MODELING APPROACH SHOWS THE GROWTH DIFFERENCE OF FILAMENTS AND FLOC FORMERS INSIDE THE ACTIVATED SLUDGE FLOCS

摘要

Kinetic selection (KST) and substrate diffusion limitation (SDL) are two important factors thataffect the competition between filaments and floc formers in activated sludge system. Thecombination of both effects has been previously used to explain our contradictory experimentalresults (Lou and de los Reyes, 2008), from which a conceptual qualitative framework wasdeveloped with three regions (bulking, intermediate and non-bulking regions) suggested. Howeverthis framework has not been confirmed and the range of the substrate concentration for each regionwas not determined. To approve the framework quantitatively, a basic model integrating KST andSDL was developed in this study for simulating the growth rates of filaments and floc formersinside the activated sludge flocs. The kinetic parameters measured in our previous experiment wereused to incorporate into the model. The model was further extended to verify the results from ourprevious experiments that were operated in the sequencing batch reactors (SBRs) at differentinfluent substrate concentrations (100 mg/L, 300 mg/L and 600 mg/L). The effect of differences indecay rates of both organism types, and oxygen limitation were also tested in this study to evaluatetheir effects on the growth rates coming KST and SDL. The basic model simulation results showedthat the model was successful for confirming the proposed conceptual framework with three regionsdetermined by the substrate concentration. The results of the extended model were consistent withthe experimental data that bulking occurred at large floc while non-bulking happened at small flocs.The sensitivity analysis indicated that kinetic parameters have greater effect than diffusionparameters on the simulation results, and the growth of floc formers were more sensitive to theparameters than filaments.