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Sequencing Batch Reactor (SBR)

A sequencing batch reactor is a fill and draw activated sludge treatment system, the unit processes involved (aeration and clarification) being identical to conventional activated sludge systems. However, in conventional activated sludge plants the processes are carried out simultaneously in separate tanks whereas in SBR operation the processes are carried out sequentially in the same reactor vessel/tank. As the process is a batch process, it is usual to have a minimum of two reactor vessels or sufficient inlet flow balancing capacity to ensure continuous treatment capability. The usual operational sequence for an SBR is:

Fill phase - usually un-aerated but can be aerated from commencement.
Reaction phase - tank contents aerated.
Quiescent phase - sedimentation and clarification of tank contents.
Decant phase - supernatant liquor (treated effluent) removed from tank.
Idle phase - surplus sludge removed to maintain a balanced microbial population.

Optimum performance of an SBR is achieved when the reaction vessel is filled as rapidly as possible during the Fill phase and emptied as quickly as possible during the Decant phase. However, care must be taken to ensure that a rapid decant does not exceed any volumetric discharge consent that may apply to the site.

As all the unit processes occur within a single vessel there is no requirement for a return activated sludge (RAS) system

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