Iron and Manganese Removal: Treating Red and Black Water

One of the most common complaints from private well owners is "red water" or water that tastes like a rusty nail. This is caused by Iron. Its close cousin, Manganese, causes similar issues but leaves black, slimy stains.

While usually not a health risk, these metals wreak havoc on plumbing, ruin laundry, and make water undrinkable. Here is how we remove them.

The Two Forms of Iron

To treat iron, you must first know what kind you have:

1. Ferrous Iron (Clear Water Iron): Soluble iron. The water comes out of the tap clear, but turns red after sitting in a glass. This is dissolved in the water.
2. Ferric Iron (Red Water Iron): Insoluble iron. The water comes out of the tap already red or yellow. The iron has already rusted (oxidized).
3. Iron Bacteria: Living organisms that feed on iron, creating a slimy sludge that clogs pipes.

The Chemistry of Rust

To remove Iron, we must speed up the "rusting" process. The chemical reaction looks like this:

4Fe²⁺ + O₂ + 10H₂O → 4Fe(OH)₃ + 8H⁺

• Fe²⁺ (Ferrous): Dissolved and invisible (Clear Water).
• Fe(OH)₃ (Ferric Hydroxide): Solid, red, and filterable (Red Water).

Media Comparison: Choosing the Right Filter

Advanced Oxidation Methods

1. Aeration Tower: Cascading water over trays to pull oxygen from the air. Best for large flows.
2. Vuri Tube / Injector: Sucking air into the pipe before the filter. Cheap but can cause "milky" water (micro-bubbles).
3. Chemical Injection: Using a dosing pump to inject Chlorine (Bleach). Not only does it oxidize iron instantly, but it also kills Iron Bacteria which clog other filters.

Design and Maintenance

Tank Sizing

Iron filters need a lot of water for backwashing. Because iron is heavy, the water必须 flow fast enough to lift the heavy media and flush out the trapped rust.

• Rule of Thumb: Backwash flow rate should be $3 \times$ higher than the service flow rate.

Maintenance Checklist

• Weekly: Regenerate the media (if using Greensand).
• Monthly: Clean the injectors/aerators. They often clog with the very rust they produce!
• Quarterly: Test inlet and outlet water. If iron is leaking, the media may be "passivated" or exhausted.