Mechanical Aerator for Activated Sludge Process

Mechanical aerator is another option other than diffused aeration to introduce more air into the wastewater system. There are two different designs of aerators, one is a vertical axis type and another is the horizontal axis type. Both designs can either be submerged aerator or either surface aerator depending on whether certain systems require pure oxygen to be introduced from aeration tank bottom.

Design of vertical axis aerators is mainly focused on whether there is a need to induce updraft wastewater flow or to obtain reverse downdraft flow. The mechanical construction is rather simple as it only has an impeller attached to a motor mounted on the aeration tank concrete structure and turning of the impeller will entrain air from the atmosphere to mix with the wastewater. This will create high air to water exchange surface area and thus leads to more air being dissolved in the water. Usually design of the mechanical aeration system has an inverter to control motor speed that will receive input from a transmitter that measures dissolved oxygen level. Lower DO will induce the motor to operate at higher speed and thus increase the amount of oxygen introduced to the wastewater. Such system is not only considered energy efficient but it will also lead to huge savings especially on power utilization.

Mechanical surface aerators with horizontal axis is basically made up of rotating cylinders with bristles that will spray the wastewater across the surface of the tank to entrain air into it and at the same time create vigorous agitation. For the submerged type, usually there is presence of multiple paddles that are attached to the rotating shaft and as it turns, each paddle that enters the water will entrain air together with it. In order to control and maximize amount of dissolved air, the spacing of each paddle has to be adjusted accordingly to get the right orientation.

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