Aeration is the process used to either mix, circulate, or dissolve air into a liquid or other substance.
We actually encounter aerated water each day. Most water taps or faucets are fitted with an aerator to smooth the water flow. If you have an aquarium or are a home brewer, you are also familiar with aeration.
Perhaps the most fun example of aeration at work: the water-agitating Jacuzzi , commonly used for hydrotherapy. The concept was built on the Jacuzzi brothers’ jet pump technology. Their pumps, patented in 1927, were first used in irrigation and are credited with revolutionizing domestic water delivery.
However, aeration is a commonly used secondary wastewater treatment method. Aerating mixers or diffusers are used to expose sewage or dirty water to air. When air is added, it releases some of the gases – such as carbon dioxide and hydrogen sulfide, the latter of which causes water to have a foul taste and odor — from the water.
The United States Geological Survey explains:
As organic matter decays, it uses up oxygen. Aeration replenishes the oxygen. Bubbling oxygen through the water also keeps the organic material suspended while it forces “grit” (coffee grounds, sand and other small, dense particles) to settle out. Grit is pumped out of the tanks and taken to landfills.
The process also oxidizes dissolved metals and can remove some volatile organic chemicals (VOC) in the water, according to the Minnesota Rural Water Association. Once oxidized, the chemicals are suspended in the water and can be removed by filtration.
There are two general aerator types conventionally used in the aeration process.
One introduces air into the water via small bubbles. Air into water systems are not typically used for water treatment, but for aerating activated sludge. The technologies include pressure aerators, which spray water into either high pressure air or porous stone to add oxygen to the water; and air stripping, which is used to remove volatile organic chemicals such as benzene and trichloroethylene.
The other aeration method creates tiny water drops that fall or cascade through the air. This approach is common in water treatment systems. These types of aeration devices include cascade aerators, which mimic flowing streams — adding air when the water splashes; cone aerators, in which water cascades top to bottom through a cylindrical device; and slat and coke aerators, which are a system of slatted trays that are filled with coke, rock, or limestone to provide more surface contact between the air and water. Two other technologies in this category use blowing or spraying air: draft aerators and spray aerators. These technologies are purportedly effective in oxidizing iron and manganese that might be found in the feed water.
One challenge created with the addition of oxygen to water is that the increased dissolved oxygen – while it has many benefits, including improving the water’s taste – causes the water to be more corrosive. This can damage, for example, copper or other metal that might be found in pipes.
Various technologies have been created based on these fundamental concepts. There are, for example, submerged aerators designed to keep deep water flowing or diffused air aerators that disturb surface water. How effective these processes are is wholly dependent on the surface contact between the air and water.
In addition to being a key step in water treatment, aeration is also used in allied processes and is frequently a portion of a comprehensive treatment facility. Aerators can be used in conjunction with various other technologies such as skimmers, aerobic sludge digesters, or sequencing batch reactors.
There are a wide variety of aeration technologies currently available on the market, each of which is designed to address a specific challenge or range of challenges.
Jacuzzi: A Father’s Invention to Ease a Son’s Pain by Ken Jacuzzi and Diane Holloway
Spirit, Wind & Water: The Untold Story of the Jacuzzi Family by Remo Jacuzzi
Image by Dan Hartung used under its Creative Commons license