This study explored the potential use of a sulfate radical (SO4 center dot-)-based photochemical oxidation process to treat the commercial nonionic surfactant octylphenol polyethoxylate (OPPE) Triton (TM) X-45. For this purpose, the effect of initial S2O82-(0-5.0 mM) and OPPE (10-100 mg/L) concentrations on OPPE and its organic carbon content (TOC) removal were investigated at an initial reaction pH of 6.5. Results indicated that very fast OPPE degradation (100%) accompanied with high TOC abatement rates (90%) could be achieved for 10 and 20 mg/L aqueous OPPE at elevated S2O82- concentrations (>= 2.5 mM). S2O82-/UV-C treatment was still capable of complete OPPE removal up to an initial concentration of 40 mg/L in the presence of 2.5 mM S2O82-. On the other hand, TOC removal efficiencies dropped down to only 40% under the same reaction conditions. S2O82-/UV-C oxidation of OPPE was also compared with the relatively well-known and established H2O2/UV-C oxidation process. Treatment results showed that the performance of S2O82-/UV-C was comparable to that of H2O2/UV-C oxidation for the degradation and mineralization of OPPE. In order to elucidate the relative reactivity and selectivity of SO4 center dot- and HO center dot, bimolecular reaction rate coefficients of OPPE with SO4 center dot- and HO center dot were determined by employing competition kinetics with aqueous phenol (47 mu M) selected as the reference compound. The pseudo-first-order abatement rate coefficient obtained for OPPE during S2O82-/UV-C oxidation (0.044 min(-1)) was found to be significantly lower than that calculated for phenol (0.397 min(-1)). In the case of H2O2/UV-C oxidation however, similar pseudo-first-order abatement rate coefficients were obtained for both OPPE (0.087 min(-1)) and phenol (0.140 min(-1)). From the kinetic study, second-order reaction rate coefficients for OPPE with SO4 center dot- and HO center dot were determined as 9.8 x 108 M-1 s(-1) and 4.1 x 109 M-1 s(-1), respectively. The kinetic study also revealed that the selectivity of SO4 center dot- was found to be significantly higher than that of HO center dot.