<p>Plum pits represent an abundant agricultural food by-product that remains largely unexploited despite their disposal costs and environmental burden. In this work, plum pit biochar was valorised as feedstock for biochar production via slow pyrolysis at temperatures of 300–800 °C. The resulting biochar samples (B-300, B-400, B-500, B-600, B-700, and B-800) were comprehensively characterized and evaluated for the adsorption parameters of methylene blue (MB) and Pb²⁺. Adsorption efficiency strongly depended on pyrolysis temperature, with the maximum removal efficiencies of MB (72.5%±9.5%) and Pb²⁺ (84.9%±8.4%) achieved by B-700 and B-800, respectively. Principal component analysis (PCA) identified the surface area, carbon-to-oxygen (C:O) ratio, and aromaticity of structure as key factors, while energy normalization highlighted 600 °C as the most sustainable pyrolysis temperature, balancing performance, yield, and energy input. Importantly, tests of the adsorption efficiency of pharmaceuticals in real wastewater effluent demonstrated the practical feasibility of the developed biochar. This study provides a detailed analysis of material properties, adsorption performance, and pollutant-removal mechanisms, alongside an evaluation of energy costs relative to removal efficiency, offering insight into the potential of plum-pit-derived biochar for wastewater treatment and sustainable waste management within a circular-economy framework.</p> Graphical abstract <p></p>