Removal of organic impurities in an aqueous solution using UV irradiation produced from high and low pressure Hg lamps

Organic impurities such as ethanol, methanol, acetonitrile, and acetone contained in a used cyclotron target water should be removed so it can be used as a target again. In this investigation, removal efficiency of the organic impurities contained in an aqueous solution using UV irradiation induced oxidation was evaluated under various experimental situations. A low pressure Hg lamp (L-lamp) with the UV emission of 185 and 254 nm and a high pressure Hg lamp (H-lamp) with the UV emission of 254 nm were used to irradiate the water mixed with the organic substances. A quartz UV absorption flow cell was situated closely to the UV lamp in the reactor maximizing the UV absorption dose in the medium. For most cases, the decomposition of acetone was the fastest while acetonitrile was decomposed the slowest. To determine the effects of the wavelength, the UV absorption dose, and the catalytic reaction on decomposition of the organics, generation of the intermediate species and the degrees of organic decompositions were observed by various spectroscopic means including gas chromatography (GC), Fourier transform infrared (FTIR), and UV-vis spectrometers depending on the experimental schemes. With the aid of the catalytic reaction of dissolved oxygen (DO) in the medium, the organics and the other intermediate byproducts such as acids, acetone, and acetaldehyde, etc. produced from the L-lamp UV irradiation were removed faster by about 3-fold when compared to the irradiation without the catalytic reaction of DO. For H-lamp irradiation, however, organic removal was very slow and intermediate acids were not removed efficiently even with DO. Overall decomposition efficiency of the UV irradiated organics under L-lamp UV irradiation with the aid of DO, as a result, was much higher than that with H-lamp UV irradiation.