Regeneration of Pinus patula-derived biochar employed in crystal violet removal in water

Biochar (BC) is a promising adsorbing material used to eliminate different contaminants from water, including dyes. However, the applicability and cost-effectiveness of this adsorbent also depend on its regeneration capacity. Several approaches to BC regeneration are known, each yielding variable efficiencies, risks of generating secondary pollution, difficulties of application, and contrasting cost/benefit ratios. Chemical regeneration is one of the adsorbent regeneration techniques yielding the best results in contaminant desorption from the BC surface. The present study evaluated the regeneration of Pinus patula pellet-derived BC employed in Crystal Violet (CV) adsorption from water using several acids, bases, and solvents. The tested desorption agents included solutions of hydrochloric acid (HCl) 0.1 M, acetic acid (CH3COOH) 1 M, 75 % ethanol (C2H6O), and two 95:5 mixtures of ethanol (75 % and 96 %) and concentrated acetic acid. The 95:5 mixture of 96 % ethanol-concentrated acetic acid was the best-performing solvent with a desorption efficiency of 21.1 %. Therefore, it was chosen as the desorption agent and used for six consecutive adsorption-desorption cycles. After these cycles, the BC removal efficiency decreased up to 54.4 %. This work revealed that the BC used has a good regeneration capacity, which could reduce the costs of implementing water decontamination process having a positive impact on sustainable development by aligning with circular bioeconomy principles.