MTBE oxidation by conventional ozonation and the combination ozone/hydrogen peroxide: Efficiency of the processes and bromate formation
The present study investigates the oxidation of methyl tert- butyl ether (MTBE) by conventional ozonation and the advanced oxidation process (AOP) ozone/hydrogen peroxide under drinking water treatment conditions. The major degradation products identified were tert-butyl formate (TBF), tert-butyl alcohol (TBA), 2-methoxy-2-methyl propionaldehyde (MMP), acetone (AC), methyl acetate (MA), hydroxyisobutyraldehyde (HiBA), and formaldehyde (FA). The rate constants of the reaction of ozone and OH radicals with MTBE were found to be 0.14 and 1.9 x 10(9) M-1 s(-1), respectively. The rate constants for the same oxidation processes were also measured fort he degradation products TBF, MMP, MA, and HiBA (k(O3-TBF) = 0.78 M-1 S-1; k(OH-TBF) = 7.0 x 10(8) M-1 s(-1); k(O3-MMP) = 5 M-1 s(-1); k(OH-MMP) = 3 x 10(9) M-1 s(-1), k(O3-MA) = 0.09 M-1 s(-1), k(O3- HiBA) = 5 M-1 s(-1); k(OH-HiBA) = 3 x 10(9) M-1 s(-1)). Since all compounds reacted slowly with molecular ozone only the degradation pathway of MTBE with OH radicals as been determined, including the formation of primary degradation products. In experiments performed with several natural waters, the efficiency of MTBE elimination and the formation of bromate as disinfection byproduct have been measured. With a bromide level of 50 mug/L, only 35-50% of MTBE could be eliminated by the AOP O-3/ H2O2 without exceeding the current drinking water standard of bromate (10 mug/L). The transient concentrations of MTBE and its primary degradation products were modeled using a combination of kinetic parameters (degradation product distribution and rate constants) together with the ozone and OH radical concentration and were in good agreement with the experimental results.
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