Use of steady-state biofilm model to characterize aerobic granular sludge

In this study, a steady-state biofilm model was utilized to elucidate the aerobic granular sludge process. In order to describe the experiment data using the model, two different sizes of stabilized aerobic granules (with mean diameters of 0.6 mm and 3 mm, respectively) were investigated through the laboratory operations of sequencing batch reactors (SBRs). On the basis of the estimated parameters from experiments, the model was established to describe the biofilm functions in aerobic granules, such as substrate transfer and substrate concentration variations within the granules. In the modeling at different chemical oxygen demand (COD) concentrations (100-1000 mg/L), the biofilm functions were affected by the characteristics of aerobic granules, such as diameter and density. The larger granules modeled higher substrate fluxes (1.8-14 mg/cm(2)-d) and deeper effective film thicknesses (0.18-1.3 cm). The multi-aspect simulation results demonstrated that the substrate either approaches zero in the film (at low concentration) or penetrates the granules (at high concentration). The sum of aerobic granules in the SBRs can be considered as a mass of biofilm, where the substrate approaches zero at sufficient depth. The steady-state biofilm model could be an effective prediction method for optimizing the aerobic granular sludge process.