This document provides a technical description of treatment options for removing iron and manganese from drinking water. The technical abbreviation for iron and manganese is (Fe/Mn) respectively. These contaminants act similarly and are treated by the same processes and thus are discussed together in this document.

This document is intended to provide detailed information useful when purchasing a new Fe/Mn treatment device or diagnosing operational problems with existing equipment.

UNDESIRABLE EFFECTS OF IRON AND MANGANESE
Fe/Mn occur naturally in New Hampshire's geology both in the bedrock and unconsolidated sand/gravel deposits. Fe/Mn dissolve into water as acidic rainfall percolates through the soil and bedrock. In higher concentrations Fe/Mn cause the following problems:

EPA has established "secondary" limits for Fe/Mn in drinking water as shown below. These limits are based on aesthetic concerns only. These limits are called secondary maximum contaminant levels (SMCLs):

Iron                 0.30 mg/L (milligrams per liter) or ppm (parts per million)
Manganese      0.05 mg/L

In most cases in New Hampshire, the staining problems described above do not become objectionable until the actual concentrations of Fe/Mn are at least double the secondary standards. Treatment is not thought to be necessary to remove minor Fe/Mn levels above these aesthetic SMCLs unless you are actually experiencing a staining problem.

FACTORS THAT MUST BE KNOWN WHEN CHOOSING A TREATMENT PROCESS
Type of Fe/Mn Present
Fe/Mn may be present in any of three different forms ranging from clear to discolored as described below. In some wells Fe/Mn may be present in multiple forms simultaneously. Not all treatment methods work on all forms of Fe/Mn.

1. Your water is totally clear when drawn from the tap (90% of New Hampshire cases).

Fe/Mn is present in the dissolved form. The terms "clearwater iron", or "clearwater manganese" are often used to describe this form. The scientific name for clearwater iron is called "ferrous" and for manganese, "manganous."

When exposed to oxygen or other oxygen like chemicals, clearwater Fe/Mn will precipitate to form fine brownish (ferric) or blackish (manganic) "rust" particles. The tendency to precipitate these minerals is also influenced by changes of water temperature, pH and other factors. It is the precipitated forms of Fe/Mn which stain water use fixtures and discolor laundry. These "rust particles" will settle out if the water is not disturbed.

In this case the Fe/Mn have probably combined with dissolved organic matter in the water.

1. The concentrations of Fe/Mn.
2. pH (acidity) and hardness.
3. Dissolved oxygen for some treatment types; this must be field measured.
4. The presence of Fe/Mn bacteria.

OVERVIEW OF ALL CATEGORIES OF TREATMENT
Shown below is a summary of available methods for treating Fe/Mn. A separate explanation for each type is then presented.

NO Fe/Mn REMOVAL: STAIN PREVENTION IS ACCOMPLISHED BY ADDITION OF SEQUESTERING CHEMICALS
The undesirable staining caused by Fe/Mn can sometimes be minimized by adding a food grade polyphosphate chemical to the water to prevent the formation of the rusty colored forms of Fe/Mn. These chemicals "coat" and "tie up" the dissolved Fe/Mn ions preventing a reaction with oxygen and subsequent precipitation. (An ion is the dissolved form of an atom or compound.) Sequestering prevents the staining effect but does not remove Fe/Mn.

Sequestering only works when the Fe/Mn is initially in the dissolved "clearwater" form. Sequestering chemicals may be reasonably effective for iron in concentration as high as 0.6 mg/l and for manganese concentrations as high as 0.10 mg/L. As the Fe/Mn concentration continues to increase, the level of expected success using a sequestering method, decreases.

The sequestering agent is added by a chemical feed pump which starts and stops in tandem with your water well pump. More phosphate chemical is needed for manganese than for iron. Maintenance is minimal.

Advantages of Sequestering
- Low cost equipment and chemicals.
- Small space requirements.
- Other water quality factors are not too important.

Disadvantages of Sequestering
- The effectiveness of the treatment is reduced at higher water temperatures or when the water is aerated or when bleach is added.
- Sequestering chemicals looses effectiveness with time. They revert from the "poly" to the "ortho" form of phosphate.
- Phosphate compounds could foster bacterial growth within your home plumbing system and residual phosphate in septage causes weed and algae growth in lakes.
- Not effective for that portion of the Fe/Mn that has already turned rusty.
- Not commonly used in a private well single family home situation.

REMOVAL OF DISSOLVED Fe/Mn USING WATER SOFTENERS
A water softener removes Fe/Mn which is in the dissolved "clearwater" form. Softening also removes calcium (Ca) and magnesium (Mg) ions which are the primary minerals responsible for "hard" water. The treatment process consists of passing the water through an ion exchange resin media bed. The Fe/Mn ions and also calcium and magnesium ions in the water are "exchanged" for sodium (Na⁺) ions which have been temporarily stored in the resin material.

As the hardness and Fe/Mn are removed from the water, sodium is added proportionally. For every 10 mg/l of hardness and Fe/Mn removed, approximately 5 mg/l of sodium will be added to the treated water. For those concerned with elevated sodium levels in their drinking water, potassium chloride (KCl) can be used in place of sodium chloride (NaCl). The cost of KCl can be higher than sodium chloride. Potassium, one of the three principal elements in fertilizer, is a valuable soil nutrient.

Eventually the removal capacity of the ion exchange resin material will become exhausted and the media will need to be regenerated. The regeneration process begins with a physical backwash of the media to remove fine particles. The resin is then immersed in a strong salt brine solution. The sodium (or potassium) from the salt enters the resin and displaces the previously removed Fe/Mn and hardness. After a period of time (approximately 20 minutes), the remaining brine, along with the displaced Fe/Mn and hardness, are flushed out of the device and disposed of into a dry well, septic tank or sewer. Studies by the Water Quality Association (a trade organization of the home water conditioning industry) indicate that waste brine does not injure leach fields or septic tanks.

Ion exchange (IE) softening is described as effective for water containing less than 2 - 5 mg/L of dissolved Fe/Mn. IE will not work at all where the Fe/Mn have turned to a rusty color. Other aspects of water quality such as pH or alkalinity are not important in the efficiency of IE.

Hardness in drinking water is normally categorized as shown:

Sometimes hardness is expressed as grains per gallon (gpg). One grain per gallon equals approximately 17.2 mg/L. A hardness level of less than 100-150 mg/L generally is not considered sufficiently hard to need water softening however, this is a judgement decision.

In general, DES does not recommend the use of softeners to treat only Fe/Mn due to the disadvantages listed below. Where both Fe/Mn and hardness are high, softening is an appropriate treatment technique. For further information see fact sheet WD-WSEB-3-6 and 2-12.

Advantages of Water Softening
- Softener resin can be rejuvenated and re-used.
- IE can consistently remove dissolved Fe/Mn from water to extremely low levels.
- Softeners have lower backwash water requirements than oxidizing filters.
- The Fe/Mn removal is not appreciably affected by the water pH or other factors.

Disadvantages of Water Softening
- Softening will not operate satisfactorily if iron bacteria or rusty colored water exists, even if occasionally. If particles are present, a sediment prefilter is often placed before the resin tank.
- A water softener will not remove hydrogen sulfide odor.
- Water softeners produce waste brine that must be disposed of. If you do not have a sewer, disposal of the waste brine will likely be into the ground. This creates the potential of polluting the groundwater and subsequently your own well or the wells of your neighbors downhill.

The newest design concept for water softeners incorporates the regeneration mode called demand regeneration. This approach allows the frequency of softener regeneration cycles to be reduced. The controls on these devices include those that measure the water's electrical conductivity or those that measure the volume of water treated. In each case, rejuvenation is triggered based on actual need rather than the passage of time. Historically clock timers backwashed a water softener whether it needed regeneration or not, such as during vacation periods. This excessive backwashing needlessly increases salt use and the generation of waste brine.

In addition, customers can also set the softener unit to use a high or low level of salt during each regeneration cycle. Use of a low level of salt (6-7 lbs) per cubic foot of resin gives the best efficiency of contaminant removal, per pound of salt used. We recommend this low level regeneration option. See fact sheet WD-WSEB-2-12 for a further discussion.

GENERAL INTRODUCTION TO OXIDIZING FILTERS - REMOVAL OF Fe/MN
In oxidizing filters, all Fe/Mn is first purposely converted to the rusty colored form. These larger particles are then strained out on the filter media. Periodically the filter media is backwashed to remove the collected rust particles. The Fe/Mn laden backwash is discharged into a dry well, leach field or sewer.

Fe/Mn REMOVAL USING POTASSIUM PERMANGANATE GREENSAND FILTRATION
In this filtration type, potassium permanganate (KMnO₄), a purple crystal or liquid, is used to precipitate (meaning to convert to a solid) Fe/Mn. Chlorine or aeration may also be used. The KMnO₄ can be added either continuously (at a very dilute concentration) or in a more concentrated form at the time of backwash (batch mode). In the latter option, the KMnO₄ enhances a special oxygen rich coating on the greensand media that causes precipitation of the Fe/Mn within the media during normal filter operation.

For this filtration type, the pH needs, at a minimum, to be over 7 and preferably over 7.5 to assure full precipitation of Fe/Mn. Where manganese concentration is high, a pH greater than 8 is recommended. Where the pH is low, a chemical feed pump may be needed to raise the pH. A contact/detention tank is sometimes installed to allow more time for the oxygen and the Fe/Mn contaminants to produce a sizeable rust particle.

KMnO₄ greensand filtration is effective for very high levels of Fe/Mn. Where the manganese level is high, feeding a dilute chlorine solution may improve manganese removal. KMnO₄, chlorine or aeration can also remove hydrogen sulfide odor. See fact sheet WD-WSEB-3-16.

Periodically the greensand filter is backwashed. The rusty water is typically discharged into an approved dry well, septic tank or sewer. This discharge of Fe/Mn to a septic field does not have the groundwater pollution consequences of water softener brine.

Advantages and Constraints of Oxidizing Filters
- Filter can be backwashed and recharged for re-use.
- Can consistently remove high concentrations of Fe/Mn to extremely low levels.
- Adds no sodium to the water
- Can significantly reduce "rotten egg" odors.
- There are minimum flow rates required for backwash.

Disadvantages & Limitations of Oxidizing Filters
- The pH of the water is critical to the filter's effective operation. The raw water pH should be 7.0 or higher for iron (pH = 8 or higher for manganese) or pH adjustment will be necessary. If you have a shallow (dug) well, an inexpensive way to raise the pH is to add marble chips (also called calcite chips) to the well. Don't forget to disinfect the well after this operation. Calcite will somewhat increase the water's hardness. See fact sheet WD-WSEB-3-4.
- The rate of required backwash water is high. Keep this in mind in selecting the size of the oxidizing filter suitable to your source water output. Where well output is low and the required filter size is large, two smaller filters might be substituted so that each can be backwashed separately. This duplication would create additional expense.

Fe/Mn REMOVAL BY VENTURI AERATION - FOLLOWED BY FILTRATION
This is a variation of the oxidation filtration method. Many homeowners would prefer not to add "foreign" chemicals to their water supply. One filtration media that accommodates this preference is the so-called "birm" catalyst media. Where dissolved oxygen in the water is low, ordinary air is added to the water by a special venturi nozzle. The mixture of air and water then passes into a detention tank where the oxygen dissolves into the water. An air release valve allows the unused nitrogen and excess air to be bled off. The water then enters the birm media filter tank. The coating on the birm media acts as a catalyst to force the completion of the chemical reaction between the dissolved oxygen and Fe/Mn so as to form Fe/Mn rust particles.

The Fe/Mn precipitate is then physically caught by the birm media. The birm is backwashed periodically to remove the precipitates, but no chemical rejuvenation of the birm is needed. This method is effective for very high levels of Fe/Mn.

Constraints When Using Birm Media.
Where the dissolved oxygen level of the raw water is above 15 percent, there is no pressing need to install the venturi nozzle, however, such installation is often still done in view of the low cost of the device and in consideration of possible source water variation. The pH should be over 7.0+ for iron and 8.0+ for manganese. If both Fe/Mn are substantially present, the pH should be under 8.5 so as to not produce colloidal iron. There are minimum flow requirements for backwash.

Other manufacturer comments recommend that tannins and hydrogen sulfide should be low. These other contaminants will produce a precipitate that fouls the media. Organic material should be less than 5 ppm. Effectiveness of the birm media will be reduced by long term exposure to chlorine however, short term chlorination to kill Fe/Mn bacteria is acceptable. No appreciable phosphate should be present. The precipitate of Fe/Mn tends to lower the pH and thus the alkalinity or pH adjustment may be needed. An "enriched" media is often necessary to remove manganese.

Advantages
- No "foreign" chemicals are added to the water.
- Low labor cost.
- Can handle a wide range of Fe/Mn levels.
- Can often reduce some objectionable odor.

Disadvantages
- Few

BAG FILTRATION
This equipment is often used to remove Fe/Mn which is fully oxidized as the water comes from the well. The particles are removed from the water by passage through bag filters. The cost of this system is low. The bags must be manually cleaned which creates higher operational costs.

TREATMENT TYPES NOT RECOMMENDED

- Magnetic/Electronic Fe/Mn Removal Devices
The Water Quality Association (the professional association representing the home water treatment industry) has indicated that there is no proof that magnetic/ electronic Fe/Mn removal devices are effective. It is difficult to obtain objective test data for methodologies that do not remove the contaminants. See fact sheet WD-WSEB-2-10.

- Reverse Osmosis
This process will become clogged by rust particles, Fe/Mn bacteria, silt, etc., and cannot be regenerated. New membranes would be required frequently. See fact sheet WD-WSEB–2-11.

This document has been prepared for educational purposes and should not be the only basis for deciding which type of Fe/Mn treatment system to purchase or what improvements should be made to an existing system. Your decision should be based on information from equipment suppliers and other independent professional sources.

FOR FURTHER INFORMATION
For more information regarding iron and manganese removal, please contact DES at (603) 271-3139. For an overall listing of water supply related fact sheets, please request fact sheet WD-WSEB-15-2. Drinking water fact sheets are available through the DES web site at: www.des.state.nh.us/ws.html and then select: fact sheets. Please check the internet annually for updates to this document. We would appreciate your suggestions concerning this fact sheet. 10/00