Alternatives for Iron Removal
An iron problem is characterized by the red-brown
staining of bathroom fixtures and laundry. In well
water, iron usually occurs in its ferrous state. The water
is
clear when drawn but once exposed to air the iron changes
into a ferric (oxidized) state. The water turns red and
forms insoluble “rust” particles. Staining can
be caused by
as little as 0.3 milligrams per litre (mg/L). Depending on
the iron concentration there are several solutions to this
aggravating water problem.
Iron Bacteria
Often an iron problem is the direct result of an infestation
of iron bacteria. Although these bacteria do not present
a health hazard, they stain fixtures, can clog pipes and
valves, and make the water unpalatable. The best control
can often be accomplished by shock chlorination. Shock
chlorination is the direct treatment of a well and water
system with 15 to 20 L of chlorine bleach. This strong
chlorine solution is held in the well and water system for
at least eight hours before being flushed out. Shock
chlorination won’t solve the problem permanently, but
it
will usually keep the bacteria in check. This procedure
should be carried out before selecting iron removal
equipment. Shock chlorination in spring and fall is
recommended for the continued successful operation of
any water treatment equipment.
Continuous chlorination of the well, using dry pellets or
liquid chlorine, is another option. Occasionally this
treatment may be needed when iron bacteria cannot be
effectively controlled by shock chlorination.
1. Air Injection (See Terminator
System and Birm)
These iron filters use the oxygen in the air to oxidize
the iron in the water. A small venturi type air injector
is installed between the pump and pressure tank to draw the
air into the water. The iron oxidizes to form rust particles
which are then strained out by a filter. These filters have
worked very well, and are presently replacing the
manganese greensand filter in the market place. Some
companies selling these units claim iron removal capability
up to 30 ppm of iron. High iron situations often require
extra equipment, such as retention tanks, air release valves,
and air mixing devices.
Conditions for use include: adequate pump and well
capacity for backwash and air injector operation, adequate
time for iron to oxidize before passing through the filter,
proper adjustment of the air injector.
2.
Manganese Greensand Iron Filter (See Manganese
Greensand System)
The manganese greensand iron filter used to be the most
common iron removal device. It can be used successfully
for iron concentrations up to approximately 6 mg/L. Iron
is oxidized by a coating on the manganese greensand. The
greensand must be periodically regenerated with
potassium permanganate to replenish the oxygen on the
greensand.
Continued successful operation requires an availability at
least 20 L per minute flow for proper backwash, pH
above seven, and regular regeneration. Failure to
regenerate often enough can ruin the filter media.
3. Water Softener
A water softener will generally remove up to 3 mg/L of
iron. The iron must be in the ferrous (clear water) state
or the iron will damage the softener resin. Care must be
taken if a softener is used to remove iron because iron
tends to clog and foul the softener resin. A resin cleaning
compound must be used regularly to protect the resin.
The most common resin cleaning compounds contain
sodium hydrosulfite or phosphoric acid. Some water
softener salt contains a resin cleaner.
5. Chlorination-Filtration
Another system for iron removal is chlorination.
Chlorination and filtration can remove high
concentrations of iron, iron bacteria, and hydrogen sulfide
gas. The iron is oxidized by the chlorine. A sediment filter
is used to remove the rust particles and an activated
carbon filter is used to remove excess chlorine. The pH of
the water must be above seven.
6. Aeration, Settling and Filtration
High levels of iron can be removed from water by
spraying the water into a storage cistern. The iron is
oxidized by spraying it through the air. Some of the
resulting iron particles are settled out in the cistern,
the rest are filtered out by repumping through a sediment
filter. This alternative is particularly useful where the
well has a low capacity. Most iron removal equipment requires
four to five gallons per minute for proper operation |
