Photocatalytic treatment of colored wastewater from medical laboratories: photodegradation of Nuclear Fast Red

The degradation and organic content reduction of Nuclear Fast Red (NFR, a counterstain reagent widely used in biochemical and biomedical laboratories) in aqueous solutions has been studied by heterogeneous photocatalytic oxidation under artificial irradiation. For the heterogeneous processes, the performance of different commercial titanium oxides on the degradation and the organic content reduction (DOC) of the wastewater was examined. The decomposition of the NFR follows quite well a pseudo-first kinetic order in the whole pH range, in line with the Langmuir-Hinshelwood model. The effects of catalyst concentration, of the initial solution pH and of H2O2 concentration upon the reaction rate, were also investigated. NFR degradation was accompanied by the formation of ammonium, nitrate, and sulfate ions, as they have been detected as mineralization products in the liquid phase.