Novel vacuum-UV-(VUV) and UV-excimer flow-through photoreactors for waste water treatment and for wavelength-selective photochemistry

Abstract

In treatment of waste waters, the efficiency of the vacuum-UV (VUV) oxidation of organic water contaminants in excimer flow-through photoreactors at λ=172 nm without addition of supplementary oxidizing agents is demonstrated. The consecutive double irradiation of pure air-saturated water at λ=172 nm and λ=222 nm leads to the intrinsic formation of hydrogen peroxide and of ozone by 172-nm-photolysis, which is followed by their UV-photodegradation at λ=222 nm. Therefore, VUV/UV-excimer technology combines the principles of the conventional H2O2-UV and O3-UV processes within an efficient photoreactor. The bleaching of rhodamine B and of naphthol AS dyes is accompanied by TOC-elimination via photomineralization. Chloro-hydrocarbons (VOC) dissolved in water are largely photomineralized by VUV/UV-irradiation. The superiority of this novel technique over the conventional UV-oxidation is evaluated by the TOC-reduction of formaldehyde-containing industrial waste water. In molecular photochemistry, the production of previtamin D3 was optimized by wavelength-selective double irradiation of 7-dehydrocholesterol with UV-excimer lamps at λ1=259 nm and at λ2=342 nm. In conclusion, excimer technology has enormous impact on the development of advanced oxidation processes for water treatment and on industrial molecular photochemistry. © 1995 Indian Academy of Sciences.