Parametric Optimization of Selenite and Selenate Biosorption Using Wheat Bran in Batch and Continuous Mode

The present work has successfully optimized the biosorption of selenite and selenate species using wheat bran in both batch and continuous column mode with the help of central composite design (CCD). In batch mode the parameters which were taken into account were pH, biomass dose, initial selenium concentration, and temperature, whereas in continuous mode bed height, flow rate, and initial selenium concentration were studied. A second-order polynomial regression model was used, and results showed high regression coefficients (R 2 , that is, 97.65 % for both Se(IV) and Se(VI) in batch mode and 97.95 % and 97.61 % for Se(IV) and Se(VI), respectively, in continuous mode), indicating good agreement with experimental data. Low values of standard deviations were also obtained, showing the adequacy of the proposed regression models in both batch and continuous mode. Contour plots predicted the maximum uptake of Se(IV) (49.56 µg ·g -1 ) and Se(VI) (41.37 µg ·g -1 ) at pH 2, initial selenium concentration of 1000 µg ·L -1 , temperature of 20 °C, and biomass dose of 20 g ·L -1 in batch mode, whereas it was (73.05 and 58.29) µg ·g -1 for Se(IV) and Se(VI) at a bed height of 25 cm, flow rate of 1.66 mL ·min -1 , and initial selenium concentration of 1000 µg ·L -1