Biomass-derived ceramic packing coupled with an Fe–Mn modified graphite felt cathode for enhanced bioelectro-Fenton/biotrickling filtration of gas-phase styrene

Gas–liquid interfacial resistance limits the removal and mineralization of hydrophobic gas-phase styrene. In this study, a two-stage system coupling bioelectro-Fenton (BEF; Stage 1) with a biotrickling filter (BTF; Stage 2) was developed to improve styrene treatment. In Stage 1, Fe–Mn@GF served as the optimal cathode by supporting Mn-assisted Fe 3+ /Fe 2+ cycling and promoting the 2e − oxygen reduction reaction for H 2 O 2 generation. Relative humidity played a key role in controlling gas-phase mass transfer and interfacial reaction. The best performance was obtained at 70 ± 5% relative humidity, where sufficient surface wetting favored ion transport and reactive oxygen species generation without causing excessive water-film resistance. Under 1000 ppm styrene, the BEF system achieved 95% removal efficiency and 81% mineralization efficiency. Coupling with the downstream BTF further improved treatment stability at a short empty bed residence time of 60 s, reaching 95% removal efficiency, 91% mineralization efficiency, and an elimination capacity of 230.5 g/m 3 /h. The BTF also accelerated the removal of residual aromatic intermediates, including styrene, toluene, and phenol. Acute toxicity decreased after BTF treatment, with 5-min Aliivibrio fischeri luminescence inhibition falling from 50.11% after BEF alone to 9.18% after BEF–BTF treatment. Microbial analysis showed enrichment of Geoalkalibacter , Pseudomonas , and Thauera , suggesting improved anodic electron-transfer conditions. Overall, the BEF–BTF system provides a coupled oxidation–biodegradation strategy for hydrophobic volatile organic compound control with improved mineralization and reduced residual toxicity. • Humidity regulation enhances mass transfer in gas-phase BEF systems. • Coupled BEF–BTF improves styrene removal and mineralization efficiency. • Fe–Mn cathodes facilitate Fe 2+ cycling and 2e − ORR-driven .•OH generation. • Optimized EBRT sustains stable styrene removal under high loading.