Iron is one of the major secondary contaminant in both domestic and industrial water supply. Iron have caused water industries several billions of dollars . Iron is the second most abundant metal in the earth's crust behind Aluminum(8%), of which iron accounts for about 5%. Elemental iron is rarely found in nature, as the iron ions Fe2+ and Fe3+ readily combine with oxygen- and sulfur-containing compounds to form oxides, hydroxides, carbonates, and sulfides.
As rain fall, rain water infiltrates the soil and underlying geologic formations and dissolves iron, causing it to seep into aquifers that serve as sources of groundwater for wells. In surface water, such as rivers and lakes, dissolved iron is hardly ever found, because it readily reacts with oxygen, forms insoluble compounds and sinks out into the bottom of the water body.
Iron is seldom found at concentrations greater than 10 milligrams per liter (mg/L) or 10 parts per million. The iron that seep into the sources of groundwater is in the reduced iron II form. This iron II is soluble and normally does not cause any problems by itself. But, when underground water comes in contact with air, Iron II in the presence of sufficient oxygen is oxidized to iron III or by the action of iron bacteria. Iron III forms insoluble hydroxides in water. These are rusty red and cause staining and blockage of pumps, pipes, e.t.c as shown below.
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| Figure 1. Water pipe during installation |
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| Figure 2. Water pipe clogged due to iron bacteria activities |
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| Figure 3. Clogged water pipe with iron III oxide |
Iron hydroxide deposits produced by iron bacteria are usually worse. The presence of iron bacteria may be indicated by rusty slime which result in reduced water flow form the bore and unpleasant odor from water pumped from the bore hole, and produce the worse pipe blockage.
Iron-oxidizing bacteria are chemotrophic bacteria that derive the energy they need to live and multiply by oxidizing dissolved ferrous iron. They are known to grow and proliferate in waters containing iron concentrations as low as 0.1 mg/L. Some of these iron bacteria includes; Thiobacillus ferrooxidans and Leptospirillum ferrooxidans. Although iron bacteria can make water unsightly and cause an unpleasant taste and odor; there is no health risk associated with iron bacteria.
Although, nobody can drink enough water to consume toxic levels of iron. The Environmental Protection Agency and World Heath Organization considers iron in well water as a secondary contaminant, which means it does not have a direct impact on health. But, In addition to this, high iron content leads to an overload which can cause diabetes, hemochromatosis, stomach problems, nausea, and vomiting.
Iron as a Secondary contaminant in drinking water do not pose health risks to humans at levels usually found in water. The drinking water standard for iron is >0.3 milli- grams per liter (mg/l) WHO and EPA standard. Iron is essential for good health, iron helps transport oxygen in the blood, it is excess of it that is bad for human body.
Treatment
Before choosing a water treatment method or device, make sure you have answers to the following questions correctly
1. What form of iron do I have in my water source.
2. Will the treatment unit treat the water at the flow rate required for my water system?
3. Based on the results of the water tests, will this method effectively remove iron? For example, will the pH have to be adjusted prior to a particular treatment?
4. Would the construction of a new well or the reconstruction of an existing well be more cost effective than a long-term iron removal treatment
The following methods can be use in treatment of iron in water
1. Manganese Green sand:
A naturally occurring mineral or manufactured material, treated with potassium permanganate that is capable of removing iron; it absorbs dissolved iron and requires chemical regeneration.
2. Catalytic Filtration: A granular filter medium that enhances the reaction between oxygen and iron and then filters the insoluble iron.
3. Water softeners, this method uses the same principle used in softening of water, ion exchanger
4. Aeration systems, this method employed either natural aeration or artificial aeration system to pump and diffuse air into water.
5. Iron filters are can be use to treat iron contaminated water
6. Chemical oxidation, the use of chlorine is also effective in the precipitation of iron
7. Combination of two or three or more of these methods will achieve a more effective result.
On iron bacteria, technically, iron bacteria problem in well water can be treated using;
1. Physical removal,
2. Pasteurization (injecting steam or hot water into the well and maintaining a water temperature of 140°F/60°C for 30 minutes)
3. Chemical treatment, use of chlorine, shock chlorination.
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