KDF vs Carbon — Which is better for my home filter?
The Fight Begins
As with most great challenges, the winner is the one most suited for the fight. Both media types are highly efficient at removing chlorine, but choosing which is best for a filter system gets complicated. Also, there are different types of KDF and carbon filters, which makes it even more challenging to choose the correct filter. I will try to shed some light on this sometimes confusing and even heated discussion. (Yes, water folks can actually get uptight about this issue so fire away in the comments section.) I will walk through the most common uses of each media type and offer some guidance on which wins each challenge.
The principle mechanism for carbon media is adsorption where contaminants collect on the surface of the carbon. The contaminants are removed from the water, but they are not chemically alternated. Once the available surface area of the media is covered with contaminants, any additional contaminants will pass through. Since the contaminants are only sitting on the surface of the media, they can become a breeding ground for new bacteria over time if the media is not regularly replaced. The replacement period is typically in the range of 6 to 12 months, but it is more dependent on the volume of water going through the filter and the level of contaminants in the water.
The Chlorine Challenge
Before getting too deep into this issue, a few terms need defining since these are key in determining the winner. These definitions are taken from the EPA.
Definition and Uses
|Chloramine (as Cl2) (CAS No. 10599–90-3)||Chloramine (as CI2) is a water additive used to control microbes, particularly as a residual disinfectant in distribution system pipes. It is formed when ammonia is added to water containing free chlorine. Monochloramine is one form of chloramines commonly used for disinfection by municipal water systems. Other chloramines (di– and tri-) are not intentionally used to disinfect drinking water and are generally not formed during the drinking water disinfection process.||Some people who use water containing chloramine in excess of the maximum residual disinfectant level could experience irritating effects to their eyes and nose, stomach discomfort or anemia.|
|Chlorine (as Cl2) (Cas No. 10049–04-4)||The gaseous or liquid form of chlorine (CL2) is a water additive used by municipal water systems to control microbes. It is relatively inexpensive and has the lowest production and operating costs and longest history for large continuous disinfection operations. Chlorine is a powerful oxidant.||Some people who use water containing chlorine well in excess of the maximum residual disinfectant level could experience irritating effects to their eyes and nose. Some people who drink water containing chlorine well in excess of the maximum residual disinfectant level could experience stomach discomfort.|
|Trihalomethane (THM) (Cas No. 67–66-3)||One of a family of organic compounds named as derivative of methane. THMs are generally byproducts of chlorination of drinking water that contains organic material.||Trihalomethane is a suspected human carcinogen.|
Water utilities will use either chloramine or chlorine, but not both, to maintain a disinfectant residual in the potable water. Maintaining this residual is a regulatory requirement meant to make sure the water remains pathogen free after it leaves the treatment plant. Typically, large utilities will use the chloramine because it does not dissipate as quickly and it will produce fewer disinfection by-products like THMs and chloroform. Maximum allowable levels of disinfectant by-products are tightly controlled by the regulatory agencies. Suffice it to say the disinfection by-products issue is highly complex and heated. For more information on this topic, I recommend you start at EPA’s website dedicated to this issue.
Although adding chlorine to treated water has saved countless people over the years from water-borne diseases, it is also one of the reasons many people do not like the taste and odor of tap water. Chlorine in the water can also have a drying affect on the skin since it is a strong oxidant. It’s important to keep up the chlorine residual in the water system; however, there are no health benefits of actually consuming it. To decide which filter media product is the most effective at removing the chlorine, check the water quality report provided by the water utility and find out if the utility uses chlorine or chloramine.
KDF is highly efficient at removing chlorine, but it does not perform as well as carbon/GAC in removing chloramine. Carbon is also effective at reducing the THMs and other disinfection by-products, where KDF has little effect on them. There are some advantages that KDF has over carbon. The media works better at higher temperatures than carbon so it performs well on warmer water. KDF is also cheaper to operate per gallon of water treated and a little amount can last for a long period. If possible, use of KDF media upstream of a carbon filter works quite well. The KDF extends the life of the carbon, and the carbon works well reducing the chloramine and THM levels.
The Organics Challenge
In this challenge, carbons wins hands down. Carbon efficiently reduces organic chemicals like disinfection by-products, pharmaceuticals, pesticides and other trace organic compounds. KDF has little effect on many of these compounds. Carbon also reduces the organic compounds that cause some of the taste issues that can commonly occur in surface waters. Many of the taste issues are the result of chlorine added during the treatment process or from a naturally occurring compound called geosmin that is not efficiently removed in conventional water treatment processes. Carbon works well at reducing the concentrations of each of these compounds.
The Metals and Inorganics Challenge
KDF is the clear winner of this challenge. KDF is a copper-zinc formulations that reacts with chlorine to form safer chloride compounds. Copper, lead, mercury and some other metals react to plate out onto the media’s surface, which effectively removes them from the water supply. Both KDF and carbon reduce H2S concentrations that cause the rotten egg smell associated with some groundwaters.
Generally, KDF and carbon make a great team. Rather than having to choose the best for an application, use both in the filter system. Place the KDF before the carbon filter to extend the life of the carbon, improve the performance efficiency of the system, and cut the operating cost.