Improved Computational Model (AQUIFAS) for Activated Sludge, Integrated Fixed‐Film Activated Sludge, and Moving‐Bed Biofilm Reactor Systems, Part III: Analysis and Verification

Abstract

Research was undertaken to analyze and verify a model that can be applied to activated sludge, integrated fixed-film activated sludge (IFAS), and moving-bed biofilm reactor (MBBR) systems. The model embeds a biofilm model into a multicell activated sludge model. The advantage of such a model is that it eliminates the need to run separate computations for a plant being retrofitted from activated sludge to IFAS or MBBR. The biofilm flux rates for organics, nutrients, and biomass can be computed by two methods-a semi-empirical model of the biofilm that is relatively simpler, or a diffusional model of the biofilm that is computationally intensive. Biofilm support media can be incorporated to the anoxic and aerobic cells, but not the anaerobic cells. The model can be run for steady-state and dynamic simulations. The model was able to predict the changes in nitrification and denitrification at both pilot-and full-scale facilities. The semi-empirical and diffusional models of the biofilm were both used to evaluate the biofilm flux rates for media at different locations. The biofilm diffusional model was used to compute the biofilm thickness and growth, substrate concentrations, volatile suspended solids (VSS) concentration, and fraction of nitrifiers in each layer inside the biofilm. Following calibration, both models provided similar effluent results for reactor mixed liquor VSS and mixed liquor suspended solids and for the effluent organics, nitrogen forms, and phosphorus concentrations. While the semi-empirical model was quicker to run, the diffusional model provided additional information on biofilm thickness, quantity of growth in the biofilm, and substrate profiles inside the biofilm. Water Environ. Res., 80, 633 (2008).

Comparative modeling of biological nutrient removal from landfill leachate using a circulating fluidized bed bioreactor (CFBBR)

“…AQUIFAS ® is developed to model fixed film process using semiempirical equations and a 2-dimensional biofilm model [20][21][22]. The model equations are based on the kinetics of COD uptake, nitrification, denitrification, and biological phosphorus removal by biofilm carrier particles, as measured under different substrate conditions within the length of a biological reactor.…”

“…The equations incorporate Monod kinetics with mass flux to simulate the variation in substrate uptake rates, as a result of changes in external substrate concentrations, and associated changes in the biofilm thickness and fraction of nitrifiers in the biofilm that develop in a different cell reactors. The detailed model equations are presented elsewhere [20][21][22].…”

“…One-dimensional (1-D) fully dynamic and steady-state simulation models are widely used to simulate the full-scale wastewater treatment plant (WWTP) such as the stratified dynamic multi-species model introduced and implemented in the AQUASIM software [13,[15][16][17][18] and Activated Sludge Models (ASM1, ASM2, ASM2d, ASM3) introduced by International Water Association (IWA) [19]. The IWA model is available in several user-friendly forms, the most common of which are the Simba ® (Ifak GmbH, Magdeburg, Germany), ASIM ® (EAWAG, Switzerland), EFOR ® (DHI Inc., Denmark), BioWin ® (Envirosim Associates Ltd., Burlington, ON), GPS-X ® (Hydromantis Inc., BioWin ® and AQUIFAS ® developed a fixed film model and successfully simulated the integrated fixed-film activated sludge (IFAS) process, moving bed biofilm reactor (MBBR), and biological aerated filter (BAF) systems for municipal wastewater treatment plants using a wide range of BOD loadings and biofilm thicknesses [20][21][22][23][24][25]. The developed models improved the accuracy of diffusional models by evaluating results against semi-empirical data based on experimental measurements from different full-scale WWTPs.…”

Biofilm Fixed Film Systems

“…A multi layer biofilm diffusion model was developed applicable to integrated fixed-film activated sludge (IFAS) or moving bed biofilm reactor (MBBR) system and linked to the activated sludge model (Sen and Randall, 2008). The model was able to calculate biofilm thickness and the impact of the thickness on the performance of reactor.…”

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.…”