Kinetics of iohexol degradation by ozonation and formation of DBPs during post-chlorination

Degradation kinetics of the widely used iodinated X-ray contrast medium, iohexol, was investigated in this study by ozone advanced oxidation process (AOP). Factors influencing iohexol degradation, pH, ozone dosage, and the presence of different background ions were also evaluated. Results show that iohexol degradation during ozonation followed the pseudo-first-order kinetics well; the degradation rate increased with the increase of pH values and reached a maximum of 1.29( +/- 0.05) x 10(-1) min(-1) at pH 9. As the ozone concentration gradually increased from 0.342 to 1.13 mg/L, the corresponding pseudo-first-order rate constant of iohexol degradation increased from 7.25 ( +/- 0.30) x 10(-3) to 5.77( +/- 0.26) x 10(-2) min(-1). At pH 7, the presence of background ions have different inhibitory effects on iohexol during ozonation degradation. Br exhibited the strongest inhibitory effect followed by HCO3- and CO32-, while Cl possessed negligible influence. Less disinfection by-products (DBPs) were formed at circumneutral pH values and low bromine concentrations (< 10 mu M), which can be beneficial for the operation of drinking water treatment plants to supply safe drinking water to the public.