Process and system for purifying pure water or ultrapure water

Abstract

Ultrapure water of extremely high purity, i.e. a so-called ultra-ultrapure water is formed by the present system for purifying a pure water or ultrapure water, (1) the TOC component which was contained in pipes, etc. and which was subsequently dissolved in a pure water or ultrapure water to be treated, is decomposed and the pure water or ultrapure water is simultaneously sterilized, by the combined use of an oxidizing agent and ultraviolet irradiation, (2) the DO contained in the water to be treated and the DO derived from the addition of the oxidizing agent are decomposed into H.sub.2 O and simultaneous sterilization is effected, by the combined use of H.sub.2 gas and ultraviolet irradiation, (3) the remaining H.sub.2 gas is removed by a membrane degassing unit, and (4) the resulting water is subjected to an ion exchange treatment and an ultrafiltration treatment, in the above order, whereby the pure water or ultrapure water whose purity has been reduced by, for example, the dissolution of the impurities contained in pipes can be purified and converted to an ultrapure water of extremely high purity. The resulting ultrarapure water is particularly utilized as a rinsing water in the electronics industry where ultrahigh density integrated circuits (ULSI circuits) represented by 4 megabit dynamic memory are produced.