The photocatalytic organic content reduction of two selected synthetic wastewater from the textile dyeing industry, by the use of heterogeneous and homogeneous photocatalytic methods under solar irradiation, has been studied at a pilot plant scale at the Plataforma Solar de Almeria. The effect of two different TiO2 modifications with oxidants such as H2O2 and Na2S2O8 on the decolourisation and the dissolved organic content reduction (DOC) of the wastewater was examined. The TiO2/H2O2 system seems to be more efficient in comparison to the synergetic action that appears when using persulphate and TiO2 in this specific wastewater. By an accumulated energy of 50 kJ l(-1) the synergetic effect of TiO2 P-25 with H2O2 and Na2S2O8 leads to a 70% and 57% DOC reduction, respectively, in the case of cotton synthetic wastewater, while the decolourisation was almost complete. The photocatalytic decolourisation, as well as the DOC reduction in the case of nylon simulated wastewater is a slower process and an accumulated energy of 50 kJ l(-1) leads to almost 54% mineralisation in both cases. The photo-Fenton process in both types of wastewater was more efficient in comparison to the TiO2/oxidant system. An accumulated energy of 50 kJ l(-1) leads to 90% reduction of the organic content. (C) 2004 Elsevier Ltd. All rights reserved.