Sludge-derived biochar with multivalent iron as an efficient Fenton catalyst for degradation of 4-Chlorophenol

Fe-rich biochar with multivalent iron compounds (Fe⁰, Fe_0.95C_0.05, Fe₃O₄, and FeAl₂O₄) pyrolyzed from sludge cake conditioned with Fenton's reagent and red mud was utilized as an efficient Fenton catalyst for the degradation of 4-chlorophenol (4-CP). Effects of pyrolysis temperature and sludge conditioner composition on the transformation of iron compounds were studied. Both homogeneous Fenton reaction initiated by Fe²⁺ leached from both low-valent Fe⁰ and Fe_0.95C_0.05, and heterogeneous Fenton reaction initiated by solid iron phases of Fe₃O₄ and FeAl₂O₄ were revealed to contribute to the degradation of 4-CP. The removal efficiency of 4-CP remained 100% after five successive degradation rounds. The homogeneous Fenton reaction mainly works in the first degradation round, and the heterogeneous Fenton reaction dominates in subsequent degradation rounds. The findings of this study suggest that sewage sludge derived Fe-rich biochar could be utilized as an efficient Fenton catalyst for recalcitrant organics degradation.