Carbon - Black Gold
Carbon, in the form of ashes, has been used to treat drinking water since Biblical Times. Granular Activated Carbon [GAC] is created by exposing a carbon-containing material [usually charcoal] to high temperatures and steam in the absence of oxygen. The GAC used in most quality systems is from anthracite coal [almost pure carbon]. GAC is honeycombed with minuscule channels that branch and twist within each granule. These channels greatly increase the surface area and thereby account for activated carbon's impressive absorptive powers. As the water passes over the positively charged carbon surface [microscopic labyrinth], the negative ions of the contaminants are drawn to the surface of the carbon granules. This is known as ADSORPTION [to adhere] and can be closely compared in principle to magnetism. As a general rule the adsorption ability of GAC depends largely on a number of factors. They are as follows:
TURBIDITY: How clean is the water from fine particulate matter. The cleaner the incoming water, the greater is the ability to adsorb. The DOULTON GAC stage does not have to contend with high levels of bacteria, sediment or particulates as they are filtered by the ceramic candle in Stage One.
FLOW RATE: Gushing water is not filtered as well as water flowing at slower speeds. Example, if you were to throw a nail past the head of a magnet the odds of it adhering would be slight. The DYNAMIC Water Purifier controls the flow rate at less than 1 gpm.
CONTACT TIME: Water must be in contact with the GAC for a sufficient period of time to allow the GAC to effectively adsorb the contaminants. A filter cartridge with mesh or wound string sides will allow water to pass through the sides of the filter providing minimal contact time. In the design of the DYNAMIC GAC filter, water enters from one end of the filter cartridge only and exits from the opposite end, thus ensuring contact with the entire carbon bed for the maximum time.
DEPTH OF THE BED: There must be a sufficient amount of GAC in any filter cartridge to be able to effectively remove contaminants from water. A lab standard formula is used to determine how much carbon is required to filter a known quantity of water depending on the style of GAC being used.
GRANULAR SIZE: Filters that use only one style of GAC will be effective in removing high percentages of only certain contaminants as varying styles are more efficient on certain chemicals than on others. Multi-cartridge DOULTON systems use a combination of GAC styles to provide for maximum performance over a wide range of contaminants.
MAINTENANCE: Poor quality systems will all too often exaggerate the volume of water that their filters can process. Common statements such as; it's time for a change if the bad tastes and odours return or if the water flow is severely reduced because sediment has clogged the filter are very poor methods of monitoring. Once the tastes have returned, it is already far too late. A carbon cartridge may be able to control taste and odours long after the carbon has lost its ability to effectively reduce toxic contaminants. The real life of GAC is strictly limited to the number of gallons it can EFFECTIVELY process. This should be stated and either calculated for you based on your average consumption, or monitored via a flow control device.
STAND ALONE CARBON SYSTEMS: Many cheap filtration systems are nothing more than simple cartridges with solid carbon blocks, granulated or powered carbon stuffed inside them. Powdered carbon cartridges are prone to channelling inside the cartridge as water will always try to find the path of least resistance. Powdered felt pads are probably the least effective in removing contaminants as they become clogged with the finer particulate matter found in most water supplies if not used in conjunction with a high quality pre-filter. Stand alone GAC filters are widely used to clean up bad tastes and odours, but one thing GAC cannot do is adsorb bacteria. Unfortunately, bacteria will be physically trapped, along with the dirt in the carbon if it is packed into a cartridge or when the carbon is in a block form. This is a highly undesirable condition.
BACTERIA: The major problem associated with carbon in any form is bacterial contamination. Wet activated carbon, richly infused with trapped organic matter, provides an ideal breeding ground for bacteria. High bacterial levels occur when the carbon is fully saturated and then let to stand [e.g., overnight]. As the water temperature inside the carbon cartridge rises, bacteria breeding escalates. Silver impregnated GAC does reduce the amount of bacterial growth that occurs, but even the silver can be overcome by the increased rate of growth. Granulated Carbon cannot hold onto bacteria, so when water flow is reintroduced a highly contaminated sample can be output. Bacteria gets into the GAC filter in the first place because disinfection at the water treatment plant does not guarantee the destruction of all bacteria. It is for this reason that many health officials consider GAC filters to be a potential health hazard. The EPA has concluded that carbon filters of any type, even those impregnated with silver show no significant bacteria reduction effect on drinking water. It is specifically for this reason that the DOULTON ceramic ensures physical removal of bacteria by the ceramic wall before the water is allowed to come into contact with the inner stage GAC element. The DOULTON candle then also uses silver to control bacteria growth on the outer wall of the candle.
BACTERIOSTATIC: The interpretation of this term is widely misused by the filter industry. A device may call itself bacteriostatic if it inhibits the further growth of bacteria within itself. That is to say that it safeguards itself from becoming a breeding ground for bacteria while water flow is stopped. The use of silver in a carbon filter will accomplish this, but it does not mean that the device will kill all or any bacteria flowing through the filter while in use. Bacteria should never be able to come in contact with carbon.
BACKWASHING: GAC filters that claim they can be restored by simple backwashing ,flowing water in the reverse direction through the unit need to be closely examined. Backwashing is a common practice for whole house and commercial units which are treating large volumes of water for utility purposes but it is not a recognized practice for small Point of Use (POU) drinking water systems. Flow rate can be restored in cheap POU systems by the unclogging of dirt and sediment which has blocked the generally poor quality pre-filter sealed within these units, but unfortunately the number of gallons of water that the GAC can effectively process remains unchanged. Backwashing with extremely hot water may unload some of the contaminants which have adhered to the GAC but there is no way to calculate the amount released, not even in a laboratory. Therefore no quality treatment system will recommend backwashing as a means of extending the economic life
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