KDF Water Filters for Iron, Chlorine, and More
KDF is a popular filter media that is used in water filter systems to remove up to 95% of chlorine, iron, hydrogen sulfide, heavy metals, and more.
This article will cover what KDF is and how it works. We will also highlight an example of how it could be used in a whole house iron filter for well water.
It’s important to remember that filter media is only one component of a complete water filtration system. KDF is exceptionally heavy, and very hard to maintain. If great care is not taken when designing a system, you could end up with a system that fails prematurely, and costs $1000’s of dollars to maintain.
What is KDF?
KDF Process media is a high purity copper-zinc formulation that is manufactured by KDF Fluid Treatment, Inc. in Three Rivers, MI. As you can imagine, the dramatic increase in the price of copper has made KDF extremely expensive.
There are primarily two versions of KDF, one for city water, and one for well water:
KDF55 (city water)
KDF 55 is a gold colored granule that can be used for chlorine removal. It is often found in showerhead filters for this purpose. KDF55 cannot remove other contaminants like chloramines, disinfection byproducts, or organic contaminants – all of which easily absorb through skin. A carbon filter would be a better choice for those chemicals.
KDF85 (well water)
KDF 85 is a brown colored granule that can remove ferrous (clear water) iron and hydrogen sulfide (rotten egg smell). A filter using KDF85 could be used to help protect water softeners or purification technologies like reverse osmosis from iron fouling.
Both KDF55 and KDF85 can also be used to remove up to 99% of water-soluble lead, mercury, nickel, chromium, and other dissolved metals. All KDF Process Media forms are also effective in controlling the buildup of bacteria, algae, fungi and scale.
KDF Filter Media Specifications
|Service Flow Rate||15gpm/sq. ft.|
|Backwash Flow Rate||30gpm/sq. ft.|
|Total Limit for Iron, Hydrogen Sulfide, etc.||5ppm|
|Average Reduction Performance||95%|
|Average Life||6-12 years|
How Does KDF Work?
KDF works by reducing contaminants in water using oxidation/reduction (redox) reaction.
Redox is an electro-chemical reaction where electrons are transferred between molecules to create new elements. Harmful contaminants are changed into harmless components.
Chlorine, Iron, Hydrogen Sulfide, and Heavy Metal Removal
Free chlorine is changed into water-soluble chloride, which is then carried harmlessly through the water supply.
Soluble iron is changed into insoluble ferric hydroxide, and hydrogen sulfide is changed into insoluble copper sulfide. These new byproducts are mechanically strained through the filter bed, and then periodically removed by backwashing.
Heavy metals such as copper, lead, mercury and others are removed by simply bonding to the KDF media and are effectively removed from the water supply.
Microorganisms are controlled by two separate actions:
First, the exchange of electrons in the redox reaction creates an electrolytic field that most microorganisms can’t survive.
Second, KDF process media may catalyze the formation of radicals and peroxides in certain circumstances. The radicals can interfere with microorganisms’ ability to function.
The reaction of KDF media modifies the crystal structure of hard water scale (calcium carbonate), changing it from calcite to aragonite. In this modified form, aragonite is suspended in water until it’s removed by a filter. Once the filter backwashes, the scale is literally flushed down the drain.
KDF Whole House Iron Filter Example
Let’s say you figure out your flow rate requirements for your family, and you need 8gpm (gallons per minute) to operate several sinks and appliances at once.
A 10” diameter filter has 0.55 sq. ft. of surface area. KDF’s service flow rate is 15gpm, so this 10” filter would provide just over 8gpm of filtered water (0.55 x 15). Easy enough.
Here’s where KDF has problems:
KDF requires a MASSIVE 30gpm backwash and rinse rate. In comparison, our Iron Curtain systems require 11gpm.
KDF also requires at least 3 regenerations each week with a 10 minute backwash cycle, and a 3 minute rinse/purge cycle (also done at 30gpm).
This means that this same 10” diameter filter will require 16.5gpm to backwash and rinse. Every 2 days the system would use 215 gallons of water in only 13 minutes. That is A LOT OF WATER for any drain to take!
A better system would use (2) 8” diameter filter vessels plumbed in parallel. This system would deliver 10.5gpm of filtered water, and only require 10.5gpm to backwash. The total water usage for both systems would increase to 272 gallons, but the slower discharge would be much easier for a drain to take.
Iron Filters fail from inadequate backwash more than anything else. A system will plug up in a matter of months if the system can’t deliver the required amount of water to flush itself out!
KDF’s huge water requirements make a proper backwash almost impossible to achieve.
KDF’s chemical-free operation is definitely a plus. The microbial protection and scale reduction are also worthwhile attributes. We like to use KDF as part of a mixed media filter along with carbon. Our Pureoflow System uses a mixture like this to pre-treat water to protect its membranes.
That being said, KDF’s limited contaminant removal of only 5ppm, and its extreme backwash requirements make it a poor choice for iron removal.
Who We Are
Premier Water is a local, family-owned water treatment company based in Chanhassen, MN. Since 1978, Premier Water has successfully implemented 1000’s of Residential and Commercial Filters and Purification Systems. We offer a FREE WATER TEST to gather information and help our clients with the right solution for their needs. We can also be reached at (952) 479-4553 for more information.