Enhanced sludge dewaterability with sludge-derived biochar activating hydrogen peroxide: Synergism of Fe and Al...

Reuse of sludge-derived Fe-rich biochar as sludge conditioner is an attractive route for management of waste activated sludge at source. Homogeneous and heterogeneous Fenton reactions have been proved in sludge conditioning with Fe-rich biochar activating H₂O₂ to enhance sludge dewaterability. The FeAl₂O₄ phase in Fe-rich biochar was first identified during pyrolysis of sewage sludge after adding both Fe₂O₃ and Al₂O₃, since Fe and Al elements are two of major metal elements in Fe-rich sludge. Compared with the Fe-rich biochar that did not comprise FeAl₂O₄ phase, the capillary suction time (CST) and specific resistance to filterability (SRF) of the sludge conditioned with the Fe-rich biochar comprising FeAl₂O₄ phase could be efficiently decreased by 23% and 44%, respectively. The results indicated that FeAl₂O₄ phase in Fe-rich biochar could improve sludge dewaterability by enhancing heterogeneous Fenton reaction. Synergistic effect between Fe and Al in FeAl₂O₄ contributed to weak the O-O bond in H₂O₂ and reduce the activation energy of H₂O₂ decomposition for enhancing ·OH generation, which could be explained by density functional theory (DFT) calculations for the first time. Thus, the decomposition rate of H₂O₂ and the amount of ·OH generation were obviously promoted by FeAl₂O₄ phase in sludge-derived biochar during sludge conditioning, attributing to the destruction of sludge flocs, the release of bound water, and the improvement of sludge dewaterability.