TM 5-814-3/AFM 88-11, Volume III
e. Extended aeration. Extended aeration activated sludge plants are designed to provide a 24-hour
aeration period for low organic loadings of less than 20 pounds biochemical oxygen demand per 1,000 cubic
feet of aeration tank volume. This approach, which can be used for treatment plants of less than 0.1 million
gallons per day capacity, reduces the amount of sludge being wasted for disposal.
Oxidation ditch. The closed-loop reactor, also known as an oxidation ditch (fig 15-5), is a form of
the extended aeration process. The wastewater is propelled around an oval racetrack-configured basin by
mechanical aerator/mixing devices located at one or more points along the basin. These devices can be either
brush aerators, surface aerators or jet aerators. The velocity in the basin is designed to be between 0.8 and
1.2 feet per second. The closed-loop reactor is the preferred type of activated sludge system for Army
installations. The design or provision of any other system for Army installations requires prior approval from
HQDA (CEEC-EB) WASH DC 20314-1000. Appendix C contains a sample design calculation.