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Pyrolysis temperature controls long-term stability of heavy metals in sludge-derived biochar after soil application and oxidative aging
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DOI：10.1016/j.jclepro.2026.149185.png)
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Abstract
En 中文
We evaluated how pyrolysis temperature and post-application aging jointly control heavy-metal speciation and ecological risk in sewage sludge-derived biochars. Metal-enriched sludge was pyrolyzed at 300, 500, 700, and 900 °C, mixed with soil, and aerobically incubated for 300 days; metal partitioning was quantified using a modified BCR (European Community Bureau of Reference) sequential extraction. To evaluate the resistance of metal stabilization to accelerated oxidative aging, pristine materials were pretreated with hydrogen peroxide (H2O2; 1% or 5%, w/v) before 30-day soil incubation. A temperature-dependent transition in metal stabilization occurred between 500 and 700 °C, with metal partitioning shifting from oxidizable fractions (F4) to mineral-dominated residual fractions (F5) at ≥700 °C. During pyrolysis, Hg was almost completely volatilized at 300 °C, and Cd decreased markedly at ≥700 °C, indicating volatility-driven reduction in solid-phase risk. In contrast, Pb, Cr, Cu, Zn, Ni, and As were largely retained and exhibited element-specific redistribution during soil incubation. Pb, Cr, Cu, and Zn showed progressive enrichment in F5, whereas Ni stabilization was mainly established during pyrolysis. Arsenic remained comparatively sensitive to oxidative alteration, displaying measurable redistribution during aging. The fraction-based modified ecological risk index values were lowest for ≥700 °C biochars and remained low after aging, indicating that high-temperature pyrolysis enhances long-term stability but requires emission control for volatilized metals.
Keywords:
Sewage sludge
Biochar
Heavy metals
Chemical speciation
Soil incubation
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36.8W
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