How to regenerate Manganese Greensand ?
This can be done in a bucket or the filter unit. An easy procedure to follow is to mix one pound of KMnO4 per five gallons of water. Apply the solution to the filter media until it is covered, then allow it to rest overnight.
One thing to consider is if manganese and hydrogen sulfide are the primary contaminants the filter may remain effective for several weeks before regeneration is needed. However, with levels of iron ranging from 0.5 up to 10 or more mg/L, regeneration may be needed from every two days down to every 4 hours, depending on whether there is continuous or intermittent flow through the filter. If chlorine and/or KMnO4 are used for pre-filter oxidation of iron, the run time can be extended for higher iron levels with the addition of an anthracite layer on top of the greensand media. A primary concern is to not trap too much ferric hydroxide within the greensand because you can have precipitated iron coming through and a much greater pressure will be needed for adequate back flushing and regeneration. NOTE: Keep in mind that runs time for a filter unit on a private water system is based on the time water is actually flowing through the filter.
For example, your water system may have a pump capacity to provide a flow rate of over 10 gallons per minute and a 20-gallon storage tank. If your filter recommends using a 36-hour backwash and regeneration cycle for the iron level in your water for its 1 square foot surface area, this is based on continuous flow time. The 36 hours of flow time on the filter may take more than a month depending on your water use. If your household uses about 600 gallons of water per day, your pump would run about 60 minutes per day and your backwash cycle would be every 36 days. Most of the manufactured units have timers and are set up for automated backwash and regeneration, just like water softeners.
The following morning the marinated media is backwashed until no permanganate (pink color) remains in the wash water. If chlorine is being used as a pre-oxidant followed by KMnO4 for continuous regeneration (CR) of the greensand, maintaining a chlorine residual at the filter effluent of greater than 0.5 mg/L will ensure that the greensand retains its manganese oxide coating on the sand particles. NOTE: If residual chlorine level is too high, it should be reduced to a safe human consumption level by carbon filtration.
KMnO4 Dosage………………………… 1.5 – 2.0 0z/cu.ft
(1.5 – 2.0 kg/m3)
KMnO4 Stock solution strength…… 2-4 0z/gallon
( 15-30 kg/m3)
KMnO4 Regeneration volume ……… 7.5 gal/cu.ft*
KMnO4 Regeneration rate……………. 0.25 gpm/cu.ft
KMnO4 Regeneration time………….. 30 min. optimum
Rinse rate (raw water)…………………. 1gpm/cu.ft
Rinse volume……………………….. …..40-50 gal./cu.ft
(5.3 – 6.7 BV)
or until all traces of
KMnO4 are gone.
*Using 0.5 – 10 gallons (67 -134 L) of stock solution
and 6.5 – 7.0 gallons (870 – 940 L) of dilution water.
BV = bed Volume ( 1BV = 7.5 gal/ft3)
Note: recycle of regenerate and rinse water will
conserve both KMnO4 and rinse waste water.