Extended Activated Sludge Model No.1 with Floc and Biofilm Diffusion for Organic and Nutrient Removal

Abstract

This paper presents a modified mathematical model for substrate degradation and nutrient removal by aerobic microorganisms. The modified model is based on Activated Sludge Model No.1 (ASM1) for bacterial growth incorporated with substrate diffusion into flocs and biofilms. Monod kinetics are modified to consider the proton translocation theory for substrate dissociation in ASM1. Microbial growth rate coupled with mass transport rate was studied for heterotrophs and autotrophs in bulk solution and the boundary layer of biofilms to reveal the extra degree of freedom of this dynamic model. Moreover, the sensitivity analysis of the modified model was discussed at steady state using the Newton–Raphson technique. A decrement in the removal efficiency of chemical oxygen demand (COD) and ammonia nitrogen (NH4-N) was obtained under the influence of the diffusion principle compared with modified Monod substrate conversion. However, the decline in biofilm thickness to 50 μm at heterotrophic and autotrophic biomass concentration of 15 kg/m3 and 1 kg/m3, respectively, enhanced the removal of both influent COD of 200 mg/L and influent NH4-N of 30 mg/L in an Integrated Fixed Film Activated Sludge (IFAS) pilot plant experiment established at Zenein wastewater treatment plant (WWTP), Giza, Egypt.