A novel wastewater treatment technique using 8W low-pressure mercury lamps in the presence of uniform-sized microbubbles (diameter=5.79 mu m) was investigated for the decomposition of methyl orange as a model compound in aqueous solution. Photodegradation experiments were conducted with a BLB black light blue lamp (365nm), a UV-C germicidal lamp (254nm) and an ozone lamp (185nm + 254nm) both with and without oxygen microbubbles. The results show that the oxygen microbubbles accelerated the decolorization rate of methyl orange under 185 + 254 nm irradiation. In contrast, the microbubbles under 365 and 254 nm irradiation were unaffected on the decolorization of methyl orange. It was found that the pseudo-zero order decolorization reaction constant in microbubble system is 2.1 times higher than that in conventional large bubble system. Total organic carbon (TOC) reduction rate of methyl orange was greatly enhanced by oxygen microbubble under 185 + 254 mm irradiation, however, TOC reduction rate by nitrogen microbubble was much slower than that with 185 + 254 nm irradiation only. Possible reaction mechanisms for the decolorization and mineralization of methyl orange both with oxygen and nitrogen mirobubbles were proposed in this study. (C) 2008 Elsevier B.V. All rights reserved.