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Abstract

A new process step for purifying water from a small amount, particularly a last trace amount, of organic impurities included in total organic carbon (TOC) content is incorporated into known processes for the preparation of ultra pure water comprising one or more previous filtration steps and a series of purification steps known per se. The new step comprises irradiating the water to be treated with a light in the presence of a photocatalyst comprising an inorganic semiconductor selected from TiO.sub.2, SrTiO.sub.3 and CdS in fine particulate form and a noble metal and/or an oxide thereof selected from Pt, Pd, Ru, RuO.sub.2 and Rh deposited on said semiconductor particles for a period of time sufficient to oxidatively decompose the organic impurities, resulting in a decrease in TOC content of the water to a level lower than the minimum detection level of TOC detectors, typically <0.05 mg C/l or <0.01 mg C/l depending upon the sensitivity of particular detectors available up to date.

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First Claim