List cycles of SBR.

• A. Fill, React, Settle, Decant, Idle
• B. Inflow, Aerate, Clarify
• C. Feed, Mix, Sludge removal
• D. Stage, Reaction, Settling, Decanting

Answer: (A)

In a Sequencing Batch Reactor, treatment happens in a defined batch cycle with five phases: Fill, React, Settle, Decant, and Idle. The Fill phase introduces wastewater into the reactor and starts mixing; during React, aeration or mixing promotes biological treatment to remove organics and nutrients; Settle allows solids to settle to the bottom; Decant withdraws the clarified supernatant as effluent; Idle provides a non-operational interval to finish settling, relieve flows, and prepare for the next batch. This exact sequence is why the combination of Fill, React, Settle, Decant, Idle matches the standard SBR cycle.

The other options omit one or more of these essential phases or use terminology that doesn’t reflect the full batch sequence, so they don’t describe the complete SBR cycle.