Eco-approach for pharmaceutical removal: Thermochemical waste valorisation, biochar adsorption and electro-assisted regeneration

In the present research, an eco-approach for the removal of pharmaceuticals from aqueous environment was developed under de principles of circular economy. Therefore, an eco-friendly adsorbent, biochar, was synthesized by the thermochemical valorisation of rice production waste. The rice bran was pyrolyzed at different temperatures (300-750 degrees C) and a thermal post-treatment was evaluated with the aim to investigate its impact on characteristics and chemical composition of biochars. The obtained biochars were assayed for the removal of a model target pollutant, fluoxetine (FLX), and the biochar adsorption process was characterized in detail. The biochar obtained after the pyrolysis process at 500 degrees C and autoclave post-treatment (BC500A) achieved the highest pollutant removal (92.6%). The pseudo-2nd order kinetic and Freundlich isotherm described well the process, and the primary adsorption mechanism was explained by electrostatic attractions. After that, the regeneration of this eco-friendly adsorbent was evaluated by an innovative electro-Fenton-like process using peroxymonosulfate (PMS) as oxidant agent. To our knowledge, this is the first attempt to regenerate biochar using this combined technology. The optimization of operational variables such as current intensity, PMS/FLX ratio, electrode material, and addition of enhancing agents (Fe and citric acid) were evaluated. The regeneration of spent biochar was effectively accomplished under the optimal conditions (150 mA, 75/1 PMS/FLX, and 0.15 mM citric acid). No external addition of Fe was necessary because the metal content on biochar was enough for the reaction to take place. Finally, 5 cycles of adsorption-regeneration were performed demonstrating the viability of the developed system. Accordingly, the proposed approach fits with the principles of circular economy, because the global removal of pollutant and valorisation of wastes were achieved. (C) 2021 The Author(s). Published by Elsevier Ltd.