How Aeration Systems for Water Treatment Work
Aeration is used in water treatment as a pre-treatment in the process of removing iron and hydrogen sulphide (rotten egg smell) from water. Air is a powerful oxidizer of both iron and hydrogen sulphide. It quickly converts irremovable ferrous iron to filterable ferric iron, and it reduces hydrogen sulphide 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, showing one of the ways that air can be introduced into water to treat iron and hydrogen sulphide. 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 sulphide 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 centre 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 circuit 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.
The "Venturi" System
The venturi system uses no power. When the well's pump comes on in response to low pressure in the pressure tank, air is sucked into the main water line through the small venturi valve just before the pressure tank. The air is mixed with the water inside the aeration tank at right. Some of the air is vented to the atmosphere through the small vent valve on top of the aeration tank. After a short residence in the aeration tank, the aerated water continues to the next treatment stage via the water pipe at right.
Venturi systems are simple and relatively inexpensive, but they have the disadvantage of restricting water flow (the venturi itself pinches the water stream to create the vacuum needed to pull in air).
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