About Greensand Filters
Posted by Gerry Bulfin CWS-VI on 03 August 2012 04:55 AM
Q. Why are these systems called "greensand" iron filters?
A. These filters use a specially formulated filter media made from a naturally mined form of glauconite greensand. The greensand filter media has a special coating of manganese oxide, which oxidizes iron, manganese and iron in water, upon contact with the filter media.
Q. How do they remove iron and manganese from water?
A. Iron and manganese are metals often found dissolved in water. They cause stains when exposed to air in the laundry, bath, etc. by oxidizing or "rusting." The greensand filter media oxidizes dissolved iron and manganese on contact, as the water flows through the greensand filter, and causes these elements to precipitate (or form solids) in the bed of the filter. The iron filter backwashes these small particles to drain every few days in the middle of the night (or some other preset time), thereby cleaning and restoring the filter media. To provide the oxidizing power to precipitate these metals, the filter is automatically cleaned and restored with potassium permanganate (a purple liquid) during each backwash cycle.
Q. What does the potassium permanganate do exactly? What is it for?
A. The Greensand media can only work so long to oxidize (which means convert the dissolved iron to a type of oxidized or rusted iron) before the media become exhausted. When the oxidizing capacity power of the ManganeseGreensand bed is exhausted, the bed has to be regenerated with a weak potassium permanganate (KMnO4) solution thus restoring the oxdizing capacity of thebed. The iron filters are set to automatically use 1� to 2 ounces of potassium permanganate, in solution, per cubic foot of greensand. It is required to backwash and regenerate the bed when it is first placed in service and before its oxidation capacity is totally exhausted. Operating the bed after oxidation capacity is exhausted will reduce its service life and may cause staining.
Q. Is potassium permanganate toxic or harmful?
A. Potassium permanganate is a powerful oxidizer and, similar to chlorine, can cause skin irritation or burns if direct contact were to occur. But, no permanganate is added to the filtered water. The permanganate is only used to backwash and clean the greensand filter media. A special rinse cycle makes sure the filter bed is free of any permanganate residual.
Q. What is the difference between "greensand filters" and "greensand-plus filters"?
A. The difference between GreensandPlus and manganese greensand is in the substrate that forms the core of the media and the method by which the manganese dioxide coating is attached to that substrate. GreensandPlus has a silica sand core and the coating is fused to it while Manganese Greensand has a glauconite core and the coating is ionically bound to it. The silica sand core of GreensandPlus allows it to better withstand operating conditions in waters that are low in silica, TDS and hardness.Greensand-plus does not require potassium permanganate, but it does require one feed in chlorine ahead of the greensand-plus filter. If you are planning on using chlorination we usually recommend greensand-plus iron filters, if you don't plan to chlorinate (or use ozone) ahead of the filter system, the regular greensand filter works better.
Q. Do these systems come in different sizes?
A. Yes. The size of the system is directly proportional to the flow rate of the water, in gallons per minute. The higher the flow, the larger the system required. Recommended backwash flow rates must be observed.
Q. Do these filters have any special conditions in order to work properly?
A. Yes! There are very specific conditions required. The water must have a pH of 6.7 to 8.8. If the water has a pH of less than 6.8 we usually recommend treating the water first with a neutralizer filter or a soda ash feeder. The best applications have feed or raw water of less than 15 PPM of iron and manganese, combined. The maximum practical removal rate for hydrogen sulfide is 5 PPM. The water should contain no tannins or oil.
Q. My water has a very bad smell of sulfur, will this be removed?
A. While these greensand filters will remove up to 5 PPM of hydrogen sulfide, in some cases the odor can be coming from conditions that exist after the water enters the plumbing. For instance, water heaters often have decaying anode rods that create hydrogen sulfide gas, so that even if the water entering the water heater is clean and odor-free, you can still have an odor problem. It is important to identify the source of the odor and to verify that it is in the cold water also, which would indicate that all the incoming water has an odor. In many cases, a thorough sanitizing of the household plumbing with chlorine is recommended after installation. Also see our report on How To Treat Odors in Well Water.
Q. If I want to use a chlorinator for my water, can I use this type of iron filter?
A. Yes. These iron filters actually work better with a chlorine feed. They also work great after the water has been ozonated. With ozone or chlorine pretreatment, the permanganate dosage can be drastically reduced.
Q. I have very high manganese (greater than .05 PPM), will these iron filters remove manganese also?
A. Yes, these systems work great to remove manganese, both dissolved and oxidized. For manganese removal these are an excellent option, as many iron filters do a good job of removing iron, but do not do a good job at removing manganese.
Q. What maintenance is required?
A. Once every one to three months depending on how often the iron filter is set to backwash, a few pounds of dry potassium permanganate powder is added to the little solution tank. Once a year there is some general maintenance that should be done to the iron filter and permanganate solution tank, which takes about one hour. No special tools are required.
Q. Will there be a pressure drop through the system?
A. Properly sized, the system produces a very low pressure drop at service flow rates, usually around 5 psi. Most people don't see any pressure loss in their household piping.
Q. Can I route the backwash water to my septic tank?
A. Yes. The backwash water can be routed to the septic tank with no problem in almost all cases.
Q. How frequently do I have to replace the filter media?
A. The filter media will last for 4 to 8 years depending on usage and conditions. It is easily replaced. Need more information? E-mail us: firstname.lastname@example.org
Q. Can I get assistance in choosing an iron filter system for my application?
A. Yes! You should first have your water tested, and then contact our technical staff for help on selecting the best iron filter system for your application. Also see our Custom Water System Design Questionnaire which makes it easy to help you select a system.
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