Iron is one of the most troublesome elements in water supplies. Making up at least 5 percent of the earth’s crust, iron is one of the earth’s most plentiful resources. Rainwater as it infiltrates the soil and underlying geologic formations dissolves iron. It is understandable, therefore, that most groundwater supplies contain some measurable amount of iron. Although present in water, iron is seldom found at concentrations greater than 10 milligrams per liter (mg/l) or 10 parts per million. However, as little as 0.3 mg/l can cause water to turn a reddish brown color. Iron stains and contaminates anything it contacts. The resulting stains are usually yellowish-brown to reddish-brown, but may be gray to black in the presence of some organics. Iron may also cause undesirable odors and tastes in water.

Iron is mainly present in water in various forms but the two most common forms are either the soluble ferrous iron or the insoluble ferric iron. Water containing ferrous iron is clear and colorless because the iron is completely dissolved. When exposed to air or the atmosphere, the water turns cloudy and a reddish brown substance begins to form. This sediment is the oxidized or ferric form of iron that will not dissolve in water.

Manganese is frequently found with and is similar to iron but forms a brownish-black precipitate and stains. Manganese is less commonly found in groundwater than iron, rarely found alone in a water source, and generally found with dissolved iron

Health

Iron in water is not hazardous to health, but it is considered a secondary or aesthetic contaminant. Essential for good health, iron helps transport oxygen in the blood.

Taste and Food

Dissolved ferrous iron gives water a disagreeable taste. When the iron combines with tea, coffee and other beverages, it produces an inky, black appearance and a harsh, unacceptable taste. Vegetables cooked in water containing excessive iron turn dark and look unappealing.

Stains and Deposits

Concentrations of iron as low as 0.3 mg/l will leave reddish brown stains on fixtures, tableware and laundry that are very hard to remove. When these deposits break loose from water piping, rusty water will flow through the faucet.

Iron Bacteria

When iron exists with certain kinds of bacteria, problems can become even worse. To survive, the bacteria metabolize the iron, leaving behind a reddish brown slime that can clog plumbing and cause an offensive odor. This slime or sludge is noticeable in the toilet tank when the lid is removed. An extensive study by Johnson Filtrations Systems, St. Paul, MN, found that with concentrations of more than 6 ppm Fe, the presence of iron bacteria was almost always a certainty. Likewise at less than 2 ppm the iron bacteria was rarely found.

Iron bacteria do not cause health problems in people, but they may have the following unpleasant and possibly expensive effects:

• Unpleasant odors and taste following the death of the bacteria
• Increased organic content in water favoring the multiplication of other bacteria
• Piping clogged with rusty sludge
• Corroded piping and plumbing equipment
• Increased chances of sulfur bacteria infestation

Organic Iron

Since iron combines with different naturally occurring organic materials, it may also exist as an organic complex. Organic iron is picked up as groundwater passes through decaying or decayed vegetation. This is commonly known as “tannin or lignin” and gives the water a brown or yellow tint similar to dilute tea or coffee. This combination of naturally occurring organic material and iron can be found in shallow wells and surface water. This type of iron is usually yellow or brown but may be colorless.

Well Construction

One alternative in solving an iron problem may be to construct a new water well, eliminating the need for treatment. Not always, but shallow wells (less than 125ft.) in glacial drift and unconsolidated sediments may have greater amounts of iron than deeper aquifers. Most well drilling contractors associated with the National Water Well Association (NWWA) or the National Ground Water Association (NGWA) can provide assistance and information.

Treatment Methods

Iron and manganese treatment should be based on a chemical analysis of the water showing the type and concentration present. There are many treatment methods for the removal of iron and manganese from water systems. Before selecting the proper method you need to know:

• What form of iron do I have in my water system?
• According to the water test results, will the water treatment unit remove the total iron concentration? (Total iron includes both soluble and insoluble iron.)
• Will the treatment unit treat the water at the flow rate required for my water system?
• Will the pH have to be adjusted prior to a particular treatment?
• Would the construction of a new well or the reconstruction of an existing well is more cost effective than a long-term iron removal treatment process?

Water Softener (Ciation Exchange)

A water softener can remove moderate amounts of ferrous iron and manganese. Iron and manganese in untreated water are flushed from the softener medium (ion exchange) by backwashing (forcing sodium-rich water back through the unit). This process adds sodium to the resin medium, and iron and manganese are carried away in wastewater.

The amount of iron and manganese a softener can remove depends on the water properties, the types of regeneration and backwash controls, and the ion exchange resin used. At low pH levels (<6.5) up to 15 – 20 ppm of iron can be removed by this method.

You must maintain a clean resin bed by frequent and thorough backwashing and regeneration. Manufacturer literature should be carefully studied and system set-up and operation instructions followed. Water Softeners How They Work.

Years ago, it was thought that unsoftened water should be used for drinking and cooking, and a separate hard water line was run to the kitchen. Today this is not done. The amount of sodium added to softened water is insignificant. See the section on Sodium in Drinking Water. One order of fries from McDonald’s will have more sodium than you would get in a months worth of drinking water. The presence of iron and hardness minerals in water cause many problems in food and drink preparation.

Aeration

Dissolved iron and manganese are easily oxidized to a solid form by mixing with air. A compressor or other air injection system mixes air with the water; the iron is oxidized and then filtered out in a mixed media or multi media filtration bed. See section on AerMax Iron removal systems

This method adds no chemicals to the water and is effective against nearly ALL forms of iron including iron bacteria. Iron bacteria are anaerobic, or grow in the absence of oxygen. When exposed to high concentrations of oxygen in the air they are destroyed and filtered out. An added benefit is that organics that contribute to tastes and odors are also removed at the same time. For proper operation the filter must be backwashed at the proper flow rate and frequency to properly maintain the system.

Oxidizing (Catalyst) Filter

When the total combined iron and manganese concentration is less than 15 mg/l, an oxidizing filter such as a manganese greensand. These are commonly known as Iron-Sulfur filters, since they also remove hydrogen sulfide. The filter media is coated with a manganese oxide and is regenerated by using a potassium permanganate solution. An oxidizing filter supplies oxygen to convert ferrous iron into a solid form, which can be filtered out of the water.

Frequent backwashing of the manganese greensand bed helps prevent an iron-fouled bed. The greensand filter should be regenerated with potassium permanganate to regenerate (recoat) the greensand to allow adsorption of more iron and manganese. Potassium permanganate is a very strong oxidizer, and is extremely corrosive to seals, injectors, and components of the iron removal equipment. In residential systems that use intermittent regeneration, only low flow rates can be treated. For higher volumes of water needed for sprinkler irrigation continuous permanganate feed systems are suggested.

Other catalyzing media such as BIRM from Clack Corporation are good but depend on the presence of dissolve oxygen in the water, and typically have to be replaced every 1-3 years.

Chlorination and Filtration

When the iron and manganese content of the water is extremely high (above 10 ppm), a combination of chlorination and filtration can be used. Small chemical feed pumps are used to add chlorine bleach, calcium hypochlorite solution, or hydrogen peroxide into the water. After an adequate retention time to allow for oxidation of ferrous iron into the insoluble ferric form, the solid particles are filtered out. This is essentially the same as the aeration system but uses chlorine which is a much stronger oxidizer. Chlorine injection rates need to be carefully monitored and if too high will need to be removed with an activated carbon system after the iron removal system. An additional benefit of continuous chlorination is that the water will be disinfected which will prevent the build-up of iron bacteria.

Related Water Problems

Cleaning Iron Stains

Plumbing fixtures and surfaces that have been stained by iron in water can be cleaned by soaking or washing the parts in a solution of sodium metabisulfite (sold as commercial products "Iron Out", "Rust Out", etc) and water. Follow the recommended instructions for cleaning plumbing fixtures. The bisulfite solution will react with (reduce) the iron oxide so that it dissolves. A quarter to a half cup of the powder to your salt tank for the softener every 4-6 months will also help to clean the ion exchange resin of iron build up. Don’t overdo it-every few months is enough.

Manganese

Manganese is rarely found alone in a water source but is generally found in conjunction with dissolved iron. Concentrations as low as 0.1 mg/l are considered troublesome. Deposits of manganese will collect in plumbing systems and the tap water will contain a black sediment and blackish turbidity. Manganese bacteria may be present and, like iron bacteria, cause black staining, and clogging of piping and fittings.

Manganese reduction and removal is commonly accomplished by the same techniques applied to iron removal. Like iron, there is no health-related standard for manganese in drinking water. The USEPA set a recommended limit of 0.05 mg/l for aesthetic reasons (taste, discoloration, and staining of laundry and plumbing).

Hydrogen Sulfide

Hydrogen sulfide (H2S) is a gas that gives water a rotten egg taste and odor. Sulfur is a common element that occurs naturally in many ground water supplies, especially those that also contain iron. Besides its offensive odor, hydrogen sulfide is highly corrosive and can eat away at metal piping and plumbing connections. Like dissolved iron and manganese, hydrogen sulfide in water supplies can also be treated for removal by chemical oxidizing agents like chlorine.

Sulfate Reducing Bacteria

Sulfate reducing bacteria (SRBs) are another source of hydrogen sulfide in water. These bacteria live where there is little or no oxygen and convert sulfate and other sulfur compounds into hydrogen sulfide. SRBs are often found inside thick iron bacteria incrustations. Like iron bacteria, chlorination, periodic flushing and elimination of dead-end lengths of piping can control SRBs.

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