Aerators

The goal of an aerator is to increase the surface area of water so that more air can come in contact with the water.  

There are several different methods used to aerate water, but all either involve passing water through air or air through water.  Water can be exposed to air by spraying or by distributing it in such a way that small particles or thin sheets of water come in contact with the air.  Water can also be aerated by pumping large volumes of air through the water. 

The method of aeration to be used depends on which materials on the water are to be removed.  The chemical characteristics of the water to be treated can also influence which treatment method is used.  Finally, each method has a different efficiency.  In general, pumping water through air is much more energy efficient than pumping air through water.  Different types of aeration and other methods of treatment should all be compared to determine the most efficient and practical method of treatment in each case. 

Air diffusion is a type of aerator in which air is blown through a trough of water.  As water runs through the trough, compressed air is blown upward through porous plates on the bottom.  This method is not very efficient due to limited air transfer.

Most of the other aeration methods work by passing raw water through air in small streams rather than by passing air through water.  A few, such as spray nozzle aerators, pump water through nozzles breaking the water into a fine spray. 

Cone tray aerators and cascade aerators both work by forming little waterfalls. 

Cone tray aerators consist of several cones in which water flows through the cone and over the rim of the cone. 

Cascade aerators allow water to flow in a thin layer down  steps.  In both cases, the waterfalls allow the water to come in contact with air.

Coke tray aerators also pass water through air in small streams.  A coke tray aerator is comprised of a series of activated carbon trays, one above another, with a distributing pan above the top tray and a collecting pan below the bottom tray.  The distributing pan breaks the water up into small streams or drops.  The holes in the trays should be designed to develop some head loss to provide for equal distribution to the lower tray. 

As the water moves through the coke tray aerator, small streams of water flow through the air from tray to tray.  A great amount of water surface area is also exposed to air as the water passes over the coke beds.  The water is collected in the bottom pan and given
further treatment if necessary. 

In addition to aerating water, the activated carbon trays in a coke tray aerator filter organic contaminants out of the water.  A similar method was once used to treat people who had swallowed poison.  Bread was toasted in the oven until it blackened, turning into activated carbon.  Then the patient ate the burnt toast.  The carbon drew the poison into the carbon and out of the patient's system. Coke tray aerators work in a similar manner, drawing contaminants out of the water.  

The last type of aerator which we will discuss here, the forced draft aerator, combines both methods: it blows air through water which has been broken into fine streams.  The forced draft aerator consists of a series of trays over which raw water runs.  As the water comes to the end of each tray, it cascades off and falls down to the collecting tray (also known as a drip pan).  At the same time, a fan at the top of the aerator pulls air up through the water.  So, as small streams of water fall from the trays, they comes in intimate contact with the strong updraft of air.  This type of aerator is most effective in the reduction of hydrogen sulfide and carbon dioxide.