BACKGROUND: Over the past several decades methyl tert-butyl ether (MTBE) as additive to gasoline, intended to either boost ratings of fuel or to reduce air pollution, has been accepted worldwide. Since MTBE has high water solubility, the occurrence of fuel spills or leaks from underground storage tanks or transferring pipeline has led to the contamination of natural waters. In this study the degradation of aqueous MTBE at relatively high concentrations was investigated by a UV-visible/ZnO/H2O2 photocatalytic process. The effects of important operational parameters such as pH, amount of H,0,, catalyst loading and irradiation time were also investigated. Concentration of MTBE and intermediates such as tert-butyl formate and tert-butyl alcohol were measured. RESULTS: Time required for complete degradation increased from 20 to 150min when the initial concentration was increased from 10 to 500 mg L-1. The first-order rate constants for degradation of MTBE were estimated to be 0.183-0.022 min(-1) as the concentration increased from 10 to 500mg L-1. Study of the overall mineralization monitored by total organic carbon analysis showed that at an initial concentration of 100 mg L-1 MTBE complete mineralization was obtained after 100 min under UV-visible/ZnO/H2O2 photocatalysis. CONCLUSION: The data presented in this paper clearly indicated that UV-visible/ZnO/O-2 as an advanced oxidation process provides an efficient treatment alternative for the remediation of MTBE-contaminated waters. (C) 2008 Society of Chemical Industry