Sludge wasting is an important step in the SBR
process and largely affects system performance. It
is not considered a basic phase since the sludge is
not wasted at a specific time period during the
cycle. The quantity and rate of wasting is
determined by performance requirements. An SBR
system does not require an RAS system, as both
aeration and settling occur in the same tank. This
prevents any sludge from being lost during the react
step and eliminates the need to return sludge from
the clarifier to the aeration chamber (Metcalf and
Eddy, 1991).