The potential of compost-based organic nano-adsorbent (Compost/Fe3O4NPs) for contaminated soil remediation

One of the most important emerging pollutants in human health, food safety, and environmental protection challenges is phthalate esters. Among these, the contamination of agricultural soils with the endocrine-disrupting chemical Di (2-ethylhexyl) phthalate (DEHP) has been confirmed globally. In this research, the DEHP-absorption potential of compost enriched with Fe3O4 NPs was identified. The effects of the sorbent dose in the range of 2–5 g.L-1, 3–11 pH, and DEHP concentration at 5–10 mg.L-1 on absorption efficiency (%) were optimized via response surface methodology in design expert software. The kinetic equilibrium experiment results showed a two-step process, requiring 6 hours of equilibrium time for the exothermic adsorption process at 25ºC. The adsorption process of DEHP fitted best to the pseudo-second-order kinetic (R2 = 0.9932) and the linear form of the Freundlich isotherm models. In the central composite design, the significant quadratic model was validated and used to predict the interaction of variables (P-value <0.0001, adjusted R2 = 0.9753). The optimum conditions of absorption efficiency (74.173%) were obtained at a sorbent dosage of 4.157 g.L-1, pH 5.85, and a DEHP concentration of 4.88 mg.L-1 with a desirability of 0.987. The comparison of FTIR absorption spectra confirmed the active participation of O-H bands (functional groups of phenol, alcohol, and carboxyl) and primary amine (N-H) in the DEHP absorption through interaction with the oxygen atom of the phthalate ester group (C=O). As a result of its successful and acceptable efficiency, using compost/Fe3O4 NP absorbent based on organic wastes is a low-cost and eco-friendly technique for DEHP removal from sensitive ecosystems and also to improve the efficiency of bioremediation in agricultural soils amended by compost.