Synthesis of a flower-clustered biochar-iron composite by ball milling for enhanced trichloroethylene degradation in permeable reactive barriers

Permeable reactive barrier (PRB) groundwater remediation faces prominent limitations including high filler costs and severe pore clogging, while conventional Fe 0 -based PRBs further suffer from particle aggregation and surface passivation that degrade long-term field performance. To address these issues, a novel flower-clustered biochar‑iron composite (MBC/Fe-F) was synthesized via mechanochemical ball milling of biomass with ferric chloride and KOH as grinding aid, followed by carbonization at 700 °C. Material characterization including XRD, XPS, TEM and density functional theory calculations confirmed that iron species were uniformly dispersed on the biomass-derived char with ferrous iron (Fe 2 + and Fe 3 +) as the dominant valence state. In static batch experiments lasting 600 min under standard simulated groundwater matrix containing 50 mg/L trichloroethylene (TCE), the optimized MBC/Fe-F composite removed 89.0% of TCE; quantitative chloride release tests verified that 76.3% of TCE was eliminated via reductive dechlorination and the rest 12.7% via irreversible adsorption, demonstrating synergistic adsorption and reduction pathways; moreover, MBC/Fe-F-15 still maintained the highest removal capacity across the tested concentration range. When coupled with acclimated activated sludge in a simulated PRB system over an operation period of 80 pore volumes, the composite achieved around 90% of TCE removal efficiency and maintained stable permeability coefficients of 0.0043–0.0061 cm/s, which fully meet the permeability requirements for field PRB applications. Post-operation material characterization and microbial 16S rRNA sequencing confirmed that the composite significantly enriched functional dechlorinating bacteria and exhibited excellent biocompatibility, realizing a three-way synergy of adsorption, chemical reduction and biodegradation.