Kinetics of methyl tert-butyl ether degradation and by-product formation during UV/hydrogen peroxide water treatment

Methyl tert-butyl ether (MTBE) was removed from aqueous solution by exposure to a low-pressure mercury lamp in the presence of hydrogen peroxide in a recirculating batch reactor. Dark and UV-only tests were conducted to separate the effects of MTBE loss to system components and photolytic processes. Experiments were conducted at initial peroxide:MTBE molar ratios of 4:1, 7:1 and 15:1. Benzene was added in some experiments to estimate the hydroxyl radical concentration. The concentrations of MTBE, benzene and by-products were measured over a 120-min period using a purge-and-trap GC-MS method. UV/H2O2 treatment resulted in >99.9% removal of MTBE with the major purgable by-product identified as tert-butyl formate (TBF). The second order rate constant for the degradation of MTBE from the hydroxyl radical was estimated to be 3.9 (±0.73)×109 M−1s−1. The second order rate constant for the reaction of TBF with the hydroxyl radical was estimated to be 1.2 (±0.40)×109 M−1s−1. The yield for the formation of TBF from the reaction of MTBE and the hydroxyl radical was 0.28±0.032. After 1 h of treatment the TBF remaining exceeded the remaining MTBE by as much as a factor of 35; this finding is important given the unknown human health impacts of TBF.