EquipmentCare must be taken when considering iron removal advice from different regions of the country as water temperature, PH, alkalinity, dissolved oxygen content and other factors will affect the actual results. Most application failures are caused simply by not selecting the right equipment for the water conditions present. It is important to follow manufacturer's guidelines regarding flow rates, backwash rates, PH levels, maximum iron input levels, water temperatures and any other application limitations that the manufacturer has noted in order for the equipment and media to deliver their best result as designed.
What Is Iron?
Iron can often be detected visibly in water or by staining on plumbing fixtures. There is one rule to keep in mind when selecting a method for iron removal and that is there is no rule. You will find as with all problem water applications the solution is 50 percent science and 50 percent experience. The following information describing the different types of iron removal process applications are the basics. Before using any of these applications, it's good to have an understanding of the type of iron present; the equipment and its limitations; and the product and processes involved with method.
Iron is the presence in water is probably the most common water problem faced by consumers and water treatment professionals. The secondary (aesthetic) maximum contaminant levels (MCL) for iron and manganese are 0.3 milligrams per liter (mg/l) and 0.05 mg/l, respectively. Iron and manganese in excess of the suggested maximum contaminant levels (MCL) usually results in discolored water, laundry, and plumbing fixtures.
Well water from the faucet or tap is usually clear and colorless. However, when water containing colorless, dissolved iron is allowed to stand in a cooking container or comes in contact with a sink or bathtub, the iron combines with oxygen from the air to form reddish-brown particles (commonly called RUST). Manganese forms brownish-black particles. These impurities can give a metallic taste to water or to food.
Soaps or detergents cannot remove the rusty or brown stains on plumbing fixtures, fabrics, dishes, and utensils. Bleaches and alkaline builders (Often Sodium Phosphate) can make the stains worse. Over time, iron deposits can build up in pressure tanks, water heaters, and pipelines, reducing the quantity and pressure of the water supply.
Unluckily, iron and manganese can often be quite difficult to treat. This is due primarily to the fact that iron can be present in several forms, and each form can potentially require a different method of removal.
PreambleIron is an objectionable constituent of a drinking water. Appreciate amounts of Iron in water impart a bitter characteristic, metallic taste and cause oxidized precipitate. Coloration of water which may be yellowish brown to reddish brown and renders the water objectionable or unsuitable for domestic purpose. In addition Iron stain everything with which it come in contact. In hotels, hospitals, clubs, Institutions, office buildings, and homes, Iron-bearing water stain wash basins, toilets, urinals, bath tubs, showers, tiled floors and walls. Iron tolerances for municipal or house hold use should not exceed 0.3 PPM. Concentration of Iron in excess of 0.2 to 0.3 mg/l may cause nuisance even though its presence does not affect the hygienic quality of water.
Types of iron Iron & manganese exists in water in three main levels. One as the bi-valiant , Ferrous Iron ( Fe++) and the second one as the tri-valiant, Ferric Iron (Fe+++) & other one is Bacterial iron Other types are much rarer.
The Ferric Iron generally occurring in the precipitated form. Iron forms complexes of hydroxides and other in-organic complexes in solution with substantial amounts of bi-carbonate, sulphate, Phosphate, Cyanide or Halides. Presence of organic substances induces the formation of organic complexes which increase the solubility of Iron. The waters of high alkalinity have lower iron than waters of low alkalinity.
The commonest form in which Iron is found in water supplies is as Ferrous bi-carbonate which is a soluble, colorless salt and exists only in solution. Its solubility is increased by increasing the free Carbon-di-oxide content of the water. The underrated water is clear and colorless. It develops a slight whitish haze, which on longer standing turns yellowish and then forms yellowish brown to reddish brown deposits of hydrated Ferric oxide after aeration.
Ferrous ironThis type of iron is often called "clear water iron" since it is not visible in poured water. Ferrous iron usually appears as rust to black colored particles in the water it is found in water which contains no oxygen, such as water from deep wells or groundwater. Carbon dioxide reacts with iron in the ground to form water-soluble ferrous bicarbonate, which, in the water, produces ferrous ions (Fe++). There are a variety of ways for removing ferrous iron, each with its own strengths and limitations. These methods fall into two categories: properly sized & type Ion exchange and Oxidation / filtration as water quality.
Ferric ironFerric iron is also known as "red water iron". This type of iron is basically ferric iron which has been exposed to oxygen (Oxidized), usually from the air. As carbon dioxide leave the water, oxygen combines with the iron to form ferric ions (Fe+++). These oxidized particles are generally visible in poured water. In theory, the elimination of ferric iron is simple use a properly sized & type media filter to filter it from the water. In practice, however, there may be other issues :
* Some iron may be present in colloidal form. Unlike ferric iron, which will generally stick together to form large flakes, the tiny particles of colloidal iron do the opposite. Their large surface area and charge relative to their mass causes the individual particles to repel one another. As a result they will not coagulate. Their small size, then, makes them difficult to filter, and a coagulating agent is often required to obtain adequate filtration.
* Most water containing ferric iron also contains ferrous iron. This can add complexity to the process, since some of the methods for removing ferrous iron will also remove ferric iron.
Bacterial ironSlime depositing in toilet tanks or fouling water filters and softeners is a good indication of the presence of bacterial iron. Better described as iron bio fouling, the iron bacteria problem is both complex and widespread. It attacks wells and water systems around the world in all sorts of aquifer environments, both contaminated and pristine. In some places, it causes great damage; in others, it is considered a minor nuisance. Iron bacteria can be controlled by periodic well chlorination or it can be treated in the building. The treatment involves the following: chlorination, retention, and filtration. After filtration most important to remove the excess chlorine.