The Oxidation Ditch

This is a sometimes used for sewage treatment and is characterised by a con-structed ellipsoidal ditch, in which the effluent is forced to circulate around the channel by brush aerators. The ditch itself is trapezoidal in cross-section to maintain uniform effluent velocity throughout the channel. Effluent is fed into the system without any prior primary sedimentation and typically gives rise to only 50% of the surplus sludge produced by a typical activated sludge process.