pH-tuneable simultaneous and selective dye wastewater remediation with digestate-derived biochar: adsorption behaviour, mechanistic insights and potential application

The use of biochar for organic pollutants adsorption has emerged as a key component in wastewater remediation research. In this study, biochar prepared from digestate was subjected to nitric acid functionalization to enhance its adsorption capacity for organic dye mixtures of methylene blue and methyl red in synthetic wastewater. Based on experimental evidence, modified biochar BC750_NM, with a micro-mesoporous structure and a specific surface area of ∼454.15 m²/g had the best adsorption performance at optimum conditions. This adsorbent exhibited both selective and simultaneous dye adsorption upon pH control, mainly attributable to a multi-interaction process in the medium. Notably, the adsorption of both methylene blue and methyl red approached 90% under acidic pH, while methylene blue was preferentially adsorbed over methyl red at alkaline pH to attain an excellent adsorption rate of 100% for methylene blue. Our approach not only yields a valuable resource for mitigating water pollution but also offers a sustainable solution for digestate management, showcasing the potential for innovative techniques to produce synergistic environmental solutions.