The oxidation of phenol and two substituted species (4-nitrophenol and 4-chlorophenol) has been carried out by means of the O-3, UV-ViS, O-3 + UV-vis, TiO2 + UV-Vis, O-3 + UV-vis + TiO2 and O-3 + TiO2 systems. From UV-vis experiments, the quantum yield of these organics has been calculated (0.018, 0.005 and 0.017 mol per Einstein for phenol, 4-nitrophenol and 4-chlorophenol, respectively). Broadly speaking, the addition of titania powder results in a slight inhibition of the parent compound degradation rate, although a positive effect is experienced when measuring the chemical oxygen demand (COD) and total organic carbon (TOC) removals. Amongst the technologies investigated, those combining ozone and radiation show the best efficiency in terms of phenols elimination and also COD and TOC decay rates. A simple economy analysis of the processes illustrates how the combinations O-3 + UV-vis and O-3 + UV-vis + TiO2 are the most attractive technologies, although some additional considerations have to be taken into account. (c) 2004 Elsevier B.V. All rights reserved.