Adsorption of phosphorus in wastewater by lanthanum-modified magnetic sewage sludge biochar

In this study, we developed a highly efficient sewage sludge biochar for phosphorus adsorption. Lanthanum-modified biochar with magnetic properties (VFD-MSBC) was synthesized in a one-pot hydrothermal process using vacuum freeze-drying (VFD) pretreated sewage sludge as biomass to remove phosphorus from wastewater. The characterization analysis revealed that the VFD-treated SS exhibited an increased specific surface area and pore volume, and promoting the retention of abundant functional groups following hydrothermal carbonization. VFD-MSBC exhibits a large BET-specific surface area of 7.111 m2g−1. The maximum adsorption capacity of VFD-MSBC was 97 mg/g, and the monolayer adsorption capacity was 79.419 mg/g at 25 °C. The adsorption performance remains stable in the presence of high concentrations of coexisting anions (0.1 mol/L). Mechanistic studies demonstrate that the adsorption behavior of VFD-MSBC towards phosphorus involves both physisorption and chemisorption processes. Surface precipitation, intraparticle diffusion, hydrogen bonding, ligand exchange, and electrostatic attraction were identified as primary mechanisms for phosphorus adsorption. The present study contributes to the optimization of synthetic design for phosphate multifunctional composites, while presenting a novel approach for sludge phosphorus recovery.