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5538300 
Journal Article 
[Optimal conditions for applying an ozone-hydrogen peroxide oxidizing system] 
Paillard, H; Brunet, R; Dore, M 
1988 
1 
Water Research
ISSN: 0043-1354
EISSN: 1879-2448 
Elsevier 
22 
1 
91-103 
French 
Among the oxidation treatments used in potable water production, none allows significant removal of organic matter of natural and human origin under acceptable economic conditions. Ozone, having the highest normal oxido-reduction potential of all, shows only minor Total Organic Carbon removal. It has no effect on saturated chlorinated solvents found at abnormally high levels in some natural waters before and even after a classic treatment of purification.

With an oxidation treatment, the only way to obtain high removal of ozone refractory compounds is to generate very highly reactive but poorly selective radical species like the hydroxyl radical (Hoigné, 1979). On means to produce those radicals in the aqueous phase is to combine two oxidants (Prengle, 1977; Nakayama, 1979; Hango, 1981). This work deals with the ozone-hydrogen peroxide (O3/H2O2) system.

Initially, the optimal conditions for applying the O3/H2O2 system were sought using oxalic acid. The effect of the pH, the H2O2 concentration, the concentration and the nature of the organic compound, the radical traps (HCO3) and the mode of injection of the H2O2 on the oxidation velocities and yields are highlighted. In a closed reactor with oxalic acid and 1,1,2 trichloroethane the oxidation velocity is faster with a pH of 7.5 (Figs 4 and 5), an initial H2O2 concentration of 0.6-0.7·10−4 M (Figs 8 and 9) and a consumption of 0.5 mol H2O2 mol−1 of ozone introduced. In an open reactor, optimal conditions with oxalic acid are obtained when the H2O2 is injected by impulse at a rate of 0.6-0.7·10−4M so that 0.5 mol H2O2 are consumed per mol of O3 injected (Figs 11 and 12). The bicarbonates (Fig. 10) cause a sharp drop in the yield and velocity of the oxidation of the oxalic acid and the trichloroethane.

Secondly, the O3/H2O2 system is next applied to oxidizing other organochlorinated compounds that are refractory to ozonation, in the same optimal conditions as defined above. It leads to the degradation of the pentachloroethane (Fig. 14) but does not oxidize the carbon tetrachloride (Fig. 15) and hexachloroethane.

The type of organic compound to be oxidized, its concentration and the concentration of inhibiting mineral compounds (bicarbonates) do not seem to modify the above defined optimal conditions but do influence the yield and the oxidation velocity of the system.

The results are discussed using a reaction scheme (Fig. 16) draw up in accordance with the data gathered from the bibliography. The radical mechanism leading to the degradation of organo-chlorinated compounds cannot be initiated by the cleavage of the CCl bond. It is probable that the CH bond is the first site on which the hydroxyl radicals react and start the radical oxidation mechanism. This latter hypothesis remains to be verified.