From the design to the development of a continuous fixed bed photoreactor for photocatalytic degradation of organic pollutants in wastewater

Abstract

For industrial applications of photocatalytic processes aimed to the removal of pollutants from wastewater, a good solution for a final scale-up would be the choice of a continuous catalytic fixed bed photoreactor, able to work both with artificial light and with solar light. The optimal design needs a deep study starting from fluid dynamic considerations, together with the evaluation of the light׳s distribution inside the reactor core. In this work, flat plate geometry was chosen and a structured bed photoreactor for wastewater treatment was designed and implemented starting from an optimized N-doped TiO2 photocatalyst immobilized on glass spheres. The fluid dynamic study of the structured bed reactor was intensely carried out through a CFD model. Instead of the traditional LVRPA, the Helmholtz equation, set with the Dirichlet conditions on the boundary, was used to model the light distribution inside the photoreactor. Based on the results of the modeling optimization, a laboratory scale photoreactor was developed. In order to obtain kinetic parameters, photocatalytic tests were carried out using a model pollutant. The Langmuir–Hinshelwood kinetic model was applied for estimating the kinetic parameters of the catalyst, starting from experimental data collected at different inlet pollutant concentrations. The kinetic expression together with the photons׳ spatial distribution was incorporated in the mass balance to achieve the theoretical distribution of the pollutant concentration in the reactor. The model was validated comparing the experimental data obtained at different contact times. The developed mathematical modeling allows to determine the best operating conditions to optimize the irradiation and the reactor volume, being a flexible method for a further scale-up of the photoreactor. The developed flat plate structured bed photoreactor was able to operate in continuous mode.