Pilot-scale treatment of p-Nitrophenol wastewater by microwave-enhanced Fenton oxidation process: Effects of system parameters and kinetics study

A pilot-scale microwave-Fenton (MW-Fenton) process in a continuous flow microwave irradiation system was studied by the degradation of p-Nitrophenol (p-NP) in wastewater. The results showed that the amount of hydroxyl radicals (OH) in MW-Fenton process was 2.8 times higher than that in conventional Fenton process at 7min. The maximum p-NP removal efficiency (93.2%) was measured at pH 3.3 when n_H2O2/n_p-NP was 13.9, n_H2O2/n_Fe(II) was 81.6 and the hydraulic detention time was 12min by mixing p-NP and H₂O₂ solution firstly, and then adding Fe(II) solution. The energy efficiency in the pilot-scale process was estimated to be 75.5%, superior to our previous lab-scale treatment result (less than 70%). The process obeyed the pseudo first-order kinetics by assuming a constant concentration of OH·. The apparent activation energy of p-NP degradation, calculated by Arrhenius equation, was 44.89kJmol^-1. The range of intrinsic reaction rate constants of p-NP degradation under optimal conditions in the continuous flow MW irradiation system was from 1.09×10⁸Lmol^-1s^-1 to 2.63×10⁸Lmol^-1s^-1. The pilot-scale study prompts the potential industrial application of MW-Fenton oxidation process in rapid and effective removal of refractory toxic organic pollutants from wastewater.