Modelling of an Intermittently Aerated Completely Mixed Activated Sludge Reactor

Abstract

Mathematical models for description of dynamic behaviour of simultaneous nitrification and denitrification processes carried out in an intermittently aerated completely mixed activated sludge reactor (CMASR) are presented. The general IAWPRC activated sludge model has been extended with volatilisation process of wastewater impurity. The influence of wastewater composition on oxygen transport rate is also included. Different approaches for dissolved oxygen incorporation in biochemical reaction kinetics have been applied. Determination of some biokinetic parameter values by evaluating steady-state measurements of process variables is implied in one version of the proposed models. Experimental modelling of simultaneous nitrification and denitrification processes, carried out in an industrial Carrousel activated sludge reactor, was performed in the lab-scale intermittently aerated CMASR. Organic, ammonium, and heavy metal shock loads were applied in order to simulate transient behaviour of the lab-scale reactor and the influence of heavy metal on biochemical processes and biokinetic parameter values has been investigated. Dissolved oxygen concentration in activated sludge reactor, COD, ammonium, nitrate and biomass concentration responses of reactor were measured and evaluated. Good agreement between the observed data and calculated values by verified models has been achieved. Estimated values of biokinetic parameters, found by optimisation procedure, are close to those recommended for simulation of domestic wastewater treatment processes. The applicability of the IAWPRC kinetic and stoichiometric concept for dynamic behaviour description of an intermittently aerated CMASR reactor, including the above mentioned extension and modification, is demonstrated in the work.