Which aspect of water treatment involves the use of membranes to selectively remove ions?

Electrodialysis is the process that involves the use of membranes to selectively remove ions from water. This method employs ion-selective membranes, which allow positively charged ions (cations) to pass through one membrane and negatively charged ions (anions) to pass through another, effectively separating these ions from the water. This process is often utilized for the desalination of brackish water or for reducing ion concentrations in drinking water systems.

In contrast, ozonation and chlorination are disinfection processes that focus on killing pathogens and preventing microbial growth but do not involve selective ion removal. These methods rely on chemical reactions rather than physical separation techniques. Filtration, on the other hand, typically removes suspended solids and particulate matter from water but does not specifically target ions like electrodialysis does. Thus, electrodialysis stands out as the correct answer due to its unique operation involving ion exchange through membranes.