OPTIMIZATION OF ADSORPTION CONDITIONS FOR NUTRIENT REMOVAL FROM AQUEOUS SOLUTIONS: INTEGRATED RSM MODELLING, MECHANISTIC INSIGHTS, AND MULTI-SCALE STATISTICAL VALIDATION
Abstract
Global water systems are increasingly affected by nutrient pollution, particularly nitrate and phosphate from industrial discharge, agricultural intensification, and urban expansion. Ecosystem degradation, harmful algal blooms, loss of oxygen, and the dangers that result for marine life as well as human beings are some of the effects that arise due to such pollutants. The need for sustainable adsorption process can be understood from the limitations of the conventional systems such as biological denitrification, chemical precipitation and membrane filtration, including expensive process, formation of sludge, lack of selectivity and inability to regenerate the system. This study develops an optimized adsorption system for nutrient removal using an integrated framework combining Response Surface Methodology (RSM), mechanistic evaluation, and multi-scale statistical validation. An iron-based metal–organic framework (Fe-MOF), Fe-UPH.COHSE-NH₂, was synthesized via a controlled solvothermal method and functionalized with polyethyleneimine (PEI) to introduce amine-rich active sites. Optimization using a Doehlert design identified an optimal FeCl₃·6H₂O to H₂BDC ratio of 2:1.5, producing a highly crystalline and functionally enhanced adsorbent. A porous and robust matrix with high specific surface area of 533.94 m²/g and good accessibility of active sites (BET R² = 0.9999) was proved from characterisation results obtained from powder x-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscope (SEM), and Brunauer-Emmett-Teller (BET) surface area measurement (“BET”). The durability and reusability of the substance were shown from its high crystallinity, rod-shaped porous structure, and high thermal stability at temperatures up to 350°C. This compound had functional groups such as -NH₂ and -COO⁻. Nitrate and phosphate adsorption study with RSM and the assistance of kinetic and isotherm models showed excellent removal efficiency with high predictive accuracy (R² > 0.99). The mechanisms discovered through mechanistic studies were electrostatic attraction, chemisorption of Fe-OH and Fe-NH₂, ligand exchange and intraparticle diffusion. Therefore, in summation, Fe-UPH.COHSE-NH2 provided an environmentally friendly solution for the effective removal of nutrients from wastewaters, due to high efficiency and recyclability.
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