OXIDATION OF HUMIC ACID BY OZONE OR CHLORINE-DIOXIDE

The electroreduction of chlorite ion in the concentration range 3 x 10('-7 )-(' )3(' )x(' )10('-4) M and in weakly acidic solutions (2 < pH < 6) was investigated. At a mercury electrode surface the reduction was found to be irreversible. The current is diffusion controlled and is a linear function of chlorite ion concentrations up to 3 x 10('-4) M, with a detection limit of 1.2 x 10('-7) M, using differential pulse polarography. The mechanism of the reduction is postulated to be a two stage process, with hypochlorous acid being involved as a stable intermediate. The rate determining step of the reduction is proposed to be: ClO(,2)('-) + H('+) + e('-) (--->) HClO(,2)('-); A sample treatment procedure is outlined which provides for the determination of chlorite ion concentrations as low as 8 (mu)g/L in potable water. The method utilizes differential pulse polarography with prior sample clean-up using Chelex 100. Blank corrections are carried out by the catalytic decomposition of chlorite ion using acetic anhydride.; A technique of comparisons based on kinetic principles allowing the evaluation of analytical methods for residual ozone measurements is described. The kinetic technique has a number of advantages over conventional comparisons, which lead to the minimization of sampling anomalies. The evaluation of analytical methods designed for use at concentration levels below that of the normal range of a standard method is conveniently handled by this technique. The technique was tested by comparing phenylarsine oxide (PAO) and inorganic arsenic(III) as direct reductants for ozone. No major differences in the behavior of these reductants toward ozone were found down to a concentration of 1 mg/L of ozone. This would imply that no significant decomposition of PAO was taking place. A method involving the measurement of iodate ion, by differential pulse polarography, formed during or after the oxidation of iodide ion by ozone is also described. It was found that the kinetic technique can be used to reliably extrapolate ozone concentrations below 1 mg/L using data obtained above 2 mg/L by the standard iodometric method. The detection limit of the iodate method in terms of ozone equivalents was found to be 3.7 (mu)g/L, with a sensitivity of 23.1 (mu)A/mg/L of ozone.; Humic acid was oxidized using either chlorine dioxide or ozone. The major reduction product of chlorine dioxide is chlorite ion. It is possible to control the amount of chlorite ion formed by using a mixture of chlorine dioxide and chlorine as the oxidant. Using a mixture of chlorine dioxide and chlorine to degrade humic acid also results in the formation of chloroform, but in lesser amounts than expected from the use of chlorine alone.; Ozone was found to be more effective in degrading humic acid than chlorine dioxide. Using ozone, the final oxidation product of humic acid is carbon dioxide. Some of the intermediate by-products are oxalic, maleic, glyoxalic acids and glyoxal. A considerable number of fatty acids are also identified to be intermediate ozonolysis products of humic acid.