Activated Carbon Filtration FAQ.
Choices;
*Whole house carbon filters
*Carbon block candle PB1 (with lead reduction) for Doulton housings.
* Extruded solid carbon block cartridges for industry standard filter housings and RO membrane. None Doulton products.
Most Popular Water Purification Technologies for Domestic Drinking Use (FAQ)
* Doulton Ceramic Technology
* Activated Carbon (AC)
* Granulated Activated Carbon (GAC)
* Extruded Solid Carbon Block (CB)
* Powdered Activated Carbon (PAC)
* Reverse Osmosis (RO)
* Ultraviolet Radiation (UV)
* Ion Exchange (IEX)
* Distillation or Demineralization (DI)
*Absolute vs. Nominal Ratings
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:
alachlor
atrazine
benzene
carbofuran
carbon tetrachloride
chlorobenzene
2,4-D
dibromochloropropane (DBCP)
O, P-dechlorobenzines
forms of dichloroethylens 1, 2-dechloropropane
cis-1,3-dichloropropylene
toxaphene
chlordane
radon
lindane
simazine
PCB’s
toluene
xylenes etc., etc.
What other chemicals AC by it’s self is not reducing?
None carbon based anions (-) and cations (+) such as arsenic, fluorides, some heavy metals, nitrate, etc.
What forms does it come in?
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).
What is granulated activated carbon (GAC)?
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.
What are the advantages of GAC vs. other form of carbon?
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.
Powdered activated carbon used in CB and PAC cartridges Fine granule carbon used in GAC cartridges Coarse mesh carbon used for industrial and municipal gravity filters
Can I make my own GAC water filter?
Sure. If you are a bit handy you can make a GAC filter using standard 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 our filtration principle.
Can silver impregnated GAC remove bacteria?
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.
My inexpensive GAC filter is rated for 10.000 gallons while more expensive “block” filters are only rated for 500 gallons, why are they so much more expensive?
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.
What micron pore rating is my GAC filter?
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.
What is “channeling” or “dumping” means?
“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 phenomenon can also happen with PAC filters.
Sounds like the GAC filters are terrible buy?
Not quite. If your water is municipally supplied a well designed GAC filter with changeable cartridge is all you’ll need, don’t forget to change the cartridge at least every 6 months. Avoid those “high capacity” throw away filters unless you use that capacity within 6-9 months.
Why should I buy expensive carbon block filter instead of less expensive pitcher-style or faucet-mounted water filters?
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.
Extruded Carbon Block (CB)
Of all carbon forms solid carbon block (CB) filters are the most efficient and cost effective method of 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.
CB’s are made of single or various blends of carbons combined with plastic polymers which are pulverized to a fine dust then shaped in varieties of forms under high pressure (600 to 800 tons). Unlike the other carbon forms, the CB’s are industrial grade filters. They are made in various sizes and micron ratings (nominal), are physically strong therefore they do not “channel” nor “collapse” under pressure change, however they “dump” if their media is exhausted.
Most 1/2 micron nominally rated CB filters are effective in cysts and asbestos reduction (not removal). CB’s are the best choice for POU filters.
If used for potable water, pre and or post-filtration, including a ceramic filter element, will ensure microbiological protection.
Powdered Activated Carbon (PAC)
Unlike CB’s, molded or powdered activated carbon (PAC) filters are an old carbon technology and is effective method of removing volatile organic compounds (insecticides, pesticides and industrial solvents) from drinking water. These filters are often mistaken or misrepresent as a solid carbon block (CB’s).
Unlike CB’s, which use binding material with the carbon for strength (extrusion), PAC filters are made of powdered carbon compressed around a synthetic tube with an outer synthetic or cotton wrap to hold the powder in place.
As with GAC, PAC filters do “channel” and this can be observed on a used filter with large yellow or reddish stains on the white wrap. Those spots indicate that over time water created erosions through the powdered cake like filter (when wet). Water travels through the least resistant path and the stains are a reaction of chlorine and or iron with the pre-filter material. Bacteria may also break down the support media of the filter for additional nutrients. Some PAC manufacturers incorporate various ion exchange media for none carbon based cationic and anionic contaminants such as arsenic, fluorides, nitrates etc.
As with GAC and CB change these filters often and do not wait until quality of the water taste has deteriorated. By this time they have long been “dumping” contaminants in concentrated level.
NOTE: All POU activated carbon filters should be used on microbiologically safe water only.
In most cases, pre and or post filtration, including a ceramic filter element, will improve the effectiveness of the PAC filter.
One must keep in mind that any water treatment “filter” media have finite capacity in removing organic and inorganic compounds for example: Inorganic arsenic can occur in ground and or surface waters, and thus in drinking-water, it is mostly found as trivalent arsenite (As(III)) or pentavalent arsenate (As (V)). The arsenite form is several times more toxic (and more difficult to reduce) than arsenate therefore if your water source is none chlorinated (chlorine converts As+3 to As+5) look for filter that would remove both form of arsenic. Cationic and anionic “filters” capacity are rated on parts per billion (ppb) or micrograms per liters (µm/L) rather than in gallons/liters capacity.
CONCLUSION
There is a range of water purification products on the market and there is CWF. Effective and cost efficient drinking water treatment technology. You need to TRUST that your water purifier is doing what it claims to do.