Pollution mitigation systems are rapidly evolving to address societal challenges and this work uses multiphase flow theory for studying and improving the performance of novel solid/liquid and liquid/liquid separation systems. The first part focuses on large (approx. 29,400 Mt) solid-in-liquid systems used for treating wastewater coming from Combined Sewer Overflows. Use of multiphase theory is needed to study the performance and design changes to a novel system introduced in Dearborn (MI) and other locations around the USA due to the significant costs of these systems. A recently developed Combined Sewer Overflow detention system (called the Treatment Shaft system) is investigated and its performance for separation of suspended solids from water is evaluated using both Eulerian-Lagrangian and Eulerian-Eulerian multiphase flow approaches for various particle sizes and for a 10-year, 1-hour rainstorm event. In order to improve the efficiency of solid separation in the Treatment Shaft system, the impact of a flocculating agent is evaluated using a Population Balance Model coupled with a multiphase flow solver to model particle aggregations and breakups. The effect of design changes on the performance of the system is evaluated.Multiphase flow theory is used again in the second part to investigate the performance of membranes for liquid-in-liquid separation. An emphasis is put on oil-in-water emulsion separation using crossflow filtration. Various membrane configurations are first analytically studied, and new analytical solutions are introduced for estimating the flow field in such systems. In order to improve membrane efficiency, the impact of using charged membranes on oil droplet separation is then evaluated in various cylindrical membrane configurations. A significant issue in using membranes for oil/water separation is membrane fouling. To incorporate membrane fouling in a computational fluid dynamics simulation, a new model that employs a novel film model is developed and implemented in this work for the first time. The multiphase mixture model and the wall film model are coupled with a population balance model. The proposed approach is then used to model and predict the early stages of membrane fouling that account for hydrodynamic interactions. A parametric study is carried out to demonstrate the features of the model and to evaluate the impact of different parameters such as transmembrane pressure, density ratio, viscosity ratio, and contact angle on the performance of a membrane separation system. The model is also validated using experimental data and found to correlate well.
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