Electrochemical degradation of carbamazepine in water by a flow-through and pilot-scale reactor with carbon felt electrodes: Parametric study under realistic operational conditions

Abstract

Carbamazepine (CBZ) is one of the most stable pharmaceutical compounds that is commonly found in the effluents of wastewater treatment plants (WWTP). In this context, this contribution presents a comprehensive analysis of the different operating parameters of a flow-through and pilot-scale cylindrical reactor for hydrogen peroxide (H2O2) generation, in which the degradation of CBZ takes place. The electrochemical system was evaluated using 8 L of electrolytes prepared with tap water in the presence of methanol as dissolved organic matter or spiked tertiary WWTP effluent, at a volumetric flow of 7 L min−1. This reactor (i) improves the mass transport due to its flow-through configuration using fibrous quasi-three-dimensional carbon felt electrodes, (ii) operates without an external oxygen supply to promote the H2O2 electrosynthesis because it is incorporated by a jet aerator (iii) achieves the Fenton reaction at circumneutral pH due to Fe(II) disposition from a cation exchange resin. At first, the carbonaceous materials were electrochemically characterized by cyclic voltammetry measurements. Different operating parameters were evaluated by factorial design methodologies for H2O2 generation, energetic consumption and CBZ removal. The application of a current density of 1.4 mA cm−2, in a cathode-anode-cathode arrangement immersed in a 120 mM ionic strength solution, allowed to obtain up to 6.4 mg H2O2 L−1 after 40 min, consuming 0.44 kWh m−3. Later, the Fenton reaction was validated by a florescence study, and by the incorporation of 0.75 g of granular activated carbon and 5 g of Fe(II) loaded resin, CBZ abatement yields of 68 % and 32 % were obtained using a synthetic solution and a spiked tertiary WWTP effluent, respectively, and up to 28 % of the dissolved total organic carbon was removed. Finally, an analysis of the stability of the carbon felt electrodes was tackled using scanning electron microscopy and energy-dispersive X-ray spectroscopy.