Kill three birds with one stone: Iron-doped graphitic biochar from biogas residues for ammonium persulfate activation to simultaneously degrade benzo[a]pyrene and improve lettuce growth

A graphitized magnetic biochar material, Fe-impregnated biochar (FBC), was synthesized using biogas residue, a product of food waste after anaerobic fermentation. The FBC coupled with ammonium persulfate (APS) exhibited excellent performance in the catalytic degradation of benzo[a]pyrene (BaP), a pentacyclic polycyclic aromatic hydrocarbon (PAH). In the FBC-APS system, the pyrolysis temperature of biochar, the initial pH, and the FBC and APS dosages were all influencing factors for Bap degradation. The FBC at the pyrolysis temperature of 700 degrees C performed the best catalytic performance, and FBC-APS efficiently degraded BaP at a wide pH range of 3-11. Results from quenching experiments, electron spin resonance measurement, and electrochemical analysis were used as the basis to propose the possible degradation mechanisms of BaP by FBC-APS, including the radical and non-radical pathways. The radical-induced oxidation was attained by SO4.- and O2.- . The non-radical pathway involved two aspects, one contributed by 1O2 and the other achieved through electron transfer. Five BaP intermediates were tentatively determined. Finally, FBC-APS was applied to BaP-polluted soil, and the overall degradation rate reached 91.7% after 72 h. Lettuce growth experiment showed that FBC-APS enhanced soil nitrogen and potassium availability and lettuce growth. In summary, FBC-APS application to soil can degrade BaP, improve the manurial effect, and solve environmental problems brought by biogas residues, that is, killing three birds with one stone.