Modeling the Transition from Zone Settling to Compression of a Bulking Activated Sludge.

Abstract

One of the most important functions of the settling tanks in an activated sludge process is thickening the sludge to a high enough suspended solids concentration so that the return sludge flow will maintain the desired mixed liquor suspended solids concentration. The settling phenomena which result in the thickening are zone settling and sludge compression. Both zone settling and sludge compression have been studied extensively. However, the transition from zone settling to compression has previously received only superficial treatmenThe objective of this study was to characterize the transition of activated sludge from zone settling to compression by using simple laboratory methods. Batch settling tests were conducted using samples of activated sludge from one treatment plant. The samples were obtained over a period of fourteen month and the sludge volume index (SVI) values ranged from 80 ml/g to 213 ml/g. A model for predicting a first order rate constant for the transition from zone settling to compression was developed by analyzing the experimental data By classifying the sludges into six groups according to the SVI range, the transition from zone settling to compression was successfully characterized with respect to the initial suspended solids concentratfon