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Greensand (GS) is the name commonly applied to a sandy rock or sediment containing a high percentage of the mineral glauconite. Glauconite is a greenish-black to blue-green mineral which forms in shallow marine sedimentary deposits.

GS Filtration is a water treatment process that employs a pressure filter vessel utilizing a single manganese dioxide coated glauconite media. It is commonly used in commercial, industrial filtration and water treatment plants for removing manganese, soluble iron, hydrogen sulfide, arsenic and radium.

GS filters are typically designed to flow at 2-5 gallons per minute (gpm) per square foot (ft2) of filter
surface area. A minimum of 12 gpm/ft2 during the cleaning cycle, called “backwash”, is required. Backwash is initiated manually or by pressure differential switch when the differential pressure across the filter increases by 12 psi. Excessive delta P can damage the media

During backwash the bed is lifted (or “fluidized”) to loosen the filter media and release trapped dirt removed in the backwash flow. After the backwash cycle, the bed is allowed to settle before the filter is returned to service (i.e., normal flow).


Chemical Pretreatment: Filtration with GS media often requires pretreatment with an oxidizing agent.
On small commercial or residential systems, this may be accomplished by oxygen in the air using a
small air pump and a contact tank upstream of the GS filter. In larger flows, such as with industrial
water filtration, it is typically accomplished with chlorine and / or potassium permanganate, a strong
oxidizer. Because the oxidation reaction required to convert the soluble material into solid particles,
followed by successful filtration must be accomplished in 1-2 minutes of filter residence time, the
water chemistry must be conducive to rapid reaction kinetics. Technical literature typically recommends
pH in the 6.2 to 6.5 range (optimal pH as high as 6.8 is dependent on the water source)

GSeensand filters can have graded support media layers or be directly installed over or on a distribution plate. The greensand is stored in the filter vessel with the bottom of the filter containing a porous collector. Greensand filtration is often combined with other filtration techniques such as activated carbon.


Conventional gravity and pressurized GS filters operate in the downflow direction. The filter media is usually a 30-36 inches deep bed of GS or sufficient media to allow for 50% expansion during backwash.

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