Iron and
Manganese in Household Water
Prepared by:
Glenda M. Herman, Extension Housing Specialist
Iron and manganese are
minerals found in drinking water supplies. These minerals will not harm you, but
they may cause reddish-brown or black stains on clothes or household fixtures.
Under guidelines for public water supplies set by the Environmental Protection
Agency (EPA), iron and mangenese 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 affect 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. Private water
supplies are not subject to federal standards, but these standards can be used
as guidelines to evaluate the quality of water from wells or springs.
The four forms of iron and
manganese commonly found in drinking water are ferrous, ferric, organic and iron
bacteria. Normally, water appears clear when first drawn from the cold water
faucet. If yours is not, it may contain ferric iron or organic iron. Both color
the water. Ferric iron precipitates or settles out. Organic iron does not settle
out. In well water, insoluble iron oxide is converted to a soluble form of
ferrous (dissolved) iron. Ferrous iron is colorless, but when in contact with
air, it oxidizes readily, creating reddish- brown, solid particles that then
settle out as ferric oxide. Manganese is similar to iron but forms a
brownish-black precipitate and stains. Manganese is less commonly found in
groundwater than iron, rarely found alone in a water source, and generally found
with dissolved iron.
Health
Considerations
The presence of iron and
manganese in water is not considered health problem. In fact, small
concentrations are essential to human health. However, high concentrations of
iron may give the water an unpleasant metallic taste while still being safe to
drink. When iron combines with tea, coffee, and alcoholic beverages, it
produces an unappetizing inky, black appearance and a harsh, offensive taste.
Vegetables cooked in iron-contaminated water turn dark and look unappetizing.
Iron bacteria (a harmless
bacteria), occur in soil, groundwater, and some surface waters. Iron bacteria
are considered harmless to health, how- ever, they may give water an off taste
or color, cause splotchy yellow stains on laundry, and clog water systems.
Iron bacteria usually appear as stringy, slimy, mucous-like substances
suspended in fresh water and may be colored brown, red, or white. They thrive
on iron in the sink or metal parts of the water system and are most easily
seen on the inside surface of the toilet tank.
Testing
A water analysis should be
done to determine the source of the iron and manganese. Iron and manganese may
be present in the water supply or be caused by corroding pipes (iron or
steel). Iron from pipe corrosion indicates low pH that may need to be
corrected.
A water treatment equipment
company or testing laboratory can test water for dissolved or oxidized iron or
manganese. Call the North Carolina Cooperative Extension Service center in
your county or the public health office for names of laboratories that perform
tests for colloidal or organic complexed iron and manganese.
Ask the testing laboratory
how to collect a water sample for an iron and manganese test. Generally, you
should take the sample from the faucet closest to the pump. Allow the water to
run for 5-10 minutes before sampling to obtain fresh water that has not been
exposed to air. Do not sample water that has gone through a water heater or a
water treatment unit such as a softener. If the water is clear when first
drawn, but red or black particles appear after the water settles, dissolved
iron and manganese are present. If the water has a red tint but no particles
settle out after a time, colloidal iron is the cause. Reddish brown or black
brown slimy masses inside the toilet tank indicate iron or manganese bacteria.
Laboratory tests are recommended in all cases to determine iron and manganese
concentrations.
Treatment
Iron and manganese treatment
should be based on a chemical analysis of the water show- ing the type and
concentration present. There are five treatment methods for the removal of iron
and manganese from home water systems.
WATER SOFTENER (CATION
EXCHANGE)
A water softener can remove
small amounts of ferrous iron and manganese. Iron and manganese in untreated
water are flushed from the softener medium (ion exchange) by backwashing
(forcing sodium-rich water back through the unit). This process adds sodium to
the resin medium, and iron and manganese are carried away in waste water.
The amount of iron and
manganese a softener can remove depends on the water properties, the types of
regeneration and backwash controls, and the ion exchange resin or zeolite
used. You must maintain a clean resin bed by frequent and thorough backwashing
and regeneration. Manufacturer literature should be carefully studied and
system set-up and operation instructions followed. Caution: Water softeners
treat hard water by adding sodium to the water, a health concern for people on
sodium-restricted diets. For this reason, you may want to connect a softener
only to the hot water line leaving cold, unsoftened water for cooking and
drinking. In iron and manganese removal, the softener must treat both hot and
cold water since sinks, laundry, and dishwashing equipment are affected. A
separate tap can be installed to provide unsoftened water for cooking and
drinking.
AERATION
Dissolved iron and
manganese are easily oxidized to a solid form by mixing with air. A pressure
aerator mixes air with the water, the air is vented, and then the solid
particles are filtered from the water.
This method adds no
chemicals to the water and is most effective in warm climates. The filter must
be backwashed frequently to properly maintain the system. To protect the water
from contamination by bacteria in the air, the system should be totally
enclosed and only biologically safe water should be used. The appropriate
pumping capacity must be maintained for adequate air intake.
OXIDIZING (CATALYST) FILTER
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 pumicite), 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.
Frequent backwashing and
stirring of a manganese greensand bed helps prevent an iron-fouled bed. After
several weeks of use, the greensand filter should be backwashed with potassium
permanganate to remove solid particles and regenerate (recoat) the greensand
to allow absorbation of more dissolved minerals. Synthetic filters, such as
zeolite, requires less backwash water and softens the water as it removes the
iron and manganese.
CHLORINATION AND FILTRATION
When the iron and manganese
content of the water is extremely high (above 10 ppm), a combination of
chemical treatment and filtration is necessary. Small chemical pumps are used
to add chlorine bleach, potassium permanganate, or hydrogen peroxide into the
water. After a retention time of at least 20 minutes to allow for oxidation of
ferrous iron into the insoluble ferric form, the solid particles are filtered
out.
When chlorine is used, the
treated water can have an unpleasant taste if a particle filter of calcite,
sand, anthrocite, or aluminum silicate is used. Use an activated carbon filter
to remove both excess chlorine and solid iron and manganese particles.
Backwash frequently. Some units have an automatic backwash cycle.
OTHER TREATMENTS
Complexation is a simple
and low cost method for removing iron and manganese up to 3 mg/L. A phosphate
compound is added to the water to complex (tie up) the dissolved iron or
manganese. However, adding phosphates to water supplies is not allowed by law
in North Carolina.
If organic-complexed or
colloidal iron/ manganese is present in the untreated water, a longer contact
time and higher levels of chemical are necessary for the oxidation reaction to
take place. Aluminum sulfate (alum) eases filtration by causing larger
iron/manganese particles to form.
A multistage treatment
operation may be necessary if your water has high levels of iron and manganese
and they are in both the dissolved and solid forms. For example, the water
could first be aerated, than chlorinated to oxidize residual iron and kill
iron bacteria, and then filtered through a mechanical device to remove
particles. This can be followed by activated carbon filtration to remove
excess chlorine and a water-softener for hardness control as well as removal
of any residual dissolved iron and manganese.
Summary of Treatment
Options for Iron and Manganese
Symptom Cause Treatment
Water clear when drawn, Dissolved iron or Water softener (less than 5 mg/L of
reddish-brown or black particles manganese. iron)
appear as water stands; reddish- Aeration (less than 25 mg/L of iron).
brown or black stains on fixtures Oxidation/Filtration (less than 15
or laundry. mg/L of iron plus manganese).
Chlorination-Filtration (greater than
10 mg/L of iron).
Water contains reddish-brown Iron particles from Raise pH with neutralizing filter that
particles when drawn; particles corrosion of pipes also filters particles.
settle out as water stands. and equipment.
Water contains reddish-brown Oxidized iron, Particle filter (if quantity of oxidized
or black particles when drawn; manganese, or both material is high, use larger filter than
particles settle out as water due to exposure of in line, e.g. sand filter).
stands. water to air prior to
tap.
Reddish-brown or black slime Iron bacteria. Kill bacteria masses by shock treat-
appears in toilet tank or from Manganese bacteria. ment with chlorine or potassium
faucet. permanganate, then filter; may re-
quire continuous feed of chlorine or
potassium permanganate, then filter.
Reddish or black color that Colloidal iron, Chemical oxidation with chlorine or
remains after 24 hours. manganese, or both. potassium permanganate.
Organic-complexed
iron, manganese, or
both.
Summary
Iron and manganese are
common household water contaminants with no known direct health effects at
levels found in water. Their presence may cause staining and offensive tastes
and odors. Treatment of these secondary contaminants de pends on the form in
which they occur, and the levels of concentration. Iron and manganese removal,
bacteria control, water softening and treatment for any other contamination
may be separate problems, yet they must be considered together. Accurate
testing is important prior to selection of a treatment system. The table on
page 3 may help you identify and determine treatment(s) for iron and manganese
in household water supplies.
References
Kolega, John J. Water
Conditioning and Treatment of Iron and Manganese. Fact Sheet 9. University of
Connecticut Cooperative Extension Service. 1989.
Machmeier, Roger E. Iron in
Drinking Water. University of Minrkesota Agricultural Extension Serivce. 1971.
Plowman, Faye T. Iron and
Manganese. Fact Sheet 5. University of New Hampshire Cooperative Extension
Service. 1989.
Wagnet, Linda and Ann Lemley.
Iron and Manganese in Household Water. Fact Sheet 6. Cornell Cooperative
Extension. 1989.
North Carolina Cooperative
Extension Service
Path:
Home>Education>Healthy
Home Information>Iron
and Manganese in Household Water
|
