Calibrating a side-stream membrane bioreactor using Activated Sludge Model No. 1

Membrane bioreactors (MBRs) are attracting global interest but the mathematical modeling of the biological performance of MBRs remains very limited. This study focuses on the modeling of a side-stream MBR system using the Activated Sludge Model No. 1 (ASM1), and compares the results with the modeling of traditional activated sludge processes. ASM1 parameters relevant for the long-term biological behaviour in MBR systems were calibrated (i.e. Y_H = 0.72gCOD/gCOD, Y_A = 0.25gCOD/gN, b_H = 0.25d⁻¹, b_A = 0.080d⁻¹ and f_P = 0.06), and generally agreed with the parameters in traditional activated sludge processes, with the exception that a higher autotrophic biomass decay rate was observed in the MBR. Influent wastewater characterization was proven to be a critical step in model calibration, and special care should be taken in characterizing the inert particulate COD (X_I) concentration in the MBR influent. It appeared that the chemical–biological method was superior to the physical–chemical method. A sensitivity analysis for steady-state operation and DO dynamics suggested that the biological performance of the MBR system (the sludge concentration, effluent quality and the DO dynamics) are very sensitive to the parameters (i.e. Y_H, Y_A, b_H, b_A μ_maxH and μ_maxA), and influent wastewater components (X_I, S_s, X_s and S_NH).