The untreated effluent (1) is fed by gravity or pump to the center distributor (2) where it mixes with the air released from the recycled air carrier water and then enters the tank. Fine air bubbles lift the suspended, flocculated solids to the water surface (3) Heavier particles settle rapidly to the tank floor (4). The zone of clear water formed between the floated and settled solides is then discharged into the outlet annulus (5) where it overflows through an adjustable outlet weir (6). Adjustment of this weir controls the water level in the tank.

Floated matter is removed by the rotating spiral scoop (7) which discharges the sludge through the sludge pipe in the center distributor (2) to a sludge well (8) at the tank periphery.

A suspended bottom scraper (9) is supported from the structure and moved forward by the scoop drive. The settled sludge is scraped to the center of the tank and into a sludge pit (14) constructed in the foundation. From here, the sludge is removed intermittently through an automatically operated pneumatic valve (10). The scraper is so constructed as to allow it to rise and slip over any excessive obstructing sludge build-up in order to prevent any damage to the scoop drive.

The recycled air carrier water is pumped (11) at a pressure of about 80 psi into the retention tank (12). Compressed air (13) enters the retention tank directly. The air carrier water is then released into the center distributor after mixing with the raw influent. For small installations, it may be more economical to pressurize the whole of the effluent inflow.