Bubble-less photocatalytic ozonation with ceramic membranes and static mixers enhances the total organic carbon removal and degradation of iodinated X-ray contrast agents

Abstract

Conventional bubble-based ozonation of wastewater creates several issues, e.g., the low degradation of certain micropollutants like X-ray contrast agents, mass transfer limitations due to inhomogeneous mixing, and the waste of undissolved ozone. In contrast, this work uses tubular ceramic membranes for bubble-free and bubble-less ozonation. Static mixers are placed around the membrane to enhance the radial mixing of ozone, creating homogeneous reaction conditions throughout the membrane contactor. Additionally, the ozone mass transfer significantly increases with static mixers. Furthermore, the membrane is made of a photocatalyst (TiO2) on the shell-side to improve the micropollutant degradation by photocatalytic ozonation. An ozone-stable hydrophobic treatment method is developed to use ceramic membranes as a membrane contactor for the ozonation of water. After hydrophobic treatment, the ozone mass transfer coefficient is in the order of 1.3 ⋅ 10−6 ms−1 using bubble-less operation resulting in an ozone concentration up to 4.0 mg L−1. Overall, bubble-less operation significantly increases the ozone mass transfer compared to bubble-free operation. Photocatalytic ozonation in a membrane contactor with static mixers increases the degradation of diatrizoate by 37% compared to sole ozonation in the same membrane contactor. Furthermore, this process increases the removal of total organic carbon in experiments with a water matrix consisting of four different micropollutants by 115% compared to sole ozonation.