A variety of aeration equipment types are used for effective mechanical oxidation and gas removal. The most common, and most efficient, is positive draft aeration. This is accomplished in cylindrical or rectangular vessels where a counter-current flow of air and water is created.
To increase contact surface area and exposure time, media is used in the form of loose fill of special shapes, easily cleaned PVC slats, or wood trays. Water is discharged into a tray at the top of the aerator that evenly distributes flow over the unit cross section with orifices or nozzles. It then drops into the aeration zone that contains the appropriate media and provides space for the air to move up through the finely dispersed water droplets.
The air countercurrent is produced by electric operated blowers by either of two methods. The most commonly used air movement method is by induced draft, which employs a suction blower located at the top of the unit. The blower induces flow through screened air inlet baffles near the bottom of the vessel, up through the media/water mix of the aeration section, through air stacks located in the distributor tray to ensure even collection, and finally through a vane style moisture separator and the blower itself.
A forced draft unit accomplishes the same flow pattern, but forces the air in the inlet baffle, and exhausts it through the screened hood located at the unit top.