Thursday, January 6, 2011

Iron and Manganese in Well Water

Many of the perceived problems with well water are caused by the presence of iron and manganese. Iron and manganese can give water an unpleasant taste, odor and color. Iron causes reddish-brown stain on laundry, porcelain, dishes, utensils, glassware, sinks, fixtures and concrete. Manganese causes brownish-black stains on the same items. Detergents do not remove these stains. Chlorine bleach and sodium carbonate may even make the staining worse. Iron and manganese deposits build up in pipelines, pressure tanks, water heater and water softening equipment. These deposits restrict the flow of water and reduce water pressure. More energy is required to pump water through clogged pipes and heat water if the hot water tank’s heating rods are coated with minerals deposits. In addition, water contaminated with iron and manganese often contains iron or manganese bacteria which feed on the minerals. These bacteria do not cause health problems, but can form a reddish brown or brownish black slime in toilet tanks and clog filters.

Iron and manganese are naturally occurring elements commonly found in groundwater in many parts of the country. Interestingly enough, few surface water sources have high levels of these metals. At t levels naturally present in groundwater 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. In addition, a persistent bacteria/ biofouling problem may be caused by iron bacteria. Under guidelines for public water supplies set by the Environmental Protection Agency (EPA), iron and manganese are considered secondary contaminants. Secondary standards apply to substances in water that cause offensive taste, odor, color, corrosion, foaming, or staining but have no direct impact on health. 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.

Iron and manganese exist in many different chemical forms. The presence of a given form of iron or manganese in geologic materials or water depends on many different environmental factors. Dissolved iron and manganese are easily oxidized to a solid form by mixing with air. In surface water, iron and manganese are most likely to be trapped within suspended organic matter particles. Groundwater tends to be an oxygen poor environment; typically, the deeper the aquifer the less dissolved oxygen is present. Iron and manganese carbonates in an oxygen poor environment are relatively soluble and can cause high levels of dissolved iron and manganese to be carried from a deep well. If sulfur is present in the water then the iron will form iron sulfide rather than iron carbonate and the water may have the familiar unpleasant rotten egg smell. Sometimes oxygen poor conditions can also occur in relatively shallow wells that have stagnant water with very slow turnover. When the iron and manganese are oxidized reddish brown or black particles form and settle out as water stands. These particles are often found trapped in washing machine filters, water treatment equipment, in plumbing fixtures and on clothing, dishes and utensils.

As mentioned above some types of bacteria react with soluble forms of iron and manganese and form persistent bacterial contamination in a water system (especially one with any type of filter or treatment system to capture these iron or manganese bacteria). These organisms are usually found in waters that have high levels of iron and manganese in solution. The reaction changes 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. They also slough off in globs that become iron or manganese stains on laundry. Bacterial reactions with iron and manganese do not cause any additional precipitation compared to normal exposure to oxygen. However, precipitation caused by bacteria occurs faster and the slime tends to concentrate staining making it more annoying.

All systems of removing iron and manganese essentially involve oxidation of the soluble form or killing and removal of the iron bacteria.  When the total combined iron and manganese concentration is less than 15 mg/l, an oxidizing filter (natural manganese greensand, manufactured silica gel zeolite coated with manganese dioxide, plastic resin beads, or birm, is recommended. Some filters are coated with a manganese oxide and are 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. Synthetic zeolite is a water softener and while it requires fewer backwashes, it can impact the taste of the water, thought anything might be better than the iron and manganese impacts.

Higher concentrations of iron and manganese can be treated with an aeration and filtration system. This system is not effective on water with iron/ manganese bacteria, but is very effective soluble iron and manganese. In this system an aspirator valve pulls air into the water stream to oxidize the iron and manganese to the carbonate form. The air saturated water then enters a precipitator vessel to allow the iron and manganese time to precipitate out and then is passed through a filter. Backwashing the filter is very important to maintain the filter’s function. This system of removal does not involve any chemical additives.

Chemical oxidation can be used to remove high levels of dissolved or oxidized iron and manganese as well as treat the presence of iron/manganese bacteria. The system consists of a small pump that puts an oxidizing agent into the water before the pressure tank. The water will need about 20 minutes for oxidation to take place so treating before a holding tank or pressure tank is a must. After the solid particles have formed the water is filtered often through a sand filter with aluminum sulfate added to improve filtration. The oxidizing agent is used is chlorine, potassium permanganate or hydrogen peroxide. If chlorine is used, an activated carbon filter is often used to finish the water and remove the chlorine taste. Chlorine oxidation requires a pH of 7 +/_ 0.5. Potassium permanganate is more effective on water with a pH above 7.5, but is poisonous and a skin irritant and requires very careful calibration, maintenance and monitoring. Hydrogen peroxide is less pH sensitive.

Careful monitoring and maintenance of a water treatment is necessary to maintain a high quality of treated water. Testing and maintaining your water supply and treatment system is your responsibility. Without regular monitoring, maintenance and adjustments your results are likely to be disappointing.

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