Operation of a photoelectrolyser fitted with a semitransparent semiconducting WO3 film photoanode is described. Due to its band-gap energy of 2.5 eV, the photoresponse of the WO3 electrode extends into the blue part of the visible spectrum up to 500 nm. The WO3 photoanode exhibits particularly high incident photon-to-current efficiencies for the oxidation of several organic species with the maximum occurring at ca. 400 nm. Experiments conducted under simulated AM 1.5 solar illumination demonstrated efficient photodegradation of a variety of organic chemicals including small organic molecules as well as EDTA and anthraquinonic Acid Blue 80 dye. Although, due to the inherent mass transport limitations, the described device appears best suited to the treatment of industrial wastewater containing from 100 ppm to few g L−1 of impurities, almost complete removal of organic carbon was observed in several photoelectrolysis runs. This is apparently associated with the concomitant photooxidation of sulphate-based supporting electrolyte resulting in the formation of a powerful chemical oxidant-persulphate.