Dynamic modelling and simulation of activated sludge process using orthogonal collocation approach

This paper deals with the improvement in modelling of the dynamics of activated sludge wastewater treatment process using a distributed parameter approach. A computational algorithm, based on the global orthogonal collocation technique, for the activated sludge process is developed in this work. Steady-state and dynamic simulations are performed based on this algorithm. The system configuration considers backmixing or intermixing, which can represent the actual process more accurately than the idealised flow schemes commonly employed for the design and modelling of the activated sludge reactors. Based on a dispersed plug flow model for activated sludge bioreactor formulated in this work, a Peclet number in the order of 0.5 to 5 and 5 to 7 internal collocation points are recommended for modelling channel-type activated sludge bioreactor. The dynamics of substrate is predicted well whereas the prediction for biomass is fair, when compared to the experimental data. It is also demonstrated in this paper that the proposed algorithm can give superior prediction of process dynamics than the commonly-used tanks-in-series technique. Dynamic responses caused by disturbances in the influent wastewater which propagates at various spatial positions along the bioreactor can be correctly predicted through simulations.