Green sand filters are a type of water treatment system designed to remove specific contaminants, primarily iron, manganese, and hydrogen sulfide.
At their core, green sand filters operate through a process that combines oxidation with filtration.
The Core Mechanism: Oxidation and Filtration
Green sand filters work by utilizing a specific filter media with unique properties. This media is specially formulated filter media made from a naturally mined form of glauconite greensand. The crucial element of this media is its special coating of manganese oxide.
Here's how the process unfolds:
- Oxidation: When water containing dissolved iron, manganese, or hydrogen sulfide comes into contact with the manganese oxide coating on the greensand media, a chemical reaction occurs. The manganese oxide oxidizes iron, manganese and hydrogen in the water upon contact with the filter media. Oxidation converts these dissolved substances into solid particles. For example, dissolved iron (ferrous iron) is converted to solid iron particles (ferric iron). Hydrogen sulfide gas is oxidized into elemental sulfur particles.
- Filtration: Once these contaminants are oxidized into solid particles, the greensand filter media bed physically traps and removes them from the water as the water passes through.
Over time, the greensand media bed accumulates the trapped oxidized particles. To maintain effectiveness, the filter must be periodically cleaned through a process called backwashing, which reverses the water flow to flush out the accumulated solids. The manganese oxide coating, which is depleted during the oxidation process, can typically be regenerated using a solution of potassium permanganate.
What Green Sand Filters Remove
Green sand filters are highly effective at treating water issues caused by:
- Iron: Often causes reddish-brown staining on fixtures and laundry, and can give water a metallic taste.
- Manganese: Can cause black staining and greasy deposits, and may give water a bitter taste.
- Hydrogen Sulfide: Responsible for the unpleasant "rotten egg" odor in water.
By oxidizing and filtering these specific contaminants, green sand filters help improve water clarity, taste, and odor, while also preventing staining.
