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| This is an actual photo of staining
found on a tub. This is the classic brown (not orange) stain caused by iron and manganese. |
Forms of Iron Found in Water
Iron will cause an orange stain and will many times be accompanied
by manganese and hydrogen sulfide gas odor. In combination with manganese, Iron staining will sometimes be chocolate
or brown. At high concentration (> .3ppm ) the iron will cause the water to have a metallic taste and metallic
odor.
The iron itself can exist in four forms:
- Ferrous iron
(often referred to as clear-water iron) - This form of iron is invisible in the water just like dissolved sugar
is. Just like sugar water, the iron can not be mechanically filtered from the water.
- Ferric
(often referred to as red-water iron) - It is called red water iron because it gives the water a cloudy colored
appearance. The iron has precipitated and formed a solid that is no longer in solution - it has turned to rust
- "oxidized". This form of iron can be mechanically filtered. An easy way to remember which kind of iron
is visible (ferrous or ferric) is to remember that the "i" and the "c" at the end of the word
ferric say the same thing as "I see" it.
- Organic iron
(sometimes called heme-iron or pink water iron)- This form is actually iron combined with the dissolved organic
matter (tannins) in the water and is held in solution with the organic materials. The water will appear clear but
may or may not have color. Sometimes this iron will begin to oxidize and form a suspension in the water. We refer
to this suspended iron mixture as colloidal iron.
- Colloidal iron
- This will look like red-water iron but can
not be easily filtered. The iron has precipitated
(turned to ferric iron) but the molecules formed do not stick together to form large enough pieces to settle to
the bottom of a container or be trapped with normal filtration. This water/solid combination is called a colloidal
mixture. To test if you have this type of water, collect a sample in a clear glass container. Shine a flashlight
beam through the water and see if you can see the light (tyndall effect)
in the water. Then, let the water set overnight. If after setting over night you can still see the beam of light
as it passes through the water and there was no settling of material on the bottom of the container, the chances
are very good that you have colloidal iron.
Treatment
Ferrous iron can be treated two ways. The most common way is to use a water conditioner
or softener to remove the iron by ion exchange.
This method can be used on almost any level of iron. We have treated iron concentrations in excess of 100ppm successfully
with a water conditioner. This method will only be successful by itself if all the iron is in the ferrous form,
the TDS is relatively low (generally <500ppm), the pH is
low ( generally <7) and there is very little oxygen in the water. The TDS
has to be low to assure that there is no bleed through due to the iron being removed from the resin once attached.
High TDS indicates there are other minerals(ions)
in the water competing for the sites on the resin (media) the iron has attached to. The low pH and low oxygen content assure
that the iron will not oxidize to ferric iron while attached to the media (resin). If the iron oxidizes once attached
to the media, it can not be removed during regeneration.
A second method to remove iron, is a two step process called
oxidation filtration.
The iron is first oxidized by the use of either oxygen, chlorine or potassium permanganate. The oxidation causes
the ferrous iron to form ferric iron. The ferric iron is then removed by filtration. This method is not typically
used on very high concentrations (> 8 or 10ppm) of iron because the filter beds will require more frequent back
washing (automatic cleaning) then is reasonably possible. This method may also require the use of some kind of
pH correction because iron will not oxidize below a pH of 6.8. There are several types of oxidation filtration
systems used today. They are-
- Air Injection
- Oxygen in the air is used to oxidize the iron. The system requires the use of a venturi or an air pump(compressor)
to inject the air. The system is therefore called an air injection system. There are many brand names for this
type of system but they all require a minimum flow (usually at least 5 gpm) from the well pump to make the venturi
work. This flow must be tested before this type of system can be used. Good systems will consist of 3 parts- venturi,
air release tank, and filter tank. The air release tank removes any undissolved air and allows for the retention
of the water. If the air is not released, severe spitting will result at the faucet. The retention allows time
for some of the oxidation reaction to take place. The rest of the oxidation occurs in the filter on a catylitic
media. The filter tank media removes the precipitated (ferric) iron that was formed by the oxidation process. THESE SYSTEMS DO NOT WORK WELL WITH WATER THAT HAS LOW pH AND LOW
ALKALINITY.
- Chlorination Systems - Chlorine is introduced into the water by one of two methods. The chlorine
can be pumped in with a solution feed pump or it can be dropped in tablet form directly into the well. The water
is then either sent to a retention tank and then to a filter or it can be sent directly to a filter. The choice
of methods will be determined by the severity of the iron problem and the type of media chosen for the filter tank.
If chorine is used, it may be desirable to remove it with carbon. If the iron levels are low (<2ppm), the carbon
can also be used as the filter that removes the ferric iron that is formed. If the iron is greater than this (2ppm)
than a separate filter with filter AG media should be used to remove the ferric iron so the carbon will
not be fouled. Some customers will opt to use filter AG in the filter and only use carbon at a sink as a P.O.U
(point of use) treatment to remove the chlorine from the drinking water. If this is done, there will still be chlorine
in the water at all other faucets and showers. The chlorine should be able to be regulated so that it is of no
higher a concentration than that found in city water. CARBON
IS NOT TO BE USED UNTIL THE WATER IS CHECKED FOR RADON BECAUSE THE CARBON CAN BECOME A RADIOACTIVE SOURCE.
- Greensand Systems
(NOT USED BY US)- This
method uses a catalytic media (called greensand) coated with manganese that is treated periodically (like the salt
regeneration of a softener) with potassium permanganate. The potassium permanganate acts as an oxidant (like the
chlorine or oxygen). When the iron in the water comes in contact with the surface of the media it oxidizes and
the ferric iron is then filtered out by sticking to the media before it finds it way through the filter. We do
not use this method because these systems can easily bleed manganese into the water, they general require a lot
of maintenance and the potassium permanganate is not only poisonous, but, if spilled, stains badly. The manganese
that bleeds into the water can get to levels high enough to be toxic. You will hear these filters referred to as
iron filters, greensand filters or potassium permanganate filters.
- Catalytic Media
(NOT USED BY US)-
This method uses a media similar to greensand. The media has many different trade names but is usually a naturally
occurring mineral called pyrolucite (manganese dioxide). This method of treatment relies on there being enough
oxygen in the water to turn the ferrous iron into ferric iron. This media can also bleed manganese into the water.
It doesn't work to remove iron in the water we find locally because there is not enough naturally dissolved oxygen.
A second major draw back is that the media is so heavy it is very difficult to back wash properly with the flows
available from most residential pumps.
Ferric iron
can be removed by any of the back washing filters commonly used. Since the iron is already oxidized the water,
it only needs to be filtered. Generally the iron will be filtered with AG or Calcite filter media.
Organic iron is usually treated with an anion resin in a tank that uses salt like a water
conditioner or softener. The resin usually is very expensive and has a short life( 1-2 years). At the end of the
resins life, the resin must be replaced at a cost of 400 or more dollars.
Colloidal iron is probably the most difficult form of iron to deal with and usually comes
with many other water problems. The treatment usually involves either flocculation
or ultrafiltration. Flocculation systems require two solution feed systems, static mixers,
retention tanks and filters. The goal is to floc the iron (make the particles grow large enough to filter) and then
filter it. These are very expensive systems (typically $4000-$5000). The ultrafiltration systems
tend to be a little less expensive and require much less maintenance by the homeowner. There are no water treatment
companies that want to deal with this type of iron, very few that will and even less know how. We have had very
good success and will continue to provide our solution to those who want it.
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