Tech Talk 46
If iron is in your water, you can either move to another location or spend some effort to remove it. The presence of iron above .1 ppm is considered detrimental to most freshwater fish-keeping (.5 is lethal). Iron-bearing water, when fresh out of the ground, is usually clear because iron is in the soluble ferrous iron form. As soon as it reacts with a little oxygen (.14 ppm per part of iron), the iron is changed to the ferric state and turns brown or orange. Then, it either drops out (precipitates) or remains suspended as a colloid.
There are three general classes of iron-bearing ground water:
- Those that precipitate immediately after aeration.
- Those that do not precipitate (acid waters).
- Those that precipitate only part of the iron.
To remove iron that precipitates readily, simply aerate or spray water into the air using the well pump's pressure. Hold the water in a settling basin, followed by a slow rate sand filter of about two gallons per square foot per minute.
For removing more difficult iron, the aerated water may be passed over coarse contact media (lava, stones, coke, etc.) in a multilevel tray. The media soon becomes coated with iron hydroxide, which promotes catalytic precipitation of iron and manganese from the water.
All three classes of iron can be removed by the lime-softening process and/or the zeolite process, sometimes called greensand.
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