Degradation of iopromide by combined UV irradiation and peroxydisulfate

The aqueous degradation of iopromide, an iodinated X-ray contrast media (ICM) compound, by the combination of UV254irradiation and potassium peroxydisulfate (K2S2O8) has been studied in laboratory scale experiments. The influence of various parameters on the performance of the treatment process has been considered, namely the UV irradiation light intensity, the initial concentrations of iopromide and peroxydisulfate, and the initial solution pH. Iopromide degradation increased with UV light intensity and peroxydisulfate concentration, but decreased with initial pH. Under specific conditions complete removal of iopromide was achieved within 30min, and near-complete mineralisation (loss of solution TOC) within 80min. Degradation was believed to be caused by a combination of direct photolysis, sulphate radical attack, and, to a minor degree, direct oxidation by peroxydisulfate. Approximate values for the reaction rate constants have been determined and found to be equal to 1-2×104M-1s-1for sulfate radicals, and 1-2M-2s-1for S2O82-. Overall compound degradation was observed to follow first-order kinetics where the rate constant decreased with initial solution pH. During the reaction, the solution pH decreased as a consequence of sulfate radical scavenging.