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.