From Waste to Resource: Evaluating Biomass Residues as Ozone-Catalyst Precursors for the Removal of Recalcitrant Water Pollutants

Five different biomass wastes—orange peel, coffee grounds, cork, almond shell, and peanut shell—were transformed into biochars (BCs) or activated carbons (ACs) to serve as adsorbents and/or ozone catalysts for the removal of recalcitrant water treatment products. Oxalic acid (OXL) was used as a model pollutant due to its known refractory character towards ozone. The obtained materials were characterized by different techniques, namely thermogravimetric analysis, specific surface area measurement by nitrogen adsorption, and elemental analysis. In adsorption experiments, BCs generally outperformed ACs, except for cork-derived materials. Orange peel BC revealed the highest adsorption capacity (Qe = 40 mg g−1), while almond shell BC showed the best cost–benefit ratio at €0.0096 per mg of OXL adsorbed. In terms of catalytic ozonation, only ACs made from cork and coffee grounds presented significant catalytic activity, achieving pollutant removal rates of 72 and 64%, respectively. Among these materials, ACs made from coffee grounds reveal the best cost/benefit ratio with €0.02 per mg of OXL degraded. Despite the cost analysis showing that these materials are not the cheapest options, other aspects rather than the price alone must be considered in the decision-making process for implementation. This study highlights the promising role of biomass wastes as precursors for efficient and eco-friendly water treatment processes, whether as adsorbents following ozone water treatment or as catalysts in the ozonation reaction itself.