Iron is known to leach into water supplies throughout the United States
from rock and soil formations. It has been said, probably an
exaggeration, that there is hardly a square foot of soil that does not
have some iron content. Iron is at least 5% of the earth's crust.
A yellow to reddish discoloration can appear in water in concentrations
as low as 0.3 ppm (parts per million) and begin the staining and scale
process, depending on the pH, as well as taste and odor problems.
Five types of iron that can be found in potable water
Sequestering agents are used by municipalities & industry for
treatment of large quantities of water. It is not important to farming
where private wells are the principal source of water.
Heme iron-- Iron Found in organics
This type of iron can not be removed by softening resins. Heme iron is
most common in surface water and shallow wells. It is usually a yellow
/ brown color. Heme iron is a breakdown product of dead vegetation.
The iron and organics (tannins) require one ppm of sodium hypochlorite
and a retention time of 20 to 25 minutes in a pH range of 6.5 - 7.5.
Following the oxidation, a filtration media must be used to remove the
oxidized iron and the residual of chlorine.
Favorable conditions for the growth of Crenothrix, Gallionella, and
Clonothrix (or "iron bacteria") can exist at very low levels of iron.
Oxygen creates an oxidizing energy to precipitate ferrous iron into
bicarbonate that is necessary for iron bacteria to exist. This
bacterium can now live in a very wide range of conditions.
Iron bacteria water will have a reddish color and an objectionable
odor. These organisms's growths cause a jelly-like bio-mass. This mass
can render media and resin filtration ineffective, reduce the
effectiveness of any oxidizing agent, and plumbing fixtures. Iron
bacteria is, because of its organic nature, the most difficult to
remove and control.
Ozonation is the recommended solution to this problem.
Ferric Iron-- Red water iron
In nature, iron is usually found in its oxidized insoluble form. Clear
water iron, or soluble iron, once exposed to an oxidant or to oxygen
will precipitate into an insoluble hydroxide form usually yellowish or
reddish in color. This iron, while in the clear water state, could be
removed by softening resins or by activated multi-media filtration. If
one uses a 5-25 micron filter it may pack out in a short time and
reduce flow and pressure. Changing these filters then become expensive
and time consuming. Multi-media filters are more expensive to purchase
upfront but the cost per gallon of water filtered is much less and
requires little or no time.
Ferrous Iron-- Clear water iron
Sometimes this iron is called ferrous bicarbonate iron. This iron may
be removed by a softening resin with a positive charge; however, it
must be in the invisible soluble form until it is filtered. To prevent
the iron from precipitating to its insoluble form frequent
regenerations are necessary. If the iron does precipitate, fouling on
the resin surface will occur, as well as within the matrix of the bead.
This fouling can be minimized by pre-treating the incoming water with
an activated carbon filter or by adding chemical cleaners to the brine
or potassium regenerate. There are a number of chemical cleaners that
will reduce red water iron to clear water iron. These cleaners are
necessary when iron levels are high and normally they do not harm the
resins. Many filter medias available today oxidize ferrous iron into
ferric iron which can then be removed physically.