The treatability of a commercial naphthalene sulphonic acid being frequently used in the textile preparation and dyeing industry, via titanium dioxide-mediated heterogeneous photocatalysis (TiO2/UV-A at pH's 3 and 7), Fenton (Fe2+/H2O2 at pH 3) and Photo-Fenton processes (Fe2+/H2O2/UV-A at pH 3) was investigated and compared with ferrous sulphate coagulation experiments (pH 7.5-8.3). Treatment performance of the studied advanced oxidation processes were compared in terms of chemical oxygen demand (COD) and total organic carbon (TOC) removal efficiencies. No significant treatment efficiency could be obtained via applying TiO2/ UV-A process, whereas both Fenton and Photo-Fenton processes resulted in appreciable COD and TOC removals. Increasing the ferrous ion concentration from 1 mM to 10 mM thereby keeping the initial H2O2 concentration constant at 20 mM accelerated the Fenton treatment performance considerably. In the presence of UV-A irradiation (I-o=2.8x 10(-5) Einstein/s) COD and TOC removal rates were also significantly improved. Acute toxicity tests carried out with the marine microalgae Phaeodactylum tricornutum indicated that the highest degree of detoxification of the naphthalene sulphonic acid formulation was achieved via Photo-Fenton oxidation, whereas an increase in toxicity was observed for the coagulated samples.