H₂O₂-modified tyre biochar for phosphorus adsorption and fertiliser application

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Abstract Background and aims Phosphorus (P) is an essential nutrient for global food production, and its depletion poses a major threat to agricultural sustainability. Concurrently, improper disposal of end-of-life tyres causes serious environmental risks. Converting waste tyres into functional biochar for P recovery offers a promising route to addressing both challenges by closing nutrient loops and valorising a problematic waste stream. This study investigated the potential of hydrogen peroxide (H₂O₂)-modified tyre-derived biochar (MTB) to enhance P adsorption from simulated P-rich wastewater and to enable its subsequent reuse as a slow-release fertiliser. Methods Untreated tyre biochar (PTB) was produced by pyrolysis and then oxidised with 10% H₂O₂ (1:10 w/w) at room temperature for 48 h to produce MTB. The P adsorption performance of PTB and MTB was tested at varying pH using batch experiments, with adsorption isotherms and kinetic models used to elucidate the removal mechanisms. A pot experiment with maize ( Zea mays L.) grown in nutrient‑poor soil amended with P‑loaded PTB vs P‑loaded MTB was conducted to evaluate fertiliser value. Results H₂O₂ modification significantly improved the biochar's surface properties, leading to higher P adsorption via chemisorption and electrostatic interactions. MTB achieved 99% P removal efficiency from the solution, compared to 20% for PTB. When applied to nutrient-poor soil, P‑loaded MTB increased maize shoot and root biomass by nearly threefold relative to P‑loaded PTB and unamended control, indicating enhanced P availability and nutrient use efficiency. Conclusion This study demonstrates that the H₂O₂-treated tyre biochar can effectively recover P from wastewater and act as a slow-release fertiliser, promoting plant growth and soil fertility to achieve both environmental and agronomic benefits. This dual application supports the development of circular waste management systems and sustainable agriculture.

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