Aeration is the process of contacting water with air or other gases to transfer volatiles from the liquid to the gaseous phase and dissolve beneficial gases in the water. It is possible to remove volatiles such as dissolved gases, volatile organic compounds, and various aromatic compounds that cause taste and odor through aeration. The gases that dissolve in water during this process are oxygen and carbon dioxide. The purpose of aeration in water treatment is to:

1. Reduce the concentration of taste and odor-causing substances, such as hydrogen sulfide and various organic compounds, by volatilization or oxidation
2. Oxidize iron and manganese and convert them to insoluble forms
3. Dissolve gas in water (for example, adding oxygen to groundwater and adding carbon dioxide to water after softening and for re-carbonation)
4. Remove compounds that may interfere with subsequent treatment processes or increase costs (for example, removing hydrogen sulfide before chlorination and removing carbon dioxide before softening).

Types of Aerators

Four types of aerators are commonly used, namely:

1. Gravity Aerators
2. Spray Aerators
3. Diffusers
4. Mechanical Aerators The main design consideration for all aerators is to provide maximum contact between the air and the water with minimum energy consumption.

Gravity Aerators

Gravity aerators use weirs, cascades, steps, inclined flat plates, vertical towers with upward air flow, perforated tray towers, or packed towers filled with media such as coke or rock.

Spray Aerators

Spray aerators spray water droplets into the air through fixed or movable nozzle openings. The water travels vertically or at an angle upward and falls back into a container, contact bed, or collection basin. Spray aerators are also used as decorative water features. A large amount of energy is required to produce a spray that breaks water into fine droplets, and the water must be free of coarse solids. Losses due to wind and freezing in cold weather can be a major problem.

Diffusion aerators

In this type, water is aerated in large tanks. Compressed air is injected into the tank through porous plates and tubes. The rising air bubbles create turbulence, providing ample opportunity for volatiles to exchange between the air bubbles and the water. Aeration times vary from 10 to 30 minutes. Aeration rates are typically between 0.1 and 1 cubic meter per minute per cubic meter of tank volume.

Mechanical aerators

Mechanical aerators use motor-driven impellers, or a combination of impellers and air injection devices. Common devices used are submerged paddles, surface paddles, propeller blades, turbine aerators, and centerline aerators.

Aeration can also be done in the tank using turbine aerators or centerline air flow tubes. This is the first step in the treatment of large tanks with stagnant or ice-covered water during the winter months. These systems are also used to raise warmer water from the bottom in winter and prevent the tank surface from freezing.