UV degradation kinetics and modeling of pharmaceutical compounds in laboratory grade and surface water via direct and indirect photolysis at 254 nm.

Direct and indirect photolysis of pharmaceutically active compounds (PhACs) was investigated in laboratory-grade water (LGW) and a local surface water using a low-pressure ultraviolet batch reactor. The PhACs selected in this study belong to different therapeutic classes and are known to occur in environmental samples. Fundamental photolysis and advanced oxidation process parameters obtained in LGW (such as the decadic molar absorption coefficient, quantum yield, and degradation rate constants) are reported and discussed. These parameters, together with the incident photon irradiance, solution depth, and solution absorbance were used to develop UV and UV/ H202 photolysis models that were compared with experimental results obtained in the surface water. The model predicted the experimental UV photolysis removals well but underestimated the UV/H2O2 photolysis results. These models were used to discuss the effects of optical path length and H2O2 concentration on the UV-based rate constant predictions.