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Posted on Oct 21, 2014

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 Mech­a­nisms

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

 Health Effects

 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.


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