are primarily used for aesthetic water treatment, since they can reduce chlorine and particulate matter as well as improve the taste and odor of the water.

· Loose granules of carbon do not restrict the water flow to the extent of Solid Block Activated Carbon (SBAC) filters, which makes them suitable in situations, like whole house filters, where maintaining a good water flow rate and pressure is important.

· Simple, economical maintenance. Typically an inexpensive filter cartridge needs to be changed every few months to a year, depending on water use and the manufacturer’s recommendation.

· GAC filters do not require electricity, and do not waste water.

· Many dissolved minerals are not removed by activated carbon. In the case of calcium, magnesium, potassium, and other beneficial minerals, the taste of the water can be improved and some (usually small) nutrient value can be gained from the water.

· The bottom line is that GAC filters are effective and valuable water treatment devices, but their limitations always need to be considered. A uniform flow rate, not to exceed the manufacture’s specifications, needs to be maintained for optimal performance, and the filter cartridge must be changed after treating the number of gallons the filter is rated for.

The disadvantages of GAC filters:

· Water flowing through the filter is able to "channel" around the carbon granules and avoid filtration. Water seeks the path of least resistance. When it flows through a bed of loose carbon granules, it can carve channel where it can flow freely with little resistance. Water flowing through the channel does not come in contact with the filtration medium.The water continues to flow, however, so you do not realize that your filter has failed - you get water, but it is not completely filtered.

· Pockets of contaminated water can form in a loose bed of carbon granules. With changes in water pressure and flow rates, these pockets can collapse, "dumping" the contaminated water through the filter into the "filtered" flow.

· Since the carbon granules are fairly large (0.1mm to 1mm in one popular pitcher filter), the effective pore size of the filter is relatively large (20 - 30 microns or larger). GAC filters, by themselves, can not trap bacteria.

· As described above, hot water should NEVER be run through a carbon filter.

· Granular Activated Charcoal (GAC) filters have relatively large, and irregular sized pores (10 microns would probably be the minimum size to expect), so it is impossible to state with any certainty what size particles would be removed. Channeling can also dump unfiltered water into the output stream. GAC only filters should never be relied on exclusively to provide protection from small particulate contaminants.

· Also, if you think of a bed of charcoal that traps an occasional bacterium, picks up a bit of organic material, and removes the chlorine from the water, you can see how these filters might become breeding grounds for the bacteria they trap. You will see warnings about GAC filters suggesting you run water through them for a few minutes each morning to flush out any bacteria.

Unless the filter plugs up or you notice an odor in the "filtered water", it may be difficult to know when the filter has become saturated with contaminants and ineffective. That is why it is necessary to change filter cartridges according to the manufacturer’s recommendation.