Aerators (Aeration) is used in water treatment as a pre-treatment in the process of removing iron and hydrogen sulfide (rotten egg smell) from water.
Air is a powerful oxidizer of both iron and hydrogen sulfide. It quickly converts unfilterable ferrous iron to filterable ferric iron, and it reduces hydrogen sulfide to elemental sulfur, which is easily removed from water by a filter.
Air is a very fast oxidizer–considerably faster than chlorine.