Electro-Fenton degradation of a ternary pharmaceutical mixture and its application in the regeneration of spent biochar

Abstract

This study proposed an integrated valorisation system, by combining adsorption and electro-Fenton processes for fast and effective micropollutant remediation of a complex pharmaceutical mixture. The pharmaceuticals venlafaxine, fluoxetine and trazodone, commonly detected in the environment (river water and sediment), were selected in this study as target pollutants. Initially, the electro-Fenton degradation process of the ternary mixture was optimised. For this, a Box-Behnken experimental design was used and the degradation of each pollutant, as a response function, was evaluated using three key operational process parameters (iron concentration, current intensity and solution pH). The pharmaceutical mixture was removed by total adsorption onto the biochar, the regeneration of which was then carried out under the optimal electro-Fenton conditions (0.24 mA, 0.33 mM Fe2+ and pH 3.2). In addition, different options in relation to the presence of iron were considered: i) iron dissolved in aqueous solution; ii) iron supported on the biochar; iii) no addition of iron (“self-cleaning”). The results confirmed that the natural content of iron in the biochar was enough to catalyse the electro-Fenton regeneration. The adsorption-electro-Fenton regeneration process was repeated over several cycles with no reduction in the efficiency of either process. Finally, this combination (adsorption and electro-Fenton process) was tested using an aqueous matrix from a wastewater treatment plant.