Certain rocks in the earth contain radioactive elements, and these are known as NORM, i.e. Natural Occurring Radioactive Materials. When drinking water comes in contact with these rocks, the radioactive elements react with it and form, for example, radioactive iodine. If rocks containing radioactive elements come in contact with river flow, then the water becomes impure because of the radioactive elements present.
The elements that may present in these rocks are:
- Radium and its products
- Uranium and its products
- Thorium and its products
- Strontium and its products
- Radioactive Iodine-131
However, the nuclear disasters like the nuclear plant damage that recently happened in Japan may also be the cause of radioactive impurity in drinking water. Radioactive iodine escapes from the damaged plant in the form of gas. The gas mixes into the atmosphere, and when rain occurs, it settles in the water supply.
It is estimated that the U.S. generates 260,000 metric tons of TENORM (“Technology Enhanced” NORM) every year. This is in addition to 600 metric tons generated by per utility. The radioactive iodine and strontium are very dangerous for your health, and it may cause certain diseases. Because of this, radioactive iodine and strontium removal from water is very important.
The processes that can remove the drinking water radioactive iodine and like radium and strontium from drinking water are given below.
Methods to Remove Radioactive Elements from Drinking Water
Lime Softening Method
This method is considered the best method to remove radioactive elements like radium and strontium. This method involves a simple water softening procedure. You will need to add calcium hydroxide (lime water) in drinking water to perform the task. The calcium hydroxide increases the pH of water that leads to settling out of the calcium and magnesium in the form of solid sludge. Most of the radioactive elements, radioactive iodine and strontium, are also mixed with this sludge, and they are then removed by sedimentation and filtration.
This method is very useful for removing radioactive iodine and strontium in smaller water supply system.s In this process, the softening of water takes place using ion exchange method. The calcium and magnesium ions are replaced by sodium ions. The replaced ions make sludge, in which radioactive iodine and strontium is also present. This process can remove up to 95% of radioactive elements in the form of sludge. The sludge containing radioactive iodine is then discharged to the storm sewers or septic tanks. The sludge is then backwashed for the selective removal of radioactive iodine, and then it can be reused for other purposes.
Reverse Osmosis Method
This method gives 99% accuracy to remove uranium, radium, strontium, and radioactive iodine from drinking water. It uses sa emi-permeable membrane to remove the radioactive elements. The membrane works on the principle of concentration difference. The low concentrated radioactive iodine and other elements move inside this membrane in the form of sludge.
Methods to Disposing of the Sludge
There are number of methods that can be used to dispose of drinking water treatment sludge. These methods are required to reuse the sludge after the removal of radioactive elements.
- In Lagoons: When the sludge is disposed of in lagoons, the radioactive iodine, strontium, and other radioactive elements settle down in its sediments. However, the elements settled down at the bottom need to dredged and removed periodically.
- In Landfills: These are also good places to dispose of sludge. When you dispose the sludge here, you should emplace clay layer above and below the sludge. It will restrict the emission of radioactive nuclides.
- In Sewer Systems: This is another good option to dispose of the sludge. In this method there is one advantage: the treatment of the sludge can be done with the help of sewage treatment facilities.
- Through Land Spreading: This sludge can also be used as a fertilizer, and soil conditions can be improved by this fertilizer. Because of this, it can be disposed of on land. Spreading this sludge in land is also helpful to limit water runoff.
The whole process of removing drinking water radioactive iodine and strontium removal from water is based upon two processes. First, you need to make sludge that contains radioactive elements from the drinking water, and the second job is then proper disposal of the sludge. When you dispose of it properly and use different treatments, that useless things become useful for other important areas.