Numerical simulation of chlorine disinfection processes in non-ideal reactors

The efficacy of disinfection processes in water purification systems is governed by several key factors including reactor hydraulics, disinfectant chemistry and microbial inactivation kinetics. The objective of this work was to develop a computational fluid dynamics (CFD) model to predict flow structure, mass transport, chlorine decay and microbial inactivation in a continuous flow reactor. The significance of this dissertation is that comprehensive 3D numerical model was developed to address all major components of the chlorine disinfection process in continuous flow systems (flow structure, mass transport, chlorine decay, microbial inactivation). Prior models have only predicted chlorine contactor flow structure and residence time distribution (Stambolieva et al., 1993; Hannoun and Boulos, 1997; Crozes et al., 1997; Wang and Falconer, 1998). Furthermore, the present model incorporates experimentally measured chlorine decay and non-linear microbial inactivation kinetics. The 3D, Eulerian-Eulerian model was implemented with a general-purpose commercial code (CFX4, AEA Technology) and executed on a personal computer (Windows® NT platform). Numerical predictions for tracer transport, chlorine decay and microbial inactivation correlated well with experimental measurements of Haas et al. (1995). The experimental program of Haas et al. investigated the kinetics of the chlorine disinfection process in a continuous flow pilot reactor for varying source waters, chlorine doses (free and combined) and microorganisms (E. coli, MS2 bacteriophage and Giardia muris. The CFD model yielded more accurate predictions of inactivation efficacy than the Integrated Disinfection Design Framework (IDDF) protocol (Bellamy et al., 1998) for the experimental data set. The numerical model demonstrates that inlet configurations can significantly affect reactor hydrodynamics, and that both mixing and kinetics affect disinfection efficiency. As such, both factors should be considered in reactor design for disinfection processes. The IDDF protocol relies on the assumption of complete segregation in real reactors and thus does not consider mixing effects. This assumption may lead to over- or under-estimation of disinfection efficiencies. The Eulerian-Eulerian model of this study does not rely on an assumption of mixing state and thus yields a better prediction of microbial inactivation.Ph.D., Civil and Architectural Engineering -- Drexel University, 200