Engineered biochar with MgO impregnation: A phosphorus vector bridging aquatic systems and agricultural soils via targeted adsorption and controlled release

The global community is confronted with two interconnected issues: phosphorus contamination in water bodies and the diminishing reserves of phosphate rock. This research presents an innovative dual-purpose strategy, which utilizes MgO-modified biochar (MgO-BC) to extract phosphorus from wastewater and subsequently recycle it into a controlled-release fertilizer. MgO-BC was synthesized using a chemical foaming strategy, with corn stalk as a carbon precursor and Mg(HCO₃)₂ as both an activation agent and metal source, resulting in a honeycomb-like MgO-modified biochar. The phosphorus adsorption onto MgO-modified biochar (MgO-BC) adhered to pseudo-second-order kinetics, achieving a maximum adsorption capacity of 189.90 mg/g, suggesting that chemical processes predominantly govern phosphorus capture. The primary mechanisms for phosphorus removal by MgO-BC are electrostatic interactions and complexation reactions. Field and laboratory tests demonstrated that MgO-BC-P ads effectively released 59.02 % of the absorbed phosphorus into the soil within 35 days. Moreover, compared to the CK group, the MgO-BC-P ads treatment significantly increased the dry weight (131.58 %), leaf length (14.37 %), and leaf number (57.14 %) of the bok choy. It also enhanced root length (52.24 %) and surface area (76.39 %) compared to the superphosphate treatment (CF). This research highlights the potential of MgO-BC as a viable and sustainable approach for waste management and agricultural enhancement. • The study explored the circular path of " biomass to biochar to biofertilizer ". • MgO-BC show a high PO 4 3- adsorption capacity of 189.90 mg·g⁻¹ • MgO-BC-P ads releases 59.02 % of the absorbed phosphorus over 35 days. • MgO-BC-P ads promotes a 131.58 % increase in the yield of bok choy.