The ultrasonic irradiation (28kHz, 60W) in pre-cavitation regimes was employed to enhance the reduction of hexavalent chromium Cr(VI) ions in aqueous media was studied using remarkably low dosages of commercial titania nanoparticles. A direct imposed irradiation sono-photo-reactor equipped with UV lamp (250W) was utilized. Design of experiments, modeling and process optimization were provided using central composite design (CCD) of response surface methodology. Accordingly, a reduced quadratic expression was developed to predict the reduction efficiency versus four influencing parameters, and analysis of variance showed the high model agreement with experimental data. Using a desirability function for the highest photoreduction of about 81 and 60% efficiency for 5 mg/L of initial Cr(VI), the optimum [TiO2], pH, temperature and time were identified to be 33.1 mg/L, 2.50, 36 °C and 120 min respectively. Photocataiytic reduction of Cr(VI) when the process is assisted with ultrasonic (US) irradiation about 96% of Cr(VI) reductes in about 80 min under the above-mentioned. These efficiencies are much higher than those obtained with only photocatalysis process. Also, reduction kinetic and electrical energy consumption of the both photocatalytic and sono-assisted photocatalytic reduction process (US/UV/TiO2) were studied under the optimized condition.
