Synthesis and use of efficient adsorbents under the principles of circular economy: Waste valorisation and electroadvanced oxidation process regeneration

Abstract The requirement of feasible adsorption-regeneration systems in the treatment of emerging pollutants such as pharmaceuticals is a social demand. In this work, the treatment of a mixture with sulfamethoxazole (SMX) and methyl paraben (MP) was performed by the preparation of biochar derived from the lime fiber waste at different conditions (320–500 °C and residence time 5–30 min). Based on the adsorption efficiency (maximum uptake of MP 54.25 mg/g and SMX 64.04 mg/g) and energy expenditure, the biochar obtained at 320 °C with a residence time of 30 min was selected as the best material. Subsequently, a deep study of this biochar adsorption process demonstrated that pseudo-second order model fitted well the adsorption kinetics of both pollutants and the Freundlich isotherm model describes the binary system equilibrium. After that, the regeneration of the adsorbent was carried out by advanced oxidation processes. Initially, Fenton process was considered and the regeneration of the adsorbent was performed in homogeneous and heterogeneous systems. The necessity of continuous addition of H2O2 led to the evaluation of other alternatives (electro-oxidation-H2O2 or electro-Fenton). The optimisation of the conditions was performed in liquid phase and operational parameters such as cathode electrode (carbon black modified electrodes), H2O2 production, intensity, pH and degradation kinetics were studied. Among them, the electro-Fenton process demonstrated to be quite successful in the removal of the pollutants and it was applied in successive cycles of adsorption-regeneration.