Greensand Plus Media for Iron Filtration
Greensand Plus is Inversand’s latest filter media for removing iron, manganese, arsenic, radium and hydrogen sulfide.
First and foremost, filter media is merely one component of a complete filtration system. It is not the be-all, end-all that will “make or break” a system. Like many things on the internet, different filtration medias end up with magical qualities that may not be entirely accurate.
Our job is to help clarify the water treatment technologies available, and to engineer and install the most reliable filter systems possible. This article will cover basic application guidelines to help keep you out of trouble. Future articles will cover exact information for removal of iron, arsenic, etc.
New Name, Same Basic Filter Media
Manganese Greensand has been used for years as a reliable iron and odor filtration media. The original Greensand formula used a glauconite core that was coated with manganese dioxide.
“Greensand Plus” is black granular media that is made by coating silica sand with manganese dioxide. The silica sand core of Greensand Plus allows it to withstand waters that are low in silica, TDS and hardness without breaking down.
Greensand Plus can be used as an exact substitute for Manganese Greensand as it has the same effective size, uniformity coefficient, density, weight, capacity, service flow rate, backwash and pressure drop curve. While it works exactly the same as it’s predecessor, the silica core is much harder, and will have a longer service life before eventually crushing.
How Greensand and Greensand Plus Work
Soluble iron and manganese are oxidized and precipitated as they come in contact with the greensand granules. Hydrogen sulfide gas is reduced by oxidation into an insoluble sulfur precipitate.
These precipitates are then filtered (mechanically strained) out of the water by the filter bed. Once the filter bed is full of these oxidized particles, it must be cleaned by backwashing or flushing them away.
It’s important to note that Greensand has a limited oxidizing capability before it must be regenerated to continue working.
Batch Regeneration – The Old Way
Periodic regeneration (every 3 days, etc.) is known as batch regeneration. Once the oxidizing capacity power is exhausted, the filter bed can be regenerated with a weak potassium permanganate (also known as PotPerm) solution. This is very much like the way a water softener uses salt, and is the only way the original Manganese Greensand could be operated.
1½ to 2 ounces of potassium permanganate, in solution, per cubic foot of Greensand Plus is considered sufficient for normal regeneration.
Constant Regeneration – A Better Way
This method involves feeding chlorine (CI2) into a retention or storage tank before the Greensand Plus Filter. A chlorine residual carried through the filter will maintain Greensand Plus in a continuously regenerated condition for superior performance.
**It should be noted that Inversand DOES NOT recommend using Greensand Plus with air injection unless iron levels are very low (0.3ppm).
Because this approach requires an extra tank and a chemical feed pump, it is both more expensive and larger in size. That being said, the filter performance is SIGNIFICANTLY BETTER, operating cost is much lower, and maintenance is more convenient and less messy than the Potassium Permanganate (PotPerm) route.
Service Flow Rates
Like all filters, Greensand Plus has a limitation as to how fast you can push water through it before iron, etc. will bleed through.
5 gallons per minute/square foot of surface area(5gpm/sq. ft.) is the maximum service flow rate recommended for iron and hydrogen sulfide removal. 3gpm/sq. ft. is recommended for Arsenic removal.
A 14″ diameter tank has a little over 1.07sq. ft. of surface area, and would deliver about 5.4gpm of clean water. So if you needed 20gpm of iron/odor-free water, you would need 4 square feet of filter media, or roughly (4) 14″ diameter tanks.
Backwash Flow Rates
It is required to vigorously backwash the filter bed once it has become loaded up with oxidized matter.
A 12gpm/sq. ft. backwash flow rate is required to properly backwash Greensand Plus. This means a 14″ tank would require 12.9gpm to backwash and would require a 1″ drain line.
If the filter is not sufficiently backwashed, iron, etc. will load up in the filter and quickly destroy it. Once that has occurred, the entire filter bed must be replaced.
Hopefully this article has cleared up what Greensand Plus is, and how it can be effectively used.
When space or budget is limited Premier Water has designed and built systems using batch regenerations with PotPerm.
By far our highest customer satisfaction with Greensand Plus systems has come with systems using constant chlorination for applications where iron, hydrogen sulfide, and arsenic removal was needed.