The clear water discharge phase at the end of a process cycle is a crucial process step in ensuring the quality of the treated sewage. Only the cleaned sewage may pass into the outflow, floating matter must be safely held back.

During the previous treatment phases (infeed, aeration, stirring and sedimentation) the discharge unit has been positioned at a safety distance above the maximum possible water level. Upon starting the discharge process the discharge unit is gradually lowered using an electrically operated winch and the discharge pipe is immersed in the clear water zone. As a rule, the clear water is fed in below the dropping water level to retain floating sludge. Draining is done by gravity.

The discharge process has been completed upon reaching the minimum surfacing height as well as the bottom end position and the discharge unit is moved up to its initial position.