.There are normally five phases in the SBR
treatment cycle: fill, react, settle, decant, and idle.
The length of time that each phase occurs is
controlled by a programmable logic controller
(PLC), which allows the system to be controlled
from remote locations (Sloan, 1999). In the fill
phase, raw wastewater enters the basin, where it is
mixed with settled biomass from the previous cycle.
Some aeration may occur during this phase. Then,
in the react phase, the basin is aerated, allowing
oxidation and nitrification to occur. During the
settling phase, aeration and mixing are suspended
and the solids are allowed to settle. The treated
wastewater is then discharged from the basin in the
decant phase. In the final phase, the basin is idle as
it waits for the start of the next cycle. During this
time, part of the solids are removed from the basin
and disposed of as waste sludge (Kappe, 1999).
Figure 3 shows this sequence of operation in an
SBR