Dynamic behavior of hydroxyl radical in sono-photo-Fenton mineralization of synthetic municipal wastewater effluent containing antipyrine

The aim of this study was to examine the kinetics of the different mechanisms (radical pathway, photolysis, molecular reaction with H₂O₂ and reaction with ultrasonically generated oxidative species) involved in the homogeneous sono-photoFenton (US/UV/H₂O₂/Fe) mineralization of antipyrine present in a synthetic municipal wastewater effluent (ASMWE). The dynamic behavior of hydroxyl (HO^[rad]) radical generation and consumption in mineralization reaction under different systems was investigated by measuring hydroxyl radical concentration during the reaction. The overall mineralization process was optimized using a Central-Composite Experimental Design (CCED) with four variables (initial concentrations of H₂O₂ and Fe(II), amplitude and pulse length). The response functions (pseudo-first order mineralization kinetic rate constants) were fitted using neural networks (NNs). Under the optimal conditions ([H₂O₂]_o= 500 mg L⁻¹, [Fe(II)]_o= 27 mg L⁻¹, Amplitude (%) = 20 and Pulse length = 1), the TOC removal was 79% in 50 min. The radical reaction in the bulk solution was found be the primary mineralization pathway (94.8%), followed by photolysis (3.65%), direct reaction with H₂O₂ (0.86%), and reaction by ultrasonically generated oxidative species (0.64%). The role of the Fe catalyst on the radical reaction and the presence of refractory intermediates towards hydroxyl radical were also studied.