Rethinking Chemical Pretreatment of Waste-Derived Carbons for Pesticide Removal

Chemical pretreatment is widely used to improve waste-derived carbon adsorbents, although its added value is strongly precursor-dependent. Here, spent rabbit litter (RL) was directly carbonized or pretreated with H3PO4 (P) or NaOH (N) before carbonization at 900 °C, and the resulting materials were evaluated for chlorpyrifos (CHP) and dimethoate (DMT) removal. Directly carbonized RL developed the most favorable texture, with a specific surface area of 573 m2 g−1, compared with 419 and 109 m2 g−1 for RL-P and RL-N, respectively. Chemical pretreatment also reduced adsorption performance: Langmuir capacities of RL reached 197 mg g−1 for CHP and 116 mg g−1 for DMT, while both pretreated materials showed lower values. The RL-containing filtration system maintained approximately 87–92% CHP removal over ten regeneration cycles, and CHP removal reduced AChE inhibition from (92 ± 3)% to (3 ± 1)%. Biological assessment further indicated no significant genotoxic or cytotoxic effects of RL under the tested conditions. A preliminary sustainability assessment showed a 90.9% reduction in fresh adsorbent demand during reuse, with direct costs comparable to repeated single use. Approximately 98.3% of retained CHP was recovered during ethanol regeneration, with the recovered CHP showing retention time and PDA spectral characteristics comparable to those of the initial compound. These results show that, under the applied conditions, direct carbonization outperformed additional chemical pretreatment and provided a reusable platform with potential for pollutant recovery.