Application of activated persulfate for removal of intermediates from antipyrine wastewater degradation refractory towards hydroxyl radical

Complete mineralisation of reaction intermediates refractory towards hydroxyl radical, generated from a previous ineffective degradation of urban wastewater containing antipyrine by HO-mediated sono-photo-Fenton reaction, has been attained using persulfate anions simultaneously activated by heat energy (thermally, ultrasound) and UV-C light. The SO₄^--based mineralisation process enables another reaction pathway generating more easy degradable derivatives. The influences of the initial concentration of persulfate, ultrasound amplitude, temperature and the reaction time in the previous HO-based previous oxidation on the mineralisation degree were studied by using a Central-Composite Experimental Design. Under optimal conditions ([S₂O₈^2-]_o = 1200 mg L^-1, temperature = 50 °C, amplitude = 10%, pH 2.8, HO-based reaction time = 25 min) practically complete degradation was achieved in approximately 120 min. The contribution of HO and SO₄^- radicals in this system was also evaluated. The presence of chloride ion in urban wastewater can benefit the oxidation of acetate by sulfate radical.Results demonstrated that this activated persulfate-based oxidation system is a potential alternative to degrade intermediate compounds, which are refractory against hydroxyl radicals, generated in Advanced Oxidation Processes used to treat wastewater containing emerging contaminants such as antipyrine.