Investigation of fill and batch periods of sequencing batch biological reactors

Early use of sequencing batch (fill and draw) biological reactors was abandoned in favor of conventional continuous flow constant volume treatment systems because of operational difficulties. Recent advances in process control and the need to provide more reliable and consistent treatment have called for the re-evaluation of present biological treatment practices. Fill and draw reactors provide for equalization of flow and concentration, treatment of organics and quiescent sedimentation in the same system. This system also benefits from the theoretical advantages of the volume reductions expected from a plug flow system. Laboratory studies were conducted on fill and draw reactors. A mathematical model was developed to describe, as a function of time, the waste and organism concentration and the oxygen uptake rate. Close agreement between the measured and predicted values was obtained. These results plus the obvious potential benefits of batch treatment suggest that sequencing batch systems may serve as a process alternative to conventional treatment schemes.