Modeling and Design of an Ultraviolet Water Disinfection System

The goal of this research is to design an ultraviolet (UV) disinfection reactor that will inactivate pathogenic microorganisms present in the wastewater generated during long-term space missions, such that complete reuse (i.e., direct potabilization) can be accomplished. This design must ensure microbial inactivation efficacy, as well as minimize volume, mass, power and maintenance requirements. The means to achieve this design goal is a numerical modelling tool developed in this research, which is based on Computational Fluid Dynamics (CFD), UV radiation intensity field models and microbial inactivation kinetics. The inputs to this numerical model are the desired reactor size and geometry, the inlet velocity and boundary conditions, the UV lamp output power and radiation intensity profile as well as the characteristics of the aqueous media. The outputs of the model are the UV dose distribution delivered to the microorganisms traversing the reactor and the degree of microbial inactivation achieved. Based on these outputs, the performance of the UV reactor can be assessed for the entire range of practical operating conditions. The validity of the numerical model was assessed with biodosimetry experiments employing Bacillus subtilis spores as the target microorganism and a commercially available UV disinfection reactor. The numerical model is used to investigate alternative UV reactor geometries which can be incorporated into an Advanced Life Support (ALS) water purification system for long-term space missions. The simulation input flow rate is based on the daily water output from six crewmembers and the biomass production chamber, which is included in the ALS closed-loop water system. UV reactor designs are evaluated based on dual criteria: process efficiency expressed as the degree of achieved microbial inactivation, as predicted by the numerical model, and Equivalent System Mass (ESM) values