Solar photoelectro-Fenton degradation of paracetamol using a flow plant with a Pt/air-diffusion cell coupled with a compound parabolic collector: Process optimization by response surface methodology

The degradation of 10 L of 157 mg L-1 paracetamol solutions in 0.05 M Na2SO4 has been studied by the solar photoelectro-Fenton (SPEF) method. A solar flow plant with a Pt/air-diffusion electrochemical cell and a compound parabolic collector (CPC) photoreactor was used operating under recirculation mode at a liquid flow of 180 Lh(-1) with an average UV irradiation intensity of about 32W m(-2). A central composite rotatable design coupled with response surface methodology was applied to optimize the experimental variables. Optimum SPEF treatment was achieved by applying a current of 5 A, 0.40 mM Fe2+ and pH 3.0 at 120 min of electrolysis, being reduced total organic carbon (TOC) by 75%, with an energy cost of 93 kWh kg(-1) TOC (7.0 kWh m(-3)) and a mineralization current efficiency of 71%. Initial N was partially converted into NH4+ ion. Under these optimized conditions, paracetamol decays followed a pseudo first-order kinetics. HPLC analysis of the electrolyzed solution allowed the detection of hydroquinone, p-benzoquinone, 1,2,4-trihydroxybenzene, 2,5-dihydroxy-p-benzoquinone and tetrahydroxy-p-benzoquinone. All aromatics were destroyed by the attack of (OH)-O-center dot. Maleic, fumaric, succinic, lactic, oxalic, formic and oxamic acids were identified as generated carboxylic acids, which form Fe(III) complexes that are quickly photodecarboxylated under UV irradiation of sunlight. A reaction sequence involving all the detected byproducts was proposed for the SPEF degradation of paracetamol. (C) 2011 Elsevier B.V. All rights reserved.