Kinetic model of photo-Fenton degradation of paracetamol in an annular reactor: main reaction intermediates and cytotoxicity studies

A kinetic model derived from a simplified reaction sequence is proposed for the photo-Fenton degradation of Paracetamol (PCT), employing an annular photoreactor. The kinetic model explicitly included the effects of radiation absorption on pollutant degradation kinetics through the evaluation of the Local Volumetric Rate of Photon Absorption (LVRPA). Irradiated experiments achieved an average PCT conversion of 99.3% at 5 min of reaction, and a maximum of 69% of mineralization. Conversely, non-irradiated experiments reached an average PCT conversion of 86.6% at 5 min of reaction, and a maximum of 35% of mineralization. Kinetic parameters (k5 = 5.82 x 109, k6 = 3.01 x 1010, k7 = 6.01 x 1010 M- 1s- 1) were estimated employing a nonlinear, multi-parameter regression method, and the validated kinetic model was used to predict temporal variations of the concentrations of HP, PCT, and the main reaction intermediates: hydroquinone (HQ) and 1,4-benzoquinone (BQ). The root mean square error (RMSE) values obtained for HP, PCT, HP, HQ and BQ were 1.16 x 10-2, 7.13 x 10-1, 3.53 x 10-3, 3.05 x 10-3 mM, respectively, showing a good agreement between experimental and predicted data. Moreover, the kinetic model was validated with a new set of experimental tests, confirming its predictive capacity. Beyond the degree of mineralization attained, additional cytotoxicity tests proved that the photo-Fenton process is effective in generating a non-toxic effluent under the operating variables investigated.