Adsorptive ozonation using high silica zeolite adsorbents and its application for drinking water treatment.

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The adsorption properties of water-dissolved ozone on high silica zeolites were investigated. Adsorbed ozone was desorbed almost reversibly. The adsorption equilibrium relations were described by a linear expression written as q = βC, where q is the amount adsorbed, C is the equilibrium concentration and b is the equilibrium constant. Also, the β values were strongly dependent on the SiO_2/Al_2O_3 ratio (mol/mol) and on the pore structure of the high silica zeolites. The larger the SiO_2/Al_2O_3 ratio, the larger the value of b. ZSM-5 (SiO_2/Al_2O_3 ratio : 3000), which gave the highest adsorption capacity of water-dissolved ozone, was able to highly concentrate water-dissolved ozone on the adsorbent. The decomposition behavior of adsorbed ozone was also investigated. Ozone adsorbed on high silica zeolite was observed to be a little more stable than ozone existing in bulk water. The decomposition rate was independent of SiO_2/Al_2O_3 ratios in the range of 30-3000 or a solution pH in t … More he range of 4-6.On the basis of the upper mentioned results, we developed a novel ozonation process for water treatment using high silica zeolites as an adsorptive concentrator of water-dissolved ozone and organic pollutants, resulting in a significant increase in reaction rate. In experiments involving trichloroethene (TCE) decomposition using a tubular flow reactor, TCE decomposition was much greater in the presence of ZSM-5 (SiO_2/Al_2O_3 ratio=3000) than in its absence, possibly due to the high concentrations of ozone and TCE inside the adsorbent. The TCE conversion obtained in our experiments was found to reach its theoretically maximum limit.Furthermore, the applicability of the process on drinking water treatment was also investigated. The effectiveness of the process using USY (SiO_2/Al_2O_3 ratio=70) for 2-methylisoborneol (MIB) decomposition with preventing bromate formation was clarified. This decomposition ability was also demonstrated in natural water containing natural organic matter (NOM). Less