MODELING THE COMPETITION BETWEEN FILAMENTS AND FLOC FORMERS: INTEGRATING DECAY RATE, STORAGE, KINETIC SELECTION, AND FILAMENTOUS BACKBONE THEORY

Filamentous bulking in activated sludge systems occurs when filamentous organisms outgrow floc-forming bacteria, and interfere with sludge settling. The kinetic selection and filamentous backbone theories have been used in previous research to predict the outcome of competition between filaments and floc formers. We hypothesize that differences in decay rates and storage abilities also affect this competition. This paper attempts to integrate these four factors into a unified model to predict and explain coexistence in a Completely Mixed Reactor (CMR). The modeling results were shown to generically predict coexistence of the two types of microorganisms, and sensitivity analysis was performed at a specific dilution rate to identify the main parameters that significantly impact the simulation results. Monte-Carlo simulation was performed to assess the potential for bulking in the reactor. The ranges of dilution rates wherein one group outcompeted the other were delineated. This analysis showed that the effect of storage was high at low dilution rates, while the decay effect became significant at high dilution rates.