|
Calcium and magnesium cause
hard water, and high levels can precipitate and clog pipes. The best way to
soften water in household water systems is to use a water softener unit
connected into the water supply line. You may want to consider installing a
separate faucet for unsoftened water for drinking and cooking. Water softening
units also remove iron.
General Description
The most common way
to soften household water is to use a cation-exchange water softener. Softeners
may also be safely used to remove up to about 5 milligrams per liter of
dissolved iron if the water softener is rated for that amount of iron removal.
Softeners are automatic, semi-automatic, or manual. Each type is available in
several sizes and is rated on the amount of hardness it can remove before
regeneration is necessary.
Limitations
Using a softener to
remove iron in naturally soft water is not advised; a green-sand filter is a
better method.
Maintenance
When the resin is filled to
capacity, it must be recharged. Fully automatic softeners regenerate on a preset
schedule and return to service automatically. Regeneration is usually started
by a time clock; some units are started by water use meters or hardness
detectors.
Semi-automatic softeners have automatic controls for
everything except for the start of regeneration. Manual units require manual
operation of one or more valves to control backwashing, brining and
rinsing.
In many areas, there are companies that provide a water
softening service. For a monthly fee the company installs a softener unit and
replaces It periodically with a freshly charged unit.
Need for Iron
Removal
Iron in the ferric form and manganese will stain clothes and
plumbing fixtures. Ferrous iron is in the dissolved form and cannot be seen in
water. When water containing ferrous iron is exposed to air, the iron oxidizes
and ferric iron is formed. Ferric iron usually appears as rust colored particles
floating in the water.
Water with a high iron or manganese content is not
considered a health problem, but it can be very objectionable in taste, odor or
appearance. Iron bacteria are nuisance organisms often associated with soluble
iron in water. Because they cause a slime buildup they can be quite
objectionable. Calcium is an essential nutrient for this bacteria. The presence
of iron bacteria is indicated by a gelatinous slime on the inside wall of the
toilet flush tank and gelatinous "rusty slugs" being discharged at the tap. High
dosages (200 to 500 milligrams per liter) of chlorine (known as shock
chlorination or disinfection) are required to control iron bacteria. Shock
chlorination must include the well and system.
General
Description
Four types of iron-removal equipment are
available:
Iron Filters. Iron filters are only useful for removal of
ferrous iron and manganese; ferric iron will plug them. They appear similar to
water softeners but contain a bed of natural or synthetic manganese green sand.
Manganese dioxide oxidizes iron and manganese and the oxidized particles are
then filtered out in the lower part of the bed.
Water softeners. All
water softeners will remove iron; the rating for iron depends on whether the
regeneration will remove the iron from the zeolite or not. Water softeners
contain a zeolite mineral that will remove soluble iron on an ion-exchange basis
(the same way calcium and magnesium are removed in water softening). The slime
produced by iron bacteria will clog the zeolite and reduce its
effectiveness.
Polyphosphate feeders. These units contain a phosphate
compound which coats the soluble iron and prevents its oxidation when the water
is exposed to air. The compound is not effective against iron that has already
oxidized. When some waters are heated, the raised temperature will reduce the
effectiveness of the polyphosphate so that oxidized iron will accumulate in the
water heater. (Polyphosphate is only effective in cold water. Heating the
water will release the iron.) The heated water will be rusty and unsatisfactory
for home uses.
Chlorination and filter. Chlorination followed by
filtration through a sand filter can remove any quantity of iron in any form.
The chlorine oxidizes and precipitates the iron and the filter strains out the
particles. Carbon filtration may be required to remove excess chlorine
residue. This method also destroys iron bacteria. When the bacteria cannot be
permanently eliminated by shock chlorination, continuous chlorination is
required.
Neutralizers: Primary Use This system treats corrosive
(acidic) water. Alkalinity and pH are increased through
processing.
General Description
Passing the water through granular
calcite (marble, calcium carbonate or lime) is the most common method of home
treatment. A mix of calcite and magnesium oxide also is used. if the water is
very acidic or if a high flow rate is needed, a system to chemically feed soda
ash,
sodium carbonate or caustic soda (sodium hydroxide) may be necessary.
These systems increase the sodium content of water, whereas using calcite or
lime increases calcium.
Disinfection Methods
Chlorination - Both
municipal systems and households can disinfect water by adding
chlorine.
Household systems commonly use household bleach. Chlorination does
not remove nitrates or other chemicals, but may oxidize organics and some
minerals such as iron. Chemical metering devices must be maintained carefully.
Using a carbon filter after chlorination will remove any excess chlorine and
chlorinated chemicals that form.
Other Methods
Other methods of
disinfecting water include boiling, pasteurizing, treating with ultraviolet
light, and treating with ozone. These methods are usually less practical than
chlorination or not readily available. Note that sterilization (boiling water
vigorously for at least two minutes) kills all organisms. Disinfection reduces
the concentration of organisms to safe levels. Devices to kill or remove
bacteria or viruses are termed purifiers. Chlorination, distillation, or boiling
for 15 minutes are the usual methods used to purify water for household
use.
Disinfection by ozonation or ultraviolet light methods are replacing
chlorination in some water
treatment plants, but are not yet readily
available for home use.
Some filtration units with silver-coated
activated charcoal blocks are being sold for removal or killing of bacteria.
Before purchasing such a unit, evaluate it carefully and check for sufficient
test data and certification to assure its effectiveness.
The above information
comes from North Dakota State University Extension bulletin E-430, Household
Water Treatment.
Figures: Automatic
Water Softener - 23K,
Backwash
Filter - 20K
Please read the MSU
disclaimer for important
information about using our
site.
Reprinted from The Michigan State University
Extension. - Michigan State University
Extension Home Page
|
