Phosphorus removal from aqueous solution using modified walnut and almond wooden shell and recycling as soil amendment

Modified walnut wooden shell (MWWS) and almond wooden shell (MAWS) as novel anion exchangers were used to remove phosphorus (P) from aqueous solution. The raw and modified agricultural wastes were characterized using total N, total P, FT-IR spectra, SEM, BET, and EXD analysis. The effect of different parameters such as pH (4 to 8), contact time (5 to 600 min), and adsorbent dosage (1 to 8 g L⁻¹) on P adsorption was investigated. Adsorption of P onto MWWS and MAWS was studied using the batch technique with different concentration of P (5 to 200 mg L⁻¹) at 25 ± 2 °C. The P adsorption isotherms were fitted with the Freundlich and Langmuir equations. The k and n values were 1.57 mg g⁻¹ and 1.88 for MWWS and 1.91 mg g⁻¹ and 2.24 for MAWS, respectively. The maximum P adsorption capacities for MWWS and MAWS were 22.73 and 14.71 mg g⁻¹, respectively. The desorption-regeneration experimental results indicated about 4% and 3% reductions in MWWS and MAWS P adsorption efficiency after four consecutive regeneration cycles, respectively. The data well fitted with Pseudo-second-order kinetic model (R² ≥ 0.99), indicating that chemical interactions dominate the P adsorption process. Incubation studies showed the rate of P release in treated soil with P-loaded modified biosorbents was higher than control. Therefore, the MWWS and MAWS can potentially be used as an excellent adsorbent in remediation of contaminated waters by P and then recycled to soil.