Improved Computational Model (AQUIFAS) for Activated Sludge, Integrated Fixed‐Film Activated Sludge, and Moving‐Bed Biofilm Reactor Systems, Part II: Multilayer Biofilm Diffusional Model

Abstract

Research was undertaken to develop a diffusional model of the biofilm that can be applied in lieu of a semi-empirical model to upgrade an activated sludge system to an integrated fixed-film activated sludge (IFAS) or moving-bed biofilm reactor (MBBR) system. The model has been developed to operate with up to 12 cells (reactors) in series, with biofilm media incorporated to one or more of the zone cells, except the anaerobic zone cells.The values of the kinetic parameters for the model were measured using pilot-scale activated sludge, IFAS, and MBBR systems. The biofilm is divided into 12 layers and has a stagnant liquid layer. Diffusion and substrate utilization are calculated for each layer. The equations are solved simultaneously using a finite difference technique. The biofilm flux model is then linked to the activated sludge model. Advanced features include the ability to compute the biofilm thickness and the effect of biofilm thickness on performance. The biofilm diffusional model is also used to provide information and create a table of biofilm yields at different substrate concentrations that can be used in the semi-empirical model. Water Environ. Res., 80, 624 (2008).

Biofilm Fixed Film Systems

“…Sen and Randall [38] combined the integrated fixed-film activated sludge (IFAS), and moving-bed biofilm reactor (MBBR) systems in a model. The model embeds a biofilm model into a multicell activated sludge model.…”

“…The biofilm flux rates for organics, nutrients, and biomass could be computed by two methods-a semi-empirical model of the biofilm that is relatively simpler, or a diffusional model that is computationally intensive. Later Sen and Randall [39] developed a diffusional model of the biofilm that can be applied in lieu of a semi-empirical model to upgrade an activated sludge system to an integrated fixed-film activated sludge (IFAS) or moving-bed biofilm reactor (MBBR) system. The model has been developed to operate with up to 12 cells (reactors) in series, with biofilm media incorporated to one or more of the zone cells, except the anaerobic zone cells.…”

Removal of hard COD, nitrogenous compounds and phenols from a high-strength coal gasification wastewater stream

“…Higher aeration rates increased the mixing energy (roll pattern) of the plastic media, resulting in higher shear forces across the biofilm layer (Sen and Randall, 2008), which influenced the biofilm thickness, microbial population and rate of growth. The mixing energy provided by the aeration is critical for sloughing of biomass and the formation of a thin biofilm yielding higher kinetic rates than previously measured in thick biofilm (Hubbell et al, 2006).…”

“…Thin biofilms increase available surface area and reduce variability of solids discharge due to sloughing (Goode, 2010). Sen and Randall (2008) reported that the rate of sloughing and the biofilm yield for heterotrophs and nitrifiers in each cell are dependent on (i) shear forces imparted by mixing and roll pattern, (ii) design of biofilm carrier particle (media), and (iii) substrate and electron acceptor level in each cell. The biofilm thickness is a function of the substrate concentration in the bulk liquid, average mixed liquor volatile suspended solids (MLVSS) of the biofilm and shear forces (Sen and Randall, 2008).…”

Activated Sludge and Other Aerobic Suspended Culture Processes

“…The steady-state model represents a continuous flow, stirred tank reactor. Sen and Randall [2][3][4] developed a computational model (AQUIFAS) for activated sludge, IFFAS, and MBBR systems. The model uses a biofilm model embedded in a multi cell activated sludge model.…”