Thursday, May 9, 2019

Treating Iron and Manganese in Your Well

In the Piedmont region of Virginia iron and manganese are commonly found in well water and are one of the causes of the perception that the well water is “bad.” Iron and manganese are often found together and 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. This staining does not wash out with detergent, and chlorine bleach may even make the staining worse.

Iron and manganese deposits can 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 reducing bacteria (often called iron 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, hot water heaters, water softeners and in filters.

Iron and manganese are naturally occurring elements commonly found in groundwater here and many other 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 and significantly impact the perceived quality of the water. In addition, a persistent bacteria/ biofouling problem may be caused by iron bacteria.

Iron and manganese are considered secondary contaminants under the U.S. EPA’s Safe Drinking Water Act. Secondary contaminants are 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. 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 can form iron sulfide rather than iron carbonate and the water may have the familiar and unpleasant rotten egg smell. 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, and in plumbing fixtures.

As mentioned above some types of bacteria react with soluble forms of iron and manganese and form persistent bacterial contamination in a water system. 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). Iron bacteria often produce unpleasant tastes and odors commonly reported as: "swampy," "oily or petroleum," "cucumber," "sewage," "rotten vegetation," or "musty." The taste or odor may be more noticeable after the water has not been used for some time. Recently, the VA DEQ has been examining wells in Fauquier County and found, according to Brad White of the DEQ Groundwater Characterization Program, he found iron bacteria in every well examined.

The recommended strategy is to treat the well with a 500-1,000 parts per million chlorine and then dilute the remaining water in the well. Chemical treatment with chlorine is inexpensive, but may require repeated treatments. Effective treatment requires sufficient chlorine strength and time in contact with the bacteria, and is often improved with agitation. Be warned that too high a concentration can make the well to alkaline and reduce effectiveness. In addition high concentrations of chlorine may affect water conditioning equipment, appliances such as dishwashers, and septic systems, so it is important to not draw the chlorinated water into the house until it has been diluted. This can be accomplished by allowing a significant amount of the water to runoff to a safe disposal location using hoses until the water runs clear, and allow the well to refill and dilute the concentration then introduce the water into the house water system to disinfect the household treatment units, appliances and piping with lower concentrations circulated through the water system. Always check with the equipment manufacturer before you treat any equipment with chlorine.

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 also called an iron filter is recommended. These filters convert dissolved iron, manganese, or hydrogen sulfide into a solid form and then filters the solid particles from water. The device uses the same casing as other products by the manufacturer, but the media in the oxidizing filter is typically a manganese-treated greensand or manufactured silica gel zeolite coated with manganese dioxide, plastic resin beads, or other trade named media. Maintenance typically involves periodically recharging the greensand media with an oxidizing agent (typically potassium permanganate) and backwashing. The potassium permanganate forms a coating that reacts with the dissolved iron, manganese, or hydrogen sulfide to form solid particles that are then trapped in the filter media. The backwashing and recharging frequency depend on the type and amount of impurities. Iron filters need to be selected to match the pH of the water. If pH is not in the range of any of the iron filters, then it is best to use chemical oxidation.

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. The chemical feed has to be properly calibrated for the specific water chemistry. 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.

Low levels of iron and manganese can technically be removed by a water softener. Water softeners are expensive pieces of equipment and using a softener to remove iron or manganese will reduce the softening capacity of the unit. Water softeners can become clogged when levels of iron or manganese in the water exceed manufacturer recommendations. In addition the softening may result in lower pH, and therefore slightly more corrosive water. Additionally, a sodium-based ion exchange system will increase the level of sodium in the treated water and should never be used for cooking or drinking. Since iron and manganese are often a taste issue additional treatments would be necessary and it is usually, best to use other methods of iron and manganese removal.

Careful monitoring and maintenance of a water treatment is necessary to maintain a high quality of  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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