Abstract
The ultraviolet photochemical degradation process is widely recognized as a low-cost, environmentally friendly, and sustainable technology for water treatment. This study integrated computational fluid dynamics (CFD) and a photoreactive kinetic model to investigate the effects of flow characteristics on the contaminant degradation performance of a rotating annular photoreactor with a vacuum-UV (VUV)/UV process performed in continuous flow mode. The results demonstrated that the introduced fluid remained in intensive rotational movement inside the reactor for a wide range of inflow rates, and the rotational movement was enhanced with increasing influent speed within the studied velocity range. The CFD modeling results were consistent with the experimental abatement of methylene blue (MB), although the model slightly overestimated MB degradation because it did not fully account for the consumption of OH radicals from byproducts generated in the MB decomposition processes. The OH radical generation and contaminant degradation efficiency of the VUV/UV process showed strong correlation with the mixing level in a photoreactor, which confirmed the promising potential of the developed rotating annular VUV reactor in water treatment.
Highlights
Use of ultraviolet-based photoreactors in water-treatment processes is rapidly increasing, and ultraviolet-based advanced oxidation processes (UV AOPs) have been studied for over 30 years
This work aimed to develop a comprehensive computational fluid dynamics (CFD) simulation tool able to make an in-depth analysis of the VUV/UV process applied to water treatment
The results from this study revealed crucial hydrodynamic characteristics in the VUV/UV photoreactor, and provide useful suggestions for the design and optimization of VUV/UV photoreactors, promoting the practical application of VUV/UV techniques in the water-treatment field
Summary
Use of ultraviolet-based photoreactors in water-treatment processes is rapidly increasing, and ultraviolet-based advanced oxidation processes (UV AOPs) have been studied for over 30 years. The H2 O2 /UV process presents increased economic cost and technical complexity due to the treatment of residual peroxide, leading to its application only in small and medium-sized water treatment facilities. The VUV/UV process uses ozone-generating mercury lamps that emit 185 nm VUV and 254 nm UV radiation, in which the 185 nm radiation reacts with water to produce hydroxyl radicals (·OH). Plenty of experiments have yielded promising results at lab-scale, the VUV/UV AOP has not yet been implemented at a full-scale plant in water treatment. There are still problems that impede large-scale application of VUV/UV photoreactors in the water-remediation field. An effective modeling of the VUV/UV process involves the simultaneous solution of momentum equations, mass transfer equations, and radiation energy equations (UV and VUV radiations), along with a complex kinetic scheme of more than 40 reactions
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