Enhanced simultaneous removal of phosphate and ammonium from swine wastewater using magnetic magnesium–loaded Chinese herbal medicine residues: Performance, mechanism, and resource utilization

Abstract

Magnetic magnesium (Mg)–loaded Chinese herbal medicine residues (MM–TCMRs) were fabricated to simultaneously remove and recover phosphate and ammonium from wastewater. The MM–TCMRs exhibited larger specific surfaces and rougher structures with massive spherical particles than those of original residues. They could be separated by adjusting the magnetic field. The phosphate and ammonium adsorption by MM–TCMRs were matched with the pseudo–second–order model, while the Langmuir model yielded the maximum adsorption capacities of 635.35 and 615.57 mg g−1, respectively. Struvite precipitation on the MM–TCMRs surface was the primary removal mechanism with electrostatic attraction, ligand exchange, intra–particle diffusion, and ion exchange also involved. The recyclability of MM–TCMRs confirmed their good structural stability. More importantly, the nutrient–loaded MM–TCMRs enhanced alfalfa growth and improved soil fertility in planting experiments. Collectively, the MM–TCMRs are promising candidates for nutrient removal and recovery from wastewater.