Nano-water treatment residuals: Enhancing phosphorus kinetics and optimization in saline soils

Phosphorus (P) use in agriculture has witnessed a global increase, leading to significant environmental problems. Nevertheless, the understanding of P kinetics in saline soils amended with nano-water treatment residuals (nWTR) remains limited. This study aimed to (1) Investigate the impact of different nWTR addition rates (0%, 0.10%, 0.20%, and 0.50%) on the adsorption-desorption kinetics of P applied to five soils with different salinity levels (1.47–58.50 dS m⁻¹) using batch adsorption experiments. (2) Using different optimization models via Fit Quadratic Model and principal component analysis to predict the optimal utilization of nWTR. The X-ray diffraction and Fourier transform infrared patterns proposed that the main mechanisms controlling the process are ligand exchange and precipitation. The results revealed that the adsorption level of P in amended soils was rapid, then decreased gradually until reaching equilibrium after 24 h/25°C. The kinetics data were well described by a pseudo-second-order model, suggesting a chemisorption-dependent adsorption process. Increasing soil salinity and nWTR addition led to decline the phosphorus desorption. The application of 0.5% nWTR decreased P-desorption from 33.95% to 16.22% in the non-saline soil and from 18.43% to 10.63% in the highly saline soil. principal component analysis distinguished a positive association between P-adsorbed and nWTR. The optimization models predicted that applying 0.5% nWTR for 965 min maximizes the P-adsorption rate, reaching 1041 mg Kg⁻¹ in highly saline-soils. Therefore, nWTR can serve as a cost-effective and efficient absorbent for mitigating P mobility and reducing its transport in saline soils.