Can reactor design-hydrodynamics interplay intensify the photocatalytic bacterial inactivation? A CFD study

초록

Implementation of scalable photocatalytic inactivation systems still remain limited due to the absence of information regarding the impact of reactor design on bacterial inactivation. To elucidate the fundamental understanding of hydrodynamics, photocatalyst dispersion, and efficiency in batch and continuous flow reactors, this work combines computational fluid dynamics (CFD) and photocatalytic inactivation of Escherichia coli (E. coli), using Fe-doped ZnO nanoparticles (Fe/ZnO NPs) as visible-light-responsive photocatalysts in batch stirred tank reactor (BSTR) and continuous flow helical tube reactor (CFHTR). The key variables that influenced the process efficiency were identified by systematically running the reactions with varying catalyst and bacterial loading, flow rate, and pH. Total inactivation of E. coli was achieved within 60 min at a low catalyst loading (25 mg/L) in CFHTR, while the BSTR required 210 min at higher catalyst loading (1000 mg/L). The role of reactive oxygen species (ROS) in inactivation which induces membrane disruption was investigated by metabolic activity analysis and electron microscopy. To relate photocatalytic stress with the regulation of resistance genes in both of the reactor modes, parallel genomic profiling of E. coli genes was conducted. The CFD analysis suggested that the synergistic impact of velocity, turbulence kinetic energy and its gradient along with eddy viscosity varies with the change in the reactor design and hence, intensify the inactivation efficiency. Furthermore, a user-friendly, menu-driven simulation tool is developed to facilitate efficient optimization and performance evaluation of the proposed system. Findings of this study may help to design and upscale photocatalytic inactivation systems for water treatment.

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