In the present study, Photo-Fenton oxidation of the commercially important K-acid (2-naphthylamine-3,6,8-trisulfonic acid) was optimized and modeled by employing response surface methodology and central composite design. The experimental design tool was used to assess the influence of treatment time (t(r)), initial COD of aqueous K-acid solutions (COD.) as well as H2O2 and Fe2+ concentrations on K-acid, COD and TOC removal efficiencies. According to the established second-order polynomial regression models, K-acid removal efficiency was affected by the process variables in the following decreasing order; t(r) > COD0 (negative impact) > Fe2+ > H2O2, while the effect on COD and TOC removals was COD. (negative impact) > H2O2 > t(r)> Fe2+. Analysis of variance indicated that the experimental design models obtained for the Photo-Fenton oxidation of aqueous K-acid and its organic carbon content (expressed as COD and TOC) were statistically significant and satisfactorily described the treatment process for the entire PhotoFenton treatment period (up to 125 min) as well as different treatment targets (partial and full oxidation) and initial COD values (150-750 mg/L). Complete K-acid removal accompanied with high COD (70-100%) and TOC (55-100%) abatements were achieved under relatively mild Photo-Fenton treatment conditions. (C) 2010 Elsevier B.V. All rights reserved.