Direct UV photolysis of pharmaceutical compounds: Determination of pH-dependent quantum yield and full-scale performance

When using municipal wastewater as a potable water source, advanced treatment is mandatory for the removal of trace organic contaminants, including pharmaceuticals. UV-radiation (254 nm) is frequently used in combination with hydrogen peroxide at the end of the advanced treatment train for simultaneous disinfection and degradation of trace organic contaminants. In this work, a comprehensive study on the direct UV photolysis of eleven organic compounds (including ten pharmaceuticals and N-Nitrosodimethylamine (NDMA)) was conducted at varying pH of 5-8 using a collimated beam apparatus. Molar extinction coefficient (epsilon) and quantum yield (QY) values of different ionic forms (cationic, neutral and anionic) for eleven organic compounds were estimated in the tested pH range. Furthermore, direct UV photolysis at a full-scale UV photoreactor with 30 low-pressure UV lamps was performed at pH 6.2 and 7.8 by varying water flow rates (375-2700 L min(-1)) and UV fluences (400-4000 mJ cm(-2)). A process model was developed to determine the log reduction of the test compounds. The model combines a Lagrangian fluence model in the photoreactor with a pH-dependent photochemical kinetic model that ulilized the measured molar extinction coefficient and quantum yield values. The observed log reductions matched well with the model predictions for most of the tested compounds.