Fe-modified porous biochar for efficient adsorption of low-concentration phosphate from municipal wastewater: Performance, mechanism, and fixed-bed behavior prediction

To address the issue of water eutrophication caused by low-concentration phosphate in municipal wastewater and overcome the limitations of traditional biochar technologies, this work proposed a new strategy for preparing Fe-modified biochar (FeBC-3) from waste coffee grounds via microwave pyrolysis. This method utilized the rapid and uniform heating characteristics of microwaves to efficiently activate the material, resulting in FeBC-3 with a high specific surface area and abundant pore structure, which was a powerful basis for treating low-concentration phosphate. FeBC-3 demonstrated excellent low concentration phosphate removal capability (99.26 % removal in 2 h), wide pH adaptability (>80 % removal under strong acid and alkali), and excellent anti-disturbance capability. Laboratory-scale continuous flow adsorption tower experiments further confirmed the applicability of FeBC-3, and the Yoon-Nelson model accurately predicted the point at which phosphate permeation reached 50 %. Through advanced characterization and modeling, particularly using density functional theory (DFT) calculations, the inner sphere complex was revealed to be the key mechanism for the efficient adsorption of phosphate by FeBC-3 at the molecular level, providing a new perspective for understanding its mechanism. The present study confirmed that FeBC-3, as a low-cost and environmentally friendly adsorbent, had a great application prospect for the efficient treatment of low concentration of phosphate in municipal wastewater, which brought a new breakthrough in the field of water pollution control.