Changes

In some areas where more land is available, sewage is treated in large round or oval ditches with one or more horizontal aerators that drive a mixture of sludge and wastewater around the ditch to provide aeration. These are oxidation ditches, often referred to by manufacturers' trade names such as Pasveer, Orbal, or Carrousel. They have the advantage of being relatively easy to maintain and are resilient to shock loads that often occur in smaller communities, such as at breakfast time and in the evening.  Oxidation ditches typically have a hydraulic retention time of 24 - 48 hours and a sludge age of 12 - 20 days.