Ferric Tannate-Enhanced Electrochemical Conditioning Process for Improving Sludge Dewaterability

Sludge dewatering is a key step in the overall process of sludge treatment and disposal. In this study, ferric tannate was synthesized by chemically complexing tannic acid with Fe2(SO4)3 under various conditions and then was innovatively employed to enhance electrochemical conditioning (ECC) for municipal sludge dewatering. The optimal preparation conditions of ferric tannate were determined as a tannic acid to iron ion molar ratio of 0.8:10, pH of 10, and reaction time of 2 h. Subsequently, ferric tannate-enhanced ECC was investigated under different dosages and operating parameters. The optimal conditions were identified as ferric tannate dosage of 20% total solid, voltage of 50 V, and reaction time of 30 min, under which capillary suction time, specific resistance to filtration, and water content of dewatered sludge cake decreased by 84.3%, 84.2%, and 17.6%, respectively. Results of the mechanism analysis indicated that ferric tannate effectively reduced sludge viscosity, increased zeta potential, and neutralized the negative surface charges via charge neutralization, hydrophobic interactions, and hydrogen bonding. Meanwhile, adsorption bridging promoted floc aggregation and particle growth. Compared with the ECC process alone, the addition of ferric tannate in the ferric tannate-enhanced ECC process generated more •OH, promoting the extracellular polymeric substance degradation and protein removal, thereby improving sludge hydrophobicity. Furthermore, the floc structure was reconstructed into a more compact and smooth morphology, facilitating the release of bound water during filtration. These findings provide new technical and theoretical support for the development of eco-friendly and efficient sludge conditioning and dewatering processes.