Modeling the nutrient removal process in aerobic granular sludge system by coupling the reactor- and granule-scale models.

We developed a model for nutrient removal in an aerobic granular sludge system. This model can quantitatively describe the start-up of the system by coupling a model for studying the population dynamics of the granules in the reactor (reactor-scale model) and a model for studying the microbial community structure in the granules (granule-scale model). The reactor-scale model is used for simulation for 10 days from the start, during which the granule size is relatively small; the granule-scale model is used after Day 10. The present approach proposes the output data of the reactor-scale model after 10 days as initial conditions for the granule-scale model. The constructed model satisfactorily describes experimental data in various spatial and temporal scales, which were obtained in this study by performing the anaerobic-aerobic-anoxic cycles using a sequencing batch reactor. Simulations using this model quantitatively predicted that the stability of nutrient removal process depended largely on the dissolved oxygen (DO) concentration, and the DO setpoint adaptation could improve the nutrient removal performance.