Iodized X-ray contrast media (XRC) for medical applications are responsible for the high concentration of AOX (halogenated organic compounds adsorbable on activated carbon) in hospital wastewater exceeding the legal German discharge limit. The refractory properties of these substances lead to an accumulation in the natural waterbody. The elimination of contrast media from hospital wastewater by photochemical oxidation with hydrogen peroxide was investigated. The mechanism and the kinetics of the degradation of XRC were examined. These experiments demonstrate that a complete removal of the organically bonded iodine and a partial mineralization is feasible. The degradation in the UV reactor could be enhanced by adding hydrogen peroxide and by using a bubble column to remove the formed elemental iodine from the solution by stripping. Furthermore, the influence of various operating parameters such as gas flowrate, H2O2 input, XRC concentration and kind of XRC were investigated. Experiments showed that a recycling of elemental iodine from the exhaust gas is technically and economically possible.
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Sprehe et al. (2001) studied this question.