Radiation can be removed from water using established physical and chemical processes. Radiation refers to radionuclides, which are unstable atoms that release energy as they decay, typically as alpha, beta, or gamma particles. Since these radionuclides are usually dissolved solids or suspended particles, they can be physically or chemically separated from the water molecules. The success of removal depends heavily on the specific type of radionuclide present and the treatment method deployed.
Sources of Radioactive Contamination in Water
Contamination stems from two distinct categories: naturally occurring and man-made sources. Naturally Occurring Radioactive Materials (NORM) are the most common source, where elements like Uranium and Thorium leach from rock and soil formations into groundwater. Radium and its decay product, the radioactive gas Radon, are frequently found NORM contaminants in drinking water supplies.
Man-made, or anthropogenic, radionuclides are introduced into water supplies through nuclear processes, industrial activities, or medical applications. Notable examples resulting from nuclear fission events include Cesium-137 and Strontium-90, which are often highly soluble in water.
Fundamental Principles Governing Removal
The efficacy of water decontamination relies on manipulating the fundamental properties of the radionuclide atoms. The first principle leverages the ionic charge of the dissolved contaminant. Many radionuclides, such as Strontium and Cesium, exist as charged ions in water, allowing for separation via electrostatic attraction to a material with an opposing charge.
A second principle utilizes particle size and filtration to physically block contaminants. Although radionuclides are atomic in size, they often adhere to larger suspended particles or exist as dissolved solids. These solids are significantly larger than the water molecule itself, making filtration possible.
Finally, the principle of solubility and phase change exploits the non-volatile nature of most radionuclides. These heavy elements do not easily transition into a gaseous state when heated. When water is boiled and converted to steam, the radioactive contaminants are left behind in the remaining liquid concentrate.
Established Water Decontamination Technologies
Practical application of these principles uses several proven technologies for both large-scale municipal and smaller point-of-use systems.
Ion Exchange (IX) Resins
Ion Exchange (IX) Resins function by swapping harmless ions on a resin bead for the charged radionuclide ions in the water. This process can achieve removal rates up to 99% for contaminants like Radium and Uranium, which have a strong positive charge. Specialized resin, such as cation exchange types, targets positive ions like Cesium and Strontium.
Reverse Osmosis (RO)
Reverse Osmosis (RO) is used for comprehensive removal of a wide range of contaminants. This technology forces water under high pressure through a semi-permeable membrane that physically rejects larger dissolved solids, including most radionuclides. RO systems are a common option for home use, capable of removing approximately 95% of gross alpha and beta activity. The process does create a concentrated waste stream that requires careful disposal.
Distillation
Distillation directly utilizes the solubility and phase change principle. Water is heated to steam, leaving the non-volatile radioactive salts and heavy metal contaminants behind in the boiling chamber. The purified steam is then condensed back into liquid water.
Coagulation and Flocculation
For large-scale municipal treatment, Coagulation and Flocculation bind radionuclides into larger, filterable particles. Chemicals are added to neutralize the charges of the dissolved contaminants, causing them to clump together into heavier particles called floc. This floc, which contains the radionuclides, is then removed through settling or subsequent filtration. Enhanced lime softening processes can achieve up to 99% removal for Uranium.
Verifying Water Safety After Treatment
Successful removal of radionuclides cannot be confirmed visually, as radiation is odorless, tasteless, and invisible in water. Verification requires specialized laboratory analysis using techniques such as alpha, beta, and gamma spectroscopy. These methods measure the energy and quantity of the radiation emitted by individual radionuclides, confirming that concentrations are below regulatory limits.
Water samples are collected and sent to certified laboratories where specialized detectors are used for precise measurement. This post-treatment monitoring ensures the efficacy of the purification system over time. Simple household methods are generally ineffective; carbon filters are not designed to capture most dissolved radioactive ions, and boiling water concentrates non-volatile radioactive material in the reduced volume of liquid.