Food and household water Food and household water

Food and household water

Food and household water

Removing radioactive materials from household water

Removing radioactive materials from household water

There are effective methods available for removing radioactive materials, such as uranium and radium, from household water. In the case of a private well, other water supply opportunities should be clarified first. Water supply plants need a removal method that is suitable for the processing of large amounts of water.

Private wells

If the radon concentration in water is high or the water contains harmful quantities of other radioactive materials, other water supply opportunities should be clarified first. Then, the first alternative is to join the municipal water supply network or share a supply of water with a neighbour. If there are no other opportunities, household water can be purified from harmful materials.

Radon must be removed from all household water, since it is released to indoor air during water consumption and increases indoor air radon concentration. In terms of other radioactive materials, it is sufficient that they are removed from drinking water. They are not released to indoor air similarly as radon.

Radon can be removed from water either with an aeration method or using an activated carbon filter. More than 90% of radon in water can be removed using a correctly installed and designed device. The selection of method is affected by the radon concentration of water and water consumption.

The aeration method suits all radon concentrations, whereas activated carbon filtering is only suitable for concentrations below 5,000 becquerels per litre. Furthermore, an activated carbon filter may not be placed in a building with permanent residents, since the filter will start to radiate once radon is collected in the filter. It is recommended that the activated carbon filter be installed in a separate technical building or in the inspection well connected to the well. An aeration device does not cause radiation, so it can also be installed in a residential building.

There is no need to remove uranium or radium from all household water, since they cause exposure to radiation only when ingested. In other words, they do not cause exposure to radiation during a shower or in connection of other water use, as does radon. Uranium and radium can be effectively removed from water using an ion exchange technique either simultaneously or separately.

Lead and polonium can be reliably removed either with nanofiltration or reverse osmosis filtration. However, these methods required tertiary treatment of water. Activated carbon and ion exchange also remove lead and polonium. Reductions have varied to a wide degree, being 50–100%.

Other qualities of water also affect the functionality of the removal device. Large amounts of iron, manganese and humus may interfere with the functioning of filters or aeration devices. Therefore, the selection of the removal device must be planned on a case-by-case basis.

Waterworks

Aeration is the economically most sensible method for removing radon in waterworks, since it is suitable for processing large volumes of water. In addition to radon, aeration removes also other gases, such as hydrogen sulfide and carbon dioxide, from water which improves the taste and smell of water. There are three different principles on aeration in waterworks: Diffused bubble aeration, spray aeration or packed tower aeration. Activated carbon filtration is not commonly used for radon removal in waterworks.

Diffused bubble aeration is carried out either in an open basin or in a closed container in which the air is led through nozzles at the bottom of the container. Radon reduction increases when the bubble size decreases, air–water ratio increases and aeration period is extended. A sufficient reduction can usually be reached with air–water ratio 10:1, and the reduction will not significantly improve by increasing this air–water ratio.

Spray aeration is usually the most economical alternative for waterworks where the radon concentration of water is not high and which have basins for the removal, for example, of iron. Water is sprayed into the basin as droplets that are as fine as possible in order to ensure the most efficient removal of radon. Spray and diffused bubble aeration methods can also be combined.

Packed tower aeration is a more effective method than spray aeration. A packed tower aerator is a long cylinder that has been filled, for example, with plastic balls or rings. Water is led to the cylinder through its upper part and air is blown upstream from the lower part of the cylinder. Water forms a thin membrane on the surface of the fill material, through which radon can easily transfer to air.

Other traditional water treatment methods in waterworks remove varying quantities of radioactive materials, such as uranium, radium, lead and polonium. The most effective method is the membrane filtration. Alkalisation and slow filtration are the least efficient methods to remove radioactive materials.

Harmaa tietolaatikko Food and Household water

Household water refers to water that is intended for human consumption and for preparing food. The Decree of the Ministry of Social Affairs and Health Relating to the Quality and Monitoring of Water Intended for Human Consumption (1352/2015) sets limits for radiation exposure caused by radioactive substances. Decree 1352/2015 (Finlex.fi)