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.
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.
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