Activated carbon water filters – Drinking Water Treatment
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:
Activated carbon filtration can effectively reduce certain organic compounds and chlorine in drinking water. It can also reduce the quantity of lead, dissolved radon, and harmless taste- and odor-causing compounds.
This guide discusses the principles, processes and requirements of activated carbon filtration systems for the domestic (household) user.
Contaminants Removed From Water by Activated Carbon Filtration
Homeowners are increasingly concerned about contaminants in their water supply that may affect health or cause taste and odor problems. Sources of these contaminants might include solvents, pesticides, industrial wastes, or contaminants from leaking underground storage tanks. Contaminants such as benzene, chlorobenzenes, trichloroethylene, carbon tetrachloride, methylene chloride, and vinyl chloride in drinking water may pose health risks if they are present in quantities above the EPA Health Advisory Level (HAL).
Pesticides, such as Atrazine, also can pose a health risk if present in quantities above EPA guidelines. Activated carbon (AC) filtration can effectively reduce some of these organic chemicals as well as certain harmless taste- and odor-producing compounds.
Some drinking water may be disinfected with chlorine or chloramines. During disinfection the reaction of chlorine with organic matter can produce compounds such as trihalomethanes (THMs) as byproducts. These disinfection byproducts may increase the risk of certain cancers. The EPA mandates that public systems have less than 80 parts per billion (ppb) of THMs in their treated water. AC filtration can be effective in removing chlorine, chloramines, and some disinfection byproducts.
In addition, lead from some older pipes and soldered joints may be present in water from some taps. AC filtration can reduce lead in drinking water, though another filter medium is commonly used in addition to AC filtration for this purpose. Only very specialized AC filters effectively adsorb heavy metals. Radon, a radioactive decay product of natural uranium that has been related to lung cancer, can be found in some groundwater. Radon gas also can be removed by AC filtration, though removal rates for different types of AC filtration equipment have not been established.
No one piece of treatment equipment manages all contaminants. All treatment methods have limitations and often a combination of treatment processes is required to effectively treat the water. Different types of carbon and carbon filters remove different contaminants and no one type of carbon removes all contaminants at maximum efficiency. AC filters will not remove microbial contaminants (such as bacteria and viruses), calcium and magnesium (hard water minerals), fluoride, nitrate, and many other compounds. Refer to Extension Circular 703, Drinking Water Treatment: An Overview for a discussion of possible water quality problems and appropriate treatments for these contaminants. Further information can be obtained from the appropriate treatment guide in the Drinking Water Treatment series (listed as part of this publication’s Web resources).
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.
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 water filters|
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
Regardless of which water treatment system is considered, the water should be tested first to determine what substances are present. Public water systems routinely test for contaminants. Water utilities are required to publish Consumer Confidence Reports (CCRs), which inform consumers on the source of the water, contaminants that are present, potential health effects of those contaminants, and methods of treatment used by the utility. Depending on the population served by the utility, CCRs may be mailed, published in newspapers or posted on the Internet, but copies can be obtained from the local water utility. Public supplies must conform to federal standards established by the Safe Drinking Water Act. If contaminants exceed the Maximum Contaminant Level (MCL), the water must be treated to correct the problem and/or another source of water suitable for drinking must be provided.
In contrast, monitoring of private water systems is the homeowner’s responsibility. Therefore, contamination is more likely to go undetected in a private water supply. Knowing what contaminants may be present in the water should guide the testing, since it’s not economically feasible to test for all possible contaminants. It is essential to know what contaminants are present, their quantities, and reasons for removal (i.e., to reduce contaminants posing health risks, to remove tastes or odors, etc.) prior to selecting water treatment methods or equipment. Refer to NebGuide 907
Drinking water treatment using activated carbon (AC) filtration is one option for a homeowner to treat drinking water problems. AC filtration is an effective method for treating certain organic compounds, unpleasant tastes and odors, and chlorine, though it is not effective for metals, nitrate, microbial contaminants and other inorganic contaminants. An AC filtration system should be selected based on water analysis and assessment of individual homeowner’s needs and situation. Regular replacement of the filter/cartridge is critical to maintain effectiveness and reduce bacterial contamination of the filter. The NSF and the WQA test and certify products. This certification can help guide selection.
Activated Carbon Filter Adequate to Clean Water?
Answer: An activated carbon filter may be adequate, but it really depends on the condition of your water. If your water is already treated such as with most municipal tap water, it may be safe to drink and an active carbon filter can help to remove odor-causing chemicals and other particulates, as well as improve the taste of drinking water.
However, water treatment facilities do not always remove all threat and traces of bacteria, viruses, lead, chemicals or other impurities in water. In such a case, an activated carbon filter may be inadequate filtration because it does have limitations.
An activated carbon filter is an affordable choice of water filtration for treated tap water if you’re merely looking at improving the taste of your drinking water. But it will only remove certain particles and some chemical residue; it really depends on what it is designed to accomplish, and some are more effective at particle removal than others.
If you suspect the presence of bacteria, lead or other contaminants in your water, you may need more than carbon filtration. But before buying a more involved water filtration unit, you should have your water tested. You can inquire from your local health authorities as to the nearest water testing facility. Cost is usually minimal and this will either prove your suspicions or affirm the safety of your water. Be sure to inquire as to the specific water-gathering steps for such tests, to avoid contaminating your water sample. And be prepared to repeat water sampling as the need arises.
Source: Bruce I. Dvorak, Extension Environmental Engineering Specialist
Sharon O. Skipton, Extension Water Quality Educator