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Activated Carbon For Drinking Water Filtration
What is Activated Carbon?
Activated carbon (AC) is a natural material derived from bituminous coal, lignite, wood, coconut shell etc., activated by steam and other means, and each one have different adsorption properties (e.g. bituminous carbon for high chlorine reduction capacity). Some manufacturers use various blends of carbon to achieve specific water quality and contaminants reduction (e.g. coconut shell carbon for "sweet taste").
Activated carbon surface properties are both hydrophobic and oleophilic; that is, they “hate” water but “love” oil. When flow conditions are suitable, dissolved chemicals in water flowing over the carbon surface “stick” to the carbon in a thin film while the water passes on.
This process is called adsorption. As a result of the adsorption process, activated carbon is an effective method in removing chlorine and it's by-products (TTHM's) and volatile organic compounds (carbon based VOC's). Both, man-made and naturally occurring including among others:
None carbon based anions (-) and cations (+) such as arsenic, fluorides, some heavy metals, nitrate, etc.
Most popular forms of activated carbon used in the treatment of POU drinking water filters are granular activated carbon (GAC), extruded solid carbon block (CB) and powdered activated carbon (PAC).
All activated carbon forms including granulated activated carbon (GAC) have a tremendous surface area resulting from its porous structure. GAC filters degree of effectiveness depends on the flow rate of the water and contact time with the water. If flow rate is excessive their efficiency could be as low as 0% and if the flow rate is slow their efficiency can match and or exceed those of different carbon forms.
For comparative purpose, a teaspoon of activated carbon have surface area the size of a football field.
On a large scale such as municipal water treatment pools (gravity filters) for taste, odor and chemical reduction GAC is cheaper, very effective and can be re-used.
Sure. If you are a bit handy you can make a GAC water filter using standard 3" PVC pipe, fittings and few accessories for less than five dollars. If you intend to market your "invention" you must apply a fancy label around the pipe and come up with some catchy name such as "spring", "natural water", "pure", something on that order. Kidding, take a little break from this boring technical stuff however don't leave, it's getting more interesting or, for quick and easy to understand the filtration principle go to Doulton's filtration principle.
No form of carbon filter removes bacteria. In fact under quite normal operating condition all carbon forms can and do become perfect breeding grounds for bacteria, including pathogenic bacteria. Silver based GAC's are effective in controlling bacterial growth and multiplications (bacteriostatic) only for a short time because the silver is in form of a "spray" over a small percent of granules (usually 1.05% of the total GAC content). As the water passes the granules "rub off" each other leaching the silver prematurely. As we mentioned earlier, a POU filter containing silver based GAC must register that device with EPA, that does not mean is approved by EPA.
First of all your 10K filter is rated for chlorine reduction which if properly designed and used will do the job for that quantity, a more expensive "block" filter rates their "life-span" on specific contaminants reductions such as lead, THM's etc. It's like comparing apples to oranges. Granted that you use your 10K chlorine reduction filter within short time you are fine, otherwise you are taking chances of bacterial and chemical "dumping" contaminations.
These filters cannot be measured in micron pore size due to their granular state. They are measured in mesh size similar to that of your window screen. Coarse carbon is used in different applications while in domestic POU finer mesh is used followed by a cloth like "filter" to prevent granule escaping.
"Channeling" is water passing through least resistant path of the granule bed avoiding contact time with carbon resulting lower effectiveness. "Dumping" is sudden change in your water pressure releasing the trapped contaminants into your glass. "Dumping" can occur also if your carbon filter media is exhausted (over used). Some times this is visible as a "gray" water but most often is not. This happen with pressure filter cartridges.
Sounds like the GAC water filters are terrible buy?
Let me ask you a question. Do you want your drinking water to be cleanest, semi-clean or just somewhat clean? Those gadgets are made with small amount of GAC and ion exchange media. The most popular pitcher-style "filter" was developed many years ago in Germany to strip the water from calcium and magnesium (hardness). Why? In those days car batteries required periodic refill with water. The distilled water being so acidic was eating the lead cells while hard water was shorting the cells. Of all GAC filters these are the least effective and cheapest to buy however, the most expensive to use on ongoing basis (low capacity "filters"). NSF standard 42 have 3 classes for chlorine reduction; class I is >75% reduction, class II is 50-75% reduction and class III is 25-50% reduction. Most of those filters falls under class III. It's like "you get what you pay for" rule.
Conclusion: In most cases, pre and post-filtration, including a ceramic filter element will improve the effectiveness of the GAC filter.
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Of all carbon forms solid carbon block (CB) filters are the most efficient and cost effective methodof removing volatile organic carbon compounds (VOC's, insecticides, pesticides and industrial solvents) from drinking water.
By adding various ion exchange media (e.g. zeolite, activated alumina or other media)
heavy metal, MTBE, nitrate and other water treatment effects can be achieved.
The best CB filter is inside Doulton ceramic shell and Aquasana filtration system.
Can my 1/2 micron CB protect me against bio-terrorism on our water supplies?
Not at all. For that you'll need a laboratory grade RO system, a filter with 1/2 micron or less absolute ANSI standard pore size, distillers and UV's to some extent.
As with all carbon forms change these filters often and do not wait until quality of the water taste has deteriorated.
The best and only PAC filter made in USA is Multi-Pure solid carbon block.
NOTE: All POU activated carbon water filters should be used on microbiologically safe water only.
At last, here we are, more tech stuff which you have been patiently waiting for.
What is it all this stuff about microns, pore size ratings, nominal, absolute etc. means?
There is a range of water purification products on the market and there is Doulton. Effective and cost efficient drinking water treatment technology.
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