Computational fluid dynamics (CFD) modeling of VUV/UV photoreactors for water treatment

• CFD modeling of the VUV/UV process for water treatment applications was studied.
• Using a prototype VUV/UV reactor, the CFD model was experimentally validated.
• Significant mass transfer limitation was observed within the VUV/UV reactors.
• An experimental approach for measurement of the 185 nm lamp emission was utilized.

Vacuum-UV/UV process, an incipient catalyst/chemical-free advanced oxidation process (AOP), is potentially a cost-effective solution for the treatment of persistent micropollutants from water sources. In this study, a computational fluid dynamics (CFD) model for the simulation of VUV/UV photoreactors used for water treatment was developed and evaluated experimentally. The developed model integrated hydrodynamics, species mass transport, more than 40 reactions, along with the irradiance distribution at 185 nm VUV and 254 nm UV wavelengths within the reactor. The 185 nm VUV and 254 nm UV emissions from an ozone-generating lamp were experimentally measured and fed to the model. The evaluation showed that the proposed CFD model successfully predicted the degradation rate of a model pollutant in a prototype flow-through VUV/UV reactor. The developed model was also able to trace the main by-products of the target micropollutant resulting from 185 nm and 254 nm photolysis as well as OH oxidation. Detailed analysis of the direct-photolysis of the model contaminant at 254 nm and 185 nm vs. OH radical based degradation of the contaminant revealed the latter one as the most dominant degradation pathway. The performed analysis confirmed that degradation rates of micropollutants in the VUV/UV photoreactors are strongly limited by mass transfer in proximity of the quartz sleeve.

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