Friday, October 18, 2013

A Short Q&A About Greensand Filtration and Chlorination

We recently received an e-mail from a reader who had some great questions about Greensand filtration.  We wanted to share our response here, in the hope of answering some frequently asked questions for the rest of our readers.  If you are considering Greensand filtration, or are just curious about how it works, read on:

Hi Gerry, 
1)  If I go with chlorine, do I understand right that the Greensand iron filter will not need any potassium permanganate???   
This is correct.  Your Greensand iron filter can use either a chlorine injection pump or a potassium permanganate tank - just make sure that whichever you choose is installed before the iron filter.  Keep in mind that chlorine must be fed into the system to clean it, while potassium permanganate can be drawn in from the permanganate tank automatically to backwash and regenerate the Greensand media.  However, chlorine is generally cheaper and easier to remove from your water.   
2) So do I need a pot perm tank or not? 
If you are using chlorine, you will not need a potassium permanganate tank. 
3) I got a lab test result back today for iron bacteria using Hach method,  They found iron bacteria present, labeled it "aggressive: > 9,000."  Should I use potassium permanganate or chlorine? 
Chlorination is definitely the way to go - the chlorine will destroy bacterial DNA and RNA, effectively halting reproduction and removing iron bacteria from your water supply. 
Diagram of standard chlorinator + metering pump installation 
4) You mentioned the chlorinator can be adjusted so the chlorine levels are very low in the household (similar to city water).  However, at that concentration how much contact time is needed to make sure iron bacteria is dead and iron is sufficiently oxidized? 
This depends on the size of your contact tank and the pH of your water.  Chlorine is most effective if the water has a pH in the range of 6.0 - 7.5. At pH 8.0 much more chlorine is required to have the same effect than if the water had a pH of 7.0. At pH over 8.5 chlorine becomes ineffective as a disinfectant.  Use our chart here (under Estimate Chlorine Demand, about 1/5 down the page) to determine how much chlorine you need for your specific application. 
5)  At a 5 gpm flow rate, the 40 gallon contact tank provides less than 8 minutes of contact time.  At 10 gpm, contact time is just 3.5 minutes.  Is this enough or do I need a larger tank for longer contact time? 
The 40 gallon tank is fine.  If you had e.coli, we would recommend the 80 gallon tank.  
6)  At what chlorine concentration will chlorine kill softener resin?  
Best to keep the chlorine residual under 2.0 mg/L.    
7)  You say the "softener backwash, brine rinse, etc., can be reset to any time."  Then you comment "you would not want to exhaust the resin, so there are optimum settings for each."  How is resin exhausted?  What are these optimum settings?  How much higher can they be set before resin exhaustion is a concern? 
The cycles are preset, so you don't necessarily need to change them, but here are typical times: 
  • Backwash: 8 minutes 
  • Brine rinse: 60 minutes 
  • Fast rinse: 6 minutes
  • Brine refill: 8 – 12 minutes 
What you should set yourself, depending on your water hardness, is the number of gallons used between cycles.  The method for doing so should be outlined in your installation instructions. 
8) Your CWS Plus Series Softener is a little less expensive than the Fleck 7000-SXT - how does the quality compare?
CWS Plus Greensand Iron Filter 1.5CF
The Fleck can filter 30 gallons/minute and is applicable for commercial applications and very large homes.  For 5 - 15 GPM systems, we recommend the CWS Plus softener.
9) Who makes this valve?  Is it a Clack?  
It's made by Canature, a Canadian company. It is NSF-certified as well. 
10) What type of resin does it use?  Is it recommended for iron removal? 
It uses a high capacity softener resin, same as our other systems. It can be used for iron removal, but we would recommend a fine mesh resin instead of a Greensand filter, as the mesh would be more effective at filtering rust. 
11) One more question: At service flow rate, what will be the total pressure drop?  My chlorination system, contact tank, iron filter, carbon filter & water softener are all in series - will I have enough pressure left for a decent shower, etc.? 
There is no appreciable pressure loss through the chlorination and contact tank. You could expect to see a drop of about 5 to 10 PSI through the filters at 10 gpm, but this should hardly be noticeable in most systems.  
Thanks for the e-mail, Jim from North Dakota!  We hope we have answered your questions sufficiently, and that our readers have benefited from this information as well.

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