Modeling activated sludge mass transfer in a treatment plant

To keep overflows of raw effluent to a minimum during wet weather condition s, we investigated the ability of a secondary clarifier of an activated slu dge treatment plant to accept hydraulic overloads without being washed out. The experiments, which were conducted on a full scale 8000 p,e, treatment plant, showed the feasibility of the project, and suggested some features, which were included in a one-dimensional model designed to study the behavi or of the sludge blanket in the clarifier. This model takes into account th e effect of convection currents, suspected to play an important part in the rising of sludge blankets. The sensitivity of the model to sludge settleab ility prevented its use with long times-series, unless a continuous recalib ration was performed. Nevertheless, this model appears very interesting for a better understanding of the dynamics of the clarifier, as described by m easured data. It could be used in relation with sensors to improve the oper ation of the treatment plant. (C) 1999 IAWQ Published by Elsevier Science L td. All rights reserved.