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Center for Watershed Science and Education

An Alternative to Softening with Sodium

(from Pipeline, a newsletter of the National Small Flows Clearinghouse, Winter, 2001)
 
"Sodium really has no redeeming value in the environment outside of saltwater or brackish water ecosystems. If alternatives to sodium chloride for water treatment can be developed, they should be used. Potassium chloride is a logical choice to reduce sodium discharge from water softening systems, to provide additional potassium in human diets, and to serve as a nutrient source for plants."
 
From "Potassium Chloride: Alternative Regenerant for Softening Water" by Dr. Kim Polizotto and Dr. Charles Harms
 
If you are concerned about water softening brine and its possible effects on your septic system (and the environment), an alternative chemical can be used. Potassium chloride is as effective as sodium chloride for water softening in both residential and commercial processes. Plus, using potassium chloride has several benefits: it reduces the amount of sodium in drinking water; the treated water contributes potassium to people’s diets; and it eliminates the addition of sodium from water softeners into a household’s septic system tank and drainfield.
 
Potassium chloride works exactly the same way that sodium does in the water softening process. The mineral tank is flushed with potassium (instead of sodium) from the brine tank to coat the resin beads. With its positive electrical charge, the potassium clings to the negatively charged resin beads in the tank. As hard water passes through the softener’s mineral tank, the calcium and magnesium in the water change places with the potassium on the beads.
The treated water now has a small amount of potassium in it. The mineral tank will eventually need to be regenerated when most of the potassium adhering to the resin beads has been exchanged for the calcium and magnesium carried in the water.
 
The regeneration process flushes the mineral tank with a potassium chloride solution that drives the calcium and magnesium minerals off the resin beads. The excess potassium, calcium, and magnesium-rich water in the tank is then discharged into the home’s drain pipes and into the septic system.  The regeneration brine mixes with the standing water in the tank, then eventually flows into the system’s drainfield. Potassium is an essential mineral for plants; whereas, sodium can damage plant tissues. Because sodium is replaced by potassium, this diluted wastewater is beneficial to a grass covered drain field.
 
Wastewater from water softeners that use potassium chloride in their regeneration brine can be recycled to irrigate agricultural land. An article titled “Potassium Chloride ... Alternative Regenerant for Softening Water,” written by Dr.Kim Polizotto and Dr.Charles Harms for the Potash and Phosphate Institute’s Better Crops with Plant Food (Fall 1993), suggests using potassium in water softening units and then recycling the diluted wastewater as an alternative to disposing of it.
 
Polizotto and Harms mention that several cities in California, Florida, and Michigan have called upon the water softener industry to help reduce sodium and chloride discharge into municipal sewage treatment facilities. Reduction of these chemicals is necessary to meet discharge standards set to decrease groundwater pollution in those communities.
 
These researchers also tell of other towns that want to develop secondary markets for their wastewater, such as selling it to farmers for irrigation purposes. Because sodium may harm some plants’ growth, wastewater from treatment plants might not be marketable if sodium chloride is the predominant salt used for water conditioning in the community.
 
Cost may be the only drawback in switching from the standard sodium chloride used in most water softeners to potassium chloride. Both can be found in most retail home improvement centers, but the potassium chloride can cost up to twice as much (even more on the West Coast) as the sodium chloride. The average price of sodium chloride (in the East) is around $4 for a 40 pound bag, and potassium chloride costs approximately $9 for 40 pounds. However, consumer group studies show that, for many potential users, the health and environmental benefits of potassium chloride outweigh the price difference.
 
National Small Flows Clearinghouse (NSFC)

The NSFC offers a variety of technical assistance and free and low-cost information and materials about wastewater technologies for small communities. Just a few of the NSFC’s many resources and services are mentioned in this newsletter. Call the NSFC at (800) 624-8301 or (304) 293-4191 or visit our Web site at http://www.nsfc.wvu.edu/ for more information.