IRON AND WATER TREATMENT FOR IRON
Iron and water treatment for iron can take many forms. Iron will cause an orange stain and many times it will be accompanied by manganese and hydrogen sulfide gas odor. Iron staining will be chocolate brown when it is combined with manganese. At high concentration (> .3ppm ) iron will cause the water to have a metallic taste and metallic odor. Water treatment for iron will depend on the form of the iron and the other contaminants found in the water.
Iron in water can exist in four forms:
- Ferrous iron – Ferrous iron is often referred to as clear-water iron. This form of iron is dissolved in the water. Like any dissolved material it is not visible in the water. Dissolved materials can not filtered. They must be removed with the help of chemical changes.
- Ferric iron – Ferric is refereed to as red-water iron. Ferric iron is called red water iron because it gives the water a cloudy reddish/orange appearance. Ferric iron is rust and is the result of oxidizing ferrous iron. This form of iron can be 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 when pronounced as letters says “I see” it.
- Organic iron – Organic iron is sometimes called heme-iron or pink water iron. Organic iron is actually iron combined with the dissolved organic matter in the water. This iron is held in solution with the organic materials that have chemical joined to the iron. The water will appear clear and will have color if the iron concentration is high enough. Sometimes this iron will begin to oxidize and form a suspension in the water creating yet another form of iron referred to as colloidal iron.
- Colloidal iron – Colloidal iron will look like red-water iron but can not be easily filtered. The iron has precipitated and turned to ferric iron but the molecules formed do not stick together. As a result, the iron particles do not 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 beam 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.
Ferrous iron can be removed by two methods. The most common way is to use a water conditioner (softener) . This method can be used on almost any level of iron. We have treated iron concentrations in excess of 100 mg/L successfully with a water conditioner. This method will only be successful by itself if all the iron is in the ferrous form, the total dissolved solids (TDS) is relatively low (generally <250 mg/L), 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 competition for attachment sites on the media from other dissolved mineral. The low pH and low oxygen content assures that the iron will not oxidize to ferric iron while attached to the media. If the iron oxidizes once attached to the media, it can not be removed during regeneration.
A second method to remove ferrous 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 (>10ppm) of iron because the filter media 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 – Oxygen in the air is used to oxidize the iron. Air can be introduced by any number of methods. The most common method uses a venturi 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. If the air is not released, severe spitting will result at the faucet. When the iron in the oxygen rich water comes in contact with the surface of the media, it oxidizes. The resulting ferric iron attaches to the media before it finds it way through the filter. These systems do not work well with water that has a low pH or low alkalinity because they will bleed manganese from the media. This manganese can reach toxic levels.
- Chlorination Systems– Chlorine is introduced into the water. The water is then sent to a retention tank to allow the iron time to oxidize to ferric iron. The ferric iron is then removed by the media in a filter. Any excess chlorine can be remove 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), then a separate filter with filter media should be used to remove the ferric iron so the carbon will not be fouled. CARBON IS NOT TO BE USED UNTIL THE WATER IS CHECKED FOR RADON BECAUSE THE CARBON CAN BECOME A RADIOACTIVE SOURCE.
- Greensand Systems -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 to ferric iron. The resulting ferric iron attaches 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 – 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 dissolved oxygen in the water to turn the ferrous iron into ferric iron in the presence of the catalytic media. This media can also bleed manganese into the water. The manganese that bleeds into the water can reach toxic concentrations. The media usually doesn’t work to remove iron in the water found locally because there is not enough naturally dissolved oxygen. Because the media is very heavy, it is difficult to back wash properly with the flows available from most residential pumps.
Ferric iron can be removed by any of the common medias used in back washing filters. Since the iron is already oxidized, the water only needs to be filtered.
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 $600 or more. Further more, these system depress the pH after each regeneration. The pH will need to be adjusted with additional equipment.
Colloidal iron usually comes with 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). Ultrafiltration systems cost are similar to flocculation systems 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.