Oxidation ditches are large round or oval ditches (channel reactors) used for the aerobic treatment of wastewater. One or more horizontal aerators guarantee oxygen supply and mix and move the prescreened content around the ditch. Operation can be continuous or intermittent. Primary sedimentation is usually not required, but secondary sedimentation tanks are generally used. Oxidation ditches are suitable for areas where land availability is high. They have the advantage that they are relatively easy to maintain (compared to activated sludge systems) and are resilient to shock loads as it often occurs in smaller communities (i.e. at breakfast time and in the evening).