Response surface methodological approach for the assessment of the photocatalytic degradation of NOM

In this paper, statistics-based experimental design with response surface methodology (RSM) was employed to investigate the effects of operational conditions on the photocatalytic oxidation of humic acid as a model compound of natural organic matter. Considering the vast number of the obtained experimental data, in this study, a correlative approach was employed for the assessment of the photocatalytic degradation efficiency of humic acids (HA) using an empirical method for the optimization of the key parameters such as photocatalyst dose, pH and humic acid concentration. The results of this study revealed that the regression analysis showed a close fit (R2 > 0.83) between the experimental results and the model predictions. Maximum DOC removal was achieved as 89.3% under the experimental conditions of 30 mg/L humic acid, 2.0 mg/mLTiO2 and pH = 7. Under acidic conditions (pH = 5), and in the presence of 1.0 mg/mLTiO2 almost complete removal of UV absorbing centers were attained for 30 mg/L humic acid. Exhaustive decolorization was attained under alkaline conditions (pH = 8), for the photocatalyst loading of 1.5 mg/mLTiO2 for 18.5 mg/L humic acid. The role of the irradiation period on the removal efficiency of the specified parameters were expressed by the relation between the predicted values attained for irradiation periods (40 min and 60 min) that were presented by the correlation coefficients as R2 = 0.847, 0.691 and 0.700 for DOC, UV254 and Color436 respectively. Moreover, model verification was also reported for a selected humic acid substrate and a specified photocatalyst specimen.

► An application of RSM methodology on the photocatalytic oxidation of humic acid.
► Comparative evaluation of the model predictions with respect to the observed results.
► The reaction period significantly governs the removal efficiency of humic acid.
► UV254 parameter could be successfully employed for the elucidation of the HA removal.