Photocatalytic degradation of ciprofloxacin and metformin in a continuous-flow tubular reactor†

The use of continuous photocatalytic reactors is needed for sustainable water treatment technology. However, scalability of such units is challenging due to the appropriate (uniform) illumination over the photocatalyst surface, and hence limits its application. Uniform light intensity distribution can be achieved in tubular reactors with radial illumination, and such systems are easy to scale-up (being modular in design). We investigate the photocatalytic degradation of CIP and metformin (emerging pharmaceutical pollutants) using a continuous-flow reactor equipped with a titanium dioxide (TiO₂-coated) quartz tube. Under ultraviolet (UVC) light, the system exhibits 92% degradation efficiency for both drugs individually and 85–90% for mixtures. Total organic carbon (TOC) analysis is employed to evaluate the degree of mineralization for both drugs. After a 9 hour treatment period, ciprofloxacin exhibited up to a 50% reduction in organic carbon, while metformin showed a reduction of up to 70%. Detailed liquid chromatography-mass spectroscopy (LC-MS/MS) analysis revealed the degradation pathways, confirming the fate of the pharmaceutical pollutants.