Aeration is used in water treatment as a pretreatment 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 unremovable ferrous iron to filterable ferric iron, and it reduces hydrogen sulfide to elemental sulphur, which is easily removed from water by a filter.
Air is a very fast oxidizer--considerably faster than chlorine.
The illustration on the right is of a typical residential aeration system, showiing one of the ways that air can be introduced into water to treat iron and hydrogen sulfide. It features a small air compressor and a special tank in which treatment takes place. The system above has an electrically controlled vent system to vent some of the hydrogen sulfide gas to the atmosphere, but especially to provide for a turnover of air in the tank.
The air pump delivers air into the tank and a pocket of compressed air forms in roughly the top third of the tank. As water enters the tank through the pipe at left, it hits a baffle (of the three pipes attached to the vent head, it's the short pipe on the left) and sprays down through the pocket of compressed air. The water is further aerated inside the tank before it leaves by way of the long tube (called a riser) which picks it up at the bottom of the tank and sends it out through the pipe at right. The mid-length tube in the center is the vent tube. It controls the depth of the air pocket.
When the air pump is activated, the solenoid valve opens at the same time and an air/water mixture exits the tank via the middle tube and the drain line.
The pump and vent are controlled by the same electrical circuit so that when the pump is running, the vent is open and air is being exchanged. When the pump turns off, the vent closes and the compressed air pocket is maintained.
The electrical ciruit that turns the pump/vent system off and on can be controlled in a variety of ways. The most common is by wiring them into the well's own pump circuit, so that the aeration system is activated when the well pump is running. Another way--and this is shown in the diagram--is with a specially designed control that monitors the pressure inside the aeration tank and activates the pump/vent according to aeration tank pressure. A third popular activation system is a flow switch, which turns the pump/vent system on when water is flowing to the home.
