Enhanced dewatering extent of sludge by Fe₃O₄-driven heterogeneous Fenton

Homogeneous Fenton (Fe²⁺/H₂O₂) serves as a high-efficiency conditioning method for sludge dewatering due to the generation of strong oxidizing hydroxyl radicals (OH). However, high dose of ferric salts produces iron-rich dewatered sludge and decrease sludge organic matters, which will not be conducive to the subsequent disposal and reutilization. Considering advantages of Fe₃O₄ as heterogeneous Fenton catalyst, Fe₃O₄-activated H₂O₂ (Fe₃O₄ + H₂O₂) in this study was adopted to improve sludge deep-dewatering. Reduction efficiency of the bound water (71.3 %) after Fe₃O₄ + H₂O₂ treatment (after a reaction time of 30 min) were much higher than those in the Fe²⁺+H₂O₂ treatment. Especially, the moisture content of treated sludge cake by Fe₃O₄ + H₂O₂ remarkably decreased from 86.4 % to 61.3 %. Improvement mechanism of sludge dewatering after Fe₃O₄ + H₂O₂ treatment mainly included electrostatic neutralization, reactive radical oxidation, and skeleton building by analysis of contribution factors. The generation of H⁺ in acidification could neutralize the negatively charged compounds to promote sludge hydrophobicity. Meanwhile reactive radicals generated from Fe₃O₄ + H₂O₂ destroyed sludge extracellular polymeric substances and cell structure to release intracellular water. Furthermore, Fe₃O₄ as a skeleton builder could reconstruct destructive sludge flocs and form new dewatering channels. Finally, low Fe leaching content and recoverability of Fe₃O₄ effectively will decrease environmental implication.