How Aeration Systems for Water Treatment Work
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 unfilterable 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 above of a typical residential aeration system shows 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 release 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 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 simplest and sometimes air pump control is a simple lamp timer, which is used to activate the pump and solenoid at intervals, assuing a good turnover of air and a fresh air pocket in the tank.
Air Pump and Tank Sizing Facts
Standard pumps handle flow rates up to 15 gpm. A commercial pump is used for flow rates over 15 gpm.
Output of standard pump: 0.38 cfm @ 0 pressure; 0.15 cfm @ 50 psi.
General Rule of Thumb on Tanks: The gallon capacity of the tank should be at least double the flow rate.
A flow rate of 8 gpm requires a 16-gallon tank (10 X 54). This works for most residential situations.
A flow rate of 10 gpm requires a 20-gallon tank (12 X 52).
A flow rate of 24 gpm requires a 48-gallon tank (16 X 65).
General rule on hydrogen sulfide: The standard Aer Max unit treats up to 6 or 7 ppm sulfide well. Tank size should be increased for greater amounts. For up to 12 or 13 ppm, use a 12 X 52 tank.
Where to get more information about aeration systems (and even buy one if you want). There is more specific tank sizing information below.
The "venturi" system
The venturi system shown above 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 tank, the aerated water continues to the next treatment stage via the water pipe at right.
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Close-Up of a Venturi Valve. |
Venturi systems are simple and relatively inexpensive, but they have the disadvantage of restricting water flow (the venturi pinches the water stream to create the vacuum needed to pull in air).
Aeration Tank Sizing
Sizing of aeration tanks for optimal performance in general involves providing about 2 gallons of tank space for each anticipated gallon-per-minute of service flow of the unit. In other words, If you anticipate service a service flow of five gallons per minute, be sure to provide at least ten gallons of aeration tank space. This rule is commonly violated with the less expensive venturi systems.
For most residential use, the most common aeration tank size is 10" x 54". This holds about 16 gallons of water and will therefore support a service flow of eight gallons per minute comfortably.
The chart below gives the most common mineral tank sizes that are used for residential aeration units.
Tank Size |
Approximate Gallon Capacity |
Approximate Service Flow Supported, In GPM |
7 X 44 |
7.5 |
4 |
8 X 44 |
9 |
5 |
9 X 48 |
12.75 |
6 |
10 X 44 |
13.5 |
7 |
10 X 54 |
16.5 |
8 |
12 X 48 |
23 |
11 |
12 X 52 |
24 |
12 |
13 X 54 |
27.75 |
14 |
14 X 65 |
49 |
20 |
16 X 65 |
48 |
24 |
More information:
AerMax and other air treatment system parts
Eliminator Single Tank Aeration/Filtration Treatment for Iron and Hydrogen Sulfide.