A filter-free way to purify water

Bubbling carbon dioxide in water can remove suspended particles.

Harnessing carbon dioxide to purify water uses less energy than typical filtration methods.

Water is generally purified by being pumped across expensive membranes, which uses a lot of energy. Howard Stone at Princeton University in New Jersey and his colleagues have devised a way to eliminate the need for filters. They suspended 500-nanometre-wide polystyrene particles in water and exposed one side of the mixture to CO2. The gas dissolved in the water, generating an ion gradient that drove negatively charged polystyrene particles to one side and positively charged ones to the other so that they could be removed from the water.

Many microbes are charged, so this method could be used to remove bacteria and viruses without chlorination or ultraviolet treatment, the authors say.