Effect of SRT on Floc Biodiversity in Activated Sludge Model

A comprehensive and simplified floc model describing resource competition was developed to evaluate the impact of bioreactors operating parameters and key characteristic of flocs on bacterial species dynamics and oscillation patterns. It described competition among six aerobic heterotrophs for three complementary growth–limiting nutrients in activated sludge flocs, and incorporates the effects of diffusion limitations and floc propagation. This model was an extension of a previously reported biofilm model. Simulation results showed that at certain values of solid retention time (SRT), competition of species favored sustained oscillations in the abundances of species for fully penetrated flocs. Comparison of the dispersed-growth process, the biofilm, and the suspended flocs showed that the oscillation growth pattern of species was not only a function of competition, but also depended on key physical characteristics of the ecosystem. The significance of the current study was that it was the first to examine the relationship between operating parameters, characteristic of flocs, and bacterial species dynamics in activated sludge system, and advanced the understanding of realistic biological treatment process.