Wednesday, June 1, 2011

Iron Removal From Water

Iron is known to leach into water supplies throughout the United States from rock and soil formations. It has been said, probably an exaggeration, that there is hardly a square foot of soil that does not have some iron content. Iron is at least 5% of the earth's crust.

A yellow to reddish discoloration can appear in water in concentrations as low as 0.3 ppm (parts per million) and begin the staining and scale process, depending on the pH, as well as taste and odor problems.

Five basic types of potable Iron:

1. Sequestered Iron
2. Heme iron - Iron Found in organics
3. Iron Bacteria
4. Ferric Iron - Red water iron
5. Ferrous Iron - Clear water Iron

Since iron is found in different forms, a removal problem is created as each type of iron may require different techniques and types of equipment.

One: Sequestering agents: Sequestering agents are used by municipalities & industry for treatment of large quantities of water. It is not important to farming where private wells are the principal source of water.

Best technology available is quite involved and varies from one area to another. Field testing is required to determine type of treatment and their limitations.

Two: Heme iron: This type of iron can not be removed by softening resins. Heme iron is that iron which is bound in organics is most common in surface water and shallow wells. It is usually a yellow to brown color. Heme iron is a breakdown product of dead vegetation. The iron and organics (tannins) requires one ppm of sodium hypochlorite and a retention time of 20 to 25 minutes in a pH range of 6.5 - 7.5. Following the oxidation, a filtration media must be used to remove the oxidized iron and the residual of chlorine.

Best Technology Available-Sodium Hypochlorite to oxidize both tannin and iron followed by a suitable retention time for the oxidation then filtration media to remove the oxidized iron.

Three: Iron bacteria: Favorable conditions for the growth of Crenothrix, Gallionella, and Clonothrix can exist at very low levels of iron. Oxygen creates an oxidizing energy to precipitate ferrous iron into bicarbonate that is necessary for iron bacteria to exist. This bacterium can now live in a very wide range of conditions. Iron bacteria water will have a reddish color and an objectionable odor. These organisms's growths cause a jelly like bio-mass. This mass can render media and resin filtration ineffective, reduce the effectiveness of any oxidizing agent, and foul nipples, cool pads, & foggers. Feed conversion and health matters are also affected.Iron bacteria is, because of its organic nature, the most difficult to remove and control.

Best Technology Available is the same as for Heme iron.

Four: Ferric Hydroxide-Red Water Iron: In nature iron is usually found in its oxidized insoluble form. Clear water iron, or soluble iron, once exposed to an oxidant or to oxygen will precipitate into an insoluble hydroxide form usually yellowish or reddish in color. This iron while in the clear water state could have been removed by softening resins now must be removed by activated multi-media filtration. If one use's a 5-25 micron filter it may pack out in a short time and reduce flow and pressure. Changing these filters then become expensive and time consuming. Multi-media filters are more expensive to purchase but cost per gallon of water filtered is much less and require little or no time.

Best technology available is same as for Heme iron. Money wise in ferric hydroxide iron many times multi-media filtration will remove the iron. Try filtration alone and if it does not remove the iron sufficiently then add the oxidation/retention/precipitation.

Five: Ferrous Iron-Clear Water Iron: Sometimes this iron is called ferrous bicarbonate iron. This iron may be removed by a softening resin with a positive charge; however it must be in the invisible soluble form until it is filtered. To prevent the iron from precipitating to its insoluble form frequent regenerations are necessary. If the iron does precipitate fouling on the resin surface will occur, as well as within the matrix of the bead. This fouling can be minimized by adding chemical cleaners to the brine or potassium regenerate. There are a number of chemical cleaners that will reduce red water iron to clear water iron. These cleaners are necessary when iron levels are high and normally they do not harm the resins. A pH around 6.7 would be ideal for best reduction of iron.

Best technology available is same as ferric hydroxide iron.

Exceptions and general comments: The five types of iron listed above are those generally found in potable water supplies. There are other colors, types, conditions and variances of iron that require special and unique methods, or combination of methods, to be effectively removed. Orange iron for instance is difficult to remove by regular multimedia filtration but is effectively removed by one old media presently used very little. Softening resins used for clear water iron are effective for residential use but requires a very large resin bed when large volumes of water as are used on a daily basis as in poultry houses. Ten thousand gallons of water per day is not uncommon for four broiler houses and this volume of water would require multiple regeneration cycles with cleansers to keep the resin bed from fouling.

Softeners will also add sodium or potassium chloride, whichever is used, in amounts that may exceed the amount that is desired by those proportioning salt into the feed formula. To determine how much you are adding of each test your TDS (total dissolved solids) and divide by .67 then discuss this amount with your field tech to determine the advisability of using the softening system.

Types of water treatment systems in their order of effectiveness and complete treatment:

1. Aeration/ retention/precipitation/filtration.
2. Multi-media Filtration
3. Softening resins systems.

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