Efficient Recovery of Phosphorus from Wastewater Using Calcium-Based Modified Biochar: Removal Performance, Adsorption Mechanism, and Resource Utilization

Phosphorus, a crucial yet nonrenewable resource, is essential for agriculture, life processes, and various industries. In this study, we employed co-pyrolysis of eggshells and peanut shells to prepare calcium-based biochar (EPB) with a high adsorption capacity and ecological non-toxicity, enabling effective phosphorus recovery from wastewater. EPB was characterized via X-ray diffraction, scanning electron microscopy, electron probe microanalysis, and Brunauer–Emmett–Teller analysis. Additionally, its phosphate adsorption characteristics were investigated under varying temperature, pH, and coexisting ion conditions. Phosphate adsorption followed the Langmuir isotherm with a maximum adsorption capacity of 178.08 mg/g, and the kinetics aligned with those of the quasi-second-order kinetic model. Phosphate adsorption by EPB was driven by electrostatic attraction and chemical precipitation. Moreover, we investigated the effects of phosphorus-enriched biochar on the growth and development of tobacco and soil microbial communities. Phosphorus-enriched biochar increased organic and inorganic phosphorus levels and promoted tobacco growth compared with conventional fertilizers. Phosphorus-enriched biochar reshaped tobacco rhizosphere microbial communities, promoting beneficial taxa, such as Nitrospira. Structural equation analysis showed that EPB enhanced microbial alpha diversity and key microbial communities, improving phosphorus availability and tobacco growth and development. Conclusively, this study provides a theoretical reference for phosphorus-containing wastewater treatment and reuse.