Iron and manganese are naturally occurring elements commonly found in groundwater in many part of the country were the underlying geology is igneous rocks. At naturally occurring levels iron and manganese do not present a health hazard. However, their presence in well water can cause unpleasant taste, staining and accumulation of mineral solids that can clog water treatment equipment and plumbing and discolored water. The standard Secondary Maximum Contaminant Level (SMCL) for iron is 0.3 milligrams per liter (mg/L or ppm) and 0.05 mg/L for manganese. This level of iron and manganese are easily detected by taste, smell or appearance. In addition, some types of bacteria react with soluble forms of iron and manganese and form persistent bacterial contamination in a well, water system and any treatment systems. These organisms change the iron and manganese from a soluble form into a less soluble form, thus causing precipitation and accumulation of black or reddish brown gelatinous material (slime). Masses of mucous, iron, and/or manganese can clog plumbing and water treatment equipment.
The key to iron and manganese removal is oxidation. An oxygen molecule must be supplied to change the minerals from the soluble bicarbonate to the insoluble hydroxide form so it can be filtered from the water. Four methods are typically used to deliver oxygen: aeration, ion exchange (a water softener), a greensand or iron filter, or chlorination.
If you have an iron problem, a manganese greensand filter often referred to as oxidizing, iron or red water filter might be a good solution for you. Like most home model water filters the typical manganese greensand filter is a pressure filter, a fully enclosed tank type filters that operates at the same pressure as the water delivery system so that you do not need to buy a booster pump. These devices are used for a variety of water treatment processes such as taste and odor improvement, iron and manganese removal and removal of suspended matter (turbidity) in water. The water treatment performed by a pressure filter is determined by the filter media that is inside the tank. Most companies that sell pressure filters use the same tank for all treatments but change the inside filter media depending on the type of treatment needed.
Iron filters contain a resin designed to remove iron and manganese that is in solution. It will also act as a filter and catch iron and manganese precipitates that have been oxidized before reaching the filter. Typically these filters are effective for iron and manganese removal concentrations up to 10 ppm. However, this type of filter will not tolerate iron bacteria, because the slimy material that is produced coats the greensand and fouls it. The greensand filter must be regenerated with a new solution of potassium permanganate when the oxygen is depleted. This process is similar to regenerating a softener. The filter must be backwashed every so often based on the size of the filter. The typical cycle is weekly.
The iron filters have been less successful in actual practice. Before you install any treatment system test your water thoroughly. An iron filter will not function if there is iron bacteria present in the well, because the slimy material that is produced by the iron bacteria coats the greensand and fouls it. Next, the functioning of the filter is pH dependent. Iron filters can remove iron when the pH is about 7.5 or higher, but manganese is very difficult to remove at pH values below 8.5. So to install a greensand or iron filter you first must adjust the pH of the water to the appropriate level. The final problem is iron breakthrough.
For the iron filter to work properly the correct flow rate is the secret to effective iron removal. Adequate flow is required to clear the filter bed of sediment before it becomes too dirty. Most well pumps used for private drinking water wells supply 10 to 15 gallons per minute (gpm) of flow. The size filter that can be used is limited by the backwash water available. That is why many of the home pressure filters are tall thin “bottle-type” units that are only 8 inches in diameter. This size filter can be backwashed with 8 to 10 gpm flow. However, the low surface area only provides treatment for a limited water flow of about 2 gpm on average or about 5 gpm for short peak flows. Use of higher volumes of water would result in iron breakthrough. At first the water will appear clear then often become brown or rusty after a few minutes. The chemical coating on a greensand or iron filter has limited oxidizing capabilities, but they can all be made more effective with the addition of a pre- oxidant step using air, chlorine, or peroxide in a first tank followed by the filtration step.
Before you select a treatment method for an iron and manganese problem you might want to consider all your options. Another approach for iron and manganese removal is chlorination. Chlorination and filtration can remove high concentrations of iron, iron bacteria, and hydrogen sulfide gas. The iron, manganese and hydrogen sulfide gas is oxidized by the chlorine. A sediment filter is used to remove the rust particles followed by an activated carbon filter is used to remove excess chlorine and other impurities. The resulting water has an excellent taste. For this system to work the pH of the water must be above 7. No other method of home water treatment has as many benefits as chlorination- disinfection and oxidizing agent.