Biochar has shown large potential in water treatment because of its low cost, good textural properties, and high reusability. In this study, two porous biochars were developed from the Melia azedarach seeds via direct pyrolysis process (B-700) and through hydrothermal carbonization followed with pyrolysis (HB-700). They were characterized by morphology, structural characteristics, and surface features and used to adsorb the crystal violet (CV) dye in water environment. Results of the isotherm approaches demonstrated that the removal capacity of these biochars reached 119.4 mg/g for B-700, and 209 mg/g for HB-700 (at 45°C). Also, the Avrami model best fitted the kinetic data. The electrostatic attraction was regarded as one of the adsorptions mechanisms of CV dye. The regeneration tests reveal that both B-700 and HB-700 are good reusable adsorbents. Finally, findings of the study showed that the hydrothermal carbonization method that precede the pyrolysis process can improve significantly the adsorption capacity of the produced biochar.

This study introduces an innovative hybrid approach combining salting-out and adsorption for the highly efficient removal of crystal violet (CV) dye from aqueous solutions. The method leverages high-ionic-strength brine discharge from the Complex of El-Outaya (CEO, ENASEL, Biskra, Algeria) and micro-mesoporous biochar derived from calves’ horn cores (BHC-800). Results demonstrate that both undiluted and diluted brine significantly enhance CV removal, while BHC-800, with a surface area of 258 m² g⁻¹, exhibits a maximum Langmuir adsorption capacity of 106.1 mg g⁻¹ (at 20 °C ± 2). Thermodynamic analysis confirms a spontaneous (ΔG° < 0) and exothermic (ΔH° = −0.86 kJ mol⁻¹) process, with increased interfacial disorder (ΔS° = 93.53 J mol⁻¹ K⁻¹). The synergistic effect of salting-out and adsorption achieved ~99.8% removal of CV at an initial concentration of 1000 mg L⁻¹. Furthermore, BHC-800 exhibited excellent reusability, maintaining high adsorption efficiency over multiple cycles. Economic assessment revealed operational costs of 0.45–0.89 US$ m⁻³ for 60% brine discharge. Biochar production costs were 0.076–0.18 US$ kg⁻¹, translating to 7.5–17.2 (10⁻⁴ US$) per gram of CV removed. This dual strategy not only offers an eco-friendly and cost-effective solution for dye-laden water but also promotes the valorization of saline effluents and animal byproducts, addressing critical environmental challenges in industrial wastewater treatment.