The photo-oxidative degradation of Na oxalate has been carried out in an aerated bubble column reactor. Batch (liquid phase) rate data were adequately described by a Langmuir-Hinshelwood kinetic model based,sed on a dual-site mechanism. In view of the obvious advantages of a continuous liquid flow operation on a commercial scale, experiments were conducted with co-current upward liquid and gas flows through the reactor. Whilst conversion decreased with slurry flow rate as may be expected, increased gas Bow rate, however, improved conversion. In comparison to conventional multiphase reactor, this is somewhat counterintuitive but may be explained in terms of better light-harvesting characteristics - a factor irrelevant to traditional slurry reactors - as increased gas velocity would lead to greater swirling motion and thus, longer particle residence time and/or solid recirculation, especially at low liquid flow rates which in turn permits greater UV exposure. For the present system, an optimum L:G ratio of 1 yielded a conversion of 75%.