A GENERALIZED PROCEDURE FOR MODELING AND SIMULATION OF ACTIVATED-SLUDGE PLANT USING LUMPED-PARAMETER APPROACH

Design, operation, control and derating of modern activated sludge pla nt require good modelling effort. The completely-mixed tank in series (CSTR-in-series) concept has been widely used to represent nonideal fl ow in the actual activated sludge process. However there appears to be lack of a generalised approach to model the process using this concep t. Zn this paper, a systematic procedure to model the process using th e CSTR-in-series concept is developed. Using equi-sized CSTRs, the num ber of CSTR-in-series to represent the actual process may be determine d through investigation of the steady-state and dynamic responses of t he continuous process. This procedure is proven to be simple and the p rocess can be modelled with reasonable accuracy. Based on simulation r esults and validation of model with pilot-scale experimental data, it is recommended that two CSTR-in-series model should be employed to ade quately represent the activated sludge process for carbon removal of a typical municipal wastewater plant to a satisfactory effluent quality . The transient behaviour of biomass, substrate and dissolved oxygen c oncentration at various spatial positions along-the reactor represente d by the serial number of the CSTR's may also be usefully predicted.