Modeling Integrated Fixed-Film Activated Sludge (IFAS) and Moving Bed Biofilm Reactor (MBBR) Systems: Development and Evaluation

A mathematical model for integrated fixed-film activated sludge (IFAS) and moving bed biofilm reactor (MBBR) wastewater treatment processes was developed and validated. The model includes analytical solution(s) to the 1-D biofilm diffusion and reaction equations, competition between aerobic autotrophic nitrifiers, heterotrophs, methylotrophs, slowly biodegradable chemical oxygen demand, and inert biomass for space inside the biofilm; and biofilm and suspended biomass compartments compete for both the electron donor and electron acceptor. Identical reaction kinetics for bacteria in suspended biomass and biofilm are assumed. Revised and expanded matrix notation similar to that presented as the IWA ASM 2d served as the basic model structure. The steady-state model describes a CFSTR and has been demonstrated to simulate with reasonable accuracy four wastewater treatment configurations with published operational data. Conditions simulated include combined carbon oxidation and nitrification (both IFAS and MBBR), tertiary nitrification MBBR, and post-denitrification IFAS with methanol addition as the external carbon source.