Manganese greensand is a specially processed medium for iron, manganese, and hydrogen sulphide removal. This premium non-proprietary filter medium is processed from glauconitic greensand on which a shiny, hard finite thickness manganese oxide coating is formed and is firmly attached on every grain by a controlled process.
The Greensand Process
The grains of manganese greensand are of both the size and shape to capture the fine precipitates of iron and manganese, which pass through the upper layer normally.
True manganese greensand process requires no detention time, no filter media, no high concentration of chlorine, and no sulphur dioxide.
Manganese greensand is catalytic by nature and is not soluble. There is no increase in the total dissolved solids of the treated water, and it is not necessary to backwash manganese greensand every time the well pump starts up.
Ferrosand Filter Media is manufactured to exact specifications to ensure the complete oxidation of soluble iron, manganese etc. using stoichiometric quantities of oxidising agents, without the need for long reaction times or elevated pH levels. (For arsenic removal, a prefeed of ferric chloride may be required.)
A major benefit of Ferrosand is that it can be used in two distinct methods of operation. These are described below.
Ferrosand Continuous Regeneration for Iron Removal
The Ferrosand Continuous Regeneration (CR) process is used primarily when iron removal is the objective, with or without the presence of manganese. Tthis technology has proven to be the most cost effective design when iron predominates in the raw water.
The CR method uses a continuous pre-feed of potassium permanganate (KMnO4) or a combination of chlorine (CL2) and KMnO4 to the raw water prior to contacting the Ferrosand Filter. Soluble iron and manganese are oxidised to the insoluble form and filtered out by a dual media anthracite / Ferrosand bed.
Due to the unique chemical and physical properties of the Ferrosand, attributable to the multivalent manganese oxide coating covering the greensand grains, iron and manganese are removed to levels required by the Safe Water Drinking Act or process requirements.
Manganese oxide has a well known catalytic effect on the oxidation of soluble iron and manganese, and provides a redox buffer capable of either oxidising remaining traces of iron and manganese, or reducing excess KMnO4 as required.
This not only ensures the consistent removal of iron and manganese and maintains the Ferrosand in a regenerated state.
Ferrosand Intermittent Regeneration for Manganese Removal
For groundwaters containing only manganese, or manganese with lesser amounts of iron, the Intermittent Regeneration (IR) process may be in order. It allows for extended run lengths with a minimum amount of head loss during the filter run. In this process, a filter bed of Ferrosand is periodically regenerated with a solution of KMnO4. The frequency of regeneration is contingent upon the concentration of raw water manganese and the volume of water treated.
During the service cycle, manganese is removed by utilising the oxidative capacity of the Ferrosand. Oxidation of the soluble manganese occurs directly on the Ferrosand grains, becoming an integral part of the manganese oxide coating.
Advantages
- Iron reduction over wide pH range
- Effective reduction of hydrogen sulphide, iron and manganese
- No harmful effects from a chlorine feed
- Low attraction for long bed life
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Properties
- Colour: Black
- Bulk Density: 85 Ibs./cu. Ft
- Specific Gravity: 2.4-2.9
- Effective Size: 0.30-0.35
- Uniformity Coefficient: 1.6
- Mesh Size: 16-60
- Loss Per Year: 2%
Conditions for Operation
• pH 6.2-8.5
• Max. water temperature 26.7°C
• Bed depth 30 inches
• Freeboard: 50% of bed depth (min.)
• Regeneration: 1.5-2 oz of KmnO4 by weight per cu. ft.
• Service flow rate: 3-5 gpm/sq.ft., 8-10 gpm/sq. ft. intermittent flow possible
• Backwash flow rate: 10-12-gpm/sq. ft.
• Backwash bed expansion: 40% of bed depth (min)
• Maximum practical limit of iron (Fe++) or manganese (Mn++) in raw water:15ppm
• Maximum practical limit of hydrogen sulphide (H2S): 5 ppm
Intermittent Regenerations
• 10,000 gallons of water containing 1mg/L Iron per cu. ft. regeneration
• 5,000 gallons of water containing 1mg/L Manganese per cu. ft. regeneration
• 2,000 gallons of water containing 1mg/L Hydrogen Sulphide per cu. ft. regeneration