Suspended growth aerobic treatment plants may be
designed as continuous or batch flow systems. The
simplest continuous flow units provide no flow
equalization and depend upon aeration tank volume
and/or baffles to reduce the impact of hydraulic
surges. Some units use more sophisticated flow
dampening devices, including air lift or floatcontrolled
mechanical pumps to transfer the
wastewater from aeration tank to clarifier. Still
other units provide multiple-chambered tanks to
attenuate flow. The batch (fill and draw) flow
system eliminates the problem of hydraulic
variation. This unit collects and treats wastewater
over a period of time (usually one day), then
discharges the settled effluent through pumping at
the end of the cycle. Fixed film treatment plants
operate on continuous flow.