Iron in Drinking Water
As iron is one of the most abundant elements found naturally in rocks and soils, it very often presents a problem as a drinking water contaminant. Although iron is not considered a health hazard, if levels rise above 0.3mg/L it may present a problem as it is on the list of secondary drinking water contaminants due to aesthetic problems that it imposes to both the water, and to household equipment that it comes into contact with. Iron in drinking water does not only affect the taste of the water, but it can discolor the water and stain household sanitary-ware, laundry, dishes and utensils. Deposits can also cause build up in plumbing and pipes, and as the deposits accumulate, water flow may be restricted due to reduced water availability and water pressure. Furthermore, if water has a high level of iron it may also harbor related bacteria, which while also harmless, poses additional problems as drinking water contaminants. As the iron bacteria consume iron they leave deposits of brown slime that can clog pipes. This slime also gives off an unpleasant odor, and as it tends to break free from piping in blobs, it can stain laundry.
Iron typically occurs in water in two forms. The ferrous (clear water) form is soluble and is thus dissolved in water. The ferric (red water) form is insoluble and thus stains the water red brown and leaves sedimentation of deposits. When the dissolved ferrous iron is exposed to oxygen it is converted to the insoluble ferric iron form, as a result, clear water containing dissolved iron turns a reddish brown color if left to stand, and the particles will eventually settle on the bottom of the glass. Iron may also combine with naturally occurring acids in the environment to form an organic complex known as organic iron, which, together with bacteria iron usually occurs as an insoluble ferric iron form.
Testing Water for Iron Related Drinking Water Contaminants
It is imperative that thorough water tests are conducted before undertaking any water purification measures to eradicate iron related drinking water contaminants from your water supply. Different water purification treatment options need to be implemented depending on the type of contamination that is present. Consequently you will need to determine if your drinking water contaminants are related to clear water iron, red water iron, organic iron, or bacteria iron. Water needs to be tested for concentration, presence of iron bacteria, pH and hardness.
Water Purification Methods to Remove Iron
The removal of iron from water typically involves filtration either by ion exchange, or in the case of soluble iron, filtration following oxidation, which is a two step process:
1. The soluble iron first needs to be converted to insoluble iron by oxidation.
2. Insoluble iron is then removed from the water by filtration.
Depending on the amount and type present, together with other variables, there are various methods of undertaking this as listed below:
Aeration: Introducing oxygen to the water source to convert soluble iron to its insoluble form, followed by filtration to remove suspended particles. Suitable for treating water containing dissolved ferrous (clear water) iron.
Chemical Oxidation: A chemical oxidizing agent, such as chlorine or potassium permanganate, is added to water to convert soluble iron to an insoluble form, which is then filtered out using a water filter. Suitable for treating water containing dissolved ferrous iron; and due to the strong anti-bacterial properties of chlorine, chlorination is also suitable for treating water containing the bacterial type.
Filtration: Use of water filters to entrap and filter out oxidized particles. Usually requires backwashing to remove accumulated deposits. Suitable for removing insoluble ferric (red water) iron.
Water Softener/Ion Exchange: Removal of soluble iron by ion exchange where an acceptable ion such as sodium is used to substitute soluble iron. Water softening units are capable of removing small amounts of iron, but when iron levels are higher they can become clogged, especially if iron bacteria is also present. Suitable for treating water containing dissolved ferrous iron, and organic iron.
Ozonation: A specialized form of aeration using ozone to convert soluble iron to insoluble iron. Suitable for treating water containing dissolved ferrous iron, and organic iron.
Catalytic Filtration: A granular filter medium that enhances the reaction between oxygen and iron and then filters out the insoluble iron particles. Suitable for treating water containing dissolved ferrous iron, and insoluble ferric iron.
Greensand Filtration: An ion exchange sand material containing glauconite, a mineral that is capable of removing dissolved iron through adsorption. Greensand filters need to be backwashed regularly, and the glauconite needs to be periodically rejuvenated by washing with a permanganate solution to restore the manganese coating that enables it to adsorb iron and manganese. Suitable for treating water containing iron in its dissolved ferrous form, insoluble ferric form, and organic iron.
Sequestering: Unlike the processes above, sequestering is a process whereby polyphosphates are added to water to prevent oxidation of iron in order to keep it in its dissolved form. The polyphosphates react with soluble iron to form a complex molecule that is stable in water and unable to react with oxygen. This keeps the iron in solution and prevents precipitation and the resulting red stains on laundry and household utensils. Suitable for treating water containing dissolved ferrous iron.
Image Credit: NDSU, http://www.ag.ndsu.edu/pubs/h2oqual/watsys/ae1030w.htm
The type of water purification method you choose to eliminate iron from your water supply will depend on various factors, including: water flow, pH, type and quantity of iron in your water. Consequently, it is advisable to seek professional advice to determine the best water purification solution for your situation.
Illinois Department of Public Health. Iron in Drinking Water. Environmental Health Fact Sheet. http://www.idph.state.il.us/envhealth/factsheets/ironFS.htm
Seelig, B., Derickson, R. & Bergsrud, F. Treatment Systems for Household Water Supplies: Iron and Manganese Removal. http://www.ag.ndsu.edu/pubs/h2oqual/watsys/ae1030w.htm
Wisconsin Department of Natural Resources. Iron in Drinking Water. http://dnr.wi.gov/org/water/dwg/iron.htm