This is a two-step activated sludge system treating wastewater in Houston, Texas. The first step uses five circular tanks to treat the concentrated waste. The second step (shown in this video) has seven rectangular tanks to further reduce the concentration of the influent wastewater using bidirectional jet aerators.
More air is used for the front end of the aeration tank, where the concentration is high. The rear end of the aeration tank is for maintaining dissolved oxygen, as well as treating the remaining load.
These directional jet aerators are in the process of being installed at the base of a tank. Support bases for the aerators are often anchored to the tank base (or, in the case of steel-bottom tanks, are welded to the tank base).
This tank (diameter: 180 feet, height: 33 feet) is mixed and aerated by six directional jet aerators, creating a circular flow pattern. This system is located at a pulp mill in British Columbia, Canada.