Estrogen Mineralization by a Modular Plug Flow Photocatalytic Reactor

Estrogens are currently on the watch list of contaminants of emerging concern in the aquatic environment due to their strong impact on it. Ethinyl estradiol is one of the estrogens often found in contraceptive pills, and it can easily reach water bodies mainly through insufficiently treated wastewater. Photocatalysis is one of the solutions that ensure the complete mineralization of refractory organic compounds in wastewater treatment. Therefore, this work deals with the nonlinear modeling of the photocatalytic mineralization kinetics of ethyl estradiol in aqueous solutions. A modular photocatalytic reactor operated in a plug flow system under UV-A radiation was used. The TiO₂/ZnO photocatalyst is deposited on an inert glass support arranged inside the reactor in the form of rows of glass balls. This type of photocatalytic reactor ensures the rapid mineralization of both the initial organic substrate and the formed organic intermediates. The obtained results indicated that the nonlinear modeling of the mineralization kinetics of both the initial organic substrate and the formed organic intermediates fit the experimental data well. On the contrary, the classical Langmuir-Hinshelwood kinetic model does not fit the experimental data regarding the mineralization of the organic intermediates formed, most likely due to an underestimation of the adsorption equilibrium constant of the initial organic substrate, which competes with the organic intermediates for the active centers of the photocatalyst.